Adherent Diamond Coating on Silicon Nitride Substrate

The effects of CVD parameters and preparation process on the adherent coating of diamond on a pretreated silicon nitride substrate were investigated by the two-stage microwave plasma CVD in the CO-H2 system. Fine-grained diamond was deposited by the first stage CVD into the micropores of the surface layer of the substrate, which was pretreated by etching in a hot strong acid (HF and HNO3) solution and subsequently by microflawing with diamond grains in an ultrasonic bath. Excellently adherent and thick diamond coating was prepared by the second stage CVD for long term durations. Long tool life was verified by the milling test of the diamond-coated specimens using Al-20 mass% Si alloy as work material.