Research Group in Atom Probe Tomography at Oxford Department of Materials
Publications Search: List of publications
Showing 1 to 229 of 229 publications
Towards Establishing Best Practice in the Analysis of Hydrogen and Deuterium by Atom Probe Tomography.
Gault B, Saksena A, Sauvage X, Bagot P, Aota LS, Arlt J, Belkacemi LT, Boll T, Chen Y-S, Daly L, Djukic MB, Douglas JO
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et al
September 2024
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Journal article
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Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada
As hydrogen is touted as a key player in the decarbonization of modern society, it is critical to enable quantitative hydrogen (H) analysis at high spatial resolution and, if possible, at the atomic scale. H has a known deleterious impact on the mechanical properties (strength, ductility, toughness) of most materials that can hinder their use as part of the infrastructure of a hydrogen-based economy. Enabling H mapping including local hydrogen concentration analyses at specific microstructural features is essential for understanding the multiple ways that H affect the properties of materials including embrittlement mechanisms and their synergies. In addition, spatial mapping and quantification of hydrogen isotopes is essential to accurately predict tritium inventory of future fusion power plants thus ensuring their safe and efficient operation. Atom probe tomography (APT) has the intrinsic capability to detect H and deuterium (D), and in principle the capacity for performing quantitative mapping of H within a material's microstructure. Yet, the accuracy and precision of H analysis by APT remain affected by complex field evaporation behavior and the influence of residual hydrogen from the ultrahigh vacuum chamber that can obscure the signal of H from within the material. The present article reports a summary of discussions at a focused workshop held at the Max-Planck Institute for Sustainable Materials in April 2024. The workshop was organized to pave the way to establishing best practices in reporting APT data for the analysis of H. We first summarize the key aspects of the intricacies of H analysis by APT and then propose a path for better reporting of the relevant data to support interpretation of APT-based H analysis in materials.
Multiscale characterisation study on the effect of heat treatment on the microstructure of additively manufactured 316L stainless steel
Jenkins BM, Etienne A, Baustert E, Rose G, Pareige C, Pareige P, Radiguet B
June 2024
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Journal article
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Materials Today Communications
Additively manufactured 316L components are known to exhibit complex three-dimensional microstructures on multiple length-scales. The effect of heat treatment on the stability of grains and dislocation cell structures within the microstructure has previously been investigated but there are appreciable disagreements surrounding the nature of the texture that is present in the specimens, and there is also limited published work on the compositional homogeneity of specimens, particularly on the atomic scale, after heat treatments. In this study, we investigate the effect of applying two different heat treatments to 316L components produced by laser powder bed fusion before characterising them using a combination of electron microscopy and atom probe tomography. The importance of using multiple characterisation techniques, which span from the nanometre to micrometre scale, in addition to carefully and accurately describing analysis methods when investigating the evolution of the microstructure of additively manufactured 316L steels is demonstrated. Our EBSD (Electron Back Scatter Diffraction) results show the presence of a strong texture in the build direction of the samples, and a reduction in morphological texture as a result of heat treatment. TEM (Transmission Electron Microscopy) results indicate a dissolution of the dislocation cell structure that forms during solidification. Atom probe tomography was used to investigate compositional homogeneity in the samples and indicated that there are regions enriched in Cr, Mn, Mo, and Ni in the As-Printed samples that are likely associated with the dislocation cell walls. The atom probe results also reveal the presence of impurities, such as Co, which were not detected in the feedstock powder.
