Indentation response of fullerene-like CNx

Fullerene-like CNx coatings deposited by magnetron sputtering onto samples maintained at elevated temperature have been found to exhibit excellent tribological properties. The coatings are amorphous and, in common with similar amorphous materials, show a very high Young’s modulus to hardness ratio which means that asperities are more likely to remain elastic in tribological contacts compared to conventional hard coatings with similar hardness. The fracture toughness of the film is comparable to that of other hard coatings but the interfacial toughness is lower, even on substrates such as silicon which forms strong chemical bonds with carbon. If the adhesion is good enough the coatings show low friction and better wear performance than conventional hard coatings such as TiN. However, in low frequency dynamic contacts the material shows hysteretic behaviour leading to energy dissipation in the film in the indentation cycle. This probably explains the fact that the friction coefficient is higher for these materials than is observed for the best diamond-like carbon films. Fullerene-like CNx is best regarded as a superhard rubber.