ORCID Profile
0000-0002-2338-1016
Current Organisation
Friedrich-Alexander-Universität Erlangen-Nürnberg
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Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.ULTRAMIC.2015.06.002
Abstract: Using modern wide-angle atom probes, it is possible to acquire atomic scale 3D data containing 1000 s of nm(2) of interfaces. It is therefore possible to probe the distribution of segregated species across these interfaces. Here, we present techniques that allow the production of models for interfacial excess (IE) mapping and discuss the underlying considerations and s ling statistics. We also show, how the same principles can be used to achieve thickness mapping of thin films. We demonstrate the effectiveness on ex le applications, including the analysis of segregation to a phase boundary in stainless steel, segregation to a metal-ceramic interface and the assessment of thickness variations of the gate oxide in a fin-FET.
Publisher: Elsevier BV
Date: 10-2016
DOI: 10.1016/J.ULTRAMIC.2016.07.008
Abstract: In this paper, we present pathways for improving the reconstruction of atom probe data on a coarse (>10nm) scale, based on computational geometry. We introduce a way to iteratively improve an atom probe reconstruction by adjusting it, so that certain known shape criteria are fulfilled. This is achieved by creating an implicit approximation of the reconstruction through a barycentric coordinate transform. We demonstrate the application of these techniques to the compensation of trajectory aberrations and the iterative improvement of the reconstruction of a dataset containing a grain boundary. We also present a method for obtaining a hull of the dataset in both detector and reconstruction space. This maximises data utilisation, and can be used to compensate for ion trajectory aberrations caused by residual fields in the ion flight path through a 'master curve' and correct for overall shape deviations in the data.
Publisher: Elsevier BV
Date: 08-2022
Publisher: American Chemical Society (ACS)
Date: 21-10-2021
Publisher: Springer Science and Business Media LLC
Date: 03-02-2022
DOI: 10.1007/S10853-022-06937-Y
Abstract: This study demonstrates metal fused filament fabrication (MF 3 ) as an alternative additive and highly flexible manufacturing method for free-form fabrication of high-performance alloys. This novel processing, which is similar to Metal injection molding (MIM), enables a significant reduction in manufacturing costs for complex geometries, since expensive machining can be avoided. Utilizing existing equipment and reducing material expense, MF 3 can pave the way for new and low-cost applications of IN 718, which were previously limited by high manufacturing costs. Iterative process optimization is used to find the most suitable MF 3 process parameters. High relative density above 97% after pressureless sintering can be achieved if temperature profiles and atmospheres are well adjusted for thermal debinding and sintering. In this study, the influence of processing parameters on the resulting microstructure of MF 3 IN 718 is investigated. S les sintered in vacuum show coarse-grained microstructure with an area fraction of 0.36% NbC at grain boundaries. Morphology and composition of formed precipitates are analyzed using transmission electron microscopy and atom probe tomography. The γ/γ″/γ′ phases’ characteristics for IN 718 were identified. Conventional heat treatment is applied for further tailoring of mechanical properties like hardness, toughness and creep behavior. Fabricated s les achieve mechanical properties similar to MIM IN 718 presented in literature. Graphical abstract
Publisher: Springer Science and Business Media LLC
Date: 13-04-2016
DOI: 10.1038/NCOMMS11225
Abstract: The large fraction of material residing at grain boundaries in nanocrystalline metals and alloys is responsible for their ultrahigh strength, but also undesirable microstructural instability under thermal and mechanical loads. However, the underlying mechanism of stress-driven microstructural evolution is still poorly understood and precludes rational alloy design. Here we combine quantitative in situ electron microscopy with three-dimensional atom-probe tomography to directly link the mechanics and kinetics of grain boundary migration in nanocrystalline Al films with the excess of O atoms at the boundaries. Site-specific nanoindentation leads to grain growth that is retarded by impurities, and enables quantification of the critical stress for the onset of grain boundary migration. Our results show that a critical excess of impurities is required to stabilize interfaces in nanocrystalline materials against mechanical driving forces, providing new insights to guide control of deformation mechanisms and tailoring of mechanical properties apart from grain size alone.
