Hydrogen Ingress into Copper-Nickel Alloys

Hydrogen (H) ingress into two copper (Cu)-nickel (Ni) alloys — a commercial 77% Cu-15% Ni alloy (aged) and alloy K-500 (UNS N05500, aged and unaged) — was studied using a technique referred to as hydrogen ingress analysis by potentiostatic pulsing (HIAPP). Anodic current transients obtained for these alloys in an acetate buffer (1 mol L^–1 acetic acid + 1 mol L^–1 sodium acetate [NaAc]) were analyzed using a diffusion-trapping model to determine trapping constants and H entry fluxes. A small increase was observed in the irreversible trapping constant for alloy K-500 with aging. Trapping constants of the aged alloys were similar within the limits of uncertainty, but H entry flux for the 77% Cu alloy was lower than that for aged or unaged alloy K-500. The lower flux may have accounted, at least partly, for the Cu alloy’s higher resistance to H embrittlement. Trap densities were consistent qualitatively with levels of sulfur (S) and phosphorus (P) in the two alloys. This finding supported an assumption that S and P provided the primary irreversible traps.