an investigation of properties of fgm and wafer structures … · 2017. 5. 10. · 4.i soodi, milan...
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An investigation of properties of FGM and wafer structures produced with
laser direct metal deposition
By
Mehdi Soodi BSc Materials Science and Metallurgy 1996 (Iran)
MEng.Sc. Materials Science 2005 (Monash University, Australia)
Submitted in total fulfillment of the requirements for the degree of
Doctor of Philosophy
Faculty of Engineering and Industrial Sciences
Swinburne University of Technology 2015
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Abstract
Existing range of metallic alloys and structures possess a series of physical and
mechanical properties that deem them useful or unusable in certain applications or
environments. A solution to the cases where metallic alloys lack specific properties
and therefore cannot function satisfactorily is to develop new innovative materials
which possess the desired characteristics. These characteristics may include tailored
mechanical, thermal and functional properties.
With such purpose in mind, a range of engineering alloys were selected to create two
distinct sets of structures. One was functionally graded materials (FGM) - using pairs
of these alloys - and the second type was series of wafer-layered structures using
pairs of these alloys in different combinations. The alloys were selected from among
the most commonly used alloys within the industrial and engineering applications
such as oil and gas, power generation and tool making. These selected alloys were
namely 420 SS, 316 SS, EuTroLoy 16221 (Ni based steel alloy), H13 tool steel,
Stellite® 6 and AlBrnz.
The process used to create these new structures was Laser assisted direct metal
deposition (DMD). This technology offers a unique and innovative capability which
allows deposition simultaneously of up to four different alloys – in the shape of
powder –on a substrate or on the previously deposited layer of one of these four
alloys. Laser assisted direct metal deposition offers endless opportunities to create
innovative structures to further improve material performance and characteristics.
The DMD system is equipped with sensitive close loop feedback control which
provides information for the computerized system on the process and the layer being
deposited. The DMD system is used to create 3D structures out of powder form
alloys or composites on a base plate which is later cut off and disposed of after
completion of the process. All samples in this research work were created by this
technology into a rectangular cubic shape but each with a unique structural
arrangement of one or two alloys.
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In order to understand the characteristics of the new materials produced, the samples
were tested for their physical and mechanical properties. These tests included micro-
hardness, linear thermal expansion coefficient, tensile strength and mass loss
corrosion behavior test. After careful study of the results achieved in each series of
tests, it was found that once an alloy is used in conjunction with another alloy to
create either FGMs or wafer layered structures, the overall physical and mechanical
behavior of these new structures is significantly different from that of each alloy
when measured individually. In some cases, the new set of properties these structures
possess, offer new potential applications in a wide range of industries and
engineering fields, where each single alloy on its own would not satisfy the design
engineer’s requirements before.
Tensile tests were done on all the samples and the results revealed some structures
which offered superior properties compared to each of their respective constituent
alloys on their own. This meant that for tensile tests, one or both of the combined
alloys structures i.e. FGM or wafer structure samples possessed higher tensile
strengths. In the case of both FGM and wafer structure of 316 SS and 420 SS alloys,
the ultimate tensile strength (UTS) measured was more than that of each alloy on its
own. In other alloy combinations, the FGM and the wafer showed UTS values lying
between those of the individual alloys.
All the samples were tested for their coefficient of linear thermal expansion values.
These innovative structures demonstrated much higher and in some instances lower
expansion rates than both their constituent alloys on their own. Depending on the
applications such metallic structures, selected for a significantly higher or lower
coefficient of thermal expansion, might offer notable advantages that were non-
existent before. In almost all samples and combination of alloys the FGM and wafer
samples demonstrated coefficient of linear expansion values that were between those
of the single alloy samples. However, in the case of the FGM sample of 316 SS and
420 SS, the full length of the coefficient of linear thermal expansion curve plotted
versus temperature lies well below the curve for 316 SS, 420 SS and even the curve
for wafer sample of these two alloys. This significant decrease in this physical
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property of this structure can make way to create other similarly different structures
with other alloys and use such structures in applications where the low thermal
expansion rate is of great desire and benefit.
Another series of tests to study the properties of these new structures were mass loss
corrosion tests. These tests were done using the same size samples and all with the
same surface finish dipped in the same corrosive solution for a set period of time.
The mass loss measured for all samples showed no improvement for FGM and
Wafer structure samples compared with the more corrosion resistant constituent
alloys used in their structures. However, in most cases the corrosion resistance in the
combined alloys structures was better than the lesser corrosion resistant constituent
alloys used in their structures. What was observed in some of the structures was the
galvanic corrosion mechanism, where two metals with notably different electro-
potential values are electrochemically connected together. This was more evident in
FGM or Wafer samples containing 316SS and H13 tool steel, where H13 has low
electro potential-passivity and 316SS has high electro-potential passivity so the two
alloys can form an active galvanic cell and corrode at high rates.
For future investigation, the fabrication of these new structures can be extended to
other alloys and composite materials, which can then create an extensive range of
new materials that can change the engineering definition of materials eliminating the
limitations within single alloys.
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Acknowledgement
“Knowledge is in the end based on acknowledgement.”
Ludwig Wittgenstein (Philosopher/Engineer)
I would like to acknowledge the support from the following people:
My supervisor - Prof Syed Masood – of Swinburne University of Technology for his
ongoing support throughout the course of my PhD study. His support went beyond
my expectations for which I shall always be grateful.
My co-supervisor – Prof Milan Brandt – of RMIT University whose knowledge of
industrial lasers and their applications is second to none and had a significant role in
guiding me in my endeavors to do this research. I am honored to have him as my
mentor.
Smenco (previously Eutectic) for providing the powders for the experiments,
Mr. Girish Thipperudrappa of Swinburne University of Technology for
manufacturing the samples,
The Commonwealth Scientific and Industrial Research Organization (CSIRO) for
carrying out the thermal expansion tests,
Mr. Andrew Dugan the General Manager at Hardchrome Engineering Pty Ltd who
offered the company’s ongoing support throughout the project period
Staff at Swinburne University Library
Everyone else who has made any contribution to my PhD and to this thesis
My special thanks to my dear wife Saeideh and my daughters Eva, Amy and Hannah
for selflessly encouraging and supporting me with my extra study load, which certainly
affected their lifestyle by keeping me away from them when I was supposed to be
around and have family time and fun with them.
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Dedicated to … you who acknowledge no limits to seek science and
knowledge; you who encouraged and supported me to take on the challenge of learning when it seemed difficult and you who have found my thesis worthy of your time and your work.
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Declaration by Candidate I, Mehdi Soodi, hereby declare that this thesis contains no material which has been accepted
for the award to the candidate of any other degree or diploma, except where due reference is
made in the text of the examinable outcome; and that to the best of my knowledge contains
no material previously published or written by another person except where due reference is
made in the text of the examinable outcome; and that this work is not based on joint research
or publications by any other party.
Mehdi Soodi Date: …………………………….
……………………………………………………………...
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List of Publications
1. Mehdi Soodi, Syed Masood, Milan Brandt, “Thermal Expansion of
Functionally Graded and Wafer Layered Structures produced by Laser Direct
Metal Deposition”, International Journal of Advanced Manufacturing
Technology 2013, Int J Adv Manuf Technol (2013) 69:2011–2018
2. Mehdi Soodi, Syed Masood, Milan Brandt, “Tensile Strength of Functionally
Graded and Wafer Layered Structures produced by Laser Direct Metal
Deposition, Rapid Prototyping Journal, Vol 20, Issue 5, 2014
3. Mehdi Soodi, Syed Masood, Milan Brandt, “A study of laser cladding with
420 stainless steel powder on the integrity of the substrate metal” Advanced
Materials Research Vols. 230-232 (2011) pp 949-952
4. Mehdi Soodi, Milan Brandt, Syed Masood, “A study of microstructure and
surface hardness of parts fabricated by Laser direct metal deposition process”
Advanced Materials Research Vols. 129-131 (2010) pp 648-651
5. Mehdi Soodi, Milan Brandt, Syed Masood “Investigation of metallic
structure with negative thermal expansion: A review” Materials Forum
Volume 34-2010 Institute of Materials Engineering Australasia pp 93-99
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Contents Abstract ..................................................................................................................................... i
Acknowledgement .................................................................................................................. iv
Declaration by Candidate ........................................................................................................ vi
List of Publications ................................................................................................................. vii
Contents ................................................................................................................................ viii
List of figures .......................................................................................................................... xii
Chapter 1 - Introduction .......................................................................................................... 2
1.1 Motivation for this research .................................................................................... 2
1.2 New materials & structures ..................................................................................... 2
1.2.1 Significance and applications of FGMs............................................................. 3
1.2.2 Significance and applications of WAFER structures ......................................... 5
1.3 Additive manufacturing ........................................................................................... 6
1.3.1 Laser Direct Metal Deposition ......................................................................... 7
1.3.2 LENS 3D system .............................................................................................. 10
1.4 Process parameters of laser DMD ............................................................................... 13
1.5 Project objectives ......................................................................................................... 14
1.6 Structure of thesis ........................................................................................................ 15
Chapter 2 – Literature Review ............................................................................................... 17
2.1 Novel materials and structures .................................................................................... 17
2.2 Negative Thermal Expansion ....................................................................................... 17
2.2.1 SOME NTE MECHANISMS ..................................................................................... 18
2.2.2 Discussion on NTE ................................................................................................. 24
2.3 Functionally Graded Materials ..................................................................................... 26
2.4 Wafer-layered structures ............................................................................................. 39
Summary ............................................................................................................................ 40
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Chapter 3 – Materials and Methods ...................................................................................... 42
3.1 Introduction ................................................................................................................. 42
3.2 DMD process parameters ............................................................................................ 42
3.3 Effect of laser metal deposition on the substrate ....................................................... 45
3.3.1 Laser cladding Vs. TIG welding .............................................................................. 45
3.3.2 Sample fabrication - Laser cladding ...................................................................... 47
3.3.3 Sample fabrication _ TIG welding ......................................................................... 50
3.3.4 Metallographic evaluation .................................................................................... 51
3.3.5 Micro-hardness scan ............................................................................................. 53
3.3.6 Elemental Analysis by Energy Dispersive Spectroscopy ....................................... 58
3.4 Materials ...................................................................................................................... 66
3.4.1 Stainless Steel - Grade 420.................................................................................... 66
3.4.2 Stainless Steel - Grade 316L .................................................................................. 68
3.4.3 Tool steel (H13 Steel) ............................................................................................ 69
3.4.4 Stellite 6 ................................................................................................................ 70
3.4.5 Aluminum Bronzes ................................................................................................ 72
3.4.6 EuTroLoy® 16221 .................................................................................................. 73
3.5 Fabrication of FGM and Wafer samples ...................................................................... 73
Chapter 4 - Microstructure & Microhardness Investigation .................................................. 84
4.1 Introduction ................................................................................................................. 84
4.2 Microstructure Study of Monolithic Materials ............................................................ 85
4.3 Microstructure Study of Wafer-layered structures ..................................................... 90
4.4 Functionally Graded Materials ..................................................................................... 96
4.2 Micro-Hardness .......................................................................................................... 102
Chapter 5 - Thermal Expansion Studies ............................................................................... 111
5.1 Introduction ............................................................................................................... 111
5.2 Methodology for CTE ................................................................................................. 111
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5.3 CTE of FGM and Wafer ............................................................................................... 113
Chapter 6 - Evaluation of Tensile Strength .......................................................................... 129
6.1 Introduction ............................................................................................................... 129
6.2 Tensile Testing ........................................................................................................... 131
7.3 Results and discussion ............................................................................................... 133
Conclusion ........................................................................................................................ 140
Chapter 7 - Evaluation of corrosion resistance .................................................................... 142
7.1 Introduction ............................................................................................................... 142
7.2 Types of Corrosion: .................................................................................................... 142
7.3 Methods of Corrosion Testing ................................................................................... 146
7.4 Immersion Corrosion Testing ..................................................................................... 149
7.5 Results and Discussion ............................................................................................... 151
7.6 Conclusion .................................................................................................................. 162
Chapter 8 - Conclusion & Future work ................................................................................. 164
8.1 Introduction ............................................................................................................... 164
8.2 Major Conclusions ................................................................................................ 164
8.2.1 Thermal expansion properties ............................................................................ 164
8.2.2 Micro-hardness measurements ................................................................... 165
8.2.3 Tensile Strength ........................................................................................... 165
8.2.4 Immersion Corrosion Tests .......................................................................... 166
8.3 Future work ................................................................................................................ 167
Appendices ........................................................................................................................... 168
Appendix A: ...................................................................................................................... 169
A.1 Introduction ........................................................................................................... 169
A.2 Carbon Dioxide (CO2) lasers .................................................................................. 169
A.3 Neodymium: Yttrium-Aluminium-Garnet (Nd:YAG) layers ................................... 173
A.4 Diode and diode pumped Nd:YAG lasers............................................................... 177
xi
A.5 Fibre lasers ............................................................................................................. 187
Appendix B: Powder certificates ...................................................................................... 191
Appendix C: Raw test data from the dilatometry ............................................................ 194
References ........................................................................................................................... 198
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List of figures
Chapter 1 - Introduction
Figure 1.1 - Plasma sprayed functionally graded ZrO2/NiCoCrAlY thermal barrier coating….4 Figure 1.2 - Schematics of a Direct Metal Deposition Machine……………………………………….…..8 Figure 1.3 - A DMD made structure…………………………………………………………………………………….9 Figure 1.4 - Trumph DMD 505 POM system used for this research…………………………….……..10 Figure 1.5 - Basic layout and flow paths for a typical LENS® system [7]………………………….….11
Chapter 2 – Literature Review
Figure 2.1 - Chen-Kikuchi design for NTE artificial material – [courtesy of J. QI, et al]………..19 Figure 2.2 - Left: Crystal structure of NTE material Cubic ZrW2O8 – Right: TEM picture of a ZrMo2O8/Polyimide composite [17]………………………………………………………………………………… 20 Figure 2.3- An image of the crystal structure of cubic………………………………………………………. 21 Figure 2.4 - Linear thermal expansion of the 4238um long specimen. The region near Tc is shown in the inset; the 20 Å scale indicates the absolute length change. [14]…………………. 22 Figure 2.5 – Two different types of FGM structures…………………………………………………………. 26 Figure 2.6 – Schematics of powder metallurgy method to fabricate FGMs [30]…………………27 Figure 2.7 – Fabrication process stages flow chart…………………………………………………………... 29 Figure 2.8 – A LENS® nozzle in action – Photo source: TMS.org……………………………………..… 33 Figure 2.9 –Schematics of a wafer-layered structure…………………………………………………………39
Chapter 3 – Materials and Methods
Figure 3.1 – A DMD processing head in action (source POM)…………………………………………….44 Figure 3.2 - schematics of coaxial Laser Cladding [5]…………………………………………………..…….48 Figure 3.3 - sample round bar being laser cladded with 420 SS powder…………………………….49 Figure 3.4 - Schematics of TIG welding process [6]…………………………………………………………….50 Figure 3.5 – Comparison of Laser clad and TIG welded samples…………….………………………….51 Figure 3.6 - micrograph of the Laser Clad sample showing the HAZ and the hardness profile in this region and beyond (500X)………………………………………………………………………………….…..53 Figure 3.7 - Hardness profile in the HAZ (Laser Clad sample) ……………………………………………54 Figure 3.8 - Microhardness profile of the base metal, heat affected zone, bond region and Laser deposited layer (500X)……………………………………………………………………………………………..55 Figure 3.9 - Hardness values from the microhardness tests for both Laser Clad and TIG welded samples ……………………………………………………………………………………………………………….56 Figure 3.10 - SEM image of the sample showing the bond region in the cross-section of the Laser Clad sample (1000X) ……………………………………………………………………………………………….57 Figure 3.11 - A high magnification SEM ~ in the Laser Clad sample (10000X) …………………..58 Figure 3.12 – Areas selected for EDS on both sides of the bond interface ……………………... 59 Figure 3.13 – EDS spectrum for Point 1 …………………………………………………………………….……. 60 Figure 3.14 – EDS spectrum for Point 2 …………………………………………………………………….……. 60 Figure 3.15 – EDS spectrum for Point 3 …………………………………………………………………….……. 61 Figure 3.16 – EDS spectrum for Point 4 …………………………………………………………………….……. 61 Figure 3.17 – EDS spectrum for Point 5 ……………………………………………………………….…….…… 61 Figure 3.18 - SEM image of the sample ~ of the TIG welded sample (1000X) ……………..….. 64 Figure 3.19 - A high magnification SEM ~ in the Laser Clad sample (10000X) …………….…… 65
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Figure 3.20 - A Sketch of DMD process ………………………………………………………………………….. 76 Figure 3.21 - A DMD sample of Stellite 6 ……………………………………………………………………….. 80 Figure 3.22 – Monolithic samples after machining ………………………………………………………… 81 Figure 3.23 - FGM sample comprising of AlBrnz and 420 SS ………………………………………….. 81 Figure 3.24 - Wafer sample of AlBrnz and 420 SS ………………………………………………………….. 82
Chapter 4 – Microstructure & Microhardness Investigation
Figure 4.1 - 3D monolithic structures made by DMD………………………………………………………. 85 Figure 4.2 – As cast Stellite 6 microstructure (Source: Deloro Stellite)……………………………. 86 Figure 4.3 – SEM of DMD Stellite 6 @ 1000X…………........................................................... 87 Figure 4.4 – SEM of DMD Stellite 6 @ 3000X………………………………………………………………….. 87 Figure 4.5 – SEM of DMD316 SS @ 1000X………………………………………………………………………. 87 Figure 4.6 – SEM of DMD 316 SS @ 3000X……………………………………………………………………… 87 Figure 4.7 – SEM of DMD 420 SS @ 1000X……………………………………………………………………… 88 Figure 4.8 – SEM of DMD 420 SS @ 3000X……………………………………………………………………… 88 Figure 4.9 DMD AlBrnz microstructure @100X ……………………………………………………………… 88 Figure 4.10 DMD AlBrnz microstructure @500X ……………………………………………………………. 88 Figure 4.11 EuTroLoy 16221 microstructure @100X ……………………………………………………… 89 Figure 4.12 EuTroLoy 16221 microstructure @500X ……………………………………………………… 89 Figure 4.13 Tool Steel (H13) microstructure @100X ……………………………………………………… 90 Figure 4.14 Tool Steel (H13) microstructure @500X ……………………………………………………… 90 Figure 4.15 – A mounted Wafer-layered structure of AlBrnz/Stellite 6 ………………………….. 91 Figure 4.16 – A close look at one layer between two adjacent ones in a wafer sample….. 92 Figure 4.17– 500X SEM view of the bond area…………………………………..………………………….. 93 Figure 4.18 – 1000X SEM view of the bond area…………………………………..………………………. 93 Figure 4.19- 5000X SEM view of the bond area……………………………………………………………… 93 Figure 4.20 - 20,000X SEM view of the bond…………………………………………………………………. 93 Figure 4.21 Microstructure of 316-420 Wafer @100X ………………………………………………….. 94 Figure 4.22 Microstructure of 316-420 Wafer @500X ………………………………………………….. 94 Figure 4.23 Microstructure of 316-H13 Wafer @100X ………………………………………………….. 94 Figure 4.24 Microstructure of 316-H13 Wafer @500X ………………………………………………….. 94 Figure 4.25 Microstructure of 16221-316 Wafer @100X ………………………………………………. 95 Figure 4.26 Microstructure of 16221-316 Wafer @500X ………………………………………………. 95 Figure 4.27 Microstructure of AlBrnz-420 Wafer @100X ………………………………………………. 95 Figure 4.28 Microstructure of AlBrnz-420 Wafer @500X ………………………………………………. 95 Figure 4.29 – FGM of AlBrnz/420 SS sample mounted for analysis…………………………………. 97 Figure 4.30 – A look at two adjacent layers in an FGM sample showing two phases………..98 Figure 4.31-1000X SEM view of FGM phases………………………..………………………………………… 99 Figure 4.32 - 5000X SEM view of FGM phases………………………..………………………………………. 99 Figure 4.33 – 10,000X SEM view of FGM phases…………….…………………………………………….… 99 Figure 4.34 – 20K X SEM view of FGM phases…………………………………………………………………. 99 Figure 35, 36, 37 & 38 - Microstructure of 4 FGM samples showing full cross-sections …. 101 Figure 4.39 – A mounted sample ~ machine under the diamond …………………………………… 103 Figure 4.40 - A screen shot of the ~ software on the computer screen …….……………….… 104 Figure 4.41- Hardness in wafer sample AlBrnz-420SS ……………………………………………….…… 105 Figure 4.42 - Hardness profile for St6-AlBrnz Wafer ……………………………………………………… 106 Figure 4.43 – Hardness profile for 316SS-16221 ……………………………………………………………. 106 Figure 4.44 - Hardness profile for 316-420 Wafer …………………………………………………………. 106
xiv
Figure 4.45 – Hardness profile for 316SS-Tool Steel ……………………………………………………… 106 Figure 4.46 - Hardness across different layers (wafer) ……………………………………………….…. 107 Figure 4.47 - Hardness profile for 420-AlBrnz FGM ……………………………………………………….. 108 Figure 4.48 – Hardness profile for 316-420 FGM …………………………………………………………… 108 Figure 4.49 - Hardness profile for 316SS-16221 FGM ……………………………………………………. 108 Figure 4.50 – Hardness profile for 316-Tool Steel FGM …………………………………………………. 108
Chapter 5 – Thermal Expansion Studies
Figure 5.1 – Schematics of push rod dilatometer ………………………………………………………….. 112 Figure 5.2- CTE graphs with 316 SS and 420 SS………………………………………………………………. 114 Figure 5.3 – CTE graphs with 316 SS and EuTroLoy 16221……………………………………………… 115 Figure 5.4- CTE graphs with 316 SS and Tool Steel…………………………………………………………. 116 Figure 5.5- CTE graphs with AlBrnz and 420 SS………………………………………………………………. 117 Figure 5.6- CTE graphs with AlBrnz and Stellite 6………………………………………………………..…. 118 Figure 5.7 – CTE graphs for all monolithic samples ……………………………………………………….. 119 Figure 5.8 – CTE graphs for all FGM samples …………………………………………………………………. 120 Figure 5.9 CTE graphs for all WAFER samples ……………………………………………………………….. 121 Figure 5.10 - CTE graphs for all FGM and WAFER samples …………………………………………….. 122 Figure 5.11 – CTE values for all monolithic samples measured at 450 °C ………………………. 123 Figure 5.12 – CTE values for all WAFER and FGM samples measured at 450 °C …………….. 124 Figure 5.13- Schematics of a wafer sample under thermal load …………………………….……... 125 Figure 5.14 - Schematics of an FGM sample .……………………………………………………………...…. 126
Chapter 6 – Evaluation of Tensile Strength
Figure 6.1 – Shape/dimensions of tensile test samples …………………………………………………. 131 Figure 6.2 – A dog bone shaped tensile test sample ………………………………………………….….. 131 Figure 6.3 – Stress-Strain graphs for 316 SS & 420 SS ………………………………………………….... 133 Figure 6.4 – Stress-Strain graphs for 420 SS & AlBrnz ……………………………………………………. 135 Figure 6.5 – Stress-Strain graphs for 316SS & Tool Steel .…………………………………………….... 136 Figure 6.6 – Stress-Strain graphs for 316SS and EuTroLoy 16221 ………………………………….. 137 Figure 6.7 – Stress-Strain graphs for Monolithic samples ……………………………………………… 137 Figure 6.8 – Stress-Strain graphs for FGM samples ………………………………………………………. 138 Figure 6.9 – Stress-Strain graphs for WAFER samples …………………………………………………… 138 Figure 6.10 – Brittle fracture profile of 420SS sample ………………………………………………….. 139 Figure 6.11 – Ductile fracture profile of 316 SS sample ………………………………………………… 139 Figure 6.12 – Fracture profile of 316SS-420SS Wafer …………………………………………………... 139 Figure 6.13- Fracture profile of 316SS-420SS FGM ……………………………………………………….. 139 Figure 6.14 – Fracture profile of 420/AlBrnz wafer ………………………………………………………. 140 Figure 6.15 – Fracture profile of 420/AlBrnz FGM sample ………………………………………….… 140
Chapter 7 – Evaluation of Corrosion Resistance
Figure 7.1 – A galvanic cell and its major components ………………………………………………….. 143 Figure 7.2 – The galvanic series order for some engineering metals ……………………………... 145 Figure 7.3 – Corrosion test (Material loss) test set up ………………………………………….………. 150 Figure 7.4 – Aggressively corroding Eutroloy 16221 sample ………………………………….………. 151
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Figure 7.5 – Moderately corroding Tool Steel (H13) sample …………………………………………. 152 Figure 7.6 – An AlBrnz sample in H2SO4 acid …………………………………………………………….…. 152 Figure 7.7 – Mass loss graph for all samples in the 1st run of immersion tests …………….. 154 Figure 7.8 – Mass loss graph for all samples in the 2nd run of immersion tests ……………. 156 Figure 7.9 – 2nd run sample EuTroLoy 16221 dog bone ……………………………………………..… 156 Figure 7.10 – AlBrz-420SS dog bone sample (FGM) (2nd run) ………………………………….….… 157 Figure 7.11 – Mass loss measurements for 316 & 420 SS ………………………………………….….. 157 Figure 7.12 – Mass loss graph for 420SS & AlBrnz ………………………………………………………... 158 Figure 7.13 – Mass Loss graph for 316SS & H13 alloys ………………………………………………..… 159 Figure 7.14 – Mass Loss graph for 316SS and Colmonoy alloys …………………………………….. 160 Figure 7.15 – Mass loss graph for monolithic samples ………………………………………………..… 161
Chapter 8 – Conclusion & future direction
[No Figures used in this chapter]
Appendix
Figure A.1 - Schematics of a CO2 laser system …..………………………………………………….…….… 170 Figure A.2 – Schematics of an Nd: YAG laser system Source: www.mrl.columbia.edu .….. 173 Figure A.3 - A Nd:YAG laser pumping chamber schematic ………………………………………….…. 174 Figure A.4 - Diagram of a simple laser diode, not to scale …………………………………………….. 178 Figure A.5 – A Diode Pumped Solid State Laser (green) source: Wikipedia ……………………. 184 Figure A.6 - Schematics of a Fiber laser source: www.sciencemag.org ………………………….. 187
1
Chapter 1 Introduction
2
Chapter 1 - Introduction
1.1 Motivation for this research
The purpose of this research work was to create innovative metallic combinations or
structures that can offer novel properties for applications where such properties have
been non-existent so far. Such new materials and structures would have physical
and/or mechanical properties that the constituent alloys or elements they have been
created with would lack or not possess. These could be properties such as thermal
expansion, tensile strength, corrosion resistance and hardness. With new choices for
materials in hand, design engineers and scientists will be able to solve existing
technical problems that arise from lack of the mentioned properties in the alloys they
currently use in their applications.
This research aims at creating two unique structures and investigating their
properties. These are functionally graded materials (FGM) and wafer-layered
structures.
1.2 New materials & structures As of November 2011, 118 elements have been identified, the latest being
ununseptium in 2010 [1]. Of the 118 known elements, only the first 98 are known to
occur naturally on Earth; 80 of them are stable, while the others are radioactive,
decaying into lighter elements over various timescales from fractions of a second to
billions of years. Those elements that do not occur naturally on Earth have been
produced artificially as the synthetic products of man-made nuclear reactions. These
elements possess specific physical and mechanical properties today that make them
unique for certain applications.
An alloy is a mixture or metallic solid solution composed of two or more elements
[2]. Complete solid solution alloys give single solid phase microstructure, while
partial solutions give two or more phases that may or may not be homogeneous in
distribution, depending on thermal (heat treatment) history. Alloys usually have
different properties from those of the component elements.
3
New alloys can be made simply by varying the composition of the elements in order
to achieve specific properties. However, the properties acquired by varying
elemental composition in alloys are limited. What can offer more options to create
more innovative materials is creating novel structures consisting of carefully and
purposefully selected alloys. This research is built on the definition of “alloy” and
the various properties each of thousands of alloys offers. The two proposed new
structures i.e. FGM and wafer-layered structures, can offer unique sets of properties
and expand the material selection choice put forward to scientists and engineers.
1.2.1 Significance and applications of FGMs
In materials science functionally graded material (FGM) may be characterized by the
variation in composition and structure gradually over volume, resulting in
corresponding changes in the properties of the material. The materials can be
designed for specific function and applications. To date, various approaches based
on the bulk (particulate) processing, preform processing, layer processing and melt
processing are used to fabricate the functionally graded materials.
FGMs offer great promise in applications where the operating conditions are severe.
Such applications include wear-resistant linings for handling large heavy abrasive
ore particles, rocket heat shields, heat exchanger tubes, thermoelectric generators,
heat-engine components, plasma facings for fusion reactors, and electrically
insulating metal/ceramic joints. They are also ideal for minimising
thermomechanical mismatch in metal-ceramic bonding.
In the technical world, FGMs were first proposed around 1984-85 when Japanese
researchers studied advanced materials for aerospace applications working on a
space plane project. The body of the space-plane will be exposed to a high
temperature environment (about 1700°C), with a temperature gradient of
approximately 1000°C, between inside and outside of the space-plane. There was no
uniform material able to endure such conditions. Therefore, the researchers devised a
4
concept to fabricate a material by gradually changing (grading) the material
composition (see Figure 1.1), and in this way improve both thermal resistance and
mechanical properties [3].
Figure 1.1 - Plasma sprayed functionally graded ZrO2/NiCoCrAlY thermal barrier coating [3]
There are many areas of application for FGM. The concept is to make a composite
material by varying the microstructure from one material to another material with a
specific gradient. This enables the material to have the best of both materials. If it is
for thermal or corrosive resistance or malleability and toughness, the properties of
both constituent materials may be used to avoid corrosion, fatigue, fracture and stress
corrosion cracking.
The transition between the two materials can usually be approximated by means of a
power series. The aircraft and aerospace industry and the computer circuit industry
are very interested in the possibility of materials that can withstand high thermal
gradients. This is normally achieved by using a ceramic layer connected with a
metallic layer.
5
Functionally graded structures can also be seen in nature, in bio-tissues of animals,
such as bones and teeth, and also in plants. For example a tooth and more specific
dental crowns are an excellent example of the application of a FGM. It requires a
high wear resistance outside (enamel), and a ductile inner structure for reasons of
fatigue and brittleness. Further, it requires a translucent outer area and a specific set
of colour nuances for reasons of aesthetics [4].
1.2.2 Significance and applications of WAFER structures
Another innovative structure that is selected as part of this research is to create
novel structures using two alloys, which the researches have chosen to call
wafer-layered metallic structures. This structure is created by alternatively
depositing two different alloys, where each layer is metallurgically bonded to
the adjacent layers, thus creating a 3D structure with unique mechanical and
physical properties.
Various pairs of two different alloys have been used to create purpose built
wafer components where a combination of the two specific alloys has offered a
desirable set of characteristics. A typical example of this is the bimetallic strip. A
bimetallic strip is used to convert a temperature change into mechanical
displacement. The strip consists of two strips of different metals which expand
at different rates as they are heated, usually steel and copper, or in some cases
brass instead of copper. The strips are joined together throughout their length
by riveting, brazing or welding. The different expansions force the flat strip to
bend one way if heated, and bend in the opposite direction if cooled below its
initial temperature. The metal with the higher coefficient of thermal expansion
is on the outer side of the curve when the strip is heated and on the inner side
when cooled.
In this research, it is proposed that more than one layer of each alloy be
deposited alternatively to create the 3D wafer structure. For the purpose of this
6
research, cubic sample blocks of wafer structure of a range of engineering alloys
have been made. However, cylindrical and other 3D structure shapes can also
be made for specific purposes and the structures will be able to be machined
into desired shapes and sizes.
1.3 Additive manufacturing
Additive manufacturing (AM) is a process of making three dimensional solid objects
from a digital model. AM is achieved using layer by layer fabrication processes,
where an object is created by laying down successive layers of material. AM is
considered distinct from traditional machining techniques (subtractive processes),
which mostly rely on the removal of material by methods such as cutting and
drilling.
Additive manufacturing (AM) is usually performed by layer by layer deposition
using various technologies such as Stereolithography, Fused Deposition Modelling,
Selective Laser Sintering and Laser based metal deposition. Since the start of the
twenty-first century there has been a large growth in the use of these processes.
The AM technology is used in jewellery, footwear, industrial design, architecture,
engineering and construction, tooling, automotive, aerospace, dental and medical
industries, education, civil engineering, and many other fields.
The term additive manufacturing describes technologies that create objects through a
sequential layering process. Objects that are manufactured additively can be used
anywhere throughout the product life cycle, from pre-production (i.e. rapid
prototyping) to full-scale production (i.e. rapid manufacturing), in addition to tooling
applications and post-production customisation.
A number of additive manufacturing technologies are available. They differ in the
way layers are deposited to create parts and in the materials that can be used. Some
methods melt or soften material to produce the layers, e.g. selective laser sintering
(SLS) and fused deposition modelling (FDM), while others cure liquid materials
using different sophisticated technologies, e.g. Stereolithography (SLA). With
laminated object manufacturing (LOM), thin layers are cut to shape and joined
7
together (e.g. paper, polymer, and metal). Each method has its own advantages and
drawbacks. .
In order to create metallic functionally graded materials, which is the focus of this
research, one of the two additive manufacturing techniques that are capable of
generating such structures has to be selected. These two technologies are laser
assisted direct metal deposition –DMD – and Laser engineered net shaping – LENS
– system. This capability of these two systems is due to the fact that they have
multiple powder feeders which can alternate the depositing metal throughout the
process. These techniques are rather new and not much research work has been done
involving them.
In this research, Laser assisted Direct Metal Deposition technique (DMD) was
selected to create the 3D structures, FGM, wafer-layered structure and monolithic
samples.
1.3.1 Laser Direct Metal Deposition
DMD is a form of rapid manufacturing process that makes parts from metal powder
that is melted by a laser, and then solidified in place. This process differs from
conventional Selective Laser Sintering (SLS) process (powder material processed by
laser under computer control) in that the metal powder, such as tool steel, is melted
through a nozzle rather than being sintered in a powder bed.
DMD also allows the repair or reconfiguration of parts, molds and dies that are made
out of the actual end material, such as tool steel or aluminum. It always produces a
new part or part reconfiguration directly from a CAD model.
DMD is the blending of five common technologies: lasers, computer-aided design
(CAD), computer-aided manufacturing (CAM), sensors, and powder metallurgy. The
resulting process creates parts by focusing an industrial CO2 laser beam onto a flat
work piece or preformed shape to create a molten pool of metal to lay down each
layer of metal. Figure 1.2 shows the schematics of the DMD process.
8
Figure 1.2 - Schematics of a Direct Metal Deposition process
Some of the main features of the DMD system include [5]:
• Co-axial nozzle design gives full five-axis deposition capability versus side
powder-feed systems, which can only deposit linearly in motion along with local
shielding by inert gases
• “Moving optics” capability allows processing of large, heavy parts
• A closed-loop optical feedback system monitors and controls the melt pool in real
time, resulting in a near net shape part
• Proprietary tool path software translates CAD data into the nozzle motion for six-
axis deposition
• A multiple powder delivery system (powder feeder container) allows deposition of
different materials simultaneously or consecutively at specified locations, enabling
production of on-the-fly alloys/composites
• Deposits are fully dense and create a true metallurgical bond with the
substrate/part. DMD has been used successfully on a broad range of materials,
including, tool steels, stainless steels, high speed steels, and alloys of nickel, cobalt,
titanium, and aluminum.
9
• Multi-functional software for normal production jobs and for research and
development activities
• Inert chamber atmosphere for deposition of reactive materials, such as titanium,
tantalum and molybdenum.
As-deposited material is fully dense. Its mechanical and physical properties can be as
good as or better than those of comparable cast or wrought materials. DMD materials
can be fully stress relieved, heat-treated, and aged to alter the microstructures for
specific applications and to improve ductility or toughness. DMD has also been
successfully applied in a wide range of materials including, various, steels, Ni-alloys,
Co-alloys, Ti-alloys, Al alloys, Cu-alloys, refractory metals, such as Ta, and cermet
(i.e., metal-ceramic composites). Figure 1.3 shows a 3D metallic structure created by
the POM Direct Metal Deposition system.
Figure 1.3 - A DMD made structure
The machine used for fabrication of samples for this research was a POM 505 DMD
machine at Swinburne University of Technology. Figure 1.4 shows this machine.
10
Figure 1.4 - Trumph DMD 505 POM® system used for this research
The POM Direct Metal Deposition (DMD)® 505 represents a CAD-driven process
for depositing given volumes of complex metal alloys onto the substrate or to repair
surface of turbine components, tooling, and other complex parts, using a 5 kW CO2
laser as a source of energy. The work envelope is 1m x 0.75m x 2m with 3D work
piece mounts with 5 axis moving optics capabilities.
1.3.2 LENS 3D system
It can take several years to develop a new material using conventional methods.
Conventional manufacturing processes are costly, time-consuming and allow the
researcher to evaluate just a single material chemistry at a time. New fabrication
techniques are now available, which are highly flexible to address a diverse set of
research disciplines and industry applications. With LENS systems, material
researchers have a new tool to address these needs.
LENS uses a high-power laser (500W to 4kW) to fuse powdered metals into fully
dense 3-dimensional structures. The LENS 3D printer uses the geometric
11
information contained in a Computer-Aided Design (CAD) solid model to
automatically drive the LENS process as it builds up a component layer by layer.
Additional software and closed-loop process controls ensure the geometric and
mechanical integrity of the completed part. The LENS 3D printer can process a wide
variety of metals including titanium, nickel-base superalloys, stainless steels and tool
steels - all of which are commercially available in the required powder form. The
results from LENS consistently demonstrate better metallurgical and mechanical
properties than other processes due to an improved microstructure. For example,
LENS-deposited 316 SS typically has a cellular spacing of just a few microns, which
leads to yield strengths approaching twice that of conventionally processed 316SS.
[6]. LENS® applications include the repair of worn components, performing near-
net-shape freeform builds directly from CAD files, and the cladding of materials.
Figure 1.5 - Basic layout and flow paths for a typical LENS® system [7].
Figure 1.5 shows the typical LENS process layout. The deposition substrate or
“target” is aligned to the desired start point of the deposit. The powder feeder(s) feed
the powder delivery nozzle assembly, which creates a powder stream that converges
at the point of the deposit. Next, the laser provides a focused beam that is delivered
to the point of deposit. The focused laser beam melts the surface of the target and
12
generates a small molten pool of base material. Powder that is being delivered to this
same spot is absorbed into the melt pool, thus generating a deposit that may range
from 0.127 to 1.016 mm thick and 1.016 to 4.064 mm. wide. Motion control for the
deposit may be programmed manually or may be generated from CAD files that are
processed by the system’s software. Deposits are typically made in a controlled
argon atmosphere containing less than 10 ppm oxygen. Some cladding work may be
performed utilizing a shielding gas system similar to the gas metal arc welding
process [7].
All LENS® deposits are metallurgically bonded and exhibit heat-affected zone
(HAZ) and dilution zones ranging from 0.127 to 0.635 mm thick. Low heat input and
minimal distortion are consistent deposit characteristics. Due to the small melt pool
and high travel speeds, the deposits cool fast (up to 10,000°C/s), which generates
fine grain structures that may be one order of magnitude smaller in size than
comparable wrought products. Mechanical properties and the quality of the deposits
are typically better than castings and approach properties of wrought products. In
some cases, like titanium, the properties of deposits may actually exceed typical
handbook values [7].
Stainless steels (304, 316, 410, 420, 17- 4PH), tool steels (H13), nickel alloys (617,
625, 718), cobalt alloys (#6 Stellite, #21 Stellite), titanium alloys (Ti-6-4, Ti-6-2-4-
2), and a variety of cladding alloys are some of the materials that are successfully
being deposited utilizing this process. Aluminium and copper alloys are difficult to
deposit due to their reflective properties. Research work is also being performed on
tantalum, tungsten, rhenium, and molybdenum alloys. Functionally graded deposits
are also being investigated.
Flexibility is a key ingredient guiding this technology. LENS® systems are typically
coupled with lamp-pumped Nd:YAG lasers or more recently the new fibre lasers.
