High-energy Synchrotron X-ray Research Articles

Impact of interatomic structural characteristics of aluminosilicate hydrate on the mechanical properties of metakaolin-based geopolymer

This study explores the influence of the interatomic structure of sodium aluminosilicate hydrate (N-A-S-H) with varying silica contents on the mechanical properties of metakaolin-based geopolymer. Geopolymer pastes comprising Si/Al ratios between 2.0 and 3.0 were synthesized. A larger number of Si-O-Si linkages compared to Si-O-Al linkages and a higher atomic number density were found in the geopolymers with higher silica contents, which enhanced the compressive strength of the geopolymer pastes up to the optimal Si/Al ratio of 2.5. The paste with a Si/Al = 2.5 exhibited a greater portion of Q4(1Al and 2Al) and denser morphology compared to the other geopolymer pastes. Furthermore, in-situ high-energy synchrotron X-ray scattering experiments were conducted to assess the elastic modulus of the aluminosilicate structure at a local atomic scale. The modulus value in real space decreases with increasing silica contents up to Si/Al = 2.5 and increases with the presence of excessive unreacted silica fume. The modulus value in reciprocal space for the axial and lateral directions both presented a positive value at the geopolymer comprising a Si/Al ratio higher than 2.5, indicating that the load-bearing property of N-A-S-H changed at higher Si/Al ratios. Moreover, the smallest difference between the strains along the axial and lateral directions was detected for the geopolymer with Si/Al = 2.5 in both the real and reciprocal space, owing to the most interconnected and flexible nanostructure, which led to the highest mechanical strength.

Deciphering the glass-forming ability of Al2O3-Y2O3 system from temperature susceptibility of melt structure

Despite its significance in both fundamental science and industrial applications, the glass-forming transition in the Al2O3-Y2O3 (AY) refractory system is not yet fully understood due to the elusive structure evolution upon cooling. Here, atomic-scale structural changes in AY-bearing melts with different compositions and temperatures are tracked by employing in situ high-energy synchrotron X-ray diffraction and empirical potential structure refinement simulation. We find that the glass-forming abilities (GFA) of AY-bearing melts are intriguingly correlated with the dependence of melt structure on temperature. In the case of the Al2O3 and Y3Al5O12 (YAG), the observed large structural changes from superheating to undercooling melt (i.e., higher temperature susceptibility) correspond to a low GFA. Conversely, the 74Al2O3–26Y2O3 (AY26) melt, with the smallest temperature susceptibility, exhibits the highest GFA. Simulation models illustrate that the temperature susceptibility of melt is associated with its atomic arrangement, especially the stability of cation-cation pairs. A balanced network (in AY26 melt), where the unsteady OAl3 tri-clusters are minimized and steady apex-to-apex connections between adjacent network units are abundant, contributes to stabilizing cationic interactions. This, in turn, fosters the formation of large-sized Al-O-Al rings, which topologically facilitates the subsequent glass-forming transition. Our findings provide new structural insight into the GFA of AY-bearing melts and may expand to other unconventional glass-forming systems to accelerate glassy materials design.

Achieving near zero-hysteretic superelasticity in a Ni43Fe18Ga27Co12 single-crystalline microwire via Lüders-like phase transformation

Ni43Fe18Ga27Co12 single-crystalline microwires directly fabricated by the Taylor liquid drawing method show the nature of a strong first-order martensitic transformation under external stress or load-biased temperature cycling. By eliminating the nucleation energy barrier through localized plastic deformation, a fully recoverable superelastic strain approaching 11 % with negligible hysteresis is achieved in the course of tensile deformation. Based on in-situ synchrotron high-energy X-ray diffraction analysis, the mechanism of nearly non-hysteretic transformation is unraveled as a sharp, Lüders-like phase transformation. It is found that a single martensitic domain propagates continuously in a monolithic fashion under superelastic cycling with poor crystallographic compatibility of λ2 = 0.950 and small volume change of ∆V = -0.17 % accompanying martensitic transformation. We attributed such near zero-hysteretic transformation characteristics to combining conditions of low crystal defect density, high nucleation barriers but without continual nucleation events, flexibility of the microwire, and small volume change.

