A Thermally Conductive Sic-Polycrystalline Fiber and Its Fiber-Bonded Ceramic

Abstract

A type of SiC polycrystalline fiber (Tyranno SA fiber) was obtained from polyaluminocarbosilane. The SA fiber had a high tensile strength (3GPa) and modulus (300GPa), and showed no degradation in strength or change in composition on beating to 2000°C in inert atmosphere and 1000°C in air for long times (over 2000hrs). In this research, two fiber diameters were investigated. Residual carbon was markedly reduced in the fiber with smaller diameter fiber. This type of SA fiber with an excellent high-temperature property and very high thermal conductivity (65 W\mk) has been commercialized as SA-3 grade. A type of sintered SiC fiber-bonded ceramic (SA-Tyrannohex) was synthesized by hot-pressing piled sheets of the intermediate amorphous Si-Al-C-O fiber prepared from the above-mentioned polyahminocarbosilane. The SA-Tyrannohex consists of a highly ordered, close-packed structures of very fine hexagonal columnar with a thin interfacial carbon layer. The interior of the fiber element was composed of sintered SiC crystals. This composite showed high strength, fibrous fracture behavior, excellent high-temperature properties, and high thermal conductivity (even at temperatures over 1000°C). It was also found that the initial strength of the SA-Tyrannohex, which was prepared from the smaller diameter fiber, was perfectly preserved up to 1700°C. SA-Tyrannohex also showed very long rupture time (723 hrs) at 1400°C and 100MPa in air in tensile creep testing.