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Three-dimensional X-ray diffraction was applied to characterize the strain/stress evolution in individual grains of an Al–0.3 wt% Mn polycrystal deformedin situat a synchrotron source. Methodological aspects concerning the calibration of the geometrical setup and the evaluation of the strain/stress tensors are discussed. A two-step calibration method separately treating the detector and the rotation axis allows one to determine the centre-of-mass position and crystallographic orientation of grains with standard errors of about 1.5 µm and 0.02°, respectively. Numerical simulations indicate that the error of normal strain components (about 1 × 10−4) is mainly caused by calibration errors, while the error of shear components (about 0.5 × 10−4) is largely influenced by counting statistics and random spot-centre errors due to detector distortion. The importance of monitoring the beam energy is emphasized.

cited By 0; International audience; Damage evolution during tensile straining of an AlSi12Ni alloy has been analyzed in situ at synchrotron source using microtomography and in the scanning electron microscope by surface imaging. It is shown that damage development in the analyzed alloy presenting an interconnected network of intermetallic phases is completely different from damage progression previously observed in materials with disperse distribution of particles. In the present material, which is typical for most eutectic structures, damage is dominated by the rupture of the brittle intermetallic phase while void growth is limited by a shielding effect of the intermetallic particles encasing the void. Primary voids exhibit a size close to the thickness of branches of the intermetallic phase. Final failure occurs by void coalescence, but without the formation of secondary voids. Damage analysis from tomographic scans was only possible by applying 3D image correlation to successive reconstructions, which thanks to its sub-voxel resolution, could satisfactorily detect the volume fraction of small-voids inaccessible by conventional thresholding. The presence of many small voids issued from the breakage of the intermetallic phase also was confirmed by scanning electron microscopy imaging performed at higher resolution. © 2019 Acta Materialia Inc.

The homogenous redistribution of nanosized TiB2 particles in a fine-grained in-situ AA6063/TiB2 composite has been achieved by friction stir processing (FSP). The effects of TiB2 particles on as-deformed structure in the nugget zone and its thermal stability after additional T6 heat treatment are quantitatively evaluated by using neutron diffraction, scanning electron microscopy associated with electron backscatter diffraction and synchrotron X-ray line profile analysis. The results are compared to those obtained from a FSPed AA6063 alloy and, show first that, average grain size of the FSPed AA6063/TiB2 composite is smaller than that of the FSPed AA6063 alloy, while grain size distribution is more uniform. Second, dislocation density estimated in the FSPed AA6063/TiB2 composite is higher than that in the FSPed AA6063 alloy. Third, a small number of grains are dynamically recrystallized in the FSPed AA6063/TiB2 composite compared to its alloy counterpart, which indicates that recrystallization and grain growth during FSP and T6 heat treatment are effectively inhibited by the presence of nanosized TiB2 particles. Keywords: Metal-matrix composites (MMCs), X-ray diffraction (XRD), Transmission electron microscopy (TEM), Neutron diffraction, Friction stir processing

It is shown that high-energy X-ray diffraction allows a fast and accurate texture and microstructure analysis of crystals, which can help to set up optimal industrial procedures for materials manufacturing. This paper presents the experimental and theoretical aspects of quantitative texture analysis using high-energy synchrotron beams. Intensity corrections are less important in this approach than in classical laboratory methods; however, the most important correction, related to the Lorentz factor, can introduce relative fraction changes of up to about 40% compared to the uncorrected case. The resolution of the orientation density function also influences the results. For example, the usual 5° resolution leads to relative deviations of up to 30% in the fraction of some components. The method allowed detection of small changes taking place during the recovery and continuous recrystallization of a cold-rolled Al–TiB2 nanocomposite. Texture information was combined with the results of line profile analysis, evidencing the evolution of the average dislocation density and coherent domain size of the selected grain families. It was found that recovery, as described in terms of dislocation annihilation and coherent domain coarsening, takes place at similar rates in all components.

