Synchrotron Radiography Research Articles

Growth Behaviors of Bubbles and Intermetallic Compounds in Solidifying Al-5 wt.% Mn Alloy

The growth behaviors of hydrogen bubbles and intermetallic compounds (IMCs) during solidification of an Al-5 wt.% Mn alloy was investigated by synchrotron radiography. Results show that bubble collapse can increase hydrogen concentration in nearby Al melt, thus facilitating the formation and growth of new bubbles. Under the interference of Al6Mn IMCs, the growth method of an individual bubble is changed from a Gaussian distribution to a linear model. Al6Mn crystal growth can be divided into three stages: first an isotropic spherical crystal appears, then it evolves into primary branches, and eventually forms an irregular octahedron.

Growth and pinch-off of sidearm necks: a model of dendrite fragmentation

Dendrite fragmentation commonly occurs by pinch-off of sidearms at the narrow neck with the parent stem. Comprehensive measurements of the local neck dynamics are performed using in-situ synchrotron radiography experiments in which a flat sample of a Ga–35wt%. In alloy is solidified under both steady and transient growth conditions with minimal effects of melt convection. The measurements reveal two characteristic limits where the neck radius follows universal self-similar t1/3 power laws, with a positive rate constant in the limit of steady growth and a negative rate constant in the isothermal pinch-off limit. The temporal power law for steady growth found here relates the sidearm neck radii to the tip radius of the primary dendrite stem, and the neck radius probability density distribution is shown to be symmetric. For the more general case of decelerated growth, it is observed that the neck initially widens along the steady growth limit, is then increasingly limited by the pinching tendency, and for sufficiently large decelerations converges ultimately to the pinch-off limit. A dynamical model is derived that predicts the behavior of the sidearm neck radius under arbitrary decelerating growth conditions. The highly variable nature of dendrite fragmentation is explained by the stochastic properties of the initial sidebranch development process. The model can be used to estimate the number of dendrite fragments forming during a certain time interval at any location behind the primary tips.

Revealing the Mechanisms of Smoke during Electron Beam–Powder Bed Fusion by High-Speed Synchrotron Radiography

Electron beam–powder bed fusion (PBF-EB) is an additive manufacturing process that utilizes an electron beam as the heat source to enable material fusion. However, the use of a charge-carrying heat source can sometimes result in sudden powder explosions, usually referred to as “Smoke”, which can lead to process instability or termination. This experimental study investigated the initiation and propagation of Smoke using in situ high-speed synchrotron radiography. The results reveal two key mechanisms for Smoke evolution. In the first step, the beam–powder bed interaction creates electrically isolated particles in the atmosphere. Subsequently, these isolated particles get charged either by direct irradiation by the beam or indirectly by back-scattered electrons. These particles are accelerated by electric repulsion, and new particles in the atmosphere are produced when they impinge on the powder bed. This is the onset of the avalanche process known as Smoke. Based on this understanding, the dependence of Smoke on process parameters such as beam returning time, beam diameter, etc., can be rationalized.

Streamlined synthesis of superstructure Ni-benzimidazole MOFs: Glucose electrochemical analysis

The design and synthesis of efficient electrochemical sensors are crucial transformation technologies in electrochemistry. We successfully synthesize a three-dimensional Ni-metal–organic framework (MOF) nanostructured material with a superior architecture using benzimidazole and nickel nitrate as precursors at room temperature which is being applied in glucose electrochemical sensors. The reaction mechanism of M-6 during glucose detection is thoroughly studied using various characterization techniques, such as in situ Raman spectroscopy, in situ ultraviolet–visible spectrophotometry, synchrotron radiography, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The research findings demonstrate that the M-6 material exhibits high sensitivity for glucose detection, with a sensitivity of 2199.88 mA M−1 cm−2. This study provides an important reference for designing more efficient electrochemical reaction systems and optimizing material performance. Furthermore, the superstructural design offers new ideas and possibilities for the development and application of similar materials.

