Publications
440 results found
Volz N, Xue F, Zenk CH, et al., 2021, Understanding creep of a single-crystalline Co-Al-W-Ta superalloy by studying the deformation mechanism, segregation tendency and stacking fault energy, ACTA MATERIALIA, Vol: 214, ISSN: 1359-6454
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- Citations: 13
Lilensten L, Kostka A, Lartigue-Korinek S, et al., 2021, Partitioning of Solutes at Crystal Defects in Borides After Creep and Annealing in a Polycrystalline Superalloy, JOM, Vol: 73, Pages: 2293-2302, ISSN: 1047-4838
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- Citations: 3
Luo T, Serrano-Sanchez F, Bishara H, et al., 2021, Dopant-segregation to grain boundaries controls electrical conductivity of n-type NbCo(Pt)Sn half-Heusler alloy mediating thermoelectric performance, Acta Materialia, Vol: 217, Pages: 1-8, ISSN: 1359-6454
Science-driven design of future thermoelectric materials requires a deep understanding of the fundamental relationships between microstructure and transport properties. Grain boundaries in polycrystalline materials influence the thermoelectric performance through the scattering of phonons or the trapping of electrons due to space-charge effects. Yet, the current lack of careful investigations on grain boundary-associated features hinders further optimization of properties. Here, we study n-type NbCo1-xPtxSn half-Heusler alloys, which were synthesized by ball milling and spark plasma sintering (SPS). Post-SPS annealing was performed on one sample, leading to improved low-temperature electrical conductivity. The microstructure of both samples was examined by electron microscopy and atom probe tomography. The grain size increases from ~230 nm to ~2.38 μm upon annealing. Pt is found within grains and at grain boundaries, where it locally reduces the resistivity, as assessed by in situ four-point-probe electrical conductivity measurement. Our work showcases the correlation between microstructure and electrical conductivity, providing opportunities for future microstructural optimization by tuning the chemical composition at grain boundaries.
Gault B, Chiaramonti A, Cojocaru-Miredin O, et al., 2021, Atom probe tomography, NATURE REVIEWS METHODS PRIMERS, Vol: 1
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- Citations: 85
Gault B, Poplawsky JD, 2021, Correlating advanced microscopies reveals atomic-scale mechanisms limiting lithium-ion battery lifetime (vol 12, 3740, 2021), Nature Communications, Vol: 12, ISSN: 2041-1723
Sun B, Lu W, Gault B, et al., 2021, Chemical heterogeneity enhances hydrogen resistance in high-strength steels, Nature Materials, Vol: 20, Pages: 1629-1634, ISSN: 1476-1122
The antagonism between strength and resistance to hydrogen embrittlement in metallic materials is an intrinsic obstacle to the design of lightweight yet reliable structural components operated in hydrogen-containing environments. Economical and scalable microstructural solutions to this challenge must be found. Here, we introduce a counterintuitive strategy to exploit the typically undesired chemical heterogeneity within the material’s microstructure that enables local enhancement of crack resistance and local hydrogen trapping. We use this approach in a manganese-containing high-strength steel and produce a high dispersion of manganese-rich zones within the microstructure. These solute-rich buffer regions allow for local micro-tuning of the phase stability, arresting hydrogen-induced microcracks and thus interrupting the percolation of hydrogen-assisted damage. This results in a superior hydrogen embrittlement resistance (better by a factor of two) without sacrificing the material’s strength and ductility. The strategy of exploiting chemical heterogeneities, rather than avoiding them, broadens the horizon for microstructure engineering via advanced thermomechanical processing.
Luo T, Kuo JJ, Griffith KJ, et al., 2021, Nb-Mediated Grain Growth and Grain-Boundary Engineering in Mg<sub>3</sub>Sb<sub>2</sub>-Based Thermoelectric Materials, ADVANCED FUNCTIONAL MATERIALS, Vol: 31, ISSN: 1616-301X
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- Citations: 39
Gault B, Poplawsky JD, 2021, Correlating advanced microscopies reveals atomic-scale mechanisms limiting lithium-ion battery lifetime, Nature Communications, Vol: 12, Pages: 1-3, ISSN: 2041-1723
The longevity of a lithium-ion battery is limited by cathode degradation. Combining atom probe tomography and scanning transmission electron microscopy reveals that the degradation results from atomic-scale irreversible structural changes once lithium leaves the cathode during charging, thereby inhibiting lithium intercalation back into the cathode as the battery discharges. This information unveils possible routes for improving the lifetime of lithium-ion batteries.