Both lasers have wavelengths that are ~1 micron long. The optical absorption of
these laser beams is much higher for the Nd:YAG and fibre laser beams than that of
the CO2 laser beam, whose wavelength is 10 microns. Having a higher absorption
13
percentage relates to lower overall energy required to perform a comparable laser
deposit. Typically, the Nd:YAG and fibre lasers require only one-half the wattage of
a CO2 laser to achieve the same deposition rates. The Nd:YAG and fibre laser beams
may also be delivered using fibre optics where the CO2 beam must be delivered via
reflective mirrors. This means the component being processed must be manipulated
and moved under the stationary CO2 beam. This may still be the case for the
Nd:YAG and fibre lasers, but their delivery fibres also have the ability to be
manipulated as part of the motion control system. This flexibility opens up many
more potential applications.
1.4 Process parameters of laser DMD
In order to run a DMD machine, the following parameters must be defined:
1. Powder (alloy, particle size, atomization type)
2. Laser power (Watts)
3. Powder delivery rate (gr/min)
4. Deposition speed (mm/min)
5. Shielding gas (Argon/Helium)
6. Tool path (manipulation program/CAD file)
For each new alloy to be used in a DMD process, a recipe of all the parameters must
be defined to achieve an acceptable result. This is due to the different heat
characteristics of each individual alloy and their different reactions to melting and
rapid solidification. One cannot use the same recipe of parameters for two distinctly
different alloys and expect the same outcome.
For this research, and for each individual alloy i.e. 316 SS, 420 SS, Stellite® 6,
EuTroLoy®16221, H13 Tool steel and AlBrnz, a unique set of parameters were used
to create the 3D structures.
It is also essential to consider all safety aspects of working with class 4 laser systems
when using DMD machines.
14
1.5 Project objectives
The main objective of this project was to produce and investigate new metallic
structures with superior and novel physical and mechanical characteristics which
cannot be found in existing single alloys or structures.
Some of such properties are:
Higher tensile strength
Better corrosion resistance
Higher fatigue strength
Lower thermal expansion
The added value of using a combination of two alloys in the same structure through
either wafer or FGM model has the potential to create improved physical and
mechanical properties.
This opportunity can be used as a means to solve existing problems where pre-
mature failures are occurring in systems and components which operate under high
loads, in high corrosive environments or high temperatures. The resulted structures
with positive results can also be used to widen the engineering design choices of new
components and systems considering new and superior physical and mechanical
properties.
The project then aimed to further understand and analyse such structures and create a
base for further alloys to be used in these two structures to achieve more novel
combinations and results.
This thesis and the results reported in it have a unique significance which comprises
of genuine novelty. The major contribution of this thesis is the introduction of newly
identified and developed materials with unique and novel mechanical and physical
properties. Further research can build on this thesis and develop a wider variety of
new materials and study and identify their special and new characteristics and the
areas that they can add value in engineering design and component performance.
15
1.6 Structure of thesis
After providing an introduction, literature review and a thorough description on
materials and sample production methods, the thesis presents the results of 4 sets of
materials properties tests on the samples. These tests are - as shown in the following
diagram – microstructure and Microhardness investigation, Thermal Expansion
studies, Evaluation of Tensile Strength and Evaluation of Corrosion Resistance. A
series of conclusions are consequently presented with suggestions for future
directions.
1. Introduction
2. Literature Review
3. Materials & Methods
4. Microstructure & Hardness
Investigation
5. Thermal Expansion
Studies
6. Evaluation of Tensile Strength
7. Evaluation of Corrosion Resistance
Conclusion and Future Direction
16
Chapter 2 Literature Review
17
Chapter 2 – Literature Review
2.1 Novel materials and structures
Materials and their characteristics has always been an attractive field for researches
and scientists to work in. While thousands of different unique materials ranging from
non-metallic to metallic have been identified or developed, scientists have still got
the urge to develop more new materials using the most modern techniques.
The initial focus of this research was to create metallic structures with negative
coefficient of thermal expansion. To this end, all the major work done on materials
with negative thermal expansion, NTE, was reviewed. Then based on the capabilities
of existing technologies and characteristics of available metallic alloys and this
literature review, it was decided to broaden the scope of this research project to
focus more on development of two novel metallic structures – FGM and wafer -
which will be reviewed later in this chapter.
2.2 Negative Thermal Expansion
Materials with negative thermal expansion (NTE) properties have numerous
applications that interest design engineers and scientists in aerospace, electronics,
dentistry and other industries and fields that at some stage experience unwanted
thermal expansion in parts. This section reviews research done on developing metal
alloys or solid structures from combination of metal alloys that demonstrate negative
thermal expansion properties. The review shows that a variety of alloys, composites
and structures have been used to develop NTE metallic structures, some of which
have achieved significant successes in doing so. In order to fabricate parts from a
mix of alloys or a structure comprising a series of layers from various alloys, a
technology with high flexibility was needed. Traditional welding or casting methods
could not offer such capabilities. Direct Metal Deposition (DMD) is a technology
that uses laser energy to melt metal powder injected coaxially with the laser beam on
substrates and create shapes and structures directly from CAD models with none or
minimal metallurgical defects. The technology can be used to explore the
18
manufacture of complex structures with NTE properties using a range of alloying
powders.
Among a material’s physical and mechanical specifications, thermal expansion has
certainly attracted a lot of attention from researchers, scientists and design engineers.
The effect a material’s high or low volume expansion may have on its performance
or on the performance of the machine, which it is part of, can be extremely
significant. The thermal expansion of materials is represented by their coefficient of
thermal expansion or CTE.
Materials with negative thermal expansion (NTE) are considered a minority group
amongst the big family of materials most of which possess a positive thermal
expansion (PTE) [8-13]. The classic examples of NTE materials are rubber and
water [14]. The tendency of NTE materials to contract on heating makes them an
intriguing class of anomalous materials whereby the effect of temperature mimics
(instead of counteracting) the effect of pressure. Several research projects have been
done in the area of developing materials with NTE [8, 20]. A reason for conducting
research to develop such materials with NTE seems to be the fact that in most
applications where components are subject to high temperatures, engineering
designers cannot afford to have more than a certain amount of linear or volumetric
expansion due to design issues and size limitations. The linear thermal expansion of
materials is measured according to the associating ASTM standards to ensure
consistency in results [27-29]. Such materials have a range of potential engineering,
photonic, electronic or structural applications. If, for example, one were to mix an
NTE material with a "normal" material which expands on heating one could
envisage making a zero expansion composite. So materials with NTE have exclusive
applications where materials with PTE cannot be used [8].
2.2.1 SOME NTE MECHANISMS
2.2.1.1 Bimetallic beams
A unique technique to make NTE materials has been developed by computational
scientists. In their method Sigmund [30] and independently N. Kikuchi and B-C
19
Chen [31- 32] used a 3-phase topology optimization method [33] to design an NTE
artificial material. This material is a combination of unit cells which are made of two
different material phases with positive thermal expansion and a void phase. Figure
2.1 demonstrates how the unit cell and the structure work to create a negative
thermal expansion property. As can be seen, the high thermal expansion phase pulls
the structure inward to cause the contraction on heating.
Figure 2.1 - Chen-Kikuchi design for NTE artificial material – [33]
Nickel alloy series were chosen as the materials for the two materials phases in the
design. The design is essentially an arrangement of bimetallic beams [33].
2.2.1.2 Oxide-based frameworks
The mechanisms responsible for the negative thermal expansion behaviour of
materials can be associated with magnetostriction in ferromagnetic materials,
valence transitions in intermetallic and fulleride materials, and the population of low-
energy phonon modes, as is well recognized in a number of oxide-based framework
materials [15-18].
20
Among the above-mentioned mechanisms, the oxide-based framework is probably
the most researched on mechanism of NTE materials due to the comparatively high
NTE of such materials. The mechanism is in fact a linkage of single atom metal-
oxygen-metal structure such as Zr-O-W in ZrW2O8 which is a NTE material [8].
This can be seen in figure 2.2.
Another NTE structure is metal-cyanide-metal, which shows quite large NTE figures
like in Zn(CN)2 [8, 19].
Figure 2.2 - Left: Crystal structure of NTE material Cubic ZrW2O8 – Right: TEM picture of a
ZrMo2O8/Polyimide composite [24]
Cubic zirconium tungstate (alpha-ZrW2O8), one of the several known phases of
zirconium tungstate (ZrW2O8) is perhaps one of the most studied materials to
exhibit negative thermal expansion. It has been shown to contract continuously over
a previously unprecedented temperature range of 2 to 1050 K. Since the structure is
cubic, as described below, the thermal contraction is isotropic - equal in all
directions. There is much ongoing research attempting to elucidate why the material
exhibits such dramatic negative thermal expansion [35].
This material is thermodynamically unstable at room temperature with respect to the
binary oxides ZrO2 and WO3, but may be synthesised by heating stoichiometric
quantities of these oxides together and then quenching the material by rapidly
cooling it from approximately 900°C to room temperature.
The structure of cubic zirconium tungstate consists of corner-sharing ZrO6
octahedral and WO4 tetrahedral structural units. Its unusual expansion properties are
thought to be due to vibrational modes known as Rigid Unit Modes (RUMs), which
21
involve the coupled rotation of the polyhedral units that make up the structure, and
lead to contraction.
As can be seen in Figure 2.3, the arrangement of the groups in the structure of cubic
ZrW2O8 is analogous to the simple NaCl structure, with ZrO6 octahedra at the Na
sites, and W2O8 groups at the Cl sites. The unit cell consists of 44 atoms aligned in a
primitive cubic Bravais lattice, with unit cell length of 9.15462 Angstroms.
Figure 2.3- An image of the crystal structure of cubic ZrW2O8 [35]
Figure 2.3 is an image of the crystal structure of cubic ZrW2O8, showing the corner-
sharing octahedral (ZrO6, in green - larger cubes) and tetrahedral (WO4, in red –
smaller cubes) structural units. An incomplete unit cell is shown so that the
positioning of the W2O8 unit along the body diagonal of the unit cell may be seen
[28]. Mary et al [35] report that the ZrO6 octahedra form is only slightly distorted
from a regular conformation, and all oxygen sites in a given octahedron are related
by symmetry. The W2O8 unit is made up of two crystallographically distinct WO4
tetrahedra, which are not formally bonded to each other [35]. These two types of
tetrahedra differ with respect to the W-O bond lengths and angles. The WO4
tetrahedra are distorted from a regular shape since one oxygen is unconstrained (an
22
atom that is bonded only to the central tungsten (W) atom), and the three other
oxygen are each bonded to a zirconium atom (i.e. the corner-sharing of polyhedra).
The structure has P213 space group symmetry at low temperatures. At higher
temperatures, a centre of inversion is introduced by the disordering of the orientation
of tungstate groups and the space group above the phase transition temperature
(~180C) is Pa [35]. Octahedra and tetrahedra are linked together by sharing an
oxygen atom. In Figure 2.3, note the corner-touching between octahedra and
tetrahedra; these are the locations of the shared oxygen. The vertices of the
tetrahedra and octahedra represent the oxygen, which are spread about the central
zirconium and tungsten. Geometrically, the two shapes can "pivot" around these
corner-sharing oxygens, without a distortion of the polyhedral themselves. This
pivoting is what is thought to lead to the negative thermal expansion, as in certain
low frequency normal modes. This leads to the contracting 'RUMs' as mentioned
above [35].
In another research [21], thermal expansion from powder diffraction measurements
[22, 23] of MgB2 have revealed an anomalous volume expansion on cooling below
critical temperature [21]. Figure 2.4 shows the linear thermal expansion of this
material. The length decreases with temperature, as occurs in most materials, but it
expands on cooling below Tc=38.7 K as illustrated in the inset where the 20 Å scale
reveals the absolute length change of the 4238um long specimen.
Figure 2.4 - Linear thermal expansion of the 4238um long specimen. The region near Tc is
shown in the inset; the 20 Å scale indicates the absolute length change. [21]
23
2.2.1.3 Oxides with coordination No. 2
Negative thermal expansion behaviour has been found in many oxides where oxygen
or a cation has a coordination number of two. The MO2, AM2O7, A2M3O12,
AMO5, and AO3 families, where A is an octahedral cation, M a tetrahedral cation,
and the oxygen coordination is two, have been investigated for their thermal
expansion properties. Negative thermal expansion has been found in all families
except the AO3 family, where low thermal expansion was found in the case of
TaO2F. Open networks are necessary to allow free transverse thermal motion of
oxygen, which is the apparent cause of negative thermal expansion in these families.
This openness leads to two problems. One is that structure collapse transitions tend
to occur as the temperature is lowered. There is little or no thermal expansion below
this transition. A solution to this problem is to maintain sufficient ionic character in
the bonds holding the network together. The other problem is that when the networks
become sufficiently open, they tend to hydrate. This hydration destroys the negative
thermal expansion of the network [17].
2.2.1.4 Polymer Composites
Large positive thermal expansion in polymers is one of the major drawbacks in using
polymers in applications where the sample dimensions play an important role [34].
Negative thermal expansion (NTE) materials have received considerable scientific
interest because of their potential for use as fillers in composites. Mixing of a
positive thermal expansion material with an NTE filler should reduce the overall
expansion coefficient of the composite while maintaining other desirable properties
of the matrix material.
In a research by Chandra Ameesh et al [34], a method to vary the thermal expansion
of PMMA-based polymer composites by blending with a negative thermal expansion
material, PbTiO3 was used. Chandra showed that the thermal expansion coefficient
of the composite could be tailored by suitably adjusting the ratio of polymer and
ceramic filler.
24
2.2.1.5 Synthetic approach
Dedicated research on NTE materials started only during the last decade. Much
progress has been made in the synthesis and characterization of NTE compounds,
but many show properties like irreversible phase transitions under pressure that
could interfere with the processing of composites. In addition, a number of NTE
oxides are metastable, thus requiring synthetic approaches that use kinetic control
[25].
Another example of mixing a NTE material with a PTE material is the case of AgI
and CuI [27]. AgI is a well-known superionic conductor possessing a negative
thermal expansion (NTE) coefficient while CuI is a p-type semiconductor possessing
a positive thermal expansion coefficient. Pellets of X-Ray Diffraction (XRD)
characterized compositions in the AgI–CuI system namely, β AgI, γ AgI,
Ag0.5Cu0.5I, Ag0.25Cu0.75I, Ag0.10Cu0.90I, Ag0.05Cu0.95I and γ CuI have been
examined by quartz pushrod dilatometry measurements in order to look for a zero
thermal expansion material. It is found that the systematic displacement of Ag by Cu
gradually reduces the NTE anomaly in AgI.
The composition Ag0.25Cu0.75I apparently exhibits near-zero thermal expansion.
The results are discussed qualitatively in terms of relevant models [26].
2.2.2 Discussion on NTE
The papers that were reviewed were successful in achieving some negative thermal
expansion characteristic in the materials they have examined.
The bimetallic beams technique is an effective method in achieving negative thermal
expansion in the final product. And since it is dealing with two metals which are
deposited separately, the production is not limited to a certain series of metals or a
fixed combination of the two metals. Also the major characteristic of the two alloys
is that one is a material with positive thermal expansion and the other is a material
with negative thermal expansion. This fact leaves us with a wider range of options to
select other metals and alloys which match the NTE and PTE aspect of the procedure
but might have other more desirable mechanical or physical characteristics.
25
Another point in the bimetallic beams test is that the NTE property is directional.
The final product, assuming it is a combination of unit cells on a flat surface,
demonstrates its overall NTE property only in the surface i.e. X-Y direction and not
in a vertical direction i.e. Z.
Of course there can be provisions to transfer this NTE property to the Z plane by
proper design modification. Another issue with this method is that due to the
presence of the void phase in the design of the bimetallic beam, there is always a
certain porosity portion in the part that might not be suitable for certain engineering
applications where strength and other physical and mechanical properties are vital to
the application and the void phase causes flaws or insufficiency in some of these
properties.
The second NTE material discussed here in this chapter i.e. ZrW2O8 was developed
in 1996, and from the early stages it has been widely used by design engineers. The
only flaw or problem that is reported for the material is that at high pressure,
zirconium tungstate undergoes a series of phase transitions, first to an amorphous
phase, and then to a U3O8-type phase, in which the zirconium and tungsten atoms
are disordered [35]. This will cause the NTE material to lose its NTE property at
high pressures.
The NTE seen in MgB2 is only in the cooling process and is insignificant to
engineering applications and high temperature fields. But the fact that NTE can be in
both high and low temperatures can be the subject of other NTE related researches.
The NTE observed in the oxide families, the polymer composites and the materials
fabricated through synthetic approaches are all valid successes but the values of NTE
property they have achieved puts them more into the near zero thermal expansion
range rather than pure NTE.
One major issue with carrying out research work on producing NTE materials using
the whole variety of metallic elements is the fabrication techniques and their
limitations. Direct Metal Deposition technology is capable of producing specimens
and parts from a combination of elements with a high flexibility in terms of varying
element contents to achieve a near zero or negative thermal expansion metal or alloy.
26
Research review on NTE has shown that negative thermal expansion maybe
achievable through various scientific approaches in materials with positive thermal
expansion. However, more non-metallic NTE materials have been developed
compared to metallic materials. It is also found that a structural approach to create
NTE metallic material has proved to be successful.
2.3 Functionally Graded Materials
A unique composite structure is known to be the functionally graded materials
(FGM). FGM belongs to a class of advanced material characterized by variation in
properties as the dimension varies. The overall properties of FGM are unique and
different from any of the individual material that forms it. While FGMs are
considered to be a new type of material structure, a significant deal of research has
been invested on such structures and their characteristics. This class of materials is
currently receiving a great degree of interest due to their special merits [36].
2.3.1 Production
There are several methods to make FGM components and parts each of which has
got its advantages, disadvantages, limitations and specific applications.
Overall, there are two types of graded structures of the FGMs, namely continuous
structure shown in Fig. 2.5 (a), and stepwise structure shown in Fig. 2.5 (b).
Figure 2.5 – Two different types of FGM structures: a) Continuous FGM b) Stepwise FGM
27
In the first type, the change in composition and/or microstructure occurs
continuously with position. On the other hand in the second type, the microstructure
feature changes in a stepwise manner, giving rise to a multilayered structure with
interfaces existing between discrete layers [37]. As will be described in more detail
later, the continuous graded structure can be created by a centrifugal force. In the
past, many kinds of processing methods for FGM have been proposed. A few of
such techniques are described here.
2.3.1.1 FGM by Powder Metallurgy
Powder metallurgy is one of the most important methods of producing FGMs. An
example of a typical fabrication process by the powder metallurgy is schematically
illustrated in Fig. 2.6.
Figure 2.6 – Schematics of powder metallurgy method to fabricate FGMs [30]
At first, material A and material B are weighed and mixed, as shown in Fig. 2.6 (a).
Then each mixed-powder is mixed uniformly by a V-shape mill, as shown in Fig. 2.6
(b). Next step is stepwise staking of premixed powder according to a predesigned
spatial distribution of the composition (Fig. 2.6 (c)). Last step is the sintering
process. Spark plasma sintering (SPS), as shown in Fig. 2.6 (d), is one of the more
advanced sintering methods, and it makes possible sintering high quality materials in
short periods by charging the intervals between powder particles with electrical
energy and high sintering pressure. However, usually the FGM fabricated by this
28
method should have the stepwise structure, and it is difficult to produce the FGMs
with continuous gradients [38].
Other scientists have also focused on making FGMs using powder metallurgy
technique. Shahrjerdi et al [39] demonstrate the functionally graded metal-ceramic
composite fabricated via pressure-less sintering. The pure metallic and ceramic
components are Titanium (Ti) and Hydroxyapatite (HA), which were located at the
ends of a cylindrical specimen. FG samples are prepared with mixing ratios of 100:0,
75:25, 50:50, 25:75, 0:100. The cylindrical samples had a thickness of 6 mm in size
and 20 mm radius. Samples are created by using carbon cylindrical die. The
optimum thermal load mapping is obtained experimentally. The properties of all
FGM products are characterized by shrinkage, optical microscope, scanning electron
microscope (SEM), energy dispersive spectrometry (EDX) and hardness test. The
grade of the FGM material is proven by results from all recorded measurements, as
well as linearity of shrinkage. Result from optical micrograph and SEM indicate that
the HA/Ti FG cylinder can be produced successfully by cold pressing with
developed thermal mapping. Vicker’s hardness of HA/Ti is higher than that of pure
microcrystalline Ti (metal) and reduces by decreasing the density of the layer of
HA/Ti [39].
29
Figure 2.7 – Fabrication process stages flow chart in pressure-less sintering [39]
Figure 2.7 shows the fabrication process stages. The gradation of the components
was considered from the metallic (Ti) end to the ceramic (HA) end. All of the steps
such as the selection criteria for the powders, percentages, blending, the effect of
gravity in the cold pressing, and sintering were indicated in detail. An optimum
sintering map was derived experimentally. Four technicians, shrinkage, SEM, EDX,
and Vickers’ micro-hardness, were employed to validate the results of this study.
The structure and composition analysis of the FG cylinder produced with different
layers confirmed the functionality of the design. The linear shrinkage obtained was
an appropriate indicator of validity. The Vicker’s hardness of HA/Ti was higher than
that of pure microcrystalline Ti metal and decreased in layers 3 and 4 of the HA/Ti
FG. It is considered that these examinations could lead to an estimate of the grading
30
index value that could be used for the theoretical formulation of FGM material
properties [39].
2.3.1.2 FGM by Centrifugal Solid Particle Method
One of the fabrication methods for functionally graded materials (FGMs) is a
centrifugal solid-particle method, which is an application of the centrifugal casting
technique. Functionally graded materials (FGMs) can be fabricated under a
centrifugal force, by which it is possible to produce the FGMs with continuous
gradients. Fabrication methods of FGMs under the centrifugal force are classified
into three categories, namely centrifugal method, centrifugal slurry method and
centrifugal pressurization method. Watanabe and Sato [38] have emphasized the use
of the FGM fabrication methods under the centrifugal force as ones of the practical
methods, since it has the feasibility of scaling up to mass production at a low cost.
While centrifugal solid particle method is considered as a common method to
fabricate FGMs, it is difficult to fabricate FGMs containing nano-particles by the
centrifugal solid-particle method. As a research project, Yoshimi et al. [40] proposed
a novel fabrication method, which they have named the centrifugal mixed-powder
method, by which they can obtain FGMs containing nano-particles. Using this
processing method, Cu-based FGMs containing SiC particles and Al-based FGMs
containing TiO2 nano-particles on their surfaces have been fabricated [40].
2.3.1.3 FGM by DMD and LENS® Technologies
An effective technology in creating 3D shape metallic parts and FGM is the laser
direct metal deposition (DMD) technique. This technique is an advanced version of
laser cladding. Laser cladding is a process to create advanced functional layers and
engineering prototypes with a variety of metal powders. The generation of simple
geometric shapes with no change in cross-section is relatively simple using this
process, but the generation of more complex shapes, which possess functional
properties, requires a greater degree of effort to build up these functional structures
[41].
31
Laser direct metal deposition (DMD) is a multilayer cladding method, which is
based on the mechanism of the laser beam cladding process. Numerous tracks or
numerous layers are deposited on top of each other to build up complex three
dimensional structures or bodies [42-44]. This method can be applied for small scale
production, rapid prototyping, or repair engineering. The laser deposition
advantageously copes with these problems. The laser DMD process is suitable for
use with a variety of metal powders and is therefore ideal as a basis for this FGM or
wafer building process. Besides, the laser direct metal deposition can also be used to
repair metallic parts and can improve the life cycle behaviour of costly and highly
stressed components.
Sorn Ocylok et al [45] have used the DMD technique to develop FGMs to increase
wear and corrosion protection. The growing competition in the die casting industry
requires extension of the lifetime of the moulds. This major demand can be fulfilled
by increasing the wear resistance of the mould with hard surface layers to reduce
erosion. Combining this feature with high tensile strength and high ductility, the
thermal or stress induced cracking during the casting process with its cyclic thermal
and mechanical stresses can also be minimised. However, commonly used hot
working tool steels have limitation with regards to the required properties. Laser
cladding is an established technique to increase wear and corrosion protection locally
and it offers the possibility to combine properties by multi-graded layers.
Experimental investigations show that laser cladding can be used to build up graded
layers with a smooth transition of composition. The cladded layers are assembled
without any cracks and have low porosity. Combinations of iron-based materials
have a nearly linear increase of hardness in the transition layers of the gradient [45].
There is a great deal of potential in developing more novel FGMs using the laser
DMD technique. Higher quality of the FGMs needs to be produced with no
porosities or cracks in the products. Such high quality products are essential in
industries such as aerospace and in applications such as biomedicine. Pompe et al
[46] reports that the development of new biomaterials for medical applications is one
of the challenging tasks for materials science today. There is an urgent need for
32
better implants as well as for the manufacturing of artificial tissues. They have
emphasized on the suitability of FGMs by relating them to our bone structure. One
remarkable feature of biomaterials is the formation of hierarchical structures.
Furthermore, the complex functionality of various tissues includes a continuous
change from one structure or composition to another. For instance, the graded design
of bone with a change from a dense, stiff external structure (the cortical bone) to a
porous internal one (the cancellous bone) demonstrates that functional gradation has
been utilized by biological adaptation. This structure optimises the material’s
response to external loading. Thus the optimised structure for an artificial implant
should show similar gradation. [46].
Several research works have focused on improving the common defects of
conventionally produced FGMs [47, 48]. A major benefit of laser DMD process is
the high density and rare presence of metallurgical defects in the product. Based on
this high reliability of the outcome of this technique, the DMD technology can
produce parts that can function in real life.
Like most other engineering structures, FGMs have also been the subject of interest
for numerical analysis. This can be both in design section and in performance
analysis. Ki-Hoon Shin has used FEA in designing heterogeneous objects [49] while
others have focused on the properties of this class of material structures [50, 51].
Another high power laser-based technology that is similarly suitable to be used as an
additive manufacturing technique to make FGMs is Laser Engineered Net Shaping
process (LENS®). Figure 2.8 shows a LENS® nozzle while depositing material.
33
Figure 2.8 – A LENS® nozzle in action – Photo source: TMS.org
Liu and DuPont [72] have used this technology to fabricate functionally graded
TiC/Ti composites. They report that crack-free functionally graded TiC/Ti composite
materials were fabricated by laser engineered net shaping (LENS), with
compositions changing from pure Ti to approximately 95 Vol% TiC. By delivering
the constituent materials from different powder feeders and through process control,
the LENS process can be used for fabrication of functionally graded materials [72].
Although powder metallurgy and self-propagating high-temperature synthesis (SHS)
processes can be utilized for producing bulk FGMs, the shapes and sizes are usually
limited because of the use of dies for pressure-aided densification. The LENS
process is able to fabricate complex prototypes in near-net shape, leading to time and
machining cost savings. A variety of metals and alloys have been deposited by the
LENS process, such as H13 steel, 316 stainless steel, nickel-base superalloys and
titanium alloys [52-55].
34
Thivillon et al [83] have investigated the potential of direct metal deposition
technology for manufacturing thick functionally graded coatings and parts for
reactors components. In their research they report that recently DMD has been
extended to manufacture large-size near-net-shape components. When applied for
manufacturing new parts (or their refinement), DMD can provide tailored thermal
properties, high corrosion resistance, tailored tribology, multifunctional performance
and cost savings due to smart material combinations.
The interlayer bond strength of 3D structures made by DMD was investigated by
Imran et al. [84] using tensile testing method. The bond strength measured in this
experiment between laser cladded tool steel and copper alloy substrate was much
higher compared to the bond strength between these two metals coated using other
techniques.
Table 2.1 lists most of existing direct metal rapid prototyping processes and their
applications.
35
Table 2.1 – Various Direct Metal Rapid Prototyping processes and applications
Process Applications Ref.
Welding Freeform Fabrication
Rapid Tooling [56]
Production of short to medium run tooling, ABS or polystyrene moulds and power tool component
[57]
Large sculpted metal objects and rapid tooling of moulds and dies [58]
Direct Metal Laser Sintering
Fabrication of accurate tool inserts or metal components [59]
Selective Laser Sintering (SLS)
Production of metallic, ceramic and composite parts [60]
Fabrication of a new model heat exchanger [61]
Fabricate of iron-copper composites, injection moulding tooling [62]
Fabrication of miniature components in the micro-domain [63]
SLS based rapid tooling [64]
Fabrication of non-assembly robotic systems [65]
SLS tools in sheet metal forming [66]
Shape Deposition Manufacturing (SDM)
Embedment of electronics of wearable computers in a polymer composite substrate
[67]
Direct fabrication of prototype metal shapes using robotically manipulated material deposition systems
[68]
Three-dimensional, complex-shaped, multi-material structures [69]
Production of complex shaped fugitive wax moulds [70]
Laser Engineered Net Shaping (LENS)
Fabrication of metallic components [71]
Fabrication of crack-free functionally graded TiC/Ti composite materials [72]
Repair of small, thin components and repair of un-weldable parts in a repeatable manner
[73]
Production of steel-copper die casting materials [74]
Deposition of a graded binary Titanium-Vanadium alloy [75]
Direct Light Fabrication (DLF)
Fabrication of a near net shaped nozzle part [76]
Production of components from nearly any metal and from many intermetallic compounds
[77]
Fabrication of complex near net shaped components using rhenium [78]
Direct Metal Deposition
Production of three-dimensional components from many of the commercial alloys of choice
[79,83]
Fabrication of complicated shapes and dies and tools; Production of components with predetermined performance such as negative co-efficient of expansion
[80]
Fabrication of three-dimensional heterogeneous objects [81]
Repair of expensive components (like those used in aircraft engines) and manufacturing of fully dense parts for use as system components
[82]
Welding Freeform Fabrication is a newly developed rapid prototyping method for
metals. It combines a micro-tungsten inert gas (TIG) welding with a layered
manufacturing method. A tip of a thin metal wire is melted by a micro-TIG welder to
form a small metal bead. By building up metal beads layer by layer under computer
control, a 3D metal object is eventually formed. A wide variety of metals and alloys
can be used.
36
Direct metal laser sintering (DMLS) is an additive metal fabrication technology.
The process uses a 3D CAD model. The DMLS system includes a high-powered
laser, a build chamber area that includes a material dispensing platform and a build
platform along with a blade used to move new powder over the build platform. The
technology fuses metal powder into a solid part by melting it locally using the
focused laser beam. Parts are built up additively layer by layer. This process allows
for highly complex geometries to be created directly from the 3D CAD data without
any tooling. DMLS is a net-shape process, producing parts with high accuracy and
good mechanical properties.
Selective laser sintering (SLS) is an additive manufacturing technique used for the
low volume production of prototype models and functional components. An additive
manufacturing layer technology, SLS involves the use of a high power laser to fuse
small particles of plastic, metal, ceramic, or glass powders into a mass that has a
desired three-dimensional shape. The laser selectively fuses powdered material by
scanning cross-sections generated from a 3-D digital description of the part on the
surface of a powder bed. After each cross-section is scanned, the powder bed is
lowered by one layer thickness, a new layer of material is applied on top, and the
process is repeated until the part is completed. Because finished part density depends
on peak laser power, rather than laser duration, a SLS machine typically uses a
pulsed laser. The SLS machine preheats the bulk powder material in the powder bed
somewhat below its melting point, to make it easier for the laser to raise the
temperature of the selected regions the rest of the way to the melting point. Unlike
some other additive manufacturing processes, such as Stereolithography (SLA) and
fused deposition modelling (FDM), SLS does not require support structures due to
the fact that the part being constructed is surrounded by unsintered powder at all
times, this allows for the construction of previously impossible geometries.
Shape Deposition Manufacturing (SDM) is a developing Rapid Prototyping
technology in which mechanisms are simultaneously fabricated and assembled. The
basic SDM cycle consists of alternate deposition and shaping (in this case,
machining) of layers of part material and sacrificial support material.
37
This cycle of material deposition and removal results in three key features:
1. Building parts in incremental layers allows complete access to the internal
geometry of any mechanism.
2. This access allows one to embed actuators, sensors and other pre-fabricated
functional components inside the structure.
3. By varying the materials used in the deposition process, one can spatially
vary the material properties of the mechanism itself.
The resulting mechanisms can have almost arbitrary geometry, embedded actuators
and sensor and locally-varying stiffness properties, making them more robust and
simpler to control.
Laser engineered net shaping or LENS, as already discussed, is a technology
developed for fabricating metal parts directly from a computer-aided design (CAD)
solid model by using a metal powder injected into a molten pool created by a
focused, high-powered laser beam.
A high power laser is used to melt metal powder supplied coaxially to the focus of
the laser beam through a deposition head. The laser beam typically travels through
the centre of the head and is focused to a small spot by one or more lenses. The X-Y
table is moved in raster fashion to fabricate each layer of the object. The head is
moved up vertically as each layer is completed. Metal powders are delivered and
distributed around the circumference of the head either by gravity, or by using a
pressurized carrier gas. An inert shroud gas is often used to shield the melt pool from
atmospheric oxygen for better control of properties, and to promote layer to layer
adhesion by providing better surface wetting.
LENS process is similar to other 3D fabrication technologies in its approach in that it
forms a solid component by the layer additive method. The LENS process can go
from metal and metal oxide powder to metal parts, in many cases without any
secondary operations. LENS is the only process where a metal part can be printed
38
directly without being buried in powder. It can produce parts in a wide range of
alloys, including titanium, stainless steel, aluminium, and other specialty materials;
as well as composite and functionally graded materials. Primary applications for
LENS technology include repair & overhaul, rapid prototyping, rapid manufacturing,
and limited-run manufacturing for aerospace, defence, and medical markets.
Microscopy studies show the LENS parts to be fully dense with no compositional
degradation. Mechanical testing reveals outstanding as-fabricated mechanical
properties.
The process can also make "near" net shape parts when it's not possible to make an
item to exact specifications. In these cases post production light machining, surface
finishing, or heat treatment may be applied to achieve end compliance.
Directed Light Fabrication (DLF) is a process that can be used to fuse any metal
powder directly to a fully dense, near-net shape component with full structural
integrity. A solid model design of a desired component is first developed on a
computer work station. A motion path, produced from the solid model definition, is
translated to actual machine commands through a post-processor, specific to the
deposition equipment. The DLF process uses a multi-axis positioning system, (3 and
5 axes are used) to move the laser focal zone over the part cross- section defined by
the part boundaries and desired layer thickness. Metal powders, delivered in an argon
stream, enter the focal zone where they melt and continuously form a molten pool of
material that moves with the laser focal spot. Position and movement of the spot is
commanded through the post-processor. Successive cross-sectional layers are added
by advancing the spot one layer thickness beyond the previous layer until the entire
part is deposited. The system has 4 powder feeders attached for co-deposition of
multiple materials to create alloys at the focal zone or form dissimilar metal joint
combinations by changing powder composition from one material to another.
39
2.4 Wafer-layered structures
For the purpose of this research, wafer-layered structure is a name which has been
selected for structures in which two constituent alloys are used each for creating a
layer and they alternate and repeat until the structure is fully complete. Figure 2.9
shows schematics of such structure.
Such structures are rarely found in industrial applications especially in metallic form.
Moreover, little research has been done on fabrication or properties of this type of
structure.
Figure 2.9 –Schematics of a wafer-layered structure
Wafer-layered structure has the potential to offer properties which are not present in
the single constituent alloys used in their fabrication. Such properties can offer a
wider application in engineering and industrial fields where no other alloy or non-
metallic materials could demonstrate the same level or nature of characteristics.
Recently, Imran et al. [85] did a research on a two layer wafer-layered structure
made by DMD and studied its properties. In their research, H13 tool steel powder
was clad on copper alloy substrate both directly and using 41C stainless steel (high
Ni steel) powder as a buffer layer by direct metal deposition (DMD). Cu–steel
bimetallic die casting and injection moulding tools are of high interest for reduction
of cycle time by efficient heat extraction due to high thermal conductivity of copper.
The mechanical properties of these bimetallic structures were investigated in terms
of bond strength, impact energy and fracture toughness. The bond interfaces of these
claddings showed porous and crack free transition regions. The bond strength was
higher in the directly clad H13 tool steel compared to the H13 tool steel clad with
40
41C stainless steel as buffer layer. The fracture morphology in tensile test specimens
showed ductile dimple fracture. Presence of necking just below the interface
depicted the softening of substrate in heat affected zone (HAZ) during cladding. The
Charpy impact energy is little higher in the 41C stainless steel buffered specimens
compared to the directly clad H13 tool steel specimens but the fracture toughness
results showed reduction of fracture toughness in the 41C stainless steel buffered
specimens due to the low strength in the tensile test. However the fracture toughness
value was in the ductile region for both deposits [85].
Summary
Literature review indicates that few studies have been made on the fabrication and
characterization of bulk wafer structures of engineering metals involving additive
manufacturing such as Direct Metal Deposition. Moreover, a comprehensive study of
fabrication of a range of FGM involving several superalloys using DMD has also not
been undertaken.
Based on this review on the existing literature available on FGM and WAFER
structures, there is a good potential to expand the range of materials selected for
trials on such structures. This PhD research will focus on the use of engineering
alloys which are used in day to day industrial applications such as in Oil and Gas,
Power Generation and tool making fields. This research will present fabrication
method using laser DMD and mechanical and physical properties of wafer-layered
structures and potential applications. The results of physical and mechanical tests
done on the trails as part of this research work can be transferred to such industries
for further in-service assessments.
Another major gap in the existing literature is the kind of physical and mechanical
testing and results of such tests available for FGM and Wafer structures. This PhD
project will test all the fabricated samples for their coefficient of thermal expansion,
tensile strength, corrosion resistance, and microhardness across layers. The results
will then be compared in each test category for more detailed understanding of their
properties in relation to other structures made from other such super alloys.
41
Chapter 3 Materials and Methods
42
Chapter 3 – Materials and Methods
3.1 Introduction
Laser Direct Metal Deposition technology was used to fabricate all samples for this
research. DMD™ is a break-through process that fabricates fully dense metal "from
the ground up" using powdered metal and a focused laser. Using DMD, highly
accurate functional parts can be fabricated with extremely short lead times, and
repairs and alterations can be made without the problems associated with traditional
welding processes.
DMD automatically constructs 3D components - in a variety of pure, production
intent metals - directly from computer-aided design (CAD) data. The key to the
technology is an optical heat energy source, in this case an industrial laser that is
used to directly fabricate metal parts. DMD is an additive manufacturing (AM)
process whereby CAD solid models are sliced into thin layers, then each layer built
upon one another using the laser and powdered metal. Tool steels, Nickel-super
alloys and other dissimilar metals can be combined to create a solid object, such as a
mold, die or metal prototype. The rapid cooling characteristics of DMD create a fine
grain microstructure, which results in a fully dense product with superior mechanical
and metallurgical properties.
3.2 DMD process parameters
DMD is designed for 3-dimensional, unmanned laser-aided, powdered metal fusion.
Unlike existing powdered metal technologies, DMD produces a fully dense metal
product. The laser creates a melt pool on the substrate material into which the
additive materials, in powder form, are injected in exactly measured amounts and
melted forming a metallurgical bond.
To ensure that the new material layers are of a consistently high quality, active
process regulation is indispensable. If the actual geometry deviates from the required
geometry, this is detected by process sensors developed for DMD closed loop
43
technology. The closed loop optical feedback system continuously monitors in real
time the size of the melt pool and adjusts process variables such as powder flow rate,
deposition velocity and laser power. This patented Closed Loop Feedback system
ensures the product quality and dimensional stability during fabrication.
The melt pool information for DMD layering is monitored by 3 CCD cameras. The
process PC compares the information about the actual geometry with the desired
geometry and controls the layering process accordingly. The use of three cameras in
a 3x 120° array allows a controlled DMD process in 3D mode as well. As a pre-
condition for this, it must be possible to observe the melt pool with at least one
camera (interference contours). Near net shape, dimensional stability and elimination
of post processing of the parts are the advantages delivered with the use of the
patented DMD Closed Loop Technology.
In order to run a DMD machine, the following parameters must be controlled:
1. Powder (alloy, particle size, atomization type)
2. Laser power (Watts) and laser beam diameter
3. Powder delivery rate (g/min)
4. Deposition speed (mm/min)
5. Shielding gas (Argon/Helium)
6. Tool path (manipulation program/CAD file)
Ideal results will be achievable only after multiple trial runs of single and double
track layers are deposited and metallographically analyzed for defects and levels of
dilution.
