Effect of WC-Co substrates pre-treatment and microstructure on the adhesive toughness of CVD diamond

Well separated diamond particles were nucleated and grown by hot filament chemical vapor deposition (HFCVD) onto Co-cemented tungsten carbide (WC-Co). Two carbide grades were prepared. The former one was a ISO grade K10 carbide having a 1-µm average WC grain size, 5.8 wt.% Co and 0.2 wt.% VC. The latter one had a 6-µm average WC grain size, with 6 wt.% Co. Prior to deposition the substrates were submitted to two different pretreatments. The adhesive strength of deposited diamond crystallites was quantitatively determined in terms of interface toughness by directly applying an external load to the CVD diamond particles in the scanning electron microscope (SEM). The adhesive toughness was determined from the measurement of the maximum load required to scratch off the diamond crystallites. The variation of adhesive toughness was correlated to both the microstructure and the pretreatments of the substrate.