Diamond coatings on electrical-discharge machined hardmetals

The influence of electrical-discharge machining (EDM) of WC-Co cemented carbides on the structural features and adhesion strength of subsequently deposited chemical vapor deposition (CVD) diamond coatings is investigated. Two different surface conditions are analyzed for a low binder-content hardmetal substrate. One variant corresponds to multi-pass sequential EDM, whereas the second one, used here as a reference, is attained through grinding and polishing. In all the cases, identical substrate chemical etching and arc-plasma CVD standard diamond deposition processes are applied. It is found that fine-executed EDM of hardmetals allows the deposition of diamond coatings exhibiting similar structural and adhesion characteristics to those obtained on conventionally machined cemented carbides substrates. Although surface integrity of the substrate together with quality and residual stresses of the diamond film are slightly affected by EDM, adhesion strength corresponding to this surface condition is retained because EDM-induced isotropically rough surfaces enhance mechanical interlocking of the diamond coating to the hardmetal substrate. (C) 2002 Elsevier Science B.V. All rights reserved.