Friction and wear properties of hard carbon coatings at high sliding speed

The friction and wear behaviours of hard carbon coatings have been studied mainly at low sliding speed. This paper presents a study at high sliding speed (30-35 m s(-1)). Various types of hard carbon coatings were deposited on stainless steel (304L) pins. These coatings are produced by plasma-assisted chemical vapour deposition processes under different deposition conditions, The surface properties and morphology of the coatings have been characterised by surface analysis methods such as scanning electron microscopy and Raman spectrometry. The coated pins slide against a steel XC30 rotating disc. The hardness of disc after heat treatment is 5 GPa. The experimental results show that these coatings exhibit very low friction coefficients and high wear resistances. This behaviour of hard carbon coatings can be explained by the simultaneous presence of the sp(3) and sp(2) bonds hybridisation, by the carbon-hydrogen clusters on the surface of these films, and by hydrogen desorbing from the hard carbon films during friction inducing their reconstruction or creating on them double (pi, sp(2)) bonds.