DMD® process makes use of five common technologies: lasers, computer-aided
design (CAD), computer-aided manufacturing (CAM), sensors, and powder
metallurgy. The process creates parts by focusing an industrial CO2 laser beam onto
a flat work piece or preformed shape to create a molten pool of metal.
44
Figure 3.1 – A DMD processing head in action (source POM)
A small stream of powdered metallic alloy is then injected into the melt pool to
increase the size of the molten pool (Figure 3.1).
By moving the laser beam back and forth, under CNC control, and tracing out a
pattern controlled by a computerized CAD design, the solid metal part is built, line-
by-line, one layer at a time. With this process and its focused laser beam, the molten
pool cools and solidifies, rapidly producing metal parts of superior quality and
strength with no material waste as in conventional machining operations.
The parts have consistent, fine microstructures, which yield superior quality and
strength. More importantly, with DMD, the metallic composition can be altered on-
the-fly by injecting different types of metal powders into the melt pool. This also
allows fabrication of graded metallic compositions that have never before been
possible on any other additive manufacturing technology.
45
This laser-based cladding type technology provides the manufacture of 3D metal
components or tooling with close tolerances and ideal properties directly from a
CAD model. The benefits are shorter time-to-market, lower fabrication costs, and
improved productivity.
Currently the most obvious negative aspect of the DMD is the high initial cost of the
system. However, this is improving by the introduction of a whole range of such
systems that makes them affordable for different industries.
3.3 Effect of laser metal deposition on the substrate
In order to better understand the nature of a DMD fabricated product, this project
also focused on the effects of the laser cladding process on the substrate, which can
then be interpreted as the effects of each layer on the previous layer and finally the
whole structure.
Also from a comparison perspective, the laser deposited layer in laser cladding and
its properties are compared with a Tungsten Inert Gas (TIG) welding deposited layer.
The following section is a comprehensive report on such comparison. TIG technique
has been selected as a comparison technology because it represents a range of more
traditional metal deposition techniques where the heat input during the meal
deposition process is considerably higher than that of more modern techniques such
as laser assisted metal depositions.
3.3.1 Laser cladding Vs. TIG welding
Laser cladding is a thermal process during which a metallic alloy is deposited on to a
parent metal for a range of reasons including repair of erosion, corrosion, wear or
other physical damages. The present work is looking at the effects of laser cladding
process on the integrity of base or parent metal, the bond between the clad layer and
the base metal and some physical characteristics of the clad layer, which in this case
is 420 stainless steel. To offer a better picture, a similar sample was prepared using
Tungsten Inert Gas (TIG) Welding process and the same metallographic studies were
done on the TIG sample to compare the results with those of laser cladding sample.
46
The research concluded that due to the small size of the heat affected zone in the
parent metal, which is a typical advantage of laser cladding process, the physical
properties of the parent metal are not affected as a result of this thermal process. The
bond is also found to be a full metallurgical bond with reasonable bond strength and
rigidity equal or beyond the base metal. On the other hand, there was major
distortion and dilution observed in the TIG sample.
There are numerous metal deposition technologies in today’s industrial fields. Some
of these are thermal processes such as Laser Cladding and some are non-thermal
processes like electrochemical processes such as chrome plating.
When it comes to thermal processes, there are usually concerns among the design
engineers and managers on what influence the process will have on the part being
processed and how this part will perform in service. Another question is usually on
the strength of the bond between the base metal and the deposited layer.
A wide range of key industries such as rail industries, oil and gas, power stations,
and mining suffer from physical damage on their metallic components. The
mechanism responsible for these damages can be wear, corrosion and impact. And
once the geometry of the part is below its desired values, it should either be repaired
or scraped. When it comes to choosing a repair technique to rebuild a metallic
component, thermal processes are usually a more efficient choice. But heating of the
part to high temperatures for deposition of metal and bonding with the substrate
introduces some flaws and defects such as porosity, cracks and undesired
microstructure in the base metal in the heat affected zone (HAZ), which then results
in undesired physical properties such as brittleness and lower toughness in the base
metal.
Several research works have focused on Laser Cladding with stainless steel powder
[86-88]. The present work is intended to look at Laser Cladding technology as a
repair process and investigates the physical properties of laser clad samples and
47
reports on the quality of the bond and the size of HAZ in the base metal in an attempt
to better understand the viability of the DMD laser cladding process.
3.3.2 Sample fabrication - Laser cladding
For this research, a commonly used martensitic stainless steel i.e. grade 420, was
used as the deposit material, and mild steel was the substrate.
Grade 420 Stainless Steel contains a minimum of 12 per cent chromium, just
sufficient to give corrosion resistance. It has good ductility in the annealed condition
but is capable of being hardened up to Rockwell Hardness 55HRC, the highest
hardness of the 12 per cent chromium grades. [89]
Typical compositional ranges for grade 420 stainless steels are given in Table 3.1 [89].
Table 3.1- Composition ranges for 420 grade stainless steel
Grade C Mn Si P S Cr
420 Min. Max.
0.15 -
- 1.00
- 1.00
- 0.040
- 0.030
12.0 14.0
Typical mechanical properties for grade 420 stainless steels are given in Table 3.2 [92].
Table 3.2-Mechanical properties of 420 grade stainless steel [92]
Tempering Temperature
(°C)
Tensile Strength
(MPa)
Yield Strength 0.2% Proof
(MPa)
Elongation (% in 50mm)
Hardness Brinell (HB)
Impact Charpy V (J)
Annealed * 655 345 25 241 max - 204 1600 1360 12 444 20 316 1580 1365 14 444 19 427 1620 1420 10 461 # 538 1305 1095 15 375 # 593 1035 810 18 302 22 650 895 680 20 262 42
* Annealed tensile properties are typical for Condition A of ASTM A276; annealed hardness is the specified maximum. # Due to associated low impact resistance this steel should not be tempered in the range 425-600°C
Typical physical properties for annealed grade 420 stainless steels are given in Table 3.3 [89].
48
Table 3.3- Physical properties of 420 grade SS in the annealed condition [89]
Grade Density (kg/m
3)
Elastic Modulus (GPa)
Mean Coefficient of Thermal Expansion
(m/m/°C)
Thermal Conductivity (W/m.K)
Specific Heat 0-100
°C
(J/kg.K)
Electrical Resistivity
(n.m) 0-100°C 0-315°C 0-538°C at 100°C at 500°C
420 7750 200 10.3 10.8 11.7 24.9 - 460 550
The samples for this work were prepared using a Laser Cladding process. The laser
used was a 4 kW IPG photonics fibre laser. In laser cladding, a high power laser
beam is used to create a melt pool on the surface of the parent metal. At the same
time, a metallic element or alloy is deposited onto the melt pool in the form of fine
powder (approximately 70 – 120 µm in grain size) or sometimes wires.
Argon or Helium is used as shielding gas to protect the melt pool from oxidation due
to air.
Figure 3.2 - Schematics of coaxial Laser Cladding [90]
49
Dedicated processing heads are used to carry out Laser Cladding. These heads are
manipulated by robotic arms or CNC machines.
Figure 3.2 shows the schematics of Laser Cladding process using a coaxial head.
Figure 3.3 is a snap shot of the actual Laser Cladding process which was used to
produce the round samples for this study.
Figure 3.3 - Sample round bar being laser cladded with 420 SS powder
The laser workshop at Hardchrome Engineering Company comprises of a 4 kW fibre
laser, a powder feeder unit, a 6-axis robotic arm and a rotator. Robotic programs
were used to control the laser power; the powder feed unit and the rotator to create
the deposit layer.
For this work, the following parameters were used in the process:
Laser power: 3.4 kW
Spot size: 5 mm
Spot shape: round
50
Powder feed rate: 62 g/min
Traverse speed: 900 mm/min
Shielding gas: 50%Ar – 50%He
Cooling: Air cooled
3.3.3 Sample fabrication _ TIG welding
Tungsten Inert Gas (TIG) welding technique was used to create another set of
samples using exactly the same set of substrate metal (mild steel) and deposit alloy
(420 stainless steel).
Figure 3.4 shows the schematics of TIG welding process. As seen in this figure, a
significant part of the parent metal is melted as well in this process.
Figure 3.4 - Schematics of TIG welding process [91]
51
3.3.4 Metallographic evaluation
A section of the laser clad samples was mounted for metallurgical investigations of
the cross-section. In order to avoid any microstructure change as a result of the heat
in the sectioning process, a coolant was used during the cutting. The mounted
sections were ground to 1200 grit and polished to 1 µm at the metallurgical lab at
Hardchrome Engineering. The sample was then etched so the two alloys can be seen
with naked eye and the interface can be better studied under microscope.
Figure 3.5 shows two mounted samples as a comparison. The penetration at the
substrate surface in the TIG sample is evident.
Figure 3.5 – Comparison of laser clad (left) and TIG welded (right) samples
The significant penetration in the mild steel substrate of the TIG welded sample is an
indication of the amount of the excessive heat introduced in the process of deposition
of 420 SS.
52
Such penetration will affect the integrity of the parent metal and its physical and
mechanical properties. On the other hand, the laser clad sample shows minimum or
little penetration.
The width and properties of heat affected zone (HAZ) that is produced as a result of
employed thermal process are two critical issues that can affect the overall
performance of the part or component, which is repaired with Laser Cladding
process.
Figure 3.6 is microscopic image of the laser clad sample in which the HAZ is
labelled. The difference between the HAZ and the rest of the base metal is evident.
There is a sharp interface between the clad layer and the HAZ. The width of HAZ is
approximately 600 µm.
53
Figure 3.6 - Micrograph of the laser clad sample showing the HAZ and the hardness profile in
this region (500X)
3.3.5 Micro-hardness scan
Microhardness across the HAZ and adjacent unaffected base metal was determined,
as seen from the diamond indents in Figure 3.6.
Figure 3.7 shows the micro-hardness values with the distance from the bond
interface.
54
Figure 3.7 - Hardness profile in the HAZ (Laser Clad sample)
There are no significant fluctuations in the hardness values throughout the two
sections i.e. clad layer and the substrate metal and especially in the HAZ which
indicates that the structure that may be produced will not suffer loss of mechanical
integrity as a result of mismatch in hardness.
0
50
100
150
200
250
300
0 50 100 150 200 250 300
Har
dnes
s H
V
Distance from the bond interface (µm)
55
Figure 3.8 - Microhardness profile of the base metal, heat affected zone, bond region and Laser deposited layer (500X)
Microhardness was also determined in the cross-section of all the regions including
the clad area, as shown in Figure 3.8. The hardness profiles in Figure 3.9 show how
the hardness values change in different regions of the part.
The values of hardness readings were plotted against the distance of the diamond
from the bond interface. Figure 3.9 shows how the hardness values change in
different regions of the part. The main reason is the amount of heat input into the
base which results in longer solidification times and therefore softening the metal
near the bond interface.
56
Figure 3.9 - Hardness values from the microhardness tests for both Laser Clad and TIG welded samples
The same type of hardness tests was done for the TIG welded sample (Figure 3.9).
Laser clad sample involves much less heat input and the region close to the bond
interface quenches more rapidly than the same in TIG sample. Therefore the
substrate hardness near bond interface in laser clad sample actually increases
compared to the rest of the substrate.
Further microstructure analysis of the laser clad sample involved the use of Scanning
Electron Microscopy (SEM). Figures 3.10 and 3.11 show the bond region, the
substrate and the 420 SS clad layer.
0
100
200
300
400
500
600
700
-150 -100 -50 0 50 100
HV
Position with respect to bond interface being 0 - units in microns
Hardness values for Laser cladded and TIG welded samples around the bond interface
TIG LASER
57
Figure 3.10 - SEM image of the sample showing the bond region in the cross-section of the Laser Clad sample (1000X)
The micrographs in Figures 3.10 and 3.11 suggest a good bonding between the 420
SS layer and the mild steel base. There is no sign of any porosity, micro-cracking or
other inconsistencies and contaminations such as oxidation in the microstructure.
The two metallic regions are locked into each other with a full metallurgical bond.
The bond also shows no sign of porosity and/or cracks, which is another sign of the
strength of such metallic bonds achieved through laser cladding technique.
Other more conventional processes would create bonds with metallurgical defects
such as porosity and cracking which would affect the strength of the bond and
therefore the integrity of the part as a whole.
58
Figure 3.11 - A high magnification SEM image of the bond region in the Laser Clad sample (10000X)
3.3.6 Elemental Analysis by Energy Dispersive Spectroscopy
In order to investigate the issue of dilution in Laser Cladding process, chemical
composition of multiple spots were measured using Energy Dispersive Spectroscopy
(EDS).
Energy-dispersive X-ray spectroscopy (EDX or XEDS) is an analytical technique
used for the elemental analysis or chemical characterization of a sample. It relies on
the investigation of an interaction of some source of X-ray excitation and a sample.
Its characterization capabilities are due in large part to the fundamental principle that
each element has a unique atomic structure allowing unique set of peaks on its X-ray
spectrum. To stimulate the emission of characteristic X-rays from a specimen, a
high-energy beam of charged particles such as electrons or protons, or a beam of X-
rays, is focused into the sample being studied. At rest, an atom within the sample
contains ground state (or unexcited) electrons in discrete energy levels or electron
59
shells bound to the nucleus. The incident beam may excite an electron in an inner
shell, ejecting it from the shell while creating an electron hole where the electron
was. An electron from an outer, higher-energy shell then fills the hole, and the
difference in energy between the higher-energy shell and the lower energy shell may
be released in the form of an X-ray. The number and energy of the X-rays emitted
from a specimen can be measured by an energy-dispersive spectrometer. As the
energy of the X-rays is characteristic of the difference in energy between the two
shells, and of the atomic structure of the element from which they were emitted, this
allows the elemental composition of the specimen to be measured.
Figure 3.12 shows five points that were selected for this purpose.
Figure 3.12 – Areas selected for EDS on both sides of the bond interface
60
As can be seen in Figure 3.12, the five points were:
1. 124.3 µm from bond interface into clad layer
2. 798.6 µm from bond interface into clad layer
3. 77.18 µm from bond interface into parent metal
4. 1.020 µm from bond interface into parent metal
5. Centre of parent metal round bar
The following figures, i.e. Figures 3.13 - 3.17, show the spectrums obtained at the 5
points above:
Figure 3.13 – EDS spectrum for Point 1
Figure 3.14 – EDS spectrum for Point 2
61
Figure 3.15 – EDS spectrum for Point 3
Figure 3.16 – EDS spectrum for Point 4
Figure 3.17 – EDS spectrum for Point 5
62
The results of the EDS – Tables 3.4 and 3.5 - suggest that the composition of the
parent metal didn’t show any significant change from close proximity to the bond
line to far from the bond interface even in the centre of the round bar. The only
change seen in the chemical composition of the parent metal was seen in the closest
point to the bond line which was presence of 0.35 weight percent Silicon in it, which
was absent in the other regions of the base metal. The Si has migrated from the clad
layer to the base.
Considering the thickness of the clad layer which is 2 mm, and the depth of the
parent metal that contains Si i.e. 78 µm, the dilution is limited to about 5% of the
clad layer which is negligible dilution rate.
Table 3.4 – Chemical composition of parent metal (Mild Steel)
Parent Metal point 3
77.18 µm from bond
point 4
1020 µm from bond
point 5
Centre of round bar (base)
Element Weight% Weight% Weight%
C 2.34 2.5 2.55
Si 0.35 0 0
Mn 0.93 1.04 0.85
Fe 96.37 96.46 96.59
Totals 100 100 100
Table 3.5 – Chemical composition of 420SS clad layer
420 SS layer Point 1
124.3 µm from bond
Point 2
798.6 µm from bond
Element Weight% Weight%
C 1.46 1.86
Si 0.38 0.37
Cr 8.85 10.35
Mn 1.05 0.96
Fe 88.27 86.46
Totals 100 100
63
The chemical composition of the clad layer didn’t show any significant change
throughout the clad layer to close regions to the bond line.
The same series of hardness profiling and SEM and EDS steps were performed on
the TIG welded sample.
Table 3.6 shows the EDS results for the TIG sample. There is a major concentration
of carbon around the bond region which contributes to the brittleness of the
microstructure in this region of the sample and thus decreasing its fracture toughness
and fatigue life.
Table 3.6 – EDS results of TIG welded sample
Element Point 1 Point 2 Point 3 Point 4 Point 5
C 2.46 3.59 18.97 11.61 3.39
Si 0.52 0.5 0 0 0
Cr 10.03 8.63 0 0 0
Mn 1.99 2.09 0.71 0.73 0.73
Fe 85 85.19 80.32 87.66 95.51
Totals 100 100 100 100 100
Distance from Bond in um
(+ values belong to the Laser Clad layer and - values to the Base Metal) 160 µm 70µm - 35µm -100µm -220µm
The SEM micrographs of the TIG welded sample, figures 3.18 and 3.19, show a high
dilution of the deposit layer into the mild steel.
64
Figure 3.18 - SEM image of the sample showing the bond region in the cross-section of the TIG welded sample (1000X)
In figure 3.18, the diluted area can be seen in the mild steel base region. The light
grey microstructure which is 420 SS is settled within the darker mild steel
microstructure as a result of excessive heat input throughout the process.
Figure 3.19 shows the bond region at a higher magnification which confirms that the
dilution starts at the bond line and progresses into the base metal.
This affects the physical and mechanical properties of the base metal and the bond
quality. Eventually a part that has been processed with this technique will inherit all
the metallurgical defects of the bond region and it may fail as a result of the bond
failure due to propagation of micro-cracks under load or creation of cracks from pore
present in the bond region.
65
Figure 3.19 - A high magnification SEM image of the bond region in the Laser Clad sample (10000X)
Based on the results of the metallography studies, it is evident that Laser Cladding
process does not affect the integrity of the parent metal.
The bond between the laser deposited layer and the parent metal is fully
metallurgical with no porosity or cracking in any region of the clad, bond interface,
HAZ or parent metal.
Compared with TIG welding, Laser Cladding possesses structure that can offer
significantly better integrity of the parent metal and dilution rates. Based on these
findings, it can be concluded that DMD is a superior laser cladding technology
compared to conventional techniques to produce 3D and multilayered metallic alloy
structures.
66
3.4 Materials
For the purpose of this research work and to start the specimen production, some of
the most common engineering and industrial alloys were selected. Stainless steel
grades 420, 316L, Tool steel grade H13, Cobalt alloy commonly known as Stellite®
6, and a Nickel rich alloy were some of these alloys. In the following section, these
alloys and their specifications are described.
3.4.1 Stainless Steel - Grade 420
Grade 420 Stainless Steel is a higher carbon version of 410. Like most non-stainless
steels it can be hardened by heat treatment. It contains a minimum of 12 per cent
chromium, just sufficient to give corrosion resistance properties. It has good ductility
in the annealed condition but is capable of being hardened up to Rockwell Hardness
50HRC, the highest hardness of the 12 per cent chromium grades. Its best corrosion
resistance is achieved when the metal is hardened and surface ground or polished
[92].
Martensitic stainless steels are optimized for high hardness, and other properties are
to some degree compromised. Corrosion resistance is lower than the common
austenitic grades, and their useful operating temperature range is limited by their loss
of ductility at sub-zero temperatures and loss of strength by over-tempering at
elevated temperatures.
Typical compositional ranges for grade 420 stainless steels are given in Table 3.7.
[92]
Table 3.7 Composition ranges for 420 grade stainless steel [92]
Grade C Mn Si P S Cr
420 min. max.
0.15 -
- 1.00
- 1.00
- 0.040
- 0.030
12.0 14.0
Typical mechanical properties for grade 420 stainless steels are given in table 3.8.
67
Table 3.8 Mechanical properties of 420 grade stainless steel [92]
Tempering Temperature (°C)
Tensile Strength (MPa)
Yield Strength 0.2% Proof (MPa)
Elongation (% in 50mm)
Hardness Brinell (HB)
Impact Charpy V (J)
Annealed * 655 345 25 241 max -
204 1600 1360 12 444 20
316 1580 1365 14 444 19
427 1620 1420 10 461 #
538 1305 1095 15 375 #
593 1035 810 18 302 22
650 895 680 20 262 42 * Annealed tensile properties are typical for Condition A of ASTM A276; annealed hardness is the specified maximum.
Typical physical properties for annealed grade 420 stainless steels are given in Table 3.9 .
Table 3.9 Physical properties of 420 grade stainless steel in the annealed condition [92]
Grade Density
(kg/m3)
Elastic
Modulus
(GPa)
Mean Coefficient of Thermal
Expansion
(mm/m/°C)
Thermal Conductivity
(W/m.K)
Specific
Heat 0-
100°C
(J/kg.K)
Electrical
Resistivity
(nW.m) 0-100°C 0-315°C 0-538°C at 100°C at 500°C
420 7750 200 10.3 10.8 11.7 24.9 - 460 550
Annealing - Full anneal - 840-900°C, slow furnace cool to 600°C and then air cool.
Process Anneal - 735-785°C and air cool.
Hardening - Heat to 980-1035°C, followed by quenching in oil or air. Oil quenching
is necessary for heavy sections. Temper at 150-370°C to obtain a wide variety of
hardness values and mechanical properties. The tempering range 425-600°C should
be avoided.
Pre-heat to 150-320°C and post-heat at 610-760°C. Grade 420 coated welding rods
are recommended for high strength joints, where a post-weld hardening and
tempering heat treatment is to be carried out.
If parts are to be used in the "as welded" condition, a ductile joint can be achieved by
using Grade 309 filler rod. AS 1554.6 pre-qualifies welding of 420 with Grade 309
rods or electrodes.
68
In the annealed condition this grade is relatively easily machined, but if hardened to
above 30HRC machining becomes more difficult. Free machining grade 416 is a
readily machined alternative.
3.4.2 Stainless Steel - Grade 316L
Grade 316 is the standard molybdenum-bearing grade, second in importance to 304
amongst the austenitic stainless steels.
The Chemical Composition of 316L is shown in this table. [93]
Fe C Cr Ni Mo Mn Si P S
Balance <0.03% 16-18.5% 10-14% 2-3% <2% <1% <0.045% <0.03%
The molybdenum gives 316 better overall corrosion resistant properties than Grade
304, particularly higher resistance to pitting and crevice corrosion in chloride
environments. It has excellent forming and welding characteristics. It is readily brake
or roll formed into a variety of parts for applications in the industrial, architectural,
and transportation fields. Grade 316 also has outstanding welding characteristics.
Post-weld annealing is not required when welding thin sections [93].
Grade 316L, the low carbon version of 316, is immune from sensitization (grain
boundary carbide precipitation). Thus it is extensively used in heavy gauge welded
components (over about 6mm). Grade 316H, with its higher carbon content, has
application at elevated temperatures, as does stabilized grade 316Ti.
The austenitic structure also gives these grades excellent toughness, even down to
cryogenic temperatures.
69
Table 3.10 shows the mechanical properties of 316SS.
Table 3.10 Mechanical properties of 316 grade stainless steels [93]
Grade Tensile Str (MPa) min
Yield Str 0.2% Proof (MPa) min
Elong (% in 50mm)
min
Hardness
Rockwell B (HR B) max
Brinell (HB) max
316 515 205 40 95 217
316L 485 170 40 95 217
316H 515 205 40 95 217 Note: 316H also has a requirement for a grain size of ASTM no. 7 or coarser.
Table 3.11 Typical physical properties for 316 grade stainless steels [93]
Grade Density (kg/m3)
Elastic Modulus
(GPa)
Mean Co-off of Thermal Expansion (µm/m/°C)
Thermal Conductivity (W/m.K)
Specific Heat 0-100°C
(J/kg.K)
Elect Resistivity (nΩ.m) 0-100°C 0-315°C 0-538°C At 100°C At 500°C
316/L/H 8000 193 15.9 16.2 17.5 16.3 21.5 500 740
Good oxidation resistance in intermittent service to 870°C and in continuous service
to 925°C. Continuous use of 316 in the 425-860°C range is not recommended if
subsequent aqueous corrosion resistance is important. Grade 316L is more resistant
to carbide precipitation and can be used in the above temperature range. Grade 316H
has higher strength at elevated temperatures and is sometimes used for structural and
pressure-containing applications at temperatures above about 500°C.
Solution Treatment (Annealing) - Heat to 1010 -1120°C and cool rapidly. These
grades cannot be hardened by thermal treatment.
This alloy shows excellent weld-ability by all standard fusion methods, both with
and without filler metals. AS 1554.6 pre-qualifies welding of 316 with Grade 316
and 316L with Grade 316L rods or electrodes (or their high silicon equivalents).
Heavy welded sections in Grade 316 require post-weld annealing for maximum
corrosion resistance. This is not required for 316L. [93].
3.4.3 Tool steel (H13 Steel)
Tooling materials to be used in the construction of a die casting die for casting
Aluminum, Magnesium and ZA alloys, should be high quality tool steel such as H-
70
13 especially for part designs with critical features or if high production runs are
being contemplated.
Chemical composition (% by weight) of critical alloying elements and impurities
(ASTM A-681 sec. 6) is shown in Table 3.12.
Table 3.12 – H13 Tool Steel element analysis [93]
ELEMENT MIN. MAX.
CARBON 0.37 0.42
MANGANESE 0.20 0.50
PHOSPHORUS 0 0.025
SULFUR 0 0.005
SILICON 0.80 1.20
CHROMIUM 5.00 5.50
VANADIUM 0.80 1.20
MOLYBDENUM 1.20 1.75
Hardness (ASTM A-681 sec. 7): Annealed hardness, as received, shall not exceed
235 Brinell (BHN). A steel specimen having a thickness no greater than one inch
shall exhibit a minimum hardness of 50 HRC, when air cooled, after heating for 30
minutes at 1010°C in a protective atmosphere, or when using a non-protective
atmosphere. Ensure the sample has appropriate oversize allowance [93].
3.4.4 Stellite 6
Stellite® cobalt base alloys consist of complex carbides in an alloy matrix. They are
resistant to wear, galling and corrosion and retain these properties at high
temperatures. Their exceptional wear resistance is due mainly to the unique inherent
characteristics of the hard carbide phase dispersed in a CoCr alloy matrix [95]. It’s
chemical composition is shown below.
Co Cr W C Others Base 27 - 32 4-Jun 0.9-1.4 Ni, Fe, Si, Mn, Mo
Stellite® 6 is the most widely used of the wear resistant cobalt based alloys and
exhibits good all-round performance. It is regarded as the industry standard for
general-purpose wear resistance applications, has excellent resistance to many forms
71
of mechanical and chemical degradation over a wide temperature range, and retains a
reasonable level of hardness up to 500°C (930°F).
Hardness Density Melting Range 36-45 HRC 8.44 g/cm3 2340-2570 °F
It also has good resistance to impact and cavitation erosion. Stellite® 6 is ideally
suited to a variety of hardfacing processes and can be turned with carbide tooling.
Examples include valve seats and gates; pump shafts and bearings, erosion shields
and rolling couples. It is often used self-mated [95].
Table 3.13 – Stellite 6 thermal expansion coefficients [95]
Nominal tensile properties at room temperature are given below:
Ultimate Tensile Strength Rm Yield Stress Rp (0.2%) Elongation Elastic Modulus
ksi MPa ksi MPa A(%) psi GPa
Castings 123 850 101.5 700 <1 30.3x106 209
Stellite®
HS-6 183.5 1265 109 750 3-5 34x106 237
Nominal Thermal Expansion Coefficient (from 20°C/68°F to stated temperature) 100°C 200°C 300°C 400°C 500°C 600°C 700°C 800°C 900°C 1000°C
μm/m.K 11.35 12.95 13.6 13.9 14.2 14.7 15.05 15.5 17.5
72
3.4.5 Aluminum Bronzes
Aluminum bronzes are used for their combination of high strength, excellent
corrosion and wear resistance.
Cu Al Ni Fe Si C
Balance 10.00 5.00 1.00 0.100 0.010
Aluminum bronze alloys typically contain 9-12% aluminum and up to 6% iron and
nickel. Alloys in these composition limits are hardened by a combination of solid
solution strengthening, cold work, and precipitation of an iron rich phase. High
aluminum alloys are quenched and tempered. Aluminum bronzes are used in marine
hardware, shafts and pump and valve components for handling seawater, sour mine
waters, non-oxidizing acids, and industrial process fluids. They are also used in
applications such as heavy duty sleeve bearings, and machine tool ways. They are
designated by UNS C60800 through C64210. Aluminum bronze castings have
exceptional corrosion resistance, high strength and toughness, good wear resistance
and desirable casting and welding characteristics. Aluminum bronze castings are
designated as UNS C95200 to C95900.
The microstructure of the aluminum bronzes with less than 11% aluminum consists
of alpha solid solution and the iron and nickel rich kappa phase. The kappa phase
absorbs aluminum from the alpha solid solution preventing the formation of the beta
phase unless the aluminum content is above 11%. The kappa phase increases the
mechanical strength of the aluminum bronzes, with no decrease in ductility. The
decrease in ductility of the aluminum bronzes occurs when the beta phase forms. The
beta phase is harder and more brittle than the alpha phase. Beta is formed if the
material is quenched or fast cooled, which then transforms into a hard, acicular
martensite structure. Tempering the martensite results in a structure of alpha with
kappa precipitates. The tempered structure is desirable; it has high strength and
hardness. The slow cooled, as cast structures consist of alpha and kappa phases.
Kappa is present in the lamellar form and finely divided in all the alpha areas. The
addition of iron and nickel also suppresses the formation of the gamma double prime
73
phase which has deleterious effects on the properties of aluminum copper alloys
[94].
3.4.6 EuTroLoy® 16221 The powder alloy EuTroLoy 16221 has been specially developed to meet the
metallurgical and physical standards of the plasma transferred arc (PTA) process.
Table 3.14 – Element analysis EuTroLoy 16221 [96]
C Cr B Si Fe Ni
0.2 4.0 1.0 2.5 Max 2.0 Balance
EuTroLoy 16221 is manufactured by gas atomisation to have a spherical shape and
to ensure the highest purity, in particular to keep a low oxygen content. The spherical
shape and the grain-size distribution of the particles ensure a regular flow of powder
through the equipment.
It offers excellent bonding with lamellar and spheroidal graphite grey cast iron, as
well as steel, excellent resistance to heat and thermal shock and is highly suitable for
use with molten glass.
Its main applications are glass-moulding components (mould bases, guide rings,
blowing heads), cast-iron stamping dies and coke oven doors. and as buttering layers
on lamellar and spheroidal graphite grey cast-iron parts.
Its hardness is typically 27-30 HRc [96].
3.5 Fabrication of FGM and Wafer samples
When it comes to combination of alloys in terms of creating a chemically new alloy
or a physical mixture of two or more alloys using a structural design, the possibilities
are endless and thermal expansion values –among other physical and mechanical
properties - need to be measured and studied for such new combinations.
74
Among potential structures that may be achieved using available metallic alloys and
using advanced metal deposition technology, two structures have been selected for
further investigation in this work. These are functionally graded materials (FGM)
and wafer layered structures.
Functionally graded materials are a unique class of materials which comprise of two
or more alloys with a graded transition of the alloys across an interface and hence
possessing different physical and mechanical properties across the part. The concept
of FGMs was first proposed in 1987 to develop heat-resistant materials for the
propulsion system and airframe of space planes [97]. Since then, much research has
been done to develop FGMs for various applications by using gradients in physical,
chemical, biochemical, and mechanical properties. Many researchers have focused
their attention on the modeling and determination of properties for FGMs for various
applications [98]. Dao et al [99] have used a computational micromechanics
approach to study the residual stress distribution in functionally graded materials
involving ceramics and metals. Marur and Tippur [100] developed an experimental
technique using ultra-sonic pulse-echo measurements and elastic impact testing to
determine Young's modulus, Poisson's ratio and mass density of epoxy-based FGM.
Pompe et al [101] have investigated the development of functionally graded
materials for bone implants applications involving ultra-high molecular weight
polyethylene fiber reinforced high-density polyethylene and other materials. Goupee
and Vel [102] have proposed a methodology for multi-objective optimization of
material distribution of functionally graded materials with temperature-dependent
material properties involving zirconia/titanium and tungsten/copper alloy FGMs.
Jabbari, Sohrabpour and Eslami [103] have studied the mechanical and thermal
stresses determination in functionally graded hollow cylinder involving heat
conduction and Navier equations. Lee et al [104] have used an inverse algorithm to
estimate thermal stresses in a functionally graded hollow cylinder subjected to inner
and outer heat fluxes. Cannillo et al [105] have carried out the simulation study and
experimental measurements of thermal residual stresses in glass-alumina FGMs.
75
Various conventional approaches based on the bulk (particulate) processing,
centrifugal casting, pre-form processing, layer processing and melt processing are
used to fabricate the functionally graded materials [106-108]. Now different 3D
shapes can also be fabricated as functionally graded materials using the new additive
manufacturing process of laser assisted Direct Metal Deposition (DMD) process,
which fabricates parts directly under computer control and overcomes several
limitations of conventional techniques. However, little attention has been paid to
fabricate functionally graded metallic parts using the DMD process, which allows
different types of metal powders to be deposited simultaneously under closed loop
computer control. The process thus allows both graded structures with varying
amount of deposited powder as well as wafer type structures with fixed amount of
deposited powder in alternate layers.
The focus of this research is to investigate the changes in the physical and
mechanical properties in functionally graded materials (FGMs) and wafer layered
structures. Laser assisted POM® Direct Metal Deposition DMD technique was
employed to fabricate these samples. Laser assisted DMD is an advanced 3D metal
deposition technology, which has emerged out of laser cladding technology. Figure
3.20 is a schematic illustration of a DMD process, which involves a processing head
containing the central laser beam, powder delivery and gas delivery systems, and
cameras for feedback loop for dimension control, for fabrication of 3D part on a
substrate under CAD driven motion control system [109].
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Figure 3.20 - A Sketch of DMD process
In a POM® DMD process, the thermal energy from a CO2 laser beam is used to
create a melt pool on the surface of a substrate while a metallic alloy in powder form
is fed to the melt pool through a nozzle that is coaxial to the laser beam. Up to four
powder-storage feeders can be used to deliver different metal powders to the nozzle.
Both the base metal surface and the added powder get melted and solidified rapidly
as the laser passes to other areas of the part, creating a unique microstructure as a
result of this rapid solidification. The melt pool is consciously monitored through a
close-loop feedback system to ensure the heat input stays the same at all times [110-
111]. This further ensures that the microstructure stays similar to that of the
previous layers as the Heat Affected Zone (HAZ) is kept at minimum at all times.
Thus the microstructure of the previous layers is not affected by the heat input from
the layers deposited later [110-111]. Proper selection of the process parameters of
DMD such as laser power, deposition speed and powder flow rate are of great
importance as well. These can affect the amount of heat input, hence influencing the
HAZ and the material properties of the product [112].
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This research work assesses the changes in physical and mechanical properties of a
range of engineering alloys (316 SS, 420 SS, Stellite 6, Aluminium Bronze,
EuTroLoy 16221 and H13 tool steel) - which are often used in common
manufacturing and engineering applications - when these alloys are used in
conjunction with each other to produce both functionally graded structure and wafer
layered structure made possible by laser assisted direct metal deposition technology.
Wafer layered structures are structures that are created by alternating between two
alloys when depositing them. This creates a series of bimetallic combinations which
are bonded to one another creating a structure that consists of two alloys each of
which has been used to form one layer which is bonded in between two layers of the
other alloy. This structure - like FGMs - can be made into simple shapes such as
square or a round bars or complex 3D shapes using the laser DMD technique.
Fifteen samples were made using gas atomized metal powders with particle sizes
ranging between 45 µm and 145 µm with majority of the particles being around 120
µm. The samples are listed in Table 3.15 which also lists the single alloys used in
each sample and the FGM and wafer structure type they have been made in. The
first six samples consist of monolithic single alloys (316 SS, AlBrnz, EuTroLoy
16221, Stellite 6, 420 SS, and H13 tool steel). Among these, AlBrnz is a
commercially available Aluminium-Bronze alloy containing mainly 10%
Aluminium, 5% Nickel, and 1% iron, with balance as Copper. Other five samples
are well known standard metal alloys, and have been described in section 3.1. Using
these alloys, four types of FGM and five types of wafer structures were produced for
this investigation.
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Table 3.15- List of samples made by DMD
No Structure Type Alloy A Alloy B No Structure Type Alloy A Alloy B
1 Monolithic 316 SS - 9 FGM AlBrnz 420 SS
2 Monolithic AlBrnz - 10 FGM 316 SS Tool
Steel
3 Monolithic EuTroLoy
162216 - 11 Wafer 316 SS
Tool
Steel
4 Monolithic Stellite 6 - 12 Wafer 316 SS 420 SS
5 Monolithic 420 SS - 13 Wafer EuTroLoy
162216 316 SS
6 Monolithic Tool Steel - 14 Wafer AlBrnz 420 SS
7 FGM 316 SS 420 SS 15 Wafer AlBrnz Stellite 6
8 FGM EuTroLoy
162216 316 SS - - -
The product of DMD is a multilayer 3D structure created from the powder that has
been fed into the melt pool. This 3D structure is created on top of a base plate that is
cut off in most cases and disposed of. The unique capabilities of the DMD process
were the reason for it to be selected as the fabrication process for the samples used in
this work i.e. functionally graded materials and wafer layered structures. The powder
feeder unit of the machine which was used in this experiment had two feed
containers. This meant that two different alloys could be fed into the melt pool at the
same time with varying proportions of feed rate, for example powder feed unit “A”
would inject 70% of the total metal being deposited while powder feed unit “B”
would deposit 30% of the total metal being deposited. These proportional feed rates
can be changed at will both during metal deposition and or prior to it. It is this
capability of this process that enables it to create functionally graded materials where
every layer has a different composition of two constituent alloys and this proportion
varies gradually throughout the sample making it an FGM. On the other hand, the
feed rates of the powder feed units could be alternated between different layers if
desired. This means one layer can be deposited using only the alloy from powder
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feed unit A while the next layer will be deposited only using the alloy from powder
feed unit B creating a wafer layered structure.
Figure 3.21 shows one of the DMD samples before being machined and while still
on the base plate onto which the powder was initially deposited. As can be seen next
to the 3D sample, there are single tracks which were deposited to determine the best
set of DMD parameters that result in lowest dilutions, best track width and height
and visual characteristics such as no porosity or cracks in the deposit. The best set of
parameters was then selected to create each 3D structure.
The Table 3.16 shows the parameters used for the production of samples.
Table 3.16 DMD parameters used for samples
Laser Power Deposition Speed Powder feed rate Spot size
950 Watts 900 mm/min 12 gr/min 2 mm
A typical single layer of DMD deposited metals had a thickness of 1 mm. In order to
make the samples for this project, 10 layers were deposited for each sample. The
length of each sample was 80 mm and the width was 12 mm. Each bead overlapped
the previous bead by 50% so the finished layer had a flat finish as against grooved
finish. The layers were deposited without any significant delays in between.
However enough time was given to the powder feeder to clean the carrier lines in the
case of Wafer structures of the previous alloy. This was essential to ensure each
interchanging layer is 100% of the alloy intended for that layer and that the small
amount of powder which might remain in the carrier lines after completion of the
previous layer would get deposited as part of the new layer which is supposed to be a
different alloy. The cleaning of the line was simply done by running the 2nd powder
through the lines for at least 30 seconds. Then the program would run the system to
deposit a full layer of the second alloy and this cycle was repeated until 10 layers
were deposited.
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In the case of FGM samples, after each layer was deposited, again the lines were
cleaned of the previous combination of alloys before a new combination was set for
the new layer.
The first layer for all FGM samples comprised of only one of the two alloys, then the
2nd layer would include only 90% of this alloy and 10% of the second alloy and this
proportion would be altered step by step so the last layer would be 100% of the
second alloy only.
After deposition, the samples were machined to specific sizes for the testing
purposes. The final sample dimensions were 25x10x10 mm.
Figure 3.21 - A DMD sample of Stellite 6
Figure 3.22 shows the monolithic samples after being cut off the base palte and
getting initial machining. A CNC machine was used to remove the as deposited
surface finish off the samples. The machined finish did not show any pore or cracks
in any of the samples.
