Publications
437 results found
Kim S-H, Stephenson LT, da Silva AK, et al., 2022, Phase separation and anomalous shape transformation in frozen microscale eutectic indium, Materialia, Vol: 26, ISSN: 2589-1529
The eutectic Ga-In (EGaIn) alloy has low vapour pressure, low toxicity, high thermal and electrical conductivities, and thus has shown a great potential for smart material applications. For such applications, EGaIn is maintained above its melting point, below which it undergoes solidification and phase separation. A scientific understanding of the structural and compositional evolution during thermal cycling could help further assess the application range of low-melting-point fusible alloys. Here, we use an integrated suite of cryogenically-enabled advanced microscopy & microanalysis to better understand phase separation and (re)mixing processes in EGaIn. We reveal an overlooked thermal-stimulus-response behaviour for frozen mesoscale EGaIn at cryogenic temperatures, with a sudden apparent volume expansion observed during in-situ heat-cycling, associated with the immiscibility between Ga and In during cooling and the formation of metastable Ga phases. These results emphasize the importance of the kinetics of rejuvenation, and open new paths for EGaIn as a self-healing material.
Zhu Y, Heo TW, Rodriguez JN, et al., 2022, Hydriding of titanium: Recent trends and perspectives in advanced characterization and multiscale modeling, CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE, Vol: 26, ISSN: 1359-0286
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- Citations: 6
Wu Y, Skokov KP, Schafer L, et al., 2022, A comparative study of Nd <sub>15</sub> Fe <sub>78 </sub>B<sub> 7</sub> and Nd <sub>15</sub> Co<sub> 78 </sub>B <sub>7</sub> systems: phase formations and coercivity mechanisms, ACTA MATERIALIA, Vol: 240, ISSN: 1359-6454
Saksena A, Kubacka D, Gault B, et al., 2022, The effect of gamma matrix channel width on the compositional evolution in a multi-component nickel-based superalloy, SCRIPTA MATERIALIA, Vol: 219, ISSN: 1359-6462
Kim S-H, Dong K, Zhao H, et al., 2022, Understanding the degradation of a model si anode in a li-ion battery at the atomic scale., Journal of Physical Chemistry Letters, Vol: 36, Pages: 8416-8421, ISSN: 1948-7185
To advance the understanding of the degradation of the liquid electrolyte and Si electrode, and their interface, we exploit the latest developments in cryo-atom probe tomography. We evidence Si anode corrosion from the decomposition of the Li salt before charge-discharge cycles even begin. Volume shrinkage during delithiation leads to the development of nanograins from recrystallization in regions left amorphous by the lithiation. The newly created grain boundaries facilitate pulverization of nanoscale Si fragments, and one is found floating in the electrolyte. P is segregated to these grain boundaries, which confirms the decomposition of the electrolyte. As structural defects are bound to assist the nucleation of Li-rich phases in subsequent lithiations and accelerate the electrolyte's decomposition, these insights into the developed nanoscale microstructure interacting with the electrolyte contribute to understanding the self-catalyzed/accelerated degradation Si anodes and can inform new battery designs unaffected by these life-limiting factors.
