Electrochemical characteristics of CrN thin films prepared by ion-beam-enhanced deposition

It has been known that CrN has high hardness and high resistance against wear, oxidation and corrosion. Although many studies have been done on its mechanical and high temperature oxidation properties, studies on its electrochemical and corrosion properties in aqueous solutions are still limited. The aim of this study is to produce CrN thin films by ion-beam-enhanced deposition (IBED) and to make clear the corrosion behavior of CrN by electrochemical measurements. CrN thin films were prepared by IBED under various conditions and their polarization curves were measured in 1 kmol·m^-3 H₂SO₄ and 12 kmol·m^-3HCl. Changes in the surface of the thin films by polarization were examined by XPS and in-situ ellipsometry. The thin films prepared by IBED were composed of the large amount of CrN and small amounts of Cr₂N and Cr. The fraction of CrN in the films increased with increasing flow rate of nitrogen. Potentiodynamic polarization curves exhibited that the active dissolution rate of the films decreased with increasing CrN content of the films. The films with high CrN content showed excellent corrosion resistance up to the start potential of transpassive dissolution without formation of passive films. That is, the excellent corrosion resistance of CrN results from the intrinsic inactive nature of CrN surface.