Effect of grain boundary on the crack-tip plasticity under hydrogen environment: an atomistic study

It has been found that the plasticity is significantly affected by the hydrogen interstitials in metallic materials. However, the underlying physics responsible for the dislocation/hydrogen interactions is still poorly understood. Using molecular dynamics simulations, we study the emission of dislocations from a crack-tip in fcc Ni single crystal and bicrystal samples under hydrogen environment. The results show that the critical Mode-I stress intensity factor (SIF) is reduced due to the presence of hydrogen, but the existence of Σ5 grain boundaries (GBs, with inclination angle ranging from 0 to π/4) almost not alter the critical Mode-I SIF for dislocation emission, compared with the single crystal cases. These findings suggest that further large-scale investigations should be conducted to study the influence of various microstructural factors, such as, the distance from the crack tip to GB and density of GB as well as the existence of other defects, e.g. voids and inclusions.