Short-range ordering alters the dislocation nucleation and propagation in refractory high-entropy alloys

Abstract

The role of short-range ordering (SRO) in the dislocation kinetics in refractory high-entropy alloys (RHEAs) remains controversial. On one hand, it was shown by simulations that the mobility of edge dislocations was enhanced while that of screw dislocations was reduced, leading to the conclusion that screw dislocations should be dominant. On the other hand, experiments exclusively showed the dominance of edge dislocations. Here, we investigate the impact of SRO in the grain interior and grain boundary on dislocation nucleation and propagation in a BCC MoTaTiWZr RHEA, using a combination of the density-functional theory calculations, Monte Carlo method, and molecular dynamic simulation. Our results show that this RHEA is energetically favorable to undergo SRO, thus forming a pseudo-composite microstructure. This microstructure consists of three categories of clusters: high energy clusters (HECs), medium energy clusters (MECs), and low energy clusters (LECs), with the HECs in grain boundaries acting as weak fillers to induce dislocation nucleation while the MECs/LECs serving as a strong matrix to stabilize the weak HECs. Importantly, SRO is found to enhance the energy barriers for both edge and screw dislocation motion and make the mobility of edge dislocations comparable to or even lower than screw dislocations, contributing to the dominance of edge dislocations in the BCC RHEA. Our work highlights the importance of SRO in influencing the dislocation activity of RHEAs and presents a fascinating route for designing RHEAs to achieve superior mechanical properties.