Microstructure and mechanical properties of SiC‐polycrystalline fiber and new defect‐controlling process

Abstract

Abstract A stoichiometric SiC‐polycrystalline fiber (Tyranno SA R ) shows excellent heat‐resistance up to 2000°C and relatively high strength around 3 GPa. However, presently, the higher strength has been eagerly required to extend the application field. To achieve increase in the strength, we have to perfectly understand the dominating factors of the strength. We specified the dominating factors (defects) by detecting the first fracture surface and the fracture origin. This type of fiber was found to contain several types of defects, and showed that the strength was decreased in inverse proportion to one‐half power of the defect size. The causes of the defects were clarified by an actual experimental analysis and calculation results. Tyranno SA was produced by a conversion process from an amorphous Si‐Al‐C‐O fiber to SiC polycrystalline structure accompanied by a release of CO gas. During the conversion process, undesirable change in the composition (vaporization of SiO gas), which causes an increase in the residual carbon (one of defects), occurs. To prevent the vaporization of SiO gas, we newly developed a favorable condition by shifting the equilibrium state of the conversion process, and then could remarkably reduce both an abnormal SiC grain growth and the residual carbon.