Deposition of diamond/β-SiC/cobalt silicide composite interlayers to improve adhesion of diamond coating on WC–Co substrates by DC-Plasma Assisted HFCVD

Diamond/β-SiC/cobalt silicide composite films were synthesized as an interlayer for deposition of adherent diamond coating on Co-cemented tungsten carbide (WC–Co) substrates by direct current plasma assisted hot filament chemical vapor deposition using a gas mixture of hydrogen, methane and tetramethylsilane (TMS). Scanning electron microscopy, electron probe microanalysis, X-ray diffraction and Raman scattering analyses were carried out to obtain information on the surface morphology, composition and structure of the deposited films. The composite films are composed of diamond, β-SiC and cobalt silicides (Co2Si, CoSi). Diamond and β-SiC crystallites are grown simultaneously, and there is a space competition between them during the deposition. Cobalt silicides are formed by diffusion of cobalt from the bulk. The composition of the composite films can be controlled by adjusting the concentration of TMS in the gas phase. Diamond top layers can be in situ deposited on the composite interlayers or deposited on the composite interlayers after ultrasonically seeding. Rockwell-C indentation tests show that diamond/β-SiC/cobalt silicide composite interlayers efficiently improve the adhesion of diamond coating on WC–Co substrates. Through a subsequent treatment in the atmosphere of H2 and CH4 after deposition of the composite interlayer, the adhesion of diamond coating on WC–Co substrates is further improved. It is found that cobalt silicides favour the adhesion of diamond coating on WC–Co substrates.