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Abstract

Hydrogen impurities in iron and steels can degrade the mechanical properties of the material, which is referred to as hydrogen embrittlement (HE). One of the proposed mechanisms of HE is that H interstitials segregate towards grain boundaries (GB) and weaken the bonding between Fe atoms and thus the cohesion in the interface region. In our work, we study the interaction between low-energy Σ5 and Σ3 GBs in bcc Fe using density functional theory (DFT). We find that both GBs can provide an energy trap of 0.5 eV for H interstitials. The H interstitials can change the local coordination of neighboring Fe atoms and affect the local magnetic moments of these Fe atoms. The local coordination of Fe atoms within the GBs has a significant effect on the local magnetic moments. Applying nudged elastic band calculations, migration barriers of 0.3 eV for H to diffuse within the Σ5 GB interface and of 0.6 eV for H to diffuse away from the interface are obtained. We are now setting up a lattice kinetic Monte Carlo (kMC) model to study H diffusion in the vicinity of the GBs. The input parameters of the kMC simulations are based on DFT energetics.