Microstructures and oxidation behaviors of Al-modified and Al2O3-modified SiC coatings on carbon/carbon composites via pack cementation

Al2O3-modified SiC (AOSC) and Al-modified SiC (ASC) coatings were prepared on carbon/carbon (C/C) composites by one-time pack cementation (PC). Their microstructures and anti-oxidation performances were studied. Compared with ASC coating, AOSC coating shows more conspicuous defects (micro-cracks and holes) and lower densification. ASC coating can offer better oxidation resistance and thermal shock resistance to C/C composites than AOSC coating. Al additive can more efficiently improve the sinterability of SiC, which causes the above results. Besides, Al2O3 oxidation product is more stable than SiO2 (l) of oxidized SiC at 1500 °C based on the thermodynamic analysis.