Atomic-scale simulations of strain localization in a single-component three-dimensional model amorphous solid
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Atomic-scale simulations of strain localization in a single-component three-dimensional model amorphous solid Yunfeng Shi and Michael L. Falk Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2136, U.S.A. Molecular dynamics is used to simulate model non-crystalline solids described by a singlecomponent Dzugutov system. The solids are produced by quenching equilibrium liquids at different cooling rates. These are then tested in uniaxial compression. Samples produced at high cooling rates exhibit homogenous deformation while samples quenched at low cooling rates exhibit localized deformation. Shear bands are shown to correspond to regions of depleted shortrange order as determined by a Frank-Kasper criterion. Introduction Bulk metallic glass (BMG) exhibits a combination of excellent mechanical properties and improved processability [1,2]. It is also a promising system in which to study fundamental problems related to the relationship between the glass transition and the resulting solid’s mechanical properties. However, BMG is prone to strain localization when loaded in unconfined geometries. This severely limits its potential for use in structural applications. In order to understand the nature of strain localization it is important to be able to relate the instability to well-defined changes in the atomic structure. Some interesting experimental contributions have been made in this regard. Using quantitative high resolution transmission electron microscopy (HRTEM), nanometer sized voids have been observed to arise in shear bands [3,4]. These voids are postulated to be the result of free volume coalescence. However, the nature of the structural changes responsible for the creation or relaxation of free volume remains unclear. One potential candidate for the kind of order that dominates in non-crystals is icosahedral short-range order (SRO). Icosahedral SRO has been related to the dynamics of the super-cooled liquid state that precedes the glass transition [5] and it is a fundamental building block for various quasicrystal and icosahedral glass models [6]. Five-fold symmetry has been detected in liquid lead experimentally [7]. Reverse Monte Carlo simulations combined with extend x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) data recently was used to confirm the existence of icosahedral SRO in an amorphous alloy that is not observed to precipitate quasicrystalline phases [8]. In a two dimensional model glass, we observed that quasicrystal-like SRO is depleted in shear bands [9]. Furthermore, we observed that a transition from homogeneous to localized deformation coincides with percolation of these SRO structures [10]. The purpose of this report is to extend similar analysis to a three dimensional system. Molecular system The inter-atomic potential used here is Dzugutov potential:
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c d U ( r ) = A r − m + B exp Θ ( a − r ) + B exp r − b Θ ( b − r ) . − r a
(1)
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The parameters
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