Plasma carbonitriding of cemented carbide substrate as an effective pretreatment process for diamond CVD

Diamond CVD on a cemented carbide (WC-Co) substrate pretreated using an N-2-C2H2 plasma has been investigated. The quality of a diamond film deposited on a plasma carbonitrided substrate pretreated at 600 degrees C by N-2-C2H5(5%) plasma was much better than that of a substrate pretreated by a conventional process which consisted of chemical etching and scratching with diamond powder This is because Co diffusion into the diamond and the formation of amorphous or graphitic carbon were suppressed by this plasma pretreatment. Moreover, the adhesion of the deposited film to the substrate was improved. From the results of X-ray diffraction, it was estimated that such advantages of this pretreatment originated from the formation of Co2N on the surface of cemented carbide. On the other hand, diamond film was not observed on the substrate pretreated by N-2 plasma, and furthermore, decarburization and formation of metallic tungsten occurred from decomposition of part of the WC. Accordingly it can be concluded that plasma carbonitriding is a very effective pretreatment process in order to synthesize a high quality diamond film on a cemented carbide substrate. (C) 1999 Elsevier Science S.A. All rights reserved.