Enhancing nucleation density and adhesion of polycrystalline diamond films deposited by HFCVD using surface treaments on Co cemented tungsten carbide

The deposition of diamond films by chemical vapour deposition onto tungsten carbide is an attractive proposition since it can lead to improvements in the life and performance of cutting tools. However, deposition of diamond onto cemented tungsten carbide (WC-Co) dental burs and inserts are problematic due to the cobalt binder in the WC that provides additional toughness to the tool but it causes poor adhesion and low nucleation density. A number of surface treatments can be used to overcome these problems including chemical etching, ion implanting, interlayer coating and bias treatment. Negative biasing of the substrate is attractive because it can be controlled precisely; it is carried out in-situ, gives good homogeneity and results in improved adhesion. On flat substrates, such as copper and silicon, biasing has been shown to give better adhesion, improved crystallinity and smooth surface. In this study, we have used a modified hot filament chemical vapour deposition (HFCVD) system to coat complex shaped tools such as dental burs with polycrystalline diamond films, which have good adhesion and crystallinity. By applying a negative bias to the substrate, we show that the nucleation density, adhesion and surface properties can be improved. The effects of various process parameters such as bias time, emission current, bias voltage and the filament arrangement on the film properties are reported. For machining applications CVD diamond coatings must be hard, wear resistance and having a good quality film.