A RAMAN-STUDY OF DIAMOND FILM GROWTH ON CO-CEMENTED TUNGSTEN CARBIDE

Phase purity and crystallinity of diamond films grown by hot filament chemical vapor deposition on ISO-grade K10 cemented carbide [94.2 weig ht percent (w/o) WC-5.8 w/o Co] were studied by Raman spectroscopy as a function of substrate temperature, gas phase composition, and substr ate pretreatments. High-quality diamond films were grown using 0.5% CH 4/H-2 in a rather narrow range of substrate temperatures (750 to 760 d egrees C). In all the deposited coatings, the first-order Raman band o f diamond is detected at 1337 cm. This fact indicates that a 2 GPa res idual compressive stress is present in the diamond phase. The linewidt h of the diamond Raman peak increases with deposition temperature. Thi s effect has been ascribed to a higher density of defects in diamond c rystallites. It has been observed that Co removal from the substrate s urface by wet chemical etching before deposition is less effective tha n a careful selection of deposition parameters to reduce the codeposit ion of nondiamond carbon phases. This finding has been attributed to t he fast diffusion of the binder from the bulk to the substrate surface , even for the etched substrates.