International audience; Inkjet printing has a high potential for cost reduction in solar cell and thermoelectric industry. This study demonstrates that silicon thin films can be produced by inkjet-printing of silicon nanoparticles followed by subsequent drying and annealing steps. Ink formulation is crucial for the sintering of the silicon nanoparticles and control of the microstructure at low temperature. Upon heating, the microstructure is modified from porous layer made of juxtaposed silicon nanoparticles to denser layer with coarser grains. This evolution is monitored by scanning electron microscopy and by micro-Raman spectroscopy, which offer a fast and precise characterization of the microstructure and chemical composition of thin films. Above a threshold temperature of 800 degrees C cracks appear within thin film and substrate because of the stress induced by the oxidation of the surface. An innovative sintering method, photonic annealing, is studied in order to reduce both oxidation and stress in the thin films as well as reducing processing time. Evolution of the thermal conductivity is performed by micro-Raman spectroscopy and can be tailored in a large range between similar to 1 and similar to 100 W.m(-1).K-1 depending on the sintering method and atmosphere. Therefore control of the microstructure evolution with applied annealing process allows tailoring of both microstructure and thermal conductivity of the silicon thin films. (C) 2014 Elsevier B.V. All rights reserved.

International audience; Microstructural modifications and mechanical properties of samples manufactured from conventional and nanocomposite WC/Co12 powders by means of Selective laser melting (SLM) are compared after processing with the same parameter set. Studying their homogeneity reveals that in both samples coarse and fine carbides segregate in the molten pool. X-ray diffraction (XRD) analysis shows significant changes in the microstructure and crystalline phases present in the WC/Co mixture and after SLM. Thermal decomposition of WC leads to the formation of W2C dicarbides and the appearance of the complex Co-W-C ternary phase. No residual pure cobalt after SLM was detected in the samples. The Williamson-Hall method allows determining coherent WC domain sizes of conventional and nanostructured powders (56 +/- 6nm and 10 +/- 3nm, respectively) and microstrains (approximate to 0 for both) as well as their modifications after SLM processing (180 +/- 50nm and 210(-3)+/- 410(-4) for the nanophased sample, and 330 +/- 100nm and 210(-3)+/- 410(-4) for the conventional one, respectively). The microhardness of the part produced from the nanophased powder is slightly increased in both the coarse (approximate to 1496 HV0.3) and fine (approximate to 1542 HV0.3) carbide segregation regions compared to the sample obtained from the conventional powder (1384 HV0.3 and 1515 HV0.3 for coarse and fine regions, respectively).

Based on the cross correlation analysis of the Kikuchi diffraction patterns high-resolution EBSD is a well established method to determine the internal stress in deformed crystalline materials. In many cases, however, the stress values obtained at the different scanning points have a large (in the order of GPa) scatter. As it was first demonstrated by Wilkinson and co-workers this is due to the long tail of the probability distribution of the internal stress ($P(\sigma)$) generated by the dislocations present in the system. According to the theoretical investigations of Groma and co-workers the tail of $P(\sigma)$ is inverse cubic with prefactor proportional to the total dislocation density $$. In this paper we present a direct comparison of the X-ray line broadening and $P(\sigma)$ obtained by EBSD on deformed Cu single crystals. It is shown that $$ can be determined from $P(\sigma)$. This opens new perspectives for the application of EBSD in determining mesoscale parameters in a heterogeneous sample., Comment: 5 pages, 6 figures

The calibration of high-energy X-ray diffraction setups using an area detector and a rotation axis is discussed. The characterization of the tilt and spatial distortions of an area detector was discussed in part one of this series [Borbély, Renversade, Kenesei & Wright (2014).J. Appl. Cryst.47, 1042–1053]. Part II links the detector frame to the laboratory frame comprising an additional rotation axis and introduces a general diffractometer equation accounting for all sources of misalignment. Additionally, an independent high-accuracy method for the evaluation of the crystallographic orientation and cell parameters of the undeformed reference crystal is presented. Setup misalignments are mainly described in terms of a residual strain tensor, considered as a quality label of the diffractometer. The method is exemplified using data sets acquired at beamlines ID11 (European Synchrotron Radiation Facility) and 1-ID (Advanced Photon Source) on Al and W single crystals, respectively. The results show that the residual strain tensor is mainly determined by the detector spatial distortion, and values as small as 1–2 × 10−4can be practically achieved.

