Temperature effect on the microstructural refinement of equiatomic CoCrNi medium entropy alloy via cyclically multi-directional impact

Abstract

Severe plastic deformation can effectively refine alloy microstructure and improve the mechanical properties of alloys surprisingly. In this work, a new approach of severe plastic deformation was proposed based on split Hopkinson pressure bar, i.e., cyclically multi-directional impact. Using this newly developed technique for microstructural refinement at different temperatures (77 K, 293 K, and 1073 K), bulk equiatomic CoCrNi medium entropy alloys with refined microstructures were obtained, and the stress vs. strain relation of the equiatomic CoCrNi medium entropy alloy during the cyclically multi-directional impact can be in situ measured. The strain rate of the cyclically multi-directional impact was controlled at about 1500 /s. The hardnesses of the CoCrNi medium entropy alloy increase dramatically from 216 Hv to 460 Hv after the cyclically multi-directional impact at 77 K, 484 Hv after the cyclically multi-directional impact at 293 K, and 434 Hv after the cyclically multi-directional impact at 1073 K. The microstructural evolutions of the CoCrNi MEA after cyclically multi-directional impact at three temperatures were characterized and analyzed. This study aims to provide a new approach to microstructural refinement for bulk alloys.