Xu Y, Toda H, Shimizu K, et al., 2022, Suppressed hydrogen embrittlement of high-strength Al alloys by Mn-rich intermetallic compound particles, ACTA MATERIALIA, Vol: 236, ISSN: 1359-6454
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- Citations: 13
Gomell L, Tsai S-P, Roscher M, et al., 2022, <i>In situ</i> nitriding of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Fe</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi>VAl</mml:mi></mml:mrow></mml:math> during laser surface remelting to manipulate microstructure and crystalline defects, Physical Review Materials, Vol: 6
Han L, Maccari F, Souza Filho IR, et al., 2022, A mechanically strong and ductile soft magnet with extremely low coercivity, Nature, Vol: 608, Pages: 310-316, ISSN: 0028-0836
Soft magnetic materials (SMMs) serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss1. The electrification of transport, households and manufacturing leads to an increase in energy consumption owing to hysteresis losses2. Therefore, minimizing coercivity, which scales these losses, is crucial3. Yet meeting this target alone is not enough: SMMs in electrical engines must withstand severe mechanical loads; that is, the alloys need high strength and ductility4. This is a fundamental design challenge, as most methods that enhance strength introduce stress fields that can pin magnetic domains, thus increasing coercivity and hysteresis losses5. Here we introduce an approach to overcome this dilemma. We have designed a Fe–Co–Ni–Ta–Al multicomponent alloy (MCA) with ferromagnetic matrix and paramagnetic coherent nanoparticles (about 91 nm in size and around 55% volume fraction). They impede dislocation motion, enhancing strength and ductility. Their small size, low coherency stress and small magnetostatic energy create an interaction volume below the magnetic domain wall width, leading to minimal domain wall pinning, thus maintaining the soft magnetic properties. The alloy has a tensile strength of 1,336 MPa at 54% tensile elongation, extremely low coercivity of 78 A m−1 (less than 1 Oe), moderate saturation magnetization of 100 A m2 kg−1 and high electrical resistivity of 103 μΩ cm.
Kim S-H, El-Zoka AA, Gault B, 2022, A liquid metal encapsulation for analyzing porous nanomaterials by atom probe tomography, Microscopy and Microanalysis, Vol: 28, Pages: 1198-1206, ISSN: 1083-0375
Analyzing porous (nano)materials via atom probe tomography has been notoriously difficult. Voids and pores act as concentrators of the electrostatic pressure, which results in premature specimen failure, and the electrostatic field distribution near voids leads to aberrations that are difficult to predict. In this study, we propose a new encapsulating method for porous samples using a low melting point Bi–In–Sn alloy, known as Field's metal. As a model material, we used porous iron made by direct-hydrogen reduction of single-crystalline wüstite. The complete encapsulation was performed using in situ heating on the stage of a scanning electron microscope. No visible corrosion nor dissolution of the sample occurred. Subsequently, specimens were shaped by focused ion-beam milling under cryogenic conditions at −190°C. The proposed approach is versatile and can be applied to provide good quality atom probe datasets from micro/nanoporous materials.
Gault B, Klaes B, Morgado FF, et al., 2022, Reflections on the spatial performance of atom probe tomography in the analysis of atomic neighborhoods, Microscopy and Microanalysis, Vol: 28, Pages: 1116-1126, ISSN: 1083-0375
Atom probe tomography (APT) is often introduced as providing “atomic-scale” mapping of the composition of materials and as such is often exploited to analyze atomic neighborhoods within a material. Yet quantifying the actual spatial performance of the technique in a general case remains challenging, as it depends on the material system being investigated as well as on the specimen's geometry. Here, by using comparisons with field-ion microscopy experiments, field-ion imaging and field evaporation simulations, we provide the basis for a critical reflection on the spatial performance of APT in the analysis of pure metals, low alloyed systems and concentrated solid solutions (i.e., akin to high-entropy alloys). The spatial resolution imposes strong limitations on the possible interpretation of measured atomic neighborhoods, and directional neighborhood analyses restricted to the depth are expected to be more robust. We hope this work gets the community to reflect on its practices, in the same way, it got us to reflect on our work.
Stender P, Gault B, Schwarz TM, et al., 2022, Status and direction of atom probe analysis of frozen liquids, Microscopy and Microanalysis, Vol: 28, Pages: 1150-1167, ISSN: 1083-0375
Imaging of liquids and cryogenic biological materials by electron microscopy has been recently enabled by innovative approaches for specimen preparation and the fast development of optimized instruments for cryo-enabled electron microscopy (cryo-EM). Yet, cryo-EM typically lacks advanced analytical capabilities, in particular for light elements. With the development of protocols for frozen wet specimen preparation, atom probe tomography (APT) could advantageously complement insights gained by cryo-EM. Here, we report on different approaches that have been recently proposed to enable the analysis of relatively large volumes of frozen liquids from either a flat substrate or the fractured surface of a wire. Both allowed for analyzing water ice layers which are several micrometers thick consisting of pure water, pure heavy water, and aqueous solutions. We discuss the merits of both approaches and prospects for further developments in this area. Preliminary results raise numerous questions, in part concerning the physics underpinning field evaporation. We discuss these aspects and lay out some of the challenges regarding the APT analysis of frozen liquids.
