First-principles study of hydrogen trapping and diffusion at grain boundaries in γ-Fe

The hydrogen induced intergranular crack is most common in hydrogen embrittlement phenomenon. Hydrogen atoms will preferentially diffuse into grain boundaries and then accumulate in them. Therefore, it is necessary to reveal the diffusion mechanism of hydrogen atoms at grain boundaries, which is helpful for deeply understanding hydrogen embrittlement. In this work, we performed first-principles calculations to investigate the trapping sites and diffusion behaviours of hydrogen atoms at Sigma 3 [(1) over bar 10] (111), Sigma 5 [(1) over bar 00] (021) and Sigma 9 [110] (2 (2) over bar1) grain boundary structures of gamma-Fe. Hydrogen atoms have no tendency to be segregated from the bulk to the Sigma 3 GB but hydrogen atoms tend to segregate into the Sigma 5 and Sigma 9 GBs. The solution energy of hydrogen in grain boundaries is mainly the consequence of the chemical bonding between Fe atoms in GBs and the hydrogen atom. In addition, according to the hydrogen diffusion behaviour in grain boundaries, Sigma 3 and Sigma 5 GBs act as three-dimensional barriers for hydrogen migration while the Sigma 9 GB acts as a one-dimensional barrier for H diffusion. Significantly, the difficulty of hydrogen diffusion along grain boundary mainly depends on the connectivity of low electron density region along grain boundary. This conclusion can provide a deep understanding of hydrogen distributions at different grain boundaries in metal materials, which is helpful for hydrogen embrittlement resistant materials design on the basis of grain boundary regulation. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the trapping sites and diffusion behaviors of hydrogen atoms in different iron grain boundary structures through first-principles calculations. The diffusion behavior of hydrogen in grain boundaries was found to have an impact on hydrogen embrittlement phenomenon.