Papers by Keyword: X-Ray Diffraction (XRD)

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Authors: Guillaume Geandier, Moukrane Dehmas, Mickael Mourot, Elisabeth Aeby-Gautier, Sabine Denis, Olivier Martin, Nikhil Karnatak
Abstract: In situ high energy X-ray diffraction synchrotron was used to provide direct analysis of the transformation sequences in steel-based matrix composite (MMC) reinforced with TiC particles. Evolution of the phase fractions of the matrix and TiC particles as well as the mean cell parameters of each phase were determined by Rietveld refinement from high energy X-ray diffraction (ID15B, ESRF, Grenoble, France). In addition, some peaks were further analysed in order to obtain the X-ray strain during the cooling step. Non-linear strain evolutions of each phase are evidenced, which are either associated with differences in the coefficient of thermal expansion (CTE) between matrix and TiC particle or to the occurrence of phase transformation. Micromechanical calculations were performed through the finite element method to estimate the stress state in each phase and outline the effects of differences in CTE and of volume change associated with the matrix phase transformation. The calculated results led to a final compressive hydrostatic stress in the TiC reinforcement and tensile hydrostatic stress in the matrix area around the TiC particles. Besides, the tendencies measured from in situ synchrotron diffraction (mean cell parameters) matched with the numerical estimates.
Authors: Peter Staron, Felix Beckmann, Thomas Lippmann, Andreas Stark, Michael Oehring, Florian Pyczak, Mario Salgado, Norbert Hort, Helmut Eckerlebe, Karl Ulrich Kainer, Martin Müller, Andreas Schreyer
Abstract: High-energy X-rays and neutrons offer the large penetration depths that are often required for the determination of bulk properties in engineering material research. In addition, new sources provide very high intensities on the sample, which can be used not only for high spatial resolution using very small beams, but also for high time resolution in combination with a fast detector. This opens up possibilities for a wide range of specific engineering in situ experiments. Typical examples that are already widely used are heating or tensile testing in the beam. However, there are also more challenging experiments in the field of light metals, like e.g. friction stir welding, dilatometry, solidification, or cutting. Selected examples are presented.
Authors: Hong Tao Liu, Guang Ai Sun, Yan Dong Wang, Bo Chen, Xiao Lin Wang, Qiang Tian
Abstract: The stress-induced martensitic transformation in Ni47Ti44Nb9 was examined using X-ray diffraction (XRD) during in situ uniaxial loading and unloading. A new martensitic (020) peak in XRD patterns is observed under strain from 10% to 12%. It indicates that the martensitic texture has reached the optimum orientation. After unloading, approximately 8% irreversible strain still remains. It is associated with the reorientation of martensites and the plastic deformation of the B2-phase. In addition, the deformed β-Nb particles would also reduce the driving force for the reverse transformation. The details of lattice-strain and shared applied stress (SAS) in the B2-phase and β-Nb phase are also discussed in this work.
Authors: J. Sheng, U. Welzel, Eric J. Mittemeijer
Abstract: The stress evolution during diffusion annealing of Ni-Cu bilayers (individual layer thicknesses of 50 nm) was investigated employing ex-situ and in-situ X-ray diffraction measurements. Annealing at relatively low homologous temperatures (about 0.3 - 0.4 Tm) for durations up to about 100 hours results in considerable diffusional intermixing, as demonstrated by Auger-electron spectroscopy investigations (in combination with sputter-depth profiling). In addition to thermal stresses due to differences of the coefficients of thermal expansion of layers and substrate, tensile stress con-tributions in the sublayers arise during the diffusion anneals. The obtained stress data have been discussed in terms of possible mechanisms of stress generation. The influence of diffusion on stress development in the sublayers of the diffusion couple during heating and isothermal annealing was investigated by comparing stress changes in the bilayer system with corresponding results obtained under identical conditions for single layers of the components in the bilayer system. The specific residual stresses that emerge due to diffusion between the (sub)layers in the bilayer could thereby be identified.