Visualizing the Effect of Temperature on Carbonate Salt Production in CO2 Electrolysis

Carbon dioxide (CO2) electrolysis is a novel and promising technology to tackle anthropogenic climate change by reducing our dependency on fossil fuels and creating a sustainable carbon cycle. However, current CO2 electrolysis suffers from low CO2 reduction reaction (CO2RR) selectivity and rapid gas diffusion electrode (GDE) degradation and flooding due to carbonate precipitation. As the hydrophilic precipitate accumulates in the porous structure of the cathode GDE, the liquid anolyte invades the pores, blocking the catholyte from reaching the catalyst layer. This effect promotes the adverse hydrogen evolution reaction and thus decreases the CO2RR selectivity (1). Current literature focuses on limiting carbonate precipitate formation as opposed to understanding the factors affecting its growth (2). While carbonate precipitation is dependent on the specific electrolyte in a flow cell, the impact of parameters, such as operating temperature and GDE porosity, on the nature of carbonate precipitation still need to be investigated (3).In this study, we examine the relationship between cell temperature with carbonate precipitate accumulation. A zero-gap alkaline membrane electrode assembly (MEA) was used with potassium carbonate as the anolyte and humidified CO2 as the catholyte. Electrochemical impedance spectroscopy was used to calculate the activation, ohmic, and mass transport losses of the cell before and after a constant current density phase where faradaic efficiency was measured to quantify the CO2RR selectivity degradation due to salt accumulation. Furthermore, to characterize precipitate growth, the cathode GDEs were imaged before and after electrochemical testing using scanning electron microscopy (SEM) and wavelength dispersive spectroscopy (WDS). To quantify precipitate-driven flooding over operation time, identical MEAs were imaged using operando X-ray synchrotron radiography over a range of temperatures. Through-plane images of the operating cell were processed to find the electrolyte thickness in the cathode GDE as a function of time. Radiography results revealed progressive, cyclical flooding as well as preferential gas pathways. Moreover, after four hours of constant current operation and at a cell temperature of 60℃, the catalyst layer exhibited large amounts of uniformly distributed precipitates, while the GDE contained large, localized precipitate crystals. This indicates that at high temperatures, carbonate precipitates significantly block the catalyst layer and cause flooding into the substrate layer. This work provides new insight into the effect of temperature on carbonate precipitate buildup, deepening the understanding of the mechanism responsible for precipitate degradation. M. E. Leonard, L. E. Clarke, A. Forner-Cuenca, S. M. Brown, and F. R. Brushett, ChemSusChem, 13 (2020).Y. Xu et al., ACS Energy Lett, 6, 809–815 (2021).E. R. Cofell, U. O. Nwabara, S. S. Bhargava, D. E. Henckel, and P. J. A. Kenis, ACS Appl Mater Interfaces, 13, 15132–15142 (2021).

In situ study on the oscillation of mobile droplets and force analysis during the directional solidification of Al-Bi alloy

During solidifications of immiscible alloys, the motion of droplets at the solid/liquid (S/L) interface is generally driven by dragging force, gravity force, repulsion force of interface, and thermal-solutal Marangoni force. However, there is few in situ study investigating kinetics behavior to analyze the forces on droplets. The mechanism of droplet motion remains unclear due to the unavailability or uncertainty of the effect of convection and solutal Marangoni force on droplet behavior. In this study, directional solidification of immiscible Al-Bi alloy was observed via synchrotron radiography, and the horizontal oscillation of droplets at S/L interface was detected for the first time. Forces, especially solutal Marangoni force, were calculated based on the in situ measured radius of droplets and thermal-solutal gradients. The experimental results cannot be reasonably explained by the previous analysis model which neglects melt convection. The non-negligible effect of flow on droplet motion was demonstrated, and the force balance of droplet both vertically and horizontally can be obtained considering a lift force of 6.39 × 10−9 N and a modified solute-related parameter dσdc of 0.45−0.65 J m−2, respectively.

