Diamond deposition on hardmetal substrates after pre-treatment with boron or sulfur compounds

Diamond coatings on WC-Co hardmetal tools are widely used for cutting non-ferrous materials. Until now adhesion problems of the diamond layers on the substrates are the limitation for heavy duty wear applications. The reduced adhesion is mainly caused by cobalt used as a binder phase in the hardmetal. Applying surface treatments the amount of metallic cobalt on the substrate surface can be reduced (e.g. etching procedures or formation of stable compounds like silicides and borides). This paper deals with the possibility of forming stable cobalt-compounds such as borides and sulfides during substrate pre-treatment. The substrates were put in solutions containing boric acid and ammonium sulfide. This is an uncomplicated and inexpensive way of pre-treatments. The experiments were compared with depositions on untreated hardmetal substrates as well as with other pre-treatments in former works. The diamond deposition experiments were carried out in a hot-filament CVD-reactor. The diamond layers were examined in respect of growth rate, morphology and adhesion. Increased layer adhesion was observed, compared to untreated hardmetal substrates, in case of a two-step pre-treatment starting with Murakami etching followed by boric acid treatment. Pre-treatment with ammonium sulfide was not successful. (C) 2002 Elsevier Science B.V. All rights reserved.