Dear FF, Kontis P, Gault B, et al., 2021, Mechanisms of Ti3Al precipitation in hcp α-Ti, Acta Materialia, Vol: 212, ISSN: 1359-6454
Nucleation and growth of Ti3Alα2ordered domains inα-Ti–Al–X alloys were characterised using a combination of transmission electronmicroscopy, atom probe tomography and small angle X-ray scattering. Model alloys based on Ti–7Al (wt.%) and containing O, V and Mowere aged at 550◦C for times up to 120 d and the resulting precipitate dispersions were observed at intermediate points. Precipitates grewto around 30 nm in size, with a volume fraction of 6–10% depending on tertiary solutes. Interstitial O was found to increase the equilibriumvolume fraction ofα2, while V and Mo showed relatively little influence. Addition of any of the solutes in this study, but most prominentlyMo, was found to increase nucleation density and decrease precipitate size and possibly coarsening rate. Coarsening can be described by theLifshitz-Slyozov-Wagner model, suggesting a matrix diffusion-controlled coarsening mechanism (rather than control by interfacial coherency).Solutionising temperature was found to affect nucleation number density with an activation energy ofEf=1.5±0.4 eV, supporting the hypothesisthat vacancy concentration affectsα2nucleation. The observation that all solutes increase nucleation number density is also consistent with avacancy-controlled nucleation mechanism.
Kim S-H, Zhang X, Ma Y, et al., 2021, Influence of microstructure and atomic-scale chemistry on the direct reduction of iron ore with hydrogen at 700°C, Acta Materialia, Vol: 212, ISSN: 1359-6454
Steel is the most important material class in terms of volume and environmental impact. While it is a sustainability enabler, for instance through lightweight design, magnetic devices, and efficient turbines, its primary production is not. Iron is reduced from ores by carbon, causing 30% of the global CO2 emissions in manufacturing, qualifying it as the largest single industrial greenhouse gas emission source. Hydrogen is thus attractive as alternative reductant. Although this reaction has been studied for decades, its kinetics is not well understood, particularly during the wüstite reduction step which is much slower than hematite reduction. Some rate-limiting factors of this reaction are determined by the microstructure and local chemistry of the ores. Here, we report on a multi-scale structure and composition analysis of iron reduced from hematite with pure H2, reaching down to near-atomic scale. During reduction a complex pore- and microstructure evolves, due to oxygen loss and non-volume conserving phase transformations. The microstructure after reduction is an aggregate of nearly pure iron crystals, containing inherited and acquired pores and cracks. We observe several types of lattice defects that accelerate mass transport as well as several chemical impurities (Na, Mg, Ti, V) within the Fe in the form of oxide islands that were not reduced. With this study, we aim to open the perspective in the field of carbon-neutral iron production from macroscopic processing towards better understanding of the underlying microscopic transport and reduction mechanisms and kinetics.
Palanisamy D, Kovacs A, Hegde O, et al., 2021, Influence of crystalline defects on magnetic nanodomains in a rare-earth-free magnetocrystalline anisotropic alloy, PHYSICAL REVIEW MATERIALS, Vol: 5, ISSN: 2475-9953
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- Citations: 8
Schwarz TM, Dietrich CA, Ott J, et al., 2021, 3D sub-nanometer analysis of glucose in an aqueous solution by cryo-atom probe tomography, Scientific Reports, Vol: 11, Pages: 1-19, ISSN: 2045-2322
Atom Probe Tomography (APT) is currently a well-established technique to analyse the composition of solid materials including metals, semiconductors and ceramics with up to near-atomic resolution. Using an aqueous glucose solution, we now extended the technique to frozen solutions. While the mass signals of the common glucose fragments CxHy and CxOyHz overlap with (H2O)nH from water, we achieved stoichiometrically correct values via signal deconvolution. Density functional theory (DFT) calculations were performed to investigate the stability of the detected pyranose fragments. This paper demonstrates APT’s capabilities to achieve sub-nanometre resolution in tracing whole glucose molecules in a frozen solution by using cryogenic workflows. We use a solution of defined concentration to investigate the chemical resolution capabilities as a step toward the measurement of biological molecules. Due to the evaporation of nearly intact glucose molecules, their position within the measured 3D volume of the solution can be determined with sub-nanometre resolution. Our analyses take analytical techniques to a new level, since chemical characterization methods for cryogenically-frozen solutions or biological materials are limited.
