Composition design study of strong and ductile Mo-alloyed CoCrNi medium-entropy alloys

Abstract

The assistance of alloying elements provides enormous opportunities for the discovery of high-performance face-centered cubic (FCC) medium-entropy alloys (MEAs). In this work, the influence of alloying element Mo on the phase stability, stacking fault energy (SFE), deformation mechanisms, lattice distortion, and mechanical properties of (CoCrNi)100–xMox (0 ≤ x ≤ 10) MEAs was synthetically explored with the first-principles calculations. It indicates that the FCC phase remains metastable at 0 K, and its stability degenerates with increasing Mo content. The monotonous decrease of SFE is revealed with the rise of Mo content, which promotes the activation of stacking faults, deformation twinning, or martensitic transformation. Raising Mo content also causes the aggravation of lattice distortion and thus triggers intense solid solution strengthening. Significantly, the essential criterion for the composition design of FCC (CoCrNi)100–xMo MEAs with superior strength-ductility combination was established based on the synergistic effects between multiple deformation mechanisms and solid solution strengthening. According to the criterion, the optimal composition is predetermined as (CoCrNi)93Mo7 MEA. The criterion is proved to be effective, and it can provide valuable inspiration for the development of alloying-element reinforced FCC multi-principal element alloys.