Insights into primary carbides and nanoparticles in an additively manufactured high-alloy steel
Zhang H, Peng H, Bagot PAJ, Wang Y, Venero DA, Robertson S, El-Fallah GMAM, Guo H, Moody MP, Chen B
May 2024
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Journal article
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Acta Materialia
Nano-scale corrosion mechanism of T91 steel in static lead-bismuth eutectic: A combined APT, EBSD, and STEM investigation
Zhang M, He G, Lapington M, Zhou W, Short MP, Bagot PAJ, Hofmann F, Moody MP
April 2024
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Journal article
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Acta Materialia
Microstructural evolution and transmutation in tungsten under ion and neutron irradiation
Lloyd MJ, Haley J, Jim B, Abernethy R, Gilbert MR, Martinez E, Hattar K, El-Atwani O, Nguyen-Manh D, Moody MP, Bagot PAJ, Armstrong DEJ
December 2023
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Journal article
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Materialia
Characterisation of corrosion damage in T91/F91 steel exposed to static liquid lead-bismuth eutectic at 700–715 °C
Lapington MT, Zhang M, Moody MP, Zhou WY, Short MP, Hofmann F
December 2023
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Journal article
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Journal of Nuclear Materials
Point excess solute: A new metric for quantifying solute segregation in atom probe tomography datasets including application to naturally aged solute clusters in Al-Mg-Si-(Cu) alloys
Famelton JR, Williams CA, Barbatti C, Bagot PAJ, Moody MP
December 2023
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Journal article
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Materials Characterization
Accurate, repeatable and quantitative analysis of nanoscale solute clustering in atom probe tomography (APT) datasets is a complex challenge which is made more difficult by the positional uncertainty and lack of absolute resolution inherent to the technique. In this work a new method, the point excess solute, is introduced for quantifying solute segregation in datasets with limited spatial resolution. This new method is based on measuring the matrix concentration using a dataset sampling method. We show the new method can accurately reproduce the values expected from synthetic datasets a priori and when the dataset spatial resolution and or phase contrast is too low for accurate quantification this is observable. The method is then applied to naturally aged solute clusters in the Al-Mg-Si-Cu system. Datasets were collected with a range of natural ageing times from 8 min to 76 weeks. The formation of the solute clusters is shown to be unaffected by the Cu content of the alloy.
Does SW China have Carlin-type gold deposits? A micro- to atomic-scale perspective
Xie Z, Gopon P, Xia Y, Douglas JO, Cline J, Liu J, Tan Q, Xiao J, Wen Y, Chen Y, Li P, Moody MP
November 2023
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Journal article
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Mineralium Deposita
The origin of different morphology of internal oxide precipitates in ferritic and austenitic steels
Shen Z, Zeng X, Wu S, Yu H, Jenkins BM, Karamched P, Moody MP, Zhang J, Wang Y, Lozano-Perez S
October 2023
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Journal article
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Journal of Materials Science and Technology
The internal oxide precipitates were supposed to be spherical in Wagner's original theory, while the following research demonstrated that this assumption is an exception rather than the truth, which caused deviations in the application of this theory. In this study, the internal oxide precipitates have a needle-like and a near-spherical morphology in a Fe-9Cr ferritic and a Fe-17Cr-9Ni austenitic steels after exposure to 600 °C deaerated steam for 600 h, respectively. The nano-to-atomic scale characterization shows that the morphology of the internal oxide precipitates is controlled by the structure of the interfaces between the metal matrix and the internal oxide, while the interface structure is mainly affected by the crystallographic structure of the two phases and their orientation relationship. In addition, the internal oxide precipitation-induced volume expansion and the outward Fe diffusion-induced volume shrink occur simultaneously during the oxidation process. The stress status in the internal oxidation zone (IOZ) is the competing result of the two factors, which could dynamically affect the high-temperature oxidation. The results obtained in this study suggest that there is potential to control the distribution, morphology, and interface structure of the internal oxide precipitates by selecting appropriate base metal and internal oxide-forming element, in order to obtain better high-temperature oxidation-resistant materials.
Amorphous-crystalline nanostructured Nd-Fe-B permanent magnets using laser powder bed fusion: Metallurgy and magnetic properties
Wu J, Aboulkhair NT, Robertson S, Zhou Z, Bagot PAJ, Moody MP, Degano M, Ashcroft I, Hague RJM
October 2023
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Journal article
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Acta Materialia
Laser powder-bed fusion (PBF-LB), a class of additive manufacturing (AM), has attracted wide interest in the production of Nd-Fe-B permanent magnets, benefiting from the minimisation of waste of rare-earth elements and the post-processing requirements. Most research on PBF-LB Nd-Fe-B has focused on reducing defects in printed parts alongside the improvement of the resultant magnetic properties. Detailed analysis of the microstructure that results in permanent magnetic properties is yet to be published. In this research, a combination of high-resolution microstructural investigations was conducted for this purpose. For the first time, an in-depth analysis of the grain structure in terms of morphology, size distribution, and texture is presented and correlated to the permanent magnetic performance. Melt pools showed a hierarchical grain size distribution of primary Nd2Fe14B phase grains with a polygonal morphology and random crystalline alignment, in addition to a small amount of Nd-rich and Nd-lean precipitates in the matrix of the Ti-rich amorphous grain boundaries. The permanent magnetic properties of this material are mainly determined by the nanostructured Nd2Fe14B grains and the amorphous Ti-rich iron-based intergranular phase but could be weakened by precipitates that act as magnetic pores. Remelting during PBF-LB led to the transformation of the coarse grains of the previously solidified layer to fine ones, favourable for the permanent magnetic properties. The mechanisms of these complex phase formations and transformations during processing and the development of the nanocrystalline microstructure are elucidated in this paper as a basis for informing the optimisation process for microstructural development.
