SYNCHROTRON X-RAY DIFFRACTOMETRY AND IMAGING OF STRAINS AND DEFECTS IN ICOSAHEDRAL QUASICRYSTAL GRAINS

International audienceIn order to better understand the long range propagation of quasicrystalline order as well as quasicrystal stability, it is important to know if defects are generated in the quasicrystal grains during their growth. Previously, we studied the degree of perfection of about ten icosahedral quasicrystal grains of various alloys (Al-Pd-Mn, Al-Cu-Fe, Zn-Mg-Y), as grown or annealed, and we disclosed that some of them were much more perfect than the others. In this work we have concentrated on another slice of such a grain of the Al-Pd-Mn alloy. Similarly, we have performed an extensive Synchrotron X-ray Topographic investigation of strain and defects in this grain, combined with Phase Contrast Radiography and High Resolution X-ray Diffraction examinations. Very few two-lobes contrasts associated to pores and no loop-shaped contrasts were observed on X-ray topographs, this time, but straight line segments and band contrasts have been identified. Line segments could be considered as the result of the climbing of polygonal dislocation loops as those observed, by TEM, by Caillard et al.. This would indicate that most of strains and defects observed in quasicrystal grains, at room temperature, are the result of stresses (external and internal) acting after growth

Development of a non destructive characterisation technique for the 3D investigation of micro-heterogeneous structural materials

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XTOP: high-resolution X-ray diffraction and imaging

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3D IMAGING USING COHERENT SYNCHROTRON RADIATION

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Nucleation Control and Rapid Growth of KDP Crystals in Stationary Conditions

International audienceThanks to an improved control of the nucleation, an original crystal growth method operating in stationary thermodynamic conditions has been developed. It allows rapid growth of crystals at constant temperature and supersaturation. As a case study, large KH2PO4 (KDP) crystals of high purity have been reproducibly obtained at constant temperatures and growth rates of 1 cm/day. Recorded X-ray diffraction topographs of as-grown crystals showed high crystal quality. This method opens the way for the rapid growth of high quality crystals for homogeneous intermediate compositions of solid solutions, doped crystals, and compounds exhibiting a weak solubility

Rocking Curve Imaging Investigation of the Long-Range Distortion Field between Parallel Dislocations with Opposite Burgers Vectors

International audienceWe observe a long-range distortion field between parallel dislocations with opposite Burgers vectors in a platelet-shaped single crystal of 4H-SiC with a low dislocation density (similar to 10(3) cm/cm(3)). This distortion field is in the mu radian range when the distance D between dislocations is in the similar to 50-250 mu m range. We were able to characterise this weak distortion field through Rocking Curve Imaging (RCI), a highly sensitive Bragg diffraction imaging technique using monochromatic synchrotron radiation. From the experimental images, we generate maps of the angle of maximum reflectance (peak position ) that provide a measurement of the local lattice orientation. Deviations from the crystal matrix orientation are associated with the long-range distortion field around dislocations. Between parallel dislocations with opposite Burgers vectors, this distortion does not decay to zero but towards a constant value alpha. We propose a simple model considering the angular parameter alpha characterising the distortion. This model indicates that alpha should roughly vary as 1/D. This appears to be in fair agreement with our experimental data

Investigation of grain boundary grooves at the solid–liquid interface during directional solidification of multi-crystalline silicon: in situ characterization by X-ray imaging

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Perspectives in three-dimensional analysis of bone samples using synchrotron radiation microtomography

International audienceIn this paper we present a methodology based on 3D synchrotron radiation microtomography to analyze non-destructively 3D bone samples. After a technical presentation of the imaging system and the image analysis techniques, we report results on three-dimensional analysis of vertebral samples from women of different ages. The new capabilities of this technique for the investigation of bone are discussed. They include a high spatial resolution down to the micron level, a high density resolution allowing a local quantification of bone mineralization, phase contrast imaging and advances in 3D image analysis