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Figure 3.22 – Monolithic samples after machining
The pore and crack free finishes was a representation of the high density and flaw-
free result of the DMD process in producing 3D structures.
Figure 3.23 shows a sample of FGM consisting of AlBrnz and 420 SS alloys. The
sample consists of 100% layer of AlBrnz at the top most layer and varying gradually
with 100% of layer of 420 SS at the most bottom layer.
Figure 3.23 - FGM sample comprising of AlBrnz and 420 SS
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Figure 3.24 shows a sample of wafer structure consisting of alternating AlBrnz and
420 SS alloys from bottom to top of the sample. The distinction between different
alloys in different regions is evident.
Figure 3.24 - Wafer sample of AlBrnz and 420 SS
These structures are unique and novel in the way they are fabricated. The physical
and mechanical tests which have been carried out on these structures will reveal their
unique properties and characteristics compared to monolithic structures.
The following chapters will provide a detailed and comprehensive report on such
tests.
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Chapter 4 Microstructure
& Microhardness Investigation
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Chapter 4 - Microstructure & Microhardness
Investigation
4.1 Introduction
An important aspect of every metallic alloy is its microstructure. The microstructure
of a metal can strongly influence physical properties such as strength, toughness,
ductility, hardness, corrosion resistance, high/low temperature behaviour, wear
resistance, and so on, which in turn govern the application of these materials in
industrial practice.
When it comes to development of innovative metallic structures – which is the focus
of this research work – understanding the microstructure and such novel products is
vital in order to better appreciate their unique physical and mechanical properties and
characteristics. More important than the microstructure of the bulk of these alloys
and structures is the microstructure in and around the bond interface between the
multiple layers. Since the interaction between the previous layer and the powder that
is being deposited and molten simultaneously to form the 2nd layer is crucial to the
properties of the final product, the quality of the resulting bond between the two
layers and any possible flaws in it such as pores and micro cracks can be detected
through microscopic investigation.
Another method to evaluate the bond interface and also the bulk of each layer, which
forms the 3D structure, is micro-hardness scanning across the structure. According
to ASTM E-384, microhardness testing specifies an allowable range of loads for
testing with a diamond indenter. The resulting indentation is then recorded and
converted to a hardness value. Typically loads are light, ranging from a few grams to
one or several kilograms. Since the test indentation is small, microhardness testing is
useful for a variety of applications such as testing thin materials like foils or
measuring individual microstructures. All samples in this project underwent a micro-
hardness scan of all their constituent layers.
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The specimens were produced on mild steel plates as substrates. Figure 4.1 shows
two monolithic samples on a base plate. These had to be separated from their
substrate in order for tests to be carried out on them. Disc saw equipped with coolant
was used to cut the specimens out of the substrate plates. The plates and the
specimens were kept cool using the coolant at all cutting times to ensure that the
friction heat generated from cutting wouldn’t affect the specifications of the
specimens.
Figure 4.1 - 3D monolithic structures made by DMD
Of each alloy sample, one end was cut using the disc saw to take a section for
metallographic study. The sectioned ends were then ground down to size suitable for
hot mounting to be used as metallographic specimens. The mounted specimens were
then polished with SiC polishing paper to grade 1200 and with alumina powder to
grade 0.05 µm.
4.2 Microstructure Study of Monolithic Materials
The first set of samples that were fabricated were monolithic 3D structures of each
single alloy used in this project. This was done to compare the microstructure of
DMD made samples with the as cast microstructure of the same alloys.
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Figure 4.2 shows the as cast microstructure of Stellite® 6 at 1000 times
magnification.
Figure 4.2 As cast Stellite 6 microstructure [Source: Deloro Stellite’s data sheet]
Figures 4.3 and 4.4 show the microstructure of Stellite® 6 made by DMD at two
magnifications of 1000 and 3000 times respectively taken by scanning electron
microscopy (SEM).
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Figure 4.3 – SEM of DMD Stellite 6 @ 1000X Figure 4.4 – SEM of DMD Stellite 6 @ 3000X
The main difference between the as cast microstructure and the DMD deposited one
is that the grains are more directional and elongated in the DMD sample, which is
the result of heat transfer and solidification process in each layer deposited. The
grains are also much smaller in size, which is an indication of the solidification rate
in DMD process which is much higher than in other manufacturing processes such as
casting.
This rapid solidification and directional heat transfer creates a microstructure, which
is unique to most DMD fabricated metallic structures.
Figures 4.5 and 4.6 are two SEM images of 316 Stainless Steel deposited by DMD
as part of this research. Similar to the DMD made Stellite 6, elongated fine grains
can be seen in the microstructure.
Figure 4.5 – SEM of DMD316 SS @ 1000X Figure 4.6 – SEM of DMD 316 SS @ 3000X
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Another example of the DMD made samples and their microstructure can be seen for
420SS in Figures 4.7 and 4.8. Most grains are finer than what can be seen in as cast
microstructure and there is an elongation feautre for most grains throughout the
sample.
The fine microstructure of metallic alloys in DMD samples affects their physical and
mechanical characteristics such as increased hardness.
Later in this chapter hardness values for the DMD samples will be compared to the
hardness of the same alloys in their as cast condition.
Figure 4.7 – SEM of DMD 420 SS @ 1000X Figure 4.8 – SEM of DMD 420 SS @ 3000X
Figures 4.9 to 4.14 are microscopic images of microstructures for monolithic
samples of AlBrnz, EuTroLoy 16221 alloy and H-13 Tool steel.
Figure 4.9 DMD AlBrnz microstructure @100X Figure 4.10 DMD AlBrnz microstructure @500X
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As mentioned earlier, a unique characteristic of microstructures of metals produced
by laser DMD is the fine grain structure and directionality of them. Figure 4.9 and
subsequently with a higher magnification Figure 4.10 show the DMD produced
AlBrnz alloy microstructure that confirms this fact. The majority of the grains are
elongated yet small in size. Since the melt pool size in the DMD process is small –
i.e. 2-3 mm in diameter – and the deposition speed is high i.e. 1000 mm/min in most
cases, the solidification rate is a lot higher than what one would get in a casting
process or even welding using conventional techniques. This type of microstructure
presents different physical and mechanical properties and characteristic. In general it
is known that metals with fine microstructure exhibit higher hardness values.
Figure 4.11 EuTroLoy 16221 microstructure @100X Figure 4.12 EuTroLoy 16221 microstructure @500X
The argument of fine and directional microstructure and hence its distinctively
different properties applies to all DMD fabricated samples. Figures 4.11 and 4.12
show Colmonoy – also known as EuTroloy 16221 – in two different magnifications
where the small size grain arrangement is evident. One thing should be noted that in
all microstructures of DMD produced metallic samples, the general shape and phase
arrangement of the microstructures are similar to what can be found in their as cast
state and it is only the size of the phases and slight change in the directionality that
differs between the two processes.
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Figure 4.13 Tool Steel (H13) microstructure @100X Figure 4.14 Tool Steel (H13) microstructure @500X
Tool Steel – H13 is not an exception in the DMD produced samples and it shows
signs of rapid solidification too. While there are two distinct phases in the
microstructure as shown in Figures 4.13 and 4.14, the grain size is fine, however
there is not an apparent directionality seen in this microstructure. This can be due to
different thermal characteristics of this alloy and also the image could have been
taken from a section of the sample which has maintained the process temperature for
a longer period, thus giving enough time to the microstructure to shape with little
directionality. This happens when multiple layers are deposited by laser without
allowing time for the solidified layers to cool down. This may also contribute to
higher rates of dilution between adjacent layers. In order to ensure similar
microstructure is achieved in each layer – when depositing multiple layers – one
should allow sufficient time between each layer. Also fine tuning all process
parameters such as laser power and depositing rate will help reduce dilution between
layers and hence achieve uniform microstructures within each layer and across all
layers.
4.3 Microstructure Study of Wafer-layered structures
In order to investigate the microstructure of the wafer layered 3D structures using
scattered electron microscopy (SEM), cubic samples were mounted in a way that the
layers were exposed outwards and made available for imaging. Figure 4.15 shows a
wafer-layered AlBrnz/Stellite 6 sample mounted and polished for SEM imaging.
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Figure 4.15 – A mounted Wafer-layered structure of AlBrnz/Stellite 6
Figure 4.16 shows the sample at low magnifications (111 X). It shows the bonding
region between the alloys (layers). The lighter region in Figure 4.16 is AlBrnz
which is deposited between two layers of Stellite 6.
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Figure 4.16 – A close look at one layer between two adjacent ones in a wafer sample AlBrnz/St6
Figure 4.16 shows one layer and two bonding interfaces adjacent to it. A important
feature that can be seen in Figure 4.16 is the lack of pores and/or cracks throughout
the structure especially near the bond region where such metallurgical defects are
common in parts fabricated through other more conventional technologies.
The other significant aspect of the DMD structure than can be seen in this figure is
the dilution of the alloy from one layer into the other layer. Figures 4.17 and 4.18 are
highly magnified SEM images of the bond interface region showing the diluted
particles inside the adjacent layer in AlBrnz/St6 wafer.
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Figure 4.17 – 500X SEM view of the bond area Figure 4.18 – 1000X SEM view of the bond area
Figure 4.19 and 4.20 are extremely high resolution of the bond between the
segregated diluted particles of Stellite 6 inside the AlBrnz microstructure.
Figure 4.19- 5000X view of the bond area Figure 4.20 - 20,000X view of the bond area
These two highly magnified SEM images were acquired to ensure that the diluted
particles are still perfectly bonded with their surrounding phase and that they won’t
act as crack initiation points due to poor bonding with the adjacent phase or even
presence of pores around them.
It can be seen that while dilution is an undesirable phenomena in a thermal metal
deposition process, the structure is still free from metallurgical defects.
Figures 4.21 to 4.28 are optical microscopic images of wafer samples of 316 SS with
420 SS, 316SS with Tool Steel, EuTroLoy 16221 with 316 SS and AlBrnz with
420SS. The images show the bond region between each pair of alloys.
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Figure 4.21 Microstructure of 316-420 Wafer @100X Figure 4.22 Microstructure of 316-420 Wafer @500X
In Figures 4.21 and 4.22, the 420 SS is shown on the top of the images and 316SS
bonded to it is shown at the bottom of the images. The effect of deposition tracks is
seen in Figure 4.21 as wave effects between the two layers. This of course creates no
adverse influence on the structure. However it should be monitored to ensure that
remelting of 50% of every previous track doesn’t create areas with significantly
higher dilution or penetration into the previously deposited layer. In laser DMD, the
interface between layers is the zone which is more prone to containing pores and
microscracks, which have generally been avoided in all the samples in this research
by using the right set of parameters.
Figure 4.23 Microstructure of 316-H13 Wafer @100X Figure 4.24 Microstructure of 316-H13 Wafer @500X
In Figures 4.23 and 4.24 the H13 Tool Steel alloy is shown on the top of the images
and 316SS bonded to it is shown at the bottom of the images. These figures show
that closer to the bond interface between the two adjacent layers, the shape and size
of grains change which is a product of re-introduction of heat to the previous layer
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while depositing the next layer. It is considered as a full remelt on the surface and
partial remelt in the sub-surface zone also known as the Heat Affected Zone (HAZ).
This phenomenon is of course not specific to these two images and is a general
characteristic of all multilayer DMD deposited structures which is evident in Figures
4.25 and 4.26 too.
Figure 4.25 Microstructure of 16221-316 Wafer @100X Figure 4.26 Microstructure of 16221-316 Wafer @500X
In Figures 4.25 and 4.26 the EuTroLoy 16221 alloy is shown on the top of the
images and 316SS bonded to it is shown at the bottom of the images. In Figure 4.25
signs of remelting the 316SS layer are clearly seen where instead of a rather straight
line at the interface representing the previous layer, one can see the penetraion of
316SS microstructure into the EuTRoLOy 16221 alloy at the top. At a closer look
with the magnification of 500X in Figure 4.26 though, it can be seen that the bond
ionterface is free from any pores and microcracks and the bond is intact. The
interface is distinguished by the two different directions of the microstructures of the
two adjacent layers.
Figure 4.27 Microstructure of AlBrnz-420 Wafer @100X Figure 4.28 Microstructure of AlBrnz-420 Wafer @500X
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In Figures 4.27 and 4.28, the 420 SS alloy is shown on the top of the images and
AlBrnz bonded to it is shown at the bottom of the images. What is evident in these
figures is the comparatively higher dilution between the two layers. The reason
behind this is the large difference between the melting temperature of the two
constituent alloys i.e. AlBrnz and 420SS. Aluminum Bronze alloy melts at
temperatures at or below 1000°C where as the melting point for 420 Stainless Steel is
1500°C . Therefore when we need to melt the 420SS powder in the DMD process and
deposit it on top of an AlBrnz solid layer, we need to take the 420 SS powder to
above its melting point which means the AlBrnz reaches a lot more than its melting
temperature and hence flows into the immediate areas of the top layer being the
420SS in its molten state. Figure 4.27 shows two pieces of AlBrnz trapped in 420SS
layer after solidification has been completed. Such phenmonen can be minimized by
altering the process parameters to minimize the heat input into the AlBrnz layer
when depositing the 420SS however it can never be fully avoided as one can’t help
melting the 420SS which requires temperatures of above 1500°C .
4.4 Functionally Graded Materials
Scanning Electron Microscopy (SEM) study of the Functionally Graded Material
samples was done in the same way as the wafer-layered samples. The side of a cubic
sample, which contained all the layers was mounted outwards so the bond interface
as well the layers themselves could be viewed under the microscope.
Figure 4.29 shows an FGM of AlBrnz/420 SS sample mounted and polished ready
for SEM imaging. This sample has been selected mainly because it contains two
alloys with distinctly different physical colours so that the gradual change of the
alloying elements across the structure from one side to the other can be seen. This
effect is obviously not as easily seen when the constituent alloys of an FGM or even
wafer structure are both of two different types of stainless steel.
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Figure 4.29 – FGM of AlBrnz/420 SS sample mounted for analysis
As the name suggests a Functionally Graded Material (FGM) is a structure where the
microstructure gradually changes from one side to the other side affecting its
properties and therefore functionality. In the case of Figure 4.29 for example, the top
side is 100% 420 SS with all its particular properties such as surface hardness and
toughness whereas the bottom side is 100% AlBrnz alloy which is a non-ferrous
alloy with totally different functionality and yet these two are part of the same
structure and in between these two phases or layers the rest of the structure has a
gradually altering range of a combination of the properties of these two alloys. Such
unique set of characteristics means that while only using two alloys to form such
structures, we have at our disposal a larger range of physical and mechanical
properties to use in different environments and conditions.
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Figure 4.30 is a low magnification SEM image of a bond interface region between
two layers in the centre area of the part meaning the proportion of each constituent
alloy in each layer is close to 50% in this image.
Fragmented secondary phase 420 particles can be seen precipitating throughout the
microstructure where the base is AlBrnz. This SEM image has been acquired at 500
X magnification.
Figure 4.30 – A look at two adjacent layers in an FGM sample showing two phases of AlBrnz/
Figures 4.31 – 4.34 are closer looks of AlBrnz/420 FGM at the two phases ranging
from 1000 X to 20,000 X magnification, showing the microstructure is absolutely
pore and crack free and that the two phases are bonded together as are all layers to
the adjacent layers making the whole structure a 100% solid body.
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Figure 4.31-1000X SEM view of FGM phases Figure 4.32 - 5000X SEM view of FGM phases
Much higher SEM imaging magnifications have been used here to investigate the
grain shape and microstructural integrity with much more details.
Figure 4.33 – 10,000X SEM view of FGM phases Figure 4.34 – 20,000 X view of FGM phases
The most appropriate method of presenting the microstructure of an FGM sample is
showing the full cross section of the sample showing both ends of it and the grading
microstructure in between them.
In order to show this, multiple microscopic images were taken and then attached to
each other using computer software packages.
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Figures 4.35 – 4.38 are such imagery of all the four FGM samples of this work. In
each figure, the top and the bottom alloys have been labelled and in between these
two ends, the grading microstructure can be seen at a magnification of 100X.
The wafer structures are the product of repeating two different layers each made
from a different alloy and hence produce a structure as a result of such repetition.
Therefore studying two layers in a wafer structure will be sufficient to understand its
characteristics ranging from microstructural aspects to physical and mechanical
properties. However in the case of FGM structures, since they are the product of
multiple layers each with a unique chemical composition which is different from the
previous and next layers, one has to use a full unit that starts with a layer consisting
of 100% alloy A and gradually changes composition in the subsequent layers to
finish with the last layer being 100% alloy B. The properties of an FGM structure
can only be studied when such a whole unit of structure is used for investigations.
Figures 4.35 - 4.38 provide this opportunity for the four FGM samples in this
research by showing the full structural unit of these samples. Two constant features
throughout the microstructure of all the four samples is the fine grain size and
directionality of the grain structures which is as discussed before, the result of rapid
solidification of the deposits in laser DMD process. However, a smooth gradual
change in the over phase arrangement of microstructure shape can be seen in all 4
figures from one side i.e. alloy A, to the other side i.e. alloy B. The difference in the
reaction - by the various altering layers - to the etchant used is evident in all four
figures which is a proof of the corrosion resistance of the full unit structure gradually
changing from layer to layer depending on what portion of each layer is made up of
what alloy.
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Figures 4.35 - 4.38 - Microstructure of 4 FGM samples, full cross-sections at 100X
102
A challenge in metallographic study of FGMs and wafer-layered structured
consisting of two metallic alloys is in both polishing and etching them. This is due to
the fact that the sample will have two metallic alloys with different hardness values
that react differently to the polishing process. Also finding the right etchant that
would reveal both alloys and their phases can be challenging.
4.2 Micro-Hardness
The hardness of the specimens could give some general indication of the mechanical
strength of the materials. All specimens were hardness tested using a calibrated
microhardness testing machine. The microhardness testing machine was a Leco
LM700-Series Micro-indentation Hardness Testing System.
The tests were conducted according to ASTM standard ASTM E384-99e1. In order
to measure the hardness of the alloys, their metallographic specimens were used. The
microhardness testing machine was the same for all specimens. The machine’s
calibration records were all up to date.
The samples were placed under the diamond indenter of the micro-hardness testing
machine. Figure 4.39 shows a sample while being tested for its micro-hardness.
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Figure 4.39 – A mounted sample in the micro-hardness testing machine under the diamond
When the sample is at the right distance from the diamond, the diamond presses
against the surface of the sample and leaves an indentation mark on it. Using the
optical microscope which is integrated into the system, the mark can be seen on a
coupled computer monitor. The size of this mark will be converted into hardness
values by the dedicated computer software. The softer the metal, the larger such
indentation marks will be.
Figure 4.40 shows a micro-indentation mark on the computer monitor. In this case
the metal has a hardness of 46 HRc as can be seen in the software window.
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Figure 4.40 A screen shot of the micro hardness testing software on the computer screen
In order to get a good result, the sample should be well-polished so the indentation
mark can be seen easily and also the surface roughness does not affect the diamond
shape and hence the hardness measurement.
Table 4.1 contains the hardness test results for all monolithic specimens created by
DMD.
Table 4.1 – Hardness values for DMD and as-cast alloys
Alloy Alloy code Hardness Reported hardness
Stainless Steel Grade 420 420 SS 47.3 HRC 45HRC
Stainless Steel Grade 316L 316L SS 25.3 HRC 21 HRC
EuTroLoy 16221 16221 43 HRC 27 HRC
Tool Steel H13 H13 36.2 HRC 34 HRC
Cobalt-Chrome-Fe (Stellite 6) 16006CP 42.6 HRC 38 HRC
Aluminium Bronze AlBrnz 94 HRB 82 HRB
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As can be seen all DMD samples are harder than their as-cast state. This is due to the
rapid quenching/solidification process involved in the laser metal deposition. The
focused heat input creates only a small melt pool. The small amount of heat from the
melt pool dissipates to the rest of the part rapidly causing a swift solidification of the
melt pool metal not allowing time for the grains to grow in a slow cooling process as
they would do in a casting process. The finer the grain structure, the higher the
hardness of most metal becomes.
If such high hardness is not desirable in a DMD made structure, then the part can go
under specific heat treatment cycles to decrease the hardness. This is possible for
most iron based alloys such as 420 SS.
Hardness tests on wafer structure samples were done using 10 points, each of which
was done on one alloy closest to the center of the track or layer. The results showed a
constant and regular fluctuation of hardness values from alloy A to alloy B for all
samples. Figure 4.41 shows the hardness profile for AlBrnz and 420SS wafer
sample.
Figure 4.41- Hardness in wafer sample AlBrnz-420SS
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A similar pattern of hardness profile was observed in other wafer samples. Figures
4.42 to 4.45 show micro-hardness profiles for other wafer samples. The 316 SS-420
SS wafer sample will provide the highest average hardness compared to other wafer
samples.
Figure 4.42 - Hardness profile for St6-AlBrnz Wafer Figure 4.43 – Hardness profile for 316SS-16221
In all Wafer samples, except for small variances in micro-hardness values measured,
the alternating alloy layers maintained a similar hardness value. Therefore, the
hardness of constituent alloys is unaffected throughout the production process by the
Direct Metal Deposition technique.
Figure 4.44 - Hardness profile for 316-420 Wafer Figure 4.45 – Hardness profile for 316SS-Tool Steel
The next set of hardness tests were done to investigate the hardness profile of wafer
samples around the interface between alloys A and B. In order to do so and to have a
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measure of verification of the acquired data, hardness values were measured across
two interfaces.
Figure 4.46 - Hardness across different layers (wafer)
Figure 4.46 shows the variations illustrating the hardness values for AlBrnz-420SS
wafer sample. It shows a gradual decrease of hardness values from 420SS region
towards the bond area and then continues to decline to the center of AlBrnz layer and
then starts to increase from AlBrnz region toward the bond area and continues to rise
towards the center of the 420SS region.
The fact that micro-hardness values show a smooth and regular decline and increase
throughout the bond interfaces is a confirmation that the level of dilution on one
alloy into the other is not adversely affecting the physical properties – in this case
hardness – of the alloys.
Tests on functionally graded materials samples were done using 10 points from one
side with 100% alloy A to the other side with 100% alloy B. The hardness
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measurements show a gradual change of hardness from alloy A to alloy B in all
samples. Figures 4.47 to 4.50 show the hardness profiles for the four FGM samples.
The 316 SS-420 SS FGM sample will provide the highest average hardness
compared to other FGM samples.
Figure 4.47 - Hardness profile for 420-AlBrnz FGM Figure 4.48 – Hardness profile for 316-420 FGM
Figure 4.49 - Hardness profile for 316SS-16221 FGM Figure 4.50 – Hardness profile for 316-Tool Steel FGM
Results of microhardness profiles of FGM and wafer structures on the two alloys and
on the bond interface of wafer or the middle interface of FGM between two layers
have shown a consistency in the changing trend of microhardness values throughout
the samples as the portion of each constituent alloy changed. This smooth and
regular decline and increase throughout the bond interfaces is a confirmation that the
level of dilution on one alloy into the other is not adversely affecting the physical
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properties of the wafer alloys. The same hardness profile pattern was seen for all
other samples in both FGM and Wafer structures.
In the following chapters other properties of these structures will be tested and
studied.
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Chapter 5 Thermal Expansion
Studies
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Chapter 5 - Thermal Expansion Studies
5.1 Introduction
For engineering applications including high temperature variations, one of the
critical properties of materials is their coefficient of thermal expansion (CTE). A
correct selection of materials in the design stage of a component ensures that it will
not fail sooner than expected once it is put in service. In the case of thermal
expansion behaviour of metals, if a metallic component expands more than its design
specifications, this can cause significant failures within the system in which it is
used.
The focus of this set of tests and studies described in this chapter is to investigate the
changes in the coefficient of linear thermal expansion in functionally graded
materials (FGMs) and wafer layered structures.
The main goal of this research is to find a composition and structure with the largest
reduction in the value of the coefficient of thermal expansion compared to the
thermal expansion coefficient of each of its constituent alloys individually. Such
materials and structures are high in demand in applications where metallic parts and
components are exposed to high temperatures, and excessive thermal expansions
might adversely affect the performance of these parts and components or lead to pre-
mature failures. Hence, a new bimetallic structure that does not expand as much as
monolithic alloy structures is a desirable choice for high temperature applications.
5.2 Methodology for CTE
A calibrated high resolution dilatometer machine –manufactured by Theta Industries,
US - was used to carry out all linear thermal expansion measurements. Figure 5.1
shows schematics of such a system. Pushrod dilatometry is a method for determining
dimensional changes versus temperature or time while the sample undergoes a
controlled temperature program. The degree of expansion divided by the change in
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temperature is called the material’s coefficient of thermal expansion (α) and
generally varies with temperature. To perform a dilatometric analysis, a sample is
inserted into a special holder within a movable furnace. A pushrod is positioned
directly against the sample and transmits the length change to a linear variable
displacement transducer (LVDT). As the sample length changes during the
temperature program, the LVDT core is moved, and an output signal proportional to
the displacement is recorded. The temperature program is controlled using a
thermocouple located either next to the heating element of the furnace or next to the
sample. Since the sample holder and the front part of the pushrod are being exposed
to the same temperature program as the sample, they are also expanding. The
resulting dilatometer signal is therefore the sum of the length changes of sample,
sample holder, and pushrod. Equation 5.1 is used to calculate α (Alpha) values.
𝛼 =1
𝐿𝑜(
∆𝑙
∆𝑇) (5.1)
α (Alpha) coefficient of expansion Lo initial sample length ΔT change in temperature Δl change in length
Figure 5.1 – Schematics of a push rod dilatometer
In our thermal expansion measurements, a fused silica push-rod was installed and the
thermal expansion of the system was calibrated using a Fused Silica standard (SRM
739). Measurement of the thermal expansion behavior to 500°C was carried out in
argon at a flow rate of 0.5 ml/min, according to Australian Standard AS 1774.11.
Heating increase was maintained at 5°C per minute. The test started from room
temperature which was about 21 oC and continued to rise gradually at 5 oC/min rate
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to up to 500 oC. This was the same for all 15 samples. The length of the samples was
measured with high precision once at about every 30 seconds. This produced about
190 length measurements. The final report from the machine was in the form of a
table containing each temperature and its associated length measurements in
microns. Table 5.1 is a sample section of some of the results. The full set of data can
be found in Appendix C of this thesis.
Table 5.1 A section of results from dilatometry on WAFER sample of 16221 & 316L
Sample: WAFER 16221-316L
Temp Expansion
Coefficient of Thermal Expansion (Alpha)
ｰC % mm/mm/deg C.10^-6 23.25212 0.000939 2365.183 23.25609 0.000939 12013.62 23.2529 0.000937 59.02676 23.45165 0.001178 19.36497 23.89081 0.001237 10.54525 24.40983 0.001221 8.062004
The dilatometer test machine was switched off and allowed to settle after each test
and before the next test. This was essential for accurate measurements for each
sample, and acted as a resetting of the equipment so previous tests and the heat
remaining from them wouldn’t affect the new tests.
5.3 CTE of FGM and Wafer
Figures 5.2 to 5.6 show the results acquired based on the measurements of
coefficient of linear thermal expansion (CTE) for each individual sample at different
temperatures.
In all graphs, the unit of measurement for CTE is mm/mm/deg C.10^-6.
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Figure 5.2 - CTE graphs with 316 SS and 420 SS
Each of these figures contains the graphs for single alloy samples, the FGM and/or
wafer structure sample that contain that alloy in conjunction with another alloy. This
is done to better compare the effect of each structure on the values of CTE in relation
to those of the single alloys alone.
As seen here in Figure 5.2, FGM structure comprising of 316 SS and 420 SS has a
lower CTE than each of the alloys alone or the wafer structure of these two alloys.
The wafer structure shows CTE values similar to those of 420 SS.
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Figure 5.3 – CTE graphs with 316 SS and EuTroLoy 16221
Figure 5.3 contains graphs for CTEs associated with 316 SS and EuTroLoy 16221
alloys and their FGM and wafer structures. The CTE graphs for FGM and wafer
structures are located between those of 316 SS and EuTroLoy 16221 with the latter
showing the lowest values of CTE and 316 SS the highest.
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Figure 5.4- CTE graphs with 316 SS and Tool Steel
In figure 5.4, the CTE graphs of 316 SS and tool steel grade H13 and their FGM and
wafer structures are shown. The CTE values of FGM sample are lower than the other
three samples between 60 and 220 degrees oC. However, from 220 oC the CTE
values of tool steel are the lowest in the group. The wafer structure samples shows
the lowest CTE values only at the room temperature and up to 80 oC and thereafter,
it is placed as the sample with the 2nd highest CTE values. Alloy 316 SS has the
highest CTE values in this group.
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Figure 5.5 - CTE graphs with AlBrnz and 420 SS
Figure 5.5 shows graphs for CTE values associated with Aluminium Bronze and 420
SS alloys and their FGM and wafer structure alloys. The wafer structure sample
demonstrates a constantly lowest value of CTE among the four samples. The FGM
and 420 SS samples show similar values and trend of CTE values and 316 SS shows
the highest CTE values of all.
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Figure 5.6 - CTE graphs with AlBrnz and Stellite 6
Figure 5.6 demonstrates CTE graphs for AlBrnz and Stellite 6 alloys and the wafer
structure sample. The FGM sample of these two alloys showed multiple cracks in the
deposition process and was deemed unfit for tests due to the errors the cracks would
introduce in the measurements. The CTE values for wafer structure sample are
placed between those of the single alloys in the group. However, it shows slightly
lower values in the temperature range under 100 degrees oC. AlBrnz has the highest
values of CTE among the three samples.
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Figure 5.7 – CTE graphs for all monolithic samples
Figure 5.7 shows the CTE graphs for all monolithic samples created by DMD.
AlBrnz and 316SS show the highest CTE values where Colmonoy shows the lowest.
These are material properties that are crucial in determining the application of such
alloys in engineering design.
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Figure 5.8 – CTE graphs for all FGM samples
Figure 5.8 shows CTE graphs for all the FGM samples i.e. FGM 316-420, FGM
16221 (Colmonoy) – 316SS, FGM AlBrnz-420SS and FGM 316-Tool Steel. For the
majority of the temperature range above 150 degrees C, FGM 316-420 shows the
lowest CTE values, where FGM AlBrnz-420SS shows a rather consistently high
CTE values in comparison to other samples.
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Figure 5.9 CTE graphs for all WAFER samples
Figure 5.9 shows the CTE values for all WAFER samples. The Wafer AlBrnz-420SS
shows the lowest CTE values while Wafer AlBrnz-Stellite 6 demonstrates higher
values than all between room temperature and 220 degrees C and Wafer 316-Tool
Steel shows the highest between 220 to 500 degrees. This shows within different
temperature ranges the behavior of material structures varies significantly. Therefore
the service temperature range is a critical factor in engineering component design
and material selection.
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Figure 5.10 - CTE graphs for all FGM and WAFER samples
Figure 5.10 shows all bi-alloy structure samples i.e. FGMs and WAFERs together
for a better comparison of their CTE values. Amongst all, FGM 316-420 sample
shows the lowest CTE values where WAFER 316-Tool Steel shows the highest CTE
values for the majority of the temperature range i.e. 120 degrees and above. The
alloying elements and type of structure – FGM and WAFER - significantly affect the
overall properties of the combined bi-alloy structures.
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Figure 5.11 – CTE values for all monolithic samples measured at 450 °C
Figure 5.11 shows the CTE values for all monolithic samples measured at 450°C.
This helps us understand how the materials behave at a fixed temperature and not
over a range. The 450°C has been selected because at this temperature almost all
samples have shown a significant amount of expansion and their expansion can be
meaningfully compared; whereas at temperatures below 100°C for example, such
comparison might not be as valid. The highest expansions will be expected –
amongst all these six alloys – from 316 SS and AlBrnz while the lowest values will
be observed in Tool Steel and Colmonoy alloys.
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Figure 5.12 – CTE values for all WAFER and FGM samples measured at 450 °C
Figure 5.12 shows CTE values for all bi-alloy structures i.e. FGMs and WAFERs
measured at 450 degrees C. The WAFER 316-Tool Steel sample will expand the
most at this temperature while FGM 316-420 will do the least expansion. When it
comes to material selection for applications at fixed temperatures, it is vital to select
the right material that will behave within the design parameters. Such innovative
structures will offer the design engineers a wider range of options in material
selection.
The figures showing thermal expansion measurements show that in the majority of
the samples – both FGM and wafer structures – the combinations of the two alloys
always decreased the overall thermal expansion rate to either somewhat between the
two alloys individually or lower than both of the alloys. This means that the two
structures both have a decreasing effect in the coefficient linear of thermal
expansion.
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In the case of the wafer structures, the DMD sample represents a bi-metallic
arrangement where the two metals have different thermal expansions and are fully
bonded to each other. When heated to the same temperature, due to the bi-metallic
effect, the alloy with higher thermal expansion rate tends to pull the other alloy
outward the block while the alloy with lower thermal expansion does exactly the
same thing only at a lower rate.
This difference between the thermal expansion rates results in an overall rate which
logically lies between the rates of the two alloys individually. This is true across all
samples except for the AlBrnz – 420SS wafer sample, where the thermal expansion
rate is lower than that of each individual alloy alone or even the FGM sample.
Figure 5.13 is a schematic representation of a typical wafer sample in thermal
expansion conditions. The arrows show the direction and typical comparison of
thermal expansion rates for each of the layers and alloys. The overall expansion is a
result of the two individual rates and the physical structure and arrangement of the
layers.
Figure 5.13- Schematics of a wafer sample under thermal load
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Figure 5.14 - Schematics of an FGM sample
In the case of the FGM samples, the simplest approach to analyze the thermal
behavior of the samples is to treat the samples as a multilayer structure made of
layers with varying chemical composition hence varying thermal expansion
properties. The overall thermal expansion of the sample is logically the result of each
layer expanding at a different rate which decreases from one side to the other
between the first and last layers which are 100% single alloy layers. Figure 5.14 is a
schematic representation of this structure showing indicatively how the thermal
expansion rate changes from one side to the other.
Across all samples, FGMs show CTE values between those of each alloy on its own
with the exception of the FGM of 316SS and 420SS. This sample showed CTE
values below its constituting alloy elements and its wafer counterpart. As a future
work on these samples, SEM and hardness profiling need to be carried out to further
investigate their properties.
Functionally graded materials and wafer layered structures comprising of two
different metallic alloys possess different coefficient of thermal expansion (CTE)
values than that of each individual constituent alloy. In general, the CTE values
measured for the new structures are between those of each alloy individually, one
being lower and one being higher than the CTE values for the new structures.
However, this research has also revealed that, for some combinations, the structures
possess CTE close to the alloy with the lower CTE and occasionally lower than the
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CTE of each of the alloys. The main samples which showed significantly different
CTE values were the FGM sample of 316SS and 420SS, the wafer sample of AlBrnz
and 420SS and to some extent the FGM sample of 316SS and Tool Steel (H13).
These unique sets of structures provide potential for development of new materials
for engineering applications, which require lower CTE or even negative CTE
compared to the constituent alloys.
As a final note, in a DMD fabricated sample, there are internal stresses even before
being loaded by the thermal expansion test. The stresses introduced as a result of the
laser metal deposition itself are quantifiable through specialized techniques, which is
beyond the scope of this project. There can be several factors taken into
consideration to limit the range of alloys that can be combined together to create
FGM or Wafer structures one of which is the difference between their linear thermal
expansion rates. If such differences are too large, then physical deformations can be
expected under thermal loads which may lead to component failure. Design
engineers should consider such values and the differences between them when
selecting pairs of different alloys to form FGM or Wafer structures. Another point to
consider can be the fact that this research has worked on metal with metal
combinations; and dedicated work should be done on metal with composite and
metal with ceramic combinations to evaluate their potential for creating such
combinations and structures. Regardless of such limitations in alloy selection, such
novel structures i.e. FGM and Wafer can still offer unique properties as compared to
the single constituent alloys.
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Chapter 6 Evaluation of
Tensile Strength
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Chapter 6 - Evaluation of Tensile Strength
6.1 Introduction When it comes to high load situations within engineering applications of metallic
components, the tensile strength of materials attracts a great deal of attention.
Engineers of several industrial disciplines take this characteristic of materials into
serious consideration when selecting materials for applications where significant
variations of load or force are expected or higher than normal tensile strengths are
required but the change in structure and other aspects of the materials is restricted
and options are limited. Such applications include space vehicle components,
engines and aerospace engine components and pressure vessels. A correct selection
of materials in the design stage of a component ensures that it will not fail sooner
than expected once it is put in service.
In the case of tensile strength of metals, if a metallic component fractures earlier than
its design specifications, it can cause significant and in many cases irreversible
failures within the system in which it is used. Such failures can be associated with
fracture of the parts such as failure of bolts and other connection mechanisms,
leakage of fluids or gases that are contained within the overly stretched metallic
component, and many other forms and systems of failure which can be extremely
costly and undesirable.
Tensile tests are performed for several reasons. The results of tensile tests are used in
selecting materials for engineering applications. Tensile properties frequently are
included in material specifications to ensure quality. Tensile properties often are
measured during development of new materials and processes, so that different
materials and processes can be compared.
Moreover, tensile properties often are used to predict the behavior of a material
under different forms of loading other than uniaxial tension. The strength of a
material often is the primary concern. The strength of material may be measured in
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terms of either the stress necessary to cause appreciable plastic deformation or the
maximum stress that the material can withstand.
These measures of strength are used, with appropriate caution (in the form of safety
factors), in engineering design. Also of interest is the material’s ductility, which is a
measure of how much it can be deformed before it fractures. Rarely is ductility
incorporated directly in design; rather, it is included in material specifications to
ensure quality and toughness. Low ductility in a tensile test often is accompanied by
low resistance to fracture under other forms of loading. Elastic properties also may
be of interest, but special techniques must be used to measure these properties during
tensile testing, and more accurate measurements can be made by ultrasonic
techniques.
As a solution to the limitation of using existing metals and alloys in high load
applications due to their low tensile strength values, and in order to further widen the
choice of material selection for design engineers, further research is required at
looking at creating combined alloy structures with enhanced physical and
mechanical properties with a greater focus on the possibility of achieving an
increased tensile strength compared to each of the individual alloys that have formed
the new material/structure. This means that design engineers will have new options
at their disposal when faced with the selection of metallic alloys that are going to be
used in fabrication of a part or component, which will be exposed to extreme
variations of tensile loads once in service.
The tensile strength values and mechanical behaviour trends of majority of
engineering alloys are well known, but when it comes to combination of alloys in
terms of creating a chemically new alloy or a physical mixture of two or more alloys
using a structural design, the possibilities are endless and tensile strength values –
among other physical and mechanical properties - need to be measured and studied
for such new combinations. This chapter presents the tensile strength investigation
on Functionally Graded Materials and WAFER layer structures created by Laser
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assisted Direct Metal Deposition technique. A thorough introduction and literature
review on these structures can be found in the associated chapters of this thesis.
6.2 Tensile Testing
In order to do the tensile tests, dog bone shaped samples were wire cut from the
sample blocks machined after fabrication on the DMD process. Figure 6.1 shows the
shape and dimensions of the tensile test sample which is also known as dog bone
sample.
Figure 6.1 – Shape/dimensions of tensile test samples
Figure 6.2 shows a dog bone sample before tensile testing.
Figure 6.2 – A dog bone shaped tensile test sample
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FGM and Wafers are not isotropic structures. In the study of mechanical properties
of materials, isotropic i.e. having identical values of a property in all “directions”
whereas the FGM and Wafer structures are directional structures. The direction of
each layer deposited gives specific properties to the structures alongside the direction
of layers and a different set of properties can be expected when such structures are
tested directionally in across the layers. An example of such directional tests can be
tensile test. Such differences in properties can only be measured and evaluated only
by repeating all tests in both directions. Of course there are exceptions such as the
immersion corrosion test which is not directional.
A calibrated extensometer machine – Model 43 Criterion manufactured by MTS -
was used to carry out all tensile strength measurements. Table 6.1 contains some
technical data on this machine:
Table 6.1 – Criterion Model 43 Technical Specifications
Specification Maximum Rated Force Capacity Max. Test Speed
Min. Test Speed
Unit kN Lbf mm/min mm/min Value 50 11,000 750 0.005
The tensile tests were carried out according to the ASTM E8/E8M – 11 standard test
methods for tension testing of metallic materials. In our tensile strength
measurements, two pieces of each sample were tested as a measure of verifying the
results. The initial dimensions of all samples were measured accurately using a
calibrated vernier. These dimensions were width and thickness of the middle section
of the dog bone samples and the total length of all the samples. However, since the
samples were wire-cut with high accuracy, the initial width and thickness were
consistent among all samples i.e. 3mm wide and 2 mm thick.