International audience; The three-dimensional granular and damage structure of two creep deformed copper specimens has been reconstructed using an improved serial sectioning method combining optical profilometry, scanning electron imaging and backscatter electron diffraction. The reconstructions permitted associating creep voids to grain boundaries and evaluating the damage probability of each grain boundary type. The results indicate that creep damage of oxygen free high conductivity copper is governed by topological factors. Quadruple/grain boundaries have the highest probability of damage followed by two-and three-grain boundaries with decreasing percentages. The damage probability of quadruple and three-grain boundaries increases with decreasing stress due to a larger contribution of grain boundary sliding to void nucleation. The relative frequency of damaged two-grain boundaries increases with stress, suggesting a significant role of creep plasticity and the associated grain boundary ledges. No correlation between void location and the crystallographic orientation of neighbour grains was found.

International audience; Quick scanning X-ray microscopy combined with three-dimensional reciprocal space mapping was applied to characterize intragranular orientation and strain in a single grain of uniaxially deformed Al polycrystal. The strain component perpendicular to the direction of the applied tensile load was found to be very heterogeneous with high compressive and tensile values in the grain interior and near two grain boundaries, respectively. The distribution of the magnitude of diffraction vectors indicates that dislocations are the origin of the strain. The work opens new possibilities for analysing dislocation structures and intragranular residual stress/strain in single grains of polycrystalline materials.

The grain structure of a slightly deformed Al–0.3 wt%Mn alloy was reconstructed using diffraction contrast tomography (DCT) and high-energy diffraction microscopy (HEDM). The direct comparison shows that DCT can detect subgrain boundaries with disorientations as low as 1° and that HEDM and DCT grain boundaries are on average 4 µm apart from each other., The grain structure of an Al–0.3 wt%Mn alloy deformed to 1% strain was reconstructed using diffraction contrast tomography (DCT) and high-energy diffraction microscopy (HEDM). 14 equally spaced HEDM layers were acquired and their exact location within the DCT volume was determined using a generic algorithm minimizing a function of the local disorientations between the two data sets. The microstructures were then compared in terms of the mean crystal orientations and shapes of the grains. The comparison shows that DCT can detect subgrain boundaries with disorientations as low as 1° and that HEDM and DCT grain boundaries are on average 4 µm apart from each other. The results are important for studies targeting the determination of grain volume. For the case of a polycrystal with an average grain size of about 100 µm, a relative deviation of about ≤10% was found between the two techniques.