Im HJ, Makineni SK, Oh C-S, et al., 2022, Elemental Sub-Lattice Occupation and Microstructural Evolution in γ/γ′ Co-12Ti-4Mo-Cr Alloys, MICROSCOPY AND MICROANALYSIS, Vol: 28, Pages: 1335-1339, ISSN: 1431-9276
Gomell L, Tsai S-P, Roscher M, et al., 2022, In situ nitriding of Fe2VAl during laser surface remelting to manipulate microstructure and crystalline defects, Physical Review Materials, Vol: 6, Pages: 1-12, ISSN: 2475-9953
Tailoring the physical properties of complex materials for targeted applications requires optimizing the microstructure and crystalline defects that influence electrical and thermal transport and mechanical properties. Laser surface remelting can be used to modify the subsurface microstructure of bulk materials and hence manipulate their properties locally. Here, we introduce an approach to perform remelting in a reactive nitrogen atmosphere to form nitrides and induce segregation of nitrogen to structural defects. These defects arise from the fast solidification of the full-Heusler Fe2VAl compound that is a promising thermoelectric material. Advanced scanning electron microscopy, including electron channeling contrast imaging and three-dimensional electron backscatter diffraction, is complemented by atom probe tomography to study the distribution of crystalline defects and their local chemical composition. We reveal a high density of dislocations, which are stable due to their character as geometrically necessary dislocations. At these dislocations and low-angle grain boundaries, we observe segregation of nitrogen and vanadium, which can be enhanced by repeated remelting in nitrogen atmosphere. We propose that this approach can be generalized to other additive manufacturing processes to promote local segregation and precipitation states, thereby manipulating physical properties.
Dubosq R, Schneider DA, Zhou X, et al., 2022, Bubbles and atom clusters in rock melts: A chicken and egg problem, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 428, ISSN: 0377-0273
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- Citations: 4
Klaes B, Renaux J, Larde R, et al., 2022, Analytical Three-Dimensional Field Ion Microscopy of an Amorphous Glass FeBSi, MICROSCOPY AND MICROANALYSIS, Vol: 28, Pages: 1280-1288, ISSN: 1431-9276
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- Citations: 2
Katnagallu S, Morgado FF, Mouton I, et al., 2022, Three-Dimensional Atomically Resolved Analytical Imaging with a Field Ion Microscope, MICROSCOPY AND MICROANALYSIS, Vol: 28, Pages: 1264-1279, ISSN: 1431-9276
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- Citations: 2
Sun Z, Ma Y, Ponge D, et al., 2022, Thermodynamics-guided alloy and process design for additive manufacturing, Nature Communications, Vol: 13, Pages: 1-12, ISSN: 2041-1723
In conventional processing, metals go through multiple manufacturing steps including casting, plastic deformation, and heat treatment to achieve the desired property. In additive manufacturing (AM) the same target must be reached in one fabrication process, involving solidification and cyclic remelting. The thermodynamic and kinetic differences between the solid and liquid phases lead to constitutional undercooling, local variations in the solidification interval, and unexpected precipitation of secondary phases. These features may cause many undesired defects, one of which is the so-called hot cracking. The response of the thermodynamic and kinetic nature of these phenomena to high cooling rates provides access to the knowledge-based and tailored design of alloys for AM. Here, we illustrate such an approach by solving the hot cracking problem, using the commercially important IN738LC superalloy as a model material. The same approach could also be applied to adapt other hot-cracking susceptible alloy systems for AM.
