Effect of hydrogen on dislocation structures around a mixed-mode fatigue crack tip in a single-crystalline iron–silicon alloy

The effect of hydrogen on dislocation structures around a mixed-mode fatigue crack tip in a single-crystalline iron–silicon alloy was investigated by cross-sectional electron backscatter diffraction and high-voltage electron microscopy. In contrast to the previously reported results in an inert environment, no dislocation cells were formed around the crack tip in a hydrogen environment. The microscopic features around the crack tip suggest that hydrogen promotes a mode I-type crack growth mechanism, which reasonably explains the observed macroscopic crack growth property.