Corrosion behaviour of single layered ZrNxOy thin films in artificial sweat solutions

Abstract

Applications of coloured thin films can be found on the production of high-quality consumer products, such as eyeglass frames, wristwatch casings and wristbands. These components should possess scratch and corrosion resistant surfaces through the desired lifetime. Recently, metal oxynitrides, MeNxOy (Me = early transition metal) were proposed for decorative applications. In these materials, variations on the amount of oxygen allow the film properties to be tailored, originating a wide range of colours. Additionally, these materials should also fulfil the wear and corrosion requirements above referred. In the present work the corrosion behaviour of single layered zirconium oxynitride, ZrNxOy films, immersed in artificial sweat solutions, is described. Films were produced by rf reactive magnetron sputtering at a constant substrate temperature of 300 ºC, from a pure Zr target. The main processing variable was the flow rate of reactive. The corrosion resistance was evaluated by potentiodynamic polarisation tests and Electrochemical Impedance Spectroscopy (EIS) at different immersion times, at room temperature. The corrosion resistance of the films is strongly affected by the O/N ratio. A slight tendency to improving the corrosion resistance of the films was found with the increasing in the atomic fraction of oxygen. Nevertheless, pitting was found in all samples. However, the amount of pits seems to be strongly dependent not only on the composition of the film, but also on the processing-induced defects distribution.