Pressure-induced reversal of Peierls-like distortions elicits the polyamorphic transition in GeTe and GeSe

While polymorphism is prevalent in crystalline solids, polyamorphism draws increasing interest in various types of amorphous solids. Recent studies suggested that supercooling of liquid phase-change materials (PCMs) induces Peierls-like distortions in their local structures, underlying their liquid-liquid transitions before vitrification. However, the mechanism of how the vitrified phases undergo a possible polyamorphic transition remains elusive. Here, using high-energy synchrotron X-rays, we can access the precise pair distribution functions under high pressure and provide clear evidence that pressure can reverse the Peierls-like distortions, eliciting a polyamorphic transition in GeTe and GeSe. Combined with simulations based on machine-learned-neural-network potential, our structural analysis reveals a high-pressure state characterized by diminished Peierls-like distortion, greater coherence length, reduced compressibility, and a narrowing bandgap. Our finding underscores the crucial role of Peierls-like distortions in amorphous octahedral systems including PCMs. These distortions can be controlled through pressure and composition, offering potentials for designing properties in PCM-based devices.

An operando synchrotron study on the effect of wire melting state on solidification microstructures of Inconel 718 in wire-laser directed energy deposition

Directed energy deposition (DED) with a coaxial wire-laser configuration has gained significant attention in recent years for the production of large-scale metallic components because of its low directional dependence, fast deposition rate, high feedstock efficiency, and low manufacturing costs. This work studies the coaxial wire-laser DED process of Inconel 718 alloy under a stable deposition condition with a relatively low input volumetric energy density (55.5 J/mm3). Post characterization reveals a cluster of refined grains at the center-bottom region of the as-printed track. Operando high-energy synchrotron X-ray experiments and multi-physics modeling are applied innovatively to study the fundamental mechanism responsible for the formation of this microstructure. The X-ray diffraction experiment provides direct evidence, which is supported by the simulation, that the feeding wire can reach the melt pool bottom and release solid particles (primarily carbides) near the mushy zone owing to insufficient melting. Consequently, these sub-micron sized particles suppress the growth of large columnar grains and cause the formation of unique microstructural heterogeneity. This discovery offers new opportunities for tailoring the solidification microstructure by controlling the melting state of the feedstock wire in DED process, in addition to commonly known factors such as the thermal gradient and solidification velocity.

Impact of nano-scale cavities on hydrogen storage and retention in yttrium hydride

In situ synchrotron high-energy x-ray diffraction experiments and detailed transmission electron microscopy (TEM) characterization were conducted on as-fabricated and neutron-irradiated yttrium hydrides. The high-resolution synchrotron x-ray diffraction revealed minor α yttrium and major δ yttrium hydride phases in all specimens. Specimens were subject to heat treatments (heating-cooling cycles), and the intensity of α yttrium partially and completely disappeared in as-fabricated and neutron-irradiated specimens, respectively. The disappearance of α yttrium was unforeseen because hydrogen was expected to leave δ phase, causing an increase in α yttrium diffraction peak intensity. This observation indicated a surplus of hydrogen in the specimens where it was odd for hydride-forming early transition metal elements. The subsequent through-focus TEM characterization discovered nanometric cavities in both as-fabricated and neutron-irradiated yttrium hydride specimens for the first time. Two types of cavities were identified as fabrication-caused and irradiation-induced. The fabrication-caused cavities were associated with regions having linear deformation features, interfaces, and inclusions. The irradiation-induced cavities were observed as being formed isolated in the yttrium hydride phase. The presence of such nanometric cavities was considered as potential hydrogen storage pockets where the overall hydrogen storing capacity of yttrium hydride would be enhanced.

