The dual role of hydrogen in grain boundary mobility

The effect of solute hydrogen on shear-coupled grain boundary (GB) migration is investigated with the dislocation-array type sigma 25(430)[001] GB and a dual role of hydrogen on GB mobility is unraveled. In the low temperature and high loading rate regime, where hydrogen diffusion is substantially slower than GB motion, GB breaks away from the hydrogen atmosphere and transforms into a new stable phase with highly enhanced mobility. In the reverse regime, hydrogen atoms move along with GB, exerting a drag force on GB and decreasing its mobility. These findings provide rationale for the coexistence of hydrogen hardening and softening observed experimentally in polycrystalline materials.

Automated summary

The effect of solute hydrogen on shear-coupled grain boundary migration was studied and the dual role of hydrogen on grain boundary mobility was revealed. At low temperature and high loading rate, where hydrogen diffusion is slower than grain boundary motion, the grain boundary breaks away from the hydrogen atmosphere and transforms into a new stable phase with enhanced mobility. In the reverse regime, hydrogen atoms move along with the grain boundary, exerting a drag force and decreasing its mobility. These findings provide a rationale for the coexistence of hydrogen hardening and softening observed experimentally in polycrystalline materials.