Corrosion behavior and interfacial microstructure evolution of Cu-15Ni-8Sn alloy in NaCl solutions containing various sulfide concentrations

The corrosion behaviors of Cu-15Ni-8Sn alloy in 3.5 wt.% NaCl solution with absence and presence of sulfide ion (S 2- ) are investigated in this paper. The scanning vibrating electrode technique (SVET) investigation shows the corrosion rate increasing obviously with the concentrations of S 2- greater than or equal to 10 mg L -1 in the solution. A long-term static corrosion weight loss tests, morphology observation, chemical component analysis, and electrochemical measurement are employed to explore the corrosion mechanism of the alloy in solutions with and without S 2- . The results show that Cu-15Ni-8Sn alloy has a high corrosion susceptibility to S 2- ions in Cl - coexisting solution. The corrosion rate will increase from 0.0209 mm y -1 (0 mg L -1 S 2- ) to 0.0342 mm y -1 (10 mg L -1 S 2- ). In the S 2- free solution, the continuous, dense, and well-adherent corrosion product film formed on the Cu-15Ni-8Sn surface mainly consists of an oxide located at the inner side and a basic copper chloride located at the outer layer. In the solution containing 10 mg L -1 S²⁻ ions, the corrosion product film formed on the alloy surface consists primarily of copper-nickel-tin oxides and a small amount of sulfides in the outer side and inner layers, a thin intermediate layer of copper chlorides. This porous corrosion product film is non-uniform and prone to developing numerous cracks, offering a poor protection to the substrate. The HS - ion derived from S 2- ion is more easily adsorbed onto the surface of Cu-15Ni-8Sn alloy with defective areas, leading to severe localized corrosion such as pitting and intergranular corrosion, thereby accelerating the corrosion rate of the alloy.