Sintering in seconds, elucidated by millisecond in situ diffraction

Materials, when sintered at high temperatures, undergo structural changes on multiple, hierarchical length scales but getting realtime information on these changes is difficult. To address this challenge, we developed a custom-built sample environment that allows us to investigate the structural evolution of materials during sintering using high-energy two-dimensional synchrotron X-ray diffraction (2D-XRD). Changes in the structure of SrFe12O19 ceramic magnet at multiple length scales were tracked in situ and modelled with millisecond time-resolution. In addition, we also demonstrated the ability to perform quantitative texture analysis from individual 2D-XRD images with a time resolution of 4 ms each. Owing to the high brightness X-ray source and advanced X-ray detectors, the evolution of crystallographic texture could be followed during sintering. This in situ approach can aid understanding of the synthesis–structure–property relationships in sintered materials, enabling the development of improved functional materials.

Unusual gradient stress induced superior room-temperature plasticity in brittle ferromagnetic bulk metallic glass

Ferromagnetic bulk metallic glasses (FBMGs) possess excellent soft magnetic properties, good corrosion resistance, and high strength. Unfortunately, their commercial utility is limited by their brittleness. In this work, we report the enhancement in the room-temperature plasticity during the compression (25%) and bending flexibility of Fe74Mo6P13C7 FBMG by using water quenching. The high-energy synchrotron X-ray measurements, high-resolution transmission electron microscopy, three-dimensional X-ray microtomography, and finite element simulation were performed to reveal the origin. It was found that the M-shape profile of residual stress improves the mechanical properties of FBMGs, particularly their plasticity. The reversal of the heat-transfer coefficient and cooling rate from the ‘vapor blanket’ to ‘nucleate boiling’ transition during water quenching processing is the main cause of the unusual profile of residual stress in glassy cylinders. Encouraged by the progress in developing flexible silicate glasses, this work highlights a processing method to improve plasticity and surmount technical barriers for the commercialization of FBMGs.

Imaging Liquid Water in a Polymer Electrolyte Fuel Cell with High-Energy X-ray Compton Scattering

Compton scattering imaging with intense, high-energy synchrotron X-rays allows us to visualize a light element substance in an operating electrochemical device. In this paper, we report the first experiment of Compton scattering imaging (CSI) on an operating polymer electrolyte fuel cell (PEFC). The novelty of the CSI technique is a non-destructive direct observation of cross-sectional images with a sensitivity to light elements and a capability of simultaneous measurements with fluorescent X-rays of heavy elements. Analyses of the observed images provide the cross-sectional distribution of generated liquid water and its current density dependency. The results show that the amount of generated water increases in the vicinity of the cathode catalyst layer at current densities ranging from 100 to 500 mA/cm2, while it remains constant or slightly decreases from 500 to 900 mA/cm2. In both the gas diffusion layer and the channel, liquid water is observed near the channel and rib interface above 500 mA/cm2, indicating the formation of a liquid water flow path. In addition, simultaneous measurements of fluorescent Pt-Ka X-rays reveal a significant correlation between the generated liquid water and Pt catalysts, using the Pearson correlation coefficient. The result shows that water is dispersed in the catalyst layer without any correlation with the amount of Pt catalysts at low current densities, but water tends to be distributed in the Pt-rich areas at high current densities. This study demonstrates that Compton scattering imaging is one of the unique techniques to characterize the behavior of generated liquid water in an operating PEFC.

Determination of diffraction and single-crystal elastic constants of laser powder bed fused Inconel 718

High energy X-ray synchrotron diffraction is used to investigate the elastic anisotropy of the nickel-based superalloy IN718 produced by laser powder bed fusion (PBF-LB). This material is characterized by a columnar grain morphology with some crystallographic texture. The material is subjected to elastic loading to determine the diffraction elastic constants (DECs). Furthermore, the single-crystal elastic constants (SCEC) are refined from these experiments using different micromechanical models. The results show that each micromechanical model predicts a specific set of SCEC that well describes the elastic anisotropy of PBF-LB/IN718.

