Molecular dynamics study of nanostructured polycrystalline CoCrCuFeNi high entropy alloy concerning temperature dependence of deformation-induced phase transformation

Abstract

In this paper, a series of molecular dynamics (MD) simulations was performed to identify the high-temperature tensile properties of nanostructured polycrystalline CoCrCuFeNi high entropy alloy (HEA). The mechanism of strength reduction at elevated temperatures was understood through nanostructure observation such as phase transformation and dislocation evolution in MD simulation. The applicability of this material from room temperature to 1200 ℃ as a high-temperature use of structural material was identified. The stress-strain curve was found to gradually decrease ultimate tensile strength and yield stress as the temperature applied to the material increases. The elastic modulus decreases rapidly at slightly high temperatures but decreases gradually as it goes to the extremely high temperatures. Face-centered cubic (FCC)→hexagonal close-packed (HCP) phase transformation, which is energetic process between atoms due to tensile loading, was revealed. From the vicinity of the yield stress to the quasi-plastic regime, it competitively contributes to tensile properties between FCC→HCP phase transformation and growth of voids. In dislocation analysis, the typical partial dislocations such as perfect, Shockley, stair-rod and others were measured, in which Shockley and stair-rod partial dislocations show its characteristics that contribute to tensile properties. The results in this study contribute to understanding the high-temperature applicability of nanostructured polycrystalline CoCrCuFeNi HEA.