Enhanced diamond film adhesion on cobalt-cemented WC substrates

Cobalt-cemented tungsten carbide (WC-Co) is a widely used material for maki ng cutting tools. Coating these tools with a protective diamond film should improve their lifetime and performance. However. the deposition and adhesi on of diamond films on this material are hindered by the presence of the co balt binder. To circumvent this problem, we have developed a substrate pret reatment method based essentially on carbon supersaturation of the metal su rface through ion bombardment in the cathode fall of a purr methane de disc harge. Chemical analysis of the substrate by X-ray photoelectron spectrosco py (XPS) and secondary ion mass spectroscopy (SIMS) showed that our pretrea tment method efficiently limits the cobalt migration from the bulk to the s urface and, consequently, reduces the dissolution and diffusion of carbon a toms coming from the plasma. As a result. the adhesion strength of the depo sited diamond films, evaluated by a scratch tester, is substantially enhanc ed. While adhesion is characterized by a critical load F-C of 12 N followin g standard substrate pretreatment (acid etching), additional carbon supersa turation of the substrate surface yields F-C values exceeding 30 N, the upp er limit of our scratch tester.