Stability of polycrystalline Nextel 720 fiber
- Pratt & Whitney, West Palm Beach, FL (United States)
The microstructure and tensile properties of polycrystalline Nextel 720 fiber (85 wt.% Al{sub 2}O{sub 3} - 15 wt-% SiO{sub 2}), both crystallized and precrystallized, were evaluated following prolonged thermal exposure at 982{degrees}C in air. The room temperature tensile strengths of Nextel 720 fibers did not appear to suffer degradation for exposures up to 3000 h and the microstructure remained unaffected by thermal exposures. The tensile strength of precrystallized Nextel 720 fiber was also determined at room temperature following heat treatments at 1093-1427{degrees}C in air. The precrystallized Nextel 720 fiber started to show a slight loss of strength after heat treatment at 1093{degrees}C/4 h and the strength deterioration was exacerbated for heat treatments at 1204{degrees}C/4 h and above. Microstructural characterization by x-ray and transmission electron microscopy (TEM) revealed the formation of mullite in heat treated precrystallized Nextel 720 fiber at 1204{degrees}C and a coarsening of microstructure above 1204{degrees}C. The degradation of strength in precrystallized Nextel 720 fiber heat treated at 1204{degrees}C/4 h and above may be attributed to phase instability and grain coarsening. Fractographs showed that fracture originated predominantly at the fiber surface.
- OSTI ID:
- 567443
- Report Number(s):
- CONF-960106-; CNN: Contract NAS3-26385; TRN: 98:000276-0003
- Resource Relation:
- Conference: 20. annual conference on composites, advanced ceramics, materials and structures-B, Cocoa Beach, FL (United States), 7-11 Jan 1996; Other Information: PBD: 1996; Related Information: Is Part Of Proceedings of the 20th annual conference on composites, advanced ceramics, materials, and structures - B; Greenhut, V.; PB: 465 p.
- Country of Publication:
- United States
- Language:
- English
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