Koprek A, Zabierowski P, Pawlowski M, et al., 2021, Effect of Cd diffusion on the electrical properties of the Cu(In,Ga)Se2 thin-film solar cell, Solar Energy Materials and Solar Cells, Vol: 224, Pages: 1-10, ISSN: 0927-0248
Cu(In,Ga)Se2 (CIGSe)-based solar cells are promising candidates for efficient sunlight harvesting. However, their complex composition and microstructure can change under operation conditions, for instance heating from sun light illumination can lead to a degradation in performance. Here, we investigate the thermally-induced degradation processes in a set of CIGSe-based solar cells that were annealed at temperatures between 150 °C and 300 °C. Using correlative atom probe tomography (APT)/transmission electron microscope (TEM), we found that the buffer/absorber interface is not sharp but consists of an interfacial zone (2–6.5 nm wide) where a gradient of constituent elements belonging to the CdS buffer and CIGSe absorber appears. An enhanced short-range Cd in-diffusion inside the CIGSe was observed whenever a low Ga/(Ga + In) ratio (≤ 0.15) occurred at the interface. This might indicate the presence of Ga vacancies as a channeling defect for Cd in-diffusion inside the CIGSe layer leading to a buried p/n-homojunction. We evidence that a considerable amount of Cd is found inside the CIGSe layer at annealing temperatures higher than 150 °C. Further investigations of the elemental redistribution inside the CIGSe layer combined with C–V measurements support the formation of CdCu + donor like defects deep inside the p-type CIGSe which lead to a strong compensation of the CIGSe layer and hence to strong deterioration of cell efficiency at annealing temperatures higher than 200 °C. Hence, understanding the degradation processes in Cu(In,Ga)Se2 (CIGSe)-based solar cells opens new opportunities for further improvement of the long-term device performance.
Souza Filho IR, Ma Y, Kulse M, et al., 2021, Sustainable steel through hydrogen plasma reduction of iron ore: Process, kinetics, microstructure, chemistry, Acta Materialia, Vol: 213, Pages: 1-16, ISSN: 1359-6454
Iron- and steelmaking is the largest single industrial CO2 emitter, accounting for 6.5% of all CO2 emissions on the planet. This fact challenges the current technologies to achieve carbon-lean steel production and to align with the requirement of a drastic reduction of 80% in all CO2 emissions by around 2050. Thus, alternative reduction technologies have to be implemented for extracting iron from its ores. The hydrogen-based direct reduction has been explored as a sustainable route to mitigate CO2 emissions, where the reduction kinetics of the intermediate oxide product FexO (wüstite) into iron is the rate-limiting step of the process. The total reaction has an endothermic net energy balance. Reduction based on a hydrogen plasma may offer an attractive alternative. Here, we present a study about the reduction of hematite using hydrogen plasma. The evolution of both, chemical composition and phase transformations was investigated in several intermediate states. We found that hematite reduction kinetics depends on the balance between the initial input mass and the arc power. For an optimized input mass-arc power ratio, complete reduction was obtained within 15 min of exposure to the hydrogen plasma. In such a process, the wüstite reduction is also the rate-limiting step towards complete reduction. Nonetheless, the reduction reaction is exothermic, and its rates are comparable with those found in hydrogen-based direct reduction. Micro- and nanoscale chemical and microstructure analysis revealed that the gangue elements partition to the remaining oxide regions, probed by energy dispersive spectroscopy (EDS) and atom probe tomography (APT). Si-enrichment was observed in the interdendritic fayalite domains, at the wüstite/iron hetero-interfaces and in the oxide particles inside iron. With proceeding reduction, however, such elements are gradually removed from the samples so that the final iron product is nearly free of gangue-related impurities. Our finding
Tsai S-P, Makineni SK, Gault B, et al., 2021, Precipitation formation on Σ5 and Σ7 grain boundaries in 316L stainless steel and their roles on intergranular corrosion, ACTA MATERIALIA, Vol: 210, ISSN: 1359-6454
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- Citations: 24
Kante S, Kuernsteiner P, Motylenko M, et al., 2021, Eutectoid growth of nanoscale amorphous Fe-Si nitride upon nitriding, ACTA MATERIALIA, Vol: 209, ISSN: 1359-6454
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- Citations: 6
Zhou X, Mianroodi JR, da Silva AK, et al., 2021, The hidden structure dependence of the chemical life of dislocations, Science Advances, Vol: 7, Pages: 1-9, ISSN: 2375-2548
Dislocations are one-dimensional defects in crystals, enabling their deformation, mechanical response, and transport properties. Less well known is their influence on material chemistry. The severe lattice distortion at these defects drives solute segregation to them, resulting in strong, localized spatial variations in chemistry that determine microstructure and material behavior. Recent advances in atomic-scale characterization methods have made it possible to quantitatively resolve defect types and segregation chemistry. As shown here for a Pt-Au model alloy, we observe a wide range of defect-specific solute (Au) decoration patterns of much greater variety and complexity than expected from the Cottrell cloud picture. The solute decoration of the dislocations can be up to half an order of magnitude higher than expected from classical theory, and the differences are determined by their structure, mutual alignment, and distortion field. This opens up pathways to use dislocations for the compositional and structural nanoscale design of advanced materials.
