Synchrotron X-ray Radiography Research Articles

Mitigation of DMM-induced stripe patterns in synchrotron X-ray radiography through dynamic tilting.

In synchrotron X-ray radiography, achieving high image resolution and an optimal signal-to-noise ratio (SNR) is crucial for the subsequent accurate image analysis. Traditional methods often struggle to balance these two parameters, especially in situ applications where rapid data acquisition is essential to capture specific dynamic processes. For quantitative image data analysis, using monochromatic X-rays is essential. A double multilayer monochromator (DMM) is successfully used for this aim at the BAMline, BESSY II (Helmholtz Zentrum Berlin, Germany). However, such DMMs are prone to producing an unstable horizontal stripe pattern. Such an unstable pattern renders proper signal normalization difficult and thereby causes a reduction of the SNR. We introduce a novel approach to enhance SNR while preserving resolution: dynamic tilting of the DMM. By adjusting the orientation of the DMM during the acquisition of radiographic projections, we optimize the X-ray imaging quality, thereby enhancing the SNR. The corresponding shift of the projection during this movement is corrected in post-processing. The latter correction allows a good resolution to be preserved. This dynamic tilting technique enables the homogenization of the beam profile and thereby effectively reduces noise while maintaining high resolution. We demonstrate that data captured using this proposed technique can be seamlessly integrated into the existing radiographic data workflow, as it does not need hardware modifications to classical X-ray imaging beamline setups. This facilitates further image analysis and processing using established methods.

Simultaneous accelerated stress testing of membrane electrode assembly components in polymer electrolyte fuel cells

The durability of polymer electrolyte fuel cells (PEFCs) in fuel cell electric vehicles is important for the shift from passenger cars to heavy-duty vehicles. The components of a PEFC, namely the proton exchange membrane (PEM), catalyst layer (CL), and gas diffusion layer (GDL), contribute to the degradation of the fuel cell performance. In this paper, we propose a method for simultaneously evaluating the degradation rates of these components by combining electrochemical characterization with operando synchrotron X-ray radiography. The open-circuit voltage, electrochemically active surface area (ECSA), and water saturation were used as the degradation indicators for the PEMs, CLs, and GDLs, respectively. The results of two accelerated stress tests (loading and start-stop cycles) after 10,000 cycles showed that the increase in water saturation owing to the loss of hydrophobicity due to carbon corrosion in the cathode GDL occurred on the same timescale as the degradation in the PEM and cathode CL. Specifically, during the load cycle AST, the cathode CL degraded with a 26% reduction in the ECSA along with the cathode GDL degradation with a 10% increase in water saturation. This suggests that more efforts should be devoted to studies on the durability of GDLs for heavy-duty applications.

In-situ study on the effect of Li concentration on hydrogen microporosity evolution in Al-Li alloys by synchrotron X-ray radiography

The nucleation and growth of hydrogen microporosity during the solidification of Al-Li alloys were in situ observed by synchrotron radiation X-ray radiography, and the effect of initial Li concentration on its evolution kinetics was investigated. The results show that the high Li concentration effectively contributes to the high-temperature nucleation effect of hydrogen microporosity during the solidification of Al-Li alloys, and significantly increases the nucleation and growth rates of hydrogen microporosity. When the initial Li concentration was 2.0 wt%, the nucleation supersaturation of hydrogen microporosity was 1.96, which was 3.5 times higher than that at low Li concentration (1.5 wt%), and the growth rate was up to 2.61 μm/s. In addition, the quantitative results of the final size, morphology, and distribution of the hydrogen microporosity based on 3D X-ray computed tomography (X-CT) showed that high Li concentration not only increased the volume of monolithic hydrogen microporosity, and increased the total number of microporosities, but also increased the degree of irregularity of hydrogen microporosity. The in-situ observation results can provide a new dataset for the establishment and validation of the hydrogen microporosity model of Al-Li alloys.

Comprehensive Analysis of Wettability in Waterproofed Gas Diffusion Layers for Polymer Electrolyte Fuel Cells.

