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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).

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

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.

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.

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.

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.

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 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.

The influence of the free surface on the load carried by elastic inclusions embedded in an elastic–plastic matrix was investigated by the finite element method. A 2D multi-particle model was developed based on the statistical evaluation of the microstructure of a commercial metal–matrix composite. The results of simulated tensile tests show that the average particle stresses are sensitive to the adopted boundary conditions. Inclusions near a free boundary carry in general smaller loads than the inclusions in the bulk. Damage predictions of the model are in good agreement with the experimental data obtained by X-ray microtomography.

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 different methods of diffraction profile analysis are presented. In the first, the breadths and the first few Fourier coefficients of diffraction profiles are analysed by modified Williamson–Hall and Warren–Averbach procedures. A simple and pragmatic method is suggested to determine the crystallite size distribution in the presence of strain. In the second, the Fourier coefficients of the measured physical profiles are fitted by Fourier coefficients of well establishedab initiofunctions of size and strain profiles. In both procedures, strain anisotropy is rationalized by the dislocation model of the mean square strain. The procedures are applied and tested on a nanocrystalline powder of silicon nitride and a severely plastically deformed bulk copper specimen. The X-ray crystallite size distributions are compared with size distributions obtained from transmission electron microscopy (TEM) micrographs. There is good agreement between X-ray and TEM data for nanocrystalline loose powders. In bulk materials, a deeper insight into the microstructure is needed to correlate the X-ray and TEM results.

Ball-milled WC powder has been compacted and sintered. The particle size has been determined by transmission and scanning electron microscopy and high resolution X-ray diffraction. The X-ray diffraction profiles were evaluated for particle size and dislocation densities by the recently developed procedures of modified Williamson-Hall plot and modified Warren-Averbach method. Log-normal particle size distributions have been obtained by a newly developed numerical method from the size parameters provided by X-ray line profile analysis. The size distributions obtained by TEM and X-rays are compared and discussed. The dislocation density was found to be 1.9 × 1017 m−2 in the ball-milled powder which decreases to 2.0 × 1015 m−2 after annealing.

Densities and arrangements of dislocations and mesoscopic long-range internal stresses in cold-rolled polycrystalline copper were determined in scanning mode by X-ray peak profile analysis with synchrotron radiation. The high brilliance enabled the use of a focal spot of less than 50 μm. The diffraction profiles of the 200 reflections were measured by scanning the specimen step by step in front of the beam. In this way, the heterogeneities of the deformation-induced microstructure within single grains were obtained. At small deformations including stage III, the dislocation densities and the internal stresses were uniform within the grain interior, but larger near the grain boundaries where the dislocations showed a tendency to form stress-intensive arrangements. At higher deformations towards and in stage IV, the dislocation density and the internal stresses increasingly fluctuated within the whole grain. The fluctuations were interpreted as the transformations of polarized dipolar dislocation walls (PDW) into polarized tilt walls (PTW) observed recently by macroscopic diffraction experiments on highly deformed specimens. These results are important for the current research of strengthening processes in stage IV.

The microstructural changes in a tube section of X20CrMoV12-1 due to service are investigated. The investigation was carried out by combining mechanical tests, finite element calculations and mainly quantitative characterisation of the microstructure by electron microscopy. The tensile and fatigue tests at room temperature did not show differences between the tube section and the initial state of another melt. At the approximate service temperature the deformation resistance of the service exposed material is slightly lower. The finite element calculations indicate no plastic deformation. The quantitative characterisation of the microstructure shows that the dislocation structure does not differ from the initial state of other melts. On the other hand the carbide structure grows with time at temperatures prevailing during service. The coarsening of the carbide structure may be the reason for a lower high temperature deformation resistance of the material of the tube section. The microstructural results indicate that the tube section was not influenced by plastic deformation during service.

Polycrystalline samples of Fe-0.005%-C were deformed by torsion at 300 K far into stage IV of deformation and investigated by X-ray peak profile analysis (XPA) for the microstructural evolution. The long-range internal stresses Δτ w −δτ c (τ w , τ c are the shear stresses in the cell wall and cell interior regions) pass through a maximum at the onset of stage IV, but reincrease within stage IV at higher deformation. A similar maximum is observed in the formal dislocation density derived directly from XPA which, however, is not seen in residual electrical resistivity. These results can be consistently explained by the assumption that in stages II and III the cell walls are formed as polarized dipole walls (PDW) which in stage IV change into polarized tilt walls (PTW), similarly to recent findings in cold rolled Cu. The significant constancy of total volume fraction of cell walls as well as of specific internal stresses in stage IV confirm the importance of the PTW s for stage IV strengthening.

Long-range internal stresses in dislocation cell and subgrain structures were investigated experimentally. The transition of the dislocation structure from cells to subgrains was achieved by deforming copper polycrystals in compression creep tests at constant stress normalized by the shear modulus in the temperature range from 298 K to 633 K. The long-range internal stresses were investigated by two methods. The first one was the evaluation of characteristically asymmetric X-ray line profiles. The internal stresses are the result of the analysis of the X-ray line profiles. The second one was the measurement of local lattice parameters by convergent beam electron diffraction. The internal stresses can be determined from the changes in the local lattice parameters. The results obtained from both methods show that long-range internal stresses of the same type exist in the cell as well as in the subgrain structures.

The microstructure of ball-milled iron powder has been investigated by high resolution X-ray line profile analysis. Analysis of line breadths suggested that the contrast factors related to dislocations have to be taken into account in the Williamson-Hall procedure. This concluded to a modified Williamson-Hall plot which provided, in a straightforward manner, the grain size refinement of nanocrystals ball-milled for different periods of time. At the same time it has been shown that strain broadening, even in these nanoscale small-grain particles, is caused by the presence of dislocations. The line profiles were also studied by the method of Fourier analysis, which gave the absolute values of dislocation densities.

International audience; The theoretical basis of X-ray line profile analysis and its application to microstructural characterization of plastically deformed metallic alloys is presented. The microstructure is described in terms of coherent domain size, planar fault density, dislocation density and a dislocation arrangement parameter. Two evaluation methods are introduced: the momentum method and the extended Convolutional Multiple Whole Profile fit procedure. Their use is exemplified on plastically deformed single crystals, single grains residing in the bulk of a polycrystal and family of grains making up texture components. The selected examples show the potential of X-ray line profile analysis applied to diffraction patterns recorded with laboratory or synchrotron sources.

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.

X-ray line profiles and line positions were measured on single grains of cyclically deformed polycrystalline copper specimens unloaded from characteristic points of the stress-strain hysteresis loop. A high-resolution double crystal diffractometer was used to obtain local lattice parameter changes, from which long-range internal stresses and mean stresses were evaluated. In the case of samples unloaded from the load-reversal points the asymmetry of the characteristically broadened X-ray line profiles indicated forward and backward internal stresses prevailing in the dislocation cell wals and cell interiors of the dislocation cell structure, respectively. The changes of the long-range internal stresses after unloading from different points of the stress-strain hysteresis loop can be explained in terms of the composite model. In addition, mean strains and stresses, varying from grain, could be determined from the shifts of the Bragg reflections. A detailed microstructure-based discussion of the elastic stored energy, evaluated from the analysis of the stress-strain hysteresis loop, is given.

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.