Preparation And Properties Of C/C-Sic Composites Prepared By PIP And RMI

It is necessary to improve the comprehensive performance of composite materials to meet the requirements of applying in a complex extreme service environment as the rapid development of the aerospace industry, such as the mechanical properties, antioxidant properties and so on. A C/C-SiC composite with low density can be obtained from introducing SiC ceramic to the matrix and surface of the composites by Polymer Impregnation Pyrolysis (PIP) process and Reactive Melt Infiltration (RMI) process, which can improve the antioxidant property of the composite. The high temperature ceramization mechanism of polycarbosilane (PCS) which was choosed as the precusor for PIP process has been studied in detail. Based on this, the microstructure, phase composition, mechanical properties and antioxidant properties of C/C-SiC composite prepared by PIP and PIP-RMI have been studied in detail.The gaseous and solid residual of PCS treated from room temperature to2000℃with vacuum condition were analysised to understand the ceramization of PCS by infra-red spectroscopy (FT-IR), simultaneous thermo-gravimetric analysis-differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and scanning electron microscope (SEM). The ceramization mechanism of PCS was studied through observing a series of changes such as the morphology, phase composition, microstructure. The results show that the ceramization mechanism of PCS is a very complex process which includes the volatilization of the low molar mass organic molecules and molecular fragments which from PCS cracking、the bonds breaking、the the transformation of the organic PCS into an inorganic state、the crystallization of the amorphous SiC.C/C-SiC composites with a SiC ceramic layer about25-30μm adhered to the surface were fabricated by PIP with PCS as precursor. The SiC ceramics introduced by the PIP process preferd to exist in the void between the fiber bundles arranged in different directions. C/C-SiC composites showed a significant pseudoplastic fracture behavior, and the average maximum load of samples was205N, and the average transverse rupture strength was185.8MPa. After the static oxidation, the average mass loss rate of samples was4.8%, a ceramic layer about30μm still exsited on the surface of the sample after oxidation and the surface of the layer was piled with a series of small smooth SiO2which protected the composite from oxidaton.C/C-SiC composites were fabricated by PIP and RMI, and the precusor was still PCS in PIP process. A SiC ceramic layer with good crystallinity about90μm adhered to the surface of the composites which was more dense than the composites prepared by PIP process. C/C-SiC composites showed a obvious brittle fracture behavior, and the average maximum load of samples was112N, and the average transverse rupture strength was101.6MPa. After the static oxidation, the average mass gain rate of samples was0.435%. The ceramic layer about100μm still exsited on the surface of the sample after oxidation. The surface with the smooth SiO2glass protected the composite from oxidaton. RMI process improves the oxidation resistance of the C/C-SiC composites, while the mechanical property impaired obviously.This article contains37figures,1table,70references.