Hydrogen degradation of ductile structural metals, such as Ni alloys, is often characterized by enhanced strain localization prior to failure. Plastic localization may generate “free volume” in the form of excess vacancies, which may contribute to hydrogen-assisted ductile fracture process upon coalescing into voids. Positron annihilation spectroscopy (PAS) and thermal desorption spectroscopy (TDS) were combined to investigate hydrogen-induced free volume generation in Ni-201 thermally pre-charged with 3000 appm hydrogen as a function of imposed plastic tensile strain, deformation temperature, and grain size. The results indicate that hydrogen-enhanced “free volume” contributes to increased work hardening rates and impacts the degree of intergranular failure in hydrogen-charged Ni-201. Electron microscopy and diffraction studies of coarse and fine-grained material highlight the complex interactions between defects and initial microstructure, particularly grain boundary character, during deformation of hydrogen-exposed Ni-201 at 300K and 77K. In light of complementary nanoindentation data revealing hydrogen-induced cross-slip restriction and dislocation-grain boundary interactions, the current results will aid in developing a model for vacancy-enhanced hydrogen degradation of structural metals.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2015-7040 A.