Achieving an excellent strength-ductility synergy in a medium-entropy alloy by a suitable thermo-mechanical processing

Abstract

In this study, we present a Co₂Ni₂Cr medium-entropy alloy (MEA) co-doped with Al/Mo, and systematically regulate its microstructure through thermo-mechanical processing. A representative (Co₂Ni₂Cr)₈₈Al₈Mo₄ MEA, fabricated via cold rolling followed by annealing at 765 °C, exhibits an excellent strength-ductility synergy. It achieves a high yield strength of ∼1150 MPa, an ultimate tensile strength of ∼1397 MPa, and maintains a good ductility of ∼17 %. The representative MEA undergoes partial recrystallization, with high-density L1₂ nanoparticles uniformly distributed in both recrystallized and non-recrystallized regions. Furthermore, EBSD analysis reveals the presence of high-density dislocations within the non-recrystallized region. Therefore, precipitation strengthening by L1₂ nanoparticles and dislocation strengthening are likely the primary mechanisms contributing to the high yield strength observed in the representative MEA. Simultaneously, its excellent ductility can be attributed to the highly coherent two-phase interface, the presence of high-density microbands and Lomer-Cottrell (LC) locks, as well as a certain proportion of recrystallized regions. Therefore, this study presents an effective design strategy to achieve an excellent strength-ductility synergy in a MEA through optimized thermo-mechanical processing.