The testing machine is fully automatic and computer controlled. However some
major parameters are entered by the operator, which were kept consistent for all
samples. These parameters are:
Load 25 kN Extension travel speed: 5mm/min Initial gage length 10 mm
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The test results are supplied by the computer in a tabular form comprising of three
sets of inter-related parameters, which are extension in µm, load in kN and time from
the start of the test. The extension and the load were then plotted as linear graphs of
extension-load combination.
7.3 Results and discussion
The results of all tensile tests were transformed into engineering stress (MPa) –
engineering strain graphs. Figures 6.3, 6.4, 6.5 and 6.6 show four major groups of
samples and their stress-strain graphs for comparison reasons. These four groups for
which both FGM and wafer structures were produced are: 316SS/420SS, EuTroLoy
16221/316SS, AlBrnz/420SS and 316SS/Tool Steel.
Figure 6.3 – Stress-Strain graphs for 316 SS & 420 SS
In figure 6.3, the stress-strain graphs for 316SS, 420SS, WAFER and FGM of these
two alloys are shown. As it can be seen, 316SS shows the highest ductility and
extension before fracture whereas 420SS sample shows a brittle fracture behavior
with the lowest amount of extension before fracture with respect to the other 3
samples. However the 316SS and 420SS wafer and FGM samples show distinctly
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higher ultimate tensile strength (UTS) values compared to the monolithic samples of
the same alloys. Among the 4 samples in this group, the FGM sample possesses the
highest UTS value i.e. 1100 MPa.
Table 6.2 shows the UTS and elongation values for all 15 samples.
Table 6.2 - Ultimate Tensile Strength (MPa) and Elongation (%) values for all samples
No Structure Type Alloy A Alloy B Ultimate Tensile Strength Mpa Elongation %
1 Monolithic 316 SS - 600 7.39
2 Monolithic AlBrnz - 660 2.03
3 Monolithic EuTroLoy 16221 - 1370 1.72
4 Monolithic Stellite 6 - 1250 0.5
5 Monolithic 420 SS - 882 1.84
6 Monolithic Tool Steel - 860 1.42
7 FGM 316 SS 420 SS 1100 3.10
8 FGM EuTroLoy 16221 316 SS 750 1.51
9 FGM AlBrnz 420 SS 750 1.62
10 FGM 316 SS Tool Steel 742 1.20
11 Wafer 316 SS Tool Steel 778 1.12
12 Wafer 316 SS 420 SS 1000 3.92
13 Wafer EuTroLoy 16221 316 SS 590 0.98
14 Wafer AlBrnz 420 SS 730 1.20
15 Wafer AlBrnz Stellite 6 762 0.86
A significantly unique result can been in items 7 and 12 in table 6.2 where the FGM
and Wafer samples of alloys 316 SS and 420 SS show tensile strengths higher than
that of each alloy individually. Alloy 316 SS has a tensile strength of 600 MPa and
alloy 420 has a tensile strength of 882 MPa whereas the FGM sample of these two
alloys shows tensile strength value of 1100 MPa and their Wafer structure
combination showed a tensile strength value of 1000 MPa. Alloy 420 SS is a hard
and brittle alloy as compared to the softer and more ductile 316 SS and it seems the
combination and presence of such properties in conjunction with each other in the
same sample has significantly contributed to the increased levels of tensile strength
in the FGM and Wafer samples of these two alloys.
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Figure 6.4 shows the tensile graphs for 420SS, AlBrnz and their FGM and wafer
samples. The elongation in these samples is the highest for the monolithic samples
with AlBrnz showing the highest ductility and the wafer sample showing the lowest
elongation among the four samples in this group.
The UTS values for the two new structures are between that of the two monolithic
samples with AlBrnz having the lowest UTS and 420SS the highest.
Figure 6.4 – Stress-Strain graphs for 420 SS & AlBrnz
Figure 6.5 shows the tensile strength graphs for 316SS and Tool Steel (H13) and
their FGM and wafer samples. The largest elongation at before failure belongs to
316SS and the lowest elongation is demonstrated by the wafer sample which is close
to that of FGM and monolithic H13 samples in order.
The UTS values for the two combined alloy structures are between the two
monolithic samples but closer to that of the tool steel (H13) one.
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Figure 6.5 – Stress-Strain graphs for 316SS & Tool Steel
The tensile test graphs for the last group of samples are shown in figure 6.6 which
belong to 316SS and EuTroLoy 16221 alloy and their FGM and wafer samples.
The ultimate tensile strength values for 316SS and the wafer sample of the two
alloys are close to each other at 600 MPa. The UTS value for the FGM sample is 750
MPa with EuTroLoy 16221 sample (also called Colmonoy) alone showing the
highest UTS value in this group i.e. 1370 MPa. The elongation of the samples is the
lowest for the wafer sample followed by the FGM and EuTroLoy 16221 samples and
of course the highest elongation is shown by the 316SS sample.
137
Figure 6.6 – Stress-Strain graphs for 316SS and EuTroLoy 16221
The Stress – Strain graph shown in Figure 6.7 contains all monolithic samples.
Figure 6.7 – Stress-Strain graphs for Monolithic samples
138
Figure 6.8 – Stress-Strain graphs for FGM samples
Figures 6.8 and 6.9 show Stress Vs Strain graphs for all the FGM and all the WAFER
samples. Such graphs are vital tools in material selection process when the ultimate tensile
strength of the selected materials is of significant importance.
Figure 6.9 – Stress-Strain graphs for WAFER samples
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Another aspect of the test results which is more qualitative than quantitative, were
the fracture surface profiles. These can be categorized into two sets of ductile and
brittle groups, especially for single alloy samples. However combination of alloys in
FGM and WAFER samples demonstrated distinctly different fracture surface
profiles than those of the single alloy samples. Figures 6.10 – 6.15 show six different
fracture surfaces. Figure 6.10 – 420SS sample – is the result of a brittle fracture
whereas Figure 6.11, the 316SS sample, shows a ductile – the most ductile amongst
all the samples of this work. And Figures 6.12 and 6.13 show the wafer and FGM
structure samples of 316SS and 420SS respectively, both of which demonstrate
mixed fracture profiles. The wafer and FGM samples of 420SS and Aluminium
Bronze alloys are shown in Figures 6.14 and 6.15 respectively. The mixed fracture
surface that was seen in the FGM and wafer samples of 316SS and 420SS can be
seen here in these two figures as well re-confirming the fact that FGM and wafer
structure inherit and maintain the mechanical properties of their constituent alloys to
some or full extent.
Figure 6.10 – Brittle fracture profile of 420SS sample Figure 6.11 – Ductile fracture profile of 316 SS sample
Figure 6.12 – Fracture profile of 316SS-420SS Wafer Figure 6.13- Fracture profile of 316SS-420SS FGM
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Figure 6.14 – Fracture profile of 420/AlBrnz wafer Figure 6.15 – Fracture profile of 420/AlBrnz FGM sample
A closer look at different regions of the wafer and FGM sample reveal the fact that
these structures behave like new materials while the wafer maintains the constituent
alloys properties in their respective layer whereas the FGM portrays a double sided
behavior i.e. more ductility in its side with higher 316SS alloy percentage and more
brittleness in its side with higher amounts of 420SS alloy.
Conclusion
This chapter has investigated the changes in the tensile strength in functionally
graded materials (FGM) and wafer layered structures produced by direct metal
deposition additive manufacturing process. Results show that functionally graded
materials and wafer layered structures comprising of two different metallic alloys
possess different tensile strength values and fracture mechanisms than that of each
individual constituent alloy. In general, the ultimate tensile strengths (UTS) values
measured for the new structures are between those of each alloy individually, one
being lower and one being higher than the UTS values for the new structures. At the
same time the elongation at fracture also is changed for the new structures. This
value is also lower than the more ductile alloy and higher than the less ductile alloy.
Results also reveal that while single alloy samples can be categorized into two sets of
ductile and brittle groups, the combination of alloys in FGM and Wafer samples
demonstrated distinctly different fracture surface profiles than those of the single
alloy samples.
141
Chapter 7 Evaluation of
Corrosion Performance
142
Chapter 7 - Evaluation of corrosion resistance
7.1 Introduction
Corrosion is defined as the gradual destruction of metals by chemical reaction with
their environment. It is basically the electrochemical oxidation of metals in reaction
with an oxidant such as oxygen. Corrosion can occur in materials other than metals
too, such as polymers or ceramics however instead of the term corrosion for non-
metals, degradation is more commonly used. Corrosion degrades the useful
properties of materials and structures including strength, appearance and
permeability to liquids and gases [148].
Many structural alloys corrode merely from exposure to moisture in air, but the
process can be strongly affected by exposure to certain substances. Corrosion can be
concentrated locally to form a pit or crack, or it can extend across a wide area more
or less uniformly corroding the surface. Because corrosion is a diffusion-controlled
process, it occurs on exposed surfaces. As a result, methods to reduce the activity of
the exposed surface, such as passivation and chromate conversion, can increase a
material's corrosion resistance. However, some corrosion mechanisms are less
visible and less predictable. Corrosion can pose serious problems to the safe and
economic operation of a wide variety of industrial installations. However, in order to
understand a corrosion problem or situation, it is important to be able to recognize
the type of problem one is dealing with [148]. The various types of corrosion are
listed here:
7.2 Types of Corrosion: Depending on the mechanism of corrosion and its effects, it can be categorized as
one of the following most common corrosion types [149]:
Uniform Corrosion Localized Corrosion Galvanic Corrosion Environmental Cracking Flow-Assisted Corrosion
Intergranular corrosion De-Alloying Fretting corrosion High-Temperature Corrosion
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When it comes to corrosion testing a structure with two different alloys used in it,
galvanic corrosion is more common than other types of corrosion as a minimum. In
this research work involving FGMs and Wafer structures with metals ranging from
corrosion resistant alloys like stainless steels to much less corrosion resistant alloys
such as Tool Steel, it is expected to witness some significant degree of galvanic
corrosion when placed in a suitable environment.
Galvanic corrosion is an electrochemical process in which one metal corrodes
preferentially to another when both metals are in electrical contact and immersed in
an electrolyte. Figure 7.1 is a schematics representation of a galvanic corrosion cell.
Figure 7.1 – A galvanic cell and its major components
Dissimilar metals and alloys have different electrode potentials and when two or
more come into contact in an electrolyte, a galvanic couple is set up, one metal is
acting as anode and the other as cathode. The potential difference between the
dissimilar metals is the driving force for the accelerated attack on the anode member
of the galvanic couple. The anode metal dissolves into the electrolyte, and deposition
is formed on the cathodic metal [148].
The electrolyte provides a means for ion migration whereby metallic ions can move
from the anode to the cathode. This leads to the anodic metal corroding more quickly
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than it otherwise would; the corrosion of the cathodic metal is retarded even to the
point of stopping. The presence of an electrolyte and an electronic conducting path
between the metals is essential for galvanic corrosion to occur.
In some cases, this reaction is intentionally encouraged. For example, low-cost
household batteries typically contain carbon-zinc cells. As part of a closed circuit
(the electron pathway), the zinc within the cell will corrode preferentially (the ion
pathway). Another example is the cathodic protection of buried or submerged
structures. In this example, sacrificial anodes work as part of a galvanic couple,
promoting corrosion of the anode, rather than the protected subject metal.
In other cases, such as mixed metals in piping (for example, copper and cast iron),
galvanic corrosion will contribute to accelerated corrosion of the system. Corrosion
inhibitors such as sodium nitrite or sodium molybdate can be introduced to these
systems to reduce the galvanic potential. Galvanic corrosion is of major interest to
the marine industry.
Metals can be arranged in a galvanic series representing the potential they develop in
a given electrolyte against a standard reference electrode. Figure 7.2 shows the
galvanic series for stagnant (that is, low oxygen content) seawater. The order may
change in different environments. The corrosion rate increases as the list goes down
ending to the actively corroding metal, Magnesium [150].
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Figure 7.2 – The galvanic series order for some engineering metals [150]
The galvanic series (or electropotential series) – shown in Figure 7.2 for some
engineering metals - determines the nobility of metals and semi-metals. When two
metals are submerged in an electrolyte, while electrically connected, the less noble
(base) will experience galvanic corrosion. The rate of corrosion is determined by the
electrolyte and the difference in nobility. The difference can be measured as a
difference in voltage potential. Galvanic reaction is the principle upon which
batteries are based. The relative position of two metals on such a series gives a good
indication of which metal is more likely to corrode more quickly. However, other
factors such as water aeration and flow rate can influence the process markedly.
There are several ways of reducing and preventing this form of corrosion. It is
suggested to choose metals that have similar potentials. The more closely matched
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the individual potentials, the lesser the potential difference and hence the lesser the
galvanic current. For example, consider a system that is composed of 316 SS (a 300
series stainless steel; it is a noble alloy meaning it is quite resistant to corrosion and
has a high potential) and a mild steel (an active metal with lower potential). The mild
steel will corrode in the presence of an electrolyte such as salt water. If a sacrificial
anode is used such as a zinc alloy, aluminium alloy, or magnesium, these anodes will
corrode, protecting the other metals. This is a common practice in the marine
industry to protect ship equipment. Boats and vessels that are in salt water use either
zinc alloy or aluminium alloy. If boats are only in fresh water, a magnesium alloy is
used. Magnesium has one of the highest galvanic potentials of any metal. If it is used
in a salt water application on a steel or aluminium hull boat, hydrogen bubbles will
form under the paint, causing blistering and peeling.
7.3 Methods of Corrosion Testing
Corrosion usually happens over a long period of time. In order to evaluate a
materials corrosion resistance, accelerated corrosion testing methods are employed.
In these methods, the factors and conditions which are responsible for the corrosion
mechanism are designed to be more aggressive than what they would be in real life
situations. This will in turn, increase the corrosion reaction rates and results are
obtained within hours or days as compared with months and years under normal
circumstances. Laboratory corrosion tests can be divided into four categories:
A. Electrochemical tests Electrochemical experimental methods are used to characterize the corrosion
properties of metals and metal components in combination with various electrolyte
solutions.
B. Salt fog/spray test The salt spray test is a standardized test method used to check corrosion resistance of
coated samples.
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In a previous research work titled: Surface recrystallization of ZE41 to enhance its
corrosion behaviour: Application of LASER surface modification and Friction Stir
surface modification on Magnesium alloy ZE41, Soodi [151] has investigated the
effect of laser surface remelting on the corrosion resistance of metallic alloys. In
their research, both electrochemical corrosion tests and salt spray corrosion tests
were successfully used to determine the corrosion behaviour of ZE41.
C. High-pressure/high-temperature tests HP and HTHP corrosion tests are commonly used to evaluate the corrosion
performance of metallic materials under conditions that attempt to simulate service
conditions that involve HP or HTHP in combination with service environments.
D. Immersion test Immersion testing is the most frequently conducted test for evaluating the corrosion
of metals in aqueous solutions. The test involves immersion of test specimens in a
corrosive solution for a period of time and then removal and examination of the
specimens. However, a number of factors must be considered to achieve specific
goals and to ensure adequate reproducibility of test results. Primary consensus
standard for immersion corrosion testing of metals have been developed by ASTM
International which is ASTM G31 - 72(2004) Standard Practice for Laboratory
Immersion Corrosion Testing of Metals. For proper planning of the test and
interpretation of the test results, the specific influences of the following variables
must be considered: solution composition, temperature, aeration, volume, velocity,
and waterline effects; specimen surface preparation; method of immersion of
specimens; duration of test; and method of cleaning specimens at the conclusion of
the exposure. In most cases, immersion tests are conducted to determine the
corrosion rates of metals in a given environment. However, by employing
specifically designed specimens and/or environments, immersion tests can also be
conducted to evaluate the resistance of the metal to pitting, crevice corrosion,
galvanic corrosion, hydrogen embrittlement, erosion, and stress-corrosion cracking.
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Other methods have been developed as well to measure corrosion resistance of
metals especially novel structures like FGMs. Tomo Saitoh et al [152] developed
electrochemical sensors to evaluate corrosion resistance in FGMs with success.
Since most metals suffer some sort of corrosion when exposed to a corrosive
environment, it is vital to assess the corrosion resistance of every new metallic
compound alloy or structure developed. FGMs and wafers are no exception to this
rule and since they are new structures, performing corrosion tests will help
understand their potential applications better.
There have been several research works done on the corrosion aspects of FGM
materials. Kazuhiko Noda et al [153] investigated the effect of intermetallic particles
on corrosion resistance of Al‐Al3Ni and Al‐Al2Cu FGMs which have been
fabricated through a centrifugal method. In their research, they used electrochemical
corrosion testing method to assess the corrosion behaviour of the FGM samples.
They report that the presence of Al2Cu exerted a larger effect on the corrosion
behavior of the FGMs than Al3Ni [153]. A similar work was done by Ferreira et al
[154] where they studied the effect of intermetallic volume fraction on the corrosion
behaviour of Al/Al3Ti and Al/Al3Zr functionally graded materials produced by
centrifugal solid-particle method. They report that corrosion behaviour can be
improved in these FGMs if the right intermetallic volume fraction is achieved.
FGMs are also widely used as protective coatings. Marina Malinina et al [155]
studied homogeneous and FGM environmental barrier coatings made of alumina –
NiCr deposited on steel substrates by high-velocity oxygen fuel (HVOF) spraying
technique. They characterized these coatings by DC polarization measurements and
by electrochemical impedance spectroscopy (EIS) after various exposure times in
highly aggressive basic solutions at room temperature. They also tested the corrosion
resistance of this coating in respect to sulfide – sulfate – chloride – carbonate melts
in air, which simulates environments in incinerators, kraft recovery boilers and
turbines at high temperatures (400-750°C). SEM and EDS were used to assess the
corrosion resistance of these FGM coatings.
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7.4 Immersion Corrosion Testing
In this research work, tests were done according to ASTM G31 - 72(2004) Standard
Practice for Laboratory Immersion Corrosion Testing of Metals. As the first step, all
samples were cleaned using methanol and compressed air to remove all possible
surface contamination that would affect the corrosion rate. Then each sample was
carefully weighed using a calibrated laboratory scale. The test containers were
marked using the sample names for correct traceability purposes during and after
test. All containers were also cleaned using methanol and compressed air to remove
all possible contaminations.
All containers were filled with the corrosive solution. The range of different alloys in
the test meant that some of the alloys would show extremely high corrosion
resistance behaviour to corrosive solutions that would corrode the other alloys in the
experiment rapidly. In order to ensure all samples would corrode in the test, two sets
of corrosion tests were performed each time with a different corrosive solution.
The solutions were 33% HCl and 49% H2SO4. These were selected based on the fact
that between them, all samples would certainly show some level of corrosion within
the time allocated for this test, which was around 18 hours. The solutions used across
the samples were all made in the same batch and the concentration was kept the
same for all containers. There is no specific reason why such concentrations of these
solutions were used. These are close to average concentration diluted with water to
ensure safety when working with them, avoiding rapid and aggressive corrosion and
therefore total degradation of samples, and achieving some levels of mass loss at the
conclusion of the test period.
All samples were placed in their designated containers at the same time. The room
temperature was maintained at 22 °C at all times using an air-conditioning unit. The
lids of the containers were closed during the tests.
As a corrosion rate measurement technique, all the test samples were weighed prior
and after immersion in the relevant corrosive solution. This would eventually
provide the quantity of mass lost as a result of the corrosion process. All samples
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were immersed in individual containers at the same time and in the same room so the
environment temperature was the same for all samples.
Figure 7.3 shows the set up for the tests.
Figure 7.3 – Corrosion test (Material loss) test set up
All safety aspects of the test were observed as well. The Material Safety Data Sheet
for the acids and the standard recommendations were used as basis for safety
measures.
Proper personal protective equipment (PPE) was also used. These were facial mask,
corrosion resistant gloves, and proper containers to fill the test boxes with the acid
and to put the test samples in and remove them from the solutions.
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7.5 Results and Discussion
Upon conclusion of the immersion corrosion test, all samples were safely removed
from the containers, dried and weighed using a calibrated digital scale that was also
used to weigh the samples prior to the test.
Figure 7.4 shows a EuTroLoy 16221 sample only 10 minutes after immersion in HCl
solution.
Figure 7.4 – Aggressively corroding EuTroLoy 16221 sample
Figure 7.5 shows a H13 tool steel sample in HCl solution. In this test it is the mass
loss value that determines the corrosion resistance of the metallic samples.
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Figure 7.5 – Moderately corroding Tool Steel (H13) sample And of course some samples showed no sign of corrosion even after 18 hours. Figure
7.6 shows an AlBrnz sample in the H2SO4 solution after 18 hours with no evident
sign of corrosion activity.
Figure 7.6 – An AlBrnz sample in H2SO4 acid
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After 18 hours, the samples were removed from the containers, washed properly and
dried and weight.
Table 7.1 shows the data acquired through weighing the samples before and after the
corrosion test.
Table 7.1 –Corrosion test samples and the acids used and the mass loss amounts (Run # 1)
No Sample weight grams Acid
2nd Weight measurement after
18 hours Material Loss
Mass loss rate in mpy
1 AlBrnz - Stellite 6 WAFER 5.319 49% H2SO4 5.316 0.003 1,460.00 2 316 DMD 4.782 33% HCl 4.776 0.006 2,920.00 3 Stellite 6 DMD 2.589 33% HCl 2.580 0.009 4,380.00 4 AlBrnz DMD 4.370 49% H2SO4 4.360 0.010 4,866.67 5 Colmonoy - 316 FGM 5.413 33% HCl 5.400 0.013 6,326.67 6 Colmonoy - 316 WAFER 5.339 33% HCl 5.320 0.019 9,246.67 7 316 - Tool Steel FGM 8.829 33% HCl 8.800 0.029 14,113.33 8 420 DMD 3.281 33% HCl 3.250 0.031 15,086.67 9 316 - 420 WAFER 5.084 33% HCl 5.050 0.034 16,546.67
10 316 - 420 FGM 5.150 33% HCl 5.110 0.040 19,466.67 11 420 - AlBrnz WAFER 5.060 49% H2SO4 4.920 0.140 68,133.33 12 AlBrnz - 420 FGM 5.060 49% H2SO4 4.860 0.200 97,333.33 13 316 - Tool Steel WAFER 8.721 33% HCl 8.470 0.251 122,153.33 14 Tool Steel DMD 3.668 33% HCl 3.300 0.368 179,093.33 15 Colmonoy DMD 3.428 33% HCl 2.740 0.688 334,826.67
Equation 7.1 was used to calculate the material loss per year values (mpy) which is
the common value in measuring the results of this type of corrosion tests:
𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑙𝑜𝑠𝑠 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟 =𝐾 (𝑀𝑖−𝑀𝑓)
𝑇𝑖 (7.1)
Where K is a constant which converts the unit to the appropriate material loss per
year when weight loss is measured in grams and time is measured in hours. The
value of K is calculated through 1000 X 365 X 24 equalling: 8,760,000 hours
Mi is initial weight of samples in grams (before immersion)
Mf is final weight of samples in grams (after immersion and cleaning)
Ti is immersion time in hours
The unit for the results is mpy i.e. milligrams per year.
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Figure 7.7 – Mass loss graph for all samples in the 1st run of immersion tests
Figure 7.7 shows mass loss values for all samples in the 1st run of immersion tests.
The monolithic sample of Colmonoy alloys shows the highest amount of mass loss
whereas the WAFER sample of AlBrnz – Stellite 6 shows the lowest amount of mass
loss. Tool Steel monolithic sample, the WAFER sample of 316SS- Tool Steel and
the FGM sample of AlBrnz-420SS and the WAFER sample of AlBrnz-420SS show
significantly higher mass loss values compared to the rest of the samples.
In samples where there is a corrosion resistant alloy such as AlBrnz or 316SS
coupled with a low corrosion resistant alloy in a WAFER or FGM structure, the high
mass loss values are the result of galvanic corrosion. Such combinations of materials
in bi-alloy structures are not suitable where there is a corrosive medium present.
In order to test the combined alloy structure samples with both HCl and H2SO4 acids,
a 2nd series of tests had to be done. Table 3 shows the data acquired from this series
of tests. As can be seen the acids used for alloys in the 1st run were interchanged to
get more accurate data on samples that contained two different alloys i.e. FGMs and
Wafers. Alloys behave differently when exposed to different acids so when a sample
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is made of two different alloys which may react passively or actively to HCl or
H2SO4, the best method of analysing the corrosion behaviour of such bi-alloy
structures is to study their corrosion behaviour when exposed to both acids in
separate tests.
Equation (7.1) was used for the 2nd series of tests to calculate the mpy values.
However the dividing factor was changed to 24 as the 2nd test was longer than the 1st
set of tests. The 2nd run was done using fresh untested samples.
Table 7.2 contains the data acquired from the 2nd series of tests.
Table 7.2 –Corrosion test samples and the acids used and the mass loss amounts (Run # 2)
No Sample Initial weight grams
Acid 2nd Weight
measurement 24 hours
Material Loss grams
Mass loss rate in mpy
1 316 DMD 1.6300 49% H2SO4 1.6290 0.0010 365.00
2 AlBrnz - Stellite 6 WAFER 2.3700 49% H2SO4 2.3690 0.0010 365.00
3 420 DMD 2.4500 49% H2SO4 2.4480 0.0020 730.00
4 AlBrnz DMD 2.2300 49% H2SO4 2.2260 0.0040 1460.00
5 EuTroLoy 16221- 316 FGM 2.4200 33% HCl 2.4100 0.0100 3650.00
6 EuTroLoy 16221- 316 WAFER 2.4300 33% HCl 2.4200 0.0100 3650.00
7 Stellite 6 DMD 2.5800 49% H2SO4 2.5700 0.0100 3650.00
8 316 - 420 FGM 2.3600 33% HCl 2.3400 0.0200 7300.00
9 316 - 420 WAFER 2.3900 33% HCl 2.3700 0.0200 7300.00
10 AlBrnz - 420 FGM 2.2700 49% H2SO4 2.2300 0.0400 14600.00
11 316 - Tool Steel FGM 4.0900 33% HCl 4.0100 0.0800 29200.00
12 Tool Steel DMD 2.4600 49% H2SO4 2.3500 0.1100 40150.00
13 316 - Tool Steel WAFER 4.0800 33% HCl 3.9600 0.1200 43800.00
14 420 - AlBrnz WAFER 2.2900 49% H2SO4 2.1600 0.1300 47450.00
15 EuTroLoy 16221DMD 2.3100 49% H2SO4 1.5200 0.7900 288350.00
Figure 7.8 shows mass loss values for all samples in the 2nd run of immersion tests.
Colmonoy again shows the remarkably highest mass loss values with Tool Steel
monolithic sample, WAFER sample of 420SS-AlBrnz, and WAFER sample of
316SS-Tool Steel following with higher mass loss values than other samples.
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Figure 7.8 – Mass loss graph for all samples in the 2nd run of immersion tests
Figure 7.9 shows a sample in the 2nd series of tests. This sample is the Colmonoy
also known as EuTroLoy 16221, which is immersed in H2SO4 acid.
Figure 7.9 – 2nd run sample EuTroLoy 16221 dog bone
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Figure 7.10 shows an FGM AlBrnz-420SS sample after test – washed and dried.
Figure 7.10 – AlBrz-420SS dog bone sample (FGM) (2nd run)
When the data acquired from the tests were transformed into graphs and the results
were compared it was seen that the corrosion behaviour of FGM and wafer samples
was significantly different for most individual alloys.
Figure 7.11 shows the mass loss values for 420SS and 316SS and their FGM and
Wafer samples all measured in HCl acid.
Figure 7.11 – Mass loss measurements for 316 & 420 SS
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In the case of 316SS and 420SS combined structures i.e. FGM and wafer, the
corrosion performance is similar for both and the material loss for the monolithic
316SS is less than that of both combined structures and of course of the less passive
420SS alloy.
Figure 7.12 – Mass loss graph for 420SS & AlBrnz
As shown in Figure 7.12, in the case of AlBrnz and 420SS alloy combined
structures, the mass loss has increased significantly for both FGM and wafer
structure samples compared with monolithic 420SS and AlBrnz samples, which are
passive but with different electro-potential values. Such behaviour is the result of
galvanic corrosion between the two alloys. This galvanic corrosion effect is more
apparent in the wafer sample as in this sample structure, there are multiple layers of
each of the two alloys, which create multiple galvanic cells in the presence of the
conductive solution – in this case the acids. The FGM sample does not have these
interchanging layers of each of the alloys and instead the alloying composition
changes gradually from one end being one of the alloys i.e. 420SS to the other side
of the sample which is 100% of the other alloy i.e. AlBrnz. This at best only creates
one single galvanic cell, which is not as strong as two pure layers of each of these
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alloys as is the case in the Wafer sample. Therefore we see a higher corrosion
activity rate in the Wafer sample compared to the FGM sample.
Figure 7.13 shows corrosion test data for 316SS and Tool Steel (H13) alloys and
their combined structures i.e. FGM and Wafer.
Figure 7.13 – Mass Loss graph for 316SS & H13 alloys
The graph shows that the 316SS – as expected – has little mass loss when exposed to
the corrosive solution whereas the H13 Tool steel shows a significantly higher
amount of mass loss in the same solution and for the same period of time.
When it comes to the FGM sample, the corrosion rate is about 4.5 times that of the
316SS sample but only 7.8% of the corrosion rate for H13 Tool steel. This can be
interpreted as remarkable reduction of corrosion rate of H13 Tool steel with the
assistance of 316SS in such a structure as FGM. The increased corrosion resistance
of the Wafer structure however is the result of creation of multiple galvanic cells
when combining these two distinctly different alloys in terms of their
electronegativity. Hence such a combination is not recommended for applications
where a conductive or corrosive environment is present and such a structure is
exposed to it.
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Considering the relatively high cost of 316 SS alloy compared to H13 Tool steel or
other iron based alloys which are prone to corrosion, 316SS can be used in smaller
quantities to form structure in the FGM format with these alloys that may offer other
physical or mechanical advantages that 316SS lacks – such as high hardness – to
produce desirable parts with low corrosion resistance but not at the expense of pure
316SS alone.
Figure 7.14 shows mass loss data on 316SS and Colmonoy and their combined
structures in both HCl and H2SO4 acids. It is evident that when combined with
316SS alloy, Colmonoy shows improved corrosion resistance characteristics whereas
by itself it corrodes at high rates in both acids.
Figure 7.14 – Mass Loss graph for 316SS and Colmonoy alloys
As expected 316SS shows little corrosion in H2SO4 to which it is considered passive.
However HCl creates a mass loss in the 316SS and what is important is that 316SS
lowers the corrosion rate in both FGM and Wafer combined alloy structures
significantly. On its own, Colmonoy corroded rapidly in both acidic solutions i.e.
HCl and H2SO4.
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All monolithic samples were tested individually as well in HCl except for AlBrnz
sample that showed no sign of corrosion in HCl and therefore was tested in H2SO4
for the same period of time.
Figure 7.15 shows the mass loss rates for this series of corrosion tests on monolithic
DMD samples.
Figure 7.15 – Mass loss graph for monolithic samples
Colmonoy presents itself as the least corrosion resistance alloy in this group with
H13 Tool steel following it with almost 50% its corrosion rate. With a significant
drop in mass loss rates, 420SS is the 3rd in the group with AlBrnz and Stellite 6
alloys in the next position in the mass loss graph. As expected 316SS is the most
passive alloy in this group.
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7.6 Conclusion
Functionally graded materials and wafer layered structures comprising of two
different metallic alloys possess different corrosion resistance values than that of
each individual constituent alloy. In general, the mass loss per year values measured
for the new structures are between those of each alloy individually, one being lower
and one being higher than the mass loss values for the new structures when the two
alloys have similar or close electro-potentials i.e. similar corrosion resistance rates.
However, when the two constituent alloys have significantly different electro-
potentials such as AlBrnz and 420SS, the FGM and wafer structures act as a galvanic
cell and demonstrate accelerated corrosion rates and higher mass loss values. If a
combination of the 2nd group is to be used, then special care must be taken to avoid
creating a galvanic cell by eliminating a suitable electrochemically conductive
environment containing the two metals.
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Chapter 8 Conclusion
& Future Directions
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Chapter 8 - Conclusion & Future work
8.1 Introduction
The main objective of this research was to produce new metallic structures with
superior and novel physical and mechanical characteristics which cannot be found in
existing single alloys or structures.
Two novel structures were created from a series of metallic alloys. These were
Functionally Graded Materials (FGMs) and wafer-layered 3D structures. The
technique used was laser direct metal deposition (DMD) as the most ideal additive
manufacturing technology to fabricate such structures. The project then aimed to
further understand and analyse such structures and create a base for further alloys to
be used in these two structures to achieve more novel combinations and results. The
structures were studied from both physical and mechanical properties perspective
and new findings were revealed as the result of a series of tests. These were linear
thermal expansion, tensile, corrosion and micro-hardness tests.
8.2 Major Conclusions
8.2.1 Thermal expansion properties
One aspect of the investigation was to determine if any of these structures could
offer Negative Thermal Expansion (NTE). Research literature review has shown that
NTE may be achievable through various scientific approaches in materials with
positive thermal expansion. However, more non-metallic NTE materials have been
developed compared to metallic materials. It was also found that a structural
approach to create NTE metallic material has proved to be successful. However none
of the two structures (FGM and Wafer) and the alloys used in this work showed an
NTE value.
Linear thermal expansion tests were done on the structures and it was found that
some combinations of metallic alloys in either of these two 3D forms, i.e. FGM or
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wafer, possess superior thermal expansion properties compared to their constituent
alloys on their own. Functionally graded materials and wafer layered structures
comprising of two different metallic alloys possess different coefficient of thermal
expansion (CTE) values than that of each individual constituent alloy. In general,
the CTE values measured for the new structures are between those of each alloy
individually, one being lower and one being higher than the CTE values for the new
structures.
However, this research has also revealed that, for some combinations, the structures
possess CTE close to the alloy with the lower CTE and occasionally lower than the
CTE of each of the alloys. The main samples which showed significantly different
CTE values were the FGM sample of 316SS and 420SS, the wafer sample of AlBrnz
and 420SS and to some extent the FGM sample of 316SS and Tool Steel (H13).
These unique sets of structures provide potential for development of new materials
for engineering applications, which require lower CTE or even negative CTE
compared to the constituent alloys.
8.2.2 Micro-hardness measurements
Results of microhardness profiles of FGM and wafer structures on the two alloys and
on the bond interface of wafer or the middle interface of FGM between two layers
have shown a consistency in the changing trend of microhardness values throughout
the samples as the portion of each constituent alloy changed. This smooth and
regular decline and increase throughout the bond interfaces is a confirmation that the
level of dilution on one alloy into the other is not adversely affecting the physical
properties of the wafer alloys.
8.2.3 Tensile Strength
Based on the test results, these structures possess different tensile strength values and
fracture mechanisms than that of each individual constituent alloy. In general, the
ultimate tensile strengths (UTS) values measured for the new structures are between
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those of each alloy individually, one being lower and one being higher than the UTS
values for the new structures. At the same time the elongation at fracture also is
changed for the new structures. This value is also set lower than the more ductile
alloy and higher than the less ductile alloy. Amongst all the four FGM and five wafer
samples, the FGM sample of 316 SS and 420 SS showed the highest Ultimate
Tensile Strength followed by the same combination of alloys in their wafer structure.
8.2.4 Immersion Corrosion Tests
FGMs and wafer layered structures comprising of two different metallic alloys
possess different corrosion resistance values than that of each individual constituent
alloy.
In general, the mass loss per year values measured for the new structures are
between those of each alloy individually, one being lower and one being higher than
the mass loss values for the new structures when the two alloys have similar or close
electro-potentials i.e. similar corrosion resistance rates.
However, when the two constituent alloys have significantly different electro-
potentials such as AlBrnz and 420SS, the FGM and wafer structures act as a galvanic
cell and demonstrate accelerated corrosion rates and higher mass loss values. If a
combination of such a selection of two alloys is to be used in a design, then it is
recommended that special care be taken to avoid creating a galvanic cell by
eliminating any suitable electrochemically conductive environment in contact with
the two metals.
It should be noted that when creating laser assisted DMD samples for future work,
significant attention must be paid to minimising the dilution rates by fine tuning
process parameters. By minimising such significant levels of dilution to little rates
such as 1% - 3% – which might be a challenge – the results of physical and
mechanical tests may be more predictable.
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8.3 Future work
There is great potential for FGM and wafer structures created by Laser assisted
Direct Metal Deposition in a range of industries and scientific fields. More work can
be done to further understand other characteristics of such unique and novel
structures and pave the way to apply them in engineering designs. It can also be
expected that by varying manufacturing parameters one would achieve different –
however small – results. But more important than trying to achieve different results,
the focus should be on ensuring consistency of the products specifications and
sustainability in achieving such consistency. Layer thickness, deposited track pattern,
dilution levels and solidification rates are some of the aspects of the manufacturing
process one needs to pay due attention to.
As future work on this field, the followings are suggested:
More alloys can be selected for these two structures
A more precise mathematical model can be developed to explain the
characteristics of each of these two structures
The DMD parameters can be fine-tuned to decrease the levels of dilution
between consecutive layers
Other shapes i.e. cylindrical, conical and spherical can be made for both these
two structures and tested
Other physical and mechanical tests such as wear test, compression test and
dynamic behaviour can be done on the samples of this project to further
investigate their properties
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Appendices
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Appendix A:
Industrial Laser Systems
A.1 Introduction
Industrial laser systems can be defined as high power laser systems used for
materials processing within the industrial and/or research applications fields. Other
laser systems with much lower power ranges can be used in medical,
telecommunications and vision systems.
There are three main types of laser systems based on the way they create the laser
beam. These are:
1. Carbon Dioxide (CO2) lasers
2. Neodymium: Yttrium-Aluminium-Garnet (Nd:YAG) layers
3. Diode and diode pumped Nd:YAG lasers
4. Fibre lasers
The laser system types mentioned above are all being currently used by both the
industry and research organisations to produce laser beams at the range of 100 W to
8 kW for materials processing.
A brief description of each type of laser system will follow.
A.2 Carbon Dioxide (CO2) lasers
The carbon dioxide laser (CO2 laser) was one of the earliest gas lasers to be
developed (invented by Kumar Patel of Bell Labs in 1964[113]), and is still one of
the most useful. Carbon dioxide lasers are the highest-power continuous wave lasers
that are currently available. They are also quite efficient: the ratio of output power to
pump power can be as large as 20%.
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Figure A.1 - Schematics of a CO2 laser system Image by: Jon Caywood source: www.jonslasers.com/
The CO2 laser produces a beam of infrared light with the principal wavelength bands
centring around 9.4 and 10.6 micrometres.
The active laser medium (laser gain/amplification medium) is a gas discharge which
is air-cooled (water-cooled in higher power applications).
Figure A.1 is a schematic representation of a typical CO2 laser system. The filling
gas within the discharge tube consists primarily of:
Carbon dioxide (CO2) (around 10–20%)
Nitrogen (N2) (around 10–20%)
Hydrogen (H2) and/or xenon (Xe) (a few precents; usually only used in a
sealed tube.)
Helium (He) (The remainder of the gas mixture)
The specific proportions vary according to the particular laser.
The population inversion in the laser is achieved by the following sequence:
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1. Electron impact excites vibrational motion of the nitrogen. Because nitrogen is a
homonuclear molecule, it cannot lose this energy by photon emission, and its excited
vibrational levels are therefore metastable and live for a long time.
2. Collisional energy transfer between the nitrogen and the carbon dioxide molecule
causes vibrational excitation of the carbon dioxide, with sufficient efficiency to lead
to the desired population inversion necessary for laser operation.
3. The nitrogen molecules are left in a lower excited state. Their transition to ground
state takes place by collision with cold helium atoms. The resulting hot helium atoms
must be cooled in order to sustain the ability to produce a population inversion in the
carbon dioxide molecules. In sealed lasers, this takes place as the helium atoms
strike the walls of the container. In flow-through lasers, a continuous stream of CO2
and nitrogen is excited by the plasma discharge and the hot gas mixture is exhausted
from the resonator by pumps.