Publisher: Wiley
Date: 19-08-2014
Abstract: To be able to correlate the catalytic properties of nanoparticles with their structure, detailed knowledge about their make-up on the atomic level is required. Herein, we demonstrate how atom-probe tomography (APT) can be used to quantitatively determine the three-dimensional distribution of atoms within a Au@Ag nanoparticle with near-atomic resolution. We reveal that the elements are not evenly distributed across the surface and that this distribution is related to the surface morphology and residues from the particle synthesis.
Publisher: Elsevier BV
Date: 04-2015
Publisher: Elsevier BV
Date: 12-2019
Publisher: MDPI AG
Date: 08-09-2020
DOI: 10.3390/MIN10090791
Abstract: The sphalerite from the Burgstaetter Gangzug, a vein system of the Upper Harz Mountain nearby the town of Clausthal-Zellerfeld, exhibits a very interesting and partly complementary incorporation pattern of Cu, In and Sb, which has not yet been reported for natural sphalerite. A sphalerite specimen was characterized with electron probe micro-analysis (EPMA) and atom probe tomography (APT). Based on the EPMA results and a multilinear regression, a relation expressed as Cu = 0.98In + 1.81Sb + 0.03 can be calculated to describe the correlation between the elements. This indicates, that the incorporation mechanisms of In and Sb in the structure differ substantially. Indium is incorporated with the ratio Cu:In = 1:1 like in roquesite (CuInS2), supporting the coupled substitution mechanism 2Zn2+ → Cu+ + In3+. In contrast, Sb is incorporated with a ratio of Cu:Sb = 1.81:1. APT, which has a much higher spatial resolution indicates a ratio of Cu: Sb = 2.28: 1 in the entire captured volume, which is similar to the ratio calculated by EPMA, yet with inhomogeneities at the nanometer-scale. Analysis of the solute distribution shows two distinct sizes of clusters that are rich in Cu, Sb and Ag.
Publisher: Walter de Gruyter GmbH
Date: 08-2018
DOI: 10.3139/147.110543
Publisher: Elsevier BV
Date: 06-2018
Publisher: No publisher found
Date: 2021
Publisher: Elsevier BV
Date: 2016
DOI: 10.1016/J.ULTRAMIC.2015.09.005
Abstract: Here, we present a new method that utilises shadow masks in a broad ion beam system to prepare atom probe s les. It is particularly suited to non-conductors and materials with surface layers such as surface oxides, implanted layers or thin films. This new approach bypasses the focused ion beam (FIB) lift-out step, increasing the s le throughput, dramatically reducing the required FIB beam time and decreasing the complexity of s le preparation.
Publisher: American Chemical Society (ACS)
Date: 06-05-2013
DOI: 10.1021/JA402512R
Abstract: We show that long-chain 1-alcohols can be produced with high selectivities using heterogeneous CO hydrogenation catalysis. This breakthrough is achieved through the targeted design of "CoCuMn" nanosized core-shell particles using co-precipitation of metal salts into oxalate precursors and subsequent thermal decomposition. Using stoichiometric CO/H2 feeds, the selectivities to 1-alcohols or combined 1-alcohols/1-alkenes are usually higher than 60% and occasionally up to 95%. The Anderson-Schulz-Flory chain-lengthening probabilities for these products are higher than 0.6, but usually below 0.9 so as to optimize the C8-C14 slate as feedstock for plasticizers, lubricants, or detergents.
Publisher: Elsevier BV
Date: 2020
DOI: 10.2139/SSRN.3655860
Publisher: American Chemical Society (ACS)
Date: 05-09-2017
DOI: 10.1021/ACS.LANGMUIR.7B01820
Abstract: Atom probe tomography was used to analyze self-assembled monolayers of thiophene on different surfaces, including tungsten, platinum, and aluminum, where the tungsten was examined in both pristine and oxidized forms. A glovebag with controlled atmospheres was used to alter the level of oxidation for tungsten. It was shown that different substrates lead to substantial changes in the way thiophene adsorbs on the surface. Furthermore, the oxidation of the surface strongly influenced the adsorption behavior of the thiophene molecules, leading to clear differences in the amounts and compositions of field evaporated ions and molecular ions.
