Atomic Structures of $$ [0\bar{1}10] $$ Symmetric Tilt Grain Boundaries in Hexagonal Close-Packed (hcp) Crystals
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es (GBs) that possess long-range atomic structural order tend to exhibit properties that strongly depend on the details of their structure. Details of interest include the atomic structure of the coherent regions (atomic density and periodicity) and the characteristics of the intrinsic grain boundary defects (such as screw/edge character, spacing, step height, and Burgers vector).[1,2] Based on these structural features, ordered GBs can potentially be grouped, with the intent of eventually correlating a group of GBs to a particular reaction response, for instance with an impinging lattice dislocation, or a response to an applied normal or shear traction.[3–9] In the current work, the atomic structures of symmetrical tilt grain boundaries (STGBs) in hexagonal close-packed (hcp) structures are studied. STGBs are simple grain boundaries that are fully described crystallographically by a tilt axis and tilt angle 2h. For this class of boundaries, prior studies have investigated, for instance, the effect of GB defect structure on the propensity for sliding,[4,10] partial transmission and JIAN WANG, Doctor, is with the Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545. Contact e-mail: [email protected] IRENE J. BEYERLEIN, Technical Staff Member, is with the Theoretical Division, Los Alamos National Laboratory. Manuscript submitted December 9, 2011. Article published online May 17, 2012 3556—VOLUME 43A, OCTOBER 2012
absorption,[4–9,11] and vacancy migration energies and entropies.[12,13] Most atomic-scale structural models for STGBs have been developed for high-symmetry face-centered-cubic and body-centered-cubic crystals.[6,14–21] In this large body of work, the atomic structures of cubic STGBs, differing in tilt axis and continually varying over a wide range of h, have been characterized using structural unit models or coincident site lattice (CSL) concepts. For hcp crystals, most atomistic studies, involving atomic-scale topological models, density functional theory, or molecular dynamics (MD),[22–36] have focused on coherent STGBs free of intrinsic grain boundary dislocations, such as twin boundaries (TBs). Among those studies using MD simulations, the structure predictions of the more common hcp ð1012Þ; ð1011Þ; ð2112Þ, and ð2111Þ TBs employing different interatomic potentials and c/a ratios[12,23–28,30,37,38] were consistent, suggesting that their basic structural characteristics are properties of hcp topology. Additional coherent boundaries structures, such as ð2115Þ; ð2116Þ; ð3032Þ; ð3034Þ; ð1014Þ, and ð2021Þ, not associated with experimentally observed hcp twins, have also been modeled.[37–40] Less comprehensively studied for hcp crystals are the changes in dislocation structure of STGBs as h is continually varied in orientation space, in particular, as h deviates from that of a coherent boundary. Generally, as h tilts off coherency, intrinsic GBDs should form to accommodate the deviation, an expectation that has been confirmed experimentally.[41–43] Prior studies META
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