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Two X-ray methods are applied to estimate the strain energy of crystals containing dislocations, a simpler method based on the full width at half-maximum (FWHM) of the diffraction peaks, and asymptotic line profile analysis (LPA), which exploits the functional form of the Fourier transform corresponding to small Fourier parameters. It is shown analytically that, in the single-defect approximation, the modified Williamson–Hall (mWH) plot of the FWHMs is linear and the slope of the line is directly related to the strain energy of the dislocation system. Evaluation of the numerically generated peaks for randomly arranged edge dislocation dipoles shows that the method based on the mWH plot gives accurate strain energy, while asymptotic LPA overestimates it by about 50%. The accurate result given by the mWH plot is explained by the long correlation distance associated with the FWHM, which better captures the dislocation arrangement over large distances. By contrast, asymptotic LPA is related to atomic correlations over distances smaller than the mean dislocation–dislocation spacing, where the displacement gradient is mainly determined by the field of single dislocations. Therefore, asymptotic LPA leads to a very accurate dislocation density (with error less than 1%) and the result is independent of the dislocation arrangement. However, these short-range correlations overestimate the outer cut-off radius by one order of magnitude.

Constitutive laws underlie most physical processes in nature. However, learning such equations in heterogeneous solids (e.g., due to phase separation) is challenging. One such relationship is between composition and eigenstrain, which governs the chemo-mechanical expansion in solids. In this work, we developed a generalizable, physically-constrained image-learning framework to algorithmically learn the chemo-mechanical constitutive law at the nanoscale from correlative four-dimensional scanning transmission electron microscopy and X-ray spectro-ptychography images. We demonstrated this approach on Li$_X$FePO$_4$, a technologically-relevant battery positive electrode material. We uncovered the functional form of composition-eigenstrain relation in this two-phase binary solid across the entire composition range (0 $\leq$ X $\leq$ 1), including inside the thermodynamically-unstable miscibility gap. The learned relation directly validates Vegard's law of linear response at the nanoscale. Our physics-constrained data-driven approach directly visualizes the residual strain field (by removing the compositional and coherency strain), which is otherwise impossible to quantify. Heterogeneities in the residual strain arise from misfit dislocations and were independently verified by X-ray diffraction line profile analysis. Our work provides the means to simultaneously quantify chemical expansion, coherency strain and dislocations in battery electrodes, which has implications on rate capabilities and lifetime. Broadly, this work also highlights the potential of integrating correlative microscopy and image learning for extracting material properties and physics.

The well-known mechanisms of interaction between precipitates and dislocations are shearing (for shearable precipitates) and bypassing mechanisms (for nonshearable precipitates). The transition from shearable to nonshearable precipitates in precipitation hardening alloys leads to changes of dislocation motion mode and dislocation multiplication behavior, which inevitably causes different PLC behaviors. In this study, we systematically investigate the influence of shearable and nonshearable Al3(Sc, Zr) precipitates on PLC behaviors by experimental characterization for precipitation hardening AlMgScZr alloys. We analyze the onset strain, critical strain-rate range, serration amplitude, and propagation behavior of PLC bands in detail for AlMgScZr alloys with shearable and nonshearable precipitates, respectively. We find that the transition from shearable to nonshearable precipitates changes the PLC band propagation behavior, decreases the magnitude of serration amplitude, expands the strain-rate range as well as decreases the critical strain rate between normal behavior (the critical strain increases with the increase of strain rate) and inverse behavior (the critical strain decreases with the increase of strain rate) regimes due to the different dislocation-precipitate interactions. Besides, the transition from shearable to nonshearable precipitates increases the onset strain at normal behavior while decreases the onset strain at inverse behavior depending on the different roles of precipitates in the solute-dislocation interaction. Finally, we reveal the nature of influence of different dislocation-precipitate interactions on PLC behavior considering different strengthening mechanisms based on quantitative characterization on precipitates and dislocation density.

