First-principles study of dislocations in hcp metals through the investigation of the (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>11</mml:mn><mml:mover><mml:mn>2</mml:mn><mml:mo>¯</mml:mo></mml:mover><mml:mn>1</mml:mn></mml:mrow></mml:math>) twin boundary

Lane, Nina J.; Simak, Sergei I.; Mikhaylushkin, A. S.; Abrikosov, Igor A.; Hultman, Lars; Barsoum, Michel W.

doi:10.1103/physrevb.84.184101

Cited by 50 publications

(24 citation statements)

References 54 publications

(44 reference statements)

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“…1 show (i) an overall trend towards increasing values of γ t with the magnitude of GΩ 1=3 and (ii) lower energetics for f1011g relative to f1121g TBs. The first observation is consistent with similar correlations reported previously for grain and twin boundaries in metals [31,32], and is found to hold for TBs in other hcp metals based on the calculated values given in the Supplemental Material [33]. …”

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confidence: 92%

Electronic Origins of Anomalous Twin Boundary Energies in Hexagonal Close Packed Transition Metals

et al. 2015

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Density-functional-theory calculations of twin-boundary energies in hexagonal close packed metals reveal anomalously low values for elemental Tc and Re, which can be lowered further by alloying with solutes that reduce the electron per atom ratio. The anomalous behavior is linked to atomic geometries in the interface similar to those observed in bulk tetrahedrally close packed phases. The results establish a link between twin-boundary energetics and the theory of bulk structural stability in transition metals that may prove useful in controlling mechanical behavior in alloy design. DOI: 10.1103/PhysRevLett.115.065501 PACS numbers: 62.20.-x, 61.72.Mm Twinning is a common deformation mechanism in materials where the number of active dislocation slip systems is limited [1][2][3][4][5]. In such materials, understanding of the mechanisms underlying twin boundary (TB) formation can thus be essential for optimizing mechanical properties [6][7][8][9]. Theories of the crystallography of twinning and its relation to bulk deformation are well developed, and the mechanisms of twin nucleation and growth have been investigated in many technologically important systems [2]. However, the degree to which deformation twinning can be significantly influenced through variations in composition for materials design has been investigated in only a limited number of systems (see, e.g., Refs. [10][11][12][13]).In this Letter we report results of a study of the properties of commonly observed deformation twins in hexagonal close packed (hcp) structured transition metals, a class of materials that finds use in diverse applications including aerospace alloys, cladding for nuclear fuel, and magnetic recording. Through the use of density-functional-theory (DFT) calculations, we demonstrate anomalously low TB energies (γ t ) for the group VII transition metals, Re and Tc. This finding correlates with the unique mechanical properties of hcp structured Re, which displays pronounced deformation twinning [14][15][16][17], and a unique combination of high-temperature strength and low-temperature ductility [18] that have made it of interest for structural applications in extreme environments [18,19]. To investigate the electronic origins of this anomalous twinning behavior, we introduce a new method for computing the composition dependence of γ t in alloys. Results derived with this approach demonstrate that TB energies in Re can be decreased even further through alloying with elements that lower the average number of d electrons per atom relative to pure Re. These predictions are consistent with experimental characterization studies undertaken in this work, demonstrating pronounced differences in deformation microstructures in Re versus Re-10 at. % W alloys. The anomalous TB energetics in the group VII metals are correlated with the presence of structural units near the TB plane that are similar to the Frank-Kasper polyhedra characterizing the tetrahedrally close packed (TCP) transition metal intermetallic compounds that are stable near half d...

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confidence: 92%

Electronic Origins of Anomalous Twin Boundary Energies in Hexagonal Close Packed Transition Metals

et al. 2015

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“…The reorientation occurs in this pyramidal shear band with the rotation angle of 34°, just as the misorientation angle of the f11 21g twin. Therefore, this deformation was usually defined as f11 21g twin in previous works [43][44][45].…”

Section: Details Of Initial Plastic Deformation Under Tensionmentioning

confidence: 99%

Molecular Dynamics Simulations of the Orientation Effect on the Initial Plastic Deformation of Magnesium Single Crystals

Guo

et al. 2016

Acta Metall. Sin. (Engl. Lett.)

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Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations. The angle between the loading axis and the basal \a[ direction ranges from 0°to 90°. The simulation results show that the initial defects usually nucleate at free surfaces, but the initial plastic deformation and the subsequent microstructural evolutions are various due to different loading directions. The tension simulations exhibit the deformation mechanisms of twinning, slip, crystallographic reorientation and basal/prismatic transformation. The twinning, crystallographic reorientation and basal/prismatic transformation can only appear in the crystal model loaded along or near the a-axis or c-axis. For the compression simulations, the basal, prismatic and pyramidal slips are responsible for the initial plasticity, and no twinning is observed. Moreover, the plastic deformation models affect the yield strengths for the samples with different orientations. The maximum yield stresses for the samples loaded along the c-axis or a-axis are much higher than those loaded in other directions.

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“…[6,[14][15][16][17][18][19][20][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][23][24][25][26][27][28][29][30][31][32][33][34][35][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 ð " 1012Þ; ð " 1011Þ; ð " 2112Þ, and ð " 2111Þ TBs employing different interatomic potentials and c/a ratios [12,[23][24][25][26][27][28]30,37,38] were consistent, suggesting that their basic structural characteristics are properties of hcp topology.…”

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Atomic Structures of $$ [0\bar{1}10] $$ Symmetric Tilt Grain Boundaries in Hexagonal Close-Packed (hcp) Crystals

Wang

Beyerlein

2012

Metall Mater Trans A

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Molecular dynamics simulation and interface defect theory are used to determine the relaxed equilibrium atomic structures of symmetric tilt grain boundaries (STGBs) in hexagonal closepacked (hcp) crystals with a ½0 " 110 tilt axis. STGBs of all possible rotation angles h from 0 deg to 90 deg are found to have an ordered atomic structure. They correspond either to a coherent, defect-free boundary or to a tilt wall containing an array of distinct and discrete intrinsic grain boundary dislocations (GBDs). The STGBs adopt one of six base structures, P ðiÞ B , i = 1, …, 6, and the Burgers vector of the GBDs is related to the interplanar spacing of the base structure on which it lies. The base structures correspond to the basal plane (h = 0 deg, P ð1Þ B ); one of four minimum-energy, coherent boundaries, ð " 2111Þ; ð " 2112Þ; ð " 2114Þ, and ð " 2116Þ P B ). Based on these features, STGBs can be classified into one of six possible structural sets, wherein STGBs belonging to the same set i contain the same base boundary structure P ðiÞ B and an array of GBDs with the same Burgers vector b ðiÞ GB , which vary only in spacing and sign with h. This classification is shown to apply to both Mg and Ti, two metals with different c/a ratios and employing different interatomic potentials in simulation. We use a simple model to forecast the misorientation range of each set for hcp crystals of general c/a ratio, the predictions of which are shown to agree well with the molecular dynamics (MD) simulations for Mg and Ti.

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First-principles study of dislocations in hcp metals through the investigation of the (112¯1) twin boundary

Cited by 50 publications

References 54 publications

Electronic Origins of Anomalous Twin Boundary Energies in Hexagonal Close Packed Transition Metals

Electronic Origins of Anomalous Twin Boundary Energies in Hexagonal Close Packed Transition Metals

Molecular Dynamics Simulations of the Orientation Effect on the Initial Plastic Deformation of Magnesium Single Crystals

Atomic Structures of $$ [0\bar{1}10] $$ Symmetric Tilt Grain Boundaries in Hexagonal Close-Packed (hcp) Crystals

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