Research ArticleMATERIALS SCIENCE

Direct observation of individual dislocation interaction processes with grain boundaries

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Science Advances  11 Nov 2016:
Vol. 2, no. 11, e1501926
DOI: 10.1126/sciadv.1501926
  • Fig. 1 TEM nanoindentation experiment for the Σ5 grain boundary.

    (A) Schematic illustration showing the geometric arrangement of the specimen, the [010](Embedded Image) Σ5 grain boundary, the indenter tip, and the introduced lattice dislocation. We inserted the indenter tip into the specimen edge and observed the interaction process of the lattice dislocations with the Σ5 grain boundary. (B) Dark-field TEM image taken just before the nanoindentation experiment. The weak triangular contrast at the lower right is the indenter tip, and the vertical line contrast inside the specimen corresponds to the grain boundary. The indenter tip was inserted along the parallel direction to the grain boundary plane, which corresponds to the direction of 18.4° off from the [001] direction. The sample thickness is estimated to be about 300 nm.

  • Fig. 2 Sequential TEM images captured from the movie of the nanoindentation experiment for the Σ5 grain boundary.

    Sequential dark-field TEM images captured from the movie recorded during the nanoindentation experiment. The line contrasts indicated by the green arrows correspond to the Σ5 grain boundary. The positions of the leading three lattice dislocations are indicated by the triangles. The indenter tip was gradually inserted from 0 to 42 s, and the specimen edge was fractured at 43 s. The dislocation motion was strongly impeded by the grain boundary, which resulted in the dislocation pileup. In this experiment, the first and second dislocations and the lower part of the third dislocation were trapped on the grain boundary plane even after the external stress was removed.

  • Fig. 3 Impediment mechanism of dislocation at the Σ5 grain boundary.

    (A) Schematic illustrations of the formation of a residual dislocation on a grain boundary when a dislocation is about to cross the boundary. If a lattice dislocation in the right crystal with the Burgers vector of bRight crosses the grain boundary, the Burgers vector must be rotated into bLeft. This results in the formation of a residual grain boundary dislocation with the Burgers vector of bRGB, which corresponds to the difference between that of the two lattice dislocations. (B) Dark-field TEM image after extracting the indenter tip. The first and second dislocations and the lower part of the third dislocation remain trapped on the grain boundary plane despite the intervals of other dislocations being relaxed because of the repulsive forces between them.

  • Fig. 4 TEM nanoindentation experiment with the low-angle tilt grain boundary.

    (A) Dark-field TEM image of the initial low-angle tilt grain boundary. The specimen was tilted from the edge-on condition to observe the grain boundary plane. The grain boundary consists of the periodic array of edge dislocations. (B) Schematic illustration of the geometric arrangement of the specimen, the grain boundary, the grain boundary edge dislocations, the indenter tip, and the introduced lattice screw dislocation. (C) Dark-field TEM image just before the nanoindentation experiment. The indenter tip was inserted at the direction of 25° off from the [001] direction for ease of dislocation propagation. The thickness of the specimen is about 150 nm.

  • Fig. 5 Sequential TEM images captured from the movie of the nanoindentation experiment for the low-angle tilt grain boundary.

    Sequential dark-field TEM images captured from the movie recorded during the nanoindentation experiment. The green arrows in each image indicate the grain boundary position. In this experiment, the indenter tip was gradually inserted into the specimen edge from 0 to 85 s and extracted from 86 to 109 s. The introduced lattice dislocations propagated through the crystal and crossed the grain boundary into the adjacent crystal. In the unloading process, the lattice dislocations moved backward, and some dislocations crossed the grain boundary again and back into the initial crystal, where the grain boundary impeded the dislocation propagation. In the end, the dislocation indicated by the red arrow is impeded on the grain boundary plane.

  • Fig. 6 Crossing mechanism of lattice screw dislocations across the low-angle tilt grain boundary.

    (A) Dark-field TEM image of the grain boundary edge dislocations after the nanoindentation experiment. Compared with Fig. 1B, it is clear that the grain boundary edge dislocation lines are shifted and the superjogs were formed on them. (B) Schematic illustration of the crossing process of the lattice screw dislocations. The intersection of the screw dislocation with the grain boundary edge dislocations forms the jogs on the grain boundary dislocations and the kinks on the lattice dislocation. (C) Dark-field TEM image of the same area shown in Fig. 3A, imaged with a different diffraction vector. The lattice dislocation within the red rectangle is trapped on the grain boundary plane. Only the superjog segments as indicated by the blue arrows are invisible, indicating that the Burgers vector of the superjog segments differs from that of the initial grain boundary edge dislocations. (D) Schematic illustration of the intermediate stage of screw dislocation crossing. The screw dislocation partially becomes mixed dislocations as a result of the dislocation reaction, bJog = bLattice + bGB.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/11/e1501926/DC1

    Supplementary Text

    fig. S1. TEM diffraction patterns obtained from the grain boundary region.

    fig. S2. Bright-field and dark-field TEM images of the introduced dislocations by nanoindentation for the Σ5 grain boundary.

    fig. S3. Bright-field and dark-field TEM images of the introduced dislocations within the low-angle tilt grain boundary specimen.

    fig. S4. Dark-field TEM images captured during TEM nanoindentation for the Σ5 grain boundary.

    fig. S5. Number of the trapped dislocations on the Σ5 grain boundary after nanoindentation.

    fig. S6. Dark-field TEM image of the Σ5 grain boundary plane after nanoindentation.

    fig. S7. Dark-field TEM images for the g·b contrast analyses of the trapped dislocations on the Σ5 grain boundary.

    fig. S8. Bright-field TEM image of dislocation configuration after nanoindentation for the low-angle tilt grain boundary.

    movie S1. Experimental TEM movie of the in situ nanoindentation experiment for the Σ5 grain boundary.

    movie S2. Experimental TEM movie of the in situ nanoindentation experiment for the low-angle tilt grain boundary.

    movie S3. Schematic movie showing the interaction process of lattice screw dislocations with the low-angle tilt grain boundary.

    References (3437)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. TEM diffraction patterns obtained from the grain boundary region.
    • fig. S2. Bright-field and dark-field TEM images of the introduced dislocations by nanoindentation for the Σ5 grain boundary.
    • fig. S3. Bright-field and dark-field TEM images of the introduced dislocations within the low-angle tilt grain boundary specimen.
    • fig. S4. Dark-field TEM images captured during TEM nanoindentation for the Σ5 grain boundary.
    • fig. S5. Number of the trapped dislocations on the Σ5 grain boundary after nanoindentation.
    • fig. S6. Dark-field TEM image of the Σ5 grain boundary plane after nanoindentation.
    • fig. S7. Dark-field TEM images for the g·b contrast analyses of the trapped dislocations on the Σ5 grain boundary.
    • fig. S8. Bright-field TEM image of dislocation configuration after nanoindentation for the low-angle tilt grain boundary.
    • Legends for movies S1 to S3
    • References (3437)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mov format). Experimental TEM movie of the in situ nanoindentation experiment for the Σ5 grain boundary.
    • movie S2 (.mov format). Experimental TEM movie of the in situ nanoindentation experiment for the low-angle tilt grain boundary.
    • movie S3 (.mov format). Schematic movie showing the interaction process of lattice screw dislocations with the low-angle tilt grain boundary.

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