Crack-healing behavior of Si3N4/SiC ceramics under cyclic stress and resultant fatigue strength at the healing temperature

Si3N4/SiC composite ceramics were sintered and subjected to three-point bending. A semi-elliptical surface crack of 100 mum surface length was made on each specimen. The crack-healing behavior under cyclic stress of 5 Hz, and resultant cyclic fatigue strengths at healing temperatures of 1100degrees and 1200degreesC, were systematically investigated. The main conclusions are as follows: (1) Si3N4/SiC composite ceramics have an excellent ability to heal a crack at 1100degrees and 1200degreesC. (2) This sample could heal a crack even under cyclic stress at a frequency of 5 Hz. (3) The crack-healed sample exhibited quite high cyclic fatigue strength at each crack-healing temperature, 1100degrees and 1200degreesC.