Fatigue strength of crack-healed Si3N4/SiC composite ceramics

Si3N4/SiC composite ceramics were sintered and subjected to three-point ben ding on specimens made according to the appropriate JIS standard. A semi-ci rcular surface crack of 110 mu m in diameter was made on each specimen. By using three kinds of specimen (smooth, cracked and crack healed), crack-hea ling behaviour, cyclic and static fatigue strengths were determined systema tically at room temperature and 1000 degrees C. The main conclusions are as follows: (i) Si3N4/SiC composite ceramics have the ability to heal after c racking; (ii) crack-healed specimens showed similar cyclic and static fatig ue strengths as smooth specimens, this being caused by crack healing; (iii) crack-healed zones had a sufficient fatigue strength and most fractures oc curred outside the pre-cracked zone in those crack-healed specimens.