Corrosion behaviors of Cr(N,O)/CrN double-layered coatings by cathodic arc deposition

In this study, the Cr(N,O)/CrN double-layered coatings on tool steel were deposited using cathodic arc deposition process. CrN layer was first deposited on tool steel as an interlayer to ensure better adhesion. Then Cr(N,O) was deposited as a surface layer. The Cr(N,O) composition was varied by changing the O2/N2 flow ratios during the coating process. The phase structure, chemical composition, and morphology of coatings were observed by utilizing X-ray diffractometer, Auger electron spectrometer and AFM. The corrosion behavior of coatings was investigated using polarization and immersion tests. Polarization test of coatings was carried out in the solution of 3.5 wt.% NaCl. For immersion test, Cr(N,O)/CrN double-layered coatings were exposed under H2SO4 environment for 26 h. The results showed that the corrosion resistance of Cr(N,O)/CrN double-layered coatings with thinner thickness with thinner thickness was better than that of CrN single layer since pinholes of coatings was inhibited by double layer structure.