López Freixes M, Zhou X, Zhao H, et al., 2022, Revisiting stress-corrosion cracking and hydrogen embrittlement in 7xxx-Al alloys at the near-atomic-scale, Nature Communications, Vol: 13, Pages: 1-9, ISSN: 2041-1723
The high-strength 7xxx series aluminium alloys can fulfil the need for light, high strength materials necessary to reduce carbon-emissions, and are extensively used in aerospace for weight reduction purposes. However, as all major high-strength materials, these alloys can be sensitive to stress-corrosion cracking (SCC) through anodic dissolution and hydrogen embrittlement (HE). Here, we study at the near-atomic-scale the intra- and inter-granular microstructure ahead and in the wake of a propagating SCC crack. Moving away from model alloys and non-industry standard tests, we perform a double cantilever beam (DCB) crack growth test on an engineering 7xxx Al-alloy. H is found segregated to planar arrays of dislocations and to grain boundaries that we can associate to the combined effects of hydrogen-enhanced localised plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanisms. We report on a Mg-rich amorphous hydroxide on the corroded crack surface and evidence of Mg-related diffusional processes leading to dissolution of the strengthening η-phase precipitates ahead of the crack.
Kim S-H, Yoo S-H, Shin S, et al., 2022, Controlled doping of electrocatalysts through engineering impurities, Advanced Materials, Vol: 34, Pages: 1-8, ISSN: 0935-9648
Fuel cells recombine water from H2 and O2 thereby can power, for example, cars or houses with no direct carbon emission. In anion-exchange membrane fuel cells (AEMFCs), to reach high power densities, operating at high pH is an alternative to using large volumes of noble metals catalysts at the cathode, where the oxygen-reduction reaction occurs. However, the sluggish kinetics of the hydrogen-oxidation reaction (HOR) hinders upscaling despite promising catalysts. Here, the authors observe an unexpected ingress of B into Pd nanocatalysts synthesized by wet-chemistry, gaining control over this B-doping, and report on its influence on the HOR activity in alkaline conditions. They rationalize their findings using ab initio calculations of both H- and OH-adsorption on B-doped Pd. Using this “impurity engineering” approach, they thus design Pt-free catalysts as required in electrochemical energy conversion devices, for example, next generations of AEMFCs, that satisfy the economic and environmental constraints, that is, reasonable operating costs and long-term stability, to enable the “hydrogen economy.”
Gault B, Schweinar K, Zhang S, et al., 2022, Correlating atom probe tomography with x-ray and electron spectroscopies to understand microstructure-activity relationships in electrocatalysts, Materials Research Society (MRS) Bulletin, Vol: 47, Pages: 718-726, ISSN: 0883-7694
The search for a new energy paradigm with net-zero carbon emissions requires new technologies for energy generation and storage that are at the crossroad between engineering, chemistry, physics, surface, and materials sciences. To keep pushing the inherent boundaries of device performance and lifetime, we need to step away from a cook-and-look approach and aim to establish the scientific ground to guide the design of new materials. This requires strong efforts in establishing bridges between microscopy and spectroscopy techniques, across multiple scales. Here, we discuss how the complementarities of x-ray- and electron-based spectroscopies and atom probe tomography can be exploited in the study of surfaces and subsurfaces to understand structure–property relationships in electrocatalysts.
