Heat treatment conditions for improvement of thermal stability of low-oxygen SiC fiber

In order to develop the most suitable process for the preparation of low-ox ygen SIC fiber, EB-cured PCS fibers were heated from room temperature to 15 73 K by using different combinations of heat treatment conditions such as h eating rate, keeping temperature and keeping time. Subsequently, the fibers were exposed to 1873 K in argon. While slow heating rate and long keeping periods were required for the improvement of thermal stability of fibers du ring heat treatment above 1200 K, the heat treatment time could be shortene d below 1200 K. No change in specific resistivity and composition profile o f fibers heat-treated under optimum conditions was observed before and afte r high-temperature exposure. In addition, fiber surface was dense and pore- free after high-temperature exposure. Consequently, the fibers showed a hig h level of strength both in the as-heat-treated state and after high-temper ature exposure. For example, the tensile strength was 3.6 GPa in as-heat-tr eated state and 2.2 GPa after high-temperature exposure for the fiber which was prepared by heating at 600 K/h below 1073 K and at 50 K/h above 1073 K .