Post on 26-Dec-2015
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Yong ZhangYong Zhang
University of Science and Technology Beijing University of Science and Technology Beijing
Phase Formation Rules for Phase Formation Rules for High Entropy AlloysHigh Entropy Alloys
ICAMP5ICAMP5
HIT 2008HIT 2008
AcknowledgementsAcknowledgements
Prof. GuoLiang Chen; Prof. Hywel A Davies; Prof. Peter K Liaw; Prof. George Smith; Prof. Zhaoping Lu; XueFei Wang; YunJun Zhou; FangJun Wang.
OutlinesOutlines
I. Background & Motivations
II. Results & Discussions
III. Summaries
(1) Conventional alloys
I. Background & MotivationsI. Background & Motivations
Steel, A=Fe, B=Carbon, B<2%;
Cast Iron, A=Fe, B=Carbon, B<6.5%
1.1 Alloys Design Strategy
Alloy=A+B+ C+; A>50%; …
(2) High Entropy AlloysHEAs=A+B+C+D+E; 50%<A\B\C\D\E>15%
AlCoCrFeNi=HEA , Zhou, APL, 2007
CoCrCuFeNi=HEA, Yeh, MMTA, 2004;
FCC type HEA Solid Solution
BCC type HEA Solid Solution
Al20[TiVMnHEA]80, Zhou, MSEA, 2007
Solid solution has higher entropy than the mechanical mixture does.
BBAA SXSXS
0.00 0.25 0.50 0.75 1.00
En
tro
py
Molar FractionA B
Solid Solution
Mecanical Mixture
mixBBAA SSXSXS 1.2 Thermodynamically
)( BBAAmix LnXXLnXXRS
For the regular solution:
Gibbs Free Energy
Gmix =Hmix-TSmix
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Smix, HEA
Smix, LEA
Sm
ix
Composition
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
m
ix
Composition
Hmix
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Gmix, LEA
Gmix, HEA
Gm
ix=
mix
-TS
mix
Composition
AG BG
BAG
)( BBAAABmix GXGXGG
1.3 Properties and Applications
1. High Strength; Zhou, APL, 2007;
2. High wear resistance; Lin, Surface Coating technology, 2008.
3. High corrosion resistance; Lee, Thin Solid Films, 2008;
4. High thermo-stability; Tsai, APL, 2008.
Properties
1 Coatings, Barriers, etc.Diffusion barriers for Cu interconnections; Tsai, APL, 2008
2 Structural Materials3 Energy Storage Materials, Raju, Journal of power Sources, 2008;
4 Molds
Potential Applications
To understand what is the dominant factors To understand what is the dominant factors for the phase formation of the HEAsfor the phase formation of the HEAs
1 Atomic radius, or atomic volume;
1. 1
1. 15
1. 2
1. 25
1. 3
1. 35
1. 4
1. 45
1. 5
Fe Ni Cr Co Cu V Al Ti
Atomic RadiusThe contents of Al, Ti, Cu, Co in
the HEAs were changed
N
iii rrc
1
2)/1(
i
N
iirCr
1 Kittel, Introduction to Solid State Physics
1.4 Motivations1.4 Motivations
2 Enthalpy of Mixing;
3 Entropy of Mixing
N
jiijiijmix ccH
,1
i
N
iimix LnCCRS
1
4 Cooling Rate
5 Tensile and compressive properties
Critical cooling rate? Like the BMG?
Tensile elongation=0? Like BMG?
CoCrFeNiCu1-yAly
FCC BCC, High APE to Lower APE, with larger atoms Al
2.1. Alloying with different atomic size, Al, Cu, Co, Ti2.1. Alloying with different atomic size, Al, Cu, Co, Ti
Ti0.5CoCrFeNiCu1-yAly
(y=0, 0.25, 0.5, 0.75)
II. Results & DiscussionsII. Results & Discussions
Al=1.438AAl=1.438A
3.579A
2.913A,2.872A
Cu=1.278ACu=1.278A
CoCrFeNiAlCuy
( y=0, 0.25, 0.5)
Ti0.5CoCrFeNiAlCuy
No PHASE TRANSITION
Co=1.251ACo=1.251A
The smaller BCC transit to FCC firstly after adding Co
Biger BCC1phase:2.913A; Smaller BCC2phase:2.872A
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[Al1Co1Cr1Fe1Ni1]Tix alloys
20 30 40 50 60 70 80 90
Ti0
Ti0.5
Ti1
Ti1.5
1Inte
nsi
ty (
a.u.)
2 (Degree)
1
212
2
1
2
(21
1)
(22
0)
121 2
12
(20
0)
1
2(1
10)
1
(11
0)
(20
1)
2
BCCLaves phase
Single BCC
Double BCC
Double BCC+Laves
Big BCC
BCC+Ti BCC+BCC
Ti=1.448ATi=1.448A
After adding Ti, Laves phase forms
Zhou, APL, 2008
The transition is mainly lattice distortion induced and APE related
Cu
FCC
Al
Ti
Ti BCC
Cu Co
BCC
FCC
BCC
BCC
FCC
Laves
A schematic showing the additional effects
20
Zhang, AEM, 2008
2.2. Considering of the enthalpy of mixing 2.2. Considering of the enthalpy of mixing HHmixmix
Mg based BMG
Zr based BMG
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2.3. Considering of the entropy of mixing 2.3. Considering of the entropy of mixing SSmixmix
High Entropy is not good for the formation of BMG
2.4 Cooling Rate
AlCoCrFeNi
AlCoCrFeNi
2mm 5mm
8mm 10mm
AlCoCrFeNi
2.5 Tensile and Compressive properties
XRD pattern for the CoCrCuFeNiAl0.5 alloy.
Table Room temperature mechanical test results for the CoCrCuFeNiAl0.5 alloy
This alloy P (%) 0.2 (MPa) max (MPa)
Compressive >51.5 460 >1380
Tensile 19.1 360 707
P: plastic strain; 0.2 : yield strength; max: compressive/tensile strength
510
III. SummariesIII. Summaries
1 Atomic size mismatch is the dominant factor for the phase formation of the high entropy alloys;
2 The formation of solid solution for the HEAs intends to have enthalpy of mixing close to zero;
3 High entropy of mixing facilitates the formation of the solid solution rather than the BMGs;
4 Cooling rate plays rather important role for the homogeneous microstructure than for the phase formation;
5 HEA can have tensile elongations as high as 19%.
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