First-principles investigation of hydrogen trapping and diffusion at grain boundaries in nickel

In this work, the interaction of hydrogen with high-angle GBs in nickel has been investigated by means of density functional theory simulations. Two distinct types of GBs have been considered: the Sigma 3 (1 1 1)[(1) over bar 1 0] with a close-packed interface structure and the Sigma 5(2 1 0)[0 0 1] with a less dense interface structure consisting of open structural units. Our calculations reveal that these two GBs have a markedly different interaction behavior with atomic hydrogen. The close-packed Sigma 3 GB neither traps H nor enhances its diffusion, but instead acts as a two-dimensional diffusion barrier. In contrast, the Sigma 5 GB provides numerous trapping sites for H within the open structural units as well as easy migration pathways for H diffusion along the GB plane that can enhance the H diffusivity by about two orders of magnitude compared to bulk Ni. The obtained results are analysed in detail and compared with available experimental and other theoretical data.