Electrochemical impedance spectroscopy (EIS) study on corrosion performance of CrAlSiN coated steels in 3.5 wt.% NaCl solution

CrAlSiN coatings with Si contents from 0 to 11.5 at.% were deposited on AISI420 stainless and mild steels by magnetron sputtering. According to the broadened peaks in XRD patterns, an effect of grain refinement due to Si doping was verified in the as-deposited CrAlSiN coatings. Investigations by electrochemical impedance spectroscopy (EIS) were carried out in 3.5 wt.% NaCl solution, and the dependence of the nitride/steel configuration on the corrosion behavior was revealed in this study. Two different mechanisms were proposed for the CrAlSiN/AISI420 and CrAlSiN/MS configurations. For coated AISI420 samples, the CrAlSiN coatings revealed significant improvements on charge-transferred resistance (Rct) with increasing Si content. These improvements were attributed to the dense microstructure of the CrAlSiN coatings. In contrast, CrAlSiN coatings deposited on mild steel substrates exhibited no specific trend on Rct in EIS tests. From the observation of the pitting holes, the lower Rct was attributed to serious delamination of the CrAlSiN coatings. In this case, the adhesion between coatings and mild steels was responsible for the measured Rct rather than the microstructure.