Because CO2 lasers operate in the infrared, special materials are necessary for their
construction. Typically, the mirrors are silvered, while windows and lenses are made
of either germanium or zinc selenide. For high power applications, gold mirrors and
zinc selenide windows and lenses are preferred. There are also diamond windows
and even lenses in use. Diamond windows are extremely expensive, but their high
thermal conductivity and hardness make them useful in high-power applications and
in dirty environments. Optical elements made of diamond can even be sand blasted
without losing their optical properties. Historically, lenses and windows were made
out of salt (either sodium chloride or potassium chloride). While the material was
inexpensive, the lenses and windows degraded slowly with exposure to atmospheric
moisture.
The most basic form of a CO2 laser consists of a gas discharge (with a mix close to
that specified above) with a total reflector at one end, and an output coupler (usually
a semi-reflective coated zinc selenide mirror) at the output end. The reflectivity of
the output coupler is typically around 5–15%. The laser output may also be edge-
coupled in higher power systems to reduce optical heating problems.
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The CO2 laser can be constructed to have CW powers between milliwatts (mW) and
hundreds of kilowatts (kW). It is also easy to actively Q-switch a CO2 laser by
means of a rotating mirror or an electro-optic switch, giving rise to Q-switched peak
powers up to gigawatts (GW) of peak power.
Because the laser transitions are actually on vibration-rotation bands of a linear
triatomic molecule, the rotational structure of the P and R bands can be selected by a
tuning element in the laser cavity. Because transmissive materials in the infrared are
rather lossy, the frequency tuning element is almost always a diffraction grating. By
rotating the diffraction grating, a particular rotational line of the vibrational transition
can be selected. The finest frequency selection may also be obtained through the use
of an etalon. In practice, together with isotopic substitution, this means that a
continuous comb of frequencies separated by around 1 cm−1 (30 GHz) can be used
that extend from 880 to 1090 cm−1. Such "line-tuneable" carbon dioxide lasers are
principally of interest in research applications.
Because of the high power levels available (combined with reasonable cost for the
laser), CO2 lasers are frequently used in industrial applications for cutting and
welding, while lower power level lasers are used for engraving [114]. They are also
very useful in surgical procedures because water (which makes up most biological
tissue) absorbs this frequency of light very well. Some examples of medical uses are
laser surgery, skin resurfacing ("laser facelifts") (which essentially consist of burning
the skin to promote collagen formation), and dermabrasion. Also, it could be used to
treat certain skin conditions such as hirsuties papillaris genitalis by removing
embarrassing or annoying bumps and podules. Researchers in Israel are
experimenting with using CO2 lasers to weld human tissue, as an alternative to
traditional sutures.
The common plastic poly (methyl methacrylate) (PMMA) absorbs IR light in the
2.8–25 µm wavelength band, so CO2 lasers have been used in recent years for
fabricating microfluidic devices from it, with channel widths of a few hundred
micrometers.
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Because the atmosphere is quite transparent to infrared light, CO2 lasers are also
used for military range-finding using LIDAR techniques.
A.3 Neodymium: Yttrium-Aluminium-Garnet (Nd:YAG) layers
Nd:YAG (neodymium-doped yttrium aluminium garnet; Nd:Y3Al5O12) is a crystal
that is used as a lasing medium for solid-state lasers. The dopant, triply ionized
neodymium, Nd(III), typically replaces a small fraction of the yttrium ions in the
host crystal structure of the yttrium aluminium garnet (YAG), since the two ions are
of similar size. It is the neodymium ion which proves the lasing activity in the
crystal, in the same fashion as red chromium ion in ruby lasers. Generally the
crystalline YAG host is doped with around 1% neodymium by atomic percent [115].
Laser operation of Nd:YAG was first demonstrated by J. E. Geusic et al. at Bell
Laboratories in 1964.[116]
FigureA.2 – Schematics of an Nd: YAG laser system Source: www.mrl.columbia.edu
Nd:YAG lasers are optically pumped using a flashtube or laser diodes – See figure
A.2 for a schematic of this type of laser. These are one of the most common types of
laser, and are used for many different applications. Nd:YAG lasers typically emit
light with a wavelength of 1064 nm, in the infrared[117]. However, there are also
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transitions near 940, 1120, 1320, and 1440 nm. Nd:YAG lasers operate in both
pulsed and continuous mode. Pulsed Nd:YAG lasers are typically operated in the so
called Q-switching mode: An optical switch is inserted in the laser cavity waiting for
a maximum population inversion in the neodymium ions before it opens. Then the
light wave can run through the cavity, depopulating the excited laser medium at
maximum population inversion. In this Q-switched mode, output powers of 250
megawatts and pulse durations of 10 to 25 nanoseconds have been achieved [118].
The high-intensity pulses may be efficiently frequency doubled to generate laser
light at 532 nm, or higher harmonics at 355 and 266 nm.
Nd:YAG absorbs mostly in the bands between 730–760 nm and 790–820 nm[117].
At low current densities krypton flashlamps have higher output in those bands than
do the more common xenon lamps, which produce more light at around 900 nm. The
former are therefore more efficient for pumping Nd:YAG lasers [119]. Figure 11.3
shows an Nd:YAG pumping cell.
Figure A.3 - A Nd:YAG laser pumping chamber schematic source: www.phy.davidson.edu
The amount of the neodymium dopant in the material varies according to its use. For
continuous wave output, the doping is significantly lower than for pulsed lasers. The
lightly doped CW rods can be optically distinguished by being less coloured, almost
white, while higher-doped rods are pink-purplish.
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Other common host materials for neodymium are: YLF (yttrium lithium fluoride,
1047 and 1053 nm), YVO4 (yttrium orthovanadate, 1064 nm), and glass. A
particular host material is chosen in order to obtain a desired combination of optical,
mechanical, and thermal properties. Nd:YAG lasers and variants are pumped either
by flashtubes, continuous gas discharge lamps, or near-infrared laser diodes (DPSS
lasers). Prestabilized laser (PSL) types of Nd:YAG lasers have proved to be
particularly useful in providing the main beams for gravitational wave
interferometers such as LIGO, VIRGO, GEO600 and TAMA.
Nd:YAG lasers are used in ophthalmology to correct posterior capsular
opacification, a condition that may occur after cataract surgery, and for peripheral
iridotomy in patients with acute angle-closure glaucoma, where it has superseded
surgical iridectomy. Frequency-doubled Nd:YAG lasers (wavelength 532 nm) are
used for pan-retinal photocoagulation in patients with diabetic retinopathy.
Nd:YAG lasers emitting light at 1064 nm have been the most widely used laser for
laser-induced thermotherapy, in which benign or malignant lesions in various organs
are ablated by the beam.
In oncology, Nd:YAG lasers can be used to remove skin cancers [120]. They are
also used to reduce benign thyroid nodules [121], and to destroy primary and
secondary malignant liver lesions [122-123].
To treat benign prostatic hyperplasia (BPH), Nd:YAG lasers can be used for laser
prostate surgery—a form of transurethral resection of the prostate.
These lasers are also used extensively in the field of cosmetic medicine for laser hair
removal and the treatment of minor vascular defects such as spider veins on the face
and legs. Recently used for dissecting cellulitis, a rare skin disease usually occurring
on the scalp.
Using hysteroscopy the Nd:YAG laser has been used for removal of uterine septa
within the inside of the uterus [124].
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In podiatry, the Nd:YAG laser is being used to treat onychomycosis, which is fungus
infection of the toenail. The merits of laser treatment of these infections are not yet
clear, and research is being done to establish effectiveness [125-126].
Nd:YAG lasers are also used in manufacturing for engraving, etching, or marking a
variety of metals and plastics. They are extensively used in manufacturing for cutting
and welding steel, semiconductors and various alloys. For automotive applications
(cutting and welding steel) the power levels are typically 1–5 kW. Super alloy
drilling (for gas turbine parts) typically uses pulsed Nd:YAG lasers (millisecond
pulses, not Q-switched). Nd:YAG lasers are also employed to make subsurface
markings in transparent materials such as glass or acrylic glass. Lasers of up to 400
W are used for selective laser melting of metals in additive layered manufacturing. In
aerospace applications, they can be used to drill cooling holes for enhanced air
flow/heat exhaust efficiency.
Nd:YAG lasers can also be used for flow visualization techniques in fluid dynamics
(for example particle image velocimetry or laser induced fluorescence) [127].
Nd:YAG lasers are used for soft tissue surgeries in the oral cavity, such as
gingivectomy, periodontal sulcular debridement, LANAP, frenectomy, biopsy, and
coagulation of graft donor sites.
Military surplus Nd:YAG laser rangefinder firing. The laser fires through a
collimator focusing the beam, which blasts a hole through a rubber block, releasing a
burst of plasma.
The Nd:YAG laser is the most common laser used in laser designators and laser
rangefinders. It may be used in the application of cavity ring-down spectroscopy,
which is used to measure the concentration of some light-absorbing substance.
A range of Nd:YAG lasers are used in analysis of elements in the periodic table.
Though the application by itself is fairly new with respect to conventional methods
such as XRF or ICP, it has proven to be less time consuming and a cheaper option to
test element concentrations. A high-power Nd:YAG laser is focused onto the sample
surface to produce plasma. Light from the plasma is captured by spectrometers and
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the characteristic spectra of each element can be identified, allowing concentrations
of elements in the sample to be measured.
Nd:YAG lasers, mainly via their second and third harmonics, are widely used to
excite dye lasers either in the liquid [128] or solid state[129]. They are also used as
pump sources for vibronically broadened solid-state lasers such as Cr4+:YAG or via
the second harmonic for pumping Ti:sapphire lasers.
Researchers from Japan's National Institutes of Natural Sciences are developing
laser igniters that use YAG chips to ignite fuel in an engine, in place of a spark plug
[137-138]. The lasers use several 800 picosecond long pulses to ignite the fuel,
producing faster and more uniform ignition. The researchers say that such igniters
could yield better performance and fuel economy, with fewer harmful emissions.
A.4 Diode and diode pumped Nd:YAG lasers
A.4.1 Diode lasers
A laser diode is a laser whose active medium is a semiconductor similar to that
found in a light-emitting diode. The most common type of laser diode is formed
from a p-n junction and powered by injected electric current. The former devices are
sometimes referred to as injection laser diodes to distinguish them from optically
pumped laser diodes.
A laser diode is formed by doping a very thin layer on the surface of a crystal wafer.
The crystal is doped to produce an n-type region and a p-type region, one above the
other, resulting in a p-n junction, or diode. See figure A.4 for a schematics of a
simple laser diode.
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Figure A.4 - Diagram of a simple laser diode, not to scale
Laser diodes form a subset of the larger classification of semiconductor p-n junction
diodes. Forward electrical bias across the laser diode causes the two species of
charge carrier – holes and electrons – to be "injected" from opposite sides of the p-n
junction into the depletion region. Holes are injected from the p-doped, and electrons
from the n-doped, semiconductor. (A depletion region, devoid of any charge carriers,
forms as a result of the difference in electrical potential between n- and p-type
semiconductors wherever they are in physical contact.) Due to the use of charge
injection in powering most diode lasers, this class of lasers is sometimes termed
"injection lasers “or” injection laser diode" (ILD). As diode lasers are semiconductor
devices, they may also be classified as semiconductor lasers. Either designation
distinguishes diode lasers from solid-state lasers.
Another method of powering some diode lasers is the use of optical pumping.
Optically Pumped Semiconductor Lasers (OPSL) use a III-V semiconductor chip as
the gain media, and another laser (often another diode laser) as the pump source.
OPSL offer several advantages over ILDs, particularly in wavelength selection and
lack of interference from internal electrode structures [132-133].
When an electron and a hole are present in the same region, they may recombine or
"annihilate" with the result being spontaneous emission — i.e., the electron may re-
occupy the energy state of the hole, emitting a photon with energy equal to the
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difference between the electron and hole states involved. (In a conventional
semiconductor junction diode, the energy released from the recombination of
electrons and holes is carried away as phonons, i.e., lattice vibrations, rather than as
photons.) Spontaneous emission gives the laser diode below lasing threshold similar
properties to an LED. Spontaneous emission is necessary to initiate laser oscillation,
but it is one among several sources of inefficiency once the laser is oscillating.
The difference between the photon-emitting semiconductor laser and conventional
phonon-emitting (non-light-emitting) semiconductor junction diodes lies in the use
of a different type of semiconductor, one whose physical and atomic structure
confers the possibility for photon emission. These photon-emitting semiconductors
are the so-called "direct bandgap" semiconductors. The properties of silicon and
germanium, which are single-element semiconductors, have bandgaps that do not
align in the way needed to allow photon emission and are not considered "direct."
Other materials, the so-called compound semiconductors, have virtually identical
crystalline structures as silicon or germanium but use alternating arrangements of
two different atomic species in a checkerboard-like pattern to break the symmetry.
The transition between the materials in the alternating pattern creates the critical
"direct bandgap" property. Gallium arsenide, indium phosphide, gallium antimonide,
and gallium nitride are all examples of compound semiconductor materials that can
be used to create junction diodes that emit light.
In the absence of stimulated emission (e.g., lasing) conditions, electrons and holes
may coexist in proximity to one another, without recombining, for a certain time,
termed the "upper-state lifetime" or "recombination time" (about a nanosecond for
typical diode laser materials), before they recombine. Then a nearby photon with
energy equal to the recombination energy can cause recombination by stimulated
emission. This generates another photon of the same frequency, travelling in the
same direction, with the same polarization and phase as the first photon. This means
that stimulated emission causes gain in an optical wave (of the correct wavelength)
in the injection region, and the gain increases as the number of electrons and holes
injected across the junction increases. The spontaneous and stimulated emission
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processes are vastly more efficient in direct bandgap semiconductors than in indirect
bandgap semiconductors; therefore silicon is not a common material for laser diodes.
As in other lasers, the gain region is surrounded with an optical cavity to form a
laser. In the simplest form of laser diode, an optical waveguide is made on that
crystal surface, such that the light is confined to a relatively narrow line. The two
ends of the crystal are cleaved to form perfectly smooth, parallel edges, forming a
Fabry–Pérot resonator. Photons emitted into a mode of the waveguide will travel
along the waveguide and be reflected several times from each end face before they
are emitted. As a light wave passes through the cavity, it is amplified by stimulated
emission, but light is also lost due to absorption and by incomplete reflection from
the end facets. Finally, if there is more amplification than loss, the diode begins to
"lase".
Some important properties of laser diodes are determined by the geometry of the
optical cavity. Generally, in the vertical direction, the light is contained in a very thin
layer, and the structure supports only a single optical mode in the direction
perpendicular to the layers. In the transverse direction, if the waveguide is wide
compared to the wavelength of light, then the waveguide can support multiple
transverse optical modes, and the laser is known as "multi-mode". These transversely
multi-mode lasers are adequate in cases where one needs a very large amount of
power, but not a small diffraction-limited beam; for example in printing, activating
chemicals, or pumping other types of lasers.
In applications where a small focused beam is needed, the waveguide must be made
narrow, on the order of the optical wavelength. This way, only a single transverse
mode is supported and one ends up with a diffraction-limited beam. Such single
spatial mode devices are used for optical storage, laser pointers, and fibre optics.
Note that these lasers may still support multiple longitudinal modes, and thus can
lase at multiple wavelengths simultaneously.
The wavelength emitted is a function of the band-gap of the semiconductor and the
modes of the optical cavity. In general, the maximum gain will occur for photons
with energy slightly above the band-gap energy, and the modes nearest the gain peak
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will lase most strongly. If the diode is driven strongly enough, additional side modes
may also lase. Some laser diodes, such as most visible lasers, operate at a single
wavelength, but that wavelength is unstable and changes due to fluctuations in
current or temperature.
Due to diffraction, the beam diverges (expands) rapidly after leaving the chip,
typically at 30 degrees vertically by 10 degrees laterally. A lens must be used in
order to form a collimated beam like that produced by a laser pointer. If a circular
beam is required, cylindrical lenses and other optics are used. For single spatial
mode lasers, using symmetrical lenses, the collimated beam ends up being elliptical
in shape, due to the difference in the vertical and lateral divergences. This is easily
observable with a red laser pointer.
The simple diode described above has been heavily modified in recent years to
accommodate modern technology, resulting in a variety of types of laser diodes.
Laser diodes are numerically the most common laser type, with 2004 sales of
approximately 733 million units,[137] as compared to 131,000 of other types of
lasers[138].
Laser diodes find wide use in telecommunication as easily modulated and easily
coupled light sources for fibre optics communication. They are used in various
measuring instruments, such as rangefinders. Another common use is in barcode
readers. Visible lasers, typically red but later also green, are common as laser
pointers. Both low and high-power diodes are used extensively in the printing
industry both as light sources for scanning (input) of images and for very high-speed
and high-resolution printing plate (output) manufacturing. Infrared and red laser
diodes are common in CD players, CD-ROMs and DVD technology. Violet lasers
are used in HD DVD and Blu-ray technology. Diode lasers have also found many
applications in laser absorption spectrometry (LAS) for high-speed, low-cost
assessment or monitoring of the concentration of various species in gas phase. High-
power laser diodes are used in industrial applications such as heat treating, cladding,
seam welding and for pumping other lasers, such as diode-pumped solid-state lasers.
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Uses of laser diodes can be categorized in various ways. Most applications could be
served by larger solid-state lasers or optical parametric oscillators, but the low cost
of mass-produced diode lasers makes them essential for mass-market applications.
Diode lasers can be used in a great many fields; since light has many different
properties (power, wavelength, spectral and beam quality, polarization) it is useful to
classify applications by these basic properties.
Many applications of diode lasers primarily make use of the "directed energy"
property of an optical beam. In this category one might include the laser printers,
barcode readers, image scanning, illuminators, designators, optical data recording,
combustion ignition, laser surgery, industrial sorting, industrial machining, and
directed energy weaponry. Some of these applications are well-established while
others are emerging.
Laser medicine: medicine and especially dentistry have found many new uses for
diode lasers [139-141]. The shrinking size of the units and their increasing user
friendliness makes them very attractive to clinicians for minor soft tissue procedures.
The 800 nm – 980 nm units have a high absorption rate for hemoglobin and thus
make them ideal for soft tissue applications, where good hemostasis is necessary.
Uses which may make use of the coherence of diode-laser-generated light include
interferometric distance measurement, holography, coherent communications, and
coherent control of chemical reactions.
Uses which may make use of "narrow spectral" properties of diode lasers include
range-finding, telecommunications, infra-red countermeasures, spectroscopic
sensing, generation of radio-frequency or terahertz waves, atomic clock state
preparation, quantum key cryptography, frequency doubling and conversion, water
purification (in the UV), and photodynamic therapy (where a particular wavelength
of light would cause a substance such as porphyrin to become chemically active as
an anti-cancer agent only where the tissue is illuminated by light).
Uses where the desired quality of laser diodes is their ability to generate ultra-short
pulses of light by the technique known as "mode-locking" include clock distribution
for high-performance integrated circuits, high-peak-power sources for laser-induced
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breakdown spectroscopy sensing, arbitrary waveform generation for radio-frequency
waves, photonic sampling for analog-to-digital conversion, and optical code-
division-multiple-access systems for secure communication.
A.4.2 Diode-pumped solid-state (DPSS)
Diode-pumped solid-state (DPSS) lasers are solid-state lasers made by pumping a
solid gain medium, for example, a ruby or a neodymium-doped YAG crystal, with a
laser diode.
DPSS lasers have advantages in compactness and efficiency over other types, and
high power DPSS lasers have replaced ion lasers and flashlamp-pumped lasers in
many scientific applications, and are now appearing commonly in green and other
colour laser pointers.
The wavelength of the laser diodes is tuned by means of temperature to produce an
optimal compromise between the absorption coefficient in the crystal and energy
efficiency (lowest possible pump photon energy). As waste energy is limited by the
thermal lens this means higher power densities compared to high-intensity discharge
lamps.
High power lasers use a single crystal, but many laser diodes are arranged in strips
(multiple diodes next to each other in one substrate) or stacks (stacks of substrates).
This diode grid can be imaged onto the crystal by means of a lens.
Higher brightness (leading to better beam profile and longer diode lifetimes) is
achieved by optically removing the dark areas between the diodes, which are needed
for cooling and delivering the current. This is done in two steps:
1. The "fast axis" is collimated with an aligned grating of cylindrical micro-lenses.
2. The partially collimated beams are then imaged at reduced size into the crystal.
The crystal can be pumped longitudinally from both end faces or transversely from
three or more sides.
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The beams from multiple diodes can also be combined by coupling each diode into
an optical fibre, which is placed precisely over the diode (but behind the micro-lens).
At the other end of the fibre bundle, the fibres are fused together to form a uniform,
gap-less, round profile on the crystal. This also permits the use of a remote power
supply.
Figure A.5 – A Diode Pumped Solid State Laser (green) source: Wikipedia
The most common DPSS laser in use is the 532 nm wavelength green laser pointer.
Figure A.5 is a frequency-doubled green laser pointer, showing internal construction.
Cells and electronics lead to a laser head module (see lower diagram). This contains
a powerful 808 nm IR diode laser that pumps an Nd:YVO4 laser crystal, that in turn
outputs 1064 nm light. This immediately is doubled inside a non-linear KTP crystal,
resulting in green light at the half-wavelength of 532 nm. This beam is expanded and
infrared-filtered. In inexpensive lasers the IR filter is inadequate, or is omitted.
A powerful (>200 mW) 808 nm wavelength infrared GaAlAs laser diode pumps a
neodymium-doped yttrium aluminium garnet (Nd:YAG) or a neodymium-doped
yttrium orthovanadate (Nd:YVO4) crystal which produces 1064 nm wavelength light
from the main spectral transition of neodymium ion. This light is then frequency
185
doubled using a nonlinear optical process in a KTP crystal, producing 532 nm light.
Green DPSS lasers are usually around 20% efficient, although some lasers can reach
up to 35% efficiency. In other words, a green DPSS laser using a 2.5 W pump diode
would be expected to output around 500-900 mW of 532 nm light.
In optimal conditions, Nd:YVO4 has a conversion efficiency of 60%, while KTP has
a conversion efficiency of 80%. In other words, a green DPSS laser can theoretically
have an overall efficiency of 48%.
In the realm of very high output powers, the KTP crystal becomes susceptible to
optical damage. Thus, high-power DPSS lasers generally have a larger beam
diameter, as the 1064 nm laser is expanded before it reaches the KTP crystal,
reducing the irradiance from the infrared light. In order to maintain a lower beam
diameter, a crystal with a higher damage threshold, such as LBO, is used instead.
Blue DPSS lasers use a nearly identical process, except that the 808 nm light is being
converted by an Nd:YAG crystal to 946 nm light (selecting this non-principal
spectral line of neodymium in the same Nd-doped crystals), which is then frequency-
doubled to 473 nm by a beta barium borate (BBO) or lithium triborate (LBO) crystal.
Because of the lower gain for the materials, blue lasers are relatively weak, and are
only around 3-5% efficient. In the late 2000s, it was discovered that bismuth
triborate (BiBO) crystals were more efficient than BBO and LBO and do not have
the disadvantage of being hygroscopic, which degrades the crystal if it is exposed to
moisture.
Violet DPSS lasers at 404 nm have been produced which directly double the output
of a 1,000 mW 808 nm GaAlAs pump diode, for a violet light output of 120 mW
(12% efficiency). Initially, these lasers out-performed gallium nitride (GaN) direct
405 nm Blu-ray diode lasers. As direct 405nm diode technology progressed
(primarily for use in Blu-ray disc writers) output powers of greater than 500mW
have become possible, exceeding the output powers possible from directly doubled
404nm DPSS lasers. Further, the frequency-doubled violet lasers have a considerable
infrared component in the beam, resulting from the pump diode.
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Yellow DPSS lasers use an even more complicated process: A 808 nm pump diode
is used to generate 1,064 nm and 1,342 nm light, which are summed in parallel to
become 593.5 nm. Due to their complexity, most yellow DPSS lasers are only
around 1% efficient, and usually more expensive per unit of power.
Another method is to generate 1,064 and 1,319 nm light, which are summed to 589
nm. This process is more efficient, with about 3% of the pump diode's power being
converted to yellow light.
DPSS and diode lasers are two of the most common types of solid-state lasers.
However, both types have their advantages and disadvantages.
DPSS lasers generally have a higher beam quality and can reach very high powers
while maintaining a relatively good beam quality. Because the crystal pumped by the
diode acts as its own laser, the quality of the output beam is independent of that of
the input beam. In comparison, diode lasers can only reach a few hundred milliwatts
unless they operate in multiple transverse mode. Such multi-mode lasers have a
larger beam diameter and a greater divergence, which makes them less desirable. In
fact, single-mode operation is essential in some applications, such as optical drives.
On the other hand, diode lasers are cheaper and more energy efficient. As DPSS
crystals are not 100% efficient, some power is lost when the frequency is converted.
DPSS lasers are also more sensitive to temperature and can only operate optimally
within a small range. Otherwise, the laser would suffer from stability issues, such as
hopping between modes and large fluctuations in the output power. DPSS lasers also
require a more complex construction.
Diode lasers can also be precisely modulated with a greater frequency than DPSS
lasers.
Neodymium-doped solid state lasers continue to be the laser source of choice for
industrial applications. Direct pumping of the upper Nd laser level at 885-nm (rather
than at the more traditional broad 808-nm band) offers the potential of improved
performance through a reduction in the lasing quantum defect, thereby improving
system efficiency, reducing cooling requirements, and enabling further TEM00
187
power scaling. Because of the narrow 885-nm absorption feature in Nd:YAG, certain
systems may benefit from the use of wavelength-locked diode pump sources, which
serve to narrow and stabilize the pump emission spectrum to keep it closely aligned
to this absorption feature. To date, high power diode laser locking schemes such as
internal distributed feedback Bragg gratings and externally-aligned volume
holographic grating optics, VHG’s, have not been widely implemented due to the
increased cost and assumed performance penalty of the technology. However, recent
advancements in the manufacture of stabilized diode pump sources which utilize
external wavelength locking now offer improved spectral properties with little-to-no
impact on power and efficiency. Benefits of this approach include improvements in
laser efficiency, spectral line width, and pumping efficiency.
A.5 Fibre lasers
A fibre laser or fibre laser is a laser in which the active gain medium is an optical
fibre doped with rare-earth elements such as erbium, ytterbium, neodymium,
dysprosium, praseodymium, and thulium. They are related to doped fibre amplifiers,
which provide light amplification without lasing. Fibre nonlinearities, such as
stimulated Raman scattering or four-wave mixing can also provide gain and thus
serve as gain media for a fibre laser. See figure A.6 for a schematic representation of
a fibre laser.
Figure A.6 - Schematics of a Fiber laser source: www.sciencemag.org
188
The advantages of fibre lasers over other types include:
Light is already coupled into a flexible fibre: The fact that the light is already in a
fibre allows it to be easily delivered to a movable focusing element. This is
important for laser cutting, welding, and folding of metals and polymers.
High output power: Fibre lasers can have active regions several kilometres long, and
so can provide high optical gain. They can support kilowatt levels of continuous
output power because of the fibre's high surface area to volume ratio, which allows
efficient cooling.
High optical quality: The fibre's wave-guiding properties reduce or eliminate thermal
distortion of the optical path, typically producing a diffraction-limited, high-quality
optical beam.
Compact size: Fibre lasers are compact compared to rod or gas lasers of comparable
power, because the fibre can be bent and coiled to save space.
Reliability: Fibre lasers exhibit high vibrational stability, extended lifetime, and
maintenance-free turnkey operation.
Fibre laser can also refer to the machine tool that includes the fibre resonator.
Applications of fibre lasers include material processing, telecommunications,
spectroscopy, medicine, and directed energy weapons [142].
Unlike most other types of lasers, the laser cavity in fibre lasers is constructed
monolithically by fusion splicing different types of fibre; fibre Bragg gratings
replace conventional dielectric mirrors to provide optical feedback. Another type is
the single longitudinal mode operation of ultra-narrow distributed feedback lasers
(DFB) where a phase-shifted Bragg grating overlaps the gain medium. Fibre lasers
are pumped by semiconductor laser diodes or by other fibre lasers.
Recent developments in fibre laser technology have led to a rapid and large rise in
achieved diffraction-limited beam powers from diode-pumped solid-state lasers. Due
to the introduction of large mode area (LMA) fibres as well as continuing advances
in high power and high brightness diodes, continuous-wave single-transverse-mode
189
powers from Yb-doped fibre lasers have increased from 100 W in 2001 to >20 kW.
Commercial single-mode lasers have reached 10 kW in CW power [143].
Another type of fibre laser is the fibre disk laser. In such, the pump is not confined
within the cladding of the fibre (as in the double-clad fibre), but pump light is
delivered across the core multiple times because the core is coiled on itself like a
rope. This configuration is suitable for power scaling in which many pump sources
are used around the periphery of the coil [144-147].
A fibre disk laser is a fibre laser with transverse delivery of the pump light. They are
characterized by the pump beam not being parallel to the active core of the optical
fibre (as in a double-clad fibre), but directed to the coil of the fibre at an angle
(usually, between 10 and 40 degrees). This allows use of the specific shape of the
pump beam emitted by the laser diode, providing the efficient use of the pump.
Fibre disk lasers should not be confused with the laser disks (disk-shaped devices for
storage and reading of information with laser beam) nor the disk laser or "active
mirror", which is a laser with a thin active layer where the heat sink is realized in a
direction opposite to that of propagation of the output beam.
First disk lasers were developed in the Institute for Laser Science, Japan. Several
realizations of fibre disk lasers were reported [144-147]. The fibre disk laser is so
named because the fibre is tightly coiled. Typically, no special feedback for the laser
frequency is required, as the small reflection at end of the fibre is sufficient to
provide efficient operation. In this case, both ends of the coiled fibre can be used as
output.
Fibre disk lasers are used for cutting of metal (up to few mm thick), welding and
folding. The disk-shaped configuration allows efficient heat dissipation (usually, the
disks are cooled with flowing water); allowing power scaling. When the increase of
the length of the fibre becomes limited by stimulated scattering, additional power
scaling can be achieved by combining several fibre disk lasers into a stack.
The spiral-coiled configuration is not the only possible arrangement; any other
scheme of stacking of optical fibres with lateral delivery of pump can also be called
190
a fibre disk laser, even if the resulting shape of the device is not circular. The term
fibre disk laser applies to the concept of lateral delivery of pump to the active optical
fibre rather than specifically to a disk-shaped device. The optimal shape of the fibre
disk laser may depend on the properties of the beam of pump available, as well as on
the specific application.
