Hydrogen effect on the nanohardness in the vicinity of grain boundary: Experiment and theory

Abstract The nanoindentation (NI) technique was employed to investigate the hydrogen effect on nanohardness near grain boundary (GB) of a polycrystalline nickel sample in the present work. An increase of nanohardness due to hydrogen segregation at GB was captured by nanoindentation experiments. With a newly developed GB hardening model, the observed hardening effect upon approaching GB in both H free and H charged polycrystalline Ni was explained. By combining the new GB hardening model with the model depicting dislocation transmission across GB, the hydrogen induced energy barrier enhancement was calculated, which can be used in multi-scale modeling of dislocation–GB interaction. The finding of this work is important for understanding hydrogen embrittlement mechanism of polycrystalline metals.