Raabe D, Ponge D, Uggowitzer PJ, et al., 2022, Making sustainable aluminum by recycling scrap: The science of "dirty " alloys, PROGRESS IN MATERIALS SCIENCE, Vol: 128, ISSN: 0079-6425
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- Citations: 49
ROUSSEAU L, Normand A, Morgado FF, et al., 2022, Introducing field evaporation energy loss spectroscopy
<jats:title>Abstract</jats:title> <jats:p>Identifying the chemical and bonding state of all atoms in a material in three-dimensions remains an unresolved issue. Here, we demonstrate that this information was always intrinsically present within atom probe tomography experimental data, but until now it was overlooked or consciously suppressed. Using an analytical model and robust simulations, we show that the mass peak shape contains information on the ion’s energy loss related to how the atom was bound to the surface, and its neighbourhood. We introduce a complete data processing approach, termed field evaporation energy loss spectroscopy (FEELS), that retrieves and maps variations of the chemical state in 3D with nanometric resolution. We showcase the application of FEELS by analyzing microstructural features and defects in an array of metallic materials. FEELS can be applied on any atom probe data set to more profoundly analyse a material’s characteristics.</jats:p>
Wang S, Gavalda-Diaz O, Luo T, et al., 2022, The effect of hydrogen on the multiscale mechanical behaviour of a La(Fe,Mn,Si)13-based magnetocaloric material, Journal of Alloys and Compounds, Vol: 906, Pages: 1-10, ISSN: 0925-8388
Magnetocaloric cooling offers the potential to improve the efficiency of refrigeration devices and hence cut the significant CO2 emissions associated with cooling processes. A critical issue in deployment of this technology is the mechanical degradation of the magnetocaloric material during processing and operation, leading to limited service-life. The mechanical properties of hydrogenated La(Fe,Mn,Si)13-based magnetocaloric material are studied using macroscale bending tests of polycrystalline specimens and in situ micropillar compression tests of single crystal specimens. The impact of hydrogenation on the mechanical properties are quantified. Understanding of the deformation/failure mechanisms is aided by characterization with transmission electron microscopy and atom probe tomography to reveal the arrangement of hydrogen atoms in the crystal lattice. Results indicate that the intrinsic strength of this material is ~3-6 GPa and is dependent on the crystal orientation. Single crystals under compressive load exhibit shearing along specific crystallographic planes. Hydrogen deteriorates the strength of La(Fe,Mn,Si)13 through promotion of transgranular fracture. The weakening effect of hydrogen on single crystals is anisotropic; it is significant upon shearing parallel to the {111} crystallographic planes but is negligible when the shear plane is {001}-oriented. APT analysis suggests that this is associated with the close arrangement of hydrogen atoms on {222} planes.
Varanasi RS, Gault B, Ponge D, 2022, Effect of Nb micro-alloying on austenite nucleation and growth in a medium manganese steel during intercritical annealing, ACTA MATERIALIA, Vol: 229, ISSN: 1359-6454
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- Citations: 16
Ma Y, Filho IRS, Bai Y, et al., 2022, Hierarchical nature of hydrogen-based direct reduction of iron oxides, SCRIPTA MATERIALIA, Vol: 213, ISSN: 1359-6462
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- Citations: 26
Khanchandani H, Ponge D, Zaefferer S, et al., 2022, Hydrogen-induced hardening of a high-manganese twinning induced plasticity steel, Materialia, Vol: 28, Pages: 1-10, ISSN: 2589-1529
High-manganese twinning-induced plasticity (TWIP) steels exhibit high strain hardening, high tensile strength, and high ductility, which make them attractive for structural applications. At low tensile strain rates, TWIP steels are prone to hydrogen embrittlement (HE). Here though, we study the hardening and strengthening resulting from electrochemical hydrogen-charging of a surface layer of a Fe-26.9Mn-0.28C (wt.%) TWIP steel. We observed a 20% increase in yield strength following the electrochemical hydrogen-charging, accompanied by a reduction in ductility from 75% to 10% at a tensile strain rate of 10−3s−1. The microstructural evolution during tensile deformation was examined at strain levels of 3%, 5% and 7% by electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) to study the dislocation structure of the hardened region. As expected, the microstructure of the hydrogen-hardened and the uncharged regions of the material evolve differently. The uncharged areas show entangled dislocation structures, indicating slip from a limited number of potentially coplanar slip systems. In contrast, hydrogen segregated to the grain boundaries, revealed by the deuterium-labelled atom probe tomography, delays the dislocation nucleation by blocking dislocation sources at the grain boundaries. The charged areas hence first show the formation of cells, indicating dislocation entanglement from more non-coplanar slip systems. With increasing strain, these cells dissolve, and stacking faults and strain-induced ε-martensite are formed, promoted by the presence of hydrogen. The influence of hydrogen on dislocation structures and the overall deformation mechanism is discussed in details.