Constitutive laws underlie most physical processes in nature. However, learning such equations in heterogeneous solids (for example, due to phase separation) is challenging. One such relationship is between composition and eigenstrain, which governs the chemo-mechanical expansion in solids. Here we developed a generalizable, physically constrained image-learning framework to algorithmically learn the chemo-mechanical constitutive law at the nanoscale from correlative four-dimensional scanning transmission electron microscopy and X-ray spectro-ptychography images. We demonstrated this approach on Li

In the recent decades there is a growing interest in how public and private organisations can develop abilities to innovate in order to cope with the challenges created by the changing priorities of the political market, the intensification of global competition and the higher speed of the technological changes. The ability of organisations to mobilize their internal resources into efficient and dynamic routines depends on intangible resources (e.g. creativity) and less on such traditional tangible factors as physical or financial sources. The core aim of the paper is to identify and compare the creative/learning capabilities of the workplaces in the EU–27 countries. The data of the European Working Conditions Surveys (2005, 2010 and 2015) shows that public administration boosts creative workplaces in all countries. The increasing rate of creative jobs may speed up the implementation of the “High-Engagement Civil Services”.

Objectives: The core aim of this paper is to improve our knowledge base on the innovation process comparing how public and private organisations can develop abilities to innovate in order to cope with the challenges created by the changing priorities of the political market, the intensification of global competition and the higher speed of the technological changes. The authors intend to identify and compare the creative/learning capabilities of the workplaces in the EU-27 countries. Research Design & Methods: In testing empirically the various types of jobs our analysis uses the data sets of the fourth (2005), fifth (2010) and sixth (2015) waves of the European Working Conditions Survey (EWCS). The EWCS is a crosssectional survey taken in every five years since 1990, organised by the European Foundation for the Improvement of Living and Working Conditions (Eurofound, Dublin). The recent editions of this survey cover more than 40,000 workers in the EU member states and in various other European countries (Eurofound, 2017). We used a cluster analysis in order to identify three clusters of jobs in Europe and their prevalence in different countries and country groups. Findings: The data from the European Working Condition Surveys (2005, 2010 and 2015) shows that in the public administration boosts creative workplaces in all countries. The ability of organisations to mobilise their internal resources into efficient and dynamic routines depends on intangible resources (e.g. creativity) and less on such traditional tangible factors such as physical or financial sources. Powering public sector innovation is inhibited by the following major factors: unfavourable institutional settings; weak innovation leadership; lack of systematic knowledge of the innovation process; and a shortage of the systematic data collection at both the EU and Member State levels. Implications & Recommendations: The increasing rate of creative jobs may speed up the implementation of the “High-Engagement Civil Services” to improve both efficiency and quality of work in the public sector. A more profound and evidence-based understanding of the innovation processes at the workplace level would allow us to exploit the full potential thereof in terms of positive impacts on both employment and job quality. Contribution & Value Added: Despite the fact that innovation studies have been at the heart of socio-economic research for decades now, relatively little attention has been paid on innovation in the public sector. This research topic has gained more importance only in the 2010s and thus there is often a lack of empirical evidence for this sector, which plays a crucial role in all developed economies as a major employer as well as the main actor shaping the regulatory environment. This article is among the first attempts aimed at giving insights into the job characteristics of publicsector organisations.

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.

Precipitation hardening is the most effective strategy to enhance the mechanical properties of metals. Dislocation mechanisms to control strengthening during precipitation have been demonstrated extensively. However, owing to the complexity of different precipitates in alloys, variations in ductility caused by precipitation are very complex and have not been clarified so far. In this study, the effects of precipitation on ductility in precipitation hardening aluminium alloys are investigated based on a modified dislocation-based approach and experimental characterisation. The AlMgScZr alloy with spherical Al3(Sc, Zr) precipitates is used as a model alloy system to understand the effects of precipitation on ductility. Via heat treatment, shearable and non-shearable Al3(Sc, Zr) precipitates are introduced in the AlMg matrix. The results show that the ductility of AlMgScZr alloy decreases when shearable precipitates occur, while it increases during the shearable–non-shearable transition. The variation in ductility is mainly controlled by the dynamic recovery rate of the dislocations. This dislocation mechanism is supported by analysing the different precipitation–dislocation interactions and evaluating the dislocation density evolution during deformation. This study reveals the dislocation mechanism for controlling ductility during precipitation, which can provide a theoretical foundation for the design of high-performance structural materials.

International audience; Precipitation hardening is the most effective strategy to enhance the mechanical properties of metals. Dislocation mechanisms to control strengthening during precipitation have been demonstrated extensively. However, owing to the complexity of different precipitates in alloys, variations in ductility caused by precipitation are complex and have not been clarified so far. In this study, the effects of precipitation on ductility in precipitation hardening aluminium alloys are investigated based on a modified dislocation-based approach and experimental characterisation. The AlMgScZr alloy with spherical Al3(Sc, Zr) precipitates is used as a model alloy system to understand the effects of precipitation on ductility. Via heat treatment, shearable and nonshearable Al3(Sc, Zr) precipitates are introduced in the AlMg matrix. The results show that the ductility of AlMgScZr alloy decreases when shearable precipitates occur, while it increases with shearable precipitates being replaced by nonshearable precipitates. The variation in ductility of AlMgScZr alloy is mainly controlled by the dynamic recovery rate of the dislocations. Finally, by analysing the different precipitate-dislocation interactions and evaluating the dislocation density evolution during deformation, the dislocation mechanisms of 2 ductility during precipitation for AlMgScZr alloy are demonstrated. This study reveals the dislocation mechanism for controlling ductility during precipitation for AlMgScZr alloy which can provide a theoretical foundation for the design of high-performance structural materials.

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.

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.

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

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.

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.

Comparative studies of body mass, cortical bone geometry, and preferred crystallographic orientation (texture) of bone mineral in an ontogenetic series of the sauropod, Apatosaurus sp., and recent animals are reported. The cortical bone geometry shows that sauropods have an expansion of the cortical thickness as a result of their heavier mass. It is shown that a universal power-law relationship connects body mass to bone length, suggesting the validity of Wolff's law for sauropods. Moreover, sauropod and mammalian bones seem to be exposed to the same compressive bone stress. X-ray texture measurements of long bones were used to study the orientation of carbonated hydroxyapatite (HA) crystals. All bones investigated showed a 001-fibre texture, in which the c-axis of the HA crystals is oriented along the bone axis. Texture strength (defined by the alignment of HA crystals) appears to be of only minor importance regarding the mechanical strength and seems to be influenced by the loading mode of the bone. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112, 782–798.

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; 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 microstructural evolution of in-situ TiB2 nano-particle reinforced AlZnMgCu composites during hot extrusion was investigated from micro to macro scales by a combination of various techniques, including neutron and synchrotron X-ray diffraction, optical microscopy, scanning and transmission electron microscopy and electron backscatter diffraction (EBSD). The development of microstructure has shown a bimodal grain structure with distinctive spatial distributions of TiB2 particles: the elongated coarse grain structure with smaller dispersed particles and the fine grains mixed with clusters of relatively larger particles. The particle stimulated nucleation occurs at large particle clusters, resulting in recystallized (sub)micron sized fine grains. The dispersed smaller particles are observed to promote dislocation generation and to prohibit recovery. They are shown to reduce the misorientation of low angle grain boundaries due to the pinning effects on independent dislocations, which also lead to the suppression of dynamic recovery and increase of driving force for dynamic recrystallization. Quantitative texture analysis combined with neutron diffraction and EBSD has exhibited the development of a strong 〈111〉 and 〈001〉 dual fiber texture, and both texture volume fractions are changing with the particle content. In addition, the synchrotron diffraction experiments have shown that dislocation density increases with the particle content in both texture components. The microstructure evolution is the result from a complex process of particles/matrix interaction during the deformation and dynamic recrystallization. In comparison with its particle-free alloy counterpart, the thermomechanical response of the composites at high temperature is discussed in terms of aluminum deformation and recrystallization mechanisms combined with nanosized particle effects. Keywords: Nano-sized TiB2 particles, Metal matrix composites, Neutron diffraction, Plastic deformation, Dislocation, Recovery & Recrystallization

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.

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.

Through Silicon Via (TSV) is a key enabling technology for 3D stacking. One of the main concerns regarding the TSV introduction inside the IC fabrication is the resulting stress build up in the silicon substrate that may induce warpage or expansion at the wafer level, strain and crystalline defects in the neighboring silicon of the TSV and finally can impact performances and reliability of the CMOS devices as well. Polysilicon, tungsten and copper are the three main conductors that are nowadays considered for the TSV fabrication. In a first part of this paper the different factors that contribute to the stress in these tree TSV types including the geometry, the materials and the process will be reviewed. After bonding on a temporary carrier and thinning of the substrate to expose the via the stress built up during the fabrication of the TSV can be also revealed by the expansion of the silicon membrane. Thermo-mechanical FEM simulations will be equally introduced and confronted to the experimental findings. We also present some characterizations of silicon defects by chemical revelation around the TSV structures. For characterization of the stress in TSV structures scale different techniques as EBSD, μRaman, XRD will be then presented. Finally we conclude that with the optimization of some key processing steps, the stress induced in via-first technology may be acceptable for IC integration.

