Design and optimization of the composition and mechanical properties for non-equiatomic CoCrNi medium-entropy alloys

The development of multi-principal element alloys (MPEAs, also called as high-or medium-entropy al-loys, HEAs/MEAs) provides tremendous possibilities for materials innovation. However, designing MPEAs with desirable mechanical properties confronts great challenges due to their vast composition space. In this work, we provide an essential criterion to efficiently screen the CoCrNi MEAs with outstanding strength-ductility combinations. The negative Gibbs free energy difference Delta EFCC-BCC between the face-centered cubic (FCC) and body-centered cubic (BCC) phases, the enhancement of shear modulus G and the decline of stacking fault energy (SFE) gamma isf are combined as three requisites to improve the FCC phase stability, yield strength, deformation mechanisms, work-hardening ability and ductility in the criterion. The effects of chemical composition on AEFCC-BCC, G and gamma isf were investigated with the first principles calculations for CoxCr33Ni67-x, Co33CryNi67-y and CozCr66-zNi34 (0 < x, y < 67 and 0 < z < 66) alloys. Based on the essential criterion and the calculation results, the composition space that displays the neg-ative Gibbs free energy difference AEFCC-BCC, highest shear modulus G and lowest SFE gamma isf was screened with the target on the combination of high strength and excellent ductility. In this context, the optimal composition space of Co-Cr-Ni alloys was predicted as 60 at.%-67 at.% Co, 30 at.%-35 at.% Cr and 0 at.%-6 at.% Ni, which coincides well with the previous experimental evidence for Co55Cr40Ni5 alloys. The valid-ity of essential criterion is further proved after systematic comparison with numerous experimental data, which demonstrates that the essential criterion can provide significant guidance for the quick exploitation of strong and ductile MEAs and promote the development and application of MPEAs.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The development of multi-principal element alloys (MPEAs), also known as high- or medium-entropy alloys (HEAs/MEAs), offers great possibilities for materials innovation. However, designing MPEAs with desired mechanical properties is challenging due to their vast composition space. This study provides an essential criterion to efficiently screen CoCrNi MEAs with outstanding strength-ductility combinations, combining the negative Gibbs free energy difference between face-centered cubic (FCC) and body-centered cubic (BCC) phases, enhancement of shear modulus, and decline of stacking fault energy.