Short-range order-dependent dislocation mobilities in CrCoNi medium entropy alloy: Atomistic simulations and modeling

Abstract

Understanding dislocation behavior is considered an effective way to design high performance alloys, as it is closely associated with mechanical properties. The existence of short-range order (SRO) and its ability to improve the strength and ductility of high- and medium-entropy alloys (H/MEAs) have been experimentally documented. However, few researches focused on the mechanism of dislocation motion in H/MEAs with SRO. In this study, the correlation between the degree of SRO and edge dislocation mobility in CrCoNi MEA was studied by atomistic simulations. The results show that the dislocation mobility is strongly dependent on the degree of SRO. As the degree of SRO increased, the dislocation mobility decreased linearly due to the increased energy barrier. The dislocation mobility model coupling with the SRO effects was proposed, in which the parameters were determined by molecular dynamic (MD) simulations. The energy barriers varied with the SRO degree were obtained from the model and have been compared with the theoretical predictions. A good agreement between prediction of the model and theoretical values was achieved. Using the drag coefficients obtained from this fitting, a binary linear regression model of the drag coefficient as a function of SRO degree and temperature was constructed. The proposed dislocation mobility model might be important for the construction of mechanistic predictive theory of CrCoNi MEA systems with SRO, and can also provide more accurate and reliable inputs for higher length scale simulations.