The first in-situ monitoring of plaster hydration using X-ray tomography is reported in this paper. Dissolution of hemihydrate particles and formation of a network of gypsum needles can be observed ...in 3D. A 3D quantitative analysis based on the microstructure evolution allows the determination of the degree of reaction. In particular, the size of hemihydrate particles is shown to have an influence both on the hydration kinetics and on the final microstructure of the set plaster. This work paves the way to the understanding of the relationship between microstructure evolution, chemical degree of reaction and mechanical strength development for material processed through a setting reaction.
This article reviews the use of x-ray computed tomography (XRCT) to investigate the structure and properties of cellular solids. In the first section, the possibilities offered by XRCT are presented. ...Examples of tomographic images are shown for the three classes of material (polymers, metals, and ceramics). Different characterizations of cellular solids performed thanks to XRCT images are shown: calculation of morphological parameters, in situ and ex situ mechanical tests, and use of the tomographic images to perform finite element (FE) modeling. The second part of the paper presents the existing methods to create the meshes from tomographic images and highlights some interesting results from the FE simulations.
The fracture process of commercially pure titanium was visualized in model materials containing artificial holes. These model materials were fabricated using a femtosecond laser coupled with a ...diffusion bonding technique to obtain voids in the interior of titanium samples. Changes in void dimensions during in-situ straining were recorded in three dimensions using x-ray computed tomography. Void growth obtained experimentally was compared with the Rice and Tracey model which predicted well the average void growth. A large scatter in void growth data was explained by differences in grain orientation which was confirmed by crystal plasticity simulations. It was also shown that grain orientation has a stronger effect on void growth than intervoid spacing and material strength. Intervoid spacing, however, appears to control whether the intervoid ligament failure is ductile or brittle.
In the effort of expanding the already existing applications of additively manufactured parts, improving mechanical performance is essential. Friction stir processing (FSP) is a promising ...post-treatment solution to tackle this issue. FSP of selective laser melted AlSi10Mg leads to the globularisation of the Si-rich eutectic network, microstructural homogenisation and porosity reduction. These features have been characterised using in and ex situ mechanical testing and different imaging techniques. A significant modification of the damage mechanism is reported with an increase of the fracture strain from 0.1 to 0.4 after FSP and an enhancement over two orders of magnitude in fatigue life.
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The objective of this work is to link microstructure features of foamed gypsum (lightweight gypsum board core material) and its compressive properties. Several samples of foamed gypsum with different ...microstructures were manufactured and characterized by X-ray tomography and 3D image processing. Spherical indentation tests results show that for a similar density, the size distribution of the macropores and the distribution of the three levels of porosity has only a very small influence on the mechanical properties. In contrast, the density and homogeneity of spatial distribution of macropores has a much stronger impact on hardness.
It is well known that the mechanical properties of lithium‐ion battery electrodes impact their electrochemical performance. This is especially critical for Si‐based negative electrodes, which suffer ...from large volume changes of the active mass upon cycling. Here, this study presents a postprocessing treatment (called maturation) that improves the mechanical and electrochemical stabilities of silicon‐based anodes made with an acidic aqueous binder. It consists of storing the electrode in a humid atmosphere for a few days before drying and cell assembly. This results in a beneficial in situ reactive modification of the interfaces within the electrode. First, the binder tends to concentrate at the silicon interparticle contacts. As a result, the cohesion of the composite film is strengthened. Second, the corrosion of the copper current collector, inducing the formation of copper carboxylate bonds, improves the adhesion of the composite film. The great improvement of the mechanical stability of the matured electrode is confirmed by in‐operando optical microscopy showing the absence of film delamination. The result is a significant electrochemical performance gain, up to a factor 10, compared to a not‐matured electrode. This maturation procedure can be applied to other types of electrodes for improving their electrochemical performance and also their handling during cell manufacturing.
A simple postprocessing method (called maturation) is conceived for improving the cycle life of Si‐based electrodes. This improvement originates from the increase of the mechanical strength of the electrode thank to the binder migration at the silicon interparticle contacts and to the formation of copper carboxylate bonds at the film/substrate interface.
The evolution with cycling of the three-dimensional (3D) microstructure of a silicon/carbon/carboxymethylcellulose (Si/C/CMC) electrode for Li-ion batteries is investigated by combined focused ion ...beam (FIB) / scanning electron microscopy (SEM) tomography. Using appropriate image processing methods, a volume of 20 × 8 × 11 μm3 is reconstructed in which the Si and pore phases are clearly identified. Their respective morphological characteristics (volume fraction, spatial distribution, size, connectivity, and tortuosity) are determined before and after 1, 10 and 100 cycles. The Si particles (37 vol.%, median diameter = 0.37 μm) and pores (57 vol.%, median diameter = 0.40 μm) are homogeneously distributed and fully connected in the pristine electrode. Major changes in the electrode morphology occur upon cycling due to electrode cracking and the growth of the solid electrolyte interphase (SEI) layer. It also appears that the size and shape of the Si particles change upon cycling. After 100 cycles, they display a non-spherical morphology (axial ratio of 4.6) with a median size of 0.14 μm.
Cold sintering is a promising route towards the manufacturing of dense ceramics at mild processing conditions, but our poor understanding of the process has prevented the wider spread of this ...attractive densification approach. Using nanovaterite powders with well-defined multiscale morphology, we perform in-situ X-Ray tomography on compacts subjected to controlled mechanical load and quantify the multiscale deformation processes responsible for the water-assisted cold sintering of this powder with the help of instrumented indentation experiments at the micro- and nano-scale. Our results reveal the crucial effect of water in promoting the macroscopic densification process and highlight the dominant role of the nanoparticle network inside agglomerates in controlling the cold sintering of compacts at high mechanical loads. By providing new insights into the deformation processes responsible for the densification effect, this study can potentially guide the discovery of novel chemical compositions and particle morphologies that can be more easily densified through room-temperature cold sintering with water.
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Liquids metal dealloying is a new technology to create porous materials. In this study, a commercial Incoloy 825 nickel superalloy is dealloyed for 1 h at 3 different temperatures to elaborate a ...fully porous FeCr-based metal with 3 different porous microstructures. The resulting porous metals showed unimodal pore distribution, hierarchical structure or, contain large ligaments inclusions. The passivation ability of the porous material was conformed irrespective of the microstructure. This letter proves the possibility of fabricating low cost high specific surface materials for electrochemical applications.
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Bone substitute fabrication is of interest to meet the worldwide incidence of bone disorders. Physical chitosan hydrogels with intertwined apatite particles were chosen to meet the bio-physical and ...mechanical properties required by a potential bone substitute. A set up for 3-D printing by robocasting was found adequate to fabricate scaffolds. Inks consisted of suspensions of calcium phosphate particles in chitosan acidic aqueous solution. The inks are shear-thinning and consist of a suspension of dispersed platelet aggregates of dicalcium phosphate dihydrate in a continuous chitosan phase. The rheological properties of the inks were studied, including their shear-thinning characteristics and yield stress. Scaffolds were printed in basic water/ethanol baths to induce transformation of chitosan-calcium phosphates suspension into physical hydrogel of chitosan mineralized with apatite. Scaffolds consisted of a chitosan polymeric matrix intertwined with poorly crystalline apatite particles. Results indicate that ink rheological properties could be tuned by controlling ink composition: in particular, more printable inks are obtained with higher chitosan concentration (0.19 mol·L
−1
).
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