Preparation of diamond coated cutting tool with long life and its machinability against hard work material

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The Preparation of adherent diamond coating on tools is one of the urgent subjects to be investigated to develop long life and precise cutting tool for hard work materials. Diamond with high hardness and high thermal conductivity, however, has low adherence against most substrate materials because of its own strong sp^3 covalent bonding. Excellently, adherent diamond coating technique was established in the present paper and its cutting property was evaluated as well as the machinability against hard work materials. The main results and conclusions in the project term were summarized as follows.1. Preparation of CVD diamond coating on silicon nitride tool and its machinabilityAdherent diamond coating was performed on silicon nitride substrate by the two-stage microwave plasma CVD in the CO-H_2 reactant system. A graded structure from sp^3 to sp^2 bonding was formed by a careful pretreatment of the substrate and subsequent thick diamond coating. Excellent adherence was verified by the a … More ctual cutting test against Al-20wt% Si alloy work. Detailed X-ray analysis of the residual stress between diamond film and substrate indicated that the relaxation of inner stress in the diamond film occurred on account of the formation of the graded structure.2. Preparation of CVD diamond coating on cemented carbide tool and its machinabilityAdherent diamond coating on cemented carbide substrate has been desired for its expansion to more versatile application. However, the adherence of diamond film to cemented carbide is too weak to bear the large stress in hard cutting conditions. Prior to diamond coating, electrochemical etching of cobalt phase on the surface layer was carried out to depress the graphitized carbon solution into cobalt and to increase the adherence by increasing contact area between diamond and substrate. Peeling of diamond film was prevented, even though the adherence strength was insufficient under hard cutting conditions. Further investigation is required for better adherence achieved. Less