Intermediate-temperature environmental effects on boron nitride-coated silicon carbide-fiber-reinforced glass-ceramic composites
- Oak Ridge National Lab., TN (United States)
- United Technologies Research Center, East Hartford, CT (United States)
The environmental effects on the mechanical properties of fiber-reinforced composites at intermediate temperatures were investigated by conducting flexural static-fatigue experiments in air at 600 and 950 C. The material that was studied was a silicon carbide/boron nitride (SiC/BN) dual-coated Nicalon-fiber-reinforced barium magnesium aluminosilicate glass-ceramic. Comparable time-dependent failure responses were found at 600 and 950 C when the maximum tensile stress applied in the bend bar was >60% of the room-temperature ultimate flexural strength of as-received materials. At both temperatures, the materials survived 500 h fatigue tests at lower stress levels. Among the samples that survived the 500 h fatigue tests, a 20% degradation in the room temperature flexural strength was measured in samples that were fatigued at 600 C. The growth rate of the Si-C-O fiber oxidation product at 600 C was not sufficient to seal the stress-induced cracks, so that the interior of the material was oxidized and resulted in a strength degradation and less fibrous fracture. In contrast, the interior of the material remained intact at 950 C because of crack sealing by rapid silicate formation, and strength/toughness of the composite was maintained. Also, at 600 C, BN oxidized via volatilization, because no borosilicate was formed.
- Sponsoring Organization:
- USDOE, Washington, DC (United States); Department of the Air Force, Washington, DC (United States)
- DOE Contract Number:
- AC05-96OR22464
- OSTI ID:
- 474141
- Journal Information:
- Journal of the American Ceramic Society, Vol. 80, Issue 3; Other Information: PBD: Mar 1997
- Country of Publication:
- United States
- Language:
- English
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