Electron powder bed fusion has emerged as a promising additive manufacturing process for producing Ti-6Al-4V components with complex geometries. Although prior work has examined microstructural evolution phenomena including how thermal history influences the prevalence of specific alpha/alpha grain boundary misorientation intervariants governed by the Burgers orientation relationship between the alpha and (3 phases, the solute segregation behaviour at these interfaces remains poorly understood. This study employs correlative transmission Kikuchi diffraction and atom probe tomography to quantify the Gibbsian interfacial excess of V, Fe, and Al across multiple interfaces in electron powder bed fusion produced Ti-6Al-4V. V and Fe exhibited enrichment, while Al was depleted, with V segregation generally increasing with boundary misorientation. Spatial variations in segregation were observed across interface planes, although no consistent trend with boundary curvature was identified. First-principles calculations were also performed on model alpha/alpha grain boundaries to evaluate segregation energetics, confirming a thermodynamic preference for V enrichment and Al depletion. The agreement between experimental observations and theoretical predictions highlights the influence of local defect structures and atomic-scale interactions on segregation behaviour. These findings improve understanding of grain boundary chemistry in additively manufactured Ti alloys and provide a basis for future grain boundary engineering approaches aimed at tailoring interfacial properties.

The stability of primary M6C carbides is critical for the high-temperature mechanical performance of many Co-based superalloys, yet the mechanism governing their decomposition into M23C6 remains unclear. In contrast to reports that place this transformation only after long-term ageing at 800 - 900 °C, here we show that M6C in Alloy 188 begins to decompose almost immediately under short-term exposure at 850 °C. We observe the early appearance of M23C6 films along M6C/matrix interfaces and show that their evolution is governed by the local geometry and crystallographic compatibility of the parent carbide. High-resolution chemical mapping reveals pronounced Cr enrichment and W depletion at the reaction front, establishing Cr supersaturation within M6C as the thermodynamic basis for this early instability. These results provide direct structural and chemical evidence for the onset of M6C decomposition in a Co-based superalloy and highlight new routes for tuning high-temperature microstructural stability.

Atom probe tomography (APT) is routinely used to investigate nano-scale solute architecture within multicomponent systems. However, there is no consensus on how to best quantify solute clustering within APT data. This contribution leverages recent developments in the field of non-parametric hypothesis testing of nearest-neighbour distributions to address this critical gap. We adapt a goodness-of-fit-type test statistic known as 'the level of heterogeneity' to quantitatively discern whether solute distributions exhibit clustering behaviour beyond what would be expected from a random distribution. Further, comparing APT datasets remains difficult due to the inability to directly compare their nearest-neighbour distributions. We present a method that leverages Monte-Carlo simulations, already used to calculate the non-parametric statistic, as a means of comparing APT data. The method is more powerful than comparing datasets through the Pearson coefficient, as is conventionally done.

Doped polycrystalline Si (poly-Si) contacts with a nanoscale SiOx interlayer have attracted significant interest due to their excellent surface passivation and impurity gettering properties for high-efficiency crystalline Si photovoltaics. However, there remains limited information on their atomic-scale microstructure and the mechanisms governing their strong gettering effects. This work employs atom probe tomography and scanning transmission electron microscopy to investigate 3D atomic interactions among dopants, O and Fe impurities in intrinsic and doped poly-Si structures. Observations unveil a new interfacial feature above the oxide interlayer termed the ‘O-lean’ region, posited to play a critical function in passivation. The quantification of the complex state of atomic clustering of various solute species within poly-Si reveals the first experimental validation of Fe gettering via co-clustering with P4V clusters and O. These atomic-scale observations provide novel insights into the formation mechanisms and electrical performance of doped poly-Si contacts, offering new strategies for their optimisation.

Medium- and high-entropy alloys are an emerging class of materials that can exhibit outstanding combinations of strength and ductility for engineering applications. Computational simulations have suggested the presence of short-range order (SRO) in these alloys, and recent experimental evidence is also beginning to emerge. Unfortunately, the difficulty in quantifying the SRO under different heat treatment conditions has generated much debate on the atomic preferencing and implications of SRO on mechanical properties. Here we develop an approach to measure SRO using atom probe tomography. This method balances the limitations of atom probe tomography with the threshold values of SRO to map the regimes where the required atomistic neighbourhood information is preserved and where it is not. We demonstrate the method with a case study of the CoCrNi alloy and use this to monitor SRO changes induced by heat treatments. These species-specific SRO measurements enable the generation of computational simulations of atomic neighbourhood models that are equivalent to the experiment and can contribute to the further understanding and design of medium- and high-entropy alloys and other materials systems where SRO may occur. A method is introduced to quantify short-range order in multicomponent alloys using atom probe tomography, which enables further understanding and materials design related to atomic-scale solute engineering.

