Formation of gas bubble superlattice in U-Mo alloys: A phase-field study

Abstract

The impact of grain boundary (GB) on the formation and evolution of gas bubble superlattices (GBS) in U-Mo alloys under irradiation is critical for understanding the material behavior in nuclear environments. In this study, a phase-field model coupled Kim-Kim-Suzuki (KKS) model and explicit nucleation algorithm was developed to simulate GBS formation. The accumulation of vacancies and gas atoms led to bubble nucleation, with directional migration of interstitial atoms inducing a shadow effect and causing ordered bubble arrangements. The GBS exhibited stability, with bubble size and lattice constants remaining nearly constant at higher fission densities. The GB was shown to influence GBS formation significantly, with the surrounding region divided into a denuded zone and a peak zone. The width of the denuded zone is influenced by the GB properties. In this work, the relationship between the denuded zone width and the GB absorption strength was derived using a one-dimensional steady-state vacancy diffusion equation. It was found that the denuded zone width increases with an increase in the GB absorption coefficient. The phase-field simulation results were consistent with theoretical predictions. These findings contribute to a better understanding of how GBs affect irradiation-induced microstructural changes in nuclear materials.