Exceptional Strength-Ductility Combinations of a CoCrNi-Based Medium-Entropy Alloy via Short/Medium-Time Annealing after Hot-Rolling

Strong yet ductile alloys have long been desired for industrial applications to enhance structural reliability. This work produced two (CoCrNi) Al Ti C medium-entropy alloys with exceptional strength-ductility combinations, via short/medium (3 min/30 min) annealing times after hot-rolling. Three types of intergranular precipitates including MC, M C carbides, and L1 phase were detected in both samples. Noticeably, the high-density of intragranular L1 precipitates were only found in the medium-time annealed sample. Upon inspection of the deformed substructure, it was revealed that the plane slip is the dominant deformation mechanism of both alloys. This is related to the lower stacking fault energy, higher lattice friction induced by the C solute, and slip-plane softening caused by intragranular dense L1 precipitates. Additionally, we noted that the stacking fault and twinning act as the mediated mechanisms in deformation of the short-time annealed alloy, while only the former mechanism was apparent in the medium-time annealed alloy. The inhibited twinning tendency can be attributed to the higher energy stacking faults and the increased critical twinning stress caused by intragranular dense L1 precipitates. Our present findings provide not only guidance for optimizing the mechanical properties of high/medium-entropy alloys, but also a fundamental understanding of deformation mechanisms.