A simulation framework was presented for the understanding of the fundamental issues associated with H-assisted dislocation nucleation and mobility using Monte Carlo and molecular dynamics methods. In order to study the interaction between H and dislocations and its effect on material failure, an extensive examination was made of the mode-I loading of an edge crack using molecular dynamics simulations. The molecular dynamics calculations of the total structural energy in the Ni–H system showed that H atoms preferred to occupy octahedral interstitial sites in the face-centered cubic Ni lattice. As the H concentration was increased, the Young’s modulus and the energy required to create free surface decreased, resulting in H-enhanced localized plasticity. The molecular dynamics simulations also indicate that H not only facilitates dislocation emission from the crack tip but also enhances dislocation mobility, leading to softening of the material ahead of the crack tip. While the decrease in surface energy suggested H embrittlement, the increase in local plasticity induces crack blunting and prohibits crack propagation. The mechanisms responsible for transitioning from a ductile to brittle crack behavior clearly depend on the H concentration and its proximity to the crack tip. Enhanced plasticity will occur within a general field of H atoms that results in lower stacking fault and surface energies, yet H interstitials on preferential slip planes could inhibit dislocation nucleation.

A Nanoscale Study of Dislocation Nucleation at the Crack Tip in the Nickel-Hydrogen System. K.N.Solanki, D.K.Ward, D.J.Bammann: Metallurgical and Materials Transactions A, 2011, 42[2], 340-7