AN AC-IMPEDANCE STUDY ON PVD CRN-COATED MILD-STEEL WITH DIFFERENT SURFACE ROUGHNESSES

CrN coatings produced by physical vapour deposition (PVD) technology o n mild steel of different surface roughness have been characterized us ing a.c. electrochemical impedance spectroscopy (EIS). It was found th at as the roughness of the substrate decreased, the number of flaws, e videnced by the frequency and size of initial corrosion sites, also de creased. Thus it was concluded that coating porosity controlled the in itiation of corrosion on the underlying substrate. In addition, the co ating adhesion increased substantially as the substrate roughness decr eased. As corrosion was seen to progress via an undermining mechanism with volume expansion and subsequent cracking bf the coating, it was c oncluded that coating adhesion greatly influenced the propagation of c orrosion on PVD-coated metals.