Microstructure–property relations of reactively magnetron sputtered VCxNy films

VCxNy films with a wide range of chemical composition were grown onto silicon and high-speed steel substrates using reactive unbalanced magnetron sputtering from V targets in an Ar/N2/C2H2 atmosphere at a substrate temperature of 500 °C. A nanocomposite structure is formed, consisting of a VN–VC solid solution and an amorphous carbon phase. While an increase in hardness is observed for low carbon contents due to solid solution hardening, raising the amorphous carbon phase fraction results in a hardness reduction. Dry-sliding ball-on-disk tests yield low friction coefficients with values of 0.22 for those films with the highest content of an amorphous carbon phase, while the lowest wear is observed for films with dominating vanadium carbonitride solid solution. The low friction behavior is attributed to the formation of tribo-layers with easy-shearable C―H bonds formed in humid atmospheres, and is not observed in dry nitrogen and synthetic air.