title: Nucleation of amorphous shear bands at nanotwins in boron suboxide.
abstract: The roles of grain boundaries and twin boundaries in mechanical properties are well understood for metals and alloys. However, for covalent solids, their roles in deformation response to applied stress are not established. Here we characterize the nanotwins in boron suboxide (B6O) with twin boundaries along the {0111} planes using both scanning transmission electron microscopy and quantum mechanics. Then, we use quantum mechanics to determine the deformation mechanism for perfect and twinned B6O crystals for both pure shear and biaxial shear deformations. Quantum mechanics suggests that amorphous bands nucleate preferentially at the twin boundaries in B6O because the twinned structure has a lower maximum shear strength by 7.5% compared with perfect structure. These results, which are supported by experimental observations of the coordinated existence of nanotwins and amorphous shear bands in B6O, provide a plausible atomistic explanation for the influence of nanotwins on the deformation behaviour of superhard ceramics.
authors.affiliation: Department of Chemistry, Materials and Process Simulation Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: An
authors.affiliation: WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.|Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: K Madhav
authors.initials: KM
authors.lastname: Reddy
authors.affiliation: Department of Chemistry, Materials and Process Simulation Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Qian
authors.affiliation: Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Hemker
authors.affiliation: WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Ming-Wei
authors.initials: MW
authors.lastname: Chen
authors.affiliation: Department of Chemistry, Materials and Process Simulation Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard