Phase formation rules for high entropy alloys

Acknowledgements

Prof. GuoLiang Chen;
Prof. Hywel A Davies;
Prof. Peter K Liaw;

Outlines

I. Background & Motivations
II. Results & Discussions
III. Summaries

(1) Conventional alloys

I. Background & Motivations

Steel, A=Fe,
B=Carbon, δB<2%;
Cast Iron, A=Fe,

(2) High Entropy Alloys
HEAs=A+B+C+D+E; 50%15%

AlCoCrFeNi=HEA ,
Zhou, APL, 2007

CoCrCuFeNi=HEA,
Yeh, MMTA,

Solid solution has higher entropy than the mechanical mixture does.

1.2 Thermodynamically

For

Gibbs Free Energy

ΔGmix =ΔHmix-TΔSmix

1.3 Properties and Applications

High Strength; Zhou, APL, 2007;
High wear resistance; Lin,

1 Coatings, Barriers, etc.
Diffusion barriers for Cu interconnections; Tsai, APL, 2008
2

To understand what is the dominant factors
for the phase formation

2 Enthalpy of Mixing;

3 Entropy of Mixing

4 Cooling Rate

5 Tensile and compressive properties

Critical cooling rate? Like the

CoCrFeNiCu1-yAly

FCC BCC, High APE to Lower APE, with larger atoms Al

2.1.

Cu=1.278A

CoCrFeNiAlCuy

( y=0, 0.25, 0.5)

Ti0.5CoCrFeNiAlCuy

No PHASE TRANSITION

Co=1.251A

The smaller BCC transit to FCC firstly after adding Co

Biger BCC1phase:2.913A;

[Al1Co1Cr1Fe1Ni1]Tix alloys

BCC+Ti BCC+BCC

Ti=1.448A

After adding Ti, Laves phase forms

Zhou, APL, 2008

The transition is mainly lattice distortion induced and APE

A schematic showing the additional effects

Zhang, AEM, 2008

2.2. Considering of the enthalpy of mixing ΔHmix

Mg based

2.3. Considering of the entropy of mixing ΔSmix

High Entropy is not

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

III. Summaries

1 Atomic size mismatch is the dominant factor for the