Corrosion Resistance of Tool Steel Arc-Deposited Cr-N-O Double-Layered Coatings in 3.5% Sodium Chloride

In this study, the cathodic arc deposition technique was utilized to synthesize three Cr-N-O coatings (chromium nitride [CrN], CrN/Cr[N,O], CrN/chromium oxide [Cr₂O₃]) on AISI M2 tool steel by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases. Polarization tests were performed to evaluate the corrosion resistance of the uncoated and coated specimens in 3.5 wt% sodium chloride (NaCl) solution. Structure and morphology of the coatings were separately analyzed using x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to better understand the coating effects on the corrosive behavior of M2 steel. The results showed that the CrN/Cr(N,O) and CrN/Cr₂O₃ double-layered coatings had higher surface roughness than monolithic CrN, but their dense and double-layered structures resulted in better corrosion resistance. The sequence of corrosion resistance is in the order of CrN/Cr(N,O) > CrN/Cr₂O₃ > CrN > uncoated M2 steel in 3.5 wt% NaCl medium.