Publications
520 results found
Massimi L, Clark SJ, Marussi S, et al., 2022, Time resolved in-situ multi-contrast x-ray imaging of melting in metals, Scientific Reports, Vol: 12, ISSN: 2045-2322
In this work, the application of a time resolved multi-contrast beam tracking technique to the investigation of the melting and solidification process in metals is presented. The use of such a technique allows retrieval of three contrast channels, transmission, refraction and dark-field, with millisecond time resolution. We investigated different melting conditions to characterize, at a proof-of-concept level, the features visible in each of the contrast channels. We found that the phase contrast channel provides a superior visibility of the density variations, allowing the liquid metal pool to be clearly distinguished. Refraction and dark-field were found to highlight surface roughness formed during solidification. This work demonstrates that the availability of the additional contrast channels provided by multi-contrast X-ray imaging delivers additional information, also when imaging high atomic number specimens with a significant absorption.
Brunet J, Walsh CL, Wagner WL, et al., 2022, Preparation of large biological samples for high-resolution, hierarchical, multi-modal imaging
<jats:title>Abstract</jats:title><jats:p>Imaging the different scales of biological tissue is essential for understanding healthy organ behavior and pathophysiological changes. X-ray micro-tomography using both laboratory (µCT) and synchrotron sources (sCT) is a promising tool to image the 3D morphology at the macro- and micro-scale of large samples, including intact human organs. Preparation of large samples for high resolution imaging techniques remains a challenge due to limitations with current methods, such as sample shrinkage, insufficient contrast, movement of the sample and bubble formation during mounting or scanning. Here, we describe a protocol to prepare, stabilize, and image large soft-tissue samples with X-ray microtomography. We demonstrate the protocol using intact human organs and Hierarchical Phase-Contrast Tomography (HiP-CT) imaging at the European Synchrotron Radiation Facility, but the protocol is equally applicable to a range of biological samples, including complete organisms, for both laboratory and synchrotron source tomography. Our protocol enhances the contrast of the sample, while preventing sample motion during the scan, even in case of different sample orientations. Bubbles trapped during mounting and those formed during scanning (in case of synchrotron X-ray imaging) are mitigated by multiple degassing steps. The sample preparation is also compatible with magnetic resonance imaging (MRI), CT, and histological observation. We describe a protocol for sample preparation and mounting which requires 25 to 34 days for a large organ such as an intact human brain or heart. This preparation time varies depending on the composition, size, and fragility of the tissue. Use of the protocol enables scanning of intact organs with a diameter of 150 mm with a local pixel size of one micron using HiP-CT.</jats:p>
Jonigk D, Werlein C, Lee PD, et al., 2022, Pulmonary and systemic pathology in COVID-19—holistic pathological analyses, Deutsches Ärzteblatt International, Vol: 119, Pages: 429-435, ISSN: 1866-0452
Hintergrund: Die COVID-19-Pandemie stellt den dritten weltweiten Coronavirus-assoziierten Erkrankungsausbruch der letzten 20 Jahre dar. Klinisch dominiert die pulmonale Beteiligung mit einem akuten Lungenversagen (ARDS) bei schweren Verläufen, jedoch können auch andere Organsysteme wie das Herz-Kreislauf-System, Zentralnervensystem und der Gastrointestinaltrakt betroffen sein. Der Pathomechanismus der Organschädigung sowohl für die Lunge wie auch für die nichtpulmonalen Organsysteme war zu Beginn der Pandemie weitestgehend unklar.Methode: Selektive Literaturübersicht bezüglich der morphologischen Veränderungen und zugrunde liegenden Pathomechanismen bei COVID-19 mit Fokussierung auf bildgebende Verfahren.Ergebnisse: Immunhistochemische, elektronenmikroskopische und molekularpathologische Analysen an Autopsiegewebe führten zu einem besseren Verständnis der Pathophysiologie von COVID-19 einschließlich der molekularen Regulationsmechanismen. Hierbei konnte gezeigt werden, dass die sogenannte intussuszeptive Angiogenese (IA) in den betroffenen Organen von COVID-19-Patienten ein zentrales Schadensmuster darstellt. Bei der IA verändert sich ein bestehendes Gefäß durch Einstülpung des Endothels und Ausbildung eines intraluminalen Septums, wodurch schließlich zwei neue Lumina entstehen. Hierdurch verändert sich die Hämodynamik, unter anderem durch Verlust der laminaren Strömung mit Ausbildung turbulenter inhomogener Flussgeschwindigkeiten. Die Induktion der IA ist einerseits auf eine thrombotisch bedingte Ischämie zurückzuführen, doch geht sie andererseits selbst mit einem erhöhten Risiko für weitere Mikrothromben einher, die bei COVID-19-Patientinnen und Patienten in Lunge, Herz, Leber, Nieren, Gehirn und Plazenta nachgewiesen wurden.Schlussfolgerung: In Autopsiematerial von Patientinnen und Patienten mit COVID-19 konnten ultrastrukturell in verschiede
