EIS comparison on corrosion performance of PVD TiN and CrN coated mild steel in 0.5 N NaCl aqueous solution

AC electrochemical measurement techniques such as electrochemical impedance spectroscopy (EIS) are finding their usefulness in evaluation of the corrosion behaviour of physical vapour deposition coated steel systems. In this work, EIS has been employed to study the corrosion performance of two commercially available hard coatings (TiN and CrN) on mild steel substrate. In order to improve corrosion resistance, a four-layer deposit of each coating material was used. EIS data were acquired at the corrosion potential for each coating material (TiN or CrN) on mild steel in 0.5 N NaCl solution. Interpretation of these spectra reveals the details of the corrosion process as the coated system is immersed in the solution by correlating the coating microstructure. Finally, visual inspection as immersion time increases provides the comparison on pit initiation and progression between TiN and CrN coated systems, as supportive evidence to the EIS analysis.