Polymer-Derived Silicon Carbide Fibers with Near-Stoichiometric Composition and Low Oxygen Content

ABSTRACTFine-diameter (∼ 10–15 µm), polymer-derived SiC fibers were characterized. The average tensile strength of the fibers was ∼ 2.8 GPa, although some lots had average strengths exceeding 3.5 GPa. Microstructure observations showed that fibers had fine grain sizes (mostly ∼0.05–0.2 µm), high densities (∼3.1–3.2 g'cm3), and small residual pore sizes (≤0.1 µm). Elemental analysis showed that fibers had near-stoichiometric composition. Electron and X-ray diffraction analyses indicated that fibers were primarily beta silicon carbide, with a minor amount of the alpha phase. A small amount of graphitic carbon was detected in some samples using high resolution transmission electron microscopy. The residual oxygen content in the fibers was ≤0.1 wt%. Fibers exhibited good thermomechanical stability, as heat treatment at 1800°C for 4h in argon resulted in only an ∼ 8% decrease in strength.