Deposition Of Diamond-Silicon Carbide-Cobalt Silicide Composite Film By Hot-Filament CVD

Diamond films deposited on the surface of cemented carbide can greatly improve the wear resistance of cemented carbide tools and components, prolong their life, and raise the production efficiency. However, the insufficient adhesion of diamond coating on cemented carbide substrates restricts the application of diamond-coated tools. Diamond-silicon carbide-cobalt silicide composite films were synthesized as an interlayer for deposition of adherent diamond coatings on Co-cemented tungsten carbide (WC-6 wt.% Co) substrates by hot filament chemical vapor deposition using a gas mixture of hydrogen, methane and tetramethylsilane (TMS). Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), Raman scattering (Raman) and Rockwell-C indentation tests were carried out to characterize the surface morphology, composition, and structure of the deposited films.Diamond-silicon carbide-cobalt silicide composite films are composed of diamond,β-SiC and cobalt silicides (Co2Si, CoSi). During the deposition, diamond and P-SiC crystallites grow competitively. Cobalt silicides are formed by diffusion of cobalt from the bulk. The composition and structure of the composite films can be controlled by adjusting the concentration of TMS in the gas phase and bias current. With the increase of TMS concentration in the gas phase, the content of diamond is deceased, the content ofβ-SiC is increased in the composite films, and the grain sizes of both diamond and P-SiC become smaller. Bias current enhances the growth and secondary nucleation of diamond. With the increase of the bias current, the grain size of diamond becomes larger, the content of diamond is increased, and the content ofβ-SiC is decreased.Diamond top layer can be in situ deposited on composite interlayers deposited with lower TMS concentration, because diamond grains on the surface of composite interlayer are not entirely covered by SiC. The interlayers deposited with higher TMS concentration should be ultrasonically seeded, and then diamond top layer can be deposited on them. Rockwell-C indentation tests show that diamond-silicon carbide-cobalt silicide composite interlayers efficiently improve the adhesion of diamond coating on WC-Co substrates. Through a carbon hydrogen treatment after deposition of the composite interlayer, the adhesion of diamond coating on WC-Co substrates is further improved. It is found that cobalt silicides in the composite interlayer favour the adhesion of diamond coating on WC-Co substrates.