STRUCTURE AND TRIBOLOGICAL PROPERTIES OF POST-SPUTTERED

ANNEALING NICKEL TITANIUM ALLOY COATINGS ONTO 316L

STAINLESS STEEL

ABDUL HADI BIN ABDUL AZIZ

A dissertation submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Mechanical-Materials)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

MAY 2012

iii

Specially dedicated to my beloved parents, brothers and family who have supported

and inspired,

ABDUL AZIZ BIN ABDUL RAHMAN and NURAINI BTE ISYA

iv

ACKNOWLEDGEMENT

In the name of Allah, who is the Gracious, Almighty, Most Merciful and Him

alone are worthy of all praise for giving me the strength to carry out this task.

Alhamdulillah, with His blessing and kindness, I am almost completing my thesis.

First and foremost, I would like to thank my supervisor Dr. Tuty Asma Abu

Bakar, for her valuable advice, guidances and great supervision throughout my

project. I am very grateful that she had generously shared her knowledge in

numerous scientific discussions during my studies. The assistance from the technical

staff is greatly appreciated. I would like to thank all the staff in the Materials Science

Laboratory, Universiti Teknologi Malaysia who have involved either directly or

indirectly throughout my project.

For my beloved parents and family, my deepest appreciation for their

continuous support, encouragement, understanding, love and care. Last but not least,

many thank to all my friends for the ideas and comments in improving my project

and thesis. Once again thanks to all.

v

ABSTRACT

The purpose of this study is to investigate the effect of the post-sputtering

annealing process on the structure and tribological properties of the NiTi shape

memory alloy (SMA) coatings. The NiTi SMA coatings were deposited onto the

316L stainless steel substrates using the sputtering PVD technique. The coating

thickness was measured at approximately 2µm. The unannealed NiTi SMA coating

was determined amorphous based on the differential scanning calorimetry (DSC) and

XRD results. The crystallization temperature of the NiTi SMA coating with a

composition of Ni 57.89%:Ti 42.11% was determined at a temperature of 519.23°C

by the DSC. The post-sputtering annealing process was carried out at the annealing

temperatures of 550°C and 600°C and the annealing times for a duration of 30 and

60 minutes. The unannealed and annealed NiTi SMA coatings were then

characterized to determine their structure and mechanical properties using various

characterization techniques namely optical microscopy, scanning electron

microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD),

surface roughness tester, Rockwell C adhesion test, pin-on-disc wear test and

nanoindentation test. The post-sputtering annealing process was successful in

producing a crystalline Ni-rich NiTi coating with excellent mechanical properties. In

this study, the annealing temperature of 600°C for a period of 30 minutes provided

the optimum adhesion and mechanical properties of the annealed NiTi SMA

coatings. The finding shows the potential of the post-sputtering annealing process to

create an excellent structure and tribological properties of NiTi SMA coatings.

vi

ABSTRAK

Tujuan kajian ini adalah untuk menyiasat kesan proses sepuhlindap terhadap

struktur dan sifat “tribological” bagi lapisan aloi bentuk memori (SMA) NiTi.

Lapisan NiTi SMA telah didepositkan ke atas keluli tahan karat 316L menggunakan

teknik “PVD sputtering”. Ketebalan lapisan NiTi SMA adalah kira-kira 2µm.

Struktur bagi “unannealed” NiTi SMA adalah bersifat “amorphous” berdasarkan

keputusan hasil pemeriksaan DSC dan XRD. Suhu penghabluran semula NiTi SMA

yang berkomposisi Ni 57.89%, Ti 42.11% telah diperolehi pada suhu 519.23°C

menggunakan alat DSC. Proses sepuhlindap telah dijalankan pada suhu sepuh lindap

550°C dan 600°C selama 30 minit dan 60 minit. Lapisan NiTi SMA yang asal dan

yang telah di sepuhlindap dikaji bagi menentukan struktur dan sifat-sifat mekanik

dengan menggunakan pelbagai teknik pencirian seperti mikroskopi optik, mikroskopi

imbasan elektron (SEM), penguji kekasaran permukaan, ujian lekatan “Rockwell”,

ujian haus “pin-on-disc” dan ujian kekerasan “nanoindentation”. Proses sepuhlindap

yang di jalankan telah berjaya dalam menghasilkan lapisan NiTi yang berhablur

dengan sifat-sifat mekanikal yang baik. Dalam kajian ini, proses sepuh lindap pada

suhu 600°C selama 30 minit telah memberikan kesan yang terbaik bagi sifat-sifat

mekanikal dan lekatan bagi lapisan NiTi SMA berbanding dengan sampel yang di

sepuhlindap pada parameter yang lain. Hasil kajian mendapati bahawa proses

sepuhlindap yang dijalankan berpotensi untuk menghasilkan struktur lapisan NiTi

SMA dengan sifat-sifat “tribological” yang sangat baik.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xii