Contribution of Ni microalloying to Cu dissolution in In–35Sn/Cu solder joints after multiple reflows

Multiple reflow processes are utilized in complex electronic devices with multi-layered PCBs, stacked components, or 3D configurations to ensure reliable connections and minimize defects. A systematic analysis was performed to examine the influence of multiple reflow cycles on the microstructure and interfacial reaction of In–35Sn microalloyed with 0.05 wt% Ni on a Cu substrate. The size of the primary IMC particles in the In–35Sn solder was observed during multiple reflow process on Cu using in-situ real-time synchrotron radiography imaging. Multiple reflow soldering caused the primary Cu(In,Sn)2 and interfacial Cu3(Sn,In) layer to coarsen. The Ni was present in the primary (Cu,Ni)1(In,Sn)2 particles and interfacial (Cu,Ni)3(Sn,In) layer and caused grain size refinement of the IMCs after multiple reflow soldering. The shear test showed that there was a minor increase in shear force after multiple reflows. However, the shear energy decreased, indicating a more notable decrease in displacement to fracture rather than shear force which suggests a higher tendency towards ductile fracture.

Modeling the Influence of Electrolyte Distribution in Silver Gas Diffusion Electrodes for CO2 Electroreduction

The chemical industry has been increasingly focusing on reducing CO2 emissions in recent years. One promising way to do this is via CO2 electroreduction, a technology that does not only reduce CO2 emissions but also allows CO2 to be used as a source of carbon for making commodity chemicals. A key to efficient CO2 electroreduction is the electrolyte management inside the porous system of gas diffusion electrodes (GDEs). Flooding of electrodes can severely hinder mass transfer and thereby prevent CO2 reduction, giving rise to the parasitic hydrogen evolution reaction [1]. Although the measurement of electrolyte saturation is possible through methods like synchrotron radiography, these measurements are highly expensive, and thus not always readily available [2]. Modeling can help here to better understand the influence of electrolyte saturation, and predict possible measures for improving the process.In most CO2 electrolysis models in literature, the electrolyte saturation is a fixed parameter [3,4]. This assumption does not always hold true, as effects like electro-wetting change the wetting behavior of the GDE for different operating conditions. In this new modeling approach, correlations between capillary pressure and saturation, as well as between contact angle and potential are introduced, making the description of these changes possible. These correlations are gained from pore network simulations of the electrode material reconstructed from FIB-SEM measurements. The correlations are implemented in a one dimensional continuum model that includes discretized balance spaces for liquid and gas phase inside the porous system of the GDE, ideally mixed gas and electrolyte bulk spaces on the respective sides of the electrode, as well as boundary layers between bulk and electrode. Homogeneous reactions of the carbonate buffer system in the liquid phase and electrochemical reactions inside the GDE are considered. Transport of species is calculated using Maxwell-Stefan diffusion, migration in the potential field resulting from the Nernst-Planck equation, and flow through the porous electrode according to Darcy’s law. Additionally phase transfer processes like gas dissolution and evaporation of water are considered. The GDE model is validated with experimental data for CO2 electrolysis, enabling insights into the processes in the GDE and elucidating the influence of electrolyte saturation on the CO2 mass transfer.[1] Bienen, F., Paulisch, M. C., Mager, T., Osiewacz, J., Nazari, M., Osenberg, M., Ellendorff, B., Turek, T., Nieken, U., Manke, I., & Friedrich, K. A., Investigating the electrowetting of silver‐based gas‐diffusion electrodes during oxygen reduction reaction with electrochemical and optical methods. Electrochemical Science Advances (2022) e2100158.[2] Hoffmann, H., Paulisch, M. C., Gebhard, M., Osiewacz, J., Kutter, M., Hilger, A., Arlt, T., Kardjilov, N., Ellendorff, B., Beckmann, F., Markötter, H., Luik, M., Turek, T., Manke, I., & Roth, C., Development of a Modular Operando Cell for X-ray Imaging of Strongly Absorbing Silver-Based Gas Diffusion Electrodes. Journal of The Electrochemical Society 169 (2022) 044508.[3] Löffelholz, M., Osiewacz, J., Lüken, A., Perrey, K., Bulan, A., & Turek, T., Modeling electrochemical CO2 reduction at silver gas diffusion electrodes using a TFFA approach. Chemical Engineering Journal 435 (2022) 134920.[4] Weng, L.-C., Bell, A. T., & Weber, A. Z., Modeling gas-diffusion electrodes for CO2 reduction. Physical Chemistry Chemical Physics 25 (2018) 16973–16984. Figure 1

