Hydrogen Permeability and Diffusivity in Nickel and Ni-Base Alloys

Electrochemical hydrogen permeation experiments were performed on polycrystalline nickel and nickel-base alloys in order to study the factors affecting the entry and transport of hydrogen in such materials. The diffusivity of hydrogen is found to be dependent upon alloy composition, prior cold work, and the concentration of hydrogen absorbed into the solid. The addition of P, S, and As compounds to the electrolyte promotes hydrogen absorption as expected. Within the limits of the experimental approach pursued in this study, thermal treatment intended to induce grain boundary solute segregation did not appear to affect hydrogen permeation characteristics. On the other hand, nickel-base glassy alloys, which are considered to be bulk analogs of segregated grain boundaries in nickel, are found to absorb considerable amounts of hydrogen. The latter suggests that segregated impurities may induce intergranular cracking by promoting hydrogen absorption at grain boundaries and in their vicinity.