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

• The synergistic effects of multiple deformation mechanisms and solid solution strengthening on the mechanical properties of Mo-reinforced CoCrNi medium-entropy alloys (MEAs) were revealed via first principles calculations. • The essential criterion was proposed for the composition design of strong and ductile FCC (CoCrNi) 100- x Mo x MEAs based on the synergy of multiple deformation mechanisms and intense solid solution strengthening. • The optimal composition of FCC (CoCrNi) 100- x Mo x MEAs was predicted as (CoCrNi) 93 Mo 7 according to the essential criterion and the results of first principles calculations. • The accuracy of essential criterion was validated by the comparison with previous experimental data. 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– x Mo x (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– x Mo 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) 93 Mo 7 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. [Display omitted] [ABSTRACT FROM AUTHOR]