Study On Tribochemical Polishing Technique Of CVD Diamond Film

CVD diamond film is a pure diamond material with full polycrystallinity synthesized by chemical vapor deposition method. It possesses excellent optical, physical and chemical properties including the highest hardness and thermal conductivity, wide-range transparency and good resistance to chemical erosion. The film may be well recognized as a 21st century engineering material, and probably be widely used in the field of high technology and national defense sophisticated technique. However, its industrial applications have been limited by the non-uniform thickness and rough surface. Therefore, if CVD diamond could be used in these fields, it is probably important for the surface to be planar and highly polishing.Thermochemical polishing technique is one of the most promising methods appropriate for polishing CVD diamond film with high efficiency and low cost which developed in recent years. However, the overall heating will lead polishing plate deform and oxidize, also the relatively soft materials used for polishing CVD diamond film are easy to wear and adhere to diamond film surface, which may further lead to low efficiency and poor polishing quality.In this paper, CVD diamond film is polished by tribochemical polishing technique. In this process, thermochemical reaction occurs as a result of friction between polishing plate and diamond film in the atmosphere. The preparation of polishing plate, polishing process, contact model and material removal mechanism are discussed and the main contents and results are as following.(1) Two kinds of polishing plate materials are fabricated by the combination of mechanical alloying and spark plasma sintering or hot press sintering, FeNiCr matrix-TiC composite and TiAl alloy. The hardness, microstructure and high-temperature oxidation resistance of these materials are superior to SUS304, high speed steel and cast iron. The properties can meet the needs for polishing diamond.(2) The experimental equipments are built up, and on it, CVD diamond film is polished by the prepared polishing plate. The influence of plate material, rotational rate and pressure on polishing process is discussed.(3) A dynamic contact model of the surface with large roughness is presented. The asperity distribution is evaluated taking into account the original surface, the polishing method, the polishing time, etc. Using this model, the real area and the real pressure of contact in polishing process are evaluated. (4) With detecting the changes in chemical composition of CVD diamond and plate before and after polishing, the material removal mechanism is investigated. It is found that diamond is removed by transformation diamond to graphite and then removed by mechanically oxidation or diffusion to plate during polishing process with FeNiCr matrix-TiC composite plate, While TiAl alloy plate polishing CVD diamond film mainly depends on the reaction between diamond carbon and titanium.