Evolution mechanism of element Ni on matrix, surface and interface during static soaking of copper-nickel alloy

This article uses XRF, WLI, SEM, EDS, XPS and EIS techniques to characterize the surface element segregation and the state of corrosion product films under different periods of artificial seawater immersion. The research results show that when the film is intact, a uniform Ni-rich layer is formed below the film due to the preferential dissolution of Cu elements, which weakens the segregation degree of Ni elements on the surface of the substrate. At the same time, Ni elements enter the film in the form of doping, which increases the resistance of the film. When the film layer is damaged, the Ni-rich layer between matrix and surface will be rapidly converted to NiO, the enrichment state of Ni element will be destroyed, and the segregation degree will be increased. However, NiO only plays a temporary protective role, and it is easy to hydrolysis into loose Ni (OH)2, resulting in the film layer fall off. After the matrix is exposed, the Cu element is preferentially dissolved again, and the nickel-rich layer is re-formed on the substrate surface.