Publisher: Elsevier BV
Date: 03-2019
Publisher: Springer Science and Business Media LLC
Date: 02-10-2013
Publisher: Geological Society of America
Date: 10-12-2020
DOI: 10.1130/G48417.1
Abstract: Olivine is one of the most important minerals used to reconstruct magmatic processes, yet the rare earth element (REE) systematics of Fe-rich olivine in igneous rocks and ore deposits is poorly understood. As detected by in situ laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analysis, cumulate fayalite (Fe2SiO4) in the Paleoproterozoic Vergenoeg F-Fe-REE deposit of the Bushveld large igneous province (LIP) in South Africa contains the highest heavy REE (HREE) contents ever recorded for olivine, with HREE enrichment of as much as 6000× chondritic values. Atom probe tomography maps confirm the incorporation of the HREEs into the fayalite crystal lattice, facilitated by lithium acting as a main charge balancer and by high REE contents in the highly fractionated felsic parental melt that is related to the Bushveld LIP. The high HREE concentrations of fayalite in concert with its high modal abundance (& vol%) indicate that the fayalite cumulates are the main host for the HREE mineralization of the Vergenoeg deposit. Fayalites of Vergenoeg demonstrate that Fe-rich olivine may fractionate large amounts of HREEs, and we propose fayalite cumulates as potential future targets for HREE exploration.
Publisher: Elsevier BV
Date: 07-2019
Publisher: Wiley
Date: 22-05-2020
DOI: 10.1002/MDE.3174
Publisher: Elsevier BV
Date: 02-2023
Publisher: Oxford University Press (OUP)
Date: 08-2018
DOI: 10.1017/S1431927618012370
Abstract: Understanding oxide–metal interfaces is crucial to the advancement of materials and components for many industries, most notably for semiconductor devices and power generation. Atom probe tomography provides three-dimensional, atomic scale information about chemical composition, making it an excellent technique for interface analysis. However, difficulties arise when analyzing interfacial regions due to trajectory aberrations, such as local magnification, and reconstruction artifacts. Correlative microscopy and field simulation techniques have revealed that nonuniform evolution of the tip geometry, caused by heterogeneous field evaporation, is partly responsible for these artifacts. Here we attempt to understand these trajectory artifacts through a study of the local evaporation field conditions. With a better understanding of the local evaporation field, it may be possible to account for some of the local magnification effects during the reconstruction process, eliminating these artifacts before data analysis.
Publisher: Springer Science and Business Media LLC
Date: 16-03-2018
Publisher: Elsevier BV
Date: 03-2016
Publisher: Oxford University Press (OUP)
Date: 08-2022
DOI: 10.1017/S1431927621000465
Abstract: The ability to analyze nanoparticles in the atom probe has often been limited by the complexity of the s le preparation. In this work, we present a method to lift–out single nanoparticles in the scanning electron microscope. First, nanoparticles are dispersed on a lacey carbon grid, then positioned on a sharp substrate tip and coated on all sides with a metallic matrix by physical vapor deposition. Compositional and structural insights are provided for spherical gold nanoparticles and a segregation of silver and copper in silver copper oxide nanorods is shown in 3D atom maps. Using the standard atom probe reconstruction algorithm, data quality is limited by typical standard reconstruction artifacts for heterogeneous specimens (trajectory aberrations) and the choice of suitable coatings for the particles. This approach can be applied to various unsupported free-standing nanoparticles, enables preselection of particles via correlative techniques, and reliably produces well-defined structured s les. The only prerequisite is that the nanoparticles must be large enough to be manipulated, which was done for sizes down to ~50 nm.
