Sulfidation under atmospheric conditions of Cu-Ni,Cu-Sn,and Cu-Zn binary and Cu-Ni-Sn and Cu-Ni-Zn ternary systems

The corrosion susceptibility of binary and ternary alloys can be assessed by controlled exposures to corrosive environments of samples selected from different regions of the phase diagram. To conduct such studies, we have prepared 24 high purity alloys from the Cu-Ni, Cu-Sn, and Cu-Zn binary and Cu-Ni-Sn and Cu-Ni-Zn ternary systems. Samples of these alloys were then exposed for varying periods to atmospherically realistic concentrations of hydrogen sulfide in humidified air. The resulting sulfurization of the samples is presented in a series of chromatic plots developed as part of this research. The ability of binary alloying metals to retard the sulfidation of copper follows the order Zn > Ni > Sn. The Cu-Ni-Zn ternary alloys are more resistant to sulfidation than Cu-Ni-Sn alloys for the same extent of solid solution alloying; in fact, alloys in the Cu-Ni-Zn system with ≤70 pct copper proved to be extremely resistant to sulfidation. In both ternary systems, the relative performance of the alloys was different at different exposure periods, a result that emphasizes the importance of monitoring corrosion throughout realistic exposures if the results are to be used in the selection of materials for field applications.