Mullite/SiC composite ceramics was sintered and subjected to three-point bending on specimens made according to the appropriate JIS standard. Semi-elliptical surface crack of 100-200μm in diameter was made on each specimen. By using three kind of specimens (smooth, cracked and crack healed), crack-healing behavior and cyclic fatigue strengths were determined systematically at room temperature. And static fatigue strengths was determined systematically at room temperature, 700°C and 1000°C. The main conclusions obtained are following: (a) Mullite/SiC composite ceramics has ability to heal a crack. (b) Crack healed specimen showed higher cyclic and static fatigue strength than as-received specimen, and this fact was caused by crack healing. (c) Crack healed part has enough fatigue strength and most fracture occurred outside the crack-healed zone in crack-healed specimen. (d) Crack-healed specimen has a sufficient strength for cyclic fatigue and static fatigue at room temperature. (e) The static fatigue strength of crack-healed samples at 700°C and 1000°C were similar to the values at room temperature.
