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

Defect dynamics constitutes the foundation for describing microstructural evolution in any material systems for nuclear applications, including body-centered cubic γ-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 examine 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 alloys. 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 magnitude 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 unfavorable 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 implications towards explaining radiation effects influenced by the dimensionality and rates of defect diffusion.