International audience; Damage development during tensile straining of a cast AlSi12Ni alloy has been characterized by in situ SEM imaging and synchrotron X-ray microtomography. Two main damage mechanisms consisting of intermetallic particle rupture and decohesion of Al-Si interfaces were revealed. Particle rupture takes place already from the beginning of the deformation, while decohesion of Al-Si interfaces is more characteristic at later stages. It is shown that damage evolution in the alloy is closely related to the underlying geometry of the intermetallic phase, its clustered structure playing a double role in controlling strain localization in the matrix as well as the rupture sequence of the intermetallic phase itself. The latter shows that small clusters break-off from the complex intermetallic network before large clusters, in good agreement with their load carrying capacity determined by the local volume fraction of the intermetallic phase. Finite element modeling of the alloy's tensile behavior evidences that deformation bands formed in the alloy with complex structure are similar to those developed in a model particle reinforced metal-matrix composite, where the particles correspond to the clustered regions of the intermetallic phase. (C) 2016 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Accurate strain/stress characterization has important implications in practice, where it is typically connected with safe operation of engineering components. Improving the accuracy and spatial resolution of the measurement techniques can be therefore very beneficial for materials science by helping the understanding of complex material behaviour and the development of novel materials with improved properties. Strain measurement by diffraction methods is based on Bragg’s law, which in the case of a strained crystal predicts a shift of the diffraction peaks compared to their position measured on a reference state. Classically, this shift is determined as the difference between the corresponding absolute peak positions, which requires in many cases accurate knowledge of (i) the geometrical setup and its stability, (ii) the calibration sample, and (iii) a well matching mathematical model of the intensity distribution. In view of this large number of parameters it is intriguing to ask what the accuracy of today’s X-ray diffraction (XRD) methods is and which are the possible ways of improvement. Limiting our survey to methods able to determine the strain tensor at micrometre scale, one can rapidly find that the error of most strain tensor components is about a few times 10 . Transformed to stress (using Young’s modulus of 100 GPa) this represents an uncertainty of tens of MPa, which might be too large for the study of certain phenomena, such as for example the plastic yield of metals. Therefore, efforts are continuously undertaken to ameliorate the precision of the evaluation methods. The majority of the solutions, however, concern point (i), suggesting the use of large area detectors with many pixels and without distortion, or fixing instabilities of the wavelength or micro-spot position by applying more stable optical elements. Progress in this case depends on technical advancement, which sometimes might be slow compared to the needs of the scientific community. Increasing strain/stress accuracy when working with conventional setups needs, therefore, a paradigm change, i.e. a method different from the classical approach based on absolute peak positions. Two recently published articles by Petit et al. (2015) and Zhang et al. (2015) break the tradition and introduce evaluation schemes based on the shift of diffraction peaks determined by digital image correlation (DIC). This new idea, which plays a central role in experimental mechanics, is applied in both papers to white-beam Laue microdiffraction, a popular method often analysed in terms of error sources impeding accurate determination of the deviatoric strain tensor (Hofmann et al., 2011; Poshadel et al., 2012). As argued by Petit et al. (2015), the gain in accuracy of the Laue-DIC method is related to two factors: (a) the smaller uncertainty of the peak shift determined by DIC and (b) the higher sensitivity of the merit function expressing peak positions as a function of reference cell parameters, compared to the sensitivity of the gradient of the merit function, the latter appearing in the formulation of Laue-DIC. From the point of view of the error sources highlighted above it becomes clear that the new approach eliminates the uncertainties related to the choice of an adequate mathematical model describing the experimental intensity distribution. The authors emphasize that relatively good fits can be obtained for the spots of the non-deformed reference specimen using Gaussian or Pearson VII profiles, but already as the specimen is strained, peak quality deteriorates and the uncertainty in peak position increases above 0.1 pixel, characteristic for the reference peaks. Compared to this the uncertainty of DIC is one order of magnitude ISSN 1600-5767

International audience; Synchrotron microtomography was used for in-situ characterization of high-temperature creep damage in leaded brass. Applying image registration to subsequent tomographic reconstructions, the volumetric growth rate of single cavities with equivalent radii between 2 and 4.3 mu m was assessed. We conclude from the volume dependence of the growth rates that both the viscous flow and grain boundary (GB) diffusion mechanisms influence void growth. We show that void growth in leaded brass is retarded by negative stress triaxiality, which develops in the matrix during heating the specimen to the deformation temperature.

International audience; A new evaluation procedure is presented to characterize the orientation and position of single grains within the bulk of a polycrystalline sample. Considering the symmetry properties of Friedel-pairs the contributions to reflection spot positions arising from grain orientation and position could be clearly separated. The proposed method avoids simultaneous fitting of all grain parameters with the goal of a higher accuracy. Depending on the number of reflections considered the accuracy of grain orientation may be less than 0.1 degrees, and the position of the center of mass of the grains can be accurate within one-third of the pixel size.

