On cyclic plasticity of nanostructured dual-phase CoCrFeNiAl high-entropy alloy: An atomistic study

Abstract

In this study, we have employed molecular dynamics simulations to examine plastic deformation mechanisms of a “supra-nanometer-sized dual-phase glass-crystal” (SNDP-GC) high-entropy alloy (HEA) composite under cyclic loadings. This composite is produced by embedding CoCrFeNi HEA crystalline grains into a softer CoCrFeNiAl2 HEA glass. Cyclic loadings of different amplitudes are applied on one polycrystalline CoCrFeNi sample and two SNDP-GC HEA samples mentioned above. For the polycrystalline sample, dislocation motion and grain boundary (GB)-mediated deformation control the plastic deformation process, and the sample loses its original structure after a few cycles of the set amplitude due to GB migration. However, for the two SNDP-GC samples, as the grain boundary is replaced by the metallic glass (MG) phase, the dominant plastic deformation mechanism has changed to concentrating shear transformation in the MG phase. Our results also show that structural stability is highly dependent on the MG phase thickness. For the sample with a thinner MG layer, MG cannot accommodate sufficient deformation—so voids are generated in it. However, for the sample with a thicker MG phase, MG can store adequate deformations, thus dislocation initiations in crystalline grains are reduced and void generation is prevented in the MG phase.