LIST OF FIGURES xiv

LIST OF SYMBOLS / ABBREVIATIONS xviii

LIST OF APPENDICES xxi

viii

1 INTRODUCTION 1

1.1 Background of the Study 1

1.2 Problem Statement 3

1.3 Objective of the Study 4

1.4 Scope of the Study 5

1.5 Structure of the Thesis 6

2 LITERATURE REVIEW 7

2.1 Introduction 7

2.2 Shape Memory Alloys (SMAs) 8

2.3 Nickel Titanium Shape Memory Alloys (NiTi

SMAs)

9

2.3.1 General Principles 9

2.3.2 Thermomechanical Behavior 10

2.3.3 Properties of NiTi SMA 12

2.4 Applications of NiTi SMAs 17

2.5 Coating Techniques 17

2.5.1 Physical Vapor Deposition (PVD)

Technique

18

2.5.1.1 Introduction of PVD Technique 18

2.5.1.2 Magnetron Sputtering Technique 19

2.6 Post-sputtering Annealing Process 22

ix

2.7 Effect of Post-sputtering Annealing Process on

Structure and Tribological Properties of NiTi

SMA Coating

23

2.8 Stainless Steel Material 28

2.8.1 Type of Stainless Steel 28

2.9 Stainless Steel 316L 30

2.9.1 Properties of Stainless Steel 316L 31

2.9.2 Composition of Stainless Steel 316L 35

2.10 Characterization Methods of NiTi SMA Coating 37

2.10.1 Thermal Properties 38

2.10.2 Structural, Surface and Composition

Analysis

40

2.10.3 Mechanical and Tribological Properties 49

3 RESEARCH METHODOLOGY 55

3.1 Introduction 55

3.2 Flow Chart of Research Activities 56

3.3 Substrate Materials 57

3.3.1 Preparation of Stainless Steel 316L

Substrate

57

3.4 Sputtering Physical Vapor Deposition (PVD)

Technique

59

x

3.4.1 Sputtering Process Parameters 60

3.5 Post-sputtering Annealing Process 61

3.6 Coating Characterisation Techniques 62

3.6.1 Cross-sectioned Sample Preparation 62

3.6.2 Thermal Analysis Using the Differential

Scanning Calorimetry (DSC)

