Atomistic study of hydrogen effect on dislocation nucleation at crack tip

By atomistic simulations, we show that H is mainly absorbed on the surface of the crack tip in Ni and reveal that H switches from decreasing the activation energy for dislocation nucleation at low load to increasing it at high load, owing to H-reduced activation volume. This counterintuitive finding explains experimentally observed sharp cracks in the presence of H and provides a new atomistic vision of hydrogen embrittlement.