Tribological properties of ta-CNx coatings with different nitrogen content under oil lubrication conditions

Carbon nitride (CNx) coatings exhibit a wide range of attractive properties that make them suitable for demanding mechanical and tribological applications. In this study, an ion beam assisted filtered arc deposition (IBA-FAD) method has been developed for the deposition of tetrahedral amorphous carbon nitride (ta-CNx) coatings. The ta-CNx coatings with various nitrogen contents were deposited by controlling the nitrogen flow to investigate the effects of nitrogen content on their tribological behavior. The composition and structure of the ta-CNx coatings were evaluated using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The tribological properties were examined using a ball-on-disk tribo-tester under oil lubrication condition. The results showed that nitrogen contents of ta-CNx coatings were restricted to the range of 0-11 at.% by nitrogen ion density. The hardness decreased with an increase in the nitrogen content as nitrogen decreased the fraction of sp3 carbon in the coatings. The ta-CNx coatings exhibit low friction under oil lubrication and the maximum value was obtained for samples containing 8 at.% of nitrogen. ta-CNx with 8-11 at.% of nitrogen exhibited markedly low wear rate.