Effect of alloying on the resistance of Cu-10% Ni alloys to seawater impingement

Cu-Ni castings and wrought pipes nominally contain 1% Fe to 2% Fe, which is added to improve the Cu-Ni alloy's erosion-corrosion resistance. After fabrication, Cu-Ni products are solution heat-treated to dissolve the iron uniformly and form a single-phase alloy. During welding, however, iron can precipitate from solid solution onto grain boundaries in the heat-affected zones (HAZ). During seawater service, these iron-rich precipitates can dissolve preferentially (galvanically), leading to intergranular corrosion of the HAZ. The present report described 90-10 Cu-Ni alloys in which different soluble elements were substiiutedfor iron. Jet-impingement testing in filtered natural seawater showed that 2% In also promoted improved erosion-corrosion resistance. Because indium is very soluble in copper, it should not precipitate in the HAZ during welding and cause intergranular corrosion of the HAZ during seawater service. The present study reviewed the literature on the mechanisms by which iron Is believed to improve the erosion-corrosion resistance, and proposed a different model based on doping of the thin surface oxide-film.