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The behaviour of various powder systems during high temperature sintering has been investigated by coupling X-ray microtomography and discrete element method (DEM). Both methods are particularly relevant to analyse particle interactions and porosity changes occurring during sintering. Two examples are presented. The first one deals with a copper powder including artificially created pores which sintering has been observed in situ at the European synchrotron and simulated by DEM. 3D images with a resolution of 1.5 μm have been taken at various times of the sintering cycle. The comparison of the real displacement of particle centers with the displacement derived from the mean field assumption demonstrates significant particle rearrangement in some regions of the sample. Although DEM simulation showed less rearrangement, it has been able to accurately predict the densification kinetics. The second example concerns multilayer ceramic capacitors (MLCCs) composed of hundreds of alternated metal electrode and ceramic dielectric layers. The observation of Ni-based MLCCs by synchrotron nanotomography at Argon National Laboratory with a spatial resolution between 10 and 50 nm allowed understanding the origin of heterogeneities formed in Ni layers during sintering. DEM simulations confirmed this analysis and provided clues for reducing these defects.

We describe our miniature laser powder bed fusion (L-PBF) system for in situ synchrotron x-ray micro-computed tomography (XCT) at the European Synchrotron Radiation Facility. This replicator was designed to extend the characterization of L-PBF to 3D. This instrument fills in a technical gap because the existing replicators were mostly designed to shed light on the dynamic mechanisms involved in molten pool formation but, therefore, suffered from a lack of 3D information. Technical details regarding the setup and beamline integration are given. Experimental validations via post-mortem XCT scans and in situ scans acquired during experiments conducted at the BM05 beamline of the European Synchrotron Radiation Facility are provided. Based on a few illustrative examples, we show that such a replicator opens the path to collect key 3D information that to date could not be available. Our miniature instrument complements the other replicators developed in the world by other research groups that enable operando x-ray imaging (radiography) and operando x-ray diffraction. [ABSTRACT FROM AUTHOR]

Metallic materials processing such as rolling, extrusion or forging often involves high‐temperature deformation. Usually under such conditions the samples are characterized post mortem, under pseudo in situ conditions with interrupted tests, or in situ with a limited strain rate. A full in situ 3D characterization, directly during high‐temperature deformation with a prescribed strain‐rate scheme, requires a dedicated sample environment and a dedicated image‐analysis workflow. A specific sample environment has been developed to enable highly controlled (temperature and strain rate) high‐temperature deformation mechanical testing to be conducted while performing in situ tomography on a synchrotron beamline. A dedicated digital volume correlation algorithm is used to estimate the strain field and track pores while the material endures large deformations. The algorithm is particularly suitable for materials with few internal features when the deformation steps between two images are large. An example of an application is provided: a high‐temperature compression test on a porous aluminium alloy with individual pore tracking with a specific strain‐rate scheme representative of rolling conditions. [ABSTRACT FROM AUTHOR]

Magnesium alloy Elektron 21 is commonly used in aerospace structural parts in which good creep resistance and lightness are required. This alloy maintains good mechanical properties at temperatures as high as 200 °C. One mechanism with high potential for improving mechanical properties of magnesium alloys at a high temperature is dispersion-strengthening based on nanoparticles. In this paper, we analyse the properties of magnesium Elektron 21 samples solidified with nanoparticles of aluminium nitride dispersed by an electromagnetic stirring provided from a travelling magnetic field. X-ray tomography and X-ray spectrometry as well as compression tests at several temperatures (350, 400 and 450 °C) are carried out on samples containing the nanoparticles. The present study extends the knowledge on the processing by alternative techniques and on the enhancement of creep behaviour at higher temperatures for such metal matrix composites compared to previous studies. [ABSTRACT FROM AUTHOR]

The microstructure of a high-purity Al-6.5Si-1Fe (wt pct) alloy after solidification at various cooling rates was investigated. In most of the cases, the monoclinic beta-AlFeSi phase was observed as long and thin lamellae. However, at a very slow cooling rate, Fe-bearing precipitates with Chinese script morphology appeared together with lamellae. Further analysis showed all these Chinese script precipitates correspond also to the monoclinic beta phase. This finding stresses that differentiating second phases according to their shape may be misleading. [ABSTRACT FROM AUTHOR]

Undoped and nitrogen doped TiO2 thin films were deposited by atomic layer deposition on planar substrates. Deposition on 3D-architecture substrates made of metallic foams was also investigated to propose architectured photovoltaic stack fabrication. All the films were deposited at 265 °C and nitrogen incorporation was achieved by using titanium isopropoxide, NH3 and/or N2O as precursors. The maximum nitrogen incorporation level obtained in this study was 2.9 at. %, resulting in films exhibiting a resistivity of 115 Ω cm (+/-10 Ω cm) combined with an average total transmittance of 60% in the 400-1000 nm wavelength range. Eventually, TiO2 thin films were deposited on the 3D metallic foam template. [ABSTRACT FROM AUTHOR]

