On the formation of diamond coatings on WC/Co hard metal tools

Composite cutting tools having wear-resistant superhard surface coatings (diamond) on a stiff and ductile substrate as base material exhibit excellent performances. A prime requirement for the successful production of such tools is a strong interfacial adhesion of the coating onto the substrate. Industry requires high reproducibility, reliability of each individual tool tip, and an economical mass production process. Hard metal substrates are the obvious choice for most industrial applications of diamond-coated tools. Thus the use of an appropriate hard metal grade and the application of a surface pretreatment - applied to the hard metal prior to the deposition of the diamond coating - are equally important in order to obtain a reproducible diamond coating adhesion. In order to achieve the reliable adhesion necessary for industrial tools, the appropriate interfacial modification must be made. These modifications control possible interactions which can occur at the diamond/hard metal interface. This includes a number of parameters which contribute to optimal bonding of the diamond coating to the substrate, e.g. cobalt mobility (diffusion), cobalt binder effects, diamond nucleation and growth conditions and interfacial roughness of the hard metal/diamond interface, etc. Obviously, the diamond synthesis method applied and the correct choice of deposition parameters are important to achieve a usable and economical product.