Diffusion of cobalt in diamond films synthesized by combustion flame method

It is well known that Cobalt (Co) plays an important role during diamond deposition on cemented carbide substrates (WC). The presence of cobalt on the substrate lead to decrease adhesion and increase the formation of non-diamond compounds phases. However, the diffusion phenomenon of cobalt in diamond coatings is not well understood. We have carried out a detailed study to investigate the diffusion of cobalt during the nucleation and growth of diamond on WC-Co substrate by combustion-flame method, and the influence of it on the structure and quality of the diamond coatings. At high substrate temperature T-s > 800degreesC, ball-sharp of cobalt with a ball size about 0.7 mum was observed on the top surface of diamond coatings (thickness >50 mum). The constraints in the coating are very high, the Raman peak appearance at 1341.1 cm(-1). At relatively low substrate temperature, T-s is about 550 degreesC, ball sharp of cobalt was not observed by MEB but a lot of cobalt particles dissolution carbon films were detected by EDX. Based on the above results, the influence of cobalt on the structure, the quality and the constraints in the diamond films are discussed, a model suggesting the nucleation and growth mechanisms of diamond, to explain the cobalt diffusion in diamond films, is presented. (C) 2004 Elsevier Ltd. All rights reserved.