Publisher: Elsevier BV
Date: 05-2021
Publisher: Oxford University Press (OUP)
Date: 15-12-2022
Abstract: Ultramicrotomy with automated section collection enables a reliable collection of sequential sections for 3D imaging. Here, we introduce a system for collecting several hundred ultra-thin sections on tape as a flexible polymeric substrate. The tape is stored within a portable cassette, which can be used as a modular platform for different applications. The motorized cassette with its retractable section collection cantilever is installed in front of an ultramicrotome for section collection. Section collection and imaging of the sections can be conducted without requiring any manual handling of the tape, which reduces the risk of specimen contamination and offers various options for automatization and cross-compatibility. For instance, processing steps such as a plasma glow-discharge of the substrate can be performed on the tape while it is enclosed in the cassette. As a proof of concept, more than 300 sequential sections at a thickness of 150 nm were cut from a polymer blend s le and collected on a metal-coated tape. Finally, a subset of 15 × 15 × 15 µm³ of the original s le volume was successfully imaged by confocal Raman microscopy and reconstructed at submicron resolution. The serial section cassette harbors the potential to standardize, simplify, and automate s le library collection, imaging, and storage.
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.ULTRAMIC.2015.04.014
Abstract: Due to their unique properties, nano-sized materials such as nanoparticles and nanowires are receiving considerable attention. However, little data is available about their chemical makeup at the atomic scale, especially in three dimensions (3D). Atom probe tomography is able to answer many important questions about these materials if the challenge of producing a suitable s le can be overcome. In order to achieve this, the nanomaterial needs to be positioned within the end of a tip and fixed there so the s le possesses sufficient structural integrity for analysis. Here we provide a detailed description of various techniques that have been used to position nanoparticles on substrates for atom probe analysis. In some of the approaches, this is combined with deposition techniques to incorporate the particles into a solid matrix, and focused ion beam processing is then used to fabricate atom probe s les from this composite. Using these approaches, data has been achieved from 10-20 nm core-shell nanoparticles that were extracted directly from suspension (i.e. with no chemical modification) with a resolution of better than ± 1 nm.
Publisher: Elsevier BV
Date: 06-2018
DOI: 10.1016/J.ULTRAMIC.2018.03.011
Abstract: Analysing the distribution of selected chemical elements with respect to interfaces is one of the most common tasks in data mining in atom probe tomography. This can be represented by 1D concentration profiles, 2D concentration maps or proximity histograms, which represent concentration, density etc. of selected species as a function of the distance from a reference surface/interface. These are some of the most useful tools for the analysis of solute distributions in atom probe data. In this paper, we present extensions to the proximity histogram in the form of 'local' proximity histograms, calculated for selected parts of a surface, and pseudo-2D concentration maps, which are 2D concentration maps calculated on non-flat surfaces. This way, local concentration changes at interfaces or and other structures can be assessed more effectively.
Publisher: Elsevier BV
Date: 04-2014
Publisher: Oxford University Press (OUP)
Date: 03-02-2012
DOI: 10.1017/S1431927611012530
Abstract: Atom probe tomography (APT) provides three-dimensional analytical imaging of materials with near-atomic resolution using pulsed field evaporation. The processes of field evaporation can cause atoms to be placed at positions in the APT reconstruction that can deviate slightly from their original site in the material. Here, we describe and model one such process—that of preferential retention of solute atoms in multicomponent systems. Based on relative field evaporation probabilities, we calculate the point spread function for the solute atom distribution in the “ z ,” or in-depth direction, and use this to extract more accurate solute concentration profiles.
Publisher: Wiley
Date: 29-09-2011
DOI: 10.1002/JEMT.21081
Abstract: Atom probe tomography (APT) is a mass spectrometry method with atomic-scale spatial resolution that can be used for the investigation of a wide range of materials. The main limiting factor with respect to the type of problems that can be addressed is the small volume investigated and the randomness of common s le preparation methods. With existing site-specific specimen preparation methods it is still challenging to rapidly and reproducibly produce large numbers of successful s les from specifically selected grain boundaries or interfaces for systematic studies. A new method utilizing both focused ion beam (FIB) and transmission electron microscopy (TEM) is presented that can be used to reproducibly produce damage-free atom probe s les with features of interest at any desired orientation with an accuracy of better than 50 nm from s les that require very little prior preparation.
