Abstract
The cyclic fatigue behavior of different kinds of ceramics was investigated at room temperature. Flexural specimens, with an indentation induced flaw at the center of the reduced gage section, were tested under a cyclic load applied by four-point bending. All ceramics tested were shown to be susceptible to cyclic fatigue failure. The cyclic fatigue degradation compared to its flexural strength increased in this order: hot-pressed AlN, sintered SiC, hot-pressed Si3N4, sintered Si3N4, and sintered Al2O3. The apparent fatigue limit was about 80% of the average flexural strength for AlN, and about 60% for sintered Al2O3. There existed a correlation between the scatter in fatigue and flexural strength. The scatter in fatigue strength was smaller than the scatter in flexural strength. SEM fractography revealed a dominant intergranular fracture in Al2O3 and Si3N4, which suggests a possible stress corrosion cracking mechanism in the grain boundary glassy phase. On the other hand, hot-pressed AlN showed a mixed mode fracture of intergranular and transgranular cracking, and SiC exhibited transgranular cracking only.
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