Fabrication and oxidation-resistance property of allylhydridopolycarbosilane-derived SiC/SiC composites

In order to improve the environmental resistance of a polymer-derived SiC-fiber-reinforced SiC matrix composite (SiC/SiC composite), allylhydridopolycarbosilane (AHPCS) was utilized as the matrix precursor with Tyranno-SA(TM) fiber. AHPCS showed higher densification efficiency in both intra- and interbundle areas than polycarbosilane (PCS). This may be due to its superior rheological characteristics and mass yield. For fabricating a high-performance composite, the effects of main processing factors, such as the number of densification processing, SiC particle content in consolidation slurry and curing processing, on porosity and microstructure were systematically investigated. According to the flexural tests performed for heat-treated composites, it was suggested that the AHPCS-derived composite was inferior to the PCS-derived one in oxidation resistance. On the other hand, the AHPCS-pyrolyzed product showed superior thermal stability in air at elevated temperatures to the PCS-pyrolyzed one. With this evidence, the interfacial structure formed with the AHPCS slurry-derived matrix was found to be the main reason for the deteriorating oxidation resistance of the AHPCS-derived composite. Thus the importance of a hermetic interfacial layer for improving environmental resistance was implied.