CHARACTERISTICS OF HF CVD DIAMOND THIN FILMS ON CEMENTED CARBIDES

Diamond films were deposited on the WC/Co alloy substrates by a hot-filament chemical vapor deposition (HF CVD) reactor after the substrate surfaces were chemically pretreated with the two-step etching method. Some characteristics as morphology, texture, adhesion, and chemical quality of the diamond coatings on WC/Co alloy substrates were investigated by means of X-ray diffractometer (XRD), scanning electron microscope (SEM), hardness tester, and Raman spectrum. The results indicate that increasing the Co content from 0.12% to 3.22% within the etching depth of 5–10 μm caused a morphology transformation from prism diamond to spherical diamond, and a texture one from a {111} orientation to a {110} orientation. The Raman spectrum shows that the spherical diamond film contains more non-diamond phases (graphite, amorphous carbon, diamond-like carbon, etc.) and has lower chemical quality of diamond films. The diamond coated grain sizes became about four to five times smaller when the deposition temperatures on the substrate surface were reduced from 900°C to 800°C. Compared with the spherical diamond films, the prism diamond films exhibit better adhesion on the WC–Co substrates. It is also observed that the microcrystalline orientation diamond thin films with grain sizes of 1–3 μm on WC–Co substrate were formed under the circumstances of lower deposition temperature and higher gas pressure, and the microcrystalline growth mechanism of diamond thin films with a preferential orientation on WC/Co alloy is discussed.