Fragmentation and Limits to Dynamical Scaling in Viscous Coarsening: An Interrupted in situ X-Ray Tomographic Study

X-Ray microtomography was used to follow the coarsening of the structure of a ternary silicate glass experiencing phase separation in the liquid state. The volumes, surfaces, mean and Gaussian curvatures of the domains of minority phase were measured after reconstruction of the 3D images and segmentation. A linear growth law of the characteristic length scale $\ell \sim t$ was observed. A detailed morphological study was performed. While dynamical scaling holds for most of the geometrical observables under study, a progressive departure from scaling invariance of the distributions of local curvatures was evidenced. The latter results from a gradual fragmentation of the structure in the less viscous phase that also leads to a power-law size distribution of isolated domains

Magnetic field-assisted solidification of W319 Al alloy qualified by high-speed synchrotron tomography

Magnetic fields have been widely used to control solidification processes. Here, high-speed synchrotron X-ray tomography was used to study the effect of magnetic fields on solidification. We investigated vertically upward directional solidification of an Al-Si-Cu based W319 alloy without and with a transverse magnetic field of 0.5 T while the sample was rotating. The results revealed the strong effect of a magnetic field on both the primary α-Al phase and secondary β-Al5FeSi intermetallic compounds (IMCs). Without the magnetic field, coarse primary α-Al dendrites were observed with a large macro-segregation zone. When a magnetic field is imposed, much finer dendrites with smaller primary arm spacing were obtained, while macro-segregation was almost eliminated. Segregated solutes were pushed out of the fine dendrites and piled up slightly above the solid/liquid interface, leading to a gradient distribution of the secondary β-IMCs. This work demonstrates that rotating the sample under a transversal magnetic field is a simple yet effective method to homogenise the temperature and composition distributions, which can be used to control the primary phase and the distribution of iron-rich intermetallics during solidification

Synchrotron X-Ray microtomography: a high resolution, fast and quantitative tool for rock characterization.

This article describes the current capabilities of the European Synchrotron radiation Facility (ESRF), and more particularly those of the ID19 beamline, devoted to imaging, for microtomography. Phase contrast, in situ and fast acquisitions, are emphasized, and examples illustrate the possibilities offered by the use of modern SR sources. RÉSUMÉ: Cet article expose les possibilités actuelles de l'Installation Européenne de Rayonnement Synchrotron (ESRF), et plus en particulier celles de la ligne ID19 dédiée à l' 'imagerie, en ce qui concerne la microtomographie. Les aspects contraste de phase, in situ et acquisition rapide sont soulignés. Des exemples illustrent les possibilités nouvelles

In-situ X-ray microtomography characterization of damage in SiC/SiC minicomposites

International audienceThe purpose of the present study is to characterize matrix crack propagation and fiber breaking occurrences within SiC/SiC minicomposite in order to validate later on a multiscale damage model at the local scale. An in-situ X-ray microtomography tensile test was performed at the European Synchrotron Radiation Facility (ESRF, ID19 beamline) in order to obtain 3-dimensional (3D) images at six successive loading levels. Results reveal a slow and discontinuous propagation of matrix cracks, even after the occurrence of matrix crack saturation. A few fiber failures were also observed. However, radiographs of the whole length (14 mm) of the minicomposites under a load and after the failure were more appropriate to get statistical data about fiber breaking. Thus, observations before the ultimate failure revealed only a few fibers breaking homogenously along the minicomposite. In addition, an increase in fiber breaking density in the vicinity of the fatal matrix crack was observed after failure. These experimental results are discussed in regards to assumptions used in usual 1-dimensional (1D) models for minicomposites

Fabric Investigation of Natural Sensitive Clay from 3D Nano- And Microtomography Data

