Influences of heat treatments on the strength properties of amorphous SiC fibers

Amorphous SiC fibers are known to have larger failure strain than crystalline SiC fibers, thereby facilitating manufacturing of ceramic matrix composites (CMCs). In this research, for the purpose of clarifying the influences of heat treatment temperatures and time on the failure strength of amorphous SiC fibers, the factors contributing to the changes in the failure strength of ZMI fibers, a type of amorphous SiC fibers, were examined through monofilament tensile test and microstructure observation. The failure strength of ZMI fibers was degraded with the increases in heat treatment temperatures and time in the temperature region of 1100°C or higher. As a result of the microstructure observation, it was clarified that the predominant factors contributing to the strength degradation are crystallization and grain growth in the temperature region of 1300°C or higher and the generation of defect and grain growth in the temperature region of less than 1300°C.