Corrosion and mechanical studies of chromium nitride films prepared by ion-beam-assisted deposition

Abstract

Chromium nitride films are known as good protective layers for both corrosion and wear attack. In the case of corrosion protection in particular they are expected to be superior to comparable titanium nitride layers. Therefore they are very interesting as a partial or complete substitute for the “classical” electrolytically deposited hard chromium coatings that have been in use for decades, an issue more and more critical from an ecological point of view. As it is not possible to synthesise chromium nitride, as in the case of titanium nitride, by simply evaporating chromium in a nitrogen atmosphere, the layers had to be prepared by evaporation and simultaneous irradiation with nitrogen ions. Hereby the main parameter determining the composition and properties of the films is the arrival ratio of impinging nitrogen ions to condensing chromium atoms ( I/A). The formation of chromium nitride was proved by means of Auger electron spectroscopy and additionally by corresponding X-ray diffraction (XRD) measurements. Compared with pure chromium deposited under argon irradiation, these coatings show a compressive instead of a tensile stress as measured in situ with the bending cantilever method and subsequently will be investigated with XRD. Corrosion tests and hardness measurements with the films on metal substrates were also performed. Taking into account the optimisation possibilities of the ion-assisted-beam deposition technique, these results, indicate very promising potential for future applications.