Composition-dependent transformation-induced plasticity in Co-based complex concentrated alloys

While the mechanically-induced martensitic transformation and transformation-induced plasticity (TRIP) effects have various known benefits, transformation of blocky martensite can also accelerate ductile damage nucleation and growth. Some complex-concentrated alloys (CCAs) with negative stacking-fault energy (SFE) demonstrate a rare faulting plasticity behavior with high strain hardening capability, that sets them apart from conventional low, positive SFE alloys that exhibit the TRIP effect. This study investigates the influence of dilute nitrogen on the TRIP mechanisms in a Co-rich CoCrNi CCA, and reveals, among other findings, that nitrogen interstitials can effectively reduce the extension of stacking faults and deformation-induced phase transformation, resulting in higher strain hardenability at early deformation levels and ductility. Thermodynamic calculations are coupled to various experimental analyses based on atom-probe tomography, scanning transmission electron microscopy, electron backscattered diffraction, electron-channeling contrast imaging, in situ high-energy synchrotron X-ray diffraction, and stress relaxation testing, to explore the origins of the observation. This work provides insights into the future design of CCAs with desirable TRIP, faulting plasticity, and mechanical properties.

Design of high-strength martensitic steels by novel mixed-metal nanoprecipitates for high toughness and suppressed hydrogen embrittlement

To obtain a fundamental understanding of mechanisms of hydrogen embrittlement (HE) and its prevention in advanced high-strength steels containing novel nanoscale mixed-metal precipitates, it is necessary to study local microstructure, H trapping, and crack path with new multiscale experimental and simulation approach. Spatially resolved hydrogen mapping via SKPFM is used together with investigation of the crack path using high-resolution EBSD and HMPT, and global trapping behavior of the alloys by TDS. These results are combined with newly introduced method to elucidate real-time distribution of hydrogen in the alloy using high-energy synchrotron X-ray diffraction (HES-XRD). Mixed-metal precipitates improves HE resistance of the alloy, due to nature of the trapping sites, e.g. irreversible H-trapping by carbon vacancies inside novel nanoprecipitates and high total length of PAGBs. This is because of lower possibility of build-up of critical local hydrogen content at PAGBs for intergranular hydrogen-assisted cracking due to hydrogen-enhanced decohesion mechanism. Less weakly trapped hydrogen also reduces frequency of dislocation activation and enhanced dislocation slip in {011} slip plane due to hydrogen-enhanced localized plasticity in regions with affinity for transgranular hydrogen-assisted cracking at lower local hydrogen content. Direct evidence of carbon vacancies in novel nanoprecipitates is observed for the first time via HAADF-STEM.

Effect of creep loading on the oxygen diffusion of Ti6242S at 650°C

The influence of low and steady loading on the oxidation behaviour and oxygen diffusion within Ti6242S was investigated at 650 °C in air. Electron probe microanalyser (EPMA), secondary-ion mass spectrometry (SIMS) and high energy synchrotron X-ray diffraction (S-XRD) were used to quantify the oxygen distribution within the oxygen-enriched layer beneath the external oxide scale. Rietveld and peak by peak methods were used to evaluate the average response versus the crystal-oriented response of this diffusion process under load. Interestingly, a thermo-mechano-chemical coupling occurs during the creep-oxidation experiment even for moderate applied stresses (25-70 MPa) and demonstrates: (i) a decrease of the oxygen concentration at the metal/oxide interface, and (ii) a curvature change of the oxygen diffusion profile with load application. A qualitative thermo-mechano-chemical approach is proposed to model the modification of the diffusion law of the oxygen within Ti6242S due to application of a mechanical loading to explain observed experimental results.

Role of rare earth elements addition in enhancing glass-forming ability and magnetic softness of a Co75B25 metallic glass: Theoretical prediction and experimental verification

