Defect dynamics in γ-U, Mo, and their alloys

Defect dynamics constitutes the foundation for describing microstructural evolution in any material sys-tems for nuclear applications, including body-centered cubic gamma-U, Mo, and their alloys. However, defect properties and evolution, and the impact of a large atomic size mismatch between U and Mo atoms on defect dynamics have not been elucidated. In this work, we use molecular dynamics to extensively exam-ine composition-dependent defect behavior in U-Mo alloys and the pure metals. It has been found that point defect migration is strongly correlated and mediated by minor atoms via preferential paths in al-loys. Interstitial dumbbells migrate three-dimensionally through the major atoms with a preferred (110) configuration. Vacancies are less mobile than interstitials, but become comparable (one order of magni-tude difference in diffusivity) in U-rich systems. Overall, compared with the pure metals, defect diffusivity can be tuned up or down based on the alloy composition. Finally, interstitial clustering is found to be un-favorable in U-rich systems, as opposed to Mo which exhibits an efficient formation of interstitial-type dislocation loop with 1D diffusion mode. These findings not only provide necessary input to high-fidelity meso-scale simulations of microstructural evolution in these systems, but also have important implica-tions towards explaining radiation effects influenced by the dimensionality and rates of defect diffusion. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The migration of defects in U-Mo alloys and pure metals is found to be composition-dependent, with point defect migration strongly correlated and mediated by minor atoms in alloys. Interstitial dumbbells and vacancies migrate through preferred paths, with vacancies and interstitials showing comparable diffusivity in U-rich systems. Defect diffusivity can be adjusted based on alloy composition.