Chapter 34. Oxidation-Induced Contraction and Strengthening of Boron Fibers

  1. William J. Smothers
  1. James A. Dicarlo and
  2. Timothy C. Wagner

Published Online: 26 MAR 2008

DOI: 10.1002/9780470291092.ch34

Proceedings of the 5th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings, Volume 2, Issue 7/8

Proceedings of the 5th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings, Volume 2, Issue 7/8

How to Cite

Dicarlo, J. A. and Wagner, T. C. (1981) Oxidation-Induced Contraction and Strengthening of Boron Fibers, in Proceedings of the 5th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings, Volume 2, Issue 7/8 (ed W. J. Smothers), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291092.ch34

Author Information

  1. NASA-Lewis Research Center Cleveland, Ohio 44135

Publication History

  1. Published Online: 26 MAR 2008
  2. Published Print: 1 JAN 1981

ISBN Information

Print ISBN: 9780470373903

Online ISBN: 9780470291092

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Keywords:

  • mechanistic;
  • material;
  • oxygen;
  • trichloride;
  • radiation

Summary

An investigation was conducted to measure and understand the physical and mechanical effects that occur in boron fibers during and after thermal treatment in a controlled oxygen-argon gaseous mixture. Of principal concern was the optimization of this treatment as a secondary processing method for significantly improving fiber tensile strength. Strengthening was accomplished by an oxidation-induced axial contraction of the fiber and a resulting axial compression of strength-limiting flaws within the fiber's tungsten boride core. Although contraction strains above 4% were easily obtained for 203-μm-(8-mil) diameter fibers, strengthening was not achieved for contractions above 0.3% because of the formation of new flaws in the boron sheath. Nevertheless, after a 0.3% oxidation-induced contraction near 900°C and a slight surface etch near 100°C, the average tensile strength of the 203-μm fibers increased from 3.4 GN/m2 (500 ksi) to 5.5 GN/m2 (800 ksi), and the strength coefficient of variability decreased from ≈15% to < 5%. Various physical observations were used to develop mechanistic models for oxidation, contraction, and new flaw formation. Processing guidelines are discussed for possibly exceeding the 5.5 GN/m2 strength limit and also for achieving fiber strengthening during application of boron-containing diffusion barrier coatings.