15. Root Causes of the Performance of Boron Carbide Under Stress

  1. Lisa Prokurat,
  2. Andrew Wereszczak and
  3. Edgar Lara-Curzio
  1. Giovanni Fanchini1,
  2. Dale E. Niesz1,
  3. Richard A. Haber1,
  4. James W. McCauley2 and
  5. Manish Chhowalla1

Published Online: 26 MAR 2008

DOI: 10.1002/9780470291368.ch15

Advances in Ceramic Armor II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 7

Advances in Ceramic Armor II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 7

How to Cite

Fanchini, G., Niesz, D. E., Haber, R. A., McCauley, J. W. and Chhowalla, M. (2008) Root Causes of the Performance of Boron Carbide Under Stress, in Advances in Ceramic Armor II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 7 (eds L. Prokurat, A. Wereszczak and E. Lara-Curzio), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291368.ch15

Author Information

  1. 1

    Materials Science and Engineering, Rutgers University Piscataway, NJ 08854, U.S.A.

  2. 2

    ARL, Aberdeen Proving Ground Aberdeen, MD 21005, U.S.A.

Publication History

  1. Published Online: 26 MAR 2008
  2. Published Print: 1 JAN 2006

ISBN Information

Print ISBN: 9780470080573

Online ISBN: 9780470291368

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Keywords:

  • boron carbide;
  • oxygen;
  • carbide polytypes;
  • segregated phase;
  • silicon

Summary

The absence of a plastic phase in boron carbide and its failure at shock impact velocities just above the Hugoniot elastic limit (HEL) has been the subject of several experimental investigations. Furthermore, the common presence of contaminants, such as disordered graphitic inclusions, oxygen, etc., needs to be addressed. Further, a theoretical picture accounting all these phenomena is still lacking. In the present work, using self-consistent field density functional simulations we are able to account for many experimental observations by noticing that several boron carbide polytypes [e.g. (B11C)CBC, (B12)CCC, …] coexist without significant lattice distortions. Our analysis also indicates that above a threshold pressure all such polytypes are less stable than a phase involving segregated boron (B12) and amorphous carbon (a-C) but the energy barrier for the transformation into a segregated phase of boron and carbon, is by far lower for the B12(CCC) polytype. For such a configuration, segregation of carbon occurs in layers orthogonal to the (113) lattice directions, in excellent agreement with recent transmission electron microscopy (TEM) analysis. We will also, in the actual preparation conditions of the material, show that the Gibbs free energy per site in the B12 + a-C segregate phase, in B12O2 and B4C1−xSix is not significantly lower than in most of the B4C polytypes. Silicon inclusions, however, should strongly reduce the formation of the (B12)CCC phase.