Arzilli F, Polacci M, La Spina G, et al., 2022, Dendritic crystallization in hydrous basaltic magmas controls magma mobility within the Earth's crust, NATURE COMMUNICATIONS, Vol: 13
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- Citations: 10
Xian RP, Walsh CL, Verleden SE, et al., 2022, A multiscale X-ray phase-contrast tomography dataset of a whole human left lung, SCIENTIFIC DATA, Vol: 9
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- Citations: 2
Sinclair L, Clark SJ, Chen Y, et al., 2022, Sinter formation during directed energy deposition of titanium alloy powders, INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE, Vol: 176, ISSN: 0890-6955
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- Citations: 6
Huang Y, Fleming TG, Clark SJ, et al., 2022, Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing, NATURE COMMUNICATIONS, Vol: 13
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- Citations: 73
Kondarage A, Poologasundarampillai G, Nommeots-Nomm A, et al., 2022, In situ 4D tomography image analysis framework to follow sintering within 3D-printed glass scaffolds, Journal of the American Ceramic Society, Vol: 105, Pages: 1671-1684, ISSN: 0002-7820
We propose a novel image analysis framework to automate analysis of X-ray microtomography images of sintering ceramics and glasses, using open-source toolkits and machine learning. Additive manufacturing (AM) of glasses and ceramics usually requires sintering of green bodies. Sintering causes shrinkage, which presents a challenge for controlling the metrology of the final architecture. Therefore, being able to monitor sintering in 3D over time (termed 4D) is important when developing new porous ceramics or glasses. Synchrotron X-ray tomographic imaging allows in situ, real-time capture of the sintering process at both micro and macro scales using a furnace rig, facilitating 4D quantitative analysis of the process. The proposed image analysis framework is capable of tracking and quantifying the densification of glass or ceramic particles within multiple volumes of interest (VOIs) along with structural changes over time using 4D image data. The framework is demonstrated by 4D quantitative analysis of bioactive glass ICIE16 within a 3D-printed scaffold. Here, densification of glass particles within 3 VOIs were tracked and quantified along with diameter change of struts and interstrut pore size over the 3D image series, delivering new insights on the sintering mechanism of ICIE16 bioactive glass particles in both micro and macro scales.
Disney CM, Mo J, Eckersley A, et al., 2022, Regional variations in discrete collagen fibre mechanics within intact intervertebral disc resolved using synchrotron computed tomography and digital volume correlation, ACTA BIOMATERIALIA, Vol: 138, Pages: 361-374, ISSN: 1742-7061
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- Citations: 6
Ackermann M, Tafforeau P, Wagner WL, et al., 2022, The bronchial circulation in COVID-19 pneumonia., American Journal of Respiratory and Critical Care Medicine, Vol: 205, Pages: 121-125, ISSN: 1073-449X
Bhagavath S, Gong Z, Wigger T, et al., 2022, Mechanisms of gas and shrinkage porosity formation in solidifying shear bands, Journal of Materials Processing Technology, Vol: 299, Pages: 1-8, ISSN: 0924-0136
In specialised solidification processing techniques such as High Pressure Die Casting, Twin-Roll Casting and others, an additional external deformation load is applied to achieve the required shape, leading to the formation of microstructural features such as shear bands. The mechanism for forming these features is believed to be dependent on dynamically evolving strain fields, which are dependent on the local solid fraction, applied strain rates and casting geometry. To investigate this, a semisolid ( 50 % solid fraction) Al-10 wt.% Cu alloy is isothermally injected into a bespoke die using a custom-designed thermo-mechanical rig. The semisolid deformation, formation of Cu-rich dilatant bands and subsequent pore nucleation and growth are captured using fast synchrotron X-ray radiography. The local normal and shear strains acting on the mush are quantified using digital image correlation to identify the dilatant shear bands and the dominant local strain component. Correlating the radiographs with strain maps reveals that gas pores within the dilated interstices grow, while those in compressed regions are squeezed out. A linear correlation between accumulated volumetric strain and porosity volume fraction demonstrates that higher dilations give rise to a local increase in both gas and shrinkage porosity.
