Crack-Healing under Cyclic Stress and Improvement of the Resultant Fatigue Strength of Si3N4/SiC
Si3N4/SiC composite ceramics were hot-pressed in order to investigate their crack-healing behavior under cyclic stress and the resultant static fatigue strength. Semi-elliptical surface cracks of 100 μm in surface length were made on each specimen. The pre-cracked specimens were crack-healed under a cyclic bending stress of 210MPa in air at 900, 1000, 1100, and 1200 °C. The bending strength and static fatigue strength of the crack-healed specimens were systematically investigated at each healing temperature. The specimens which has been crack-healed and static fatigue-tested at 900 and 1000 °C showed lower static fatigue strength than those tested at 1100 and 1200 °C. Detailed investigation on the fracture surface of static fatigue-tested specimens showed that oxidation of the base material had strong effects on the static fatigue strength. It was found that when the specimens were pre-oxidized in air at 1300 °C, the surface was covered by a protective oxide layer, leading to a significant improvement of static fatigue strength at 900 and 1000 °C.
T. Ohji, T. Sekino and K. Niihara
K. Takahashi, K. Ando, S. Saito, "Crack-Healing under Cyclic Stress and Improvement of the Resultant Fatigue Strength of Si3N4/SiC", Key Engineering Materials, Vols. 317-318, pp. 453-456, 2006