Plasma boronitriding of WC(Co) substrate as an effective pretreatment process for diamond CVD

Cobalt-cemented tungsten carbide (WC–Co) is a widely used material for making cutting tools. Coating these tools with a protective diamond film should improve their lifetime and performance. However, the deposition and adhesion of diamond films on this material are hindered by the presence of the cobalt binder. To overcome this problem, we have developed a simple substrate pretreatment method with plasma boronitriding. The addition of NH3 to B2O3–H2 plasma can prevent cemented carbide from being etched in the plasma pretreatment and the binder phase-cobalt in the surface of the substrate was passivated during the plasma boronitriding process. Raman spectra showed that our pretreatment method efficiently reduced the catalytic effect of cobalt that leads to the formation of a non-diamond type of carbon layer between diamond coating and substrate. Indentation tests on diamond coated tungsten carbide substrate showed that the adhesion of diamond films significantly improved with plasma boronitriding the surface of cemented carbide.