Study on the corrosion behavior and pitting mechanism of Ni-based alloy coatings in chloride ion media

The metastable pitting characteristics of Ni-based alloy coatings in chloride ion media have been investigated, and a pitting model based on empirical electron theory (EET or Yu Ruihuang electron theory) was developed to analyze the pitting mechanism. The results indicate that higher chloride ion concentrations promote the metastable pitting behavior and increase the pitting susceptibility. However, passivation films on Ni-based alloy coatings always exhibit n-p semiconductor properties over a range of chloride ion concentrations. Metastable pitting occurs in the intergranular area of Ni-based alloy coatings because of the high cohesive energy of intergranular compounds.