Deposition of diamond coating on pure titanium using micro-wave plasma assisted chemical vapor deposition

The nucleation and growth of diamond coatings on pure Ti substrate were inv estigated using microwave plasma assisted chemical vapor deposition (MW-PAC VD) method. The effects of hydrogen plasma, plasma power, gas pressure and gas ratio of CH4 and H-2 on the microstructure and mechanical properties of the deposited diamond coatings were evaluated. Results indicated that the nucleation and growth of diamond crystals on Ti substrate could be separate d into different stages: (1) surface etching by hydrogen plasma and the for mation of hydride; (2) competition between the formation of carbide, diffus ion of carbon atoms and diamond nucleation; (3) growth of diamond crystals and coatings on TiC layer. During the deposition of diamond coatings, hydro gen diffused into Ti substrate forming titanium hydride and led to a profou nd microstructure change and a severe loss in impact strength. Results also showed that pre-etching of titanium substrate with hydrogen plasma for a s hort time significantly increased the nuclei density of diamond crystals. P lasma power had a significant effect on the surface morphology and the mech anical properties of the deposited diamond coatings. The effects of gas pre ssure and gas ratio of CH4 and H-2 on the nucleation, growth and properties of diamond coatings were also studied. A higher ratio of CH4 during deposi tion increased the nuclei density of diamond crystals but resulted in a poo r and cauliflower coating morphology. A lower ratio of CH4 in the gas mixtu re produced a high quality diamond crystals, however, the nuclei density an d the growth rate decreased dramatically. (C) 1999 Kluwer Academic Publishe rs.