Molecular dynamics modelling of the stress effect on diffusion behavior of hydrogen in tungsten

It has been proved by experiments that the heat load and implantation of hydrogen atoms from plasma of fusion reactors introduce significant stress in plasma facing material, tungsten. However, the stress effect on the diffusion of hydrogen atoms remains unclear. In this work, molecular dynamics simulations combined with the nudged elastic band method were performed to investigate the influence of uniaxial and shearing loads on the site preference, diffusion path and diffusion barrier of hydrogen atoms in tungsten lattices. The simulated results show that the deformation of lattices under external stresses changes the layout of tungsten atoms around interstitial hydrogen atoms, and therefore changes the formation energy. Under uniaxial loads, the alteration of preferable sites between tetrahedral and octahedral sites was observed. Meanwhile, the variation of formation energy also results in the change of both the diffusion path and the diffusion barrier. However, no monotonic relationship between the diffusion barrier and the strain was obtained. Both compressive and tensile stresses can increase the diffusion barrier. Under both uniaxial and shearing loads, diffusion properties of hydrogen atoms differ in directions. For uniaxial compression, it is much easier to diffusion in the loading direction, while for shearing load, it is easier to jump in the direction perpendicular to the shearing plane.