Preparation And Property Research Of SiC/SiC Composite

Silicon carbide fiber-reinforced silicon carbide composite is a kind of novel materials expected to be used at high temperatures. It has widely applied in aero-engine and aerospace and is promising to be a kind of outstanding structural absorbent materials. Chemical vapor deposition (CVI) is a basic and useful method for fabricating ceramic matrix composite. In this thesis, SiC/SiC composite with pyrocarbon interphase was fabricated by low pressure chemical vapor infiltration (LPCVI).The thermodynamics and kinetics of the LPCVI process of the pyrocarbon and SiC matrix was analyzed, and the effect of deposition parameters on the deposition process was studied. The effect of composite elements and deposition parameters on the mechanical and dielectric properties was discussed. The main conclusions are as follows:(1) The thermodynamics and kinetics of the LPCVI process of the pyrocarbon and SiC matrix and the pyrolysis process of propylene and MTS-H2 system were analyzed. The effect of deposition temperature, system pressure and P_N2/P_C3H6 on the pyrocarbon morphology and deposition rate was studied. The results show that the pyrocarbon morphology can be governed by variation of the above parameters. Below 1200℃, deposition temperature can hardly change the pyrocarbon morphology; changes of system pressure can lead to changes of residence time and nucleation-propagation mode, which in turn change the morphology and deposition rate of pyrocarbons; with the decreasing of P_N2/P_C3H6, pyrocarbon deposition mode has the trend that changes from surface chemical reaction nucleation-growth mode to vapor nucleation-growth, and the pyrocarbon surface becomes rough.(2) The densification process of composites was investigated under preferable processing parameters. It is indicated that the porosity of composites remains about 20% after 6.5 hours of SiC matrix deposition. Under the same deposition condition, the porosity of composites with 40% fiber volume fraction is a little bigger than that with 30% fiber volume fraction.(3) The flexural strength of prepared SiC/SiC composite is 328MPa with desired toughness. The mechanical value is rather low compared with the best mechanical data reported in references due to the properties of the used fibers, but it shows higher strength than those composites with the same fibers. The effects of porosity, fiber volume fracture, interface thickness and interface thickness on the mechanical behavior of SiC/SiC composites were also investigated.