Dislocation-induced ordering as a source of strengthening in refractory multi-principal element alloys

In refractory multi-principal element alloys (RMPEAs), the rapid atomic diffusion occurring near dislocations facilitates local segregation and chemical ordering, leading to the formation of unique atomic environments capable of pinning dislocations on slip planes. However, previous atomistic simulations have largely overlooked how dislocations induce these unique atomic environments and influence the strengthening mechanism. In this study, we systematically investigate the atomic environments generated by dislocations during annealing and their effects on the mechanical properties of body-centered-cubic (BCC) RMPEAs using hybrid Monte Carlo/molecular dynamics simulations. A machine-learning interatomic potential is specifically trained for these RMPEAs. Our results reveal that the dislocation-core energy, elemental mixing energy, and dislocation-stress field collectively determine unique atomic environments, which strongly pin dislocations and significantly increase the critical resolved shear stress. As the atomic rearrangement near the dislocation core progresses, the enhanced pinning effect of edge dislocations arises from the continuous narrowing of the dislocation-core width, while the increased pinning of screw dislocations is attributed to the dislocation line becoming more kinked. In particular, edge dislocations exhibit a much stronger pinning effect than screw dislocations, consistent with recent experimental results.