title: Atomistic explanation of shear-induced amorphous band formation in boron carbide.
abstract: Boron carbide (B4C) is very hard, but its applications are hindered by stress-induced amorphous band formation. To explain this behavior, we used density function theory (Perdew-Burke-Ernzerhof flavor) to examine the response to shear along 11 plausible slip systems. We found that the (0111)/<1101> slip system has the lowest shear strength (consistent with previous experimental studies) and that this slip leads to a unique plastic deformation before failure in which a boron-carbon bond between neighboring icosahedral clusters breaks to form a carbon lone pair (Lewis base) on the C within the icosahedron. Further shear then leads this Lewis base C to form a new bond with the Lewis acidic B in the middle of a CBC chain. This then initiates destruction of this icosahedron. The result is the amorphous structure observed experimentally. We suggest how this insight could be used to strengthen B4C.
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: An
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Tao
authors.initials: T
authors.lastname: Cheng