Dislocations and Grain Size in Electrodeposited Nanocrystalline Ni Determined by the Modified Williamson–Hall and Warren–Averbach Procedures

Ungár, Tamás; Révész, Ádám; Borbély, András

doi:10.1107/s0021889897019559

Cited by 125 publications

(44 citation statements)

References 14 publications

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“…Using methods that allow the separation of broadening from grain size and inhomogeneous strains, [28] no increase in grain size was observed within the first regime for both HPT-Ni and ED-Ni. In other words, the extra recovery seen in ED-Ni can be entirely associated with a recovery in root-mean-square (RMS) strain, independent of deformation history.…”

mentioning

confidence: 55%

From Micro‐ to Macroplasticity

Brandstetter¹,

Swygenhoven²,

Petegem³

et al. 2006

Advanced Materials

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Early results of experimental investigations on microplasticity have been gathered into collected works and treatises. [1][2][3] The plastic events taking place at lower strains are related to short-range dislocation motion [4] and are of different origin than the dislocation mechanism occurring in the macroplastic regime.[5] Therefore, macroplasticity theories based on a mechanism involving long-range dislocation motion cannot serve to predict micro-yielding. In terms of measured stressstrain behavior, the two regimes are poorly distinguished, especially when they are characterized by positive strain-hardening, i.e., an increase in strength when the microstructure is strained. To facilitate comparison of data, metallurgists have come up with the rather arbitrary 0.2 % definition of the macroscopic yield stress. [6,7] It is one of the most frequently used engineering materials parameters and very important for the precise design of functional components ranging from construction materials down to micrometer-sized microelectromechanical (MEMS) devices. In polycrystalline materials, it is taken for granted that the majority of grains are plastically deforming at the macroscopic yield stress. However, there is no easy and suitable method to verify this assumption, and the real amount of strain that should be assigned to microplasticity is unknown. Experimental studies on granular materials have predominantly been performed by precise mechanical testing using load-unload cycles accompanied by surface-visualization techniques. The first experimental investigations on the effect of grain size on microplasticity [8,9] ascribed strain-hardening predominantly to the ability of grain boundaries (GBs) to act as barriers to dislocation motion, where the strain for a given stress varied as the cube of the grain size: large grains showed more strain than smaller grains. However, it was soon recognized that the relationship between microplastic strain and stress was not so simple. When a polycrystal is subjected to an external force, an inhomogeneous state of internal stress is developed resulting from elastic anisotropy and plastic incompatibilities arising from different resolved shear stresses within the different grains. [10] In addition to the fact that plastic yielding does not start at the same time in all grains, it was recognized that internal stresses arising from the elastic interactions of neighboring grains provide additional stresses that activate non-favored slip systems in grain interiors [11] and/or change the maximum shear direction in the vicinity of a GB. The latter may result in GBs emitting dislocations [12,13] on slip systems in the GB region that are different from the primary slip system of the grain interior. [14,15] Several plasticity models have been developed to predict the mechanical behavior in terms of stress-strain and hardening as a function of grain size. Some theories are based on the postulate that geometrically necessary dislocations account for the inherent difference in the accumulation o...

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mentioning

confidence: 55%

From Micro‐ to Macroplasticity

Brandstetter¹,

Swygenhoven²,

Petegem³

et al. 2006

Advanced Materials

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“…This is a simple method, but accurate only to the order of magnitude. However, since Scherrer's work, line profile analysis has made enormous progress 21,22,23,24,25,26,27,28,29,30 .…”

Section: Powder Patterns and Size Informationmentioning

confidence: 99%

Nanoparticle size distribution estimation by a full-pattern powder diffraction analysis

et al. 2005

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The increasing scientific and technological interest in nanoparticles has raised the need for fast, efficient and precise characterization techniques. Powder diffraction is a very efficient experimental method, as it is straightforward and non-destructive. However, its use for extracting information regarding very small particles brings some common crystallographic approximations to and beyond their limits of validity. Powder pattern diffraction calculation methods are critically discussed, with special focus on spherical particles with log-normal distribution, with the target of determining size distribution parameters. A 20-nm CeO2 sample is analyzed as example.

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“…Anisotropic crystallite shape are a delicate phenomenon [26] which has been treated by special elegance in the case of ZnO nanoparticles [23]. Finally, anisotropic strain broadening is a general feature of powder patterns [43][44][45][46][47][48][49][50][51][52][53][54][55][56], which is generally related to dislocations and the elastic properties of crystals. In the present work a few typical examples are reviewed where the microstructure of nanocrystalline materials has been characterized by the method of XLPA.…”

Section: Introductionmentioning

confidence: 99%

Nanocrystalline materials studied by powder diffraction line profile analysis

Ungár¹,

Gubicza²

2007

Zeitschrift Für Kristallographie - Crystalline Materials

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Abstract. X-ray powder diffraction is a powerful tool for characterising the microstructure of crystalline materials in terms of size and strain. It is widely applied for nanocrystalline materials, especially since other methods, in particular electron microscopy is, on the one hand tedious and time consuming, on the other hand, due to the often metastable states of nanomaterials it might change their microstructures. It is attempted to overview the applications of microstructure characterization by powder diffraction on nanocrystalline metals, alloys, ceramics and carbon base materials. Whenever opportunity is given, the data provided by the X-ray method are compared and discussed together with results of electron microscopy. Since the topic is vast we do not try to cover the entire field.

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Dislocations and Grain Size in Electrodeposited Nanocrystalline Ni Determined by the Modified Williamson–Hall and Warren–Averbach Procedures

Cited by 125 publications

References 14 publications

From Micro‐ to Macroplasticity

From Micro‐ to Macroplasticity

Nanoparticle size distribution estimation by a full-pattern powder diffraction analysis

Nanocrystalline materials studied by powder diffraction line profile analysis

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