Atomistic interpretation of extra temperature and strain-rate sensitivity of heterogeneous dislocation nucleation in a multi-principal-element alloy

Abstract

Incipient plasticity of crystals is usually initiated from versatile pre-existing crystalline defects of different geometries and length scales that formed during materials fabrication and processing, which is closely associated with the mechanical properties. Here we study the heterogeneous dislocation nucleation behaviors from an existing nanoscale void embedded in a prototypical multi-principal-element (MPE) NiCoCr alloy via atomistical exploration of possible minimum energy pathways and analyzes of the dislocation kinetics by a continuum-level mechanistic model, in comparison with the same plastic mechanism in an elemental face-centered cubic copper. It is found that the rough nucleation pathway of dislocation brings about extra thermal softening and strain-rate sensitivity for the critical nucleation stress of dislocation in the MPE alloy, which reproduces the experimental observations. The extra temperature softening is revealed to be associated with the high total entropy of the MPE alloy, in which the configurational entropy plays a dominating role rather than the vibrational counterpart. The extra strain rate sensitivity is caused by the relatively small activation volume in MPE alloy. Our strategy offers physical understanding of the experimental phenomena with atomistic details, which also emphasizes the critical role of configurational disorder in the dislocation accommodated plasticity in the generic complex concentrated alloys.