Iantaffi C, Leung CLA, Chen Y, et al., 2021, Oxidation induced mechanisms during directed energy deposition additive manufactured titanium alloy builds, ADDITIVE MANUFACTURING LETTERS, Vol: 1, ISSN: 2772-3690
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- Citations: 7
Wigger T, Andriollo T, Xu C, et al., 2021, <i>In</i><i> situ</i> synchrotron investigation of degenerate graphite nodule evolution in ductile cast iron, ACTA MATERIALIA, Vol: 221, ISSN: 1359-6454
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- Citations: 3
Xian RP, Walsh CL, Verleden SE, et al., 2021, A multiscale X-ray phase-contrast tomography dataset of whole human left lung
<jats:title>ABSTRACT</jats:title><jats:p>Technological advancements in X-ray imaging using bright and coherent synchrotron sources now allows to decouple sample size and resolution, while maintaining high sensitivity to the microstructure of soft, partially dehydrated tissues. The recently developed imaging technique, hierarchical phase-contrast tomography, is a comprehensive approach to address the challenge of organ-scale (up to tens of centimeters) soft tissue imaging with resolution and sensitivity down to the cellular level. Using this technique, we imaged <jats:italic>ex vivo</jats:italic> an entire human left lung at an isotropic voxel size of 25.08 <jats:italic>μ</jats:italic>m along with local zooms down to 6.05 - 6.5 <jats:italic>μ</jats:italic>m and 2.45 - 2.5 <jats:italic>μ</jats:italic>m in voxel size. The high tissue contrast offered by the fourth-generation synchrotron source at the European Synchrotron Radiation Facility reveals complex multiscale anatomical constitution of the human lung from the macroscopic (centimeter) down to the microscopic (micrometer) scale. The dataset provides complete organ-scale 3D information of the secondary pulmonary lobules and delineates the microstructure of lung nodules with unprecedented detail.</jats:p>
Massimi L, Clark SJ, Marussi S, et al., 2021, Dynamic Multicontrast X-Ray Imaging Method Applied to Additive Manufacturing, PHYSICAL REVIEW LETTERS, Vol: 127, ISSN: 0031-9007
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- Citations: 4
Walsh CL, Tafforeau P, Wagner WL, et al., 2021, Imaging intact human organs with local resolution of cellular structures using hierarchical phase-contrast tomography, Nature Methods, Vol: 18, Pages: 1532-1541, ISSN: 1548-7091
Imaging intact human organs from the organ to the cellular scale in three dimensions is a goal of biomedical imaging. To meet this challenge, we developed hierarchical phase-contrast tomography (HiP-CT), an X-ray phase propagation technique using the European Synchrotron Radiation Facility (ESRF)’s Extremely Brilliant Source (EBS). The spatial coherence of the ESRF-EBS combined with our beamline equipment, sample preparation and scanning developments enabled us to perform non-destructive, three-dimensional (3D) scans with hierarchically increasing resolution at any location in whole human organs. We applied HiP-CT to image five intact human organ types: brain, lung, heart, kidney and spleen. HiP-CT provided a structural overview of each whole organ followed by multiple higher-resolution volumes of interest, capturing organotypic functional units and certain individual specialized cells within intact human organs. We demonstrate the potential applications of HiP-CT through quantification and morphometry of glomeruli in an intact human kidney and identification of regional changes in the tissue architecture in a lung from a deceased donor with coronavirus disease 2019 (COVID-19).
