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.