The crystallography and chemistry of interfaces between austenite and ferrite in duplex steels control many important materials properties but remain poorly understood. In this study, we experimentally show that in an additively manufactured and heat treated duplex stainless steel, the majority of austenite-ferrite interfaces terminate on {111}A/{110}F planes, and this behaviour is more pronounced for rational interfaces with the Kurdjomov-Sachs orientation relationship. Interface segregation was found to be controlled by not only the interface crystallography but also the bonding properties of solute atoms. Solute elements showed higher interfacial excess at irrational interfaces. Furthermore, a heterogeneous distribution of selected solute elements in austenite-ferrite interfaces planes was observed. Our findings reinforce the importance and, in fact, necessity to consider five independent crystallographic parameters and chemical architecture of interphase boundaries for advanced control of mechanical and other critical properties in duplex materials.

The CAMECA Invizo 6000 atom probe microscope uses ion optics that differ significantly from the local electrode atom probe (LEAP). It uses dual antiparallel deep ultraviolet lasers, a flat counter electrode, and a series of accelerating and decelerating lenses to increase the field-of-view of the specimen without reducing the mass resolving power. In this work we characterise the performance of the Invizo 6000 using three material case studies: a model Al-Mg-Si alloy, a commercially-available Ni-based superalloy, and a Zr alloy, using a combination of air and vacuum-transfer between instruments. The ion optics of the Invizo 6000 significantly increase the field-of-view compared to the same specimen on a LEAP 4000 X Si. We also observe a significant increase in specimen yield, especially for the Zr alloy. These results combine to make the Invizo 6000 well-suited to research projects requiring large analysis volumes, particularly so for traditionally difficult samples such as oxides.

Medium and high entropy alloys (M/HEAs) are an emerging class of materials that can exhibit outstanding combinations of strength and ductility [1].As such, their high potential for challenging engineering applications has attracted much attention.Computational simulations have suggested the presence of short-range order (SRO) in CoCrNi alloys, and recent experimental evidence that supports this is beginning to emerge [2].

Complex geometries and topology optimisations for weight and materials savings are leading drivers for the additive manufacturing of Ni-based superalloys through electron beam powder bed fusion (PBF-EB). However, there is a marked departure in these geometrically complex components with respect to the thermal signatures understood in commonly studied prismatic PBF-EB test coupons. This often results in unaccounted site-specific microstructure-property variations in complex PBF-EB builds. Here, the effects of topological changes, such as intentionally engineered internal voids, on the mechanical performance of an as-fabricated Haynes 282 monolith is revealed. The internal voids serve as representative physical models for changing thermal boundary conditions with build height. Complementary local nanoindentations, multi-scale microscopy, and residual stress measurements were used to understand the mechanisms behind geometry-structure-property relationships. The results highlight the effectiveness and influence of changing thermal conditions on the local mechanical property response of PBF-EB Haynes 282.

Room temperature focused ion beam (FIB) milling is known to potentially promote the formation of hydrides in zirconium and its alloys. We used atom probe tomography (APT) to determine the composition of irradiated and as-produced Zircaloy-2 fuel cladding. We consistently found - 50 at% hydrogen in all room temperature FIB-milled specimens run in voltage pulsing APT measurements. Crystallographic analysis of APT data however showed slightly better agreement with 8-hydride (ZrH 2 , FCC, - 60-66.7 at% H) than gamma -hydride (ZrH, FCT, - 50 at% H). Electron energy loos spectroscopy (EELS) measurements prior to APT analyses confirmed the presence of 8-hydride. Hence, APT gives a systematic underestimation of hydrogen for Zr-hydride. Milling at cryogenic temperatures was found to not cause such hydride formation. However, we did not find significant differences in the clusters formed by segregation of the alloying elements Fe, Cr and Ni to irradiation induced a-loops whether the material was identified as alpha-Zr or hydride. Therefore, analyzing irradiation-induced redistribution of alloying elements in Zr fuel cladding using APT does not rely on FIB preparation at cryogenic temperatures. However, in conjunction with voltage pulsing APT cryo-FIB can be worthwhile if one aims at investigating hydrogen distribution or hydrides.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Abstract Zirconium alloys are common fuel claddings in nuclear fission reactors and are susceptible to the effects of hydrogen embrittlement. There is a need to be able to detect and image hydrogen at the atomic scale to gain the experimental evidence necessary to fully understand hydrogen embrittlement. Through the use of deuterium tracers, atom probe tomography (APT) is able to detect and spatially locate hydrogen at the atomic scale. Previous works have highlighted issues with quantifying deuterium concentrations using APT due to complex peak overlaps in the mass-to-charge-state ratio spectrum between molecular hydrogen and deuterium (H2 and D). In this work, we use new methods to analyze historic and simulated atom probe data, by applying currently available data analysis tools, to optimize solving peak overlaps to improve the quantification of deuterium. This method has been applied to literature data to quantify the deuterium concentrations in a concentration line profile across an α-Zr/deuteride interface.