Synchrotron radiography of Richtmyer–Meshkov instability driven by exploding wire arrays

We present a new technique for the investigation of shock-driven hydrodynamic phenomena in gases, liquids, and solids in arbitrary geometries. The technique consists of a pulsed power-driven resistive wire array explosion in combination with multi-MHz synchrotron radiography. Compared to commonly used techniques, it offers multiple advantages: (1) the shockwave geometry can be shaped to the requirements of the experiment, (2) the pressure (P > 300 MPa) generated by the exploding wires enables the use of liquid and solid hydrodynamic targets with well-characterized initial conditions (ICs), (3) the multi-MHz radiography enables data acquisition to occur within a single experiment, eliminating uncertainties regarding repeatability of the ICs and subsequent dynamics, and (4) the radiographic measurements enable estimation of compression ratios from the x-ray attenuation. In addition, the use of a synchrotron x-ray source allows the hydrodynamic samples to be volumetrically characterized at a high spatial resolution with synchrotron-based microtomography. This experimental technique is demonstrated by performing a planar Richtmyer–Meshkov instability (RMI) experiment on an aerogel–water interface characterized by Atwood number A0∼−0.8 and Mach number M∼1.5. The qualitative and quantitative features of the experiment are discussed, including the energy deposition into the exploding wires, shockwave generation, compression of the interface, startup phase of the instability, and asymptotic growth consistent with Richtmyer's impulsive theory. Additional effects unique to liquids and solids—such as cavitation bubbles caused by rarefaction flows or initial jetting due to small perturbations—are observed. It is also demonstrated that the technique is not shape dependent by driving a cylindrically convergent RMI experiment.

In situ observation of the specific nucleation behavior of grains during the solidification of Al alloy inoculated by Sc

The specific behavior of grains nucleation on primary Al3Sc particles and its effects on subsequent nucleation events have not been uncovered by previous ex situ analysis. Here, the real-time grains nucleation during the solidification of Al-10Cu alloy inoculated by Sc is first observed via synchrotron radiography. The results show that grains can nucleate on one face and grow along other faces of relatively large cuboid Al3Sc particles, leading to the incomplete engulfment of particles. Hence, two or more grains can nucleate on the same Al3Sc particle and grains can easily detach from particles, both of which promote grains nucleation during solidification. The discoveries modify the previous common view on the role of particles between grain boundaries and enlighten the better application of flow-induced technologies to the refinement of Al alloys inoculated by Sc.

In situ chamber for studying battery failure using high-speed synchrotron radiography.

The investigation of lithium-ion battery failures is a major challenge for personnel and equipment due to the associated hazards (thermal reaction, toxic gases and explosions). To perform such experiments safely, a battery abuse-test chamber has been developed and installed at the microtomography beamline ID19 of the European Synchrotron Radiation Facility (ESRF). The chamber provides the capability to robustly perform in situ abuse tests through the heat-resistant and gas-tight design for flexible battery geometries and configurations, including single-cell and multi-cell assemblies. High-speed X-ray imaging can be complemented by supplementary equipment, including additional probes (voltage, pressure and temperature) and thermal imaging. Together with the test chamber, a synchronization graphical user interface was developed, which allows an initial interpretation by time-synchronous visualization of the acquired data. Enabled by this setup, new meaningful insights can be gained into the internal processes of a thermal runaway of current and future energy-storage devices such as lithium-ion cells.

