HYDROGEN TRAPPING IN WORK-HARDENED ALLOYS

The ingress of hydrogen in two work-hardened nickel-base alloys (Inconel 625 and Hastelloy C-276) exposed to an acetate electrolyte (1 mol L-1 HAc/1 mol L-1 NaAc where Ac = acetate) was studied using a potentiostatic pulse technique. The data were shown to fit a diffusion/trapping model under interface control, and values were determined for the irreversible trapping constants (k) and the flux of hydrogen into the alloys. The density of irreversible trap defects in Inconel 625 was calculated from k and found to be in excellent agreement with the concentration of NbTi(C) particles. Hastelloy C-276 was characterized by two trapping constants; one is associated with quasi-irreversible traps that saturate, leaving only irreversible traps. The density of irreversible traps was shown to agree with the concentration of phosphorus segregated at grain boundaries. The irreversible trapping constants for these alloys are consistent with their relative susceptibilities to hydrogen embrittlement.