63

3.6.3 Structural, Surface and Composition

Analysis

64

3.6.4 Mechanical and Tribological Properties 67

4 RESULTS AND DISCUSSION 71

4.1 Introduction 71

4.2 Substrate Material Characterization 72

4.2.1 Composition Analysis of 316L Stainless

Steel Substrate

72

4.2.2 Composition Analysis of Silicon Substrate 74

4.3 Composition Analysis of Unannealed NiTi

Coating

75

4.4 Cross-sectioned of Unannealed NiTi SMA

Coating Sample

76

4.5 Thermal Properties 79

4.6 Phase and Crystallographic Plane 80

xi

4.6.1 Unannealed NiTi SMA Coating 80

4.6.2 Annealed NiTi SMA Coating 82

4.7 Surface Morphology and Roughness

Measurement

85

4.7.1 Surface Roughness Tester 85

4.7.2 Atomic Force Microscope (AFM) 86

4.8 Mechanical and Tribological Properties 91

4.8.1 Rockwell C Adhesion Test 91

4.8.2 Pin-on-disc Wear Test 95

4.8.3 Nanoindentation 102

5 CONCLUSION AND RECOMMENDATIONS FOR

FUTURE WORK

106

5.1 Conclusion 106

5.2 Recommendations 107

xii

LIST OF TABLES

TABLE NO TITLE PAGE

2.1 NiTi mechanical properties 25

2.2 Mechanical properties of 316L stainless steels 32

2.3 Physical properties of 316L stainless steel 33

2.4 Composition of 316 and 316L stainless steel 36

2.5 Rockwell hardness scales 50

3.1 Parameters used for grinding process 58

3.2 Parameters of post-sputtering annealing process 61

3.3 Parameters of grazing angle X-ray diffraction (GAXRD) 65

3.4 Parameters of surface roughness tester 66

3.5 Parameters of atomic force microscope (AFM) 67

3.6 Parameters of Rockwell C adhesion test 68

3.7 Parameters of pin-on-disc wear test 69

3.8 Parameters of nanoindentation 70

4.1 Chemical composition of 316L stainless steel substrate 73

xiii

4.2 Chemical composition of unannealed NiTi coated on

silicon substrate

76

4.3 The surface roughness Ra and Ra (average) of NiTi

SMA coated on the 316L stainless steel at different

parameters

86

4.4 The Ra and Rms values for the unannealed and annealed

600°C for 30 minutes NiTi SMA coating samples at 1.0

x 1.0 µm² scan area

90

4.5 The results obtained from the nanoindentation test on

the unannealed and annealed 600°C for 30 minutes NiTi

SMA coating

103

xiv

LIST OF FIGURES

FIGURE NO TITLE PAGE

1.1 Structure of the thesis 6

2.1 Martensitic transformation and hysteresis (= H) upon a

change of temperature. As = austenite start, Af =

austenite finish, Ms = martensite start, Mf = martensite

finish and Md = highest temperature to strain-induced

martensite. Gray area = area of optimal superelasticity

10

2.2 Typical stress-strain curves at different temperatures

relative to the transformation showing (a) Austenite,

(b) Martensite, (c) Pseudoelastic behavior

11

2.3 Transformation from the austenite to the martensite

phase and shape memory effect

13

2.4 The procedures are very similar: (a) starting from

martensite, (b) adding a reversible deformation for the

one-way effect or severe deformation with an

irreversible amount for the two-way, (c) heating the

sample and (d) cooling it again

15

2.5 Schematic presentation of lattice structure changes

caused by outer stress in stainless steel or superelastic

NiTi alloy

16

xv

2.6 Principle of sputter deposition process 21

2.7 The different grades of damages to classify the

indentation patterns in the Rockwell adhesion test,

after

26

2.8 Typical DSC curve 39

2.9 Schematic diagram of the SEM 41

2.10 Some electrons and X-rays ejected from the sample by

the incident beam

42

2.11 Fourteen (14) Bravais lattice patterns, 3-dimensional

(3D)

44

2.12 Working principle of XRD 45

2.13 Surface characteristic 46

2.14 A schematic diagram of atomic force microscope

(AFM)

48

2.15 Working principle of Rockwell hadrness testing 51

2.16 Schematic diagram of Pin-on-disc tester 52

2.17 Schematic diagram of nanoindenter 53

2.18 Load-displacement curve for an instrumented

nanoindentation test

54

3.1 Flow chart of research activities 56

3.2 Mechanism of sputtering process 60

4.1 EDX spectra of 316L stainless steel substrate 72

4.2 EDX spectra of silicon substrate 74

xvi

4.3 EDX spectra of unannealed NiTi coated on silicon

substrate

75

4.4 The measurement of the unannealed NiTi SMA

coating thickness by doing a cross-section process on

316L stainless steel. (a) coating layer, (b) interlayer

and (c) substrate material

77

4.5 EDX spectra of (a) coating layer, (b) interlayer and (c)

substrate material

78

4.6 DSC curve of unannealed NiTi SMA coating 80

4.7 XRD pattern of unannealed NiTi SMA coating 81

4.8 XRD pattern of the annealed NiTi SMA coatings at

temperature 550°C for duration of (a) 30 and (b) 60

minutes

83

4.9 XRD pattern of the annealed NiTi SMA coatings at

temperature 600°C for duration of (a) 30 and (b) 60

minutes

84

4.10 The AFM typical two-dimensional (2D) surface

morphology of the (a) unannealed and (b) annealed at

600°C for 30 minutes samples

88

4.11 The AFM typical three-dimensional (3D) surface

morphology of the (a) unannealed and (b) annealed at

600°C for 30 minutes samples

89

4.12 The surface morpology of Rockwell C adhesion test

with different parameters, (a) unannealed, (b) annealed

at 550°C for 30 minutes, (c) annealed at 550°C for 60

minutes, (d) annealed at 600°C for 30 minutes and (e)

annealed at 600°C for 60 minutes under the optical

observation

92

xvii

4.13 The surface morpology of Rockwell C adhesion test at

high magnification image using SEM at different

parameters; (a) unannealed, (b) annealed at 550°C for

30 minutes, (c) annealed at 550°C for 60 minutes, (d)

annealed at 600°C for 30 minutes and (e) annealed at

600°C for 60 minutes

94

4.14 Wear tracks morpologies for (a) unannealed, (b) 550°C

for 60 minutes and (c) 600°C for 30 minutes under the

optical observation

96

4.15 The wear width measurement and chemical

composition analysis of unannealed (a, b) and

annealed ((c, d) 550°C (60 min) and (e, f) 600°C (30

min)) by SEM

98

4.16 The pin-on-disc results for different type of samples;

unannealed, 550°C (60 min) and 600°C (30 min)

