Corrosion behaviors of CrNx and (Ti1−xCrx)N coatings produced by ion plating

Abstract

The corrosion behavior of CrNx and (Ti1−xCrx)N coatings, produced by reactive ion plating using thermal and electron beam evaporation, was investigated. To deposit the CrNx coatings, Cr was evaporated by resistance heating and CrNx coatings of various N/Cr composition ratios were obtained by altering the NH3 flow rate. For deposition of the (Ti1−xCrx)N coatings, Ti and Cr were evaporated by electron beam and resistant heating, respectively. The Ti and Cr concentrations were controlled by the Ti to Cr evaporation ratio. Electrochemical properties of the coatings were examined with an EG&G 273 A potentiostat in a pH 7, 0.8 M NaCl solution. The corrosion behavior of both CrN and (Ti,Cr)N coatings showed a similar trend to that of pure Cr. At voltages <0.5 V [versus saturated calomel electrode (SCE)], they showed passivity. However, at voltages >0.5 V (versus SCE), the corrosion current increased abruptly with dissolution of Cr–oxide from the surface oxide layer.