The three-dimensional (3D) fabric in natural sensitive clay is quantified from a combination of high resolution nano and microtomographies, scanning electron microscopy, and dynamic light scattering. Although the speckle arising from clay particles and the pores they enclose is discerned in the nanotomography data and compare well with scanning electron microscopy (SEM) images on the same clay, the individual platelet-shaped clay particles cannot be segmented for subsequent quantitative analysis. Regardless, a very wide range of particle sizes - 0.1-300 μm - was detected using the current state-of-the-art in imaging and postprocessing. The measured aspect ratios range was 2.5\ub11; hence, the particles identified were not clay platelets but, rather, mechanically weathered particles embedded in the clay matrix. Furthermore, the smaller particle sizes <80 μm presented a consistent 22-23\ub0 deviation in orientation from the horizontal plane, whereas the larger fractions had a horizontal orientation. The latter finding agrees well with prior findings on the inclination of the clay minerals using small angle X-ray scattering. Finally, the measured mean particle size of 450 nm determined from the nano data is corroborated by an independent determination of particle sizes using dynamic light scattering

Dendrite growth morphologies in rapidly solidified Al-4.5wt.%Cu droplets

International audienceThe impulse atomization process developed at the University of Alberta (Canada) enables metallic powders to be solidified with controlled process parameters and improved properties. In order to investigate the microstructure morphologies in droplets of Al- 4.5wt.%Cu alloys, three-dimensional reconstructions of several droplets are obtained by using synchrotron X-ray micro-tomography, allowing a visualization of the inner microstructure in three dimensions. The analysis of the reconstructed volumes reveals that a wide range of morphology, from highly branched to "finger-bundle", can be obtained for different droplets of similar diameter and produced in the same batch. Unexpectedly for this alloy, microstructural features also indicate that the development of the dendrite arms (primary and of higher orders) occurs in most droplets along crystallographic axes, instead of the usual directions observed in conventional casting technologies

Nucleation and Growth Dynamics of the α-Al / β-Al5FeSi Eutectic in a Complex Al-Si-Cu-Fe Alloy

Secondary-sourced recycled aluminium alloys can exhibit high levels of different impurities. It is well known that the presence of iron, the most common impurity, can lead to the formation of hard and brittle intermetallic phases which are detrimental to the machining properties and the mechanical behaviour of the material in service. The purpose of this work is to study the nucleation and growth of the β-Al5FeSi intermetallic phase in the framework of the eutectic reaction: Liquid → α-Al + β-Al5FeSi. In situ X-ray microtomography has been used to investigate the formation of the irregular eutectic β-phase plates during the solidification at low cooling rate of an Al-8Si-4Cu-0.8Fe alloy. The results show that only a few plates form, nucleating early near the sample surface. Next, growth occurs very rapidly in the principal growth direction and slowly in the thickness direction. The plates are highly branched and appear to form as a divorced eutectic, i.e. not coupled with the α-Al. These features are inconsistent with the common irregular eutectic solidification theory based on the Jackson and Hunt model

Caractérisation expérimentale de l'endommagement dans les minicomposites SiC/SiC

National audienceLes composites SiC/SiC sont étudiés pour leur usage potentiel comme matériau de gainage dans les réacteurs nucléaires de génération future. Afin de valider un modèle multiéchelle d'endommagement à l'échelle microscopique, une caractérisation expérimentale de l'endommagement à l'échelle du toron est mise en œuvre. Des essais de traction in-situ sur minicomposite permettent d'obtenir des données statistiques sur la cinétique d'apparition des fissures matricielles et l'évolution de leur ouverture en fonction de la contrainte. Ces observations de surface sont complétées par des observations microtomographiques réalisées à l'ESRF sur un minicomposite en traction. L'analyse des images 3D permet alors d'étudier la propagation des fissures matricielles au sein du minicomposite. Les ruptures de fibres sont également observables grâce à cette technique d'observation

Impact of cellulose ethers on the cement paste microstructure

ISBN = 3-87264-022-4 7 pagesInternational audienceComplementary investigation tools (2D and 3D observations by optical microscopy and fast X-ray microtomography and then image analysis) were developed in order to examine the effects of cellulose ethers on the cement paste microstructure. The obtained results show that the presence of cellulose ether may induce an increase of both 50-250 µm-diameter air voids. The chemistry of the cellulose ethers appears as a main controlling factor of this porous media modification. In particular, cellulose ethers seems to play an important role on the air bubbles morphological characteristics, the content of air volume and the stabilisation of the porosity from the fresh cement paste to the hardened cement paste