The effects of light/heavy rare earth (L/HRE) elements addition on local atomic structures, glass-forming ability (GFA), and soft magnetic properties of a Co75B25 metallic glass (MG) were comprehensively investigated using theoretical prediction and experimental verification methods. Ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) calculations revealed that the Co-RE-B (RE = La, Sm, Gd, and Y) MGs exhibit unique structural heterogeneities, with B-centered prism units dominating the local atomic structures. Compared to the Co-LRE-B (LRE = La and Sm) MGs, the Co-HRE-B (HRE = Gd and Y) MGs possess stronger bond strengths and higher fractions of icosahedral-like (ico-like) units, leading to remarkable enhancements in structural stability, fivefold symmetry, atomic packing density, and sluggish diffusion, ultimately resulting in enhanced GFA. Furthermore, the lower magnetic anisotropy energy (MAE) and range of the local loosely packed regions (LLPRs) in the HRE-containing MGs can significantly promote magnetic softness. The theoretical analysis predicts that the MGs containing the HRE possess higher GFA and magnetic softness with the order of Co75B25 < Co71.5La3.5B25 < Co71.5Sm3.5B25 < Co71.5Gd3.5B25 < Co71.5Y3.5B25. These predictions have been successfully verified by the experiments in both local atomic structures and properties, through the in situ high-energy synchrotron X-ray diffraction (HEXRD) characterization, as well as evaluations of thermal and magnetic properties.

Reversible Iron Oxyfluoride (FeOF)-Graphene Composites as Sustainable Cathodes for High Energy Density Lithium Batteries

Two large barriers are impeding the wide implementation of battery electric vehicles, namely driving-range and cost, primarily due to the low specific capacity/energy and high cost of mono-valence cathodes (e.g. LiNi0.8Co0.1Mn0.1O2) used in lithium-ion batteries. Iron is the ideal element of choice for cathode materials considering its abundance, low cost and toxicity. Two fundamental challenges, in particular, the poor reversibility of (de)lithiation and low electronic conductivity, prevent those iron based high specific capacity/energy multi-valence conversion cathodes from practical applications. In this work, we have developed a sustainable FeOF nanocomposite with extraordinary performance. In particular, we were able to reach the theoretical specific capacity of 621 mAh·g-1 and 1,124 Wh·kg-1 specific energy (2.1-valence change/2.1 Li+ stored per unit) and more than 100 cycles with 80% capacity retention at 0.1C (realizing the reversible (de)lithiation), which is 3 times of the specific capacity, and 2 times of the specific energy of current mono-valence intercalation LiCoO2 respectively (i.e., 145 mAh·g-1 and 551 Wh·kg-1). This is the result of an effective approach, combing the nanostructured FeOF with graphene sheets to solve these challenges, realized by (1) making the (de)lithiation reversible by immobilizing FeOF nanoparticles and the discharge products of Fe nanoparticle and LiF over the graphene surface, and sandwiching them between graphene sheets to prevent them from migration and dissolution into electrolytes and (2) providing the inter-particle electric conductivity. In situ high energy synchrotron X-ray absorption spectroscopy (XAS) reveals that this new FeOF composite has a different but reversible (de)lithiation mechanism. Importantly, it demonstrated that introducing small amount of graphene can create new materials with desired properties, opening a new avenue for altering the (de)lithiation process. Such extraordinary performance represents a significant breakthrough in developing the sustainable conversion materials for replacing the intercalation compounds, eventually overcoming the driving range and cost barriers.

In-Situ Study of Temperature- and Magnetic-Field-Induced Incomplete Martensitic Transformation in Fe-Mn-Ga

Significant interest in the stoichiometric and off-stoichiometric Fe2MnGa alloys is based on their complex phase transition behavior and potential application. In this study, temperature- and magnetic-field-induced phase transformations in the Fe41.5Mn28Ga30.5 magnetic shape memory alloy were investigated by in situ synchrotron high-energy X-ray diffraction and in situ neutron diffraction techniques. It was found that incomplete phase transformation and phase coexistence behavior are always observed while applying and removing fields in Fe41.5Mn28Ga30.5. Typically, even at 4 K and under 0 T, or increasing the magnetic field to 11 T at 250 K, it can be directly detected that the martensite and austenite are in competition, making the phase transition incomplete. TEM observations at 300 K and 150 K indicate that the anti-phase boundaries and B2 precipitates may lead to field-induced incomplete phase transformation behavior collectively. The present study may enrich the understanding of field-induced martensitic transformation in the Fe-Mn-Ga magnetic shape memory alloys.

