Correlation mechanism between corrosion product film evolution and corrosion resistance for 70/30 Cu-Ni alloy combining DFT calculation and experiments

Abstract

The structural evolution of corrosion product films and the associated mechanism of corrosion resistance change in a 70/30 Cu-Ni alloy were investigated using a combination of multi-scale characterization and in situ electrochemical analysis. The results show that the increase in corrosion resistance during the growth of the corrosion product film is attributed to the synergistic effect of Cu and Ni. First, the transformation of the outer Cu₂O layer from crystalline to amorphous/nanocrystalline structure enhances the resistance of the film to the penetration of aggressive ions. Second, Ni diffuse from the inner layer to the outer layer, doping into the Cu₂O lattice and substituting Cu in Cu₂(OH)₃Cl. This reduces electrical conductivity and enhances the stability of the lattice structure, with DFT calculations providing validation for these effects. These processes enhance the corrosion resistance and stability of the film. The final mature corrosion product film in the static immersion state consists of three layers: the outermost layer of Cu₂(OH)₃Cl, the intermediate Cu-rich layer containing Ni-doped Cu₂O, Cu₂(OH)₃Cl and (Cu, Ni)₂(OH)₃Cl, the inner Ni-rich layer comprising amorphous and nanocrystalline NiO/Ni(OH)₂, Cu₂O, and minor iron oxides.