Comparative investigations of the selective Co etching from hardmetal support layer of diamond coating

Abstract

Selective cobalt etching from WC-Co composite usually carry out prior diamond deposition was investigated. Diluted Caro's acid as primarily utilized etching reagent was used. The cobalt and tungsten dissolution from hardmetals (HM) were determined as a function of time and a comparison were done in case of different grade hardmetals. For comparison beside the hardmetals the pure metallic cobalt and binderless, plasma sprayed tungsten carbide dissolution also has been tested. Hot filament chemical vapor deposition (HFCVD) technic was used to investigate the diamond nucleation on the differently pre-treated samples. The investigation highlighted for that: a) the selective cobalt etching can due to the different rate of dissolution of the two components, however the dissolution of the WC was not zero, b) the dissolution rate governed by the composite substance structure by the pore size which has formed during the selective dissolution process, therefore the dissolution rate of both components was found to be influenced by the grain size of WC and the cobalt content of the hardmetal. c) The removed cobalt quantity from the hardmetal surface has strong effect on the diamond nucleation during HFCVD method. Based on this research a better understanding of the mechanism of the pre-treatment and a chance for optimizing the selective cobalt etching from hardmetals prior diamond deposition will be achieved.