Fatigue strength of crack‐healed Si₃N₄/SiC composite ceramics

Abstract

Si 3 N 4 /SiC composite ceramics were sintered and subjected to three‐point bending on specimens made according to the appropriate JIS standard. A semi‐circular surface crack of 110 μm in diameter was made on each specimen. By using three kinds of specimen (smooth, cracked and crack healed), crack‐healing behaviour, cyclic and static fatigue strengths were determined systematically at room temperature and 1000 °C. The main conclusions are as follows: (i) Si 3 N 4 /SiC composite ceramics have the ability to heal after cracking; (ii) crack‐healed specimens showed similar cyclic and static fatigue strengths as smooth specimens, this being caused by crack healing; (iii) crack‐healed zones had a sufficient fatigue strength and most fractures occurred outside the pre‐cracked zone in those crack‐healed specimens.