Study on composition optimization and deformation mechanisms of non- equiatomic NiCoFe medium entropy alloys

YJ Chang and ZY Bai and X Guo and JQ Ren and JC Li and HT Xue and XF Lu, MATERIALS TODAY COMMUNICATIONS, 45, 112305 (2025).

DOI: 10.1016/j.mtcomm.2025.112305

In view of the vast compositional space of multi-principal element alloys (MPEAs), the optimization of strength and plasticity in non- equiatomic medium/high entropy alloys (M/HEAs) has spurred extensive research interest. This study investigates the effects of chemical composition on the stacking fault energy (SFE), twinning tendency, elastic modulus, and mechanical properties of nanocrystalline NiCoFe MEAs using molecular dynamics (MD) simulations. The results indicate that the SFE can be reduced and the twinning tendency may be enhanced by reducing Ni content while increasing Co and Fe content, which is predicted to promote plasticity. However, this compositional alteration concurrently results in a decline in shear modulus, thereby weakening the yield strength. Based on the screening criteria for optimizing the synergy between strength and plasticity, which emphasizes a higher shear modulus and lower SFE, the optimal compositional range is predicted to be 27 at% similar to 37 at% Ni, 30 at% similar to 40 at% Co, and 26 at% similar to 40 at% Fe. Tensile simulations reveal that the Ni37Co30Fe33 MEA exhibits the highest ultimate tensile strength and flow stress. The strengthening mechanism of nanocrystalline Ni37Co30Fe33 MEA mainly arises from the contributions of stacking faults, deformation twins, hexagonal close-packed (HCP) phases, dislocation interactions, and grain boundaries. The compositional optimization criteria and insights into the deformation mechanisms outlined in this study provide critical guidance for the comprehensive enhancement of the mechanical properties of MPEAs.

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