Mechanical Self-adaptability of a SiC/PyC/SiC Composite During Oxidation in Air

An oxidation test for three-dimensional (3D) SiC/PyC/SiC composite with CVD SiC coating was performed by thermogravimetric analysis (TGA) in simulated air at temperatures ranging from 600 to 1100°C. After oxidation, the mechanical properties were evaluated by a three-point flexural test. Effects of oxidation on mechanical properties of the composite were investigated by comparing the strength and failure behaviors as well as the morphologies examination. The results showed that the failure of the as-received composite was rather brittle while that of the oxidized composite showed a non-brittle pattern. Combining the oxidation analysis with a mechanical test, the result indicated that a certain extended oxidation of the PyC interphase led to an increased toughness without strength degradation due to improved interphase bonding in the SiC/PyC/SiC, namely, the composite showed mechanical self-adaptability with improved strength and toughness. The amount and length of fiber pull-out in the as-received composites were much smaller in comparison with those of oxidized composites.