Abstract:The microstructures of two kinds of Cu-Ni alloys were observed by TEM. The results show that one of the alloys is a homogeneous solid solution. The other contains discontinuous precipitates at some grain boundaries,and the precipitate is a phase rich in Fe-Ni. By monitoring the corrosion potential (E_corr) in artifical seawater and exposure to naturral seawater for a long time, it is found that the E_corr of the former alloy steadily decreases,while the E_corr of the latter decreases a little and fluctuates, and the corrosion rate of the former is clearly lower than that of the latter. Aanalyses of SEM and EDX show that the corrosion product film of the former is thin,uniform, compact and rich in nickel, and the film of the latter is thick, loose and covered with numerous deposits.Additionally serious intergranular corrosion occurs in the underlying substrate of the latter. The author proposes that the intergraular corcosion results from preferential dissolution of discontinuous precipitates at grain boundaries. In addition, the protective characteristics of corrosion product films are related not only to the enrichment of nickel but also to their compactness.

Key words: Cu-Ni alloy  microstructure  corrosion resistance  seawater corrosion  potential  corrosion