Amorphous SiO2 interlayers for deposition of adherent diamond films onto WC–Co inserts

Amorphous SiO2 (a-SiO2) films were synthesized on WC–Co substrates with H2 and tetraethoxysilane (TEOS) via pyrolysis of molecular precursor. X-ray diffraction (XRD) pattern shows that silicon–cobalt compounds form at the interface between a-SiO2 films and WC–Co substrates. Moreover, it is observed by transmission electron microscope (TEM) that the a-SiO2 films are composed of hollow mirco-spheroid a-SiO2 particles. Subsequently, the a-SiO2 films are used as intermediate films and chemical vapor deposition (CVD) diamond films are deposited on them. Indentation tests were performed to evaluate the adhesion of bi-layer (a-SiO2 + diamond) films on cemented carbide substrates. And the cutting performance of bi-layer (a-SiO2 + diamond) coated inserts was evaluated by machining the glass fiber reinforced plastic (GFRP). The results show that a-SiO2 interlayers can greatly improve the adhesive strength of diamond films on cemented carbide inserts; furthermore, thickness of the a-SiO2 interlayers plays a significant role in their effectiveness on adhesion enhancement of diamond films.