Publisher: Oxford University Press (OUP)
Date: 08-2022
DOI: 10.1017/S1431927621012332
Abstract: We investigated a new method for estimating specimen hydrogen content in atom probe tomography (APT) in experiments where molecular hydrogen ions () originating from the measurement environment can overlap with deuterium (D+) in the mass-to-charge-state spectrum, thus preventing the direct application of isotopic marking for unambiguous hydrogen analysis. First, we applied an existing method for hydrogen content estimation, using ratios obtained from paired deuterated/nondeuterated experiments. These measurements demonstrated sufficient residual uncertainty to motivate exploring an alternative method to accurately estimate hydrogen content. By varying the time between evaporation events, it is then shown that a highly correlated relationship between field evaporation rate and hydrogen content exists and can also be used to predict hydrogen content. This leads to a new method for measuring hydrogen content within the specimen. We combine this extrapolation technique with continuous cycling of the evaporation rate or pulse frequency during an APT experiment. This could enable spatially resolved imaging of hydrogen concentrations despite the presence of a contaminant background hydrogen signal, without the need for deuteration.
Publisher: Springer Science and Business Media LLC
Date: 26-03-2018
Publisher: Oxford University Press (OUP)
Date: 08-2022
DOI: 10.1017/S1431927621013702
Abstract: Atom probe tomography (APT) is a single-ion sensitive time-of-flight mass spectrometry method with near-atomic spatial resolution. In principle, it can be used to detect any chemical element, but so far hydrogen in the form of protium (1H) had to be largely excluded. This is owing to the residual H emitted from the stainless-steel chambers and in-vacuum parts commonly used in atom probe instrumentation. This residual H is then picked up in the APT experiment. In this paper, we show that by replacing the stainless-steel chamber and in-vacuum parts with titanium parts, this residual H can largely be removed, thus enabling the direct imaging of H using APT. We show that besides the drastic reduction of H, also other contaminants such as O, OH, and H2O are reduced by employing this instrument. In the current set-up, the instrument is equipped with high-voltage pulsing limiting the application to conductive materials.
Publisher: MDPI AG
Date: 29-10-2021
DOI: 10.3390/MET11111727
Abstract: Due to their low density, magnesium alloys are very appealing for light-weight constructions. However, the use of the most common magnesium alloy, AZ91 (Mg 9 wt.% Al, 1 wt.% Zn), is limited to temperatures below 150 °C due to creep failure. Several alloys with an improved creep resistance have been developed in the past, for ex le the alloy MRI 230D or Ca-alloyed AZ91 variants. However, there is an ongoing discussion in the literature regarding the mechanisms of the improved creep resistance. One factor claimed to be responsible for the improved creep resistance is the intermetallic phases which form during casting. Another possible explanation is an increased creep resistance due to the formation of precipitates. To gain more insight into the improved creep resistance of MRI 230D, nanoindentation measurements have been performed on the different phases of as-cast, creep-deformed and heat-treated s les of MRI 230D and Ca-alloyed AZ91 variants. These nanoindentation measurements clearly show that the intermetallic phase (IP) of the alloy MRI 230D does not lose strength during creep deformation in contrast to the Ca-alloyed AZ91 variants. High-temperature nanoindentation measurements performed at 200 °C clearly show that the intermetallic phases of the MRI 230D alloy maintain their strength. This is in clear contrast to the Ca-alloyed AZ91 variants, where the IP is significantly softer at 200 °C than at room temperature. Atom probe measurements have been used to gain insight into the differences in terms of chemical composition between the IPs of MRI 230D and the Ca-alloyed AZ91 variants in order to understand the dissimilar behaviour in terms of strength loss with increasing temperature.
