| Carbon fiber composite materials are widely used in automotive, aerospace and other fields for its high specific strength, large specific stiffness, excellent fatigue and corrosion-resistant properties. However, the difficulties in machining carbon fiber composite materials have limited their practical use. Therefore, it is necessary to develop a cutting tool which is harder than carbon fiber composite materials to machine these materials. As we all know, diamond coating cutting tools have many advantages such as high hardness and wear resistance, low friction coefficient and low coefficient of thermal expansion (CTE), etc., so to deposit diamond films on rotary cutting tools is a good way to solve this problem. However, the mismatch in CTE between the cemented carbide substrate (4.5×10-6K-1) and the diamond films (1.0×10-K-1) is detrimental. And the binder Co element in the YG6X substrate will catalyze the growth of graphite, which inhibits the growth of diamond. These two factors have a great impact on the adhesion properties of substrate and diamond film. In order to improve the insufficient adhesion property of film/substrate, nanocrystalline SiC film deposited is put between substrate and top diamond film to relieve the CET mismatch and hinder the diffusion of Co element, since the CTE of SiC film is3.8×10-6K-1. In this thesis, tetramethylsilane (TMS) diluted in H2was used as the precursor gas to deposit SiC film on Si substrate by Electronic-assistant hot filament CVD (EA-HFCVD). And a mixed gas of H2and methane (CH4) was used to deposit diamond film on cemented carbide (YG6X) substrate. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman scattering analyses, nanoindentation experiments and Rockwell-C hardness tests were performed to characterize the morphology, phases, composition and mechanical properties of deposited films.The conclusions in the present work are as follows:results show that pressure, substrate temperature and TMS vol.%all have effects on the growth and properties of the nanocrystalline SiC film. In comparison, pressure and TMS vol.%affect more obviously, especially on grain size and morphology of the nanocrystalline SiC; XRD results show that all of the deposited nanocrystalline SiC films in the present work are β-SiC; EPMA and Raman results show that when the Si/C element ratio is close to1, the film has the highest hardness and elastic modulus of23GPa and320GPa, respectively. In other words, the higher purity of the film, the better mechanics properties it has. Simultaneously, the redundant C element exists in the SiC film as the form of sp2bond. Considering the experiment results of pressure, substrate temperature and TMS vol.%, the optimized parameters of deposition of nanocrystalline SiC film within the scope of this work are pressure of0.75kPa, substrate temperature of620℃and TMS vol.%of0.1%.It is found that nanocrystalline SiC interlayer can improve the adhesion property between top diamond film and substrate, compared with directly deposited diamond film on YG6X plane cutting tools. The denser the interlayer film is, the better the improvement is. Experiments proved that it is possible to deposite diamond films on YG6X drills with the experiment facility used in the present work, and film is not peeled. By adjusting the distance between the drill tip and the hot filament, the temperature of drill tip was controlled. The experiment results reveal that the drill tip over heated under the current filament arrangement, and the diamond grain is larger. SEM and Raman results show that when the substrate temperature (below drill tip) is near720-750℃, the deposited diamond film has high quality. |
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