Diamond coatings on hardmetal substrates with CVD coatings as intermediate layers

Diamond coatings on hardmetal tools are well-established and CVD-diamond coatings can significantly prolong the lifetime of tools used for cutting and milling of non-ferrous materials, e.g. Al(Si) alloys, graphite and plastics. A general problem is the reproducibility of diamond coatings with sufficient adhesion on the substrate surface, which is affected by the Co binder phase of the hardmetal. As a result some of the coatings fail due to delamination during heavy duty machining. To overcome this adhesion problem diamond was deposited on various CVD interlayers with a rough surface, i.e. Ti(C,N), (Al,Ti)N, Ti(C,N)/TiC and Ti(C,N)/SiC. Due to the roughness of the interlayers the adhesion of the diamond coatings on the substrate surface is improved. Furthermore, the deposition was varied from well-facetted crystalline diamond to nano-crystalline diamond (NCD) by adding argon to the reaction gas. Some of the diamond coatings show a sufficient adhesion and cutting tests for industrial applications are in process.