An investigation by EXAFS of local atomic structure in an Mg-Nd alloy after processing by high-pressure torsion and ageing.

The local atomic structure of an Mg-1.44Nd (wt.%) alloy was investigated after solution annealing, high-pressure torsion (HPT) processing up to 1 and 10 turns and ageing at 250 °C for 5 h using X-ray absorption fine structure (XAFS) measurements at the Nd LIII-edge. The results show that HPT processing has no effect on the atomic structure around Nd atoms compared to the unprocessed state, whereas ageing at 250 °C for 5 h induces a significant modification in the coordination number and interatomic distances around the Nd atoms. These variations are analyzed based on the correlations between precipitation, defects and atomic mobility of the chemical species

Simultaneous DAFS and XAFS analyses to evidence the Y- and Ti-species in nano-structured ODS steels

International audienceTo characterize the microstructure of neutron irradiated materials, various experimental tools are available at the present time in nuclear environment:SEM, TEM, APT, RBS and NRA… However, these techniques are local probes and bring information for an extremely limited sample volume which could be not representative of the whole volume. Therefore, a good statistic can only be obtained by performing many examinations which are very time consuming

An X-ray absorption spectroscopy investigation of the local atomic structure in Cu–Ni–Si alloy after severe plastic deformation and ageing

The local atomic structure of Cu–Ni–Si alloy after severe plastic deformation (SPD) processing and the decomposition of supersaturated solid solution upon annealing were investigated by means of X-ray absorption spectroscopy. The coordination number and interatomic distances were obtained by analyzing experimental extend X-ray absorption fine structure data collected at the Ni K-edge. Results indicate that the environment of Ni atoms in Cu–Ni–Si alloy is strongly influenced by the deformation process. Moreover, ageing at 973 K affects strongly the atomic structure around the Ni atoms in Cu–Ni–Si deformed by equal channel angular pressing and high pressure torsion. This influence is discussed in terms of changes and decomposition features of the Cu–Ni–Si solid solution

Structure of liquid oxides at very high temperatures

International audienc

X-ray diffraction and stress relaxations to study thermal and stress-assisted annealings in nanocrystalline gold thin films

International audienceThe dependence on thermal history of the plasticity mechanisms occurring in nanocrystalline gold thin films is evidenced thanks to relaxation tests combined with in-situ synchrotron X-ray diffraction. The two techniques complement one another. The activation parameters show that the films deform mainly by dislocations and give indications about their mean free paths, whereas the Bragg peak positions, widths and areas bring invaluable information on residual stress as well as on some plasticity properties, like dislocation storage inside the grains or grain rotations. For the demonstration, two sputter-deposited nanocrystalline 50 nm-thin films deposited onto stretchable substrates are studied. It is shown that an as-grown sample (at a homologous temperature of 0.22) presents a stress-assisted annealing, thus decreasing its initial defect density, whereas if a thermal annealing (3 h at [Math Processing Error], corresponding to a homologous temperature of 0.35) has been applied to the sample before the tensile test, it deforms by conventional plasticity, and the dislocations are not stored inside the grains. These mechanisms lead to different work-hardening properties. This work shows how a moderate annealing can have a profound influence on the mechanical behaviour of these thin films

Étude morphologique d'agrégats inclus dans des couches minces superficielles par diffusion centrale des rayons X en incidence rasante

Parmi les techniques d'analyse de surface et plus particulièrement celles faisant intervenir les rayons X, la plus récente est la diffusion centrale des rayons X en incidence rasante (GISAXS). Cette nouvelle technique non destructive, conduite auprès d'une source de rayonnement synchrotron, permet de caractériser morphologiquement des agrégats déposés sur un substrat plan ou contenus dans une couche superficielle. A l'aide de détecteurs bidimensionnels de type Imaging Plate, il est possible d'étudier la forme, la taille ainsi que la répartition spatiale des agrégats. Nous nous intéressons d'abord au cas des systèmes immiscibles carbone-métal : la technique GISAXS permet de mettre en évidence la forme allongée des agrégats métalliques inclus dans une matrice de carbone. Puis nous donnons les résultats obtenus dans le cas de multicouches granulaires (agrégats magnétiques de cobalt inclus dans une matrice d'alumine) qui montrent une structure tout à fait particulière et très ordonnée des multicouches avec un ordre à l'intérieur de chaque couche mais également de couche à couche.Among surface analysis techniques and specially those using X-rays, the most recent is the grazing incidence small-angle X-ray scattering (GISAXS). Full potentialities of this non-destructive technique are obtained when using a synchrotron source and when patterns are recorded with Imaging Plates. It is then possible to study the shape, the size and the spatial distribution of aggregates deposited on a flat substrate or embedded in a thin layer. We show the case of some carbon-metal layers when the solubility of carbon in the metal is weak. GISAXS patterns show that metallic aggregates embedded in a carbon matrix are elongated along the growth direction of the thin film. Results obtained with granular multilayers (magnetic cobalt aggregates in an alumina matrix) are also given. In this second case, it is shown that a spatial order exists not only in every layer, but also between the successive layers. It allows to show the particular and well-ordered structure of those multilayers

Synchrotron x-ray diffraction and Raman scattering investigations of ( Li x Na 1 − x ) NbO 3 solid solutions: Evidence of the rhombohedral phase

International audienc