In polymer electrolyte fuel cells (PEFCs), the gas diffusion layer (GDL) is crucial for managing the flooding tolerance, which is the ability to remove the water produced during power generation from the assembled cell. However, an improved understanding of the properties of GDLs is required to develop effective waterproofing strategies. This study investigated the influence of the polytetrafluoroethylene (PTFE) content on the pore diameter, porosity, wettability, water saturation, and flooding tolerance of waterproofed carbon papers as cathode GDLs in PEFCs. The addition of minimal PTFE (∼6 wt %) to carbon paper provided external waterproofing, whereas internal waterproofing was achieved at a higher PTFE content (∼13 wt %). However, excessive PTFE (∼37 wt %) led to macropore collapse within the carbon paper, reducing fuel cell performance. Although PTFE addition was expected to improve the flooding tolerance, operando synchrotron X-ray radiography revealed that the water saturation level in carbon paper increased with increasing PTFE content. These findings provide a benchmark for assessing whether GDLs meet the flooding tolerance requirements of PEFCs and may be applicable to waterproofed GDLs in electrochemical devices for water and CO2 electrolysis.

Operando X-ray radiography of liquid water distribution in 100 mm polymer electrolyte fuel cell channels

Preventing the accumulation of water in the gas diffusion layer (GDL) proves effective in enhancing the performance of polymer electrolyte fuel cells (PEFCs). To understand the water transport phenomena in GDLs and channels of PEFCs, cell hardware for operando synchrotron X-ray radiography was developed with a 100 mm channel length, facilitating the separate quantification of liquid water in the cathode and anode GDLs. The presence of liquid water in the cathode and anode GDLs was confirmed during operation with a supply of dry gas in a counter-flow configuration. Furthermore, the amount of liquid water in the cathode and anode GDLs increased toward the cathode inlet, while the amount of water in the cathode and anode channel regions increased toward each outlet. The liquid water distribution in the GDLs along the channel direction can be attributed to water transport from cathode to anode (back-diffusion), decreasing toward the anode outlet. Therefore, conducting radiography experiments aligned parallel to the GDLs and perpendicular to the channel could provide valuable insights for a more comprehensive understanding of water transport in cells.

Effect of cooling rates and Fe contents on microstructure evolution of Al-Cu-Mn-Mg-Fe-Si alloys

During the solidification process, the recycled Al-Cu alloys form coarse Fe-rich phases, which seriously deteriorate the mechanical properties of the alloy. The study employed optical microscope (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and synchrotron X-ray imaging to investigate the impact of cooling rate and Fe contents on the growth of Fe-rich phases, Al2Cu, and pores in recycled Al-Cu-Mn-Mg-Fe-Si alloys under synergistic effect ultrasonic melt processing (USMP) and Al-Ti-B. USMP can homogenize the distribution of TiB2 particles and provides more nucleation sites for the formation of Fe-rich phases. Under the synergistic effect of USMP and Al-Ti-B, increasing the cooling rate,the volume fractions of Fe-rich phases in 0.7FeUB (0.7 wt%Fe + USMP + Al-Ti-B) and 1.2FeUB (1.2 wt%Fe + USMP + Al-Ti-B) alloys decreased from 8.92% and 16.52% to 8.03% and 14.73%, respectively. The volume fraction of Al2Cu increased from 4.06% and 3.13% to 4.37% and 3.54%, respectively. Furthermore, the three-dimensional (3D) morphology of Fe-rich phases and Al2Cu became more compact and uniform. The volume fraction of pores in the 1.2FeUB alloy decreased from 0.412% to 0.072%. In-situ synchrotron X-ray radiography revealed that increasing cooling rates led to increased nucleation undercooling of primary α-Al and Fe-rich phases. These phenomena can be attributed to the combined effects of ultrasonic cavitation, ultrasonic streaming, and an increased cooling rate. These factors serve to homogenize the alloy composition, ensure uniform distribution of TiB2 particles, inhibit element diffusion, reduce solute segregation, and ultimately lead to the refinement of the grain size, α-Al, Fe-rich phases, and Al2Cu, while also inhibiting pore growth.

