MURAKAMI AND H2SO4 H2O2 PRETREATMENT OF WC-CO HARD METAL SUBSTRATES TO INCREASE THE ADHESION OF CVD DIAMOND COATINGS/

Distinct improvement in adhesion of diamond coatings on hard metal sub strates was achieved by following substrate surface pretreatment [1]: First WC was removed from the substrate surface by etching with Muraka mi solution (K;[Fe(CN)(6)] in KOH), after which the Co binder network was etched with H2SO4/H2O2 solution. Then diamond coatings were deposi ted on the substrates by hot-filament CVD. Apparently during the H2SO4 /H2O2 treatment of the Co binder a thin CoO / CoSO4 film forms, which prior to the diamond deposition would be reduced to CoS by the hydroge n and carbon species involved in the diamond synthesis. Since CoS is a stable compound at the diamond deposition temperatures, its Co vapor pressure and the Co surface mobility should be substantially lower tha n that for metallic Co. Thus the diamond/hard metal interface is no lo nger influenced detrimentally by the metallic Co binder. This explanat ion has however not yet been confirmed by analytical methods such as S IMS and XPS. An alternative explanation would be the increased roughne ss of the hard metal surface resulting from the removal of the Co bind er and the formation of deep grooves on the interface which could lead to the improved adhesion. This however does not Explain why Co migrat ion and other detrimental effects are not observed.