Hydrogen-enhanced damage accumulation during ductile crack propagation in Fe–3 wt.% Si single-crystal plates

Hydrogen-assisted cracking arises from the complex interaction between material microstructure, deformation behavior, and hydrogen transport, making its mechanistic interpretation challenging. This study investigates crack extension behavior in Fe–3 wt.% Si single-crystal thin plates with two crystallographic orientations, 001110 and 110001, under air and hydrogen environments. Using a controlled-comparative framework, the role of intrinsic fracture modes in governing hydrogen sensitivity is systematically examined. Under continuous stretching in air, ductile crack growth occurs in both orientations but follows distinct mechanisms: plasticity-dominated ductile crack growth (PD-DCG) in the 110001 orientation and damage-accumulation–controlled ductile crack propagation (DA-DCP) in the 001110 orientation. Under sustained loading in hydrogen, sub-critical crack propagation is observed only in the DA-DCP-dominated orientation. These orientation-dependent responses are associated with differences in slip activity, strain localization, and dislocation behavior at the crack tip. The results suggest that hydrogen does not introduce a new crack-propagation mechanism but instead amplifies intrinsic fracture modes. This framework provides a physically grounded basis for interpreting hydrogen-assisted cracking and identifying fracture-mode-dependent hydrogen susceptibility.