Fabrication and application of smooth composite diamond films

Composite diamond films with smooth surfaces were deposited on the interior hole surface of Co cemented carbide drawing dies, using a mixture of acetone and hydrogen as source gases by bias enhanced hot filament chemical vapour deposition (CVD). A new process was used to reduce the surface roughness of diamond films by a composite diamond film C VD procedure, including first the deposition of the rough polycrystalline diamond layer and then the smooth, fine grained nanocrystalline diamond layer. The morphology, surface roughness and diamond purity were obtained by characterising the sample with SEM, X-ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM). The results show that smooth nanocrystalline diamond layers can be deposited on conventional microcrystalline diamond layers using a two step CVD process by regulating the deposition parameters. The Raman spectroscopy and XRD patterns of the composite film indicate the presence of nanocrystalline diamond. The surface roughness of the films was measured at R-a<100nm by AFM. These composite diamond films with multilayer (nanocrystalline/microcrystalline) structure have low surface roughness and high adhesive strength on WC-Co substrates. The diamond coated dies with these composite coatings display excellent performances in the practical application.