Root causes of the performance of boron carbide under stress

Giovanni Fanchini, Dale E. Niesz, Richard A. Haber, James W. McCauley, Manish Chhowalla

Research output: Chapter in Book/Report/Conference proceedingConference contribution

5 Citations (Scopus)

Abstract

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. (B 11C)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 (812) 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 B 12(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 B 12O2 and B4C1-xSix is not significantly lower than in most of the B4C polytypes. Silicon inclusions, however, should strongly reduce the formation of the (B 12)CCC phase.

Original languageEnglish
Title of host publicationAdvances in Ceramic Armor II - A Collection of Papers Presented at the 30th International Conference on Advanced Ceramics and Composites
Pages179-188
Number of pages10
Edition7
Publication statusPublished - Dec 1 2006
EventAdvances in Ceramic Armor II - 30th International Conference on Advanced Ceramics and Composites - Cocoa Beach, FL, United States
Duration: Jan 22 2006Jan 27 2006

Publication series

NameCeramic Engineering and Science Proceedings
Number7
Volume27
ISSN (Print)0196-6219

Other

OtherAdvances in Ceramic Armor II - 30th International Conference on Advanced Ceramics and Composites
CountryUnited States
CityCocoa Beach, FL
Period1/22/061/27/06

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ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

Cite this

Fanchini, G., Niesz, D. E., Haber, R. A., McCauley, J. W., & Chhowalla, M. (2006). Root causes of the performance of boron carbide under stress. In Advances in Ceramic Armor II - A Collection of Papers Presented at the 30th International Conference on Advanced Ceramics and Composites (7 ed., pp. 179-188). (Ceramic Engineering and Science Proceedings; Vol. 27, No. 7).