Using X-ray and neutron radiography and tomography, images of material and component inhomogeneities and their development with time can be obtained. Due to their non-destructiveness and non-invasive nature both methods give insight into the function of devices and their decay processes. Fundamentals of X-ray and neutron radiography and tomography are briefly outlined, examples for both techniques are given, their complementarities are highlighted and emerging techniques and frontiers are discussed.

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.

Microstructure evolution during high-temperature creep of a CuZn40Pb2 brass alloy was characterized in situ by synchrotron microtomography. It is shown that tomographic data are sufficiently accurate for local material characterization. Imposing a constant temperature gradient along the gauge length of the sample allows the apparent activation energy of steady-state creep to be evaluated for a single specimen.

Introduction Instrument development at third-generation synchrotrons over the last decade has enabled a large variety of in-situ experiments. Among these, X-ray microtomography represents a special case due to the three-dimensional (3D) character of the information acquired [1-3]. The method combines the high photon flux with the nondestructive nature of the investigation, enabling a deeper insight into the dynamics of physical processes. In-situ microtomography is very well suited for damage investigation during high-temperature creep, providing for the first time experimental 3D data about damage evolution. Such findings are of valuable help to understand the dynamics of the underlying physical processes and to promote further developments of adequate damage theories [4-6]. It is the aim of this report to present the qualitative features of cavity evolution during high-temperature creep of a brass alloy.

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; : An in situ X-ray diffraction experiment was set up to study the microstructural evolution of a nanostructured oxide dispersion-strengthened ferritic steel produced by high-energy ball milling. Dislocation density and grain growth between 20 and 1100 degrees C were quantified by coupling-modified Williamson-Hall and Warren-Averbach methods. During the early stages of heating, recovery through the rearrangement of dislocations increases the coherent domain size from 23 to about 60 nm. Once the annealing temperature reaches 800 degrees C, recrystallization starts. Using a specific analysis of 2-D detector signal, it has been possible to grasp the occurrence of abnormal growth leading to bimodal grain size distribution with both ultrafine grains and coarser micronic grains. The grain growth kinetics upon heating were determined for both populations and separately quantified. Ultrafine grains exhibit a continuous moderate growth rate, leading to continuous recrystallization, whereas specific grains experience a rapid abnormal growth up to their final size after a short incubation time.

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.

A new approach for the estimation of the effective properties of real particle-reinforced metal–matrix composites is presented. The methodology relies on statistical functions of the three-dimensional structure of the composites, as obtained from microtomographic investigations, and uses an ergodic principle for the calculation of the overall properties. Based on the symmetrical functional form of the local volume fraction and results of finite element calculations we develop the so-called “mean window technique”, which leads to the remarkable result that the effective linear or nonlinear mechanical properties of a composite can be obtained by averaging randomly selected windows from the real structure. Such windows should have a size at least equal to the correlation length of the microstructure and the volume fraction of the particles equal to the mean value of the distribution of the local volume fraction.

The structure of a real particle reinforced metal-matrix composite, Al/Al 2 O 3 , was retrieved by high resolution X-ray tomography. The paper presents a study of the influence of local structure variability on the elastic properties of the composite. The results are in good agreement with theoretical two-point bounds.

Based on evaluations of 3-D X-ray microtomographic reconstructions simple mean-field and multi-scale models were developed for predicting the plastic response of particle reinforced metal-matrix composites. It is shown that increasing heterogeneity, by taking more details of the microstructure into account, leads to stress-strain curves, which differ only slightly from the curve of the mean-field model.

A mean-field and a multiscale model of a particle reinforced metal–matrix composite were developed based on the knowledge of its three-dimensional microstructure obtained by holotomography. Both the mean-field and the multiscale model accounting for the distribution of particles’ local volume fractions approximate well the experimental stress–strain curves.