191
Appendix B: Powder certificates
192
193
194
Appendix C: Raw test data from the dilatometry
TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
on
mm/mm/deg C.10^-6
TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC % -1455 ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
26.22 0.00 8.41 25.84 0.00 9.22 23.43 0.00 5.96 25.52 0.00 7.77 25.40 0.00 7.69 23.64 0.00 6.72 26.63 0.00 7.05 24.94 0.00 7.3226.68 0.00 7.42 26.35 0.00 8.66 23.96 0.00 6.07 26.15 0.00 7.47 26.06 0.00 7.21 24.29 0.00 6.26 27.22 0.00 6.23 25.57 0.00 6.1827.17 0.00 7.65 26.85 0.00 8.30 24.50 0.00 5.65 26.69 0.00 7.65 26.61 0.00 7.18 24.80 0.00 6.47 27.78 0.00 5.66 26.10 0.00 5.8427.62 0.00 6.85 27.33 0.00 7.39 25.02 0.00 5.57 27.31 0.00 7.62 27.09 0.00 7.22 25.33 0.00 6.00 28.27 0.00 5.58 26.61 0.00 5.5328.25 0.00 6.67 28.08 0.00 7.03 25.68 0.00 5.40 28.18 0.00 7.17 27.73 0.00 7.22 25.90 0.00 6.05 28.88 0.00 5.32 27.20 0.00 5.1828.98 0.00 6.34 28.93 0.00 6.35 26.49 0.00 5.15 29.27 0.00 7.01 28.44 0.00 7.21 26.72 0.00 5.62 29.77 0.00 4.97 28.04 0.00 4.9929.73 0.00 6.28 29.89 0.00 6.26 27.42 0.00 5.15 30.37 0.01 6.90 29.27 0.00 7.27 27.71 0.00 6.15 30.79 0.00 4.95 29.01 0.00 4.7530.56 0.00 6.17 30.83 0.00 6.25 28.33 0.00 5.22 31.47 0.01 6.92 30.12 0.00 7.36 28.71 0.00 6.23 31.78 0.00 4.93 30.03 0.00 4.7631.36 0.00 6.01 31.71 0.00 6.20 29.18 0.00 5.37 32.43 0.01 6.98 30.94 0.01 7.47 29.73 0.00 6.06 32.87 0.00 4.98 30.96 0.00 4.7332.34 0.00 5.90 32.55 0.01 6.34 30.07 0.00 5.30 33.40 0.01 7.20 31.88 0.01 7.67 30.65 0.01 5.93 33.85 0.00 5.10 31.84 0.00 4.9133.46 0.01 5.86 33.45 0.01 6.30 31.19 0.00 5.32 34.55 0.01 7.39 32.82 0.01 7.80 31.56 0.01 5.85 34.79 0.01 5.09 32.75 0.00 4.8934.68 0.01 5.88 34.44 0.01 6.34 32.30 0.01 5.44 35.79 0.01 7.49 33.78 0.01 7.91 32.73 0.01 5.80 35.93 0.01 5.10 33.73 0.01 4.9535.81 0.01 6.00 35.49 0.01 6.27 33.53 0.01 5.53 37.13 0.01 7.63 34.87 0.01 8.09 34.02 0.01 5.95 37.15 0.01 5.15 34.91 0.01 5.0036.99 0.01 6.11 36.77 0.01 6.34 34.72 0.01 5.65 38.38 0.01 7.83 36.00 0.01 8.28 35.29 0.01 6.06 38.51 0.01 5.24 36.20 0.01 5.0938.08 0.01 6.25 38.15 0.01 6.40 35.81 0.01 5.76 39.56 0.01 8.09 37.19 0.01 8.33 36.53 0.01 6.23 39.86 0.01 5.35 37.46 0.01 5.2439.40 0.01 6.38 39.50 0.01 6.49 37.24 0.01 5.85 40.84 0.01 8.33 38.34 0.01 8.46 37.73 0.01 6.37 41.11 0.01 5.48 38.60 0.01 5.3340.88 0.01 6.52 40.74 0.01 6.52 38.75 0.01 5.95 42.06 0.02 8.55 39.81 0.01 8.60 39.01 0.01 6.46 42.42 0.01 5.61 39.96 0.01 5.3842.34 0.01 6.71 42.20 0.01 6.59 40.37 0.01 6.09 43.53 0.02 8.67 41.30 0.02 8.80 40.43 0.01 6.58 43.73 0.01 5.73 41.37 0.01 5.4643.75 0.01 6.92 43.86 0.01 6.64 41.95 0.01 6.24 45.13 0.02 8.76 42.70 0.02 8.94 41.84 0.01 6.71 45.10 0.01 5.88 42.85 0.01 5.5745.07 0.01 7.14 45.49 0.01 6.74 43.34 0.01 6.43 46.93 0.02 8.84 44.12 0.02 9.12 43.20 0.01 6.81 46.41 0.01 6.02 44.33 0.01 5.7246.31 0.02 7.34 47.22 0.02 6.88 44.79 0.01 6.58 48.65 0.02 8.95 45.60 0.02 9.32 44.77 0.02 6.90 47.91 0.01 6.18 45.65 0.01 5.8347.70 0.02 7.45 48.66 0.02 7.04 46.29 0.02 6.77 50.21 0.03 9.15 47.23 0.02 9.51 46.40 0.02 6.99 49.42 0.02 6.33 47.06 0.01 5.9749.26 0.02 7.55 50.28 0.02 7.17 47.76 0.02 6.92 51.93 0.03 9.29 48.83 0.02 9.69 48.07 0.02 7.12 51.01 0.02 6.47 48.52 0.02 6.0451.09 0.02 7.68 52.05 0.02 7.30 49.36 0.02 7.03 53.56 0.03 9.44 50.37 0.03 9.87 49.65 0.02 7.25 52.54 0.02 6.62 50.01 0.02 6.1352.88 0.02 7.78 53.77 0.02 7.46 51.22 0.02 7.15 55.28 0.03 9.61 52.01 0.03 10.09 51.31 0.02 7.32 54.07 0.02 6.78 51.72 0.02 6.2554.46 0.02 7.95 55.48 0.02 7.56 53.21 0.02 7.25 57.08 0.03 9.78 53.77 0.03 10.27 53.15 0.02 7.40 55.77 0.02 6.91 53.39 0.02 6.3656.11 0.03 8.07 57.19 0.02 7.68 55.15 0.02 7.41 58.93 0.04 9.88 55.47 0.03 10.46 54.94 0.02 7.49 57.52 0.02 7.04 54.94 0.02 6.4557.84 0.03 8.23 59.08 0.03 7.79 56.92 0.03 7.53 60.88 0.04 10.03 57.09 0.03 10.63 56.78 0.03 7.60 59.36 0.02 7.17 56.67 0.02 6.5459.42 0.03 8.35 60.89 0.03 7.92 58.65 0.03 7.64 62.59 0.04 10.17 58.83 0.04 10.78 58.40 0.03 7.71 61.29 0.03 7.31 58.61 0.02 6.6361.16 0.03 8.45 62.73 0.03 8.06 60.65 0.03 7.76 64.47 0.04 10.32 60.62 0.04 10.94 60.25 0.03 7.78 62.99 0.03 7.46 60.38 0.02 6.7763.15 0.03 8.53 64.57 0.03 8.20 62.65 0.03 7.89 66.60 0.05 10.43 62.57 0.04 11.11 62.16 0.03 7.87 64.74 0.03 7.62 62.08 0.03 6.8865.20 0.03 8.66 66.43 0.03 8.33 64.60 0.03 8.09 68.57 0.05 10.56 64.37 0.04 11.28 64.19 0.03 7.98 66.60 0.03 7.76 63.84 0.03 7.0167.17 0.04 8.78 68.30 0.04 8.43 66.49 0.04 8.30 70.62 0.05 10.69 66.32 0.05 11.45 66.08 0.04 8.09 68.45 0.03 7.90 65.77 0.03 7.1468.92 0.04 8.90 70.17 0.04 8.54 68.39 0.04 8.51 72.50 0.05 10.84 68.15 0.05 11.58 67.79 0.04 8.21 70.55 0.04 8.18 67.51 0.03 7.2970.90 0.04 9.01 72.08 0.04 8.65 70.26 0.04 8.67 74.62 0.06 10.98 70.11 0.05 11.74 69.64 0.04 8.29 72.53 0.04 8.32 69.44 0.03 7.4072.74 0.04 9.15 73.92 0.04 8.76 72.01 0.04 8.82 76.52 0.06 11.12 72.07 0.06 11.91 71.51 0.04 8.37 74.46 0.04 8.45 71.40 0.04 7.5174.66 0.05 9.24 75.98 0.05 8.86 74.02 0.05 8.93 78.45 0.06 11.30 74.18 0.06 12.09 73.59 0.04 8.45 76.42 0.04 8.58 73.56 0.04 7.6576.56 0.05 9.37 77.80 0.05 8.94 76.04 0.05 9.06 80.38 0.07 11.48 76.21 0.06 12.25 75.64 0.05 8.54 78.26 0.05 8.76 75.61 0.04 7.7878.53 0.05 9.47 80.00 0.05 8.99 78.15 0.05 9.19 82.56 0.07 11.60 78.08 0.07 12.36 77.67 0.05 8.60 80.23 0.05 8.88 77.52 0.04 7.8980.49 0.05 9.56 82.35 0.05 9.05 80.07 0.05 9.29 84.91 0.07 11.70 80.17 0.07 12.49 79.94 0.05 8.66 82.19 0.05 9.02 79.76 0.04 7.9882.68 0.06 9.65 84.57 0.05 9.15 82.31 0.06 9.40 87.06 0.08 11.81 82.28 0.07 12.63 82.11 0.05 8.75 84.33 0.05 9.14 81.81 0.05 8.1084.94 0.06 9.75 86.74 0.06 9.22 84.53 0.06 9.52 89.22 0.08 11.96 84.55 0.08 12.74 84.33 0.05 8.83 86.32 0.06 9.26 83.81 0.05 8.2586.97 0.06 9.85 88.92 0.06 9.28 86.66 0.06 9.62 91.23 0.08 12.10 86.73 0.08 12.86 86.29 0.06 8.89 88.37 0.06 9.38 86.01 0.05 8.3889.2 0.1 9.9 91.4 0.1 9.4 88.7 0.1 9.7 93.4 0.1 12.3 88.9 0.1 13.0 88.7 0.1 9.0 90.3 0.1 9.5 88.1 0.1 8.591.3 0.1 10.0 93.5 0.1 9.5 90.8 0.1 9.9 95.6 0.1 12.3 91.2 0.1 13.1 90.9 0.1 9.0 92.6 0.1 9.6 90.1 0.1 8.793.5 0.1 10.1 95.8 0.1 9.5 93.0 0.1 9.9 98.2 0.1 12.4 93.4 0.1 13.3 93.2 0.1 9.1 94.9 0.1 9.7 92.5 0.1 8.895.7 0.1 10.2 98.0 0.1 9.7 95.2 0.1 10.0 100.4 0.1 12.6 95.5 0.1 13.4 95.4 0.1 9.2 97.3 0.1 9.9 94.8 0.1 8.997.9 0.1 10.3 100.2 0.1 9.7 97.4 0.1 10.1 102.7 0.1 12.7 97.8 0.1 13.5 97.6 0.1 9.3 99.4 0.1 10.0 96.9 0.1 9.0
100.1 0.1 10.4 102.4 0.1 9.8 99.8 0.1 10.2 105.0 0.1 12.9 99.9 0.1 13.6 99.8 0.1 9.4 101.6 0.1 10.1 99.2 0.1 9.1102.4 0.1 10.5 104.9 0.1 9.8 102.1 0.1 10.4 107.3 0.1 13.0 102.4 0.1 13.7 102.3 0.1 9.4 104.0 0.1 10.2 101.5 0.1 9.3104.7 0.1 10.6 107.5 0.1 9.9 104.4 0.1 10.4 109.7 0.1 13.1 105.0 0.1 13.9 104.7 0.1 9.5 106.2 0.1 10.3 103.8 0.1 9.4107.0 0.1 10.7 109.7 0.1 10.0 106.7 0.1 10.5 112.2 0.1 13.2 107.2 0.1 13.9 107.1 0.1 9.6 108.5 0.1 10.4 106.1 0.1 9.5109.5 0.1 10.7 112.2 0.1 10.0 108.9 0.1 10.6 114.6 0.1 13.3 109.6 0.1 14.1 109.4 0.1 9.6 111.1 0.1 10.5 108.4 0.1 9.6111.7 0.1 10.8 114.6 0.1 10.1 111.4 0.1 10.7 117.0 0.1 13.4 112.1 0.1 14.2 112.0 0.1 9.7 113.5 0.1 10.6 110.6 0.1 9.8114.2 0.1 10.9 116.7 0.1 10.2 114.0 0.1 10.8 119.5 0.1 13.5 114.6 0.1 14.3 114.6 0.1 9.7 116.0 0.1 10.7 113.0 0.1 9.9116.8 0.1 11.0 119.2 0.1 10.3 116.4 0.1 10.9 121.9 0.1 13.7 117.1 0.1 14.4 117.0 0.1 9.8 118.4 0.1 10.8 115.6 0.1 10.0119.3 0.1 11.1 121.9 0.1 10.3 118.8 0.1 11.0 124.4 0.1 13.8 119.7 0.1 14.5 119.4 0.1 9.9 120.9 0.1 10.9 117.9 0.1 10.1121.7 0.1 11.2 124.4 0.1 10.4 121.2 0.1 11.0 126.8 0.1 13.9 122.2 0.1 14.6 122.0 0.1 10.0 123.4 0.1 11.0 120.3 0.1 10.2124.0 0.1 11.2 126.8 0.1 10.5 123.4 0.1 11.1 129.2 0.1 14.0 124.6 0.1 14.7 124.5 0.1 10.0 125.9 0.1 11.1 122.5 0.1 10.3126.5 0.1 11.3 129.4 0.1 10.5 125.8 0.1 11.2 131.6 0.2 14.1 127.3 0.2 14.8 126.9 0.1 10.1 128.1 0.1 11.1 125.1 0.1 10.4128.8 0.1 11.4 131.6 0.1 10.6 128.3 0.1 11.3 134.2 0.2 14.2 129.8 0.2 14.9 129.3 0.1 10.2 130.4 0.1 11.2 127.6 0.1 10.5131.3 0.1 11.5 134.2 0.1 10.7 130.8 0.1 11.3 136.7 0.2 14.3 132.3 0.2 15.0 131.7 0.1 10.2 132.8 0.1 11.3 129.9 0.1 10.6133.9 0.1 11.6 137.0 0.1 10.7 133.3 0.1 11.4 139.4 0.2 14.4 134.6 0.2 15.1 134.2 0.1 10.3 135.3 0.1 11.4 132.4 0.1 10.7136.1 0.1 11.7 138.8 0.1 10.8 136.0 0.1 11.4 141.9 0.2 14.5 137.1 0.2 15.2 136.7 0.1 10.4 137.8 0.1 11.5 135.0 0.1 10.8138.7 0.1 11.8 141.4 0.1 10.9 138.8 0.1 11.5 144.2 0.2 14.7 139.5 0.2 15.3 139.2 0.1 10.4 140.3 0.1 11.5 137.4 0.1 10.9141.4 0.1 11.8 144.9 0.1 11.0 141.5 0.1 11.6 146.8 0.2 14.8 141.9 0.2 15.4 141.8 0.1 10.5 142.6 0.1 11.6 140.0 0.1 11.0143.9 0.1 11.9 148.2 0.1 11.2 144.0 0.1 11.6 149.5 0.2 14.8 144.4 0.2 15.5 144.4 0.1 10.5 145.4 0.1 11.7 142.7 0.1 11.1146.5 0.1 12.0 157.1 0.1 11.3 146.6 0.1 11.7 152.1 0.2 14.9 147.0 0.2 15.6 147.1 0.1 10.6 148.0 0.1 11.7 145.3 0.1 11.2149.1 0.1 12.1 160.7 0.2 11.3 149.2 0.1 11.8 154.6 0.2 15.0 149.5 0.2 15.7 149.6 0.1 10.6 150.5 0.1 11.8 148.0 0.1 11.3151.6 0.2 12.2 163.2 0.2 11.4 151.9 0.2 11.8 157.4 0.2 15.1 152.1 0.2 15.7 152.4 0.1 10.7 153.4 0.2 11.8 150.6 0.1 11.3154.2 0.2 12.3 166.1 0.2 11.4 154.5 0.2 11.9 159.8 0.2 15.2 154.5 0.2 15.8 154.8 0.1 10.7 156.0 0.2 11.9 153.1 0.1 11.4156.7 0.2 12.4 168.7 0.2 11.5 157.3 0.2 11.9 162.6 0.2 15.3 157.4 0.2 15.9 157.6 0.1 10.8 158.7 0.2 12.0 155.8 0.2 11.6159.3 0.2 12.5 171.4 0.2 11.5 159.9 0.2 12.0 165.2 0.2 15.3 160.2 0.2 15.9 160.3 0.1 10.8 161.3 0.2 12.1 158.4 0.2 11.6161.9 0.2 12.5 174.1 0.2 11.6 162.5 0.2 12.1 167.9 0.2 15.4 162.7 0.2 16.0 162.9 0.2 10.9 163.8 0.2 12.2 161.1 0.2 11.7164.3 0.2 12.6 176.8 0.2 11.6 165.0 0.2 12.2 170.5 0.2 15.5 165.3 0.2 16.1 165.7 0.2 10.9 166.6 0.2 12.3 163.6 0.2 11.8167.1 0.2 12.7 179.5 0.2 11.6 167.5 0.2 12.2 173.1 0.2 15.6 168.0 0.2 16.1 168.2 0.2 11.0 169.3 0.2 12.4 166.3 0.2 11.9169.8 0.2 12.8 182.3 0.2 11.7 170.3 0.2 12.3 175.8 0.2 15.7 170.7 0.2 16.2 170.8 0.2 11.0 172.0 0.2 12.4 168.9 0.2 12.0172.5 0.2 12.8 184.7 0.2 11.7 173.1 0.2 12.3 178.2 0.2 15.8 173.4 0.2 16.3 173.5 0.2 11.1 174.7 0.2 12.5 171.6 0.2 12.1175.3 0.2 12.9 187.6 0.2 11.8 175.7 0.2 12.4 180.8 0.3 15.9 176.1 0.2 16.4 176.2 0.2 11.1 177.3 0.2 12.6 174.2 0.2 12.2177.9 0.2 13.0 190.4 0.2 11.9 178.5 0.2 12.4 183.3 0.3 16.0 178.7 0.3 16.4 179.0 0.2 11.2 180.0 0.2 12.7 176.8 0.2 12.2180.6 0.2 13.0 193.0 0.2 11.9 181.3 0.2 12.5 186.1 0.3 16.0 181.3 0.3 16.5 181.8 0.2 11.2 182.3 0.2 12.7 179.5 0.2 12.3183.4 0.2 13.1 195.8 0.2 11.9 183.7 0.2 12.5 188.6 0.3 16.1 183.7 0.3 16.6 184.4 0.2 11.2 185.1 0.2 12.8 182.2 0.2 12.4186.2 0.2 13.1 198.7 0.2 12.0 186.7 0.2 12.6 191.2 0.3 16.2 186.4 0.3 16.6 187.4 0.2 11.3 187.8 0.2 12.9 184.9 0.2 12.5189.0 0.2 13.2 201.3 0.2 12.0 189.3 0.2 12.7 194.0 0.3 16.3 189.1 0.3 16.7 190.3 0.2 11.3 190.5 0.2 12.9 187.7 0.2 12.6191.6 0.2 13.3 204.1 0.2 12.0 192.0 0.2 12.7 196.6 0.3 16.3 191.8 0.3 16.7 192.7 0.2 11.4 193.4 0.2 13.0 190.4 0.2 12.6194.3 0.2 13.3 206.8 0.2 12.1 195.0 0.2 12.8 199.3 0.3 16.4 194.5 0.3 16.8 195.5 0.2 11.4 196.1 0.2 13.1 192.9 0.2 12.7196.9 0.2 13.4 209.3 0.2 12.1 197.7 0.2 12.9 201.8 0.3 16.5 197.5 0.3 16.9 198.2 0.2 11.5 198.7 0.2 13.3 195.4 0.2 12.8199.5 0.2 13.5 212.4 0.2 12.1 200.6 0.2 12.9 204.6 0.3 16.5 200.1 0.3 16.9 200.9 0.2 11.5 201.5 0.2 13.3 198.1 0.2 12.9202.2 0.2 13.5 215.3 0.2 12.2 203.3 0.2 13.0 207.5 0.3 16.6 203.0 0.3 17.0 203.5 0.2 11.6 203.9 0.2 13.4 200.9 0.2 12.9204.6 0.2 13.6 218.0 0.2 12.2 205.9 0.2 13.1 210.2 0.3 16.6 205.5 0.3 17.0 206.1 0.2 11.6 206.9 0.2 13.4 203.9 0.2 13.0207.6 0.2 13.6 220.9 0.2 12.3 208.4 0.2 13.2 212.8 0.3 16.7 208.5 0.3 17.1 208.9 0.2 11.7 209.7 0.2 13.5 206.9 0.2 13.1210.3 0.3 13.7 223.3 0.2 12.3 211.0 0.2 13.2 215.4 0.3 16.8 211.2 0.3 17.1 211.6 0.2 11.7 212.4 0.3 13.5 209.8 0.2 13.1213.1 0.3 13.7 225.8 0.2 12.4 213.7 0.3 13.3 218.0 0.3 16.8 213.9 0.3 17.2 214.3 0.2 11.7 214.9 0.3 13.6 212.5 0.2 13.2215.8 0.3 13.8 228.3 0.3 12.4 216.2 0.3 13.3 220.7 0.3 16.9 216.4 0.3 17.3 216.7 0.2 11.8 217.5 0.3 13.6 214.9 0.3 13.3218.4 0.3 13.8 230.7 0.3 12.5 218.7 0.3 13.4 223.4 0.3 16.9 219.1 0.3 17.3 219.6 0.2 11.8 220.5 0.3 13.7 217.7 0.3 13.3221.0 0.3 13.8 233.5 0.3 12.5 221.5 0.3 13.4 226.0 0.3 17.0 221.7 0.3 17.4 222.3 0.2 11.9 223.1 0.3 13.7 220.5 0.3 13.4223.8 0.3 13.9 236.5 0.3 12.6 224.4 0.3 13.5 228.9 0.4 17.0 224.4 0.3 17.5 224.9 0.2 11.9 225.9 0.3 13.8 223.2 0.3 13.4226.6 0.3 13.9 239.1 0.3 12.6 227.1 0.3 13.5 231.8 0.4 17.0 227.2 0.4 17.5 227.8 0.2 11.9 228.5 0.3 13.8 225.7 0.3 13.5229.4 0.3 14.0 241.8 0.3 12.6 229.9 0.3 13.6 234.4 0.4 17.1 229.8 0.4 17.6 230.4 0.2 12.0 231.3 0.3 13.9 228.4 0.3 13.6232.2 0.3 14.0 244.4 0.3 12.7 231.4 0.3 13.6 237.0 0.4 17.1 232.6 0.4 17.6 233.3 0.3 12.0 233.8 0.3 13.9 230.8 0.3 13.6234.8 0.3 14.1 246.9 0.3 12.7 234.3 0.3 13.7 239.6 0.4 17.2 235.1 0.4 17.7 236.1 0.3 12.0 236.7 0.3 14.0 233.5 0.3 13.7237.5 0.3 14.1 249.7 0.3 12.7 237.9 0.3 13.7 242.3 0.4 17.3 238.0 0.4 17.7 238.7 0.3 12.1 239.4 0.3 14.0 235.9 0.3 13.8240.2 0.3 14.1 252.2 0.3 12.8 242.5 0.3 13.9 244.9 0.4 17.3 240.9 0.4 17.8 241.3 0.3 12.1 242.2 0.3 14.1 238.9 0.3 13.8243.0 0.3 14.2 255.0 0.3 12.8 251.8 0.3 13.9 247.9 0.4 17.3 243.6 0.4 17.8 243.9 0.3 12.2 244.7 0.3 14.1 241.6 0.3 13.9245.5 0.3 14.2 257.8 0.3 12.8 255.7 0.3 14.0 250.4 0.4 17.4 246.1 0.4 17.9 246.5 0.3 12.2 247.4 0.3 14.2 244.2 0.3 13.9248.3 0.3 14.2 260.6 0.3 12.8 258.7 0.3 14.0 253.4 0.4 17.4 249.0 0.4 17.9 249.2 0.3 12.2 250.0 0.3 14.2 247.2 0.3 14.0
WAFER 316-420
Raw Data from Dilatometer420SS DMD 316L SS DMD AlBr2 DMD Colmonoy DMDTool Steel-H13 DMDStellite 6 DMD WAFER 16221-316L
195
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TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
on
mm/mm/deg C.10^-6
TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC % -1455 ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
251.2 0.3 14.3 263.3 0.3 12.8 261.5 0.3 14.0 255.8 0.4 17.5 251.6 0.4 18.0 251.6 0.3 12.2 252.9 0.3 14.3 249.7 0.3 14.0254.0 0.3 14.3 266.4 0.3 12.8 264.0 0.3 14.1 258.6 0.4 17.5 254.3 0.4 18.0 254.9 0.3 12.3 255.4 0.3 14.3 252.7 0.3 14.1256.7 0.3 14.3 269.3 0.3 12.9 267.0 0.3 14.1 261.2 0.4 17.6 256.9 0.4 18.1 257.7 0.3 12.3 258.2 0.3 14.4 255.4 0.3 14.1259.9 0.3 14.3 272.0 0.3 12.9 269.5 0.3 14.2 263.7 0.4 17.6 259.7 0.4 18.1 260.4 0.3 12.3 260.8 0.3 14.4 258.5 0.3 14.2262.6 0.3 14.4 274.7 0.3 12.9 272.1 0.4 14.2 266.4 0.4 17.6 262.4 0.4 18.1 263.1 0.3 12.3 263.4 0.3 14.4 261.1 0.3 14.2265.6 0.3 14.4 277.4 0.3 13.0 275.0 0.4 14.2 269.0 0.4 17.7 265.4 0.4 18.1 266.0 0.3 12.4 266.5 0.3 14.5 263.9 0.3 14.3268.2 0.4 14.4 280.0 0.3 13.0 277.9 0.4 14.2 271.9 0.4 17.7 267.9 0.4 18.2 268.6 0.3 12.4 269.2 0.4 14.5 266.8 0.3 14.3271.0 0.4 14.5 282.8 0.3 13.0 280.7 0.4 14.3 274.3 0.4 17.8 271.1 0.4 18.2 271.3 0.3 12.4 272.2 0.4 14.5 269.2 0.4 14.4273.7 0.4 14.5 285.4 0.3 13.1 283.7 0.4 14.3 277.2 0.5 17.8 273.8 0.5 18.2 273.8 0.3 12.5 275.0 0.4 14.6 272.3 0.4 14.4276.3 0.4 14.5 288.2 0.3 13.1 286.2 0.4 14.3 279.8 0.5 17.8 276.6 0.5 18.3 276.5 0.3 12.5 277.9 0.4 14.6 275.0 0.4 14.4279.1 0.4 14.6 290.9 0.3 13.1 289.5 0.4 14.3 282.5 0.5 17.9 279.6 0.5 18.3 279.4 0.3 12.5 280.8 0.4 14.6 277.9 0.4 14.5281.7 0.4 14.6 294.2 0.4 13.1 292.1 0.4 14.3 285.3 0.5 17.9 282.1 0.5 18.4 282.3 0.3 12.5 283.3 0.4 14.7 280.8 0.4 14.5284.7 0.4 14.6 296.9 0.4 13.1 295.4 0.4 14.4 288.0 0.5 18.0 285.3 0.5 18.4 285.0 0.3 12.5 286.4 0.4 14.7 283.4 0.4 14.6287.4 0.4 14.7 300.2 0.4 13.1 298.0 0.4 14.4 291.1 0.5 18.0 287.6 0.5 18.4 288.1 0.3 12.6 289.2 0.4 14.7 286.2 0.4 14.6290.3 0.4 14.7 302.9 0.4 13.1 301.0 0.4 14.4 294.1 0.5 18.0 290.9 0.5 18.4 290.5 0.3 12.6 292.1 0.4 14.8 288.8 0.4 14.6293.0 0.4 14.7 305.9 0.4 13.2 303.8 0.4 14.5 296.8 0.5 18.0 293.4 0.5 18.5 293.8 0.3 12.6 294.9 0.4 14.8 291.6 0.4 14.7295.6 0.4 14.8 308.9 0.4 13.2 306.4 0.4 14.5 299.8 0.5 18.1 296.4 0.5 18.5 296.4 0.3 12.6 297.7 0.4 14.8 294.4 0.4 14.7298.5 0.4 14.8 311.6 0.4 13.2 309.4 0.4 14.5 302.6 0.5 18.1 299.0 0.5 18.6 299.5 0.4 12.7 300.6 0.4 14.9 297.2 0.4 14.7300.9 0.4 14.8 314.5 0.4 13.2 311.8 0.4 14.5 305.1 0.5 18.1 301.7 0.5 18.6 302.1 0.4 12.7 303.1 0.4 14.9 299.7 0.4 14.8304.0 0.4 14.8 317.3 0.4 13.2 314.6 0.4 14.6 308.0 0.5 18.2 304.1 0.5 18.7 305.0 0.4 12.7 305.7 0.4 14.9 302.3 0.4 14.8306.7 0.4 14.9 319.8 0.4 13.2 317.2 0.4 14.6 310.7 0.5 18.2 307.0 0.5 18.7 307.9 0.4 12.7 308.4 0.4 15.0 305.1 0.4 14.9309.6 0.4 14.9 322.9 0.4 13.3 319.8 0.4 14.6 313.6 0.5 18.2 309.3 0.5 18.7 310.5 0.4 12.7 310.9 0.4 15.0 307.6 0.4 14.9312.4 0.4 14.9 325.5 0.4 13.3 322.5 0.4 14.6 316.2 0.5 18.2 312.2 0.5 18.8 313.6 0.4 12.7 313.5 0.4 15.0 310.4 0.4 14.9315.1 0.4 14.9 328.5 0.4 13.3 324.9 0.4 14.7 318.9 0.5 18.3 314.9 0.5 18.8 316.0 0.4 12.8 316.0 0.4 15.1 312.8 0.4 15.0318.0 0.4 15.0 331.0 0.4 13.3 327.9 0.4 14.7 321.8 0.5 18.3 317.3 0.6 18.8 319.2 0.4 12.8 319.1 0.4 15.1 315.8 0.4 15.0320.7 0.4 15.0 333.7 0.4 13.3 330.5 0.5 14.7 324.4 0.6 18.3 320.6 0.6 18.8 321.9 0.4 12.8 321.6 0.4 15.1 318.4 0.4 15.0323.6 0.4 15.0 336.5 0.4 13.4 333.0 0.5 14.7 327.3 0.6 18.3 323.1 0.6 18.8 324.7 0.4 12.8 324.3 0.5 15.2 321.2 0.4 15.0326.4 0.5 15.0 338.9 0.4 13.4 336.1 0.5 14.7 329.7 0.6 18.4 326.2 0.6 18.9 327.5 0.4 12.8 327.2 0.5 15.2 324.0 0.5 15.1329.1 0.5 15.0 342.0 0.4 13.4 338.9 0.5 14.7 332.7 0.6 18.4 329.0 0.6 18.9 330.0 0.4 12.8 329.8 0.5 15.2 326.5 0.5 15.1332.0 0.5 15.1 344.8 0.4 13.4 341.7 0.5 14.8 335.2 0.6 18.4 331.7 0.6 18.9 333.3 0.4 12.8 332.9 0.5 15.2 329.8 0.5 15.2334.6 0.5 15.1 347.6 0.4 13.4 344.1 0.5 14.8 337.9 0.6 18.4 334.7 0.6 18.9 335.7 0.4 12.8 335.4 0.5 15.3 332.2 0.5 15.2337.8 0.5 15.1 350.3 0.4 13.5 346.8 0.5 14.8 340.8 0.6 18.4 337.1 0.6 18.9 339.1 0.4 12.9 338.4 0.5 15.3 335.2 0.5 15.2340.2 0.5 15.1 352.9 0.4 13.5 349.9 0.5 14.8 343.4 0.6 18.5 339.8 0.6 18.9 341.6 0.4 12.9 340.9 0.5 15.3 338.0 0.5 15.3343.4 0.5 15.1 355.8 0.4 13.5 352.9 0.5 14.8 346.3 0.6 18.5 342.6 0.6 18.9 344.7 0.4 12.9 343.6 0.5 15.3 340.6 0.5 15.3346.1 0.5 15.2 358.4 0.5 13.5 355.5 0.5 14.8 349.1 0.6 18.5 345.0 0.6 18.9 347.6 0.4 12.9 346.5 0.5 15.4 343.7 0.5 15.4349.0 0.5 15.2 361.4 0.5 13.5 358.6 0.5 14.8 352.0 0.6 18.5 347.8 0.6 18.9 350.2 0.4 12.9 348.8 0.5 15.4 346.3 0.5 15.4351.8 0.5 15.2 364.2 0.5 13.5 361.2 0.5 14.9 354.8 0.6 18.5 350.3 0.6 18.9 353.1 0.4 13.0 352.1 0.5 15.4 349.2 0.5 15.4354.4 0.5 15.2 366.7 0.5 13.5 363.7 0.5 14.9 357.2 0.6 18.6 353.2 0.6 18.9 355.5 0.4 13.0 354.5 0.5 15.4 351.9 0.5 15.5357.2 0.5 15.3 369.8 0.5 13.6 366.8 0.5 14.9 360.5 0.6 18.6 356.0 0.6 18.9 358.0 0.4 13.0 357.5 0.5 15.4 354.6 0.5 15.5360.1 0.5 15.3 372.2 0.5 13.6 369.3 0.5 14.9 363.1 0.6 18.6 358.7 0.6 18.9 360.6 0.4 13.0 360.3 0.5 15.5 357.6 0.5 15.6362.8 0.5 15.3 375.3 0.5 13.6 372.2 0.5 14.9 365.8 0.6 18.6 361.5 0.6 18.9 363.0 0.4 13.0 362.7 0.5 15.5 360.1 0.5 15.6365.7 0.5 15.3 377.6 0.5 13.6 374.9 0.5 14.9 368.3 0.6 18.7 364.0 0.6 18.9 365.7 0.4 13.0 365.8 0.5 15.5 363.1 0.5 15.6368.0 0.5 15.3 380.7 0.5 13.6 377.9 0.5 14.9 371.2 0.7 18.7 366.8 0.7 18.9 368.5 0.5 13.0 368.5 0.5 15.5 365.7 0.5 15.7371.6 0.5 15.4 383.3 0.5 13.6 380.5 0.5 15.0 373.9 0.7 18.7 369.6 0.7 18.9 370.7 0.5 13.0 371.3 0.5 15.6 368.5 0.5 15.7374.1 0.5 15.4 386.1 0.5 13.6 383.1 0.5 15.0 376.2 0.7 18.7 372.5 0.7 19.0 373.9 0.5 13.1 373.7 0.5 15.6 371.4 0.5 15.7377.1 0.5 15.4 388.8 0.5 13.6 386.1 0.5 15.0 379.4 0.7 18.7 375.1 0.7 19.0 376.3 0.5 13.1 376.7 0.5 15.6 374.0 0.6 15.7380.0 0.5 15.4 391.3 0.5 13.6 388.4 0.5 15.0 382.1 0.7 18.8 377.6 0.7 19.0 379.1 0.5 13.1 379.4 0.6 15.6 376.9 0.6 15.8382.8 0.6 15.4 394.2 0.5 13.6 391.3 0.6 15.0 384.9 0.7 18.8 380.5 0.7 18.9 381.9 0.5 13.1 382.1 0.6 15.6 379.2 0.6 15.8385.5 0.6 15.4 396.8 0.5 13.6 394.1 0.6 15.0 387.7 0.7 18.8 383.0 0.7 19.0 384.3 0.5 13.1 385.0 0.6 15.7 382.5 0.6 15.8387.8 0.6 15.5 400.2 0.5 13.7 396.3 0.6 15.0 390.2 0.7 18.8 386.2 0.7 19.0 387.7 0.5 13.1 387.5 0.6 15.7 384.9 0.6 15.8390.9 0.6 15.5 402.6 0.5 13.7 399.3 0.6 15.0 393.4 0.7 18.8 388.6 0.7 19.0 389.9 0.5 13.1 390.6 0.6 15.7 387.8 0.6 15.8393.4 0.6 15.5 405.2 0.5 13.7 402.0 0.6 15.1 395.6 0.7 18.8 391.2 0.7 19.0 393.0 0.5 13.1 393.2 0.6 15.7 390.4 0.6 15.8396.6 0.6 15.5 408.1 0.5 13.7 404.8 0.6 15.1 398.8 0.7 18.9 394.2 0.7 19.0 395.7 0.5 13.1 396.4 0.6 15.7 393.5 0.6 15.9399.0 0.6 15.5 410.5 0.5 13.7 407.6 0.6 15.1 401.2 0.7 18.9 396.4 0.7 19.0 398.3 0.5 13.1 398.8 0.6 15.8 396.1 0.6 15.9401.6 0.6 15.5 414.1 0.5 13.7 410.0 0.6 15.1 404.3 0.7 18.9 399.7 0.7 19.0 401.7 0.5 13.1 401.1 0.6 15.8 398.3 0.6 15.9404.7 0.6 15.5 416.4 0.5 13.7 412.8 0.6 15.1 406.8 0.7 18.9 402.1 0.7 19.0 404.1 0.5 13.1 404.0 0.6 15.8 401.8 0.6 15.9407.1 0.6 15.5 419.1 0.5 13.7 415.9 0.6 15.1 409.3 0.7 18.9 405.1 0.7 19.0 407.1 0.5 13.2 406.6 0.6 15.8 403.9 0.6 15.9410.0 0.6 15.6 422.4 0.5 13.7 418.4 0.6 15.1 412.5 0.7 18.9 408.0 0.7 19.0 410.1 0.5 13.2 409.0 0.6 15.8 406.9 0.6 16.0412.8 0.6 15.6 424.6 0.6 13.7 421.0 0.6 15.1 414.8 0.7 19.0 410.6 0.7 19.1 413.0 0.5 13.2 412.2 0.6 15.9 409.6 0.6 16.0415.1 0.6 15.6 427.6 0.6 13.8 423.9 0.6 15.1 417.7 0.7 19.0 413.5 0.7 19.1 415.5 0.5 13.2 414.7 0.6 15.9 412.4 0.6 16.0418.0 0.6 15.6 430.2 0.6 13.8 426.7 0.6 15.1 420.3 0.8 19.0 415.8 0.7 19.1 417.8 0.5 13.2 417.6 0.6 15.9 415.0 0.6 16.0420.8 0.6 15.6 433.3 0.6 13.8 429.9 0.6 15.2 423.1 0.8 19.0 418.9 0.8 19.2 420.9 0.5 13.2 420.1 0.6 15.9 417.3 0.6 16.0423.1 0.6 15.6 435.7 0.6 13.8 432.5 0.6 15.2 425.7 0.8 19.0 421.3 0.8 19.2 423.0 0.5 13.2 422.9 0.6 15.9 420.8 0.6 16.0425.9 0.6 15.6 438.2 0.6 13.8 434.9 0.6 15.2 428.2 0.8 19.0 424.6 0.8 19.2 426.6 0.5 13.2 425.8 0.6 15.9 423.2 0.6 16.0428.9 0.6 15.7 441.6 0.6 13.8 438.4 0.6 15.2 431.5 0.8 19.0 427.1 0.8 19.2 428.6 0.5 13.2 428.6 0.6 15.9 425.9 0.6 16.1431.1 0.6 15.6 443.8 0.6 13.8 440.7 0.6 15.2 433.6 0.8 19.1 429.7 0.8 19.3 431.6 0.5 13.2 431.1 0.6 16.0 428.6 0.7 16.1434.7 0.6 15.7 447.0 0.6 13.8 443.6 0.6 15.2 436.6 0.8 19.1 432.8 0.8 19.3 434.3 0.5 13.2 433.3 0.7 16.0 430.9 0.7 16.1436.8 0.6 15.7 449.5 0.6 13.8 446.7 0.6 15.2 439.1 0.8 19.1 435.1 0.8 19.4 436.7 0.5 13.3 437.1 0.7 16.0 433.6 0.7 16.1439.9 0.7 15.7 452.5 0.6 13.8 449.0 0.7 15.2 442.1 0.8 19.1 438.0 0.8 19.4 439.3 0.6 13.2 439.4 0.7 16.0 436.2 0.7 16.1442.5 0.7 15.7 455.1 0.6 13.9 451.9 0.7 15.2 444.6 0.8 19.1 440.6 0.8 19.4 442.5 0.6 13.3 442.2 0.7 16.0 438.7 0.7 16.1445.0 0.7 15.7 457.4 0.6 13.9 454.9 0.7 15.3 446.8 0.8 19.1 443.5 0.8 19.5 444.5 0.6 13.3 445.0 0.7 16.0 441.5 0.7 16.1447.7 0.7 15.7 459.9 0.6 13.9 457.5 0.7 15.3 450.2 0.8 19.1 446.2 0.8 19.5 448.3 0.6 13.3 447.8 0.7 16.0 444.5 0.7 16.1450.7 0.7 15.7 463.2 0.6 13.9 460.2 0.7 15.3 452.5 0.8 19.2 448.4 0.8 19.6 450.3 0.6 13.3 450.5 0.7 16.1 447.0 0.7 16.1453.5 0.7 15.7 465.2 0.6 13.9 462.6 0.7 15.3 455.1 0.8 19.2 451.8 0.8 19.6 453.2 0.6 13.3 452.5 0.7 16.1 450.2 0.7 16.1456.6 0.7 15.8 468.8 0.6 13.9 465.0 0.7 15.3 457.8 0.8 19.2 453.9 0.8 19.7 456.2 0.6 13.3 456.1 0.7 16.1 452.2 0.7 16.1458.8 0.7 15.7 471.1 0.6 13.9 468.1 0.7 15.3 460.1 0.8 19.2 456.8 0.9 19.7 458.8 0.6 13.3 458.6 0.7 16.1 455.7 0.7 16.1462.2 0.7 15.8 473.9 0.6 13.9 470.4 0.7 15.3 462.8 0.8 19.2 459.5 0.9 19.8 461.6 0.6 13.3 461.0 0.7 16.1 458.2 0.7 16.1464.8 0.7 15.8 477.0 0.6 13.9 473.7 0.7 15.3 465.7 0.9 19.2 462.3 0.9 19.9 463.6 0.6 13.3 463.8 0.7 16.1 460.9 0.7 16.1467.5 0.7 15.8 479.6 0.6 13.9 476.3 0.7 15.4 468.1 0.9 19.3 465.1 0.9 19.9 467.1 0.6 13.3 466.4 0.7 16.2 463.8 0.7 16.2470.5 0.7 15.8 482.5 0.6 14.0 478.9 0.7 15.3 470.8 0.9 19.3 467.3 0.9 20.0 469.5 0.6 13.3 469.3 0.7 16.2 466.3 0.7 16.2472.9 0.7 15.8 484.7 0.6 14.0 482.4 0.7 15.4 474.0 0.9 19.3 470.6 0.9 20.0 472.1 0.6 13.3 472.2 0.7 16.2 469.4 0.7 16.2475.9 0.7 15.8 487.2 0.6 14.0 484.6 0.7 15.4 476.4 0.9 19.3 472.6 0.9 20.1 475.2 0.6 13.3 474.3 0.7 16.2 471.5 0.7 16.2478.0 0.7 15.8 490.3 0.7 14.0 487.5 0.7 15.4 479.4 0.9 19.3 475.5 0.9 20.1 477.4 0.6 13.3 477.0 0.7 16.2 474.9 0.7 16.2480.3 0.7 15.8 491.9 0.7 14.0 489.8 0.7 15.4 481.7 0.9 19.3 478.1 0.9 20.1 480.8 0.6 13.4 479.9 0.7 16.2 477.2 0.7 16.2483.5 0.7 15.8 494.3 0.7 14.1 491.9 0.7 15.4 485.0 0.9 19.3 480.4 0.9 20.2 483.0 0.6 13.4 482.0 0.7 16.2 480.4 0.7 16.2485.9 0.7 15.9 495.4 0.7 14.1 493.9 0.7 15.5 487.4 0.9 19.3 483.6 0.9 20.2 485.8 0.6 13.4 484.7 0.7 16.2 483.4 0.7 16.2487.9 0.7 15.9 497.1 0.7 14.1 495.0 0.7 15.5 490.3 0.9 19.3 486.3 0.9 20.3 488.5 0.6 13.4 487.9 0.8 16.3 485.4 0.8 16.2490.4 0.7 15.9 497.8 0.7 14.1 496.6 0.7 15.5 491.7 0.9 19.4 488.5 0.9 20.4 490.2 0.6 13.4 489.7 0.8 16.3 488.2 0.8 16.3491.5 0.7 15.9 499.0 0.7 14.2 497.0 0.7 15.6 494.1 0.9 19.4 490.4 0.9 20.4 492.8 0.6 13.4 491.9 0.8 16.3 489.5 0.8 16.3493.6 0.7 16.0 499.4 0.7 14.2 498.6 0.7 15.6 494.8 0.9 19.5 492.0 1.0 20.5 494.0 0.6 13.4 493.0 0.8 16.3 491.9 0.8 16.3494.2 0.8 16.0 500.2 0.7 14.2 498.8 0.7 15.6 496.6 0.9 19.5 493.6 1.0 20.5 495.9 0.6 13.5 494.9 0.8 16.4 492.8 0.8 16.3495.6 0.8 16.0 499.9 0.7 15.6 496.9 0.9 19.5 494.5 1.0 20.6 496.7 0.6 13.5 495.5 0.8 16.4 494.5 0.8 16.4496.2 0.8 16.1 500.1 0.7 15.7 498.3 0.9 19.6 495.8 1.0 20.6 498.1 0.6 13.5 497.1 0.8 16.4 495.1 0.8 16.4497.2 0.8 16.1 501.0 0.7 15.7 498.3 0.9 19.6 496.2 1.0 20.7 498.8 0.6 13.5 497.3 0.8 16.5 496.3 0.8 16.4497.6 0.8 16.1 499.5 0.9 19.6 497.2 1.0 20.7 499.7 0.6 13.6 498.6 0.8 16.5 496.7 0.8 16.5498.4 0.8 16.1 499.4 0.9 19.7 497.3 1.0 20.7 500.2 0.6 13.6 498.6 0.8 16.5 497.6 0.8 16.5498.6 0.8 16.1 500.5 0.9 19.7 498.1 1.0 20.8 499.7 0.8 16.6 498.0 0.8 16.5499.3 0.8 16.1 498.2 1.0 20.8 499.5 0.8 16.6 498.7 0.8 16.5499.3 0.8 16.2 499.1 1.0 20.8 500.5 0.8 16.6 498.7 0.8 16.5500.1 0.8 16.2 499.0 1.0 20.8 499.3 0.8 16.6499.7 0.8 16.2 499.7 1.0 20.8 499.4 0.8 16.6500.4 0.8 16.2 499.6 1.0 20.9 499.8 0.8 16.6