Experimental and Modelling Evidence for Hydrogen Trapping at a β-Nb Second Phase Particle and Nb-rich Nanoclusters in Neutron-Irradiated Low Sn ZIRLO
The present work investigates the impact of residual segregation on the underlying microstructure of a 3rd generation single crystal, nickel-based superalloy to understand potential variation in mechanical behaviour between dendrite cores and interdendritic regions. Despite the applied heat-treatments, chemical variation between dendrite cores and interdendritic regions persisted particularly for elements Re, Nb and Ta. Atom probe tomography (APT) was utilized for its nanoscale capability to map site-specific chemical changes in the γ matrix, γ’ precipitates and across the γ/γ’ interface. Greater interfacial segregation of Re, matched by a corresponding depletion of Ni were observed within dendrite cores, with the extent found to increase following heat treatment. Differences in lattice parameters between dendrite cores and interdendritic regions were identified, with larger lattice misfits associated with interdendritic regions.
Understanding the nanoscale chemistry of as-received and fast neutron irradiated Nb3Sn RRP® wires using Atom Probe Tomography
Wheatley LE, Baumgartner T, Eisterer M, Speller SC, Moody MP, Grovenor CRM
June 2023
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Journal article
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Superconductor Science and Technology
<jats:title>Abstract</jats:title>
<jats:p>Atom Probe Tomography has been used to study the effect of fast neutron irradiation on the local chemistry of Nb<jats:sub>3</jats:sub>Sn samples. Two RRP<jats:sup>®</jats:sup> wires doped with 2 at% Ti were analysed, one in the as-received condition and the other irradiated to a neutron fluence (E&gt;0.1MeV) of 2.82x10<jats:sup>22</jats:sup> m<jats:sup>-2</jats:sup> in the TRIGA-II reactor. The irradiated sample had a reduced T<jats:sub>c</jats:sub>, an increase in F<jats:sub>p</jats:sub>, a shift in the peak of the F<jats:sub>p</jats:sub> curve suggesting the introduction of secondary point pinning, and an increase in the estimated scaling field B*. Atom Probe Tomography analysis has shown that polycrystalline Nb<jats:sub>3</jats:sub>Sn has three distinct regions of composition, near stoichiometry Nb<jats:sub>3</jats:sub>Sn (low Nb), regions with a higher Nb content than expected in equilibrium Nb<jats:sub>3</jats:sub>Sn (high Nb) and grain boundaries. The summed composition of these three regions lies within the Nb<jats:sub>3</jats:sub>Sn phase for both the as-received and irradiated samples. The distinct regions of high Nb Nb<jats:sub>3</jats:sub>Sn demonstrate incomplete diffusion in the as-received sample, and the reduction in volume of these high Nb regions after irradiation implies significant radiation induced diffusion has occurred. The occurrence presence of other features in the atomic-scale chemistry, such as the extent of Cu segregation at grain boundaries, and to three types of dislocation array, and unreacted Nb nanoparticles, are compared between samples.</jats:p>
Large-Scale Atom Probe Tomography Data Mining: Methods and Application to Inform Hydrogen Behavior
Meier MS, Bagot PAJ, Moody MP, Haley D
March 2023
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Journal article
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MICROSCOPY AND MICROANALYSIS
atom probe tomography, cluster, data analysis, data mining, database, hydrogen, machine learning, mass-to-charge spectrum, t-SNE, zirconium
Effect of Alloying on the Microstructure, Phase Stability, Hardness, and Partitioning Behavior of a New Dual-Superlattice Nickel-Based Superalloy
Rodenkirchen C, Ackerman AK, Mignanelli PM, Cliff A, Wise GJ, Breul P, Douglas JO, Bagot PAJ, Moody MP, Appleton M, Ryan MP, Hardy MC
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et al
March 2023
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Journal article
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METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
Multi-length-scale study on the heat treatment response to supersaturated nickel-based superalloys: Precipitation reactions and incipient recrystallisation
Tang YT, Panwisawas C, Jenkins BM, Liu J, Shen Z, Salvati E, Gong Y, Ghoussoub JN, Michalik S, Roebuck B, Bagot PAJ, Lozano-Perez S
