Defect accumulation and evolution in refractory multi-principal element alloys

Refractory multiple principal elemental alloys (MPEAs) hold great promise for structural materials in future nuclear energy systems. Compared to the extensively studied face-centered cubic (FCC) MPEAs, the irradiation resistance of body-centered cubic (BCC) refractory MPEAs is relatively less known. In this work, we study defect accumulation and evolution in two BCC VTaTi and VTaW MPEAs comparatively through atomistic simulations. For this purpose, we have parameterized the Embedded Atom Method (EAM) potential parameters for V metals. Combined with available potential parameters for other elements, we construct average atom models for the considered alloys to elucidate the effects of chemical complexities in BCC MPEAs. Our results based on Frenkel pair accumulation simulations suggest that the major influence of chemical fluctuations in BCC MPEAs is on the clustering behavior of defects, which leads to discrete point defects or small defect clusters, in contrast to the large defect clusters observed in the average atom model. We further show that the diffusion of interstitial clusters exhibits different modes due to chemical complexity. While interstitials show either three-dimensional or one-dimensional diffusion in the average atom model, the mean free path of interstitials in the random alloy is strongly suppressed. These results provide fundamental insights into the irradiation response of BCC MPEAs and pinpoint the critical role of chemical complexity on defect evolution, which lay the basis for the future development of irradiation-resistant structural materials based on BCC MPEAs.