Abstract: Nanocrystalline diamond films are deposited on Co-cemented carbide substrates using bias-enhanced hot filament chemical vapor deposition(HFCVD) technique by appropriately controlling deposition parameters and Ar addition. The evidence of nanocrystallinity, smoothness and purity is ob-tained by characterizing the sample with scanning electron microscopy(SEM), X-ray diffraction(XRD), Raman spectros-copy, atomic force microscopy (AFM), high-resolution trans-mission electron microscopy (HR-TEM) and selected-area electron diffraction (SAED). The results show that nanocrystal-line diamond films consist of nanocrystalline diamond grains with sizes range from 20 to 80 nm and contain a large amount of grain boundaries. Surface roughness is measured at Ra< 50 nm. Smooth diamond films are liable to polishing. A new process was used to deposit composite diamond coatings by a two-step chemical vapor deposition procedure including first the deposi-tion of the rough polycrystalline diamond and then the smooth fine-grained nanocrystalline diamond coating. The dia-mond-coated drawing dies with these composite coatings dis-play excellent performances in the practical application.

Key words: Surface roughness, Cemented tungsten carbide, Composite coatings, Nanocrystalline diamond films