Surface-structure dependence of healing radiation-damage mechanism in nanoporous tungsten

摘要: Under nuclear fusion environments, displacement damage in tungsten (W) is usually caused by neutrons irradiation through producing large quantities of vacancies (Vs) and interstitials (SIAs). These defects not only affect the mechanical properties of W, but also introduce trap sites for implanted hydrogen isotopes and helium. Nano-structured W with high fraction of free surfaces has been developed to mitigate the radiation damage. However, the mechanism of the surface reducing defects accumulation is not well understood. Using multiscale simulation methods, we investigated the interaction of the SIA and V with different surfaces at across length and time scales. We found that, at a typical operation temperature of 1000K, surface (110) preferentially heals radiation damage of W compared with surface (100) and boundary (310). On surface (110), the diffusion barrier for the SIA is only 0.68eV. The annihilation of the SIA-V happens via the coupled motion of the V segregation towards the surface from the bulk and the two dimensional diffusion of the SIA on the surface. Such mechanism makes the surface (110) owe better healing capability. On surface (100), the diffusion energy barrier for the SIA is 2.48eV, higher than the diffusion energy barrier of the V in bulk. The annihilation of the SIA-V occurs via the V segregation and recombination. The SIA was found to migrate one dimensionally along a boundary (310) with a barrier of 0.21eV, leading to a lower healing efficiency in the boundary. This study suggested that the on-surface process plays an important role in healing radiation damage of NP W in addition to surface-enhanced diffusion and annihilation near the surface. A certain surface structure renders nano-structured W more radiation-tolerant.