the alloyed pleasure: metallic glasses (bmgs) high entropy...
TRANSCRIPT
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The Alloyed Pleasure: Bulk Metallic Glasses (BMGs) &High‐Entropy Alloys (HEAs)
Sheng GUOMaterials and Manufacturing Technology Department
Chalmers University of Technology
November, 2013
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Alloyed Pleasures: Science of Multi‐component Alloys
The English language insists on unalloyed pleasures, thereby implying that the sensation of pleasure must be pure and not admixed with other emotions. Exactly the opposite rules in metallurgy, where pure metals have few uses and can always be improved upon by alloying. The 20th century saw the slow transformation of the art of alloying into the science of alloying.
BMGs; Gum Metal; HEAs
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Outline Two Pleasures (main part) Bulk Metallic Glasses (BMGs) High Entropy Alloys (HEAs)
My Pleasures (or Pains…) (brief) Phase Selection Rules Metastability of Solid Solutions Mechanical Behavior Solidification Behavior
Challenges (brief)
Metallic glasses
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Metallic Glasses (Amorphous Alloys)
W Klement, R Willens, P Duwez, Non‐crystalline Structure in SolidifiedGold‐Silicon Alloys, Nature, 1960, 187: 869
Au75Si25 P Duwez
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Bulk Metallic Glasses (BMGs)
Pd42.5Cu30Ni7.5P20 BMG
80*85 mm
(NishiyamA, Intermetallics, 2012)
volu
me
melt spinning
A Inoue(~1990) Inoue’s three empirical rules to prepare BMGs (>1 mm):• at least 3 alloyingelements; • large mismatching atomic sizes ofconstituent elements• large negative heat of mixingamong major alloying elements
3.4 Kg!
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Attractive properties of bulk metallic glasses (BMGs) High strength : >2000 MPa High hardness: 600‐1300 DPH High fracture toughness: >70 MPa . m1/2 High elastic strain: ~ 2% elastic strain Good formability: >1000% elongation Superior aqueous corrosion resistance Good wear resistance Excellent soft magnetic properties: Fe‐base BMGs Other interesting optical and physical properties
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Bulk Metallic Glasses
•From Liquidmetal Technologies
Structural
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Micro‐devices: micro‐gears made of BMGs Only one casting process
100m
Super‐precision gear mold Super‐precision gear parts made of glassy alloy
Newly developed gear
Diameter = 647 mmTeeth = 14 pModule = 40 mm
Conventionalmachined gear
Diameter = 288 mTeeth = 9 p
Module = 25 m
Human hair(d= 80 m )
(Nishiyama et al, 2005)
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Microgears for micro‐device applications
Advanced medicalequipments
Precision optics Micro‐factory・Lenz drive・Small camera ・Measurements & Analytic equipments
・Micro‐robotsfor Micro‐industries
・Micro‐lathe
Rotablator
Capsule endoscope Catheter for thrombus removalMicro‐pump
Endoscope
Rotablator
Aneurysm
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Blow moulding of BMGs
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SIM tray tool
BMGs and Apple products
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Achilles heel: (Tension) Brittleness
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Glass transition is still a mystery
“What is the nature of glassy state?” was selected as one of the most important 125 scientific questions to be resolved this century‐‐‐ Science, 2005
“Glass transition is one of the deepest and most important unsolved problems in condensed matter physics” ‐‐‐‐ Nature Materials, 2008
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Introduction: High‐Entropy Alloys
(Adv.Eng.Mater, 2004)
(Yeh, et al., Mater Chem Phys, 2007)
N=1
N=2
N=3
N=4
N=5
N=6
N=7
Highly concentrated solid solutions
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New approach for alloy design
Traditional alloys have only 1 (steels, Al alloys, Cu alloys, etc.) or 2 principle elements (NiAl, FeAl, etc.)
High‐entropy alloys have at least 5 (4?) principalmetallic elements, and have equal or close‐to‐equal compositions
Example, Al‐Co‐Cr‐Cu‐Fe‐Ni systemEquimole: AlCoCrCuFeNi Non‐equimole: AlCo0.5CrCuFe1.5Ni1.2Minor element addition: AlCo0.5CrCuFe1.5Ni1.2B0.1C0.15
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Why are they called high‐entropy alloys?
(Yeh, 8th IWIAM talk)
1ln
N
i ii
R c c
High configuration entropy
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Merits of high entropy alloys (HEAs)
Hardness ranges from 100 to 1100 HV Excellent corrosion resistance, wear resistance
and oxidation resistance High electrical resistivity with a low or negative
temperature coefficient Thermally stable microstructure Excellent resistance to temper softening High‐temperature precipitation hardening
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1. Thermodynamics – high entropy2. Kinetics – sluggish diffusion3. Structure – severe‐lattice‐distortion4. Properties – cocktail effect
Core Effects of High‐Entropy Alloys (suggested by Prof. JW Yeh)
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‐‐ Thermodynamics ‐‐
High Entropy Effect
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High‐entropy effect enhances the formation of solution phasesPossible competing states
(elemental phases, compounds, solid solutions)
△Gmix =△Hmix ‐T△Smix
Solid solution phases having the highest mixing entropy
thus become highly competitive and more stable especially at high T
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Extended Crystal Structures of Solid Solutions
Conventional crystal structure can be extended for multi‐principal‐element solid solutions.
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‐‐ Kinetics ‐‐
Sluggish Diffusion Effect
1. Lower diffusion rate
2. Lower phase transformation rate
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Sluggish Diffusion Kinetics: Diffusion couple experiments
• Lower diffusion coefficients• Higher activation energies(Tsai KY, et al., Acta Mater, 2013)
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Fine precipitation in cast alloysMany high‐entropy cast alloys have nano or submicron precipitates in the matrix.
