Self crack-healing behavior under stress of silicon nitride ceramics and resultant strength at the crack-healed temperature

Si3N4/SiC composite ceramics were sintered and subjected to three-point bending. A semi-elliptical surface crack of 100 μm in surface length was made on each specimen. A crack was healed under static bending stress of 210 MPa at 800, 900 and 1000°C Applied stress of 210 MPa is ∼70% of the bending strength of as-cracked specimen. Bending strength and static fatigue strengths of crack healed specimens were systematically investigated at each crack-healed temperature. The bending strength of crack healed specimen showed almost the same value as the smooth specimen. Thus, Si3N4SiC composite ceramics could heal a crack even under static bending stress of 210 MPa at 800, 900 and 1000 °C. Moreover, crack-healed zone bad sufficient static fatigue strength at each crack-healed temperature. These conclusions indicate that Si3N4/SiC composite ceramics has the ability to heal a crack under service condition, i.e. high temperature and applied stress.