3D characteristics and growth behavior of Fe-rich phases in Al−Si−Fe−Mn alloys during melt holding

The morphological evolution and growth behavior of Fe-rich phases in the Al−7.0Si−1.0Fe−1.2Mn alloy during melt holding were studied using scanning/transmission electron microscopy, thermodynamic calculations and synchrotron X-ray imaging. The results show that with a decrease in holding temperature, the Fe-rich phase underwent a morphological transformation from coarse star-like and polygonal structures to fine Chinese-script and coupled structures consisting of Chinese-script and polygonal shapes. The 3D structure of the star-like phase was composed of multibranched primary phases and irregular secondary phases; the coupled structure was composed of polyhedrons and dendrites; the Chinese-script phase was composed of dendrites. When the holding temperature was decreased, the number and volume fraction of Fe-rich phases were significantly reduced. A similar trend was also obtained for the largest volume particles and their connectivity. In situ synchrotron X-ray radiography results indicated that two types of primary Fe-rich phases were formed during the solidification process, and the smaller phase that remained in the melt could act as nucleation sites for the formation of the coupled eutectic structures.

Elastic wave velocity measurements of sodium aluminosilicate glass and melt at high pressure and temperature

The combination of ultrasonic technique with synchrotron X-ray diffraction and radiography in a multi-anvil apparatus was utilized to measure the elastic wave velocities of sodium aluminosilicate glass and melt with the partially depolymerized composition of Na3AlSi3O9 (NAS). The measurements were conducted at pressure and temperature of up to 7.3 GPa and at ambient temperature for glass and up to 4.3 GPa and 2120 K for melt, respectively. The compressional wave velocity (VP) of the NAS glass remained mostly constant up to 4 GPa; subsequently, it increased with increasing pressure. Additionally, the NAS glass exhibited a minimum shear wave velocity (VS) at 4–5 GPa. Alternatively, the VP of the NAS melt was smaller than that of the NAS glass, showing a velocity minimum at ∼2 GPa. The negative pressure dependence of VP of the NAS melt is completely different from the depolymerized diopside (Di) melt, which shows a monotonic increase in VP with pressure. The contrasting behavior of the NAS and Di melts is caused by the difference in their structure, characterized by their degree of polymerization. Natural magma found in the interior of the Earth, such as basalt, has a partially depolymerized composition. This study indicates that the magma can exhibit elastic properties with negative pressure dependence, similar to the NAS melt.

Quantification of melt pool dynamics and microstructure during simulated additive manufacturing

The dynamics of laser spot melting and metallic alloy solidification are investigated through synchrotron x-ray radiography, 3D electron backscatter diffraction data, and computational fluid dynamics (CFD) simulations on a model NiMoAl alloy. Solidification velocities are measured from in-situ images to validate a CFD model of the spot melt. TriBeam tomography is used to reconstruct the melt pool in 3D, characterize the microstructure, and validate the CFD model melt pool dimensions. 3D geometrically necessary dislocation (GND) density calculations reveal extensive deformation at the sample surface. GND calculations integrated with the CFD model reveal that the halo of small, equiaxed grains adjacent to the fusion line is a result of recrystallization that occurred in the heat affected zone. By combining in-situ and ex-situ data modalities across a variety of temporal and spatial length scales, the microstructure formation mechanisms and their relationship to melt pool solidification are quantified.

Observation of Damage Initiation for Trans-laminar Fracture Using in situ Fast Synchrotron X-ray Radiography and ex situ X-ray Computed Tomography

AbstractTrans-laminar fracture is an important topic for engineering composites. In this study, trans-laminar fracture initiation in quasi-isotropic carbon/epoxy laminates made of non-crimp fabrics was examined using in situ fast synchrotron X-ray radiography and ex situ X-ray computed tomography. The maximum split lengths were measured by in situ radiography and were compared with the predicted values in a detailed FE model using cohesive elements. Ex situ computed tomography scans were also conducted to confirm that no fibre breakage occurs before the final load drop in the experiments. In situ and ex situ observations are complementary for the understanding of damage initiation.

