Atomistic insights into the influence of hydrogen on crack propagation in tungsten

Abstract

Tungsten (W) is regarded as a viable choice for plasma-facing materials in nuclear fusion reactors. However, its mechanical properties are significantly degraded by hydrogen (H) atoms during irradiation, of which the mechanism is still elusive. In this study, we conduct molecular dynamics (MD) simulations to study the impact of H atoms on the propagation of a crack in single crystal W. The results show that the propagation rate of the crack slows down with increasing temperature. This is due to the enhanced plastic deformation, leading to blunting of the crack tip. A pre-existing crack in W is then considered at various temperatures and uniaxial applied tensile strain conditions. The propagation rate of the crack decreases with the increase of the applied tensile strain rate. This phenomenon occurs due to the relaxation of the stress around the crack tip following the emission of the dislocation at high strain rates. After introducing H atoms, it can be observed that at low temperatures, H impedes the propagation of the crack, while at high temperatures, H promotes it. This is primarily due to the formation of voids at the slip traces of dislocations and the reduction in surface energy. Additionally, the crack tip becomes blunted and its propagation rate decreases with increasing strain rate. These results indicate that providing sufficient time for H atoms to migrate is a key factor affecting the mechanical properties of W. The current results provide valuable insights into understanding the interaction mechanism of a crack and H atoms in W.