Preparation and properties of SiC/SiC composites with various matrices

In order to improve mechanical properties of conventional SiC/SiC composites at a high temperature in air, new type matrices and interphase were developed. The addition of ZrSiO₄ particles into SiC-based matrix improved the strength of SiC/SiC composite at high temperature in air, even the SiC-based matrix has included a lot of excess carbon. Tyarnno fiber ZMI-S6/C/SiC composite with ZrSiO₄-dispersed matrix, which had the carbon interphase, exhibited about 400MPa of tensile strength at 1673K in air. For the purpose of reducing the excess carbon, co-polymer of polymethylsilane (PMS) and carbosilane oligomer (CSO) were synthesized as the precursor for SiC-based matrix. The co-polymer consisting 30 mass% CSO and 70 mass% PMS could be converted into a near-stoichiometric SiC matrix. In order to prepare the dense SiC/SiC composite, two methods were developed. One is the combined process (PIP/MI process) with PIP process and melt infiltration route (MI process). MI process was curried out after the PIP-process. In general, the SiC fiber in the SiC^F/SiC composites by Mi-process is easily damaged by the reaction with molten Si. In the case of PIP/MI process, the matrix phase formed by the PIP process protected the SiC fiber from the reaction with molten Si. Another is the sintering method using nano-sized SiC powder and sintering agent for the matrix. A cylindrical SiC_F/SiC composite using polycrystalline SiC fiber (Tyranno-SA) was formed in near-net shape by the sintering method employing a pseudo-HIP. It causes the drop in mechanical properties of SiC^F/SiC composites that the fiber fuses with the matrix after the degradation of interphases by oxidation. The crystallized ZrSiO₄ interphase was not adhered to oxidized SiC fibers at a high temperature. Therefore, it is promising that the ZrSiO₄ interphase is effective for toughening SiC^F/SiC composites at high temperature in air. In this work, the ZrSiO₄/C double interphase employed for a SiC^F/SiC composite. The SiC^F/SiC composite with the ZrSiO₄/C double interphase exhibited about 350MPa of tensile strength at 1673K in air.