Medrano S, Zhao H, Gault B, et al., 2021, A model to unravel the beneficial contributions of trace Cu in wrought Al–Mg alloys, Acta Materialia, Vol: 208, Pages: 1-12, ISSN: 1359-6454
The softening and strengthening contributions in pre-deformed and aged Al–Mg–Cu alloys containing 3 wt.%Mg and 0.5 wt.%Cu are evaluated by a combination of microscopy, mechanical testing and modelling. A refined phenomenological model for the work hardening response, accounting for the separate effects of recovery and precipitation, is shown to be suitable for an unambiguous determination of the precipitation hardening contribution in these alloys. Significantly, it is found that the mechanical response of these alloys is not strongly impacted by Cu content (in the low Cu content regime), pre-deformation level or aging temperature meaning that the alloys are robust with respect to variations in composition. This is interesting from the perspective of alloy design concepts based on ‘recycling friendly’ compositions in applications that include paint-baking.
Antonov S, Shi R, Li D, et al., 2021, Nucleation and growth of α phase in a metastable β-Titanium Ti-5Al-5Mo-5V-3Cr alloy: Influence from the nano-scale, ordered-orthorhombic O" phase and α compositional evolution, SCRIPTA MATERIALIA, Vol: 194, ISSN: 1359-6462
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- Citations: 12
Ma Y, Wang Q, Zhou X, et al., 2021, A novel soft-magnetic B2-based multiprincipal-element alloy with a uniform distribution of coherent body-centered-cubic nanoprecipitates, Advanced Materials, Vol: 33, Pages: 1-7, ISSN: 0935-9648
Multiprincipal‐element alloys (MPEAs), including high‐entropy alloys, are a new class of materials whose thermodynamical properties are mainly driven by configuration entropy, rather than enthalpy in the traditional alloys, especially at high temperatures. Herein, the design of a novel soft‐magnetic nonequiatomic, quaternary MPEA is described, via tuning its chemical composition to deliberately manipulate its microstructure, such that it contains ultrafine ferromagnetic body‐centered‐cubic (BCC) coherent nanoprecipitates (3–7 nm) uniformly distributed in a B2‐phase matrix. The new alloy Al1.5Co4Fe2Cr exhibits high saturation magnetization (MS = 135.3 emu g‐1), low coercivity (HC = 127.3 A m‐1), high Curie temperature (TC = 1061 K), and high electrical resistivity (ρ = 244 μΩ cm), promising for soft magnets. More importantly, these prominent soft‐magnetic properties are observed to be retained even after the alloy is thermally exposed at 873 K for 555 h, apparently attributable to the excellent stability of the coherent microstructure. The versatility of the magnetic properties of this new alloy is discussed in light of the microstructural change induced by tuning the chemical composition, and the enhanced performance of the alloy is compared directly with that of the traditional soft‐magnetic alloys. The perspective is also addressed to design high‐performance soft‐magnetic alloys for high‐temperature applications.
Gomell L, Roscher M, Bishara H, et al., 2021, Properties and influence of microstructure and crystal defects in Fe2VAl modified by laser surface remelting, Scripta Materialia, Vol: 193, Pages: 153-157, ISSN: 1359-6462
Laser surface remelting can be used to manipulate the microstructure of cast materials. Here, we present a detailed analysis of Fe2VAl following laser surface remelting. Within the melt pool, elongated grains grow nearly epitaxially from the heat-affected zone. These grains are separated by low-angle grain boundaries with 1°–5° misorientations. Segregation of vanadium, carbon, and nitrogen at grain boundaries and dislocations is observed using atom probe tomography. The local electrical resistivity was measured by an in-situ four-point-probe technique. A smaller increase in electrical resistivity is observed at these low-angle grain boundaries compared to high-angle grain boundaries in a cast sample. This indicates that grain boundary engineering could potentially be used to manipulate thermoelectric properties.