Kondarage AI, Gayani B, Poologasundarampillai G, et al., 2021, Detection and tracking volumes of interest in 3D printed tissue engineering scaffolds using 4D imaging modalities., 43rd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), Pages: 1230-1233, ISSN: 1557-170X
Additive manufacturing (AM) platforms allow the production of patient tissue engineering scaffolds with desirable architectures. Although AM platforms offer exceptional control on architecture, post-processing methods such as sintering and freeze-drying often deform the printed scaffold structure. In-situ 4D imaging can be used to analyze changes that occur during post-processing. Visualization and analysis of changes in selected volumes of interests (VOIs) over time are essential to understand the underlining mechanisms of scaffold deformations. Yet, automated detection and tracking of VOIs in the 3D printed scaffold over time using 4D image data is currently an unsolved image processing task. This paper proposes a new image processing technique to segment, detect and track volumes of interest in 3D printed tissue engineering scaffolds. The method is validated using a 4D synchrotron sourced microCT image data captured during the sintering of bioactive glass scaffolds in-situ. The proposed method will contribute to the development of scaffolds with controllable designs and optimum properties for the development of patient-specific scaffolds.
Jakumeit J, Zheng G, Laqua R, et al., 2021, Modelling<i> the</i><i> complex</i> evaporated gas flow<i> and</i><i> its</i><i> impact</i> on particle spattering during laser powder bed fusion, ADDITIVE MANUFACTURING, Vol: 47, ISSN: 2214-8604
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- Citations: 14
Ahmed FF, Clark SJ, Alex Leung CL, et al., 2021, Achieving homogeneity in a high-Fe β-Ti alloy laser-printed from blended elemental powders, Materials & Design, Vol: 210, Pages: 1-9, ISSN: 0264-1275
Blended Elemental powders are an emerging alternative to pre-alloyed powders in metal additive manufacturing due to the wider range of alloys producible with them and the cost savings from not developing novel feedstock. In this study, in situ alloying and concurrent microstructure evolution during SLM are investigated by performing SLM on a BE Ti-185 powder while tracking the surface temperatures via Infra-red imaging and phase transforma- tion via synchrotron X-ray Diffraction. We then performed post-mortem electron microscopy (Backscatter Electron imaging, Energy Dispersive X-ray Spectroscopy and Electron Backscatter Diffraction) to further gain insight into microstructure development. We show that although exothermic mixing aids the melting process, laser melting results only in a mixture of alloyed and unmixed regions. Full alloying and thus a consistent microstructure is only achieved through further thermal cycling in the heat-affected zone.
Xu C, Wigger T, Azeem MA, et al., 2021, Paper Unraveling compacted graphite evolution during solidification of cast iron using in-situ synchrotron X-ray tomography, CARBON, Vol: 184, Pages: 799-810, ISSN: 0008-6223
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- Citations: 5
Soundarapandiyan G, Johnston C, Khan RHU, et al., 2021, The effects of powder reuse on the mechanical response of electron beam additively manufactured Ti6Al4V parts, Additive Manufacturing, Vol: 46, Pages: 1-14, ISSN: 2214-8604
High cost of metal powders has increased the demand for recycling of unmelted powder in electron beam powder bed fusion additive manufacturing process. However, powder characteristics are likely to change during manufacturing, recovery and reuse. It is important to track the evolution of powder characteristics at different stages of recycling to produce components with consistent properties. The present work evaluates the changes in Ti6Al4V powder properties during manufacturing by characterising powder particles at different locations in the powder bed; recovery and reuse, through evaluating the effects of the powder recovery system and sieving for 10 build cycles. Heterogeneous powder degradation occurred during manufacturing with the particles closer to the melt zone showing higher oxygen content and thicker α laths with β phase boundaries. Most of them had a hard-sintered and agglomerated powder morphology in contrast to particles at the edges of the powder bed. Recovery and reuse resulted in a refined particle size distribution, but only marginal change in powder morphology. The increased oxygen caused a slight increase in the yield and tensile strengths of the build. The effect of powder reuse on material elongation, hardness and Charpy impact energy was negligible. The high cycle fatigue performance deteriorated with reuse due to the increased lack-of-fusion defects. This might be attributed to the voids formed in the powder bed due to decrease in the number of fine particles coupled with an increase in the number of high-aspect ratio particles.
