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Characteristic boundaries associated with three-dimensional twins in hexagonal metals

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Science Advances  08 Jul 2020:
Vol. 6, no. 28, eaaz2600
DOI: 10.1126/sciadv.aaz2600
  • Fig. 1 Schematics of the atomic structure in K1 plane and the facets in {1¯012} twin boundaries.

    (A) Atomic configuration in the {1¯012} twinning plane and low-index crystallographic directions. (B) Schematic of the facets identified from {1¯012} twins observed by HRTEM from the six low-index crystallographic directions indicated in (A) and (B). A 3D twin domain of arbitrary shape could be built by combining the basic elements of CTBs and these facets in different length/height ratios.

  • Fig. 2 Simulated diffraction patterns and images from {1¯012} twins viewed along a <12¯10> zone axis within a K1 plane.

    (A) Simulated overlapping diffraction patterns from twin (red dots) and matrix (black dots). (B) HRTEM image from an extended twin boundary containing CTBs and a BP facet. (C) HRTEM image from twin tip containing CTBs and BP facets. The inset is the selected-area electron diffraction (SAED) pattern from both the matrix and twin. (D) HRTEM image of a BP facet showing the atomic structure of the facet. The dislocations in the interface are labeled by dislocation symbols.

  • Fig. 3 Simulated diffraction patterns and images from {1¯012} twins viewed along a <54¯1¯3> zone axis within a K1 plane.

    (A) Simulated overlapping diffraction patterns from twin (red dots) and matrix (black dots). (B) Relatively low-magnification HRTEM image from a twin tip showing the overall shape of the twin tip boundaries. The inset is the SAED pattern from both the matrix and twin. (C) GPA result for the square area in (B) overlapped with the corresponding HRTEM image, showing the relative rotation of {01¯11¯} planes from twin to matrix. (D) Enlarged HRTEM image of the square area in (C) with the interface and accommodating dislocations labeled in the image. (E) HRTEM image from an extended twin boundary containing CTBs and PyPy1 facet. (F) GPA result for the image in (E), showing the relative rotation of {01¯11¯} planes from twin to matrix.

  • Fig. 4 Simulated diffraction patterns and images from {1¯012} twins viewed along a <422¯3> zone axis within a K1 plane.

    (A) Simulated overlapping diffraction patterns from twin (red dots) and matrix (black dots). (B) Relatively low-magnification HRTEM image from a twin tip showing the overall shape of the twin tip boundaries. The inset is the SAED pattern from both the matrix and twin. (C) Enlarged HRTEM image of the square area in (B) showing the {01¯10}{1¯21¯2} and {14¯32¯}{1¯43¯2} facets. (D) HRTEM image from an extended twin boundary containing CTB and {01¯10}{1¯21¯2} facets.

  • Fig. 5 Simulated diffraction patterns and images from a {1¯012} twin viewed along the <101¯1> shear direction.

    (A) Simulated overlapping diffraction patterns; all diffraction spots from the twin (red dots) overlap with the spots from the matrix (black dots). (B) Low-magnification image showing the twin boundaries by diffraction contrast. The inset is the SAED pattern from both the matrix and twin. (C) HRTEM image from the extended twin boundary indicated in (B); the inset enlarges the image of the step along the CTB. (D) Enlarged image of the square area in (C), showing the CTBs and PyPy1 facet at the step. (E) Relative low-magnification HRTEM image from a twin tip indicated in (B) showing the overall shape of the twin tip boundaries. (F) Enlarged image of rectangle area in (E), showing the PyPy1 and possible PrPr2 facets.

  • Fig. 6 MD characterization of {1¯012} twin interfaces.

    (A) The 18 nm × 8 nm × 17 nm initial structure of the 3D (1¯012) twin without stress relaxation of facets. (A′) The 21 nm × 8 nm × 41 nm final structure of the 3D (1¯012) twin under 1-GPa shear stress associated with twinning at 100 K but without stress relaxation of facets. Cross-section view of twin tips/facets with (B) [12¯10], (C) [54¯1¯3], (D) [42¯2¯3], and (E) [101¯1] crystallographic directions. ZA, zone axis.

  • Table 1 Facets identified in 3D {1¯012} twin domains and the corresponding observation directions.

    Observation directionsAngle between
    observation directions
    and <12¯10>
    FacetsAngle between facet and
    CTB
    <12¯10>BP/PB137°
    K2/K286°
    541¯3>50°PyPy1, {01¯11¯}{011¯1}90°
    <422¯3>67°{01¯10}{1¯21¯2}110°
    {14¯32¯}{1¯43¯2}89°
    <101¯1>90°PyPy1, {1¯101}{01¯11}130°
    PrPr2, {1¯21¯0}{12¯10}90°

Supplementary Materials

  • Supplementary Materials

    Characteristic boundaries associated with three-dimensional twins in hexagonal metals

    Shujuan Wang, Mingyu Gong, Rodney J. McCabe, Laurent Capolungo, Jian Wang, Carlos N. Tomé

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