Coupling effect of grain boundary and hydrogen segregation on dislocation nucleation in bi-crystal nickel

Abstract

Both hydrogen segregation and grain boundary (GB) have the profound effects on mechanical properties of materials. In this work, the coupling effect of GB and hydrogen on the tensile response in Fcc Ni were investigated by molecular dynamics simulation. The results reveal that hydrogen at 0.01 at.% bulk concentration can increase the yield strength of the bicrystal with the Σ 3/(1 1 1)/109.47° GB from 13.57 GPa to 14.09 GPa, while it can decrease the yield strength of the bicrystal with the Σ 9/(2 2 1)/141.06° GB from 5.97 GPa to 5.37 GPa, which indicates that both hydrogen and GB play the important roles in dislocation nucleation. In addition, hydrogen-induced GB instability and hydrogen segregation promote dislocation nucleation and emission in the high energy grain boundary (HEGB) and then decreases the yield strength of the bicrystal with the HEGB; whereas the low energy grain boundary (LEGB) is the opposite. We also calculated the energy barriers for dislocation nucleation at various classifications of GB. There is a strong correlation between the energy barrier and grain boundary energy. The LEGB requires higher stress and activation energy to dislocation nucleation compared to the less stable HEGB.