TEM microstructures of as‐cast equimolar AlCoCrCuFeNi alloy
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Advantages of Sluggish Diffusion
Slow down phase transformation Easy to get supersaturated state and fine precipitates
Raise recrystallization temperature Slow down grain growth Slow down particle coarsening improve creep resistance
These advantages might benefit microstructure and property control
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‐‐ Structure ‐‐
Severe‐Lattice‐Distortion Effect
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e-
phonon
X-ray
Severe‐Lattice‐Distortion Effect
Lattice distortion affects properties and reduces the thermal vibration effect:
Hardness and strength Temp. coefficient Electrical conductivity Temp. coefficient Thermal conductivity Temp. coefficient XRD peak intensity Temp. coefficient
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Thermal conductivity and resistivity
1 2 3 4 5
10
20
30
40
50
60
70
80
90
CoNiFeCrMn
CoNiFeCrAl0.25CoNiFeCr
Ther
mal
con
duct
ivity
(W
/m‧
K)
Number of elements
CoNi
CoNiFe
Ni-RT
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‐‐ Properties ‐‐
Cocktail EffectRule of mixture
Excess properties due to mutual interactions
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Arise from the basic features and mutual interactions among all constituent elements in a solution phase.
Cocktail Effect
-5 0 5 10 15 20 25 30 35 40
100
200
300
400
500
600
700
BCC phaseFCC + BCC phasesFCC phase
H
ardn
ess
(Hv)
Al content (at.%)
Example: AlXCoCrCuFeNi alloys
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Mechanical Properties of HEAs
Very high hardness can be achieved
(after 1000 oc/12h)
(Yeh, et al., Adv Eng Mater, 2004)
AlCoCrFeNiTi0.5y=2.26GPa
f=3.14GPa
p=23.3%
(Zhou et al., APL, 2007)
Disordered bcc solid solution was reserved even after annealing at 1400 oc for 19h
(Senkov, et al., Intermetallics, 2011)
460 MPa@1600 oCbetter than superalloys
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CoCrFeNiTi parts in high‐temperature wear test
wear testing machine performed up to 1000
connection rods
rotation diskholder
• High strength, toughness and oxidation resistance at high‐temperatures• Low thermal conductivity
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WC grains in AlCoCrCuFeNi matrix are much smaller than that in Co matrix
80%WC+20%AlCoCrCuFeNi (1400 ) 80%WC+20%Co (1400 )
Hardmetals based on HEAs
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For protective coatings on heat exchangers and high‐temperature components
304 substrate HV150
AlCoCrFeNiSiTi HV800
Thermal spray coatings of HEAs
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Oxidation ResistanceThermal annealing at 1100 for 10 hours only causes a dark gray color on the surface of HEA coatings.
HEA coatings provides an excellent protection for alloy substrate.
Dense oxide layerOxide debris detached from unprotected substrate
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Hardfacing HEAs
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HE Nitrides Hardness (GPa)Modulus (GPa)
(AlCrMoTaTiZr)N 40 379
(AlCrTaTiZr)N 36 360
(AlCrMoSiTi)N 35 325
(AlCrSiTiV)N 31 300
(AlBCrSiTi)N 25 260
(AlCrNbSiTiV)N 42 350
(AlCrSiTaTiZr)N 34 343
(AlMoNbSiTaTiVZr)N 37 350
HE Nitride CoatingsAll HE nitrides have simple FCC structure.The FCC structure is stable even after 1100 /5h annealing.
Strengthening
mechanisms:1. Strong bonding
2. Nanograin structure
3. Solid solution hardening
4. Residual stress
AlN+CrN+TaN+TiN+ZrN (AlCrTaTiZr)N
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(AlCrTaTiZr)‐Si‐N coatingson carbide inserts
Film thickness is 1 μm. (AlCrTaTiZr)‐Si‐N has better flank‐
wear resistance than that of TiN and TiAlN commercial coatings.
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Potential applications in hard coatings
TiN
TiAlN
CrN
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(Hemphill, et al., Acta Mater, 2012)
(Chuang et al., Acta Mater, 2011 )
HEAs
Excellent Wear Resistance & Fatigue Properties of HEAs
40
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Other application examples
Diffusion Barrier(AlCrTaTiZr)N
AlCrFeMnNi, rolling extension up to 4900%(304 SS: 1543%)
Flexible Substrate
(HV: 160)
(Chang et al., APL, 2009)
Cu interconnects
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My Research AreaOverall: Alloy Design and Mechanical Behavior of HEAsMore specifically, Phase Selection Rules
• Solid solutions/Amorphous phase/Intermetallic compounds• Single solid solutions• fcc or bcc solid solutions
Metastability of Solid Solution Phases• Thermolmechanical tests + Thermo‐Calc
calculations (¤)• Solid solution limit
Mechanical BehaviorHardness/Tensile property/Toughness
Solidification Behavior• Eutectic solidification microstructure• Directional solidification/Single crystal (¤)(¤) collaboration
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Challenges in the field Some real and scalable applications Conflict between strength and
ductility/toughness
Al0.5, fcc
Al0.8, fcc+bcc
Al1.0, fcc+bcc
(Tong et al., Metall Mater Trans A, 2005)
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Thanks for your attention!Dr. Sheng Guo
Assistant ProfessorMaterials and Manufacturing Technology Department
Chalmers University of TechnologyGothenburg, Sweden