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Bright field images and statistical distributions of grain size for the [(a) and (c)] as-deposited nc Ni and [(b) and (d)] deformed nc Ni.
A series of in situ micrographs and corresponding NBED patterns of grain G and grain R. The letters G and R represent the investigated grain and the reference grain, and their NBED patterns are close to ⟨112⟩ axis and ⟨100⟩ axis, respectively. The dash line representing the bright arc of NBED shows grain rotation.
A series of in situ TEM DF images shows the complete process of grain rotation and grain growth during straining.
(a) and (b) are bright field and dark field images on dog-bone specimen’s gauge section after tensile deformation. (c) is an enlarged image of the individual grain delineated by dot line in (a). (d) is a HRTEM image of the rectangle in (c); sub-GB is highlighted by the asterisks.
Proposed deformation mechanisms of nc materials: GB sliding transforms into crystal lattice rotation in neighboring grain. (a) Before plastic deformation, the nc Ni possessed high angle GBs. (b) Shear of two nc grains 1 and 2 by gliding GB dislocations, and subsequent occurrence of the crystal lattice rotation in the neighboring nc grain 3 by climbing GB dislocations. (c) Multiple grain rotations leading to grain agglomerate. (d) A large grain formed with sub-GBs (highlighted by dotted line) due to incomplete grain coalescence.
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