Grain-level plasticity response of pure Nickel based on the presence of hydrogen charging

The presence of hydrogen affects the plasticity response and mechanical properties of structural metals and alloys, thus playing a critical factor under aggressive environmental conditions. Nevertheless, a knowledge gap is present at the mesoscale level regarding the role of hydrogen in the relation between the nanoscale characteristics and macroscopic plastic response. Pure nickel specimens in the non-charged and hydrogen-charged conditions were characterized using high-energy X-ray diffraction microscopy (HEDM) during in-situ mechanical loading to retrieve the grain-level evolution of stresses. The HEDM experiments revealed that hydrogen induces a tensile average hydrostatic stress at the grain-level, consistent with hydrogen atoms positioned at vacancy sites instead of interstitial locations. The resulting lattice distortion indicates the capability of hydrogen atoms to reduce the material cohesive strength and promote crack propagation and fracture. Additionally, the hydrogen-charged specimens presented a higher resolved shear stress, representing a higher resistance against crystallographic slip, while exhibiting no difference in the work hardening rate compared to non-charged specimens.