Processing Of SiC_f /SiC Composites Prepared With LPVCS As Precursor Polymer

Continuous silicon carbide fiber reinforced silicon carbide matrix (SiC_f/SiC) composites have been considered to be the attractive potential high temperature structural materials for fusion energy systems and advanced gas turbine engineering in aerospace vehicles because of their high strength, high modulus, pseudo-ductile fracture behavior, inherent low activation characteristics under severe environments and excellent thermal stability. The polymer impregnation and pyrolysis (PIP) is a common method to fabricate the SiC_f/SiC composites. In PIP process, the pyrolysis route, porosity and the mechanical properties of the composites are strongly influenced by the selected polymer precursor. On the other hand, for the fiber reinforced composites, it is commonly agreed that the controlling of the interphase between the fibers and the matrix is a key parameter for the enhancement of the composite's mechanical properties.In this research, we selected the LPVCS with active Si-H and–CH=CH2 groups as the polymer precursor and the polymer-derived KD-I fiber bundles (provided by National University of Defense Technology, NUDT, China) were used as the reinforcements. PyC coatings were deposited onto the KD-I SiC fibers prior to the fabrication and densification of SiC_f/SiC composites by PIP method. The pressure-assisted consolidation process was taken at the time of cured. The microstructure and the mechanical properties of composites were characterized and evaluated. Then, we investigated the effects of different precursors, pressure-assisted consolidation process and interfacial coatings on the properties of composites.The results show that, using LPVCS as the precursor, the open porosity and density of the fabricated SiC_f/SiC composite are 5.12% and 2.11g/cm~3 after 10 cycles of impregnation and pyrolysis. While after 14 cycles of impregnation and pyrolysis with the PCS as the precursor, the open porosity and density of SiC_f/SiC composite are 8.80% and 1.97g/cm3. That means, the using of LPVCS can increase the density and decrease the open porosity of the composites, so as to reduce the cost of fabrication.The pressure-assisted consolidation process reduces the route of impregnation and pyrolysis to 9 times with the LPVCS as the precursor and the volume proportion of SiC fibers was increased from 40% to 50%. The densities of the composites were above 2.11g/cm~3. During the pressure-assisted consolidation process, the compressive stress and compressive time also influenced the properties of SiC_f/SiC composite. The optimized pressure-assisted consolidation process is as following: loading press at the beginning of the LPVCS curing, and releasing immediately after the curing completed, keeping the compressive stress between 1MPa~5MPa and the compressive time about 5 hours. The introduction of the carbon nano-tubes, the PyC coating, or the mixed interfacial with carbon nano-tubes and PyC coating could keep SiC fibers away from destroyed during the pressure-assisted consolidation process. The PyC coating effectively amended the interface between fibers and matrix and substantially enhanced the mechanical properties of the composites. For example, the flexural strength reached 657.88MPa,the fracture toughness was 26.80MPa/m1/2 and the flexural modulus was 94.30GPa.