Investigation Of PIP Pocess And Ablating-resistance Of SiC Matrix Composites Reinforced By Carbon Fibers

C/SiC composite is a kind of great potential high-temperature structural material in aeronautics and astronautics with high specific strength, high specific modulus, good abrasivity, good thermal stability, high temperature and oxidation resistance. In this dissertation, three dimensional orthogonal C/SiC composite was prepared by polycarbosilane infiltration pyrolysis (PIP). Effects of infiltration solution, infiltration process, pyrolysis process on the microstructure and properties were discussed, and the optimal process was determined. C/SiC composites were ablated by oxy-acetylene torch in the temperature range of 1600~2900oC. Microstructure, phase composition and linear ablation rate were investigated after ablation test. The main conclusions are as follows:(1) The infiltration solution was composed of polycarbosilane as preceramic and divinylbenzene as solvent (mass ratio 1:0.4). Heating of solution at the initial infiltration stage decreased viscosity for infiltration conveniently. Cooling at later stage increased the residual rate of solution in the carbon fiber braid.(2) Effects of pyrolysis processes on microstructure and mechanical properties of C/SiC composite were investigated. Slow heating rate and rapid heating rate were adopted to form interconnected small pores at initial stage for further densification and reduced cracks at later stage, respectively. Pyrolysis at 1600oC to crystallized the matrix at last.(3) Effects of fiber types on mechanical properties of C/SiC composites were investigated. The mechanical properties of composite reinforced by M30 fibers with high strength and modulus are better than composite reinforced by T300 fibers with low strength and modulus. Strong interface stress between fiber and matrix is benefit for the mechanical properties of C/SiC composite.(4) C/SiC composites were ablated by oxy-acetylene torch at 1600oC, 1800oC, 2200oC, 2900oC for 180s. The composites maintained the integrity and no macro-cracks were found after ablation, which showed C/SiC composites combined good thermal shock resistance and oxidation resistance.(5) There were three regions on the surface of ablated samples. The centre region was covered by a gray coating composed of turbostratic carbon. Some micropores appeared on the coating of 1600oC and 1800oC ablation sample. Some white dross attached on the coating of the 2900oC ablation sample. The coating of 2200oC ablation sample was smooth.(6) As the gas flow and ablation temperature increased, the linear ablation rate increased, the mechanical erosion and oxidation enhanced. The ablation mechanisms of C/SiC composite under the oxy-acetylene condition are synergistic effects of deposition of turbostratic carbon, oxidation and mechanical erosion.