Hydrogen embrittlement severely degrades mechanical properties of austenitic stainless steels (γ-SS), yet the bulk deformation microstructures responsible for this phenomenon have not been directly observed. While the internal microstructure is essential to define metal plasticity, deformation, and fracture, no technique has been able to image the deep subsurface structure. In this work, we use dark-field X-ray microscopy (DFXM) to compare the structure of an annealed single crystal γ-SS sample to one with the same annealing conditions and subsequently hydrogen pre-charged in a high pressure and temperature environment. While the non-charged sample exhibited features characteristic of dislocations packed into boundaries, the pre-charged sample showed diffuse features with a distinctly broader rocking curve characteristic of a higher geometrically necessary dislocation (GND) density. Our results demonstrate the utility of DFXM to characterize the unique subsurface microstructures, offering opportunities for future studies to resolve how these features cause fracture or embrittlement.
Pal et al. (Sun,) studied this question.