Growth of diamond films on spherical surfaces by hot filament CVD

A growth system has been designed and built for depositing diamond films onto spherical surfaces; the initial experiments have been carried out using 1.5 cm tungsten carbide (6% Co) balls, as substrates. The films are deposited by hot filament chemical vapour deposition (HFCVD), using an hydrogen/methane mixture as the source. The ball is heated (typically to 925 degrees C) by tantalum filaments, which also provide the source of atomic hydrogen. Provision is made to support and rotate the ball simultaneously either continuously, or in a programmed manner. It has proved possible to coat balls uniformly and reproducibly with good quality diamond coatings, typically 3 mu m thick. Raman measurements confirm that the coatings are indeed diamond, but with some graphite incorporation. The soft impressor method, first presented at ICNDST 5 (1996), has been used to investigate the mechanical properties of the coating system. Results obtained, using both single loading and fatigue measurements, indicate that the films do protect the balls and failure of the system occurs as the result of substrate failure. (C) 1998 Elsevier Science S.A.