FACTORS AFFECTING THE THERMAL-STABILITY OF CONTINUOUS SIC FIBERS

The thermal stability of SiC fibre synthesised from polycarbosilane precursor was studied in terms of the relationship between heat-treatment temperature and the mechanical properties at ambient temperature. When heat treated in vacuum, the mechanical properties of the fibre depend on the size of SiC grains formed by pyrolysis and corresponding to the molecular size of polycarbosilane. The reaction between excess carbon and SiO in the grain boundaries lowers the fibre strength beyond 1200°C. When heat treated in an argon atmosphere, the mechanical properties of the fibre decrease beyond 1300°C. By using a polycarbosilane having SiCl bonds in its molecule, the mechanical properties of the SiC fibre annealed beyond 1500°C are far improved with respect to those of a conventional SiC fibre. © 1989.