Rapid grain refinement and compositional homogenization in a cast binary Cu50Ni alloy achieved by friction stir processing

Friction stir processing (FSP) has been increasingly adopted for joining and processing materials in automotive, aerospace and industrial construction. During FSP a dynamic competition between high-speed shear deformation and deformation-induced heating brings about a complex competition between multiple dynamic microstructural evolution mechanisms making it difficult to predict the microstructural evolution pathway. Hence, improved understanding of microstructural evolution mechanisms during FSP can be beneficial for continued growth in the adoption of FSP for demanding applications of future. Towards this goal, this study uses a model binary Cu – 50 at.% Ni alloy to clarify the effect of single and double pass FSP on the microstructural evolution of a coarse grained and compositionally heterogeneous cast microstructure. High energy synchrotron X-ray diffraction, electron backscatter diffraction, and nanoindentation are used to clarify the microstructural evolution due to FSP. The process of compositional homogenization of as-cast segregations is studied by energy dispersive spectroscopy and atom probe tomography. Our results show that a single fast FSP pass at 30 mm.s−1 produces a 100 μm deep layer of submicrometric and hall-petch hardened CuNi grains. The initial cast compositional heterogeneities in a micrometric scale is rapidly transformed to nano-sized domains, mainly confined at grain boundaries. Double pass FSP increases the penetration depth of the processed layer and leads to a 2.9 times grain growth relative to single pass FSP. Grain fragmentation, discontinuous dynamic recrystallization, grain growth, and twinning mechanisms are discussed. These results highlight the value of FSP for ultrafast grain refinement and compositional homogenization of cast alloys.

Deformation processes of additively manufactured interstitial-strengthened high entropy alloy: In-situ high-energy synchrotron X-ray diffraction and microstructural appraisal

Deformation processes of additively manufactured interstitial-strengthened high entropy alloy: In-situ high-energy synchrotron X-ray diffraction and microstructural appraisal

Synchrotron High-Energy X-ray &amp; Neutron Diffraction, and Laser-Scanning Confocal Microscopy: &lt;i&gt;In-Situ&lt;/i&gt; Characterization Techniques for Bulk Nanocrystalline Metals

This report is aimed at giving an overview of the significance of the novel and innovative microstructural and microscopic characterization techniques for bulk nanostructured metals processed by severe plastic deformation, specifically high-pressure torsion (HPT). In practice, the microstructural relaxation behavior upon heating of nanostructured 316L stainless steel and CoCrFeNi high-entropy alloy was characterized by in-situ heating neutron diffraction measurements; the heterogeneous phase distribution of an HPT-bonded hetero-nanostructured Al-Mg alloy was examined using synchrotron high-energy X-ray diffraction; and the microstructural evolution upon heating of a nanostructured CoCrFeNiMn high-entropy alloy was examined by laser-scanning confocal microscopy. These novel techniques are complementary to each other and any other in- or ex-situ testing methods, especially when nanocrystalline metals are transforming microstructurally and compositionally with temperature and time in a hierarchical manner. The outcomes of the studies emphasize the importance of the methodologies and the development of characterization techniques for further in-depth exploration in the research field of severe plastic deformation.

Time resolved insights into abnormal grain growth by in situ synchrotron measurements

Large oligo-crystalline or single-crystalline metallic materials are of great interest for numerous applications, and a recently developed strategy for promoting abnormal grain growth induced by a cyclic heat treatment opens up new opportunities to manufacture single crystals with a size of several centimeters. So far, the entire available knowledge on this kind of abnormal grain growth has been elaborated based on time discrete observations and, thus, detailed insights into the interplay of elementary mechanisms are still lacking in open literature. The present study reveals time resolved insights into this kind of abnormal grain growth for the first time. It was possible to break down the influence of the individual heat treatment phases by in situ synchrotron high energy X-ray diffraction analysis during cyclic heat treatment. The results obtained not only help to gain a deep understanding of the abnormal grain growth mechanisms, they will also be the basis for an adjustment of the cyclic heat treatment process to improve its efficiency and to eventually obtain even larger single crystals.