Maximum strength and dislocation patterning in multi-principal element alloys

Abstract: Multi-principal element alloys (MPEAs), commonly termed as medium- or high-entropy alloys containing three or more components in high concentrations, render a tunable chemical short-range order (SRO). Leveraging large-scale atomistic simulations, we probe the limit of Hall-Petch strengthening and deformation mechanisms in a model CrCoNi alloy and unravel chemical short-range ordering effects. It is found that, in the presence of SRO, the maximum strength is appreciably increased, and the strongest grain size drifts to a small value. Additionally, the propensity for faulting and deformation transformation is reduced and accompanied by the intensification of planar slip and strain localization. We reveal strikingly different deformation microstructures and dislocation patterns that prominently depend on crystallographic grain orientation and the number of slip planes activated during deformation. Grain of single planar slip attains the highest volume fraction of deformation-induced structure transformation, and grain with double active slip planes develops the densest dislocation network. These results advancing the fundamental understanding of deformation mechanisms and dislocation patterning in MPEAs suggest a mechanistic strategy for tuning mechanical behavior through simultaneously tailoring grain texture and local chemical order.