Three point bending specimen was made from mullite/SiC composite ceramics. A semi-elliptical surface crack of 75μm or 100μm in diameter (aspect ratio ≈0.9) was introduced on the specimen. Basic crack-healing behavior of the cracked-sample was studied systematically as a function of crack-healing temperature, time, environment and cyclic stress applied. Followings are main conclusion obtained; (1) Mullite/SiC composite ceramics are able to recover strength of cracked sample by heat treatment in air. (2) The recovery was caused by the crack-healing behavior, and the activation energy was evaluated as Q=413kJ/mol. (3) This sample was able to heal a crack even under cyclic stress at service temperature. This behavior was defined as in situ crack-healing. (4) The crack-healed sample from 1273K to 1473K exhibited same level bending strength to crack-healed sample at 1573K just at the healed temperature. This behavior was defined as in situ bending strength of in situ crack-healed sample.
