Pulsed Laser Treatment of WC, Co Tool Substrates to Improve Co Removing and Diamond Nucleation

Diamond coated cutting tools seem to be one of the most promising system to machine non ferrous, very hard materials, like metal matrix composites (MMC), carbon fibers, hypereutectic Al/Si alloys. The widespread used and cheaper bulk material for tool inserts, the WC,Co hard metal, is convenient and profitable as a substrate for diamond film coatings. Unfortunately, the Co-rich binder phase constitutes a severe obstacle for diamond deposition. Because of the catalytic effect for amorphous carbon or soot formation, the presence of Co actually results in a detrimental effect both on diamond nucleation and adhesion to substrate. Several chemical and physical methods have been developed to etch Co from the surface, no conclusive and perfectly reliable procedure, however, has been achieved, as far as a strong adhesion is concerned.In our experiments, we used ArF (λ = 193 nm, hv ≅ 6.4 eV) and Nd:YAG (λ= 532 nm, hv ≅ 2.3 eV) pulsed laser treatment to selectively remove Co from the surface and to seal the structural voids, coming out after Co chemical etching from the substrate, and responsible of surface segregation of Co from the bulk, during CVD diamond deposition. The sealing efficiency, after a thermal treament (3h, 800°C) in an inert atmosphere, resulted to be quite good, compared to the untrated surface. The morphological and chemical effects have been studied by SEM/EDAX microscopy.