Effects of cemented carbide surface pretreatment in combustion flame chemical vapour deposition of diamond

Abstract

Effects of different pretreatment procedures on WC-6%Co surface modification and some properties of diamond coating deposited by combustion flame CVD on the pretreated surfaces have been systematically studied. The pretreatment procedures examined were: action of an oxidising oxygen/acetylene flame at 1000 degrees C, scratching with diamond (D) particles or their mixture with iron (D + Fe) in an ultrasonic bath, and seeding with a nanometer diamond colloidal suspension. An acid treatment was always included in the pretreatment sequence. The oxidising flame was found to produce fine-grained W, W2C and WO2, resulting in an increased diamond particle density and a lower coating roughness, and leading to a relatively smooth and adherent diamond coating. However, the products of WC oxidation were detectable only if Co had been removed from the substrate surface prior to the action of flame. Otherwise, compounds of Co with P and O were formed, making a skin on the surface, which hindered action of the flame on WC. The acid treatment was found to remove Co effectively from the surface. Seeding resulted in a good coverage of the substrate surface with nano-particles of diamond, leading to a maximum diamond particle density, adhesion improvement and minimum coating roughness. Scratching with D + Fe mixture produced maximum roughness of both substrate and diamond coating surface, as well as low adhesion, while scratching with D particles showed a similar but smaller effect. Minimum surface roughness and maximum adhesion of the diamond coating were obtained for the substrate pretreated by oxidising flame, followed by the acid action and seeding with diamond nano-particles. (C) 1999 Elsevier Science S.A. All rights reserved.