Electrochemical noise and impedance study on the corrosion of electroplated Ni-Cr coatings in HBF4 aqueous solution

Abstract

This work aimed to investigate the corrosion mechanisms of NiCr electroplated coatings in HBF4 aqueous solution, using electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (EN). Among coatings with various Cr content, the polarization resistance of Ni-19 wt% Cr electrodeposited at 0.3 A cm−2 was three times higher than that of pure Ni, and its localization index was 0.06 compared to 0.36 for pure Ni coating. These results, together with the cumulative probability plots of event frequency, according to Shot noise theory, indicated the effective presence of Cr in diminishing both uniform and localized corrosion. Also, using stochastic theory, it was revealed that by introducing Cr up to 19 wt% into the coatings, the initiation rate of the pitting nuclei could be reduced to one-sixth value compared to that of pure Ni coating. Subsequently, the propagation probabilities of the metastable pits were considerably decreased.