Unveiling the Inhomogeneous Dissolution Behavior of Polycrystalline Substrate at the Liquid–Solid Bimetal Interface by Synchrotron Radiography and First-Principles Calculations

Unveiling the Inhomogeneous Dissolution Behavior of Polycrystalline Substrate at the Liquid–Solid Bimetal Interface by Synchrotron Radiography and First-Principles Calculations

A Modular in-Situ Cell to Monitor Gas Diffusion Electrodes during ORR and CO2RR

Metal-based gas diffusion electrodes (GDE) are utilized to achieve high current densities during the reaction in energy conversion systems, such as chlor-alkali electrolysis or the electrochemical reduction of carbon dioxide. By intense contact between the liquid and the gas phase with the catalytically active surfaces within the metallic electrodes, industrially required current densities can be accomplished. Their almost bulk-like silver structures with the 3D porous design and the strong absorption of the extended material make radiographic measurements extremely demanding. To receive in-depth information on electrolyte intrusion into the electrode's porous structure and the distribution during electrochemical measurements, lab-based and synchrotron radiography allows for monitoring this process operando 1, 2 .In this work, we describe the development of a cell design that can be modularly adapted and successfully used to monitor both the ORR and the CO2RR as exemplary and currently very relevant examples of gas-liquid reactions. The applied half-cell set-up designed for ORR allowed for operando synchrotron radiation measurements at electrochemically stable operation at viable industrial conditions and current densities to follow the electrolyte distribution within Ag-based GDE during chlor-alkali-electrolysis. By adding one additional electrolyte compartment, extending the X-ray window, and implementing an anion exchange membrane, the in-house built half-cell set-up designed for operando synchrotron radiation measurements of ORR, was converted into a full-cell set-up for imaging CO2RR of strongly absorbing metal-based GDEs. With the reported cell design, we were able to observe the electrolyte distribution within GDEs during cell operation at technically relevant current densities for CO2RR up to 300 mAcm-2 (Figure 1). By high-resolution synchrotron radiation operando measurements, we demonstrated crystallization of electrolyte caused by the hydrophobic character of the GDE. At high overpotentials, hydrogen evolution reaction caused blockade of the Ag-based GDE, resulting in declining current densities, which could be imaged and monitored during realistic potentiostatic operation. M. C. Paulisch, M. Gebhard, D. Franzen, A. Hilger, M. Osenberg, S. Marathe, C. Rau, B. Ellendorff, T. Turek, C. Roth and I. Manke, ACS Appl. Energy Mater., 4(8), 7497–7503 (2021).M. Gebhard, M. Paulisch, A. Hilger, D. Franzen, B. Ellendorff, T. Turek, I. Manke and C. Roth, Materials (Basel, Switzerland), 12(8) (2019). Figure 1

(Keynote) Pro and Con of Bi-Decorated Carbon Felts in Vanadium Redox Flow Batteries