Mouton I, Chang Y, Chakraborty P, et al., 2021, Hydride growth mechanism in zircaloy-4: Investigation of the partitioning of alloying elements, Materialia, Vol: 15, Pages: 1-11, ISSN: 2589-1529
The long-term safety of water-based nuclear reactors relies in part on the reliability of zirconium-based nuclear fuel cladding. Yet the progressive ingress of hydrogen during service makes zirconium alloys subject to delayed hydride cracking. Here, we use a combination of electron back-scattered diffraction and atom probe tomography to investigate specific microstructural features from the as-received sample and in the blocky-α microstructure, before and after electrochemical charging with hydrogen/deuterium followed by a low temperature heat treatment at 400 °C for 5 h followed by furnace cooling at a rate of 0.5 °C/min. Specimens for atom probe were prepared at cryogenic temperature to avoid the formation of spurious hydrides. We report on the compositional evolution of grains and grain boundaries over the course of the sample's thermal history, as well as the ways the growth of the hydrides modifies locally the composition and the structure of the alloy. We observe a significant amount of deuterium left in the matrix, even after the slow cooling and growth of the hydrides. Stacking faults form ahead of the growth front and the segregation of Sn at the hydride/matrix interface and on these faults. We propose that this segregation may facilitate further growth of the hydride. Our systematic investigation enables us discuss how the solute distribution affects the evolution of the alloy's properties during its service lifetime.
Donate-Buendia C, Kuernsteiner P, Stern F, et al., 2021, Microstructure formation and mechanical properties of ODS steels built by laser additive manufacturing of nanoparticle coated iron-chromium powders, ACTA MATERIALIA, Vol: 206, ISSN: 1359-6454
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- Citations: 53
Morsdorf L, Emelina E, Gault B, et al., 2021, Carbon redistribution in quenched and tempered lath martensite, ACTA MATERIALIA, Vol: 205, ISSN: 1359-6454
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- Citations: 44
Wei Y, Varanasi RS, Schwarz T, et al., 2021, Machine-learning-enhanced time-of-flight mass spectrometry analysis, Patterns, Vol: 2, Pages: 100192-100192, ISSN: 2666-3899
Mass spectrometry is a widespread approach used to work out what the constituents of a material are. Atoms and molecules are removed from the material and collected, and subsequently, a critical step is to infer their correct identities based on patterns formed in their mass-to-charge ratios and relative isotopic abundances. However, this identification step still mainly relies on individual users' expertise, making its standardization challenging, and hindering efficient data processing. Here, we introduce an approach that leverages modern machine learning technique to identify peak patterns in time-of-flight mass spectra within microseconds, outperforming human users without loss of accuracy. Our approach is cross-validated on mass spectra generated from different time-of-flight mass spectrometry (ToF-MS) techniques, offering the ToF-MS community an open-source, intelligent mass spectra analysis.
Rao Z, Dutta B, Kormann F, et al., 2021, Beyond Solid Solution High-Entropy Alloys: Tailoring Magnetic Properties via Spinodal Decomposition, ADVANCED FUNCTIONAL MATERIALS, Vol: 31, ISSN: 1616-301X
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- Citations: 43
Dubosq R, Rogowitz A, Schneider DA, et al., 2021, Fluid inclusion induced hardening: nanoscale evidence from naturally deformed pyrite, CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, Vol: 176, ISSN: 0010-7999
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- Citations: 9
Kuehbach M, Bajaj P, Zhao H, et al., 2021, On strong-scaling and open-source tools for analyzing atom probe tomography data, NPJ COMPUTATIONAL MATERIALS, Vol: 7
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- Citations: 9
Katnagallu S, Vernier S, Charpagne M-A, et al., 2021, Nucleation mechanism of hetero-epitaxial recrystallization in wrought nickel-based superalloys, SCRIPTA MATERIALIA, Vol: 191, Pages: 7-11, ISSN: 1359-6462
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- Citations: 20
He J, Cao L, Makineni SK, et al., 2021, Effect of interface dislocations on mass flow during high temperature and low stress creep of single crystal Ni-base superalloys, SCRIPTA MATERIALIA, Vol: 191, Pages: 23-28, ISSN: 1359-6462
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- Citations: 17
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