Oxidation Behaviors and Mechanisms of C/Si–C–N with a Mullite Interlayer

Carbon fiber reinforced Si–C–N matrix composite with a mullite interlayer (C/Mullite/Si–C–N) was fabricated via CVI and PIP process. The oxidation behaviors of C/Mullite/Si–C–N were investigated in air by comparison with that of C/PyC/Si–C–N using thermogravimetry and SEM technique. The results indicate that the weight loss of the C/Mullite/Si–C–N increases with the increase of the temperature below 800°C, decreases in the range of 800–1000°C, and increases again above 1000°C. The increase of the weight loss below 800°C results from the increase of the oxidation temperature. The closure of the matrix microcracks at 800–1000°C leads to the decrease of the weight loss, and the reopening of microcracks results in the increase above 1000°C. The oxidation resistance of C/Mullite/Si–C–N was improved greatly as compared to C/PyC/Si–C–N within the temperature range from 600°C to 1200°C. The mullite interphase changes the oxidation mode of C/Si–C–N and leads to the non-uniform oxidation of carbon fibers in the composite. At 600°C, the oxidation curve of C/Mullite/Si–C–N shows obvious non-linearity, which mainly results from the non-uniform oxidation of carbon fibers.