Crack‐Healing Behavior of Si₃N₄/SiC Ceramics under Cyclic Stress and Resultant Fatigue Strength at the Healing Temperature

Abstract

Si3N4/SiC composite ceramics were sintered and subjected to three‐point bending. A semi‐elliptical surface crack of 100 μm surface length was made on each specimen. The crack‐healing behavior under cyclic stress of 5 Hz, and resultant cyclic fatigue strengths at healing temperatures of 1100° and 1200°C, were systematically investigated. The main conclusions are as follows: (1) Si3N4/SiC composite ceramics have an excellent ability to heal a crack at 1100° and 1200°C. (2) This sample could heal a crack even under cyclic stress at a frequency of 5 Hz. (3) The crack‐healed sample exhibited quite high cyclic fatigue strength at each crack‐healing temperature, 1100° and 1200°C.

Crack-Healing Ability of Structural Ceramics and Methodology to Guarantee the Reliability of Ceramic Components

“…If the crack could be healed under even service conditions, and the healed zone had sufficient strength, the reliability and lifetime of ceramic components could be increased. The crack-healing behaviors under constant or cyclic stress have been systematically studied for Si 3 N 4 /SiC www.intechopen.com Advances in Ceramics -Characterization, Raw Materials, Processing, Properties, Degradation and Healing 362 (Ando et al, 2002b;Takahahi et al, 2005), Mullite/SiC Takahashi et al 2007), Al 2 O 3 /SiC (Nakao et al, 2005b), and SiC (Lee et al, 2005a). Pre-cracks of 100 µm can be healed completely, even under constant or cyclic stress.…”

“…Crack-healed specimen (1573K for 1h) Crack-healed and proof-tested specimen (1573K for 1h, proof test at R.T.) Moreover, the guaranteed theory can be applied to Si 3 N 4 (Ando et al, 2002b;Ando et al, 2005) and coil spring made of Si 3 N 4 (Nakatani et al, 2005). The results obtained can be seen in Fig.…”

Crack-healing ability of structural ceramics and a new methodology to guarantee the structural integrity using the ability and proof-test

“…With this motivation, the authors developed Si 3 N 4 , 7 mullite, 8,9 alumina 10,11 and SiC 12 with very strong crack-healing abilities. To use these materials with a high degree of efficiency, the following topics should be studied systematically: (a) the effect of the healing condition on the strength of the crack-healed zone, 1,9,10,12,13 (b) the maximum crack size which can be healed completely, 14 (c) the high temperature strength of the crack-healed member, 1,[11][12][13][14] (d) the cyclic and static fatigue strength of the crack-healed member at elevated temperature, [14][15][16][17][18][19][20] (e) a new methodology to guarantee structural integrity of the ceramic component using the crack-healing ability. 21 Systematic studies were made on the above subjects by the authors.…”

New Technology for Increasing Through-Life Reliability of Ceramics Components Using Self-Crack-Healing Ability

“…If the crack can be healed under service conditions and the components recover their strength completely, the reliability and lifetime of ceramics components can be increased. Crackhealing behavior under constant or cyclic stress has been systematically studied for Si 3 N 4 /SiC [5,20], mullite/SiC [21,22], Al 2 O 3 /SiC [23], and SiC [17]. Standard precracks were healed, and the samples completely recovered their strength at the healing temperature, even under constant or cyclic stress.…”