Atomistic studies of hydrogen effects on grain boundary structure and deformation response in FCC Ni

The effect of hydrogen in the grain boundary on the mechanical response of random microstructures was studied by using atomistic simulation techniques and model interatomic potentials. The model interatomic potentials mimic properties of interstitial H in fcc materials within the limitations of empirical force laws. We report fully three-dimensional atomistic molecular dynamics studies of the mechanical response of identical samples with and without H in the grain boundaries. H content changes the structure of the grain boundaries and plays a critical role in the emission of dislocations from the grain boundaries under an applied stress. For lower deformation levels, the presence of H increased the yield strength of the samples, whereas for higher deformation levels, it increased dislocation emission from grain boundary sources, resulting in an increase in the number of dislocations in pile-ups at the grain boundaries. Increasing the H content resulted in increasingly larger cracks being formed on the grain boundaries, consistent with decreased grain boundary cohesion. Our results support a picture of hydrogen embrittlement resulting from the combined effects of hydrogen on plasticity as well as grain boundary decohesion. (C) 2016 Elsevier B.V. All rights reserved.