Publisher: Elsevier BV
Date: 09-2017
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.ULTRAMIC.2013.03.004
Abstract: In this paper we present new methods for feature analysis in atom probe tomography data that have useful applications in materials characterisation. The analysis works on the principle of Voronoi subvolumes and piecewise linear approximations, and feature delineation based on the distance to the centre of mass of a subvolume (DCOM). Based on the coordinate systems defined by these approximations, two ex les are shown of the new types of analyses that can be performed. The first is the analysis of line-like-objects (i.e. dislocations) using both proxigrams and line-excess plots. The second is interfacial excess mapping of an InGaAs quantum dot.
Publisher: Elsevier BV
Date: 08-2014
Publisher: Springer Science and Business Media LLC
Date: 16-03-2012
Publisher: Wiley
Date: 23-09-2021
Abstract: Fabrication of titanium components is very cost intensive, partly due to the complex machining and limited recyclability of waste material. For electrochemical applications, the excellent corrosion resistance of pure titanium is of high importance, whereas medium mechanical strength of fabricated parts is sufficient for such a use case. For smaller parts, metal fused filament fabrication (MF 3 ) enables the fabrication of complex metallic structures densified during a final sintering step. Pure titanium can be processed to near‐net‐shape geometries for electrochemical applications if the parameters and the atmosphere during sintering are carefully monitored. Herein, the influence of thermal debinding and sintering parameters on the fabrication of high‐density pure titanium using MF 3 is investigated. Particular focus is placed on enhancing sintered density while limiting impurity uptake to conserve the high chemical purity of the initial powder material. Relative densities of 95% are repeatedly reached inside the bulk of the s les. An oxygen content of 0.56 wt% as a result of vacuum processing induces the formation of the retained α‐Ti phase (925 HV 0.2 ) inside the α matrix (295 HV 0.2 ). Fabricated parts exhibit high mechanical strength, albeit reduced elongation due to remaining pores, and, in terms of electrochemistry, enhanced stability toward anodic dissolution.
Publisher: Elsevier BV
Date: 2013
Publisher: Elsevier BV
Date: 2013
Publisher: Elsevier BV
Date: 09-2023
Publisher: Springer Science and Business Media LLC
Date: 13-11-2021
DOI: 10.1007/S11661-021-06516-X
Abstract: Materials processed by additive manufacturing often exhibit a very fine-scaled microstructures due to high cooling rates in the process. In this study, single-layer surface electron beam melting is used to create very high cooling rates similar to additive manufacturing processes to investigate the resulting microstructure. In the case of Nb-Si-Cr in-situ composites, a nano-scaled eutectic microstructure is beneficial for improving the mechanical and oxidational properties. Fast solidification results in the formation of supersaturated phases of Nb ss and Cr 2 Nb with phase diameters down to 10 nm as well as in the stabilization of the metastable Nb 9 (Cr,Si) 5 phase at room temperature. After processing with different solidification rates, the decomposition of the Nb 9 (Cr,Si) 5 phase has been studied in detail with atom probe microscopy. The stabilization of mixed silicide phases by electron beam melting shows a new pathway for improving hardness and enhancing oxidation resistance of nanostructured eutectic in-situ composites, by which the inherent weaknesses of Nb-Si-Cr can be overcome without further alloying elements. Graphical Abstract
Publisher: Elsevier BV
Date: 03-2021
Publisher: MDPI AG
Date: 21-11-2020
Abstract: The Ni content is a crucial factor for the development of γ′-strengthened Co-based superalloys and some studies have systematically addressed its influence on various properties in model superalloys. In this paper, we report for the first time the influence of the Co/Ni ratio in the more advanced nine-component superalloy ERBOCo-1: exchanging Co and Ni in this Co/Ni-based superalloy while keeping the other alloying elements constants has a big influence on a variety of material properties. The elemental segregation after casting is slightly more pronounced in the alloy with higher Ni-content. Microstructural characterization of this alloy termed ERBOCo-1X after heat-treatment reveals that the precipitates are cuboidal in the Co- and spherical in the Ni-rich alloy, indicating a decrease in the γ/γ′ lattice misfit. Analyzing the elemental partitioning behavior by atom probe tomography suggests that the partitioning behavior of W is responsible for that. Furthermore, it is found that even though Ni exhibits the highest overall concentration, the γ matrix phase is still Co-based, because Ni is strongly enriched in the γ′ precipitates. Creep tests at 900 °C reveal that even though the microstructure looks less favorable, the creep resistance of the Ni-rich alloy is slightly superior to the Co-rich variant.
