Effects of the Ar flow rate on the composition, structure, and properties of near-stoichiometric SiC fibres that were annealed at 1600°C

SiC fibres are widely used in the aerospace and nuclear fields due to their unique high-temperature resistance. Maintaining excellent high-temperature resistance is necessary for the application of fibres. This study involved processing nearly stoichiometric SiC fibres in Ar at 1600 °C for 1 h. The effects of the Ar flow rate on the composition, structure, and properties of fibres after high-temperature treatment were investigated by elemental analysis, SEM, EDS, TEM, XRD, and Raman spectroscopy. The results showed that the nearly stoichiometric SiC fibres did not undergo noticeable pyrolysis or active oxidation at a low Ar flow rate (<0.2 L/min) with a weight loss rate of less than 1% and that the tensile strength retention rate was as high as 86%. As the Ar flow rate was gradually increased above 0.2 L/min, an active oxidation reaction occurred, and the reaction products of SiO and CO were deposited on the fibre surfaces to form large SiC grains. The fibres gradually evolved into a skin-care structure, and the mechanical properties degraded rapidly. A high-temperature inert gas environment with a low flow rate is very important for preserving the mechanical properties of near-stoichiometric SiC fibres at high temperatures.