Huang Y, Fleming T, Clark S, et al., 2021, Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing
<jats:title>Abstract</jats:title> <jats:p>Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, the dynamics of keyhole porosity formation, i.e., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyhole and bubble behaviours, quantifying their formation mechanisms. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also transition keyhole regimes, created by high laser power-velocity conditions, causing fast radial keyhole fluctuations (~ 10 kHz); (ii) transition regime collapse tends to occur part way up the rear-wall; and (iii) immediately after keyhole collapse, the bubble grows as pressure equilibrates then shrinks due to metal-vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The physics revealed here can guide the development of real-time monitoring and control systems for keyhole porosity.</jats:p>
Ma L, Fauchille A-L, Ansari H, et al., 2021, Linking multi-scale 3D microstructure to potential enhanced natural gas recovery and subsurface CO2 storage for Bowland Shale, UK, Energy and Environmental Science, Vol: 14, Pages: 4481-4498, ISSN: 1754-5692
Injection of CO2 into shale reservoirs to enhance gas recovery and simultaneously sequester greenhouse gases is a potential contributor towards the carbon-neutral target. It offers a low-carbon, low-cost, low-waste and large-scale solution during energy transition period. A precondition to efficient gas storage and flow is a sound understanding of how the shale’s micro-scale impacts on these phenomena. However, the heterogeneous and complex nature of shales limits the understanding of microstructure and pore systems, making feasibility analysis challenging. This study qualitatively and quantitatively investigates the Bowland shale microstructure in 3D at five length scales: artificial fractures at 10-100 µm scale, matrix fabric at 1-10 µm-scale, individual mineral grains and organic matter particles at 100 nm- 1 µm scale, macropores and micro-cracks at 10-100 nm scale and organic matter and mineral pores at 1-10 nm-scale. For each feature, the volume fraction variations along the bedding normal orientation, the fractal dimensions and the degrees of anisotropy were analysed at all corresponding scales for a multi-scale heterogeneity analysis. The results are combined with other bulk laboratory measurements, including supercritical CO2 and CH4 adsorption at reservoir conditions, pressure-dependent permeability and nitrogen adsorption pore size distribution, to perform a comprehensive analysis on the storage space and flow pathways. A cross-scale pore size distribution, ranging from 2 nm to 3 µm, was calculated with quantified microstructure. The cumulative porosity is calculated to be 8%. The cumulative surface area is 17.6 m2/g. A model of CH4 and CO2 flow pathways and storage with quantified microstructure is presented and discussed. The feasibility of simultaneously enhanced gas recovery and subsurface CO2 storage in Bowland shale, the largest shale gas potential formation in the UK, was assessed based using multi-scale microstructure
Wang K, Chandler M, Wang J, et al., 2021, Time-lapse nanometre-scale 3D synchrotron imaging and image-based modelling of the response of shales to heating, International Journal of Coal Geology, Vol: 244, Pages: 1-17, ISSN: 0166-5162
The development of pore and fracture networks at the nano-scale as a response to heating can reveal coupled physical relationships relevant to several energy applications. A combination of time-lapse 3D imaging and finite-element modelling (FEM) was performed on two typical thermally immature shale samples, Kimmeridge Clay and Akrabou shale, to investigate thermal response at the nm-scale for the first time. Samples were imaged using Transmission X-ray Microscopy (TXM) with a voxel resolution of 34 nm at the I13–2 beamline at Diamond Light source, UK. Images were taken after heating to temperatures of 20 °C, 300 °C, 350 °C and 400 °C. The initiation of nano-pores within individual minerals and organic matter particles were observed and quantified alongside the evolution from nano-pores to micro-fractures. The major expansion of pore-volume occurred between 300 and 350 °C in both samples, with the pores elongating rapidly along the organic-rich bedding. The internal pressures induced by organic matter transformation influenced the development of microfractures. Mechanical properties and strain distributions within these two samples were modelled under a range of axial stresses using FEM. The results show that the overall stiffness of the shale reduced during heating, despite organic matter becoming stiffer. The varied roles of ductile (e.g., clay minerals, organic matter) and brittle materials (e.g., calcite, pyrite) within the rock matrix are also modelled and discussed. The configurations of organic matter, mineral components, porosity and connectivity impact elastic deformation during shale pyrolysis. This work extends our understanding of dynamic coupled processes of microstructure and elastic deformation in shales to the nm-scale, which also has applications to other subsurface energy systems such as carbon sequestration, geothermal and nuclear waste disposal.
