Uniaxial Compression Behavior of Bulk Nano-twinned Gold from Molecular Dynamics Simulation
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1049-AA08-05
Uniaxial Compression Behavior of Bulk Nano-twinned Gold from Molecular Dynamics Simulation Chuang Deng, and Frederic Sansoz School of Engineering, University of Vermont, Burlington, VT, 05482 ABSTRACT Parallel molecular dynamics simulations were used to study the influence of pre-existing growth twin boundaries on the slip activity of bulk gold under uniaxial compression. The simulations were performed on a 3D, fully periodic simulation box at 300 K with a constant strain rate of 4×107 s-1. Different twin boundary interspacings from 2 nm to 16 nm were investigated. The strength of bulk nano-twinned gold was found to increase as the twin interspacing was decreased. However, strengthening effects related to the twin size were less significant in bulk gold than in gold nanopillars. The atomic analysis of deformation modes at the twin boundary/slip intersection suggested that the mechanisms of interfacial plasticity in nano-twinned gold were different between bulk and nanopillar geometries. INTRODUCTION The uniaxial deformation of micro/nano-sized gold pillars by nanoindentation has provided new fundamental insights into the influence of sample size on plasticity and strengthening in metals [1-3]. Clearly, it is important to understand the underlying mechanisms of deformation in gold at limited length scale. Molecular dynamics (MD) simulation has been commonly used to investigate the atomic-level mechanisms of plastic deformation at high strain rate in gold nanobeams and nanowires [4-10]. In recent MD work, Afanasyev and Sansoz [10] have studied the compression behavior of gold nanopillars (12 nm in diameter) consisting of nanoscale twin boundaries, a special type of grain boundary existing in this material. It was found that the presence of twin boundaries strongly influences the strength of gold nanopillars. Strengthening effects by interfacial plasticity were also found to largely depend on the twin interspacing. However, meaningful results related to the strength of gold nanopillars deformed by nanoindentation can only be accomplished if the influences of microstructure and sample size are fully understood. Particularly, further research effort must be undertaken to describe the bulk behavior of nano-twinned gold under uniaxial compression. In this work, we used MD simulations to investigate the atomic mechanisms of plasticity in bulk nano-twinned gold under compression. A 3D, fully periodic simulation box was used to represent the bulk behavior of gold, excluding the effects of free surfaces. The deformation of single crystal Au was also considered. The next section describes the simulation method. The last section presents the effects of twin boundary on the compression behavior, and the atomic mechanisms operative at the intersection between slip and twin boundaries in bulk gold.
SIMULATION METHOD Classical MD simulation was performed using LAMMPS Molecular Dynamics Simulator [11]. The interatomic potential used was an embedded-atom-method potential for FCC gold developed by Grochola et al. [12].
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