Improvement of high-temperature properties of low-oxygen SiC fiber for reinforcement of ceramic-matrix-composites

Electron-beam-irradiation-cured polycarbosilane fiber was fired for 0-36 ks at 1273-1673 K in a tube evacuated to 1.33 Pa, and then exposed at 1873 K in argon. The optimum firing condition for the thermal stability of the fib er was investigated by examining gas evolution, grain growth, resistivity, morphology and strength. The strength was low for the fibers fired below 13 73 K, because of imperfect ceramization. The firing of 3.6 ks at 1473 K yie lded the highest strength (3.5 GPa). The high strength of 1.9 GPa was retai ned when exposed at 1873 K in argon. Above 1573 K, the fiber strength was d egraded by the thermal decomposition of amorphous SiCXOY phase. The residua l oxygen in the tube caused the active-oxidation of beta -SiC crystals duri ng firing at 1673 K, resulting in the loss of fiber strength.