International audience; Synchrotron X-ray diffraction and transmission electron microscopy (TEM) were applied to quantitatively characterize the average particle size and size distribution of free-standing TiB2 particles and TiB2 particles in an in-situ grown Al-TiB2 composite. The detailed evaluations were carried out by X-ray line profile analysis using the restricted moment method and multiple whole profile fitting procedure (MWP). Both numerical methods indicate that the formed TiB2 particles are well crystallized and free of crystal defects. The average particle size determined from different Bragg reflections by the restricted moment method ranges between 25 and 55 nm, where the smallest particle size is determined using the 110 reflection suggesting the highest lateral-growth velocity of (110) facets. The MWP method has shown that the in-situ grown TiB2 particles have a very low dislocation density (similar to 10(11) m(-2)) and their size distribution can be described by a log-normal distribution. Good agreement was found between the results obtained from the restricted moment and MWP methods, which was further confirmed by TEM. (C) 2015 Elsevier Inc. All rights reserved.

Colloidal suspensions of nanoparticles are increasingly employed in the fabrication process of electronic devices using inkjet-printing technology and a consecutive thermal treatment. The evolution of internal stresses during the conversion of silver nanoparticle-based ink into a metallic thin-film by a thermal sintering process has been investigated by in-situ XRD using the sin2ψ method. Despite the CTE mismatch at the film/substrate interface, the residual stress in silver films (below 70 MPa) remains lower than in conventional PVD thin-films, as a result of the remaining porosity. A Warren-Averbach analysis further showed that the crystallite growth is associated with a minimization of the twin fault density and the elastic microstrain energy above 150°C. A stabilization of the microstructure and internal stress is observed above 300°C. Inkjetprinting technology thus appears as a good alternative to conventional metallization techniques and offers significant opportunities asset for interconnect and electronic packaging. cop. (2014) Trans Tech Publications, Switzerland. 'Conseil General de l'Aube'; Conseil National de la Recherche Scientifique (CNRS); et al; Grand Troyes; Proto Manufacturing; Region Champagne-Ardenne

Two flat hollow cylinders made of martensitic 9 wt.% Cr steels were creep deformed under in-service conditions typical of steam pipes at fossil-fuel fired power plants. Damage in the tubes was assessed through synchrotron X-ray microtomography by evaluating the shape, size and spatial-distribution of voids. The analysis of the size distribution of non-coalesced voids suggested that void growth is controlled by the plasticity constrained diffusional mechanism, a hypothesis verified by micromechanical simulations. A much higher void density was found in steel grade P91 compared to E911.

The geometry of high-energy X-ray diffraction setups using an area detector and a rotation axis is analysed. The present paper (part 1) describes the methodology for determining continuously varying spatial distortions and tilt of the area detector based on the reference diffraction rings of a certified powder. Analytical expressions describing the degeneration of Debye rings into ellipses are presented and a robust calibration procedure is introduced. It is emphasized that accurate detector calibration requires the introduction of spatial distortion into the equation describing the tilt. The method is applied to data sets measured at the Advanced Photon Source and at the European Synchrotron Radiation Facility using detectors with different physical characteristics, the GE 41RT flat-panel and the FReLoN4M detector, respectively. The spatial distortion of the detectors is compared with regard to their use in structural and strain tensor analysis, a subject treated in part 2 of the calibration work [Borbély, Renversade & Kenesei (2014).J. Appl. Cryst.Submitted].

International audience; It was documented by Derby in 1992 that the flow stress is in power-law relationship with the steady-state grain size obtained in dynamic recrystallization. This relation has been found valid in this paper also for ultrafine-grained metals that can be obtained by severe plastic deformation. For these materials, the exponent is -0.5, which is the Hall-Petch relation. In copper, a uniform dislocation density without geometrically necessary dislocations is valid for this state. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

International audience

Damage localization during power law creep of copper has been investigated in situ with synchrotron X-ray microtomography. The analysis of the area fraction of cavities corresponding to a given material slice has revealed that damage localization begins relatively early at half of the creep lifetime. The amplitude of the maximum fluctuation shows parabolic behavior as a function of mean void volume fraction. Existing models of damage evolution underpredict the amount of real damage and overpredict power-law creep life-time.