Authors: Radomír Kužel, Zdeněk Matěj, Miloš Janeček
Abstract: X-ray diffraction (XRD) studies of ECAP (equal-channel angular pressing) materials were performed after annealing and by in-situ measurements in XRD high-temperature chamber for samples prepared by different number of passes and number of revolutions, respectively. Main attention was given to Cu and Cu-Zr samples. Significant dependence on number of passes was found for ECAP samples. In-situ measurements were focused not only on temperature dependence but also on time evolution of the diffraction line profiles. Evaluation in terms of dislocation densities, correlation and crystallite size and its distribution was performed by our own software MSTRUCT developed for total powder diffraction pattern fitting. Abnormal growth of some grains with annealing is well-known for copper and leads to the creation of bimodal microstructure. Therefore a special care must be given to the evaluation and a model of two Cu components (larger and smaller crystallites) was fitted to the data if an indication of some crystallite growth appears either in the XRD line profile shape or in two-dimensional diffraction patterns.
Authors: Wolfgang Kowalski, Markus Dammer, Frank Bakczewitz, Olaf Kessler
Abstract: Stents are medical implants, which are applied to keep cavities in the human body open, e.g. blood vessels. Typically they consist of tube-like grids of suitable metal alloys. Typical dimensions depend on their applications: outer diameters in the mm-range and grid bar thickness in the 100 µm range. Before implantation, stents are compressed (crimped) to allow implantation in the human body. During implantation, stents are expanded, usually by balloon catheters. Crimping as well as expansion causes high strains and high stresses locally in the grid bars. These strains and stresses are important design criteria of stents. Usually, they are calculated numerically by Finite Element Analysis (FEA) [1,2]. The XRD-sin²ψ-technique is applied for in-situ-determination of stress conditions during crimping and expansion of stents of the CoCr-alloy L-605. This provides a realistic characterization of the near-surface stress state and an evaluation of the numerical FEA results. XRD-results show an increasing compressive load stress in circumferential direction with increasing stent expansion. These findings correlate with the numerical FEA results. Further residual stresses after removing the expansion device have been measured.
Authors: Qian Tang, Roger Brooks, Serena Best
Abstract: Hydroxyapatite and silicon-substituted hydroxyapatite powers were prepared in-house through a wet precipitation method and then vacuum plasma sprayed onto Ti-6Al-4V discs. Two plasma gun input powers were employed, 37 kW and 40 kW. All coatings were nearly phase pure, except small traces of impurities (TTCP, -TCP and CaO). Coatings prepared under the lower plasma gun input power had lower crystallinity. In vitro studies showed that human osteoblast-like cells attached and spread very well on all coated discs. Among the four kinds of discs, SiHAC37 was the most supportive to cell growth.
Authors: A. Zięba, W. Dąbrowski, P. Gryboś, W. Pawroźnik, J.R. Słowik, T. Stobiecki, K. Świentek, P. Wiącek
Abstract: Silicon strip detectors represent a new class of one-dimensional position-sensitive single photon counting devices. They allow a reduction of measurement time at the powder diffractometers by a factor up to 100 compared to instruments with a single counter, while maintaining comparable count statistics. Present work describes a 128-channel detector working with a standard diffractometer. The detector is 12.8 mm long and covers the angular range of 3.2 deg. We discuss the diffraction geometry in real and reciprocal space, the FWHM of diffraction peaks, and the background level. Measurements were made on standard samples and on complex samples of industrial importance (e. g., portland clinker). Applications of the detector to diffraction measurements of single crystals and thin films are discussed briefly.
Authors: Anne Henry, Xun Li, Henrik Jacobson, Sven Andersson, Alexandre Boulle, Didier Chaussende, Erik Janzén
Abstract: The growth of 3C-SiC on hexagonal polytype is addressed and a brief review is given for various growth techniques. The Chemical Vapor Deposition is shown as a suitable technique to grow single domain 3C epilayers on 4H-SiC substrate and a 12.5 µm thick layer is demonstrated; even thicker layers have been obtained. Various characterization techniques including optical microscopy, X-ray techniques and photoluminescence are compared for the evaluation of the crystal quality and purity of the layers.
Authors: Ulrich Lienert, Jonathan Almer, Bo Jakobsen, Wolfgang Pantleon, Henning Friis Poulsen, D. Hennessy, C. Xiao, R.M. Suter
Abstract: The implementation of 3-Dimensional X-Ray Diffraction (3DXRD) Microscopy at the Advanced Photon Source is described. The technique enables the non-destructive structural characterization of polycrystalline bulk materials and is therefore suitable for in situ studies during thermo-mechanical processing. High energy synchrotron radiation and area detectors are employed. First, a forward modeling approach for the reconstruction of grain boundaries from high resolution diffraction images is described. Second, a high resolution reciprocal space mapping technique of individual grains is presented.
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