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PREDICTIVE SCIENCE AND TECHNOLOGY IN MECHANICS AND MATERIALS

Atomistic Modeling of Grain Boundaries and Dislocation Processes in Metallic Polycrystalline Materials

[+] Author and Article Information
Douglas E. Spearot

Department of Mechanical Engineering, University of Arkansas, Fayetteville, AR 72701dspearot@uark.edu

David L. McDowell

G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405; School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

J. Eng. Mater. Technol 131(4), 041204 (Aug 27, 2009) (9 pages) doi:10.1115/1.3183776 History: Received February 02, 2009; Revised April 03, 2009; Published August 27, 2009

The objective of this review article is to provide a concise discussion of atomistic modeling efforts aimed at understanding the nanoscale behavior and the role of grain boundaries in plasticity of metallic polycrystalline materials. Atomistic simulations of grain boundary behavior during plastic deformation have focused mainly on three distinct configurations: (i) bicrystal models, (ii) columnar nanocrystalline models, and (iii) 3D nanocrystalline models. Bicrystal models facilitate the isolation of specific mechanisms that occur at the grain boundary during plastic deformation, whereas columnar and 3D nanocrystalline models allow for an evaluation of triple junctions and complex stress states characteristic of polycrystalline microstructures. Ultimately, both sets of calculations have merits and are necessary to determine the role of grain boundary structure on material properties. Future directions in grain boundary modeling are discussed, including studies focused on the role of grain boundary impurities and issues related to linking grain boundary mechanisms observed via atomistic simulation with continuum models of grain boundary plasticity.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Schematic diagram of the five macroscopic degrees of freedom associated with a grain boundary (adapted from Ref. 1). (b) Atomic structure of a symmetric tilt Σ5(210)⟨001⟩ interface. Translations parallel and perpendicular to the interface plane result in a periodic repeating structure at the interface.

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Figure 2

Schematic illustration of (a) a bicrystal grain boundary model, (b) a 3D periodic nanocrystalline model, and (c) a columnar nanocrystalline model. Periodic boundary conditions are typically applied in all directions for each model to avoid the influence of free surfaces on the mechanisms associated with dislocation activity. For the bicrystal model, this results in a repeating planar defect in the Y-direction.

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Figure 3

(a) Bicrystal interface model for a Σ9(221)⟨110⟩ symmetric tilt grain boundary after thermodynamic equilibration at 10 K. (b) Partial dislocations emitted from the grain boundary during a uniaxial tensile deformation. (c) Mechanism by which the E structural unit collapses during the partial dislocation nucleation event. Atoms are colored by the centrosymmetry parameter; atoms in a perfect FCC arrangement are removed. Reproduced with permission from Ref. 53.

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Figure 4

(a) Stress-strain diagrams generated during uniaxial tensile deformation of a pure Cu nanocrystalline sample. Simulations contain approximately 20×106 atoms and are performed at 300 K. (b) Flow stress versus grain diameter for pure nanocrystalline Cu showing a maximum strength around 15 nm.

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Figure 5

Stress-strain response of nanocrystalline Cu–Sb solid-solution alloys with 0.1 at. % and 0.5 at. % Sb at the grain boundaries. Nanocrystalline samples are deformed in uniaxial tension at 300 K. Partial dislocation sources at the grain boundaries correlate qualitatively with regions of Sb concentration.

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