Low-valence ion addition induced more compact passive films on nickel-copper nano-coatings
School of Engineering
Funding information available at: https://doi.org/10.1016/j.jmst.2019.05.051
Ni-Cu nano-coatings were prepared by pulsed electroplating technique in the baths containing various amount of boric acid. Their microstructure, morphologies and corrosion resistance were characterized in detail. The addition of boric acid strongly influences on the microstructure of the Ni-Cu coatings. The coating with a grain size of 130 nm, obtained from the bath containing 35 g L−1 boric acid, shows the highest corrosion resistance. This is attributed to the low-valence Cu ion (Cu+) additions in nickel oxide, which could significantly decrease the oxygen ion vacancy density in the passive film to form a more compact passive film. The higher Cu+ additions and the lower diffusivity of point defects (D0) are responsible for the formation of more compact passive film on the coating obtained from the bath with 35 g L−1 boric acid.