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Silicon carbide (SiC) exhibits good strength at high temperatures and resistance to radioactivity. However, it has poor fracture toughness. The ability to heal cracks represents a very desirable means of overcoming this weakness. This study focuses on the crack-healing behavior and bending strength of SiC ceramics to which sintering additives have been added. Optimized crack-healing condition was found to be 1hr at an atmospheric level of 1100 °C. The maximum crack size that can be healed at the optimized condition was a semi-elliptical surface crack of 450 µm in diameter. Si oxide was revealed to be the principle material involved in crack-healing.

Three Al₂O₃/SiC composite ceramics were prepared, which included 1, 3 or 5 wt. % Y₂O₃, and their high-temperature bending strengths and in-situ crack-healing behaviors examined. A surface elliptical-crack of about 100 µm in diameter was introduces on the specimens using a Vickers hardness indenter. From in-situ observations, the Al₂O₃/SiC composite ceramic with 3 wt.% Y₂O₃ showed superior crack-healing ability than the 1 and 5 wt.% Y₂O₃ ceramics. The as-cracked specimen with 3 wt.% Y₂O₃ showed strength recovery on healing for 1 hr at 1473 K in air, which may have been due to the lower crack-healing temperature on the addition of 3 wt.% Y₂O₃. The heat-resistance limit temperatures of the crack-healed Al₂O₃/SiC composite ceramics were 1073, 1373 and 873 K for 1, 3 and 5 wt.% Y₂O₃, respectively.