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et al
January 2023
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Journal article
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Additive Manufacturing
A supersaturated γ phase microstructure is produced in Ni-based superalloys using laser powder bed fusion (L-PBF) – the cooling rate arising from the process is shown to suppress the solid-state precipitation of the γ′ phase. The response of the material to a heat treatment therefore requires new understanding at the fundamental level, since the first population of γ′ precipitate forms upon heating, in contrast to cooling from homogenisation above the γ′ solvus. Here, we have interrogated two new nickel-based superalloys designed for the L-PBF technology, both in situ and ex situ, at multiple length scales using advanced characterisation methods. First, we conducted in situ synchrotron X-ray diffraction during various heat treatments to trace the evolution of the γ′ volume fraction with temperature. The first structural changes were detected at an unexpectedly low temperature of ∼445 °C. Second, the temperature for γ′ nucleation and its sensitivity to heating rate was studied using an electrical resistivity method. Then, the γ′ composition upon heating, isothermal holding and cooling is analysed using atom probe tomography (APT), the result is rationalised by further scanning-transmission electron microscopy and nanoscale secondary ion mass spectroscopy. Finally, static recrystallisation during isothermal exposure was investigated, which occurs within minutes. This work sheds light on a new strategy of tailoring microstructure for additively manufactured superalloys by manipulation of the γ′ precipitate distribution upon heating.
Multi-Scale microscopy of Reactive sintered boride (RSB) neutron shielding materials
Marshall JM, Tang F, Han Y, Bagot PAJ, Moody MP
October 2022
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Journal article
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Nuclear Materials and Energy
Protecting superconducting magnets from neutron irradiation is critically important when demonstrating the utility of spherical tokamaks. Reactive Sintered Borides (RSBs) are promising radiation-dense materials and excellent attenuators of slow (
Refinements for Bragg coherent X-ray diffraction imaging: electron backscatter diffraction alignment and strain field computation
Yang D, Lapington MT, He G, Song K, Zhang M, Barker C, Harder RJ, Cha W, Liu W, Phillips NW, Hofmann F
October 2022
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Journal article
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Journal of Applied Crystallography
Bragg coherent X-ray diffraction imaging (BCDI) allows the 3D measurement of lattice strain along the scattering vector for specific microcrystals. If at least three linearly independent reflections are measured, the 3D variation of the full lattice strain tensor within the microcrystal can be recovered. However, this requires knowledge of the crystal orientation, which is typically attained via estimates based on crystal geometry or synchrotron microbeam Laue diffraction measurements. Presented here is an alternative method to determine the crystal orientation for BCDI measurements using electron backscatter diffraction (EBSD) to align Fe–Ni and Co–Fe alloy microcrystals on three different substrates. The orientation matrix is calculated from EBSD Euler angles and compared with the orientation determined using microbeam Laue diffraction. The average angular mismatch between the orientation matrices is less than ~6°, which is reasonable for the search for Bragg reflections. The use of an orientation matrix derived from EBSD is demonstrated to align and measure five reflections for a single Fe–Ni microcrystal via multi-reflection BCDI. Using this data set, a refined strain field computation based on the gradient of the complex exponential of the phase is developed. This approach is shown to increase accuracy, especially in the presence of dislocations. The results demonstrate the feasibility of using EBSD to pre-align BCDI samples and the application of more efficient approaches to determine the full lattice strain tensor with greater accuracy.
