AlSi10Mg manufactured by laser powder bed fusion (or selective laser melting) benefits from a very fine microstructure that imparts significant mechanical strength to the material compared to the ...cast alloy. The build platform temperature stands out as a significant processing parameter influencing the microstructure as it affects the cooling rate and thermal gradient during manufacturing. Setting the build platform temperature to 200°C yields a negligible residual stress level. However, the strength is lower compared to that obtained using a build platform temperature of 35°C, with a similar fracture strain. A detailed 3D microstructural analysis involving focused ion beam/scanning electron microscopy tomography was performed to describe the connectivity and size of the Si-rich eutectic network and link it to the strength and fracture strain. The coarser microstructure of the 200°C build platform material is more prone to damage. The α-Al cells as well as the Si-rich precipitates present a larger size in the 200°C material, the latter thus having a lower strengthening effect. The Si-rich eutectic network is also less interconnected and has a larger thickness in the 200°C material. An analytical model is developed to exploit these microstructural features and predict the strength of the two materials.
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The compression behavior of hollow architectured structures obtained by additive manufacturing was investigated in this work. Two face-centered cubic structures with the same shape and repetitive ...pattern but different struts and nodes thicknesses were produced using the selective laser melting (SLM) technique. Deformation of the structures under compression was imaged by in-situ and ex-situ X-ray tomography scanning. The initial state of the structure was scanned using the stitching tomography method to capture detailed 3D images illustrating both the macroscopic hollow structure and local microporosity in the nodes and struts. A 3D image-based conformal finite element model was then built for the simulation of the compression test using Gurson-Tvergaard-Needleman (GTN) porous plasticity and a new procedure allowing to inform the local porosity of each element directly from high resolution tomography. Simulations considering a homogeneous matrix with an average initial porosity everywhere were compared to the new heterogeneous model. A fairly good agreement was found between the heterogeneous model and experiments especially in the prediction of fracture location.
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As-built Ti-6Al-4V thin parts were manufactured in three different orientations using EBM and characterized by laboratory X-ray tomography. Fatigue tests were performed. The comparison with results ...for machined samples from the literature showed a large reduction of fatigue strength. SEM observations of the fracture surfaces showed that surface defects which were identified as notch-like defects on tomographic images caused the failure. Their impact on fatigue results was rationalized by Kitagawa-Takahashi diagrams. A build orientation impact on the fatigue properties was observed and linked to its effect on defects distributions and crack growth. The limits of roughness measurements were also discussed.
High strength and high toughness are usually mutually exclusive in engineering materials. In ceramics, improving toughness usually relies on the introduction of a metallic or polymeric ductile phase, ...but this decreases the material's strength and stiffness as well as its high-temperature stability. Although natural materials that are both strong and tough rely on a combination of mechanisms operating at different length scales, the relevant structures have been extremely difficult to replicate. Here, we report a bioinspired approach based on widespread ceramic processing techniques for the fabrication of bulk ceramics without a ductile phase and with a unique combination of high strength (470 MPa), high toughness (22 MPa m(1/2)), and high stiffness (290 GPa). Because only mineral constituents are needed, these ceramics retain their mechanical properties at high temperatures (600 °C). Our bioinspired, material-independent approach should find uses in the design and processing of materials for structural, transportation and energy-related applications.
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Microheterogeneous materials such as metal foams exhibit a strong structure-property-relationship. The macroscopic material properties depend on the pore geometry and especially on ...the strut geometry and the microstructure of the struts such as the grain structure. Since the grain structure in the struts differs from that of the corresponding bulk material, it is of utmost importance to perform microtensile tests on individual struts. Previous works on aluminium foams outlined strong scattering in this micromechanical properties. A possible reason for the scattering might be micro-porosity and inclusions in the struts resulting from the manufacturing of metal foams by investment casting. The present contribution deals with ex situ and In situ microtensile tests to elucidate reasons for the scattering in the micromechanical properties determined from microtensile tests on individual struts. In situ tensile tests using high resolution X-ray computed tomography were used to study the microstructural failure mechanisms in aluminium foam struts. The results were further proven by additional ex situ tensile experiments on struts, which were analysed by low resolution X-ray computed tomography prior to tensile testing to allow for more specimens and hence for better statistics. Micro-porosity and primary inclusions were found to be the main reason for differences in the micromechanical properties of individual aluminium foam struts.
The alloying reaction of silicon with lithium in negative electrodes for lithium‐ion batteries causes brutal morphological changes that severely degrade their cyclability. In this study, the dynamics ...of their expansion and contraction, of their cracking in the bulk and of their debonding at the interface with the current collector are visualized by in situ synchrotron X‐ray computed tomography and quantified from appropriate 3D imaging analyses. Two electrodes made with same silicon material having reasonable particle size distribution from an applied point of view are compared: one fabricated according to a standard process and the other one prepared with a maturation step, which consists in storing the electrode in a humid atmosphere for a few days before drying and cell assembly. All morphological degradations are significantly restrained for the matured electrode, confirming the great efficiency of this maturation step to produce a more ductile and resilient electrode architecture, which is at the origin of the major improvement in their cyclability.
The morphological degradation of Si‐based anodes for Li‐ion batteries is characterized by in situ synchrotron X‐ray computed tomography. The dynamics of the electrode expansion and contraction, of its cracking in the bulk and of its delamination from the current collector are visualized and quantified. The efficiency of a maturation procedure to enhance the mechanical strength of the Si‐based electrodes is highlighted.
This paper describes an in-situ tensile test in synchrotron tomography achieved for the first time with a frequency of 20 tomograms per second (20 Hz acquisition frequency). This allows us to capture ...rapid material fracture processes, such as that of a metal matrix composite composed of 45 % of alumina particles embedded into 55 % of pure aluminium, which fractures by the sudden coalescence of internal damage. Qualitatively, the images show the nucleation and propagation of a crack during 9 s leading to total fracture of the sample. The images are then post-processed quantitatively to analyze the evolving shape of the crack and to derive the instantaneous speed of its tip. It is shown that the crack clearly propagates from one particle to the next, pausing briefly before propagating to the next particle, lending experimental support to a local load sharing analysis of the fracture of this class of composite.
•Microporous ferritic stainless steel was produced from Incoloy 800 via LMD.•LMD can be used industrially to produce inexpensive porous materials.•Minor elements in commercial alloys tend to slow ...down coarsening kinetics.•Nitric acid that serves for Mg dissolution also induces a passivation treatment.•The pore size (0.5–1.5 μm) has no significant effect on pitting sensitivity.•The pore size plays a role on diffusion processes through the porous structure.
Liquid metal dealloying is a newly available technology used to create bulk porous materials. In this study, a commercial nickel-based superalloy, Incoloy 800, was dealloyed to elaborate a fully porous ferritic stainless steel. The Mg selective dissolution in nitric acid solution acts as a passivation treatment that enhances the passive film resistance.
Corrosion tests confirm the beneficial effect of the nitric acid treatment on the Cr enrichment of the passive film thus improved the material resistance. The electrochemical characterizations show a higher effect of the size porosities on the diffusion kinetics of the electrolyte rather than on the pitting sensitivity.
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.
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