Effect of Vacuum Heat Treatment on Electron-Beam-Irradiation-Cured Polycarbosilane Fibers

Electron-beam-cured polycarbosilane fibers were heat-treated at 673–1773 K in a tube evacuated to 1.3 × 10⁻¹ Pa and then exposed at 1873 K in argon. The effect of vacuum heat treatment on improving the high-temperature stability of low-oxygen SiC fibers was investigated by examining gas evolution, grain growth, surface composition, tensile strength, and morphology. The fibers heat-treated at <1173 K lost strength, because of the vigorous generation of residual hydrogen. A minute amount of oxygen in the atmosphere caused the active oxidation of SiC during heat treatment at >1673 K, resulting in severe strength degradation for the as-heat-treated fibers. Vacuum heat treatment at 1573 K provided the best characteristics in low-oxygen SiC fibers.