Towards accurate atom scale characterisation of hydrogen passivation of interfaces in TOPCon architectures
BONILLA OSORIO RUY
October 2022
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Journal article
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Solar Energy Materials and Solar Cells
A Correlative Study of Interfacial Segregation in a Cu-Doped TiNiSn Thermoelectric half-Heusler Alloy
Halpin JE, Jenkins B, Moody MP, Webster RWH, Bos JWG, Bagot PAJ, Maclaren DA
September 2022
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Journal article
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ACS Applied Electronic Materials
The performance of thermoelectric materials depends on both their atomic-scale chemistry and the nature of microstructural details such as grain boundaries and inclusions. Here, the elemental distribution throughout a TiNiCu0.1Sn thermoelectric material has been examined in a correlative study deploying atom-probe tomography (APT) and electron microscopies and spectroscopies. Elemental mapping and electron diffraction reveal two distinct types of grain boundary that are either topologically rough and meandering in profile or more regular and geometric. Transmission electron microscopy studies indicate that the Cu dopant segregates at both grain boundary types, attributed to extrusion from the bulk during hot-pressing. The geometric boundaries are found to have a degree of crystallographic coherence between neighboring grains; the rough boundaries are decorated with oxide impurity precipitates. APT was used to study the three-dimensional character of rough grain boundaries and reveals that Cu is present as discrete, elongated nanoprecipitates cosegregating alongside larger substoichiometric titanium oxide precipitates. Away from the grain boundary, the alloy microstructure is relatively homogeneous, and the atom-probe results suggest a statistical and uniform distribution of Cu with no evidence for segregation within grains. The extrusion suggests a solubility limit for Cu in the bulk material, with the potential to influence carrier and phonon transport properties across grain boundaries. These results underline the importance of fully understanding localized variations in chemistry that influence the functionality of materials, particularly at grain boundaries.
Automated calibration of model-driven reconstructions in atom probe tomography
Fletcher C, Moody MP, Fleischmann C, Dialameh M, Porret C, Geiser B, Haley D
September 2022
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Journal article
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JOURNAL OF PHYSICS D-APPLIED PHYSICS
atom probe tomography, correlative microscopy, data reconstruction, field evaporation, level set method, optimisation, semiconductor imaging
PosgenPy: An Automated and Reproducible Approach to Assessing the Validity of Cluster Search Parameters in Atom Probe Tomography Datasets
One of the main capabilities of atom probe tomography (APT) is the ability to not only identify but also characterize early stages of precipitation at length scales that are not achievable by other techniques. One of the most popular methods to identify nanoscale clustering in APT data, based on the density-based spatial clustering of applications with noise (DBSCAN), is used extensively in many branches of research. However, it is common that not all of the steps leading to the selection of certain parameters used in the analysis are reported. Without knowing the rationale behind parameter selection, it may be difficult to compare cluster parameters obtained by different researchers. In this work, a simple open-source tool, PosgenPy, is used to justify cluster search parameter selection via providing a systematic sweep through parameter values with multiple randomizations to minimize a false-positive cluster ratio. The tool is applied to several different microstructures: a simulated material system and two experimental datasets from a low-alloy steel. The analyses show how values for the various parameters can be selected to ensure that the calculated cluster number density and cluster composition are accurate.
Improving the Quantification of Deuterium in Zirconium Alloy Atom Probe Tomography Data Using Existing Analysis Methods
Jones ME, London AJ, Breen AJ, Styman PD, Sikotra S, Moody MP, Haley D
August 2022
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Journal article
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Microscopy and Microanalysis
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.
3D Nanoscale Analysis of Implanted Deuterium in Tungsten using Atom Probe Tomography
Meier MS, Bagot PAJ, Hollingsworth A, Wohlers A, Moody MP, Haley D
Tungsten is the primary candidate materials for the high neutron flux, high temperature components of a future demonstration fusion reactor. Despite this, there is a lack of data on W under fusion relevant neutron doses and irradiation temperatures. In this study, single crystal and polycrystalline W samples irradiated at the High Flux Reactor (HFR) at 900 ∘C were characterised using Atom Probe Tomography (APT) and Scanning Transmission Electron Microscopy (STEM). Bulk chemical and isotopic concentration predictions were validated by analysing the mass spectrum from APT experiments. A post irradiation composition of W-1.26 ± 0.15 at.%Re - 0.08 ± 0.02 at.%Os - 0.01 ± 0.01 at.%Ta was measured in the single crystal sample, whereas W-1.09 ± 0.07 at.%Re - 0.08 ± 0.02 at.%Os - 0.01 ± 0.01 at.%Ta was measured for the polycrystalline. APT and STEM showed that a high number density of Re and Os rich precipitates had formed under neutron irradiation. These typically consisted of a core rich in Re and Os, surrounded by a less dense Re rich cloud. Multiple analysis methods were applied to investigate the composition of these clusters. APT showed that the centres of some of the precipitates had a rod shaped core which were rich in both Re and Os. Line profile analysis suggests that in the centre of the precipitates, the threshold composition for σ phase formation may have been reached, as has been observed in higher transmutation rate experiments. In addition, dislocations, sub grain boundaries and dislocation loops were all shown to be decorated with both Re and Os, in agreement with predictions from DFT simulations.
