Grain Boundary Contributions to Hydrogen-Affected Plasticity in Ni-201

Hydrogen embrittlement of structural materials, such as nickel-based alloys, is often characterized by enhanced dislocation processes as well as grain boundary decohesion leading to macroscale intergranular fracture. Nanoindentation and scanning probe microscopy (SPM) were used to characterize slip transfer across random grain boundaries and Σ3 recrystallization twins in annealed Ni-201. Thermal hydrogen charging leads to an increase in slip step width within pileups produced by nanoindentation along grain boundaries. The likelihood of slip transmission in the presence of hydrogen depends on the ease of slip within adjacent grains as well as on the misorientation of the grain boundary between them. The observed changes suggest that hydrogen limits dislocation cross-slip while increasing overall dislocation mobility. Coupled nanoindentation and SPM investigations provide a unique, local method for analyzing hydrogen effects on dislocation plasticity, which will be useful in developing grain-boundary-engineered materials.