Chapter 1. Stability of Polycrystalline Nextel 720 Fiber
- John B. Wachtman Jr.
Published Online: 28 MAR 2008
Copyright © 1996 The American Ceramic Society
Proceedings of the 20th Annual Conference on Composites, Advanced Ceramics, Materials, and Structures - B: Ceramic Engineering and Science Proceedings, Volume 17, Issue 4
How to Cite
Das, G. (1996) Stability of Polycrystalline Nextel 720 Fiber, in Proceedings of the 20th Annual Conference on Composites, Advanced Ceramics, Materials, and Structures - B: Ceramic Engineering and Science Proceedings, Volume 17, Issue 4 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470314876.ch1
- Published Online: 28 MAR 2008
- Published Print: 1 JAN 1996
Print ISBN: 9780470375433
Online ISBN: 9780470314876
- crystalline sic fiber;
- polycarbosilane fibers;
- electron beam irradiation
The microstructure and tensile properties of polycrystalline Nextel 720 fiber (85 wt.% Al2O3 -15 wt.% SiO2), both crystallized and precrystallized, were evaluated following prolonged thermal exposure at 982°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°C in air. The precrystallized Nextel 720 fiber started to show a slight loss of strength after heat treatment at 1093°C/4 h and the strength deterioration was exacerbated for heat treatments at 1204°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°C and a coarsening of microstructure above 1204°C. The degradation of strength in precrystallized Nextel 720 fiber heat treated at 1204°C/4 h and above may be attributed to phase instability and grain coarsening. Fractographs showed that fracture originated predominantly at the fiber surface.