Arc-evaporated CrN, CrN and CrCN coatings

The results of investigations of some tribological properties of chromium nitride, carbonitride and carbide films, prepared by cathodic arc-evaporation method (CAE) are presented in this article. The chemical composition of films was determined by the WDXs and EDXs. The different carbon content was obtained by using nitrogen and acetylene mixtures of various concentrations as the deposition atmosphere. The carbon content was ranging from 0 to 53 at.%. The adhesion of CrCN films was estimated from the analysis of scratch-test results comprising tangential (friction) force, acoustic emission and morphology of scratch surface. The films showed very good adhesion to steel substrates, expressed by L_c (critical load) value, as high as 90 N for carbon free films. The L_c decreased slightly as the carbon content increased. The hardness of films was investigated as a function of carbon content and was estimated by Jönsson-Hogmark method. The L_c value and hardness seem to be correlated in the same way with carbon content. The highest hardness (30 GPa) was obtained for CrN films, while carbon rich films (CrC) showed hardness at the level of 20 GPa. The tribological tests were performed in the ball-on-disk geometry in room air under the load of 1 N and 10 N. The wear rate of investigated films increased with carbon content above 20 at.%. The maximum value of the friction coefficient was 0.55, the same as for CrN films. It decreased to 0.33 as the carbon content increased.