Crack healing behavior and high temperature strength of Mullite/SiC composite ceramics have been investigated systematically, as a function of Y2O3 added (0-2.5wt%). The specimen was sintered by hot-pressing at 1650°C. Semi-elliptical surface crack of 100μm in diameter was made on the specimen. Cracked specimen was heat-treated at 1100°C for 3 hours, or at 1300°C for 1 hour in an air. Bending strength was measured by a 3-point bending test system. The bending strengths of smooth specimens were reduced to 40%-25% by the above cracking. For the case of mullite/SiC/Y2O3, the bending strength of heat-treated specimens with crack recovered completely up to that of smooth specimens. On the contrary, for the case of mullite/Y2O3 (Y2O3=0-2.5wt%), the bending strength was recovered incompletely. This strength recovery of both materials was caused by crack-healing. This crack-healing ability was increased considerably by adding SiC particle to mullite. By adding 0.5-2.0wt% Y2O3 to mullite/SiC composite ceramics, heat-resisting limit temperature of crack-healed sample was increased from about 1100°C to 1200°C.
