Thermochemical instability effects in SiC-based fibers and SiCf/SiC composites

Thermochemical instability in irradiated SiC-based fibers with an amorphous silicon oxycarbide phase leads to shrinkage and mass loss. SiCf/SiC composites made with these fibers also exhibit mass loss as well as severe mechanical property degradation when irradiated at 800 degrees C, a temperature much below the generally accepted 1100 degrees C threshold for thermomechanical degradation alone. The mass loss is due to an internal oxidation mechanism within these fibers which likely degrades the carbon interphase as well as the fibers in SiCf/SiC composites even in so-called 'inert' gas environments. Furthermore, the mechanism must be accelerated by the irradiation environment