Publisher: Wiley
Date: 28-07-2021
Abstract: Allvac 718Plus is a derivative of alloy 718 for applications at higher temperatures in rotating and static components of gas turbines. According to literature, various phases as γ, γ′, η, δ, and γ″ can form with so far contradicting results. Herein, the precipitation behavior in different alloy conditions is investigated using transmission electron microscopy and atom probe tomography. The aim is to clarify how local variations in chemical composition alter the sequence of precipitation and type of precipitates that form. Material conditions with a minor volume fraction of η/δ phase and a high fraction of primary γ′ precipitates form γ″ phase due to excess of available Nb. Spherical γ′ precipitates with disc‐shaped γ″ precipitates at γ′ interfaces are observed. During discontinuous coarsening of η/δ plates mainly Nb is consumed which leads to an enrichment of γ′ forming elements and hence the heterogeneous nucleation of γ′ at the η/γ interface. The coexistence of thin η plates embedded in δ phase in grain boundary pinning precipitates could additionally be confirmed. These results show under which conditions certain primary phases form and how the resulting consumption and redistribution of phase promoting elements trigger the formation of other secondary phases.
Publisher: MDPI AG
Date: 10-08-2019
DOI: 10.3390/MA12162547
Abstract: In this study, we demonstrate how Zn and Sn influence hardening behavior and cluster formation during pre-aging and paint bake treatment in Al–Mg–Si alloys via hardness tests, tensile tests, and atom probe tomography. Compared to the standard alloy, the Sn-modified variant shows reduced cluster size and yield strength in the pre-aged condition. During the paint bake cycle, the clusters start to grow very fast and the alloy exhibits the highest strength increment. This behavior is attributed to the high vacancy binding energy of Sn. Adding Zn increases the formation kinetics and the size of Mg–Si co-clusters, generating higher yield strength values for both the pre-aged and paint baked conditions. Simultaneous addition of Zn and Sn creates a synergistic effect and produces an alloy that exhibits moderate strength (and good formability) in the pre-aged condition and accelerated hardening behavior during the paint bake cycle.
Publisher: Elsevier BV
Date: 08-2012
Publisher: Elsevier BV
Date: 04-2022
Publisher: Elsevier BV
Date: 10-2013
Publisher: Wiley
Date: 20-05-2020
Abstract: The strength of superalloys is strongly influenced by γ′ precipitates, whose size and volume fraction which can be adjusted by heat treatments. According to classical precipitation strengthening models, an increasing precipitate diameter should lead to a transition from weak to strong coupling of the dislocation pairs that form superdislocations in the γ′ phase. We show that long‐term annealing of the Ni‐base superalloy A718Plus at 670 and 680 °C increases the alloy's strength without significantly changing the grain size and η fraction. To understand the effect of the slight increase in γ′ size, detailed atom probe tomography (APT) was performed. Here, different field evaporation rates of the phases strongly affect the determination of the volume fraction when using the usual isosurface construction. This can be mitigated by considering the number density of atoms inside and outside the γ′ precipitates. Using an approximation of the precipitate shapes and arrangements from the APT data in atomistic simulations revealed that precipitate shearing by both, weakly and strongly coupled dislocations can occur in the same s le due to the wide distribution of precipitate sizes. These results highlight the need for advanced strengthening models that take into account the γ′ size distribution.