A new class of alumina-forming superalloy for 3D printing
A new class of crack-resistant nickel-based superalloy containing high γ′ fraction is studied for the laser-powder bed fusion (L-PBF) process. The effects of the (Nb+Ta)/Al ratio is emphasized, a strategy that is shown to confer excellent low-temperature strength whilst maintaining oxidation resistance at high temperatures via stable alumina scale formation. The processability of the new alloys is characterized with respect to defect assessment by micro-focus X-ray computed tomography; use is made of a prototype turbine blade geometry and the heritage alloy CM247LC as a benchmark. In all cases, some processing-related porosity is present in thin wall sections such as the trailing edge, but this can be avoided by judicious processing. The cracking seen in CM247LC – in solid-state, liquation and solidification forms – is avoided. A novel sub-solvus heat treatment strategy is proposed which takes advantage of AM not requiring solutioning; super-solvus heat treatment is inappropriate since it embrittles the material by deterioration of the texture and coarsening of grain boundary carbides. The tensile strength of the new superalloy is greatest when the Nb+Ta content is highest and exceeds that of CM247LC up to ∼900°C. The oxidation resistance is best when Al content is highest, and oxidation-assisted cracking resistance maximized when the (Nb+Ta)/Al ratio is balanced. In all cases these are equivalent or superior to that of CM247LC. Nevertheless, the creep resistance of the new alloys is somewhat inferior to that of CM247LC for which the γ′, C, and B contents are higher; this implies a processing/property trade-off which requires further clarification.
Microstructure understanding of high Cr-Ni austenitic steel corrosion in high-temperature steam
Shen Z, Zhang J, Wu S, Luo X, Jenkins BM, Moody MP, Lozano-Perez S, Zeng X
March 2022
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Journal article
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Acta Materialia
The microstructure and microchemistry of the oxide scales formed on Fe-21Cr-32Ni and Fe-17Cr-9Ni steels after exposure to deaerated high-temperature high-pressure steam at 600 °C for 1500 h have been analysed and compared by several advanced characterization techniques. By comparing the oxide scales formed at different-stages of exposure, it is shown that Fe-21Cr-32Ni steel was internally oxidized at the early-stage, and then an external oxide scale was developed together with an inner chromia band under the internal oxidation zone. In comparison, Fe-17Cr-9Ni steel was internally oxidized together with an external Fe-rich oxide scale during the entire experimental period. The thicknesses of the internal oxidation zone of Fe-21Cr-32Ni and Fe-17Cr-9Ni steels were ∼7 and ∼70 µm, respectively. Further characterisation revealed that the internal oxidation zone contained (Cr, Fe, (Ni))3O4 and nanoscale nickel networks, together with numerous nano-pores. The effects of these structures on mass transfer and reaction product formation were discussed, in connection with the alloy composition and the formation of the chromia layer.
APT and TEM Study of Behaviour of Alloying Elements in Neutron-Irradiated Zirconium-Based Alloys
JENKINS B, HALEY J, Hyde J, MOODY M, GROVENOR C
February 2022
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Journal article
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Scripta Materialia
On the influence of microstructure on the neutron irradiation response of HIPed SA508 steel for nuclear applications
Carter M, Gasparrini C, Douglas JO, Riddle N, Edwards L, Bagot PAJ, Hardie CD, Wenman MR, Moody MP
February 2022
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Journal article
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Journal of Nuclear Materials
The neutron irradiation response of a novel hot isostatically pressed SA508 Grade3 steel was studied, such to deduce any influence this unconventional RPV microstructure has on radiation response. In particular, the role of elevated ferrite fraction was investigated. Neutron irradiation was conducted at 155 ± 10°C to induce 0.1dpa of damage, this corresponded 2.53 ± 0.63 GPa hardening for the ferrite and 1.94 ± 0.57 GPa for the bainite as measured by nanoindentation. Atom probe tomography detected the presence of Mn-Ni-Si type clusters in both microconstituent phases. The ferrite microstructure showed a greater percentage of solute atoms available to form clusters than bainite, but it also contained a lower cluster volume fraction and number density compared to the bainite.
