HYDROGEN INGRESS INTO COPPER-NICKEL-ALLOYS

Hydrogen (H) ingress into two copper (Cu)-nickel (Ni) alloys - a comme rcial 77% Cu-15% Ni alloy (aged) and alloy K-500 (UNS N05500, aged and unaged) - was studied using a technique referred to as hydrogen ingre ss analysis by potentiostatic pulsing (HIAPP). Anodic current transien ts 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 diffus ion-trapping model to determine trapping constants and H entry fluxes. A small increase was observed in the irreversible trapping constant f or 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 r esistance to H embrittlement. Trap densities were consistent qualitati vely with levels of sulfur (S) and phosphorus (P) in the two alloys. T his finding supported an assumption that S and P provided the primary irreversible traps.