Crack healing behavior and mechanical property of mullite/SiC composite ceramics

Mechanical properties of sintered Mullite/SiC ceramics related with its significant crack healing behavior are discussed in this paper. This investigation was made on four kinds of specimens such as as-received smooth, heat treated smooth, pre-cracked and pre-crack healed. Pre-crack sizes were 100 mu m and 200 mu m and they were semi-elliptical in shape. The crack healing was done at 1300 degreesC for 1 hour in air. The main conclusions were obtained as follows: (a) Mullite/SiC composite ceramic has ability to heal crack (b) Maximum crack size able to be healed is semi-elliptical crack of 200 mu m in diameter (c) Crack-healed zone has enough strength up to 1100 degreesC and most specimens failed outside the crack-healed zone (d) The crack healed specimens recovered their cyclic fatigue and static fatigue strength completely by the healing process (e) The crack healed specimens showed higher cyclic fatigue and static fatigue strength than as-received smooth specimens, and this fact was caused by crack healing.