101

4.17 Mechanical proeprties versus indentaion depth (a) H

versus penetration depth (b) E versus penetration depth

and (c) H/E Ratio versus penetration depth

104

xviii

LIST OF SYMBOLS/ABBREVIATIONS

Af - Austenite Finish Temperature

AFM - Atomic Force Micriscope

Amrec - Advance Materials Research Centre

Ar - Argon

As - Austenite Start Temperature

ASTM - American Society for Testing and Materials

BCC - Body Centered Cubic

BSE - Backscattered Electrons

Cr - Chromium

CVD - Chemical Vapour Deposition

d - Diameter

DC - Direct Current

DSC - Differential Scanning Calorimetry

E - Young’s Modulus

EDX/EDAX - Energy Dispersive X-ray Spectroscopy

FCC - Face Centered Cubic

Fe - Iron

xix

GDS - Glow Discharge Spectroscopy

GAXRD - Grazing Incidence Angle X-ray Diffraction

GPa - Giga-Pascal

H - Hardness

H/E - Ratio of Hardness to Young’s Modulus

IBAD - Ion-Beam Assisted Deposition

mbar - Milibar

Md - Highest Temperature To Strain-Induced Martensite

Mf - Martensite Finish Temperature

MEMS - Micro-Electro-Mechanical System

MPa - Mega-Pascal

Ms - Martensite Start Temperature

Ni - Nickel

NiTi - Nickel Titanium

OM - Optical Microscopy

PDF - Powder Diffraction File

PECVD - Plasma Enhanced Chemical Vapour Deposition

PVD - Physical Vapour Deposition

Ra - Average Roughness

RF - Radio Frequency

RMS - Root Mean Square Roughness

SE - Superelasticity / Secondary Electrons

SEM - Scanning Electron Microscopy

xx

Si - Silicon

SiC - Silicon Carbide

SMA - Shape Memory Alloy

SMAs - Shape Memory Alloys

SME - Shape Memory Effect

Ti - Titanium

TiN - Titanium Nitride

TTRs - Transformation Temperatures

VDI - Verein Deutscher Ingenieure

XRD - X-ray Diffraction

2D - Two-Dimension

3D - Three-Dimension

xxi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Powder diffraction file (PDF) 117

B XRD pattern list 119

C GDS composition analysis (316L stainless

steel)

120

D Pin-on-disc measurement 121

CHAPTER 1

INTRODUCTION

1.1 Background of the Study

Nickel Titanium Shape Memory Alloys (NiTi SMAs) have two unique

properties namely shape memory effect and superelasticity [1-3]. Since their first

discovery in 1960s, NiTi SMAs have been extensively studied [4]. Both shape

memory effect, and superelasticity have been exploited to design functional and

smart structures in mechanical and biomedical engineering. For instance, shape

memory and superelastic NiTi SMAs have been widely used in medical field and

micro-electro-mechanical systems (MEMS). In both applications, the wear

performance of the NiTi SMA plays a critical role [5-7].

2

NiTi SMAs are well-known for their extraordinary shape memory and

superelastic properties [8, 9]. These properties are due to the intrinsic thermoelastic

martensitic transformation under thermal or mechanical loading conditions at

different temperatures. At relatively low temperature and under external force, the

initial parent phase (austenite) can transform into a martensite phase accompanied by

macroscopic deformation. Upon unloading to zero, the material remains in a

martensite state with residual strain. Then, when the material is heated to a certain

temperature, the martensite can transform back to the initial austenite phase with the

material returning to its initial shape. This is the shape memory effect [10-12]. For

the same material, when the load is given at the higher temperature, the martensite

structure can transform back to austenite during unloading while recovering a large

amount of the prior deformation. This extraordinary recoverable deformation

behavior is called superelasticity or pseudoelasticity [13, 14].

However, there are still some concerns for the wide application of SMA

coatings because of their unsatisfactory mechanical and tribological performances,

chemical resistance and biological reliability. High nickel content in NiTi SMAs

often stimulated suspicion for their medical use because of nickel toxicity. The

limited hardness and wear resistance of NiTi SMAs make them difficult to be used in

orthodontic and MEMS applications [15]. In order to improve surface properties,

corrosion resistance and suppression of Ni ions release of NiTi SMAs, through

several techniques such as nitrogen ion implantation, laser surface treatment, thermal

and anodic oxidation, have been employed. The problems of these surface treatments

are high cost, possible surface or ion induced damage, amorphous phase formation,

or degradation of shape memory effects. The magnetron sputtering deposition

technique has important specific advantages such as low levels of impurities and

easy control of the deposition rate and also enables the production of various

coatings morphologies and crystallographic structure [3, 4, 10].

