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Direct observation of dislocation structure evolution in SRF cavity niobium using electron channeling contrast imaging

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Journal of Applied Physics

AIP Publishing

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      Most cited references 21

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      Dislocation avalanches, strain bursts, and the problem of plastic forming at the micrometer scale.

      Under stress, many crystalline materials exhibit irreversible plastic deformation caused by the motion of lattice dislocations. In plastically deformed microcrystals, internal dislocation avalanches lead to jumps in the stress-strain curves (strain bursts), whereas in macroscopic samples plasticity appears as a smooth process. By combining three-dimensional simulations of the dynamics of interacting dislocations with statistical analysis of the corresponding deformation behavior, we determined the distribution of strain changes during dislocation avalanches and established its dependence on microcrystal size. Our results suggest that for sample dimensions on the micrometer and submicrometer scale, large strain fluctuations may make it difficult to control the resulting shape in a plastic-forming process.
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        Statistics of dislocation slip avalanches in nanosized single crystals show tuned critical behavior predicted by a simple mean field model.

        We show that slowly sheared metallic nanocrystals deform via discrete strain bursts (slips), whose size distributions follow power laws with stress-dependent cutoffs. We show for the first time that plasticity reflects tuned criticality, by collapsing the stress-dependent slip-size distributions onto a predicted scaling function. Both power-law exponents and scaling function agree with mean-field theory predictions. Our study of 7 materials and 2 crystal structures, at various deformation rates, stresses, and crystal sizes down to 75 nm, attests to the universal characteristics of plasticity.
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          New developments of computer-aided crystallographic analysis in transmission electron microscopy

          A new computer program for on-line crystallographic analysis in transmission electron microscopy (TEM) is presented. The program is based on the fast on-line determination of single-crystal orientations from Kikuchi and spot patterns. Spot patterns, which are particularly useful in the case of highly deformed metals, are analyzed by a new digital image processing procedure. This procedure improves the precision and ease of the orientation measurement. The program permits the on-line measurement of glide systems characterized by the Burgers vector and the crystallographic line direction of dislocations and their glide planes. The determination of twin systems, based on the misorientation calculation for any crystal structure, is included as well. The possibility of determining the foil thickness permits the complete crystallographic characterization of interfaces. Finally, the program facilitates the discrimination of phases and includes the fit of the lattice parametersa,bandcfrom diffraction patterns. The new procedures are described in detail. Application examples are given for all functions.
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            Author and article information

            Affiliations
            [1 ]Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA
            Journal
            Journal of Applied Physics
            Journal of Applied Physics
            AIP Publishing
            0021-8979
            1089-7550
            October 21 2018
            October 21 2018
            : 124
            : 15
            : 155105
            10.1063/1.5050032
            © 2018

            https://publishing.aip.org/authors/rights-and-permissions

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