DIAMOND DEPOSITION ON STEEL WITH CVD TUNGSTEN INTERMEDIATE LAYER

Diamond deposition on steel with enhanced adhesion has been performed by using a CVD tungsten intermediate layer between substrate and diamo nd as a diffusion barrier for iron and carbon. The tungsten buffer lay ers of 15-45 mu m thickness with highly faceted surface relief have be en grown on #R18 steel (79% Fe, 17% W, 4% Cr) by the CVD process from tungsten hexafluoride in a ''hot-wall'' reactor. This technique is sui table for large-scale production with deposition rate up to a few mill imeters per hour over a large area. The diamond films were grown in a d.c. are discharge in 5%CH4/H-2 mixture. The samples characterized by X-ray diffraction, Auger electron spectroscopy and cross-section exami nation revealed a tri-layer coating structure: diamond/tungsten carbid e/tungsten. The carbide layer, consisting mainly of WC phase with a sm all fraction of W2C phase, provides good adhesion, as confirmed by Roc kwell indentation tests. As determined from Raman spectra, the films w ere under high compressive stress, sigma approximate to 7 GPa, origina ting from the large mismatch in thermal expansion coefficients of stee l and diamond. Yet the adhesion accommodates the stress without film d elamination.