All-Solid-State Battery Safety Investigation in Calorimeter Coupled with Fast X-Ray Radiography

All-solid-state battery (ASSB) are expected to be a solution to increase energy density in Li-ion technology. However, high-energy storage capacities make the safety a crucial issue. The main reactions leading to thermal runaway in conventional LiB are anode/electrolyte at 110 °C, electrolyte decomposition at 150 °C and cathode/electrolyte at 300 °C. Therefore, without liquid electrolyte, it can be expected that ASSB are less likely to have a thermal runaway.To assess safety of such non-fully mature battery technologies, a new methodology is proposed and a closed calorimeter was designed to perform operando experiments in abuse conditions with high-speed synchrotron X-ray radiography and measurement of temperature, pressure and energy. The data and image of thermal runaway of all-solid-state batteries are presented and compared to the result of Li-ion batteries with liquid electrolyte. An 11 % decrease of heat release was measured for cell with solid electrolyte. Gas volume, amount of matter that reacts in the cell and reaction kinetics have also been compared.Such a methodology allows deepening hypotheses on associated material degradation and that can assist in development of new battery technologies, by evaluating battery safety from the start of the design from battery composition to cell shape.

Improving Water Management and Reactant Distribution in PEM Fuel Cells Via Flow Fields with Biomimetic Auxiliary Channels

The bipolar plate, a component of the polymer electrolyte membrane (PEM) fuel cell is responsible for reactant delivery, product removal, and mechanical stability of PEM fuel cell stacks. Bipolar plates also account for 70-90% of the weight and volume, and 18-28% of the production cost of stacks (1). Improving the function of the flow fields embedded in the bipolar plates can significantly impact the energy density of PEM fuel cells by improving liquid water management and reactant distribution. Previous works show that water preferentially accumulates under the lands of flow fields in the gas diffusion layer (GDL) for various GDL materials, creating a heterogeneous distribution of water and reactants, thereby increasing cathode mass transport overpotential(2–4). Biomimetic channel architectures have been shown to enhance preferential water flow; however, these designs have not been tailored to control water accumulation for improved reactant distribution (5,6). Targeting areas of known water accumulation such as the under-land regions of GDLs, could have a profound impact on reducing mass transport losses and improving reactant homogeneity, thereby improving the power density and efficiency of the PEM fuel cell.In this work, biomimetic auxiliary channels were laser-cut into the lands of a parallel PEM fuel cell flow field to enhance the liquid water removal and reactant distribution in the under-land region of the GDL. Constant-current electrochemical testing and electrochemical impedance spectroscopy revealed a 29% increase in peak power density resulting from a 54% decrease in oxygen mass transport overpotential using the biomimetic flow field (BFF) compared to a baseline trapezoidal flow field (TFF). Operando synchrotron X-ray radiography revealed reduced GDL water accumulation when using the BFF compared to the TFF. Water accumulation under the BFF flow fields was more homogenous especially near the catalyst layer (CL) – GDL interface, indicating enhanced reactant distribution near the CL reaction sites. Therefore, the reduced mass transport overpotential and corresponding power density increase were attributed to enhanced liquid water removal and reactant distribution due to the biomimetic auxiliary channels. These results demonstrate that significant performance enhancements can be realized by embedding alternate pathways for air and water in the lands of flow field components. Ultimately, this work can be used to further optimize the design of bipolar plates for more efficient stacks and accelerate the commercialization of PEM fuel cells. Y. Wang, D. F. Ruiz Diaz, K. S. Chen, Z. Wang, and X. C. Adroher, Materials Today, 32, 178–203 (2020).N. Ge et al., Electrochim Acta, 328, 135001 (2019).D. Muirhead et al., Int J Hydrogen Energy, 42, 29472–29483 (2017).S. Chevalier et al., J Electrochem Soc, 164, F107–F114 (2017)N. Guo, M. C. Leu, and U. O. Koylu, Int J Hydrogen Energy, 39, 21185–21195 (2014).S. Feng et al., Science, 373, 1344–1348 (2021).

