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. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.