Bhagavath S, Gong Z, Wigger T, et al., 2021, Role of the local stress systems on microstructural inhomogeneity during semisolid injection, Acta Materialia, Vol: 214, Pages: 1-11, ISSN: 1359-6454
High pressure metal die casting is an extremely dynamic process with widely ranging cooling rates and intensifying pressures, resulting in a wide range of solid fractions and deformation rates simultaneously existing in the same casting. These process parameters and their complex interplay dictate the formation of microstructural solidification defects. In this study, fast synchrotron X-ray imaging experiments simulating high pressure die casting of aluminium alloys were conducted to investigate the effect of solid fraction, loading conditions and semisolid flow on local microstructural inhomogeneity. While most of the existing literature in this field reports speeds up to 10 µm/s for in situ deformation, the present work captures much faster filling and solidification, at speeds closer to 100 µm/s and at different solid fractions. Semisolid deformation of low solid fractions reveals two typical microstructural features: (i) coarser grains in the middle and finer ones near the walls, and (ii) remelting near the solid-liquid interface due to Cu enrichment in the liquid by the flow. Ex situ scans and digital image correlation analysis of the higher solid fraction samples reveal a porosity formation mechanism based on the local state of stresses, microstructure and feeding. Four different characteristics were identified: (i) plug flow, (ii) dead zone (densified mush), (iii) shear and (iv) bulk zones. These insights will be used to develop zone-specific strategies for the numerical modelling of defect formation during die casting.
Le Gall N, Arzilli F, La Spina G, et al., 2021, In situ quantification of crystallisation kinetics of plagioclase and clinopyroxene in basaltic magma: Implications for lava flow, Earth and Planetary Science Letters, Vol: 568, Pages: 1-11, ISSN: 0012-821X
Crystallisation is a complex process that significantly affects the rheology of magma, and thus the flow dynamics during a volcanic eruption. For example, the evolution of crystal fraction, size and shape has a strong impact on the surface crust formation of a lava flow, and accessing such information is essential for accurate modelling of lava flow dynamics. To investigate the role of crystallisation kinetics on lava flow behaviour, we performed real-time, in situ synchrotron X-ray microtomography, studying the influence of temperature-time paths on the nucleation and growth of clinopyroxene and plagioclase in an oxidised, nominally anhydrous basaltic magma. Crystallisation experiments were performed at atmospheric pressure in air and temperatures from 1250 °C to 1100 °C, using a bespoke high-temperature resistance furnace. Depending on the cooling regime (single step versus continuous), two different crystal phases (either clinopyroxene or plagioclase) were produced, and we quantified their growth from both global and individual 3D texture analyses. The textural evolution of charges suggests that suppression of crystal nucleation is due to changes in the melt composition with increasing undercooling and time. Using existing viscosity models, we inferred the effect of crystals on the viscosity evolution of our crystal-bearing samples to trace changes in rheological behaviour during lava emplacement. We observe that under continuous cooling, both the onsets of the pāhoehoe-‘a‘ā transition and of non-Newtonian behaviour occur within a shorter time frame. With varying both temperature and time, we also either reproduced or approached the clinopyroxene and plagioclase phenocryst abundances and compositions of the Etna lava used as starting material, demonstrating that real-time synchrotron X-ray tomography is an ideal approach to unravel the final solidification history of basaltic lavas. This imaging technology has indeed the potential to provide i
Leung CLA, Elizarova I, Isaacs M, et al., 2021, Enhanced near-infrared absorption for laser powder bed fusion using reduced graphene oxide, Applied Materials Today, Vol: 23, Pages: 1-10, ISSN: 2352-9407
Laser powder bed fusion (LPBF) is a revolutionary manufacturing technology that fabricates parts with unparalleled complexity, layer-by-layer. However, there are limited choices of commercial powders for LPBF, constrained partly by the laser absorbance, an area that is not well investigated. Carbon additives are commonly used to promote near infra-red (NIR) absorbance of the powders but their efficiency is limited. Here, we combine operando synchrotron X-ray imaging with chemical characterisation techniques to elucidate the role of additives on NIR absorption, melt track and defect evolution mechanisms during LPBF. We employ a reduced graphene oxide (rGO) additive to enable LPBF of low NIR absorbance powder, SiO2, under systematic build conditions. This work successfully manufactured glass tracks with a high relative density (99.6%) and overhang features (> 5 mm long) without pre/post heat treatment. Compared to conventional carbon additives, the rGO increases the powder's NIR absorbance by ca. 3 times and decreases the warpage and porosity in LPBF glass tracks. Our approach will dramatically widen the palette of materials for laser processing and enable existing LPBF machines to process low absorbance powder, such as SiO2, using a NIR beam.
