Basic Research On The Control Of Crystalline Of Nano-crystalline Diamond Films And Its Application In Cutting Tools

Chemical Vapor Deposition (CVD) nano-crystalline diamond (NCD) has excellent mechanicalproperties. CVD nano-crystalline diamond coating has broad application prospects as tool coating forits small surface roughness, good toughness and high thermal conductivity. In this thesis, CVDnano-crystalline diamond with different grain size was produced by hot filament CVD (HFCVD). Theeffects of the critical process parameters on CVD nano-crystalline diamond grain and the film qualityhas been studied. The multi-layer Micro/nano diamond coated cutting tool has been preparedsuccessfully. The cutting performance of the multi-layer composite coated cutting tool was tested andverified. The main work and results are as follows:1. The effects of critical process parameters on the grain size of CVD diamond crystallinedesposited by HFCVD have been studied. Under the experimental conditions, the grain size of CVDnano-crystalline diamond increases with the pressure increasing; The grain size of CVD nano-crystalline diamond decreases with the methane concentration increasing; The grain size of CVDnano-crystalline diamond has little changes with the substrate temperature increasing.2. The variations of CVD nano-crystalline grain and quality have been systematicallyinvestigated by Raman spectrum. The results show the lower pressure and higher methaneconcentration are conducive to the reduction of the crystal grains, but these will cause the graincrystallinity decreased. The defects in grain internal increased and diamond content in films reduced.Conversely the higher pressure and lower concentration of methane are conducive to improve the filmquality, but these will lead to the increase of the grain size. The quality of the film will be decreasedwhen the substrate temperature is higher.3. The multilayer micro/nano-structured composite coating was prepared. The sectional structureof the coating was observed by scanning electron microscope; Raman spectroscopy was used to detectthe composition of each cross-sectional layer. The interfacial adhesion and bond strength betweencoating and substrate were tested by indentation experiments. The results show that suitable substratepretreatment can effectively improve the interfacial bond strength. The structural parameters of thecomposite coating have a greater effect on the interfacial bond strength. The composite coating withthe specific structure can greatly enhance the interfacial bond strength.4. The diamond coated cutting tool with micro/nano multilayer structure was produced. Thecutting experiments were done with the coated tool produced. The results show this coated cuttingtool has a good interfacial bond strength and can be applied to machine high-silicon aluminum alloy.