Scanning electrochemical microscopy study on the electrochemical behavior of CrN film formed on 304 stainless steel by magnetron sputtering

The electrochemical behavior of CrN film formed on 304 stainless steel (304 SS) by magnetron sputtering was investigated by scanning electrochemical microscopy (SECM) in redox competition mode and X-ray photoelectron spectroscopy (XPS) in 0.2 M H₃BO₃ + 0.05 M Na₂B ₄O₇ (pH = 8.4) buffer solution containing 3.5 wt% NaCl. The results demonstrated that passive film could form on the surface of CrN film with the chemical compositions of Cr, Cr₂O₃, CrN, Cr(OH)₃, and CrO₃. When applied with 0.9 vs SCE/V potential, the pitting propagation sites corresponded to the high oxygen consumption region. While above stable pit, the Pt microelectrode showed an enhanced faradic current. Separated anodes and cathodes were observed in the scratch, which suggested that the dominant corrosion mechanism is pitting corrosion induced and promoted by galvanic corrosion. These results provide a more explicit description of the corrosion mechanism and processes of CrN film.