Crack-healing behavior under stress of mullite/silicon carbide ceramics and the resultant fatigue strength

Mullite/SiC composite ceramics were sintered and subjected to three-point bending of specimens made according to the appropriate JIS standard. A semicircular surface crack 100 to 250 μm in diameter was made on each specimen. We systematically studied crack-healing behavior and cyclic- and static-fatigue strengths at room temperature and 1000°C (crack-healing temperature) by using three types of specimens (smooth, cracked, and crack-healed). The main conclusions are as follows: (i) mullite/SiC composite ceramics have the ability to heal after cracking; (ii) crack-healed specimens exhibited higher static and fatigue strengths than those of smooth specimens, which was caused by crack-healing; (iii) a sample crack-healed at 1000°C had a high fatigue strength at 1000°C; and (iv) mullite/SiC ceramics can heal a crack under stress at 1000°C, and this behavior was considered using crack-driving force and crack-healing force, qualitatively.