(Invited) Pulsed Neutron and Synchrotron X-Ray Imaging of Liquid Water Formation and Transport in Polymer Electrolyte Fuel Cells

Fuel-cell electric vehicles (FCEVs) powered by hydrogen are expected to be the ultimate eco-friendly cars, and so developing low-cost, high-performance, and highly reliable FCEVs is strongly demanded. Polymer electrolyte fuel cells (PEFCs) consist of an electrolyte membrane sandwiched between an anode and a cathode, where both the anode and cathode have laminated structures composed of a catalyst-coated membrane (CCM) and gas channels in contact with a gas diffusion layer (GDL). The GDL consists of a microporous layer (MPL) and a substrate. One problem with PEFCs is that liquid water generated as a by-product of the electrochemical reaction at the catalyst accumulates in the GDL, and prevents oxygen from being transported through the gas channels to the catalyst. Therefore, to achieve a high power density, it is necessary to develop new materials and optimize the design of the gas channel to discharge water from the cathode to the exterior of the cell. We are currently constructing a multiscale analysis methodology that combines quantum beam analysis using X-rays and neutrons to clarify water behavior in a PEFC [1-9].In this presentation, we introduce three topics related to water behavior on scales ranging from several micrometers (pores in GDLs) to hundreds of millimeters (automotive fuel cells). The first topic concerns imaging the liquid water distribution in an MPL [2, 6]. The imaging analysis was performed using time-resolved synchrotron X-ray computed tomography while water vapor was supplied to the MPL side of the GDL. With increasing exposure to water vapor, the average volume of wet domains in the MPL initially increased, whereas the overall number of such domains decreased. This implies that wet domains expand by absorbing water vapor and combining with each other. As the exposure to water vapor was further increased, the volume fraction of wet domains in the MPL reached a steady state, indicating that liquid water was discharged to the outer surface of the MPL and to the substrate side. The second topic is obtaining mechanistic insights into water behavior in a subscale PEFC [8]. Time-resolved operando synchrotron X-ray radiography to determine the effects of temperature and relative humidity on the condensation and transport of water in PEFCs. The results show that condensation and transport to the channel can be classified into four categories: 1) concurrent liquid and vapor transport, 2) mainly liquid transport, 3) vapor transport, and 4) accumulation near the ribs. X-ray imaging experiments were conducted at the TOYOTA Beamline (BL33XU) at the SPring-8 facility. The third topic is operando neutron imaging of the water distribution and identifying water/ice phases in large automotive PEFCs during a cold start. We developed an experimental system using a pulsed spallation neutron beam at the RADEN instrument at BL22 of the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). The results showed direct evidence of stepwise freezing inside the PEFC. The water initially accumulated in the center of the PEFC and began to freeze, and this was followed by PEFC shutdown as freezing progressed. We defined the time interval between the beginning of freezing and shutdown as the “extended time”. This is expected to be useful as an indicator for optimizing the cold-start protocol, cell design, and choice of material.Reference1) Y. Nagai, J. Eller, T. Hatanaka, S. Yamaguchi, S. Kato, A. Kato, F. Marone, H. Xu and F. N. Büchi, J. Power Sources, 435 (2019) 226809.2) S. Kato, S. Yamaguchi, W. Yoshimune, Y. Matsuoka, A. Kato, Y. Nagai and T. Suzuki, Electrochem. Commun., 111 (2020) 106644.3) S. Yamaguchi, S. Kato, A. Kato, Y. Matsuoka, Y. Nagai and T. Suzuki, Electrochem. Commun., 128 (2021) 107059.4) Y. Higuchi, D. Setoyama, K. Isegawa, Y. Tsuchikawa, Y. Matsumoto, J. D. Parker, T. Shinohara and Y. Nagai, Phys. Chem. Chem. Phys., 23 (2021) 1062-10715) S. Yamaguchi, S. Kato, W. Yoshimune, D. Setoyama, A. Kato, Y. Nagai, T. Suzuki, A. Takeuchi and K. Uesugi, J. Synchrotron Radiat., 29 (2022) 1258-1264.6) S. Kato, S. Yamaguchi, Y. Matsuoka, A. Kato, T. Suzuki and Y. Nagai, InterPore2022, Book of s, p139.7) K. Isegawa, D. Setoyama, Y. Higuchi, Y. Matsumoto, Y. Nagai and T. Shinohara, Nucl. Instrum. Methods Phys. Res. A 1040, 167260 (2022).8) A. Kato, S. Kato, S. Yamaguchi, T. Suzuki and Y. Nagai, J. Power Sources, 521 (2022), 230951.9) Y. Higuchi, W. Yoshimune, S. Kato, S. Hibi, D. Setoyama, K. Isegawa, Y. Matsumoto, H. Hayashida, H. Nozaki, M. Harada, N. Fukaya, T. Suzuki, T. Shinohara and Y. Nagai, to be submitted.