International audience; Two complementary techniques. X-ray diffraction and transmission electron microscopy, were used to analyze the size and size distribution of apatite crystallites in subfossil mammal and fossil sauropod dinosaur bones. The transmission electron microscope (TEM) samples were prepared by Focused Ion Beam (FIB). X-ray diffraction indicates that crystals in sauropod bones are larger than in subfossil mammal bones. For sauropods the average crystallite size (both in length and width) does not seem to increase with bone length. A similar result was obtained from TEM investigations regarding crystallites aspect ratio (length/width). The distribution of crystallite sizes in a juvenile sauropod was found to be much wider compared to an adult bone originating from the same bed and locality, consistent with the hypothesis that young animal bone contains a mixture of crystallite sizes, with a beneficial effect on mechanical properties. Diagenesis effects on crystal size dimensions have been considered. (C) 2011 Elsevier B.V. All rights reserved.

International audience; Application of in-situ microtomography to characterization of power law creep and creep damage in structural materials is presented. It is shown first that the successively reconstructed volumes are adequately monitoring the macroscopic sample shape and that microtomography is an optimal tool to characterize inhomogeneous specimen deformation. Based on a two-step image correlation technique the evolution of single voids is revealed and the basis of a pioneering approach to creep damage studies is presented. The method allows the unequivocal separation of three concurrent damage mechanisms: nucleation, growth, and coalescence of voids. The results indicate that growth rate of voids with equivalent diameters in the range of 2-5 mm is of about one order of magnitude higher than the prediction of continuum solid mechanics. Analysis of void coalescence points out the presence of two stable growth regimes related to coalescence between primary and secondary voids, respectively.

International audience; Growth of grain boundary voids during high-temperature power-law creep of metals is usually approximated as the growth of a hole in a nonlinearly viscous solid. Using synchrotron tomography, we show that the functional form of the continuum law is valid but that the real growth rates in copper are higher than the prediction of the viscous model by a factor of about 40. Submicrometer resolution tomography showing faceted void shapes as well as the large scatter of individual growth rates suggest that local dislocation glide has significative contribution to void growth.

Development of synchrotron tomography at the end of the 20th century and the following improvements in radiation source, X-ray detectors as well as X-ray optics boosted the application of the tomographic technique in materials science. It became possible for the first time to reveal the three dimensional structure of heterogeneous materials with sub-micrometer spatial resolution, the length scale where the basic mechanisms of plastic deformation and damage are taking place and determine the macroscopic behavior of engineering components. The present chapter introduces the basic features of the tomographic method developed at synchrotron sources, related mainly to the high flux and lateral coherence of the beam. These allow performing high resolution tomographic scans within a reasonable time, but also to use the optical phase of the transmitted X-ray beam to increase the sensitivity by revealing the spatial distribution of electron density. After the introduction of the technique several application examples in the field of materials science are presented.

International audience; Damage distribution in a notched hollow cylinder made of E911 steel and crept for 26,000 h at 575 °C under multi-axial stress state is assessed. Based on high-resolution tomographic reconstructions the size, shape and spatial distribution of voids along the notch radius have been characterized. The spatial distribution of void density shows strong correlation with stress triaxiality, maximum principal stress and the equivalent von Mises stress. The analysis of the size distribution of non-coalesced voids in terms of general power-law functions describing nucleation and growth indicates that void growth in E911 steel is dominated by the constrained diffusion mechanism.

International audience; A new method for the evaluation of the apparent activation energy of steady-state creep in metals is presented. It is based on in situ monitoring by microtomography the geometry of a specimen subjected to uniaxial load and inhomogeneous temperature distribution. It is shown that microtomography acting as a three dimensional extensometer enables the evaluation of local strain-rates of small material volumes and is an adequate tool for characterization of inhomogeneously deforming specimens. Activation energies obtained with the new method for stainless steel agree within an error of 5% with values obtained according to the classical procedure.