Tan Q, Yan Z, Wang H, et al., 2022, The role of β pockets resulting from Fe impurities in hydride formation in titanium, Scripta Materialia, Vol: 213, Pages: 114640-114640, ISSN: 1359-6462
The corrosion potential of commercially pure titanium in NaCl solutions is dramatically affected by trace Fe additions, which cause the appearance of submicron pockets of β phase at grain boundary triple points. Furthermore, the low solubility of hydrogen in hexagonal close-packed α-Ti makes titanium alloys prone to subsequent hydride-associated failures due to stress corrosion cracking. We analyzed α-α and α-β sections of the abutting grain boundary of a β pocket in a Grade 2 CP-Ti, and the α-β phase boundary. Fe and H partition to β and segregate at the grain boundary, but no segregation is seen at the α-β phase boundary. In contrast, a significant Ni (>1 at%) accumulation is observed at the α-β phase boundary. We propose that the β-pockets act as hydrogen traps and facilitate the nucleation and growth of hydrides along grain boundaries in CP-Ti.
Tan Q, Yan Z, Li R, et al., 2022, <i>In</i>-<i>situ</i> synchrotron-based high energy X-ray diffraction study of the deformation mechanism of δ-hydrides in a commercially pure titanium, SCRIPTA MATERIALIA, Vol: 213, ISSN: 1359-6462
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- Citations: 4
da Silva AK, Souza Filho IR, Lu W, et al., 2022, A sustainable ultra-high strength Fe18Mn3Ti maraging steel through controlled solute segregation and alpha-Mn nanoprecipitation, Nature Communications, Vol: 13, Pages: 1-8, ISSN: 2041-1723
The enormous magnitude of 2 billion tons of alloys produced per year demands a change in design philosophy to make materials environmentally, economically, and socially more sustainable. This disqualifies the use of critical elements that are rare or have questionable origin. Amongst the major alloy strengthening mechanisms, a high-dispersion of second-phase precipitates with sizes in the nanometre range is particularly effective for achieving ultra-high strength. Here, we propose an alternative segregation-based strategy for sustainable steels, free of critical elements, which are rendered ultrastrong by second-phase nano-precipitation. We increase the Mn-content in a supersaturated, metastable Fe-Mn solid solution to trigger compositional fluctuations and nano-segregation in the bulk. These fluctuations act as precursors for the nucleation of an unexpected α-Mn phase, which impedes dislocation motion, thus enabling precipitation strengthening. Our steel outperforms most common commercial alloys, yet it is free of critical elements, making it a new platform for sustainable alloy design.
Joseph S, Kontis P, Chang Y, et al., 2022, A cracking oxygen story: a new view of stress corrosion cracking in titanium alloys, Acta Materialia, Vol: 227, Pages: 117687-117687, ISSN: 1359-6454
Titanium alloys can suffer from halide-associated stress corrosion cracking at elevated temperatures e.g., in jet engines, where chlorides and Ti-oxide promote the cracking of water vapour in the gas stream, depositing embrittling species at the crack tip. Here we report, using isotopically-labelled experiments, that crack tips in an industrial Ti-6Al-2Sn-4Zr-6Mo alloy are strongly enriched (>5 at.%) in oxygen from the water vapour, far greater than the amounts (0.25 at.%) required to embrittle the material. Surprisingly, relatively little hydrogen (deuterium) is measured, despite careful preparation and analysis. Therefore, we suggest that a combined effect of O and H leads to cracking, with O playing a vital role, since it is well-known to cause embrittlement of the alloy. In contrast it appears that in α + β Ti alloys, it may be that H may drain away into the bulk owing to its high solubility in β-Ti, rather than being retained in the stress field of the crack tip. Therefore, whilst hydrides may form on the fracture surface, hydrogen ingress might not be the only plausible mechanism of embrittlement of the underlying matrix. This possibility challenges decades of understanding of stress-corrosion cracking as being related solely to the hydrogen enhanced localised plasticity (HELP) mechanism, which explains why H-doped Ti alloys are embrittled. This would change the perspective on stress corrosion embrittlement away from a focus purely on hydrogen to also consider the ingress of O originating from the water vapour, insights critical for designing corrosion resistant materials.
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