Formation of Multilayer Film Composed of Titanium Nitride and Chromium Nitride, and Its Pitting Corrosion Resistance

Abstract

Monolayer TiN films often display poor corrosion resistance due to localized weak spots, and multilayer film composed of several TiN and thin Cr₂N layers was therefore studied in an effort to improve pitting corrosion resistance. A thin Cr₂N layer with a mixing layer formed with the underlying materials was produced by N⁺+N₂⁺ ion implantation into the Cr layer. The multilayer film showed a dense, homogeneous rupture face, unlike the columnar structure observed in the monolayer TiN film. In an anodic polarization test in 3.5wt.% NaCl solution, austenitic SUS 304 stainless steel coated with the multilayer film showed better pitting corrosion resistance than specimens coated with the monolayer TiN film. After this corrosion test, many shallow corrosion marks were observed in the surface of the multilayer film in contrast to the deep pits observed in the surface of the monolayer TiN film. It is thought that the improved pitting corrosion resistance of the multilayer film was due to its stronger inter-column characteristics obtained by the interposing of the multiple thin Cr₂N layers.