3

The purpose of this study is to investigate the structure and tribological

properties of the annealed and unannealed NiTi SMA coatings. A physical vapour

deposition (PVD) magnetron sputtering was used to deposit the NiTi SMA coatings

onto the 316L stainless steel substrates and the post sputtering annealing process was

conducted to crystallise the unannealed NiTi SMA coatings. The mechanical and

tribological tests namely; Rockwell C adhesion test, nanoindentation and pin-on-disc

wear measurements were conducted to investigate their adhesion and wear properties

of the unannealed and annealed NiTi SMA coatings. While the surface

characterization equipment namely optical microscopy (OM), scanning electron

microscopy with energy dispersive X-ray spectroscopy (SEM/EDAX), X-ray

diffraction (XRD), atomic force microscope (AFM), surface roughness tester and

differential scanning calorimetry (DSC) were used to characterize the structure,

surface, composition and thermal analysis of unannealed and annealed NiTi SMA

coatings.

1.2 Problem Statement

Shape Memory Alloys (SMAs) are well-known for possessing shape memory

effect and superelasticity behaviour due to intrinsic microstructure transition of

thermoelastic martensitic transformation. Both shape memory effect and superelastic

nickel–titanium alloys are widely used in implants and identified as possible

materials for micro-electro mechanical systems (MEMS) [5-7]. In these applications,

the wear performance of the material plays a critical role [3]. For instance, medical

industries are very interested in the high compliance of NiTi alloy for use in joint

replacement, an application where wear plays an important role. Recent research

works have shown that NiTi alloys exhibit high resistance to wear. The tribological

4

behavior of NiTi alloys has been investigated and compared to many conventional

engineering materials such as steels, Ni-based and Stellite alloys. These

investigations have demonstrated higher wear resistance of NiTi compared with

many tribological materials. The wear resistance of conventional tribo-materials

strongly depends on their mechanical properties such as hardness, toughness, and

work-hardening [1-4, 10, 11]. However, it appears that these properties are not the

main factors responsible for high wear resistance of NiTi alloys. It is believed that

the high wear resistance of shape memory NiTi is mainly due to the recovery of the

superelastic deformation. Some researchers indicated that the wear resistance of NiTi

SMA was mainly dependent on the recoverable strain limit, for examples the sum of

the pseudoplastic and pseudoelastic strain limits. It seems more research is required

for fundamental understanding of tribological behavior of the martensite and the

austenite phases of NiTi alloys [5, 9, 12,].

1.3 Objective of the Study

To investigate the effect of post sputtered annealing process on structure and

tribological properties of the NiTi SMA coatings.

5

1.4 Scope of the Study

The coated NiTi SMA onto the 316L stainless steel substrates were used in

this study. The scope of this study can be divided into three stages as the following:

(i) To conduct the post-sputtered annealing process in a vacuum furnace at

various annealing temperatures and annealing times.

(ii) To determine the structure of the unannealed and annealed NiTi SMA

coatings.

(iii)To investigate the effect of the post-sputtering annealing process on their

structure and tribological properties. The surface morphology, surface

roughness, hardness, adhesion and wear properties of the coatings were

determined using the selected characterization techniques.

6

1.5 Structure of the Thesis

Figure 1.1 : Structure of the thesis

Chapter 1

(Introduction)

Describes the background of this study, problem statement,

objectives, scope and the project flow chart. This chapter

also provides information of the overall study.

Chapter 2

(Literature

Review)

Provides information and the theory related to the shape

memory alloys (SMAs), types and properties of SMAs. This

is followed by a review about the NiTi SMA, production of

SMA and the characterization of NiTi SMA coatings.

Chapter 3

(Research

Methodology)

Provides the information on the experimental with details of

the coating process, the equipment used and the

characterization of the coatings.

Chapter 4

(Results and

Discussion)

Presents all the results obtained from the study carried out

and discusses in detail the results observed for each analysis.

Chapter 5

(Conclusion and

Recommendation)

Presents the conclusions and the contributions from the

present study. All the experimental data and results to

become one short note that briefed completely about the

whole project. Besides that it also presents some

recommendations for future work in order to improve and

enhance the structure and tribological properties of post-

sputtered annealing NiTi SMA coatings. The list of

references and appendices are presented at the end of this

thesis.