Crack healing behavior and high temperature strength of Mullite/SiC composite ceramics containing Y_2O_3 have been investigated systematically. The specimens were sintered by hot-pressing at 1650℃. Semielliptical surface crack of 100μm in diameter was made on the specimens. Cracked specimens were heat-treated at 1100℃ for 3hours, or at 1300℃ for 1hour in air. Bending strength was measured by a 3-point bending test system. The bending strength of pre-cracked specimens was decreased by about 150MPa in comparison with the strength of as-received specimens. However, the bending strength level of heat-treated specimens that had cracked defects recovered completely up to that of as-received specimens. In conclusion, crack healing due to oxidation resulted in the recovery of bending strength because cracked defects were filled with oxides, which were produced by heat treatment in air. High temperature strength was dependent on the material that was produced by heat treatment.
