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The structure of compacted Cu_(60)Fe_(40) powder in various stages of thermomechanical processing (with a logarithmic strain varied within e = 0-7.4) has been studied by X-ray diffraction. It is established that the atomic order e...
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The structure of compacted Cu_(60)Fe_(40) powder in various stages of thermomechanical processing (with a logarithmic strain varied within e = 0-7.4) has been studied by X-ray diffraction. It is established that the atomic order evolution in this system is characterized by a certain critical strain (e = 4.6), at which a spe_cific deformation-induced nanostructure is formed. In this structure, clusters of a bcc a-Fe phase with dimensions on the order of 200 A are coherently conjugated with a polycrystalline fcc structure of copper, thus representing a new class of materials.
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Finite-element modelling has been used to simulate local strains and stresses within free-standing polycrystalline slabs of W, Cu and W–Cu, heated with free or constrained boundaries. The elastic strain values in crystallites tha...
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Finite-element modelling has been used to simulate local strains and stresses within free-standing polycrystalline slabs of W, Cu and W–Cu, heated with free or constrained boundaries. The elastic strain values in crystallites that satisfied the diffraction condition were used to simulate the lattice strain data that would be obtained from diffraction analysis, from which the average stresses within diffracting domains were computed. Comparison of direct-space stresses in the model with the average stresses determined from diffraction analysis shows that the representative volume elements (RVEs) required to obtain equivalent stress/strain values depend on the deformation mode suffered by the material. Further, the direct-space and diffraction stress values agree only under strict sampling and strain/stress uniformity conditions. Consequently, in samples where measurements are conducted in volumes smaller than the RVE, or where the uniformity conditions are not satisfied, further experimental and numerical techniques might be needed for the accurate determination of applied or residual stress distributions.
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A computer program for the simulation of polycrystalline electron diffraction patterns is described. PCED2.0, an upgraded version of the previous JECP/PCED, can be used as a teaching aid and research tool for phase identification,...
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A computer program for the simulation of polycrystalline electron diffraction patterns is described. PCED2.0, an upgraded version of the previous JECP/PCED, can be used as a teaching aid and research tool for phase identification, microstructure texture analysis, and phase fraction determination. In addition to kinematical theory for diffraction intensity calculation of polycrystalline samples, Blackman two-beam dynamical correction is included. March model is used for out-of-plane and in-plane texture simulation. A pseudo-Voigt function is used for the peak profile fitting of diffraction rings. User-friendly interface is improved in the handling of experimental diffraction data and the flexibility of indexing. Application of the program for the analysis of FePt thin films is given as an example.
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Standard mica was used to correct the X-ray powder diffraction instrument error and mathematic methods were employed to find the correction equation. By analyzing mullite sample and comparing the corrected and uncorrected analysis...
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Standard mica was used to correct the X-ray powder diffraction instrument error and mathematic methods were employed to find the correction equation. By analyzing mullite sample and comparing the corrected and uncorrected analysis results we found the former is obviously more reasonable. So the conclusion is that the X-ray powder diffraction instrument error greatly affects the crystalline structure analysis, and the above method is convenient and effective for the correction of instrument error.
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A computer program for simulation of polycrystalline electron diffraction pattern and phase identification is described. In addition to simulating electron diffraction pattern for a single phase, the program has the ability to mod...
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A computer program for simulation of polycrystalline electron diffraction pattern and phase identification is described. In addition to simulating electron diffraction pattern for a single phase, the program has the ability to model two phases with selected mass ratio. Experimental polycrystalline electron diffraction patterns can be directly compared to simulated patterns for phase identification. Examples of how to use the program are also given.
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Traditional neutron imaging is based on the attenuation of a neutron beam through scattering and absorption upon traversing a sample of interest. It offers insight into the sample's material distribution at high spatial resolution...
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Traditional neutron imaging is based on the attenuation of a neutron beam through scattering and absorption upon traversing a sample of interest. It offers insight into the sample's material distribution at high spatial resolution in a non-destructive way. In this work, it is expanded to include the diffracted neutrons that were ignored so far and obtain a crystallographic distribution (grain mapping). Samples are rotated in a cold neutron beam of limited wavelength band. Projections of the crystallites formed by the neutrons they diffract are captured on a two dimensional imaging detector. Their positions on the detector reveal their orientation whereas the projections themselves are used to reconstruct the shape of the grains. Indebted to established synchrotron diffraction contrast tomography, this 'cold neutron diffraction contrast tomography' is performed on recrystallized aluminium for experimental comparison between both. Differences between set-up and method are discussed, followed by the application range in terms of sample properties (crystallite size and number, mosaicity and typical materials). Neutron diffraction contrast tomography allows to study large grains in bulky metallic structures.
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The elastic (diffraction) component of the neutron scattering cross section, which carries information on the atomic structure of solid helium confined in silica aerogel, has been studied. Analysis of the crystalline structure of ...
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The elastic (diffraction) component of the neutron scattering cross section, which carries information on the atomic structure of solid helium confined in silica aerogel, has been studied. Analysis of the crystalline structure of solid helium in a porous medium, which is determined from the existing neutron diffraction data, indicates that the superfluid phase is localized inside a hexagonal close-packed phase and is not present in a body-centered cubic crystal. It has also been revealed that the addition of the 3He isotope changes the structure of solid helium and hardly affects the formation of a superfluid phase.
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A hitherto unrecognized resolution effect in neutron Larmor diffraction (LD) is reported, resulting from small-angle neutron scattering (SANS) in the sample. Small distortions of the neutron trajectories by SANS give rise to a blu...
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A hitherto unrecognized resolution effect in neutron Larmor diffraction (LD) is reported, resulting from small-angle neutron scattering (SANS) in the sample. Small distortions of the neutron trajectories by SANS give rise to a blurring of the Bragg angles of the order of a few hundredths of a degree, leading to a degradation of the momentum resolution. This effect is negligible for single crystals but may be significant for polycrystalline or powder samples. A procedure is presented to correct the LD data for the parasitic SANS. The latter is accurately determined by the SESANS technique (spin-echo small-angle neutron scattering), which is readily available on Larmor diffractometers. The analysis technique is demonstrated on LD and SESANS data from alpha-Fe2O3 powder samples. The resulting d-spacing range agrees with experimental data from high-resolution synchrotron radiation powder diffraction on the same sample.
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A new high pressure cell for neutron diffraction experiments using nano-polycrystalline anvils is presented. The cell design, off-line pressure generation tests and a gas-loading procedure for this cell are described. The performa...
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A new high pressure cell for neutron diffraction experiments using nano-polycrystalline anvils is presented. The cell design, off-line pressure generation tests and a gas-loading procedure for this cell are described. The performance is illustrated by powder neutron diffraction patterns of ice VII to similar to 82 GPa. We also demonstrate the feasibility of single crystal neutron diffraction experiments of Fe3O4 at ambient conditions using this cell and discuss the current limitation and future developments.
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Quantitatively reliable atomic pair distribution functions (PDFs) have been obtained from nanomaterials in a straightforward way from a standard laboratory trans-mission electron microscope (TEM). The approch looks very promising ...
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Quantitatively reliable atomic pair distribution functions (PDFs) have been obtained from nanomaterials in a straightforward way from a standard laboratory trans-mission electron microscope (TEM). The approch looks very promising for making electron derived PDFs (ePDFs) a routine step in the characterization of nanomaterials be-cause of the ubiquity of such TEMs in chemistry and ma-terials laboratories. No special attachments such as energy filters were required on the microscope. The methodology for obtaining the ePDFs is described as well as some op-portunities and limitations of the method.
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