Carbon felts are commonly utilized electrodes in vanadium flow batteries due to their low cost, light weight, good electronic conductivity, and chemical inertness. In contrast, their activity in catalyzing the vanadium redox reactions is less remarkable. In particular at the negative side, where V3+ reduction competes with the parasitic hydrogen evolution reaction (HER) at low potentials. In the literature, the addition of Bi3+ into the electrolyte [1] or its deposition on the felts has been suggested as a remedy. However, it is not clear yet, whether the Bi decoration remains stable with time and cycling and which mechanisms are responsible for the observed performance increase.The aim of this work is therefore to unravel more details about the catalyzing effect of Bi and its stability on the cell level. To this effect, the electrode kinetics with and without Bi decoration were studied comparing results obtained using Friedl’s method [2] with cyclic voltammetry (CV) data analyzed by the Polarographica curve fitting routine [3]. This approach can also be generalized to obtain precise kinetic information with other decorating metals.We furthermore applied negative dynamic hydrogen bubble templating (DHBT) deposition as an interesting way to coat commercially available carbon felts with a structured metallic layer of high surface area. Using this strategy, a significant positive effect was observed. However, the drying parameters and post-processing of the felts are important parameters which severely affect the final performance.In order to study the stability of Bi deposits in realistic battery experiments, in-situ synchrotron radiography has been used to monitor the Bi-decorated felts during charge-discharge cycles [4]. The figure demonstrates the effect of different flow rates on the Bi deposition patterns. Dark spots show metal-decorated areas within the felts at flow rates of 5 mlmin-1 (left), 15 mlmin-1 (middle) and 25 mlmin-1 (right). It can be easily seen that the operation conditions influence the felt decoration significantly, while Bi deposits dissolve and deposit during the charge-discharge routine. Further studies will be necessary to find out a) whether different deposit positions affect the performance enhancement and b) if DHBT-Bi remains more stable under operating conditions.In our presentation, we will not only focus on the materials, but also highlight techniques especially suitable for the stuctural and electrochemical analysis of felt electrodes.[1] B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. Wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, W. Wang, Bismuth Nanoparticle Decorating Graphite Felt as a High-Performance Electrode for an All-Vanadium Redox Flow Battery, Nano Letters 13(3) (2013) 1330-1335.[2] J. Friedl and U. Stimming, Determining Electron Transfer Kinetics at Porous Electrodes, Electrochim. Acta 227 (2017) 235–245.[3] T. Tichter, J. Schneider, D. Andrae, M. Gebhard, and C. Roth, Universal algorithm for simulating and evaluating cyclic voltammetry atmacroporous electrodes by considering random arrays of microelectrodes, ChemPhysChem 21 (2019) 428 –441.[4] M. Gebhard, T. Tichter, J. Schneider, J. Mayer, A. Hilger, M. Osenberg, M. Rahn, I. Manke, C. Roth J. Power Sources 478 (2020) 228695. Figure 1

In−situ measurements of dendrite tip shape selection in a metallic alloy

The size and shape of the primary dendrite tips determine the principal length scale of the microstructure evolving during solidification of alloys. In-situ X-ray measurements of the tip shape in metals have been unsuccessful so far due to insufficient spatial resolution or high image noise. To overcome these limitations, high-resolution synchrotron radiography and advanced image processing techniques are applied to a thin sample of a solidifying Ga-35wt.%In alloy. Quantitative in-situ measurements are performed of the growth of dendrite tips during the fast initial transient and the subsequent steady growth period, with tip velocities ranging over almost two orders of magnitude. The value of the dendrite tip shape selection parameter is found to be $\sigma^* = 0.0768$, which suggests an interface energy anisotropy of $\varepsilon_4 = 0.015$ for the present Ga-In alloy. The non-axisymmetric dendrite tip shape amplitude coefficient is measured to be $A_4 \approx 0.004$, which is in excellent agreement with the universal value previously established for dendrites.

Sinter formation during directed energy deposition of titanium alloy powders

During directed energy deposition (DED) additive manufacturing, powder agglomeration and sintering can occur outside of the melt pool when using titanium alloy powders. Using in situ synchrotron radiography we investigate the mechanisms by which sintering of Ti6242 powder occurs around the pool, performing a parametric study to determine the influence of laser power and stage traverse speed on sinter build-up. The results reveal that detrimental sinter can be reduced using a high laser power or increased stage traverse speed, although the latter also reduces deposition layer thickness. The mechanism of sinter formation during DED was determined to be in-flight heating of the powder particles in the laser beam. Calculations of particle heating under the processing conditions explored in this study confirm that powder particles can reasonably exceed 700 °C, the threshold for Ti surface oxide dissolution, and thus the powder is prone to sintering if not incorporated into the melt pool. The build-up of sinter powder layer on deposit surfaces led to lack of fusion pores. To mitigate sinter formation and its detrimental effects on DED component quality, it is essential that the powder delivery spot area is smaller than the melt pool, ensuring most powder lands in the melt pool.

