TRIBOLOGICAL BEHAVIOR OF CHEMICAL VAPOR-DEPOSITION DIAMOND FILMS ON VARIOUS CUTTING TOOLS

Abstract

Diamond films were deposited using a hot-filament-assisted chemical vapour deposition system on various cutting tool materials (i.e. cemented WC, sintered SiC, Si-Al-O-N, etc.). The friction coefficients of the films, the adhesion strengths of the films on the substrates, and the surface roughnesses of the substrates and the films were measured and their correlations analysed. The results indicate that the cutting performance of the diamond-coated inserts is strongly related to the adhesion strength and the friction coefficient of the film. Furthermore, the adhesion strength is also dependent upon the surface Co content and the surface roughness of the pretreated substrate, and the friction coefficient of the film is a function of the surface roughness and the quality and size of the diamond microcrystals. There exists an appropriate range of the substrate roughness values for an optimum adhesion strength. For the cemented WC substrates, the pretreatments of the substrate to remove the surface Co and to microscratch the surface to obtain an optimum surface roughness are essential to the growth of films with a lower friction coefficient and a better cutting performance. The cutting performance of the films on the cemented WC substrates is better than that of those on the sintered SiC or the Si-Al-O-N substrates. This is because there is a lower friction coefficient and a much higher adhesion strength of the film on the cemented WC substrates.