Structure and hardness of diamond films deposited on WC-Co by CVD technique

International audience; Diamond thin films are used to increase significantly the life time and to improve the performance of cutting tools. However, one the most important limitations to their industrial development in the case of severe mechanical conditions is their limited adhesion to the substrate. To improve the adhesion strength of the deposited diamond film on its substrate, several approaches have been suggested in literature with a relative success. For WC-Co substrates, one interesting approach consists in the neutralization of the cobalt element at the surface of the substrate by the use of a chemical agent. This methodology leads to a roughening of the surface that increases the contact area between the film and the substrate as well as the mechanical anchoring at the interface. The objective of the present paper is to study the conditions of substrate preparation as well as the conditions of deposition on the microstructure and hardness of the produced films. Diamond thin films of thickness ~ 1.5 μm were deposited on substrates made of Tungsten carbide-Cobalt submitted to different heating temperatures. The coated systems were characterized by means of physical and mechanical tests. Observations by Raman spectroscopy and scanning electron microscopy analysis confirm the good quality of the obtained diamond films. Hardness results deduced from classical indentation tests have been analyzed by means of models allowing the separation of the substrate influence on the hardness measurement. In these conditions the hardness of the diamond films was found close to 40 GPa thus confirming their excellent mechanical properties.