International audience; X-ray and electron backscatter diffraction (EBSD) have been applied to investigate misorientation distributions in copper single crystals plastically deformed in single and multiple slip. The misorientation distributions are represented by 'rocking curves' about specific rotation axes. Very good agreement for the rocking curves established by the two methods was obtained, despite the large difference between their resolution depths. Following this agreement, a new rotation axis imaging scheme, based on the EBSD data, is proposed in order to visualize the crystallite blocks and characterize the nature of their dislocation boundaries.

International audience; Single copper crystals of the stable Goss orientation {011} were deformed in plane strain compression and the deformation-induced dislocation structures were investigated by high-resolution electron backscattered diffraction. Although the orientation maps exhibited an anisotropic dislocation boundary structure it was shown that the mean disorientation angle between point pairs saturated and became isotropic if their spacing was large enough (typically >30 μm). This saturation behaviour was interpreted as being a consequence of the anti-correlations between nearby dislocation boundaries and is discussed in terms of recent stochastic models of boundary formation. It was found that the disorientation boundaries, which were considered as being formed at relatively low strains, underwent rigid body-like rotations during deformation.

The latest virtual special issue of Journal of Applied Crystallography includes some highlights of the 12th Conference on High-Resolution X-ray Diffraction and Imaging (XTOP). This biennial conference was held in Villard-de-Lans and Grenoble in September 2014, and was organized by the ESRF, Universite Grenoble-Alpes, the CEA and CNRS. A refresher school for PhD students and postdoctoral scientists took place on the first day, with lectures on new diffraction and imaging techniques. The first XTOP conference (‘X-ray Topography and High Resolution Diffraction’) took place in Marseille in 1992. The original topics covered were diffraction topography, double- and triple-crystal diffractometry of epitaxial layers, reflectometry, and the standing wave technique. Many experimental techniques have been added since, which cover today a wide range to reflect the scientific evolution of the XTOP community: coherent imaging, X-ray phase contrast imaging (radiography and microtomography), microdiffraction (monochromatic and Laue), grazing incidence and resonant diffraction, fast (time-resolved) tomography etc. The topics covered now include both synchrotron and laboratory instrumentation, including industrial developments. The materials studied include single crystals and multilayers, nanostructures (metals, oxides, semiconductors), and organic, biological and other natural (sea shells, fossils etc.) samples. A few presentations in 2014 covered advances in the theory of high-resolution X-ray diffraction, and with the occasion of the International Year of Crystallography, Andre Authier gave a presentation on the Early Days of X-ray Diffraction and the Birth of the Dynamical Theory. Among the topics presented during the XTOP conference, the most noteworthy included the development of high temporal and spatial resolution for diffraction and imaging, the use of X-ray coherent beams (including ptychography and X-ray free electron lasers), and applications to nanostructured materials. Following the traditional publication policy of the XTOP conferences, the articles presented in this issue are not selected proceedings but rather original research articles, which were first presented at the XTOP conference. These include laboratory and synchrotron studies of semiconductors, software for fast data analysis or instrumental function simulation, micro-Laue analysis of oxide fuel cells and bent nanowires, microtomography of bone structure, X-ray phase contrast imaging of bacterial endospores, and Bragg imaging of ice under applied stress. Over 200 participants attended the five-day conference, which included six tutorial lectures, 13 invited and 44 contributed presentations, and 144 posters.

The deformation mechanisms during indentation of aluminum-based metal foams are examined by use of X-ray tomography and the finite element method. The deformation was found to be almost totally restricted to a spherical cap-shape compacted zone under the indenter. An analytical expression is given which describes the changes in the size of the compacted zone as a function of the diameter of the indenter, the indentation depth and the relative density of the foam. Results of finite element simulations and the calculated function were found to be in reasonably good agreement.