EFFECT OF FIRING TEMPERATURE ON THE THERMAL-STABILITY OF LOW-OXYGEN SILICON-CARBIDE FIBERS

Low-oxygen SIC fibers which were fabricated by curing with electron-be am irradiation and firing at 1273 and 1573 K (fiber-A and fiber-B) wer e exposed at 1673 to 1973 K, Significant differences in surface compos ition, crystallinity, specific resistivity, and tensile strength were found between fiber-A and fiber-B, On exposing the fibers to high temp eratures, they both crystallized nearly completely into intermixed bet a-SiC and free carbon, and consequently the resistivity decreased mark edly. Deep voids were formed at the surface of fiber-A as a result of rapid dehydrogenation at the earliest stage of high-temperature exposu re. On the other hand, fiber-B, which decomposed mildly, had a dense p ore-free structure. The fiber strength was proportional to the recipro cal square root of SiC crystal size. At the same crystal size, the str ength of fiber-A was lower because of the surface flaws.