水蒸気環境におけるSiC繊維及びSiC/SiC複合材料の強度劣化

抄録

This study investigates the strength degradation of SiC fibers (Hi-Nicalon® Type S) and SiC/SiC composites produced by the PIP method (using Hi-Nicalon® Type S fibers) in high-temperature steam environments. SiC is known to oxidize in high-temperature steam, leading to strength degradation. SiC fibers and SiC/SiC composites with and without BN surface coating were exposed to dry and steam environments at 1000°C. Cross-sections of the exposed fibers were observed to measure fiber diameter and SiO₂ thickness. Tensile tests of SiC fibers and SiC/SiC composites were conducted before and after exposure to evaluate changes in tensile strength. The tensile strength of the SiC fibers degraded due to oxidation, with the most significant degradation occurring in the steam environment and without BN surface coating. BN surface coating decelerated the oxidation of SiC fibers and reduced strength degradation. Based on the obtained results, a method is proposed to predict the strength degradation of SiC/SiC composites.