Karagadde S, Leung CLA, Lee PD, 2021, Progress on in situ and operando X-ray imaging of solidification processes, Materials, Vol: 14, Pages: 1-25, ISSN: 1996-1944
In this review, we present an overview of significant developments in the field of in situ and operando (ISO) X-ray imaging of solidification processes. The objective of this review is to emphasize the key challenges in developing and performing in situ X-ray imaging of solidification processes, as well as to highlight important contributions that have significantly advanced the understanding of various mechanisms pertaining to microstructural evolution, defects, and semi-solid deformation of metallic alloy systems. Likewise, some of the process modifications such as electromagnetic and ultra-sound melt treatments have also been described. Finally, a discussion on the recent breakthroughs in the emerging technology of additive manufacturing, and the challenges thereof, are presented. Vi
Rowson M, Bennett CJ, Azeem MA, et al., 2021, Observation of microstructure evolution during inertia friction welding using in-situ synchrotron X-ray diffraction, Journal of Synchrotron Radiation, Vol: 28, Pages: 790-803, ISSN: 0909-0495
The widespread use and development of inertia friction welding is currently restricted by an incomplete understanding of the deformation mechanisms and microstructure evolution during the process. Understanding phase transformations and lattice strains during inertia friction welding is essential for the development of robust numerical models capable of determining optimized process parameters and reducing the requirement for costly experimental trials. A unique compact rig has been designed and used in-situ with a high-speed synchrotron X-ray diffraction instrument to investigate the microstructure evolution during inertia friction welding of a high-carbon steel (BS1407). At the contact interface, the transformation from ferrite to austenite was captured in great detail, allowing for analysis of the phase fractions during the process. Measurement of the thermal response of the weld reveals that the transformation to austenite occurs 230 °C below the equilibrium start temperature of 725 °C. It is concluded that the localization of large strains around the contact interface produced as the specimens deform assists this non-equilibrium phase transformation.
Chen Y, Clark SJ, Sinclair L, et al., 2021, Synchrotron X-ray imaging of directed energy deposition additive manufacturing of titanium alloy Ti-6242, Additive Manufacturing, Vol: 41, Pages: 1-9, ISSN: 2214-8604
Directed Energy Deposition Additive Manufacturing (DED-AM) is transformative for the production of larger, geometrically complex metallic components. However, the mechanical properties of titanium alloy DED-AM components do not always reach their full potential due to microstructural features including porosity and regions of lack of fusion. Using in situ and operando synchrotron X-ray imaging we gain insights into key laser-matter interaction and microstructural feature formation mechanisms during DED-AM of Ti-6242. Analysis of the process conditions reveals that laser power is dominant for build efficiency while higher traverse speed can effectively reduce lack of fusion regions. We also elucidate the mechanisms underlying several physical phenomena occurring during the deposition of titanium alloys, including the formation of a saddle-shaped melt pool and pore pushing. The findings of this work clarify the transient kinetics behind the DED-AM of titanium alloys and can be used as a guide for optimising industrial additive manufacturing processes.
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