Structure, Properties And Interphase Ajustment Study Of 3D C_f /SiC Composite By Gaseous Silicon Infiltration

C_f/SiC composite has great advantages in the fabrication of space telescope and photomechanical structures, because of its merits, e.g. low density, low coefficient of thermal expansion, high strength and high modulus. Low-cost fabrication is one key to the spread of 3D C_f/SiC composite, Silicon infiltration is a useful way to reach the low-cost fabrication of C_f/SiC composite. This dissertation mainly focused on the following aspects: the optimization of C content in C/C perform, the effect of CVD-SiC and PIP-SiC interphase on the mechanical properties of C_f/SiC composite, the effect of C fiber fabric structure and high temperature treatment of C/C perform on the mechanical properties of C_f/SiC composite. 3D C_f/SiC with good mechanical properties was obtained.The effect of PIP-C times on C/C perform component, 3D C_f/SiC matrix component and mechanical properties was studied. The results manifested that 3D C_f/SiC composite with 2 cycles of PIP-C has the best mechanical properties composite (flexure strength 207.4MPa, flexure modulus 80.5GPa and toughness 6.3 MPa·m^1/2), because it has fitting C content (15.3vol%) and porosity (21.8vol%) in C/C perform. The effect of CVD-SiC interphase on mechanical properties of 3D C_f/SiC was studied, it was found that the flexure strength, flexure modulus and toughness all increase at first and decrease subsequently with the CVD-SiC interphase thickness growing. The 3D C_f/SiC with CVD-SiC of 2 hours has the best mechanical properties (flexure strength 237.1MPa, modulus 87.3GPa and toughness 7.3MPa·m^1/2). The mechanical properties of 3D C_f/SiC with 1 hour CVD-SiC is lower, because C fiber is eroded by gaseous silicon, resulting from SiC interphase being too thin. The mechanical properties of 3D C_f/SiC with CVD-SiC of 4 and 6 hour is also lower, because the bonding strength between C fiber and SiC interphase is strong, resulting from SiC interphase being too thick.The effect of PIP-SiC interphase times on mechanical properties of 3D C_f/SiC was studied. The results manifested that the mechanical properties of 3D C_f/SiC all decrease with the cycle times increasing. C_f/SiC composite with 1 cycles of PIP-SiC has the best mechanical properties (flexure strength 185.2MPa, flexure modulus 91.1GPa and flexure toughness 5.5 MPa·m^1/2), because it has the lower porosity (17.8 vol%) and more SiC than 3 other groups of C_f/SiC. The properties of C_f/SiC composite with 2～4 cycles of PIP-SiC is low, because siliconization of C/C perform is worse, resulting from lower porosity of C/C perform.Interphase plays an important role in protecting C fiber and adjusting bonding strength between fiber and matrix. The carbon fiber in 3D C_f/SiC composite with noninterphase is damaged severely, in which bonging strength is strong, leading a worse mechanical properties (flexure strength 87.6MPa, flexure modulus 56.9GPa and toughness 2.1 MPa·m^1/2). The role of CVD-SiC interphase on 3D C_f/SiC composite is carrying load, obstructing nocuous eroding and fiber/matrix abjunction. The role of PIP-SiC interphase on 3D C_f/SiC composite is carrying load and obstructing nocuous erode. However, because of the bonding strength between C fiber and interphase being stronger, the adjusting effect of PIP-SiC interphase is worse than CVD-SiC interphase.The component and mechanical properties of C_f/SiC composite with 2.5D,3D-4d,3D-5d carbon fiber fabric was compared, the results indicated that 2.5D,3D-4d C_f/SiC composite with a superfluous carbon fiber volume fraction have less SiC content and higher porosity than 3D-5d, which leads to worse mechanical properties. The flexure strength, modulus and toughness of 2.5D C_f/SiC is 65.6MPa,30.5 GPa,3.6MPa·m^1/2.In allusion to high closed porosity in C/C perform, the effect of high temperature treatment on C_f/SiC composite was studied. It was found that the porosity of C/C perform increases after high temperature treatment, and the silicon infiltration is much sufficient, which leads to a higher modulus of C_f/SiC composite, however, the flexure strength and toughness of C_f/SiC composite decrease because the carbon fiber is damaged by high temperature.