Unveiling remarkable hydrogen accumulation near ferrite crack tip: Role of unloading effect

We investigate the effect of stress state and hydrogen traps on hydrogen distribution proximity to ferrite crack tip. The results of hydrogen microprint and microstructure characterization indicate that diffusible hydrogen accumulates within crack wake, but the region of hydrogen enrichment ahead of crack tip is tiny according to Ag distribution. By comparing experimental data and numerical calculations, we conclude that the unloading-induced compressive stress region ahead of the crack tip leads to the formation of an overall diffusible H-depleted zone, thereby inhibiting the forward progression of the Ag enrichment zone ahead of the crack tip, whereas the extended size of Ag clustering area within crack plastic wake is primarily attributed to the level of crack plasticity generating dislocation and vacancy traps.