The operating temperature is a critical parameter in atom probe tomography experiments. It affects the spatial precision, mass resolving power and other key aspects of the field-evaporation process. Current commercially available atom probes operate at a minimum temperature of ∼25 K when measured at the specimen. In this paper, we explore and implement changes to the mechanical design of both the LEAPⓇ and EIKOS™ atom probe microscope systems manufactured by CAMECAⓇ to enable a specimen temperature in the sub-10 K regime. We use these modified instruments to analyze four materials systems: pure Al (in both pulsed-voltage and pulsed-laser mode), pure W (pulsed-voltage mode only), doped Si, and GaN (pulsed-laser mode only). The effects of conducting atom probe experiments in the sub-10 K regime were assessed with reference to a range of quantitative analysis metrics related to spatial precision, mass resolving power, stoichiometry and charge-state ratio. We demonstrate that the spatial precision is significantly improved with decreasing temperature, whilst the effect on mass resolving power is relatively minor. The enhanced spatial precision is significant insofar as it enables lattice planes from the doped Si samples to be resolved. Furthermore, mass spectral analysis, lower noise floors and changes in the field evaporation process enabled more accurate GaN compositional measurements. We discuss the significance of these findings for the semiconductor and metallurgical industries and the potential opportunities for further investigations of this parameter space.

Magnitude and distribution of residual stresses in additively manufactured Ni-based superalloys may impact the mechanical performance of as-fabricated parts. Though electron beam powder bed fusion (E-PBF) can produce components with minimal defects and residual stresses compared to laser powder bed fusion and directed energy deposition, variations of them may occur within the complex geometry of a component, due to inherent variations of thermal signatures and the evolution of section modulus along the build direction. This work reveals the residual stress distribution, characterised from neutron diffraction, of an as-fabricated Haynes 282 monolith containing internal cube voids and thin wall struts of varying thicknesses. Complementary local hardness measurements and multi-scale microscopy were used to investigate the geometry-structure-property relationships. Observed variations in hardness were attributed to a combination of type I macro-scale residual stresses and variations in bimodal γ′ precipitation behaviour. The results highlight the influence of residual stresses and microstructure on the mechanical properties of E-PBF Haynes 282.

The following repository contains a collection of data and metadata files in different vendor formats which were collected in the fields of atom probe microscopy (LEAP instruments) and electron microscopy (Nion instruments). These files are meant for development and testing purposes of the nomad north-remote-tools-hub and the related nomad-nexus-parser software tools within the FAIRmat project.FAIRmat is a consortium lead by the Humboldt-Universität zu Berlin. FAIRmat is a member of the German Research Data Infrastructure (NFDI) initiative. A detailed description of the background and content of the individual files follows: EM.STEM.Nion.Dataset.1.zip:This is a dataset for testing the nx_em_nion reader which handles files from Nion microscopes and NionSwift software.The data were collected by Benedikt Haas and Sherjeel Shabih from Humboldt-Universität zu Berlinwho worked (at the point of publication) in the group of Prof. Christoph Koch. APM.LEAP.Datasets.*.zip:This is a collection of two datasets for testing the generic nx_apm reader which handles commercial and community file formats for reconstructed ion position and ranging data from atom probe microscopy experiments. The datasets were collected by different authors.APM.LEAP.Datasets.1.zip: R31_06365-v02.pos, was shared by Jing Wang and Daniel Schreiber (both at PNNL). Details to the dataset are availableunder the following DOIs:https://doi.org/10.1017/S1431927618015386https://doi.org/10.1017/S143192762101224170_50_50.apt, was a shared by Xuyang Zhou at his time with the Max-Planck-Institut für Eisenforschung GmbH as a open-source test data to the publication he lead on machine-learning-based techniques for composition profiling.The dataset and publication is available via the following DOI and resources:https://doi.org/10.1016/j.actamat.2022.117633The dataset specifically is also available here:https://github.com/RhettZhou/APT_GB/tree/main/example/Cropped_70_50_50The range files *.rng and *.rrng range serve as examples to develop tools for parsing them and handle the formatting of range files. The scientific content of the range files was inspired by experiments but is not related to the above-mentioned atom probe datasetsand should not be used to analyze these test data for more than pure development purposes.Use instead your own data and matching range files for scientific analyses. APM.LEAP.Datasets.2.zipR18_53222_W_18K-v01.epos, was shared with Markus Kühbach by Andrew Breenduring their time at the Max-Planck-Institut für Eisenforschung GmbH.We would like to invite the community to use the nomad infrastructure and support us withsharing data and dataset which we can then use to improve the file format parsing, the reading capabilities,and analyses services of the nomad infrastructure so that the community can profit again from these developments.

