Temperature dependence of the deformation behavior and mechanical response of CoCrNi medium-entropy alloy: Experiment and simulation

Abstract

Tailoring the microstructure of metallic materials by controlling the fabrication process is crucial to achieving superior mechanical properties. Herein, the mechanism of modifying the microstructure and mechanical properties of medium-entropy CoCrNi alloys was investigated by equal-channel angular pressing (ECAP) at room temperature (RT) and cryogenic temperature (CT) and post-deformation annealing (PDA) and was analyzed by molecular dynamics simulations. It was found that temperature influences the deformation mechanism of the alloy, dislocations, stacking faults, deformation twins, and FCC-HCP phase transitions, which assume different roles at different temperatures. The dislocation density of the ECAP-CT sample is significantly higher than that of the ECAP-RT sample; however, the ECAP-RT sample exhibits unique deformation features of kink bands and hierarchical twin structure, resulting in dynamic grain refinement effects. In addition, the HCP phase strength increment caused by annealing-induced HCP phase transformation is higher in the ECAP-RT sample than in the ECAP-CT sample, thus leading to a substantial increase in strength after PDA. The present study exhibits the strengthening mechanisms and provides a generic approach to obtaining desirable mechanical properties of alloys.