Publisher: Springer Science and Business Media LLC
Date: 12-2015
Publisher: Public Library of Science (PLoS)
Date: 19-01-2021
DOI: 10.1371/JOURNAL.PONE.0245555
Abstract: Atom probe tomography (APT) is a powerful technique to obtain 3D chemical and structural information, however the ‘standard’ atom probe experimental workflow involves transfer of specimens at ambient conditions. The ability to transfer air- or thermally-sensitive s les between instruments while maintaining environmental control is critical to prevent chemical or morphological changes prior to analysis for a variety of interesting s le materials. In this article, we describe a versatile transfer system that enables cryogenic- or room-temperature transfer of specimens in vacuum or atmospheric conditions between s le preparation stations, a focused ion beam system (Zeiss Crossbeam 540) and a widely used commercial atom probe system (CAMECA LEAP 4000X HR). As an ex le for the use of this transfer system, we present atom probe data of gallium- (Ga)-free grain boundaries in an aluminum (Al) alloy specimen prepared with a Ga-based FIB.
Publisher: Wiley
Date: 17-09-2015
Abstract: Highly abundant oxygen-rich line defects (blue) can act as fast oxygen transport paths. These defects show similar chemistry and therefore similar catalytic activity to the materials surface. These results provide the opportunity to design and produce simple scalable structures as catalysts, whose functionality derives from internal defects rather than from the materials surfaces.
Publisher: Elsevier BV
Date: 03-2015
DOI: 10.1016/J.ULTRAMIC.2014.11.015
Abstract: The analysis of the formation of clusters in solid solutions is one of the most common uses of atom probe tomography. Here, we present a method where we use the Voronoi tessellation of the solute atoms and its geometric dual, the Delaunay triangulation to test for spatial/chemical randomness of the solid solution as well as extracting the clusters themselves. We show how the parameters necessary for cluster extraction can be determined automatically, i.e. without user interaction, making it an ideal tool for the screening of datasets and the pre-filtering of structures for other spatial analysis techniques. Since the Voronoi volumes are closely related to atomic concentrations, the parameters resulting from this analysis can also be used for other concentration based methods such as iso-surfaces.
Publisher: Elsevier BV
Date: 05-2023
Publisher: Elsevier BV
Date: 09-2014
Publisher: Elsevier BV
Date: 09-2020
Publisher: No publisher found
Date: 2016
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.ULTRAMIC.2015.05.006
Abstract: Whilst atom probe tomography (APT) is a powerful technique with the capacity to gather information containing hundreds of millions of atoms from a single specimen, the ability to effectively use this information creates significant challenges. The main technological bottleneck lies in handling the extremely large amounts of data on spatial-chemical correlations, as well as developing new quantitative computational foundations for image reconstruction that target critical and transformative problems in materials science. The power to explore materials at the atomic scale with the extraordinary level of sensitivity of detection offered by atom probe tomography has not been not fully harnessed due to the challenges of dealing with missing, sparse and often noisy data. Hence there is a profound need to couple the analytical tools to deal with the data challenges with the experimental issues associated with this instrument. In this paper we provide a summary of some key issues associated with the challenges, and solutions to extract or "mine" fundamental materials science information from that data.
Publisher: AIP Publishing
Date: 2020
DOI: 10.1063/1.5128058
Abstract: Mixtures of Fe and Cu powders are cold-compacted and subsequently deformed with severe plastic deformation by high-pressure torsion, leading to bulk s les. The dilution of Fe in the Cu matrix is investigated with SQUID-magnetometry, whereas the magnetic properties change as a function of Fe-content from a frustrated regime to a thermal activated behaviour. The magnetic properties are correlated with the microstructure, investigated by synchrotron X-ray diffraction and atom probe tomography. Annealing of the as-deformed states leads to demixing and grain growth, with the coercivity as a function of annealing temperature obeying the random anisotropy model. The presented results show that high-pressure torsion is a technique capable to affect the microstructure even on atomic length scales.
Publisher: Elsevier BV
Date: 09-2023
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.ULTRAMIC.2012.12.013
Abstract: Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping.
Publisher: Elsevier BV
Date: 12-2017
Location: No location found
No related grants have been discovered for Peter Felfer.