A new experimental method is proposed to quantify the site-occupancy of substitutional solute elements in multi-component intermetallics from atom probe tomography data and is applied to the L12 ordered gamma' phase in the top, middle and bottom regions of an electron powder bed fusion produced IN-738LC build. Ti, W and Ta are found to substitute almost exclusively for the beta sites. Cr and Mo show mixed behaviour with a higher proportion substituting for the beta sites. Co also shows mixed behaviour but with a higher proportion substituting for the alpha sites. While gamma' maintains an almost constant chemistry and site-preference behaviour throughout the build, the relative site-occupancy ratio is observed to change, particularly for Co and Mo. The results suggest that local changes in thermal history inherent to metal additive manufacturing processes may induce changes to the resultant site-occupancy of gamma'. The method described here improves the experimental quantification of the local atomic site-occupancy, enabling an assessment of the substitutional solute element fractions occurring at the alpha and beta sites in L1(2) ordered structures. This is important in multi-component intermetallics because of the burgeoning interest in relating the elastic and plastic properties of these structures to their site-occupancy.

Poles and zone lines observed within atom probe field evaporation images are useful for a range of atom probe crystallography studies, including calibration of the reconstruction and crystallographic characterisation of microstructural features such as grain boundaries. However, this information is not always readily apparent. Techniques for plotting crystallographically correlated metrics contained within atom probe data to enhance pole and zone line contrast across the detector space are developed. This includes consideration of the electric field, molecular ions, lattice structure retained within the reconstruction, specific elemental species, the number of pulses between detection events, and the lateral distance between sequential detection events. These approaches are then applied to experimental atom probe tomography datasets on technically pure Al, nanocrystalline Al, highly doped Si, and additively manufactured Inconel 738, Haynes 282, and Ti-6Al-4V. The results facilitate the extension of atom probe crystallography studies to a broader range of crystalline datasets where crystallographic information is not readily apparent from existing methods, as well as a deeper understanding of field evaporation behaviour during an atom probe experiment.

Poor oxidation resistance is a key contributor to material failure within extreme environments. Understanding oxygen solubility is important for computation aided design of new high strength, high-temperature oxidation resistant alloys. Oxygen solubility within pure metals, such as Ni, has been studied using a multitude of techniques, but Atom Probe Tomography (APT) has not been used for such a measurement to date. APT is the only technique offering both a high chemical sensitivity (<10 ppm) and resolution (<1 nm) allowing for a composition measurement within nms of the oxide/metal interface. APT was employed to measure the oxygen content at different depths from the oxide/metal interface as well as grain boundaries for a high and low purity Ni sample oxidized at 1000 °C for 48 hours. The results reveal <10s of ppm oxygen solubility within Ni metal at all depths and 100s of ppm of oxygen within GBs.

An oxygen-rich face-centred cubic (FCC) Ti phase was engineered in the microstructure of a Ti-6Al-4V alloy via additive manufacturing using laser powder bed fusion. Designated 'C', this oxygen-rich FCC phase has a lattice parameter of 0.406 nm and exhibits an orientation relationship with the parent a0 phase as follows: (000 1)a0//{1 1 1}C, and h1 2 10ia0 //h1 1 0iC. We propose that the formation of the C phase is facilitated by the combined effect of thermal gradients, deformation induced by the martensitic transformation, and local O enrichment. This enables an in-situ phase transformation from the hexagonal close-packed a0 phase to the C phase at elevated temperatures. Our density functional theory calculations indicate that oxygen occupancy in the octahedral interstices of the FCC structure is energetically preferred to corresponding sites in the a0 phase. The in-situ mechanical testing results indicate that the presence of the FCC phase significantly increases the local yield strength from 1.2 GPa for samples with only the a0 phase to 1.9 GPa for samples comprising approximately equal volume fractions of the a0 and FCC phases. No loss of ductility was reported, demonstrating great potential for strengthening and work hardening. We discuss the formation mechanism of the FCC phase and a pathway for future microstructural design of titanium alloys by additive manufacturing.