Chapter 1. Stability of Polycrystalline Nextel 720 Fiber

  1. John B. Wachtman Jr.
  1. Gopal Das

Published Online: 28 MAR 2008

DOI: 10.1002/9780470314876.ch1

Proceedings of the 20th Annual Conference on Composites, Advanced Ceramics, Materials, and Structures - B: Ceramic Engineering and Science Proceedings, Volume 17, Issue 4

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

Author Information

  1. Pratt & Whitney P.O. Box 109600 West Palm Beach, FL 33410-9600

Publication History

  1. Published Online: 28 MAR 2008
  2. Published Print: 1 JAN 1996

ISBN Information

Print ISBN: 9780470375433

Online ISBN: 9780470314876

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Keywords:

  • near-stoichiometric;
  • crystalline sic fiber;
  • hi-nicalon;
  • polycarbosilane fibers;
  • electron beam irradiation

Summary

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.