Hydrogen-enhanced dislocation activity and vacancy formation during nanoindentation of nickel

The effect of hydrogen on dislocation activities during the nanoindentation of Ni(110) is studied by molecular-dynamics simulation at 300 K. The results reveal that the critical event for the first dislocation nucleation during nanoindentation is due to the thermally activated formation of a small cluster with an atom's relative displacement larger than half the magnitude of the Burgers vector of partial dislocations. Hydrogen only enhances homogenous dislocation nucleation slightly; however it promotes dislocation emission, induces slip planarity, and localizes dislocation activity significantly, leading to locally enhanced vacancy formation from dislocations. The present results, thus, prove hydrogen-enhanced localized dislocation activity and vacancy formation to be the main reason of hydrogen embrittlement in metals and alloys.