FRICTION OF DIAMOND ON DIAMOND AND CHEMICAL VAPOR-DEPOSITION DIAMOND COATINGS

In this work the friction of diamond on diamond in air was studied in an attempt to understand the friction mechanisms. The friction of diamond on chemical vapour (CVD) diamond coatings was also investigated. A reciprocating friction apparatus with a sliding configuration of a stylus on a plate, which enabled the contact area and pressure to be estimated from Hertz theory, was used. The effects of temperature, the number of sliding traversals and the environmental conditions were investigated. It was found that adhesion is important in the friction process of diamond sliding on diamond in air, and that water plays an important role in reducing the adhesion. In the case of the friction of diamond on CVD diamond coatings, relatively low loads were used because of the poor adhesion between the diamond coatings and the substrates (silicon). The friction coefficient of diamond sliding on CVD diamond coating was higher than that of diamond on diamond for the same experimental conditions. It is suggested that this is due to the rougher surface compared with that of a polished diamond. However, the friction coefficient could be substantially reduced by applying water, indicating that adhesion was also present in the friction process.