Development of a Modular Operando Cell for X-ray Imaging of Strongly Absorbing Silver-Based Gas Diffusion Electrodes

Metal-based gas diffusion electrodes are utilized in chlor-alkali electrolysis or electrochemical reduction of carbon dioxide, allowing the reaction to proceed at high current densities. In contrast to planar electrodes and predominantly 2D designs, the industrially required high current densities can be achieved by intense contact between the gas and liquid phase with the catalytically active surfaces. An essential asset for the knowledge-based design of tailored electrodes is therefore in-depth information on electrolyte distribution and intrusion into the electrode’s porous structure. Lab-based and synchrotron radiography allow for monitoring this process operando. Herein, we describe the development of a cell design that can be modularly adapted and successfully used to monitor both the oxygen reduction reaction and the electrochemical reduction of CO2 as exemplary and currently very relevant examples of gas-liquid reactions by only minor modifications to the cell set-up. With the reported cell design, we were able to observe the electrolyte distribution within the gas diffusion electrode during cell operation in realistic conditions.

Understanding the Rheological Transitions in Semi-Solid Alloys by a Combined <i>In Situ</i> Imaging and Granular Micromechanics Modeling Approach

To gain better understanding of rheological transitions from suspension flow to granular deformation and shear cracking, this research conducted shear-deformation on globular semi-solid Al-Cu alloys to study the rheological behavior of semi-solid as a function of solid fraction (38% - 85%) and shear rate (10-4 – 10-1 s-1) under real-time synchrotron radiography observation. By analyzing 17 X-ray imaging datasets, we define three rheological transitions: (i) the critical solid fraction from a suspension to a loosely percolating assembly; (ii) from the net contraction of a loose assembly to the net dilation of a densely packed assembly, and (iii) to shear cracking at high solid fraction and shear rate. Inspired by in-situ observations of semi-solid deformation showing a disordered assembly of percolating crystals in partially-cohesive contact with liquid flow, we reproduced a two-phase sample using the coupled lattice Boltzmann method-discrete element method (LBM-DEM) simulation approach for granular micromechanical modeling. In DEM, each globular Al grain is represented by a discrete element, and the flow of interstitial liquid is solved by LBM. The LBM-DEM simulations show quantitative agreement of semi-solid strain localization with the experiments and are used to explore the components involved in the shear rate dependence of the transitions, and the role of liquid pressure on the initiation of shear cracking.

In situ imaging of three dimensional freeze printing process using rapid x-ray synchrotron radiography.

Three dimensional freeze printing (3DFP) combines the advantages of freeze casting and additive manufacturing to fabricate multifunctional aerogels. Freeze casting is a cost-effective, efficient, and versatile method capable of fabricating micro-scale porous structures inside the aerogels for many different applications. The 3DFP provided the capability of fabricating highly customized geometries with controlled microporous structures as well. However, there are still many unexplained phenomena and features because of the complexity of post-processes and indirect observation methods. This study demonstrates the design and construction of the in situ imaging systems, which use the x-ray synchrotron radiography to observe freeze casting and 3DFP processes. With the advantages provided by the in situ x-ray imaging techniques, the ice crystal growth with its unique lamellar structures can be observed during the freeze casting process. The movement of freeze front, material deposition, and growth of ice crystals can also be visualized during the inkjet-based 3DFP process.

The effect of Ni on the growth morphology of primary β-phase in an In-35 wt%Sn alloy

In-35 wt%Sn alloy is a superconductive alloy and its superconductivity is highly dependent on the properties of the β-In3Sn phase. However, detail solidification behaviour with microstructure development had not been studied with minor element additions. This paper investigates the effect of minor addition of Ni on the β-phase evolution in an In-35 wt%Sn alloy during the solidification process using the in-situ real-time synchrotron radiography technique. The β-phase preferably formed a columnar dendritic structure that made a transition to a mix structure of cellular and dendrite with a unique morphology with an addition of 0.05 wt%Ni. The findings provide detailed observations of microstructure evolution, specifically β-In3Sn phase, and examine the effects of Ni addition during solidification of the In-35 wt%Sn alloy, as well as the thermal properties of the alloys by differential scanning calorimeter.