Line-length-dependent dislocation glide in refractory multi-principal element alloys

Abstract

Plastic deformation of refractory multi-principal element alloys (RMPEAs) is known to differ greatly from those of refractory pure metals. The fundamental cause is the different dislocation dynamics in the two types of metals. In this Letter, we use atomistic simulations to quantify dislocation glide in two RMPEAs: MoNbTi and NbTiZr. Edge and screw dislocations on the {110} and {112} slip planes are studied. A series of dislocation line lengths, ranging from 1 nm to 50 nm, are employed to elucidate the line-length-dependence. To serve as references, the same simulations are performed on pure metals. For the RMPEAs, the dependence of critical stresses on length becomes undetectable within the statistical dispersion for dislocations longer than 25 nm, as a result of the change in dislocation behavior. This length is in good agreement with those predicted by analytical models. Compared to the pure metals, the critical stress anisotropy among different slip planes and character angles is substantially reduced, providing an explanation for the homogeneous plasticity in RMPEAs observed in prior experiments.