Effects of the microstructure, and degradation reaction under heat-treatment on mechanical properties of SiC-polycrystalline fiber

SiC fibers are attractive structural materials with excellent mechanical properties up to very high temperatures. In particular, stoichiometric SiC-polycrystalline fibers have an excellent heat-resistance up to 2000oC. Presently, our company (Ube Industries, Ltd.) produces a stoichiometric SiC-polycrystalline fiber (Tyranno SA), and its higher strength has been desired. Accordingly, to achieve an increase in the strength, we have to detect actual defects in the first fracture surface. In order to obtain the first fracture surface, we developed a new method for capturing the all fragments during the monofilament tensile testing using liquid paraffin. Using this method, we detected the fracture origin, and then the relationship between the tensile strength and each fine structure has been studied for obtaining more excellent SiC-polycrystalline fiber. By the way, Tyranno SA is synthesized by further heat-treatment of an amorphous Si-Al-C-O fiber (intermediate fiber), which is synthesized from polyaluminocarbosilane. This intermediate fiber was heat-treated at higher temperatures in Argon atmosphere. During this heat-treatment, degradation reaction accompanied by the release of CO gas proceeds. After that, a sintering proceeded in each filament by the existence of aluminum. In this paper, the important things for controlling the strength was reported. © 2017 The American Ceramic Society.