EFFECT OF THERMOCHEMICAL TREATMENTS ON THE STRENGTH AND MICROSTRUCTURE OF SIC FIBERS

The room-temperature strength of commercially available polymer-derived SiC fibres degrades during the typical high-temperature thermal cycle used in ceramic matrix composite fabrication. Substantial improvements in retained room-temperature strength for two different commercially available fibres were observed after annealing in carbon powder at temperatures up to 1600-degrees-C. Further improvements in strength were observed for both fibres when heat treated in CO atmospheres. X-ray diffraction, TEM, SEM, auger electron spectroscopy, and optical microscopy were used to characterize the microstructure and chemistry of these heat-treated fibres in order to understand better the degradation mechanisms of the fibres as well as their improved strength retention.