Determination of structural changes and phase transformations in boron carbide by static and dynamic studies

Varun Gupta
2010
Recent transmission electron microscopy results demonstrate that the failure of B4C is commensurate with the segregation of boron icosahedra embedded in amorphous carbon in 2–3 nm wide amorphous bands along the (113) lattice direction, in good agreement with our recent theoretical results. Boron carbide is generally composed of multiple polytypes of B4C which have the same primitive lattice parameters but differ from each other by the location of the boron and carbon atoms in the unit cells.
more » ... the unit cells. The unit cells are formed by a 12-atom B12-nCn icosahedron and a 3-atom (C3-nBn) chain. Our theoretical results indicate that one polytype, B12(C3), whose formation is responsible forthe failure of the entire material. This anomalous and poorly understood glass-like behavior in boron carbide has been the subject of research since its discovery over 70 years ago. The characterization of disorder in hot pressed and powder boron carbide samplesis therefore of primary interest. The research work has focused on characterization techniques which can be used at a micrometric sampling size so that individual powder grains of the material can be utilized. Specifically, micro-Raman and electricalconductivity measurements can be used with micrometric gap cells to understand the disorder in B4C.The results also demonstrate that it is possible to induce transformations in boron carbide using electric fields that are comparable with those obtained under shock and nanoindentation. Our calculations present a hypothesis which can provide a solution to prevent thepremature failure of B4C. A route to achieve suppression of the B12(CCC) polytype without significantly affecting the elastic constants is via low concentration Silicon (Si) doping of B4C. Suppression of B12(CCC) by Si doping has implications towardsdevelopment of boron carbide armor with improved properties for protection against high velocity threats. In order to achieve this, nanostructures (nanowires, nanorods, etc.) of Sidoped boron carbide have been synthesized using a Solid-Liq [...]
doi:10.7282/t3cr5tfr fatcat:d77thjxstjbovg3hnttmgecwwm