High-temperature cyclic fatigue-crack growth behavior in an in situ toughened silicon carbide
The growth of fatigue cracks at elevated temperatures (25--1,300 C) is examined under cyclic loading in an in situ toughened, monolithic silicon carbide with Al-B-C additions (termed ABC-SiC), with specific emphasis on the roles of temperature, load ratio, cyclic frequency, and loading mode (static vs cyclic). Extensive crack-growth data are presented, based on measurements form an electrical potential-drop crack-monitoring technique, adapted for use on ceramics at high temperatures. It was found that at equivalent stress-intensity levels, crack velocities under cyclic loads were significantly faster than those under static loads. Fatigue thresholds were found to decrease with increasing temperature up to 1,200 C; behavior at 1,300 C, however, was similar to that at 1,200 C. Moreover, no effect of frequency was detected (between 3 and 1,000 Hz), no evidence of creep cavitation or crack bridging by viscous ligaments of grain-boundary glassy phases in the crack wake. Indeed, fractography and crack-path sectioning revealed a fracture mode at 1,200--1,300 C that was essentially identical to that at room temperature, i.e., predominantly intergranular cracking with evidence of grain bridging in the crack wake. Such excellent crack-growth resistance is attributed to a process of grain-boundary microstructural evolution at elevated temperatures, specifically involving crystallization of the amorphous grain-boundary films/phases.
- Research Organization:
- Univ. of California, Berkeley, CA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 20015221
- Journal Information:
- Acta Materialia, Vol. 48, Issue 3; Other Information: PBD: 9 Feb 2000; ISSN 1359-6454
- Country of Publication:
- United States
- Language:
- English
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