Fatigue strength of crack‐healed Si₃N₄/SiC composite ceramics

Abstract

Si3 N4 /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) Si3 N4 /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.

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

“…The stress 210 MPa is the fatigue limit of this sample with 2C = 100 m surface crack at room temperature. 16 At 1273 K, the 15 h-healed sample exhibited a rather low fatigue limit of 550 MPa, however, the 50 h-healed sample exhibited the very high fatigue limit of 650 MPa. At both temperatures, samples crack-healed under cyclic stress exhibited a high fatigue limit of 650 MPa.…”

“…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.…”

Improvement of static fatigue strength of Si3N4/SiC crack-healed under cyclic stress

“…Most SiC particles are located in grain boundaries and distributed uniformly. This silicon nitride was selected as a test material because it has excellent crack-healing ability, with the excellent hightemperature strength of the crack-healed zone being up to 1300 • C. 9,10 The hot-pressed material was cut into test specimens measuring 3 mm × 4 mm × 20 mm. These specimens were subjected to three-point bending with a span of 16 mm.…”

Effects of Frequency on the Crack-Healing Behavior of Si3N4/SiC Composite under Cyclic Stress

“…After heat-treatment in air, the bending strength of pre-cracked specimens recovered to a value similar to that of smooth specimens because the bonding force acting across the crack surfaces increased substantially. The crack-healed specimens showed excellent high-temperature strength and static or cyclic fatigue strengths (8), (9) . To increase the reliability of ceramic components, we proposed a methodology called the "crack-healing + proof test" (13) .…”