Threshold Stress for Crack-Healing of Silicon Nitride Ceramics

Si₃N₄/SiC composite ceramics were hot-pressed in order to investigate the crack-healing behavior under stress. Semi-elliptical surface cracks of 100 μm in surface length were introduced on each specimen. The pre-cracked specimens were crack-healed under cyclic or constant bending stress of 5 Hz at healing temperatures of 1000° and 1200°C and the resultant bending strength and fatigue strength were studied. The threshold stress for crack-healing, below which the pre-cracked specimens recovered their bending strength, was investigated. The mechanisms of crack-healing in Si₃N₄/SiC under stress were also discussed.