X-ray line profile analysis is an efficient non-destructive technique to determine some key statistical properties of dislocation structures developing during plastic deformation. In the first part of the paper recent developments describing the asymptotic behavior of the line profiles are outlined. A new evaluation method is presented to determine the average dislocation density and its spatial variation. The method is demonstrated on measurements obtained on compressed Cu single crystals. After this, it is shown that the relative dislocation density fluctuation exhibits a sharp maximum at the stages II–III transition. A nanoindentation tests indicate that the fluctuations of other quantities behave similarly. The results give new insight into the dislocation phenomena taking place in the stage III deformation regime.

Local crystallographic orientation of tensile deformed copper single crystals was investigated by the electron backscattering technique. Statistical evaluation of the data reveals the presence of an increased crystallographic correlation at the transition point between stages II and III of work-hardening. The transition state has the lowest probability of finding geometrically necessary dislocations in circular regions of radius smaller than 8 μm. According to the present results and other data showing that the relative fluctuation of the dislocation density has a maximum at the transition point, we conclude that the transition from stages II to III of work-hardening is similar to a second-order phase transformation of the statistical dislocation system.

Intergranular strain and the associated stored energy were investigated by X-ray diffraction in two texture components of cold-rolled ultra high purity (UHP) iron. Laue peaks were measured on plastically deformed samples and the center of the lines was compared with reference peaks recorded from a well-annealed powder sample of the same material. The intergranular stored energy as evaluated from the residual strain tensor was found to be much higher for the [1 1 0](0 0 1) α fibre component than for the [1 2 1](1−1 1) γ fibre component. Experimental results show that the soft α grains of the polycrystal, containing fewer dislocations, are more strained by their surrounding than hard γ grains with more dislocations. Generally intergranular strains decrease with deformation.

The elastic–plastic response of a metal–matrix composite (MMC) consisting of a AA6061-T6 aluminium matrix reinforced with 20 vol.% Al 2 O 3 particles was modeled using the finite element method. As input for the model, a real three-dimensional (3D) microstructure obtained by holotomography was used. The macroscopic behavior of the composite was obtained by multi-scale modeling based on a window-averaging and extrapolation technique. Model compression stress–strain curves obtained for a cubical volume of edge length 9–10 times larger than the two-point correlation length of the matrix show satisfactory agreement with experimental data.

The dislocation densities in individual texture components of a hot, plane strain compressed, Al–2.5%Mg alloy have been determined by high resolution X-ray diffraction using recent methods for peak broadening interpretation. After deformation at 400 °C and strains up to 1.5 dislocation densities range from 2 to 20 × 1013 m−2. Both high energy synchrotron (European synchrotron radiation facility, ESRF) transmission peak analysis and standard reflection line analysis show that the S {1 2 3}〈4 1 2〉 component develops significantly higher stored energies than the cube, brass {0 1 1}〈2 1 1〉 and Goss {0 1 1}〈1 0 0〉 components. After subsequent annealing to partial recrystallization, EBSD orientation maps over large areas demonstrate that the high energy S component is preferentially consumed by recrystallization. It is also shown that the development of the cube recrystallization texture is due to a nucleation frequency advantage, function of the applied strain.

The method of holotomography was applied to investigate the microstructure of a metal–matrix composite (MMC) consisting of an AA6061 aluminium matrix reinforced with 20 vol.% Al 2 O 3 particles. Various statistical functions characterizing the Al 2 O 3 particles and the matrix were evaluated, which facilitate a better understanding of the correlation between microstructural features and the overall physical properties of the composite. The shape of the particles is approximated by an ellipsoid and their spatial distribution is described in terms of the pair-distribution function of particle centers and the two-point probability functions of the component phases. The investigated statistical functions emphasize the existence of a short-range correlation in the microstructure, which has a correlation length of about two times the average nearest-neighbor distance. To understand better the influence of the particle shape on different statistical descriptors a comparison between the real microstructure and a system of random hard-spheres is presented.

Anisotropic strain broadening of diffraction peaks can be parameterised by dislocation contrast factors. A comprehensive software has been developed and made available through the internet to determine the individual and averaged contrast factors which are also compiled for cubic and hexagonal crystals. Using the theoretical and the measured values of contrast factor the microstructure of the specimen can be characterised in terms of active slip systems, Burgers vector populations, dislocation densities and crystallite size- and size distribution.