Synchrotron X-ray operando study and multiphysics modelling of the solidification dynamics of intermetallic phases under electromagnetic pulses

In this paper, we used synchrotron X-ray radiography and tomography to study systematically and in operando conditions the growth dynamics of the primary Al3Ni intermetallic phases in an Al-15wt%Ni alloy in the solidification process with magnetic pulses of up to 1.5 T. The real-time observations clearly revealed the growth dynamics of the intermetallics in time scale from millisecond to minutes, including phase growth instability, side branching, fragmentation and orientation alignment under different magnetic pulse fluxes. A multiphysics numerical model was also developed to calculate the alternating and cyclic Lorentz forces and stresses acting on the Al3Ni phases and the nearby melt due to the applied pulses. Combining the results of the operando experiments and modelling, for the first time, the differential forces between the growing Al3Ni phases and the nearby melt were quantified. The forces can create slip dislocations at the growing crystal front which can further develop into nm and µm crystal steps for initiating phase branching. Furthermore, the magnitudes of the shear stresses are strongly related to the size, morphological and geometric features of the growing Al3Ni phases. Dependent on the magnitude of the shear stresses, phase fragmentation could occur in a single pulse period or in multiple pulse periods via fatigue mechanism. This systematic research work elucidate some of the long-time debated hypotheses concerning intermetallic phases growth instability and phase fragmentation in pulse magnetic fields. The research establishes a robust theoretical framework for quantitative understanding of the intermetallic phase growth dynamics in solidification under pulse magnetic fields.

Synchrotron X-ray diffraction and radiography - Lattice strain characterization in thin-walled carbon fibre channel structures subjected to buckling

Carbon fibre composites are widely used in low specific stiffness and high strength structures such as airframes. Compressive loading of these assemblies can lead to buckling and localised deformation around defects and imperfections that can hinder performance and lead to overengineering via excessive safety factors. Synchrotron X-Ray Diffraction (SXRD) has recently been shown to be capable of performing lattice strain mapping within carbon fibre composites at the microscale, a previously unprecedented resolution. In this study SXRD and radiography was performed on carbon fibre composite columns produced via two different methods (standard lamination and half square) at a range of different load states: unbuckled, one-third of the buckling load and post buckling. The results provide quantitative insights into the impact of these different production methods on lattice strain and fibre orientation, as well as the influence these factors have on reducing buckling load (by up to 22%). As well as being the first use of SXRD on industrially representative full-size carbon fibre samples, these insights provide invaluable detail into the factors which limit performance and the origins of column failure; crucial factors required to optimise structural design, production and loading capability.

Dependence of vapor and liquid water removal on cross-flow in polymer electrolyte fuel cell investigated by operando synchrotron X-ray radiography

Excessive liquid water in the gas diffusion layer (GDL) of a polymer electrolyte fuel cell is known to degrade the performance. Cross-flow through the GDL is applied to reduce the liquid water in the GDL. However, cross-flow has a disadvantage with a high pressure drop and is difficult in practical use. Controlled cross-flow has the possibility to reduce the liquid water, while the pressure drop remains acceptable for application. This study experimentally quantifies the amount of liquid water in the GDL by operando synchrotron X-ray radiography and the cross-flow rate with different GDL thicknesses. The relationship between the cross-flow rate and the amount of liquid water indicates that liquid water could be reduced by a smaller pressure drop with a thicker GDL. In addition, vapor removal by cross-flow is evaluated, and the relative humidity of cross-flow does not increase to 100% after flowing through the GDL containing liquid water.

