Threshold Stress for Crack Healing of Mullite Reinforced by SiC Whiskers and SiC Particles and Resultant Fatigue Strength at the Healing Temperature

A mullite/SiC whisker/SiC particle multi‐composite, having excellent crack‐healing ability and mechanical properties, was hot pressed in order to investigate the crack‐healing behavior under stress and the resultant fatigue strength at the temperature of healing. A semi‐elliptical surface crack 100 μm in surface length was introduced on each specimen. The pre‐cracked specimens were crack healed under cyclic or constant stress by using a three‐point bending stress at 1473 K, and the resultant bending strength and cyclic fatigue strength were measured at 1473 K. The pre‐crack on the surface of the specimens could be healed even under stress. The threshold stresses for crack healing, as determined by evaluating the strengths of crack‐healed specimens at a healing temperature of 1473 K, were 170 MPa for both constant and cyclic stresses, corresponding to 77% of the bending strength of the pre‐cracked specimens. The static and cyclic fatigue behaviors of crack‐healed specimens were also investigated at a healing temperature of 1473 K.