Aluminum alloy 7050 is known for its superior mechanical properties, and thus finds its application in aerospace industry. Vertical direct-chill (DC) casting process is typically employed for producing such an alloy. Despite its advantages, AA7050 is considered as a 'hard-to-cast' alloy because of its propensity to cold cracking. This type of cracks occurs catastrophically and is difficult to predict. Previous research suggested that such a crack could be initiated by undeveloped hot tears (microscopic hot tear) formed during the DC casting process if they reach a certain critical size. However, validation of such a hypothesis has not been done yet. Therefore, a method to produce a hot tear with a controlled size is needed as part of the verification studies. In the current study, we demonstrate a method that has a potential to control the size of the created hot tear in a small-scale solidification process. We found that by changing two variables, cooling rate and displacement compensation rate, the size of the hot tear during solidification can be modified in a controlled way. An X-ray microtomography characterization technique is utilized to quantify the created hot tear. We suggest that feeding and strain rate during DC casting are more important compared with the exerted force on the sample for the formation of a hot tear. In addition, we show that there are four different domains of hot-tear development in the explored experimental window-compression, microscopic hot tear, macroscopic hot tear, and failure. The samples produced in the current study will be used for subsequent experiments that simulate cold-cracking conditions to confirm the earlier proposed model. [ABSTRACT FROM AUTHOR]

As one of the most important analysis techniques for non-destructive imaging, X-ray tomography has been widely used in materials science, medical science, and industry to evaluate the behavior of porous materials. By using this method, a three dimensional volume can be inspected in order to visualize in situ the progress of damage in materials and this can be analyzed qualitatively and quantitatively. In the present study, we have used X-ray tomography to investigate the fracture behavior of an ERG open cell aluminum foam. The process of damage development of a sample undergoing tension and the relation between the inter-metallics and the cracks can be observed totally by the X-ray tomography set-up. Local tomography has in particular been used to image the microstructure at high resolution. A finite element model has also been developed in order to simulate this process of the damage using the 3D data obtained by the tomography. [ABSTRACT FROM AUTHOR]

Ultrafast synchrotron microtomography has been used to study in situ and in real time the initial stages of silicate glass melt formation from crystalline granular raw materials. Significant and unexpected rearrangements of grains occur below the nominal eutectic temperature, and several drastically different solid-state reactions are observed to take place at different types of intergranular contacts. These reactions have a profound influence on the formation and composition of the liquids produced, and control the formation of heterogeneities. [ABSTRACT FROM AUTHOR]

Abstract: In the field of materials science, it is common to relate mechanical or physical behaviour to microstructure in order to optimize materials. Usually the observation of the microstructure is made using an optical or electronic microscope to obtain images in two dimensions. However, the measurable parameters in 2D are limited and often the techniques involved to obtain these images are destructive. Thanks to X-ray micro-tomography it is possible to overcome these two difficulties. The purpose of this article is to show the enormous contribution of this tool in the understanding and the modelling of some physical phenomena involved in aluminium alloys. [Copyright &y& Elsevier]

This work analyses the microstructure changes of various copper-based powder systems during sintering from 3D images provided by in situ synchrotron microtomography. The investigated systems include a copper powder with a wide particle size distribution of 0-63 µm poured into a quartz capillary, a pre-sintered copper compact with artificially created large pores and a mixture of copper and alumina particles. The experiments were carried out at the European Synchrotron in Grenoble, France. Powders were sintered up to 1060°C under reducing atmosphere in a furnace located between the X-ray source and the detector. During each experiment, 3D images were taken at various times of the thermal cycle. We have obtained images with a resolution of 1.5 µm and the time of acquisition of every image was ∼1 min. Quantitative analysis of these images allowed the changes of various important parameters to be followed. Such parameters characterise the sintering process at the particle length scale: interparticle coordination, pore size distribution and particle centre-to-centre distance. Moreover, by tracking the displacement of each particle centre and comparing it to the displacement predicted by classical mean field assumption, we have been able to assess the magnitude of particle rearrangement occurring during sintering. From these data, the sintering behaviour of heterogeneous powder systems is discussed with particular emphasis of collective particle phenomena. [ABSTRACT FROM AUTHOR]

Abstract: Titanium and its alloy foams have been receiving a growing interest for biomedical industry due to their biocompatibility and high potential in dental, spinal, joint and hip implant applications. Near net shape production and reproducibility of a product require a full understanding of the processing parameters’ effect on manufacturing and final properties. The shape complexity of titanium surgical implants, for example dental implants, necessitates a good control in compaction and sintering of metal skeletons containing macropores for near-net shape manufacturing. In this study, effects of processing parameters such as spacer powder size and amount on compaction, sintering and final structural properties were investigated. Commercially pure cellular titanium with porosities ranging between 35 and 75% and pore sizes between 100μm and a few millimeters were produced via powder metallurgy with spacers. Architectural parameters of the foams, before and after sintering, were quantitatively characterized via X-ray computed microtomography. Addition of fine spacer powders enhanced compaction and densification of the foam structure. Pore walls were observed to get thicker during sintering. The use of coarser space holders resulted in thicker pore walls and a wider pore wall thickness distribution. The results indicated that strength and stiffness tend to increase with increasing pore size. Among the structural features that spacer size altered, pore wall thickness and pore face roughness were found to be the most dominant effects on strength and stiffness. [Copyright &y& Elsevier]