The mechanism of Fe-rich intermetallic compound formation and growth on inoculants revealed by electron backscattered diffraction and X-ray imaging

Fe-rich intermetallics affect critically the mechanical properties and recyclability of aluminium alloys. Increasing effort has been spent on the inoculation of these intermetallics, hoping to promote a finer distribution. Recently Al-5Ti-1B (wt.%), originally developed to refine α-Al, has been shown to refine Al13Fe4, an intermetallic phase present in a variety of Al alloys. However, mechanisms of the formation and growth of the intermetallics on the inoculants are unclear. In this paper, Ti is added to Fe-containing Al alloys to produce a large number of potent Al3Ti particles, the active inoculant in Al-5Ti-1B. We use a combination of electron backscattered diffraction, in situ synchrotron X-ray radiography and post-solidification X-ray computed tomography to investigate the formation and growth of primary Al13Fe4 on Al3Ti inoculants, first in a model Al-Fe alloy, with key insights then confirmed in a high Fe-containing, recycled 6xxx alloy. Crystallographic orientation relationships between Al13Fe4 and Al3Ti are analysed comprehensively, and the formation and growth dynamics of Al13Fe4 on Al3Ti is also unveiled. A strong link is revealed between the formation of Al13Fe4 on Al3Ti and a twinning-related pseudo-symmetry of Al13Fe4. Finally, a potential strategy to refine both intermetallics and α-Al in recycled alloys with elevated Fe concentration is proposed.

In situ X-ray imaging of hot cracking and porosity during LPBF of Al-2139 with TiB2 additions and varied process parameters

Laser powder bed fusion (LPBF) additive manufacturing of 2XXX series Al alloys could be used for low volume specialist aerospace components, however, such alloys exhibit hot cracking susceptibility that can lead to component failure. In this study, we show two approaches to suppress the formation of hot cracks by controlling solidification behaviour using: (1) TiB2 additions; and (2) optimisation of LPBF process parameters. Using high-speed synchrotron X-ray radiography, we monitored LPBF of Al-2139 in situ, with and without TiB2 under a range of process conditions. In situ X-ray radiography results captured the crack growth over 1.0 ms at a rate of ca. 110 mm s−1, as well as pore evolution, wetting behaviour and build height. High-resolution synchrotron X-ray computed tomography (sCT) was used to measure the volume fraction of defects, e.g. hydrogen pores and microcracks, in the as-built LPBF samples. Our results show adding TiB2 in Al-2139 reduces the volume of cracks by up to 79 % under a volume energy density of 1000 to 5000 J mm−3, as well as reducing the average length, breadth, and surface area of cracks.

Measurement of liquid water distribution in GDL under cross-flow-inducing parallel flow field using operando synchrotron X-ray radiography

Baffles in flow field channels for air in a polymer electrolyte fuel cell are known to enhance the performance by inducing convective flow through the gas diffusion layer (GDL) with smaller pressure loss than interdigitated flow fields. This work experimentally correlates performance enhancement with the amount of liquid water in a GDL. A parallel flow field (PFF) that has different inlet and outlet opening sizes is applied to induce cross-flow in the GDL under the rib between adjacent air channels. Operando synchrotron X-ray radiography experiments are conducted to compare the amount of water in the GDL with that for a PFF having the same inlet and outlet sizes. The performance enhancement by application of different opening sizes increases with decreasing relative humidity and increasing air flow rate. A significant performance enhancement is observed when the amount of water in the GDL substrate under the rib becomes almost zero. No performance enhancement is observed under over-humidified conditions, although a decrease in the amount of water in the GDL is still observed, which suggests that the performance becomes insensitive to the difference in the liquid water saturation as the saturation increases.

Solidification sequence of CrMnFeCoCu dual-FCC multicomponent alloy

Multicomponent and multi-phase alloys derived from the CrMnFeCoNi alloy are receiving increasing interest in the field of structural materials. Such materials have large degrees of freedom compared with conventional alloys, therefore, their solidification sequence can be more complex. Herein, the solidification sequence of the CrMnFeCoCu alloy, where Ni in the CrMnFeCoNi alloy is substituted with Cu, was investigated using synchrotron X-ray radiography and X-ray diffraction. This study demonstrated that the microstructure composed of two phases with face-centered-cubic (FCC) structures was not simply formed through the conventional multiphase solidification manner. The uniform liquid phase first splits into two liquid phases, and they individually solidify into the two FCC solid phases. The massive-like body-centered-cubic (BCC) to FCC transformation for one of the solid phases was also confirmed. Understanding the liquid-liquid phase separation and the solid-phase transformation identified in this study can be useful for controlling the microstructure of multicomponent and multi-phase alloys.