Hydrogen diffusion behavior in tungsten under anisotropic strain

Abstract

In future fusion devices, the incident hydrogen plasma with high mobility can diffuse deep into tungsten bulk, which is directly relevant with hydrogen isotopes permeation and retention in tungsten. In this work, density functional theory (DFT) and object kinetic Monte Carlo (OKMC) simulations are adopted to investigate the hydrogen diffusion behavior in tungsten under anisotropic uniaxial strain from −2.5% to 2.5%. As presented by our DFT calculations, there are two types of hydrogen diffusion paths when applying strain, including one path perpendicular to the strain direction and another path largely along the strain direction. The migration energy barriers of these two paths have opposite variation tendencies in tensile or compressive condition. Our OKMC calculations based on DFT input show that, in tensile condition, the hydrogen diffusion is restrained despite the lower energy barrier of the corresponding diffusion path. In compressive condition, the hydrogen diffusion along the strain direction is enhanced, while that perpendicular to the strain direction is suppressed. The hydrogen diffusivity under anisotropic strain at the temperature range from 400 K to 1800 K is determined. It is demonstrated that tensile strain can suppress the diffusivity, while compressive strain can either suppress or facilitate the diffusivity depending on the temperature and the strain value. The anisotropic strain exhibits distinct effect on hydrogen diffusivity at lower temperature but its effect is minimal as the temperature increases.