Mechanism for amorphization of boron carbide B{sub 4}C under uniaxial compression

Journal Article · Tue Nov 01 04:00:00 EDT 2011 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.84.184112· OSTI ID:21596916

Aryal, Sitaram; Rulis, Paul; Ching, W Y ^[1]

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1. Department of Physics, University of Missouri-Kansas City, Kansas City, Missouri 64110 (United States)

Boron carbide undergoes an amorphization transition under high-velocity impacts, causing it to suffer a catastrophic loss in strength. The failure mechanism is not clear and this limits the ways to improve its resistance to impact. To help uncover the failure mechanism, we used ab initio methods to carry out large-scale uniaxial compression simulations on two polytypes of stoichiometric boron carbide (B{sub 4}C), B{sub 11}C-CBC, and B{sub 12}-CCC, where B{sub 11}C or B{sub 12} is the 12-atom icosahedron and CBC or CCC is the three-atom chain. The simulations were performed on large supercells of 180 atoms. Our results indicate that the B{sub 11}C-CBC (B{sub 12}-CCC) polytype becomes amorphous at a uniaxial strain s = 0.23 (0.22) and with a maximum stress of 168 (151) GPa. In both cases, the amorphous state is the consequence of structural collapse associated with the bending of the three-atom chain. Careful analysis of the structures after amorphization shows that the B{sub 11}C and B{sub 12} icosahedra are highly distorted but still identifiable. Calculations of the elastic coefficients (C{sub ij}) at different uniaxial strains indicate that both polytypes may collapse under a much smaller shear strain (stress) than the uniaxial strain (stress). On the other hand, separate simulations of both models under hydrostatic compression up to a pressure of 180 GPa show no signs of amorphization, in agreement with experimental observation. The amorphized nature of both models is confirmed by detailed analysis of the evolution of the radial pair distribution function, total density of states, and distribution of effective charges on atoms. The electronic structure and bonding of the boron carbide structures before and after amorphization are calculated to further elucidate the mechanism of amorphization and to help form the proper rationalization of experimental observations.

• OSTI ID: 21596916
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 18 Vol. 84; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AMORPHOUS STATE
BENDING
BONDING
BORON CARBIDES
BORON COMPOUNDS
CARBIDES
CARBON COMPOUNDS
COMPRESSION
DEFORMATION
DENSITY
DISTRIBUTION
DISTRIBUTION FUNCTIONS
EFFECTIVE CHARGE
ELECTRONIC STRUCTURE
EVOLUTION
FABRICATION
FAILURES
FUNCTIONS
JOINING
PHYSICAL PROPERTIES
PRESSURE RANGE
PRESSURE RANGE GIGA PA
SIMULATION
STOICHIOMETRY
STRAINS
VELOCITY