500.1 1.0 20.9 500.0 0.8 16.6500.2 0.8 16.6
Colmonoy DMD WAFER 316-420 WAFER 16221-316L
Raw Data from DilatometerStellite 6 DMD Tool Steel-H13 DMD 420SS DMD 316L SS DMD AlBr2 DMD
196
Section 2 of table (remaining samples):
TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
23.41 0.00 5.35 25.74 0.00 11.97 25.02 0.00 5.71 33.88 0.00 17.55 24.14 0.00 8.79 25.13 0.00 8.24 25.71 0.00 7.9523.84 0.00 4.74 26.25 0.00 10.41 25.60 0.00 4.32 34.62 0.00 14.72 24.73 0.00 7.13 25.62 0.00 6.99 26.20 0.00 7.2124.30 0.00 4.66 26.78 0.00 10.09 26.12 0.00 3.92 35.27 0.00 12.63 25.41 0.00 6.96 26.11 0.00 6.35 26.67 0.00 6.4224.75 0.00 4.95 27.23 0.00 8.90 26.61 0.00 3.65 35.91 0.00 11.87 26.08 0.00 6.65 26.57 0.00 6.05 27.14 0.00 5.6825.39 0.00 4.53 27.87 0.00 8.45 27.15 0.00 3.37 36.51 0.00 10.87 26.82 0.00 6.48 27.22 0.00 5.55 27.80 0.00 5.0026.28 0.00 4.34 28.70 0.00 7.66 27.96 0.00 3.12 37.24 0.01 9.97 27.48 0.00 6.56 28.09 0.00 5.11 28.62 0.00 4.4827.29 0.00 4.41 29.55 0.00 7.33 28.94 0.00 2.95 38.11 0.01 9.07 28.20 0.00 6.30 28.99 0.00 4.66 29.61 0.00 4.2328.22 0.00 4.36 30.46 0.00 7.24 30.03 0.00 3.11 39.19 0.01 8.30 29.02 0.00 6.27 29.97 0.00 4.77 30.57 0.00 4.3129.14 0.00 4.40 31.31 0.01 7.09 31.04 0.00 3.21 40.35 0.01 7.89 29.98 0.00 6.32 30.94 0.00 4.83 31.58 0.00 4.2630.12 0.00 4.59 32.20 0.01 6.94 31.95 0.00 3.37 41.47 0.01 7.70 30.87 0.00 6.20 31.84 0.00 4.77 32.47 0.00 4.3330.99 0.00 4.74 33.30 0.01 6.73 32.90 0.00 3.52 42.44 0.01 7.51 31.89 0.01 6.10 32.86 0.00 4.79 33.39 0.00 4.3031.96 0.00 4.80 34.62 0.01 6.61 33.99 0.00 3.58 43.55 0.01 7.34 33.14 0.01 6.03 33.94 0.00 4.79 34.41 0.00 4.3333.18 0.01 4.95 35.90 0.01 6.55 35.23 0.00 3.71 44.79 0.01 7.33 34.37 0.01 6.09 35.22 0.01 4.80 35.31 0.00 4.3734.31 0.01 5.09 37.10 0.01 6.60 36.54 0.00 3.80 46.01 0.01 7.31 35.65 0.01 6.15 36.42 0.01 4.89 36.40 0.01 4.3135.40 0.01 5.16 38.34 0.01 6.65 37.72 0.01 3.90 47.12 0.01 7.26 36.78 0.01 6.17 37.53 0.01 4.99 37.79 0.01 4.3136.66 0.01 5.26 39.45 0.01 6.66 38.89 0.01 4.04 48.44 0.01 7.22 38.08 0.01 6.21 38.75 0.01 5.05 39.20 0.01 4.3438.13 0.01 5.28 40.77 0.01 6.67 40.17 0.01 4.16 49.91 0.01 7.20 39.47 0.01 6.20 40.12 0.01 5.16 40.57 0.01 4.5139.65 0.01 5.37 42.30 0.01 6.70 41.67 0.01 4.32 51.44 0.01 7.22 41.05 0.01 6.23 41.59 0.01 5.29 41.99 0.01 4.6441.13 0.01 5.50 43.69 0.01 6.81 43.15 0.01 4.52 52.81 0.01 7.25 42.67 0.01 6.34 43.05 0.01 5.48 43.29 0.01 4.7642.43 0.01 5.58 45.00 0.01 6.91 44.62 0.01 4.74 54.21 0.02 7.25 44.09 0.01 6.45 44.38 0.01 5.64 44.89 0.01 4.8743.89 0.01 5.71 46.47 0.02 6.95 45.96 0.01 4.93 55.78 0.02 7.24 45.53 0.01 6.57 45.80 0.01 5.81 46.43 0.01 5.0245.24 0.01 5.87 48.19 0.02 7.02 47.38 0.01 5.10 57.57 0.02 7.26 46.94 0.02 6.68 47.13 0.01 5.96 48.02 0.01 5.1746.66 0.01 5.94 49.87 0.02 7.15 48.89 0.01 5.29 59.24 0.02 7.34 48.50 0.02 6.77 48.54 0.01 6.12 49.44 0.01 5.2848.21 0.02 6.01 51.36 0.02 7.21 50.30 0.01 5.46 60.89 0.02 7.42 50.08 0.02 6.88 50.18 0.02 6.24 50.95 0.01 5.4049.90 0.02 6.12 52.89 0.02 7.29 51.81 0.02 5.65 62.44 0.02 7.47 51.70 0.02 6.98 51.89 0.02 6.37 52.81 0.02 5.5051.74 0.02 6.23 54.72 0.02 7.37 53.48 0.02 5.85 64.32 0.02 7.52 53.46 0.02 7.09 53.76 0.02 6.53 54.55 0.02 5.6553.37 0.02 6.37 56.54 0.02 7.47 55.00 0.02 6.01 66.19 0.03 7.59 55.06 0.02 7.21 55.44 0.02 6.71 56.35 0.02 5.8055.10 0.02 6.45 58.29 0.03 7.57 56.64 0.02 6.19 67.93 0.03 7.68 56.79 0.02 7.29 57.15 0.02 6.85 58.10 0.02 5.9657.01 0.02 6.51 60.02 0.03 7.72 58.44 0.02 6.39 69.60 0.03 7.75 58.82 0.03 7.36 58.91 0.02 6.98 59.79 0.02 6.1159.05 0.02 6.59 61.74 0.03 7.88 60.37 0.02 6.59 71.56 0.03 7.80 60.89 0.03 7.47 60.70 0.03 7.14 61.61 0.02 6.2661.03 0.03 6.69 63.30 0.03 8.02 62.08 0.03 6.78 73.56 0.03 7.89 62.86 0.03 7.59 62.56 0.03 7.31 63.27 0.02 6.4162.73 0.03 6.82 65.15 0.03 8.14 63.82 0.03 6.97 75.42 0.03 7.96 64.71 0.03 7.69 64.26 0.03 7.43 64.91 0.03 6.6064.63 0.03 6.98 67.27 0.04 8.25 65.81 0.03 7.17 77.37 0.04 8.03 66.71 0.03 7.79 66.16 0.03 7.57 66.65 0.03 6.7166.58 0.03 7.06 69.27 0.04 8.40 67.75 0.03 7.39 79.46 0.04 8.07 68.68 0.04 7.91 68.26 0.03 7.70 68.51 0.03 6.8368.68 0.03 7.18 71.29 0.04 8.57 69.65 0.03 7.56 81.63 0.04 8.14 70.73 0.04 8.05 70.19 0.04 7.86 70.65 0.03 6.9270.70 0.04 7.30 73.17 0.04 8.72 71.53 0.04 7.75 83.55 0.04 8.22 72.68 0.04 8.14 72.19 0.04 8.01 72.66 0.03 7.0772.51 0.04 7.42 75.27 0.04 8.90 73.56 0.04 7.94 85.59 0.04 8.27 74.80 0.04 8.23 74.23 0.04 8.16 74.65 0.04 7.1874.61 0.04 7.57 77.26 0.05 9.05 75.54 0.04 8.10 87.64 0.05 8.36 77.06 0.04 8.34 76.09 0.04 8.31 76.65 0.04 7.3176.69 0.04 7.73 79.20 0.05 9.20 77.61 0.04 8.27 89.73 0.05 8.46 79.22 0.05 8.45 78.08 0.05 8.43 78.87 0.04 7.4378.68 0.04 7.85 81.30 0.05 9.35 79.69 0.05 8.45 91.75 0.05 8.52 81.30 0.05 8.53 80.14 0.05 8.54 80.87 0.04 7.5680.91 0.05 7.97 83.20 0.06 9.49 81.69 0.05 8.63 93.84 0.05 8.59 83.35 0.05 8.63 82.35 0.05 8.67 82.97 0.04 7.6883.04 0.05 8.08 85.38 0.06 9.65 83.79 0.05 8.80 96.07 0.05 8.68 85.62 0.05 8.73 84.32 0.05 8.80 85.10 0.05 7.7985.12 0.05 8.21 87.48 0.06 9.78 85.73 0.06 8.94 98.19 0.06 8.74 87.63 0.06 8.84 86.36 0.06 8.92 87.34 0.05 7.9387.2 0.1 8.4 89.6 0.1 9.9 87.9 0.1 9.1 100.5 0.1 8.8 89.8 0.1 8.9 88.5 0.1 9.1 89.4 0.1 8.089.1 0.1 8.5 91.8 0.1 10.0 90.1 0.1 9.2 102.9 0.1 8.9 91.9 0.1 9.1 90.6 0.1 9.2 91.5 0.1 8.291.2 0.1 8.6 94.2 0.1 10.1 92.3 0.1 9.4 105.2 0.1 9.0 94.0 0.1 9.2 92.8 0.1 9.3 93.8 0.1 8.393.1 0.1 8.7 96.3 0.1 10.3 94.5 0.1 9.5 107.5 0.1 9.0 96.3 0.1 9.3 94.9 0.1 9.4 96.0 0.1 8.495.6 0.1 8.9 98.8 0.1 10.4 96.7 0.1 9.6 109.6 0.1 9.1 98.4 0.1 9.4 97.2 0.1 9.5 98.1 0.1 8.598.1 0.1 8.9 100.9 0.1 10.5 98.9 0.1 9.8 111.9 0.1 9.2 100.7 0.1 9.4 99.4 0.1 9.6 100.5 0.1 8.6
100.4 0.1 9.0 103.2 0.1 10.7 101.2 0.1 9.9 114.2 0.1 9.2 103.2 0.1 9.5 101.7 0.1 9.7 102.9 0.1 8.7102.6 0.1 9.1 105.6 0.1 10.8 103.4 0.1 10.1 116.7 0.1 9.3 105.4 0.1 9.6 104.1 0.1 9.8 105.0 0.1 8.8104.9 0.1 9.3 107.7 0.1 10.9 105.9 0.1 10.2 119.1 0.1 9.4 107.7 0.1 9.7 106.4 0.1 9.9 107.3 0.1 9.0107.3 0.1 9.4 110.2 0.1 11.0 108.1 0.1 10.4 121.3 0.1 9.4 110.2 0.1 9.8 108.8 0.1 10.0 109.5 0.1 9.1109.8 0.1 9.5 112.6 0.1 11.1 110.3 0.1 10.5 123.7 0.1 9.5 112.8 0.1 9.9 111.1 0.1 10.1 111.8 0.1 9.2112.1 0.1 9.6 115.1 0.1 11.2 112.7 0.1 10.6 125.9 0.1 9.5 115.0 0.1 10.0 113.3 0.1 10.2 114.2 0.1 9.3114.5 0.1 9.7 117.3 0.1 11.3 115.1 0.1 10.7 128.5 0.1 9.6 117.3 0.1 10.0 115.5 0.1 10.3 116.5 0.1 9.4117.1 0.1 9.8 119.7 0.1 11.4 117.3 0.1 10.9 131.0 0.1 9.7 119.5 0.1 10.1 118.0 0.1 10.4 118.9 0.1 9.5119.3 0.1 9.9 122.2 0.1 11.5 119.9 0.1 11.0 133.3 0.1 9.7 122.0 0.1 10.2 120.1 0.1 10.5 121.3 0.1 9.5121.7 0.1 10.0 124.8 0.1 11.6 122.2 0.1 11.2 135.9 0.1 9.8 124.4 0.1 10.3 122.5 0.1 10.6 123.8 0.1 9.6124.1 0.1 10.1 127.4 0.1 11.7 124.7 0.1 11.3 138.4 0.1 9.9 126.7 0.1 10.4 124.8 0.1 10.7 126.3 0.1 9.7126.5 0.1 10.1 129.9 0.1 11.8 127.3 0.1 11.5 140.8 0.1 9.9 129.0 0.1 10.5 127.2 0.1 10.8 128.8 0.1 9.8129.2 0.1 10.2 132.3 0.1 11.9 129.9 0.1 11.6 143.4 0.1 10.0 131.7 0.1 10.5 129.7 0.1 10.9 131.1 0.1 10.0131.6 0.1 10.3 134.7 0.1 12.0 132.2 0.1 11.7 145.8 0.1 10.0 134.3 0.1 10.6 132.1 0.1 11.0 133.6 0.1 10.0134.0 0.1 10.4 137.4 0.1 12.1 134.9 0.1 11.8 148.1 0.1 10.1 136.6 0.1 10.7 134.8 0.1 11.0 136.1 0.1 10.1136.6 0.1 10.5 140.2 0.1 12.2 137.4 0.1 12.0 150.5 0.1 10.2 139.4 0.1 10.8 137.3 0.1 11.1 138.6 0.1 10.2139.0 0.1 10.5 142.5 0.1 12.3 139.8 0.1 12.1 153.1 0.1 10.2 142.0 0.1 10.8 139.7 0.1 11.2 141.4 0.1 10.3141.5 0.1 10.6 145.2 0.1 12.4 142.2 0.1 12.2 155.6 0.1 10.3 144.5 0.1 10.9 142.4 0.1 11.3 144.0 0.1 10.4144.0 0.1 10.7 147.5 0.2 12.5 144.8 0.1 12.3 158.2 0.1 10.3 147.1 0.1 11.0 145.2 0.1 11.4 146.6 0.1 10.5146.5 0.1 10.8 150.2 0.2 12.6 147.4 0.2 12.5 160.7 0.1 10.4 149.6 0.1 11.1 147.7 0.1 11.4 149.3 0.1 10.6149.0 0.1 10.9 153.0 0.2 12.7 150.0 0.2 12.6 163.4 0.1 10.4 152.1 0.1 11.2 150.4 0.1 11.5 151.9 0.1 10.6151.6 0.1 10.9 155.6 0.2 12.8 152.6 0.2 12.7 165.8 0.1 10.5 154.7 0.1 11.2 153.0 0.1 11.6 154.6 0.1 10.7154.1 0.1 11.0 158.4 0.2 12.8 155.0 0.2 12.8 168.4 0.1 10.6 157.4 0.2 11.3 155.6 0.2 11.7 157.1 0.1 10.8156.5 0.1 11.1 161.2 0.2 12.9 157.7 0.2 12.9 170.8 0.1 10.6 160.1 0.2 11.4 158.2 0.2 11.8 159.7 0.1 10.9159.3 0.2 11.1 163.6 0.2 13.0 160.1 0.2 13.0 173.7 0.1 10.6 162.7 0.2 11.5 160.8 0.2 11.8 162.2 0.2 11.0162.1 0.2 11.2 166.1 0.2 13.1 162.5 0.2 13.1 176.4 0.2 10.7 165.3 0.2 11.5 163.3 0.2 11.9 164.6 0.2 11.1164.6 0.2 11.3 168.7 0.2 13.2 165.2 0.2 13.2 178.9 0.2 10.7 167.8 0.2 11.6 165.7 0.2 12.0 167.3 0.2 11.1167.5 0.2 11.3 171.2 0.2 13.3 167.9 0.2 13.3 181.7 0.2 10.8 170.6 0.2 11.7 168.6 0.2 12.0 169.9 0.2 11.2170.1 0.2 11.4 174.0 0.2 13.4 170.5 0.2 13.3 184.2 0.2 10.8 173.0 0.2 11.7 171.0 0.2 12.1 172.4 0.2 11.3172.9 0.2 11.4 176.6 0.2 13.4 173.4 0.2 13.4 186.8 0.2 10.9 175.8 0.2 11.8 173.8 0.2 12.2 175.1 0.2 11.4176.0 0.2 11.5 179.3 0.2 13.5 176.0 0.2 13.5 189.2 0.2 10.9 178.6 0.2 11.9 176.4 0.2 12.2 177.6 0.2 11.4178.8 0.2 11.5 182.1 0.2 13.6 178.5 0.2 13.6 192.0 0.2 11.0 181.0 0.2 11.9 179.2 0.2 12.3 180.5 0.2 11.5181.5 0.2 11.6 184.7 0.2 13.6 180.9 0.2 13.7 194.6 0.2 11.1 183.8 0.2 12.0 181.9 0.2 12.4 183.1 0.2 11.5184.3 0.2 11.7 187.5 0.2 13.7 183.6 0.2 13.8 197.4 0.2 11.1 186.2 0.2 12.1 184.4 0.2 12.4 185.7 0.2 11.6187.1 0.2 11.8 190.2 0.2 13.8 186.4 0.2 13.9 199.9 0.2 11.2 188.9 0.2 12.2 187.2 0.2 12.5 188.7 0.2 11.7189.7 0.2 11.9 192.9 0.2 13.9 188.8 0.2 14.0 202.5 0.2 11.2 191.4 0.2 12.2 189.6 0.2 12.6 191.3 0.2 11.7192.1 0.2 11.9 195.4 0.2 14.0 191.5 0.2 14.1 205.0 0.2 11.2 194.2 0.2 12.3 192.4 0.2 12.6 194.0 0.2 11.8194.5 0.2 12.0 198.0 0.2 14.0 194.1 0.2 14.2 207.8 0.2 11.3 196.6 0.2 12.3 195.1 0.2 12.7 196.8 0.2 11.9197.1 0.2 12.1 200.7 0.2 14.1 196.7 0.2 14.3 210.6 0.2 11.3 199.7 0.2 12.4 197.8 0.2 12.8 199.5 0.2 11.9199.7 0.2 12.1 203.5 0.3 14.2 199.2 0.3 14.4 213.1 0.2 11.3 202.4 0.2 12.5 200.2 0.2 12.8 202.3 0.2 12.0202.2 0.2 12.2 206.2 0.3 14.3 201.8 0.3 14.5 215.8 0.2 11.4 205.2 0.2 12.5 203.0 0.2 12.9 204.7 0.2 12.1205.0 0.2 12.2 209.0 0.3 14.4 204.3 0.3 14.5 218.5 0.2 11.4 208.0 0.2 12.6 205.8 0.2 12.9 207.5 0.2 12.1208.0 0.2 12.3 211.6 0.3 14.4 207.2 0.3 14.6 221.5 0.2 11.4 210.8 0.2 12.6 208.4 0.2 13.0 210.2 0.2 12.2210.7 0.2 12.4 214.2 0.3 14.5 209.9 0.3 14.7 224.1 0.2 11.5 213.6 0.2 12.7 210.9 0.2 13.1 212.8 0.2 12.3213.3 0.2 12.4 217.0 0.3 14.6 212.5 0.3 14.8 227.0 0.2 11.5 216.0 0.2 12.8 213.7 0.2 13.1 215.4 0.2 12.3215.9 0.2 12.5 219.5 0.3 14.7 215.3 0.3 14.9 229.7 0.2 11.5 218.8 0.2 12.8 216.3 0.3 13.2 217.9 0.2 12.4218.4 0.2 12.5 222.3 0.3 14.7 217.9 0.3 14.9 232.5 0.2 11.6 221.2 0.3 12.9 219.1 0.3 13.2 221.1 0.2 12.4221.1 0.2 12.6 225.0 0.3 14.8 220.9 0.3 15.0 234.9 0.2 11.6 224.2 0.3 12.9 222.0 0.3 13.3 223.8 0.2 12.5223.6 0.3 12.7 228.0 0.3 14.9 223.5 0.3 15.1 237.4 0.2 11.7 226.9 0.3 13.0 224.8 0.3 13.3 226.4 0.3 12.5226.6 0.3 12.7 230.8 0.3 14.9 226.4 0.3 15.2 240.1 0.2 11.7 229.7 0.3 13.0 227.5 0.3 13.4 229.0 0.3 12.6229.4 0.3 12.7 233.7 0.3 15.0 228.8 0.3 15.3 242.6 0.2 11.8 232.3 0.3 13.1 230.1 0.3 13.4 231.6 0.3 12.6232.0 0.3 12.8 236.3 0.3 15.1 231.8 0.3 15.4 245.4 0.3 11.8 235.0 0.3 13.2 232.9 0.3 13.5 234.6 0.3 12.7234.7 0.3 12.8 238.8 0.3 15.1 234.5 0.3 15.4 247.9 0.3 11.8 237.5 0.3 13.2 235.5 0.3 13.5 237.1 0.3 12.7237.5 0.3 12.9 241.9 0.3 15.2 237.3 0.3 15.5 250.8 0.3 11.9 240.4 0.3 13.3 238.0 0.3 13.6 239.9 0.3 12.8240.2 0.3 12.9 244.5 0.3 15.2 239.9 0.3 15.6 253.3 0.3 11.9 243.2 0.3 13.3 240.9 0.3 13.6 242.6 0.3 12.9242.8 0.3 13.0 247.2 0.3 15.3 243.0 0.3 15.6 255.8 0.3 12.0 246.0 0.3 13.4 244.0 0.3 13.7 245.3 0.3 12.9245.5 0.3 13.0 250.4 0.3 15.3 245.8 0.3 15.7 258.2 0.3 12.0 248.9 0.3 13.4 246.7 0.3 13.7 247.9 0.3 13.0
FGM AlBr-420 FGM 316-TSWafer 316-TS FGM 316-420
Raw Data from DilatometerFGM 16221-316LWAFER AlBr-420 WAFER AlBr-St6
197
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TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha Temp
Expansion
Alpha TempExpansi
onAlpha
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
ｰC %mm/mm/deg C.10^-6
248.1 0.3 13.0 253.1 0.4 15.4 248.4 0.4 15.7 261.0 0.3 12.0 251.6 0.3 13.5 249.9 0.3 13.7 250.6 0.3 13.0250.6 0.3 13.1 256.1 0.4 15.5 251.2 0.4 15.8 263.6 0.3 12.1 254.3 0.3 13.5 252.5 0.3 13.8 253.2 0.3 13.1253.2 0.3 13.1 258.7 0.4 15.5 253.9 0.4 15.9 266.4 0.3 12.1 257.0 0.3 13.6 255.5 0.3 13.8 255.7 0.3 13.1256.0 0.3 13.1 261.5 0.4 15.6 256.5 0.4 15.9 269.3 0.3 12.1 259.7 0.3 13.6 258.1 0.3 13.9 258.6 0.3 13.2258.5 0.3 13.1 263.9 0.4 15.6 259.0 0.4 16.0 271.8 0.3 12.2 262.4 0.3 13.7 260.8 0.3 13.9 261.3 0.3 13.2261.3 0.3 13.1 267.0 0.4 15.6 261.7 0.4 16.1 274.9 0.3 12.2 265.1 0.3 13.7 263.8 0.3 13.9 263.9 0.3 13.3264.1 0.3 13.2 269.7 0.4 15.7 264.4 0.4 16.1 277.5 0.3 12.2 267.8 0.3 13.7 266.2 0.3 14.0 267.0 0.3 13.3267.1 0.3 13.2 272.6 0.4 15.7 266.8 0.4 16.2 280.4 0.3 12.2 270.4 0.3 13.8 269.2 0.3 14.0 269.7 0.3 13.4269.6 0.3 13.2 275.1 0.4 15.7 269.6 0.4 16.2 283.1 0.3 12.3 273.1 0.3 13.8 271.8 0.3 14.0 272.4 0.3 13.4272.5 0.3 13.3 278.1 0.4 15.8 272.2 0.4 16.3 285.9 0.3 12.3 275.8 0.3 13.9 274.8 0.4 14.1 275.7 0.3 13.5275.2 0.3 13.3 280.7 0.4 15.8 274.9 0.4 16.3 288.6 0.3 12.3 278.3 0.4 13.9 277.5 0.4 14.1 278.3 0.3 13.5277.7 0.3 13.3 283.5 0.4 15.8 277.7 0.4 16.4 291.3 0.3 12.3 281.3 0.4 13.9 280.5 0.4 14.1 281.3 0.3 13.6280.8 0.3 13.4 286.2 0.4 15.9 280.3 0.4 16.4 294.0 0.3 12.3 283.9 0.4 14.0 283.2 0.4 14.2 283.9 0.4 13.6283.5 0.4 13.4 288.9 0.4 15.9 283.3 0.4 16.5 297.1 0.3 12.4 287.0 0.4 14.0 286.0 0.4 14.2 286.9 0.4 13.6286.4 0.4 13.4 291.9 0.4 16.0 285.7 0.4 16.5 299.7 0.3 12.4 289.5 0.4 14.0 288.9 0.4 14.2 289.3 0.4 13.7288.9 0.4 13.4 294.4 0.4 16.0 288.6 0.4 16.6 302.8 0.3 12.4 292.4 0.4 14.1 291.4 0.4 14.3 292.2 0.4 13.7292.2 0.4 13.5 297.5 0.4 16.0 291.4 0.4 16.6 305.4 0.3 12.4 295.0 0.4 14.1 294.5 0.4 14.3 294.7 0.4 13.8294.9 0.4 13.5 300.0 0.4 16.0 294.3 0.4 16.6 307.9 0.3 12.4 297.7 0.4 14.1 297.1 0.4 14.3 297.2 0.4 13.8297.6 0.4 13.5 302.8 0.4 16.1 297.1 0.5 16.7 311.2 0.3 12.4 300.7 0.4 14.2 299.9 0.4 14.3 300.0 0.4 13.8300.2 0.4 13.6 305.6 0.5 16.1 299.9 0.5 16.7 313.9 0.4 12.5 303.5 0.4 14.2 302.7 0.4 14.4 302.6 0.4 13.9303.1 0.4 13.6 308.3 0.5 16.1 302.8 0.5 16.7 316.9 0.4 12.5 306.2 0.4 14.2 305.2 0.4 14.4 305.8 0.4 13.9305.5 0.4 13.6 311.0 0.5 16.2 305.3 0.5 16.7 319.5 0.4 12.5 308.9 0.4 14.3 307.7 0.4 14.4 308.5 0.4 13.9308.4 0.4 13.7 313.6 0.5 16.2 308.5 0.5 16.8 322.5 0.4 12.5 311.4 0.4 14.3 310.5 0.4 14.5 311.5 0.4 14.0311.2 0.4 13.7 316.9 0.5 16.2 311.1 0.5 16.8 325.1 0.4 12.6 314.7 0.4 14.3 312.8 0.4 14.5 314.0 0.4 14.0313.9 0.4 13.7 319.3 0.5 16.3 313.8 0.5 16.8 327.8 0.4 12.6 317.5 0.4 14.3 315.5 0.4 14.6 316.6 0.4 14.0316.9 0.4 13.8 322.1 0.5 16.3 316.6 0.5 16.9 330.2 0.4 12.6 320.4 0.4 14.3 317.9 0.4 14.6 319.4 0.4 14.1319.4 0.4 13.8 324.9 0.5 16.3 319.1 0.5 16.9 332.9 0.4 12.6 323.5 0.4 14.4 320.7 0.4 14.6 322.1 0.4 14.1322.2 0.4 13.8 327.5 0.5 16.3 322.4 0.5 17.0 335.5 0.4 12.6 326.0 0.4 14.4 323.4 0.4 14.7 324.9 0.4 14.2325.0 0.4 13.9 330.6 0.5 16.4 325.1 0.5 17.0 338.3 0.4 12.7 329.3 0.4 14.4 325.7 0.4 14.7 327.7 0.4 14.2327.4 0.4 13.9 333.3 0.5 16.4 328.0 0.5 17.1 341.4 0.4 12.7 331.6 0.4 14.4 329.0 0.4 14.7 330.6 0.4 14.2330.7 0.4 14.0 336.1 0.5 16.4 330.7 0.5 17.1 343.8 0.4 12.7 335.1 0.5 14.5 331.3 0.5 14.7 333.4 0.4 14.3333.4 0.4 14.0 338.7 0.5 16.4 333.6 0.5 17.1 347.1 0.4 12.7 337.6 0.5 14.5 334.2 0.5 14.7 335.8 0.4 14.3336.4 0.4 14.0 341.5 0.5 16.5 336.4 0.5 17.2 349.7 0.4 12.7 340.5 0.5 14.6 336.7 0.5 14.8 339.1 0.4 14.3339.1 0.4 14.0 344.2 0.5 16.5 338.7 0.5 17.2 352.6 0.4 12.7 342.8 0.5 14.6 339.6 0.5 14.8 341.7 0.5 14.4341.9 0.4 14.1 346.7 0.5 16.5 342.2 0.5 17.2 355.7 0.4 12.8 345.5 0.5 14.6 342.4 0.5 14.8 344.7 0.5 14.4344.8 0.5 14.1 350.0 0.5 16.5 344.5 0.6 17.3 358.3 0.4 12.8 348.4 0.5 14.6 344.7 0.5 14.8 347.5 0.5 14.4347.1 0.5 14.1 352.6 0.5 16.5 347.3 0.6 17.3 361.2 0.4 12.8 350.9 0.5 14.7 347.8 0.5 14.8 350.4 0.5 14.5350.4 0.5 14.1 355.3 0.5 16.6 350.0 0.6 17.3 363.5 0.4 12.8 354.0 0.5 14.7 350.4 0.5 14.8 353.0 0.5 14.5353.0 0.5 14.2 357.8 0.6 16.6 352.9 0.6 17.4 366.9 0.4 12.8 356.5 0.5 14.7 353.3 0.5 14.9 355.4 0.5 14.5355.7 0.5 14.2 360.9 0.6 16.6 355.7 0.6 17.4 369.4 0.4 12.8 359.2 0.5 14.7 355.8 0.5 14.9 358.5 0.5 14.5358.3 0.5 14.2 363.5 0.6 16.6 358.0 0.6 17.4 372.3 0.4 12.8 362.1 0.5 14.8 358.5 0.5 14.9 360.9 0.5 14.5361.0 0.5 14.2 366.1 0.6 16.7 361.4 0.6 17.5 375.0 0.4 12.8 364.5 0.5 14.8 361.4 0.5 14.9 364.0 0.5 14.6364.1 0.5 14.3 369.0 0.6 16.7 363.9 0.6 17.5 377.4 0.4 12.8 367.7 0.5 14.8 364.0 0.5 14.9 366.4 0.5 14.6366.7 0.5 14.3 371.2 0.6 16.7 366.8 0.6 17.5 380.7 0.4 12.9 370.0 0.5 14.8 366.7 0.5 15.0 369.5 0.5 14.6369.6 0.5 14.3 374.8 0.6 16.7 369.6 0.6 17.6 383.2 0.5 12.9 373.1 0.5 14.8 369.1 0.5 15.0 371.8 0.5 14.6372.2 0.5 14.4 377.3 0.6 16.7 372.1 0.6 17.6 386.0 0.5 12.9 375.8 0.5 14.8 372.6 0.5 15.0 375.3 0.5 14.7375.2 0.5 14.4 380.1 0.6 16.7 375.1 0.6 17.6 388.8 0.5 12.9 378.3 0.5 14.8 374.9 0.5 15.0 377.7 0.5 14.7377.9 0.5 14.4 382.9 0.6 16.8 377.6 0.6 17.6 391.5 0.5 12.9 381.5 0.5 14.9 377.8 0.5 15.0 380.7 0.5 14.7380.8 0.5 14.4 385.5 0.6 16.8 380.5 0.6 17.7 394.4 0.5 12.9 384.1 0.5 14.9 380.6 0.5 15.0 383.5 0.5 14.8383.6 0.5 14.4 388.5 0.6 16.8 382.9 0.6 17.7 396.7 0.5 12.9 386.7 0.5 14.9 383.1 0.5 15.0 385.7 0.5 14.8385.9 0.5 14.4 390.8 0.6 16.8 386.0 0.6 17.8 400.0 0.5 12.9 389.2 0.5 14.9 386.0 0.5 15.1 389.0 0.5 14.8389.2 0.5 14.5 394.0 0.6 16.8 388.7 0.7 17.8 402.5 0.5 12.9 392.0 0.6 14.9 388.3 0.5 15.1 391.5 0.5 14.8391.5 0.5 14.5 396.7 0.6 16.9 391.3 0.7 17.8 405.2 0.5 12.9 394.8 0.6 15.0 391.6 0.6 15.1 394.3 0.5 14.8394.4 0.5 14.5 399.6 0.6 16.9 394.3 0.7 17.9 408.1 0.5 12.9 397.7 0.6 15.0 393.9 0.6 15.1 397.0 0.6 14.9397.2 0.5 14.5 402.6 0.6 16.9 397.1 0.7 17.9 410.6 0.5 12.9 400.5 0.6 15.0 396.7 0.6 15.1 399.8 0.6 14.9400.0 0.6 14.6 405.1 0.6 16.9 399.7 0.7 17.9 413.6 0.5 13.0 402.6 0.6 15.0 399.7 0.6 15.1 402.6 0.6 14.9402.7 0.6 14.6 408.0 0.6 16.9 402.0 0.7 17.9 415.7 0.5 13.0 406.2 0.6 15.0 402.2 0.6 15.1 404.8 0.6 15.0404.9 0.6 14.6 410.0 0.7 16.9 405.0 0.7 18.0 418.4 0.5 13.0 408.5 0.6 15.0 405.3 0.6 15.1 408.0 0.6 15.0408.3 0.6 14.6 413.4 0.7 17.0 407.7 0.7 18.0 421.3 0.5 13.0 411.5 0.6 15.0 407.4 0.6 15.1 410.2 0.6 15.0410.7 0.6 14.7 415.8 0.7 17.0 410.5 0.7 18.0 423.8 0.5 13.0 414.2 0.6 15.1 410.9 0.6 15.1 413.4 0.6 15.0413.3 0.6 14.7 418.5 0.7 17.0 413.2 0.7 18.0 426.9 0.5 13.0 416.4 0.6 15.1 413.0 0.6 15.1 416.0 0.6 15.1416.0 0.6 14.7 421.2 0.7 17.0 415.4 0.7 18.0 429.6 0.5 13.0 419.8 0.6 15.1 416.0 0.6 15.1 418.7 0.6 15.1418.6 0.6 14.7 423.9 0.7 17.0 418.2 0.7 18.1 432.0 0.5 13.0 422.0 0.6 15.1 418.6 0.6 15.2 421.6 0.6 15.1421.4 0.6 14.7 426.7 0.7 17.1 421.1 0.7 18.1 435.3 0.5 13.0 425.1 0.6 15.1 421.3 0.6 15.2 423.8 0.6 15.1424.4 0.6 14.7 428.7 0.7 17.1 423.4 0.7 18.1 437.5 0.5 13.0 427.9 0.6 15.1 423.9 0.6 15.2 427.4 0.6 15.2427.2 0.6 14.7 432.5 0.7 17.1 426.9 0.7 18.1 440.7 0.5 13.0 430.7 0.6 15.2 426.2 0.6 15.2 429.9 0.6 15.2430.0 0.6 14.7 434.5 0.7 17.1 429.1 0.7 18.1 443.0 0.5 13.0 433.4 0.6 15.2 428.8 0.6 15.2 432.6 0.6 15.2432.4 0.6 14.7 437.4 0.7 17.1 432.1 0.7 18.2 446.1 0.5 13.1 435.5 0.6 15.2 431.6 0.6 15.2 435.3 0.6 15.2435.9 0.6 14.7 440.1 0.7 17.1 434.8 0.7 18.2 448.6 0.5 13.1 438.3 0.6 15.2 433.7 0.6 15.3 438.2 0.6 15.2438.3 0.6 14.7 442.8 0.7 17.1 437.2 0.8 18.2 451.1 0.5 13.1 441.2 0.6 15.2 436.7 0.6 15.3 440.8 0.6 15.3441.0 0.6 14.7 445.7 0.7 17.2 440.0 0.8 18.2 454.2 0.6 13.1 443.5 0.6 15.2 439.4 0.6 15.3 442.9 0.6 15.3443.9 0.6 14.8 447.7 0.7 17.2 442.8 0.8 18.2 456.4 0.6 13.1 447.0 0.6 15.2 441.5 0.6 15.3 446.5 0.6 15.3446.6 0.6 14.8 451.4 0.7 17.2 445.5 0.8 18.2 459.6 0.6 13.1 449.6 0.6 15.2 445.0 0.6 15.3 448.7 0.7 15.3449.3 0.6 14.8 453.6 0.7 17.2 448.3 0.8 18.3 461.7 0.6 13.1 452.5 0.7 15.3 447.3 0.6 15.3 451.6 0.7 15.3451.4 0.6 14.8 456.5 0.7 17.2 450.7 0.8 18.3 465.0 0.6 13.1 455.2 0.7 15.3 450.3 0.7 15.3 454.4 0.7 15.4454.1 0.6 14.8 459.4 0.7 17.3 453.2 0.8 18.3 467.5 0.6 13.2 457.6 0.7 15.3 453.3 0.7 15.3 456.9 0.7 15.4457.1 0.6 14.8 462.2 0.8 17.3 456.8 0.8 18.3 469.7 0.6 13.2 460.8 0.7 15.3 455.7 0.7 15.3 459.7 0.7 15.4459.3 0.6 14.8 464.8 0.8 17.3 458.9 0.8 18.3 472.5 0.6 13.2 462.9 0.7 15.3 458.8 0.7 15.3 462.1 0.7 15.4462.5 0.7 14.9 467.1 0.8 17.3 461.9 0.8 18.3 475.5 0.6 13.2 465.8 0.7 15.3 461.0 0.7 15.3 464.5 0.7 15.4465.0 0.7 14.9 469.6 0.8 17.3 464.6 0.8 18.4 477.6 0.6 13.2 468.5 0.7 15.3 464.2 0.7 15.3 467.8 0.7 15.5468.0 0.7 14.9 472.5 0.8 17.3 467.1 0.8 18.4 481.1 0.6 13.2 470.5 0.7 15.3 466.5 0.7 15.4 469.9 0.7 15.5470.7 0.7 14.9 474.7 0.8 17.3 470.2 0.8 18.4 482.9 0.6 13.2 473.9 0.7 15.3 468.5 0.7 15.4 473.0 0.7 15.5472.7 0.7 14.9 478.4 0.8 17.3 473.2 0.8 18.4 486.4 0.6 13.2 476.5 0.7 15.4 472.1 0.7 15.4 475.5 0.7 15.5475.7 0.7 14.9 480.9 0.8 17.4 475.5 0.8 18.4 488.0 0.6 13.3 478.8 0.7 15.4 474.2 0.7 15.4 477.6 0.7 15.5478.6 0.7 14.9 483.3 0.8 17.4 478.7 0.8 18.4 490.3 0.6 13.3 481.5 0.7 15.4 477.3 0.7 15.4 480.5 0.7 15.6480.7 0.7 14.9 487.1 0.8 17.4 480.6 0.8 18.4 491.7 0.6 13.3 484.4 0.7 15.4 480.1 0.7 15.4 483.3 0.7 15.6483.3 0.7 14.9 488.9 0.8 17.4 484.3 0.8 18.5 493.2 0.6 13.3 487.1 0.7 15.4 482.6 0.7 15.4 485.4 0.7 15.6486.6 0.7 14.9 491.6 0.8 17.5 486.3 0.9 18.6 494.4 0.6 13.4 489.2 0.7 15.4 485.4 0.7 15.5 488.3 0.7 15.6488.8 0.7 14.9 492.6 0.8 17.5 488.6 0.9 18.6 495.1 0.6 13.4 491.0 0.7 15.5 487.1 0.7 15.5 490.0 0.7 15.7491.0 0.7 15.0 494.8 0.8 17.5 490.8 0.9 18.7 496.3 0.6 13.4 492.7 0.7 15.5 489.4 0.7 15.5 492.0 0.7 15.7492.2 0.7 15.0 495.5 0.8 17.5 491.9 0.9 18.7 496.6 0.6 13.5 493.7 0.7 15.5 490.3 0.7 15.5 493.2 0.7 15.8493.9 0.7 15.0 497.1 0.8 17.6 493.8 0.9 18.8 497.5 0.6 13.5 495.1 0.7 15.5 492.4 0.7 15.6 494.7 0.7 15.8494.5 0.7 15.1 497.4 0.8 17.6 494.2 0.9 18.8 497.6 0.6 13.5 495.6 0.7 15.6 493.1 0.7 15.6 495.5 0.7 15.8495.9 0.7 15.1 498.7 0.8 17.7 495.8 0.9 18.9 498.5 0.6 13.5 496.9 0.7 15.6 494.4 0.7 15.6 496.5 0.7 15.9496.1 0.7 15.1 498.8 0.8 17.7 495.9 0.9 18.9 498.4 0.6 13.5 497.2 0.7 15.6 495.2 0.7 15.7 497.3 0.8 15.9497.2 0.7 15.2 499.8 0.8 17.7 497.3 0.9 19.0 499.2 0.6 13.6 498.2 0.7 15.6 495.9 0.7 15.7 498.0 0.8 16.0497.2 0.7 15.2 499.7 0.8 17.7 497.4 0.9 19.0 498.9 0.6 13.6 498.4 0.7 15.6 496.5 0.7 15.7 498.5 0.8 16.0498.3 0.7 15.2 500.8 0.8 17.7 498.3 0.9 19.0 499.6 0.6 13.6 499.2 0.7 15.7 497.0 0.7 15.7 499.4 0.8 16.0498.1 0.7 15.2 498.4 0.9 19.0 499.2 0.6 13.6 499.3 0.7 15.7 497.6 0.7 15.7 499.2 0.8 16.0499.1 0.7 15.2 499.2 0.9 19.1 500.1 0.6 13.6 499.8 0.7 15.7 498.0 0.7 15.8 500.0 0.8 16.1498.7 0.7 15.2 499.2 0.9 19.1 500.0 0.7 15.7 498.2 0.7 15.8 499.8 0.8 16.1499.8 0.7 15.3 499.9 0.9 19.1 498.6 0.7 15.8 500.6 0.8 16.1499.5 0.7 15.2 499.5 0.9 19.1 498.8 0.8 15.8500.3 0.7 15.3 500.3 0.9 19.1 499.1 0.8 15.8
499.1 0.8 15.8499.4 0.8 15.8499.4 0.8 15.8499.8 0.8 15.9
FGM 316-420 FGM 16221-316L FGM AlBr-420 FGM 316-TSWAFER AlBr-420 WAFER AlBr-St6 Wafer 316-TS
Raw Data from Dilatometer
198
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