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

16

[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

21

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%.

28

Thanks for your Thanks for your attentionattention