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 language | English |
|---|---|
| Title of host publication | Ceramic Engineering and Science Proceedings |
| Pages | 179-188 |
| Number of pages | 10 |
| Volume | 27 |
| Edition | 7 |
| Publication status | Published - 2006 |
| Event | Advances in Ceramic Armor II - 30th International Conference on Advanced Ceramics and Composites - Cocoa Beach, FL, United States Duration: Jan 22 2006 → Jan 27 2006 |
Other
| Other | Advances in Ceramic Armor II - 30th International Conference on Advanced Ceramics and Composites |
|---|---|
| Country | United States |
| City | Cocoa Beach, FL |
| Period | 1/22/06 → 1/27/06 |
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ASJC Scopus subject areas
- Ceramics and Composites
Cite this
Root causes of the performance of boron carbide under stress. / Fanchini, Giovanni; Niesz, Dale E.; Haber, Richard A.; McCauley, James W.; Chhowalla, Manish.
Ceramic Engineering and Science Proceedings. Vol. 27 7. ed. 2006. p. 179-188.Research output: Chapter in Book/Report/Conference proceeding › Conference contribution
}
TY - GEN
T1 - Root causes of the performance of boron carbide under stress
AU - Fanchini, Giovanni
AU - Niesz, Dale E.
AU - Haber, Richard A.
AU - McCauley, James W.
AU - Chhowalla, Manish
PY - 2006
Y1 - 2006
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=33845924190&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33845924190&partnerID=8YFLogxK
M3 - Conference contribution
SN - 0470080574
SN - 9780470080573
VL - 27
SP - 179
EP - 188
BT - Ceramic Engineering and Science Proceedings
ER -