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Pseudoelastic stacking fault and deformation twinning in nanocrystalline Ni
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View: Figures


Image of FIG. 1.
FIG. 1.

In situ TEM observations of the reversible SF and irreversible full dislocation in nc Ni. (a) A HRTEM image of a grain with no pre-existed dislocation, before tensile loading. The inset shows the FFT pattern of , indicating that the electron beam is close to the [110] zone axis. The GB between and its adjacent grain is marked by white dashed line. (b) A low magnification image of the grain with the outlined boundary. Two arrows indicate the GB between and , as shown in (a). (c) After loading, a partial dislocation and a full dislocation, marked by black “T” and white “T,” respectively, nucleated from the GB and then propagated into the interior of . The (111) slip planes are indicated by dashed white lines. The SF left behind the partial dislocation is marked by the dotted-dashed line. (d) A magnified HRTEM image of the partial dislocation during recovering. The SF is indicated by a fold line. A Burgers circuit was drawn in the figure and the closure failure was measured as about 1/12 . (e) After holding for about 629 s, the partial dislocation was absorbed back to the GB and the SF was disappeared consequently. In contrast, the full dislocation remained in the interior of . (f) An IFFT image of the full dislocation. The Burgers circuit with a closure failure of 1/4 indicates that the BV of the full dislocation is 1/2 .

Image of FIG. 2.
FIG. 2.

In situ TEM observation of the reversible twinning in nc Ni. (a) A HRTEM image of a crack tip before loading. (b) After loading, a three-layer microtwin nucleated from the crack tip and propagated into the grain interior. The twin boundaries are outlined by the horizontal lines. The twin and the matrix are labeled by and , respectively. (c) The twinned region thickened and extended with the twinning partials (the steps on TBs) moving forward. (d) Twin growth stopped and detwinning initiated, with the twinning partials moving back toward the crack tip to shrink the twinned region. (e) Further detwinning occurs. (f) Detwinning completed, with the entire twinned region transformed into the matrix stacking. A step was formed at the crack tip, which is bounded by two {111} planes.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Pseudoelastic stacking fault and deformation twinning in nanocrystalline Ni