Fine-grained diamond coating was obtained on W, Mo or Ti wire substrates by the microwave plasma CVD method from a gas mixture of the CO-H2 system. The effects of CVD parameters on a uniform coating of polycrystalline diamond were investigated under the constant conditions of reaction time (5 h) and CO concentration (5 vol%), using the wire substrates mounted horizontally on a pyrophyllite susceptor. Homogeneous and fine-grained diamond film was prepared on the whole surface of W wire substrate

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... with the wire height of 2 mm from the susceptor, which was placed parallel to the irradiation direction of microwave power (750-1100 W). Deposition conditions under higher microwave power, lower pressure and lower wire height were found to be suited for preparation of microcrystalline and uniform coating of diamond. Plasma density and substrate temperature are considered to have great influences on the nucleation of diamond.