Microstructure-property relations of reactively magnetron sputtered VC_xN_y films

VC_xN_y 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 solid solution of VN and VC is formed for N₂ and C₂H₂ addition, with increasing fractions of an additional amorphous carbon phase for increasing C₂H₂ flow ratios. 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-disc tests yield low friction coefficients with values of 0.22 for those films with the highest content of 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.