Atom probe tomography
Gault B, Chiaramonti A, Cojocaru-Mirédin O, Stender P, Dubosq R, Freysoldt C, Makineni SK, Li T, Moody M, Cairney JM
December 2021
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Journal article
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Nature Reviews Methods Primers
Atom probe tomography (APT) provides three-dimensional compositional mapping with sub-nanometre resolution. The sensitivity of APT is in the range of parts per million for all elements, including light elements such as hydrogen, carbon or lithium, enabling unique insights into the composition of performance-enhancing or lifetime-limiting microstructural features and making APT ideally suited to complement electron-based or X-ray-based microscopies and spectroscopies. Here, we provide an introductory overview of APT ranging from its inception as an evolution of field ion microscopy to the most recent developments in specimen preparation, including for nanomaterials. We touch on data reconstruction, analysis and various applications, including in the geosciences and the burgeoning biological sciences. We review the underpinnings of APT performance and discuss both strengths and limitations of APT, including how the community can improve on current shortcomings. Finally, we look forwards to true atomic-scale tomography with the ability to measure the isotopic identity and spatial coordinates of every atom in an ever wider range of materials through new specimen preparation routes, novel laser pulsing and detector technologies, and full interoperability with complementary microscopy techniques.
Direct Observation of Hydrogen at Defects in Multicrystalline Silicon
Tweddle D, MOODY M, WILSHAW P, SHEN Z, HAMER P
November 2021
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Journal article
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Progress in Photovoltaics
Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping.
Tarantini C, Kametani F, Balachandran S, Heald SM, Wheatley L, Grovenor CRM, Moody MP, Su Y-F, Lee PJ, Larbalestier DC
September 2021
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Journal article
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Scientific reports
In recent years there has been an increasing effort in improving the performance of Nb<sub>3</sub>Sn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields (H<sub>Irr</sub> and H<sub>c2</sub>, respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties. Electron microscopy, Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and Atom Probe Tomography (APT) characterization clearly show that, in presence of oxygen, both fine Nb<sub>3</sub>Sn grains and HfO<sub>2</sub> nanoparticles form. Although EXAFS is unable to detect significant amounts of Hf in the A15 structure, APT does indeed reveal some residual intragrain metallic Hf. To investigate the layer properties in more detail, we created a microbridge from a thin lamella extracted by Focused Ion Beam (FIB) and measured the transport properties of Ta-Hf-doped Nb<sub>3</sub>Sn. H<sub>c2</sub>(0) is enhanced to 30.8 T by the introduction of Hf, ~ 1 T higher than those of only Ta-doped Nb<sub>3</sub>Sn, and, even more importantly the position of the pinning force maximum exceeds 6 T, against the typical ~ 4.5-4.7 T of the only Ta-doped material. These results show that the improvements generated by Hf addition can significantly enhance the high-field performance, bringing Nb<sub>3</sub>Sn closer to the requirements necessary for FCC realization.
The role of β-Zr in a Zr-2.5Nb alloy during aqueous corrosion: A multi-technique study
Liu J, He G, Callow A, Li K, Moore KL, Nordin H, Moody M, Lozano-Perez S, Grovenor CRM
August 2021
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Journal article
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Acta Materialia
The Zr–2.5Nb alloy is used as pressure tubes in Canadian Deuterium Uranium (CANDU) nuclear reactors, and the typical starting microstructure consists of α-Zr grains elongated in both transverse and longitudinal directions and thin layers of partially decomposed β-Zr lying between the α-Zr grains. In this study, we have used state-of-the-art microscopy techniques to characterise the long-term thermally decomposed β phase in this alloy, and the oxide scale formed on them in a reactor coolant loop with the aim of understanding the mechanisms underpinning the thermal decomposition behaviour at service temperatures and exploring the role of the decomposed β-Zr phase in controlling the microstructure and microchemistry of the zirconium oxide, and hence its influence on the general corrosion resistance of the alloy. We observe that these β-Zr layers are heavily decomposed even after the short stress stage at 400 °C at the end of the manufacturing cycle, with a closely packed array of β-Nb precipitates forming in an α-Zr matrix. We have shown that the oxidation of these bands is significantly slower than the surrounding α-Zr matrix and that zirconium oxide grains are re-nucleated under each band. We conclude that it is the combination of the Nb-rich remnants of the original β-Zr layers arising from the hot extrusion and drawing stages and this new dense oxide that offers a significant barrier to the oxidation front (and also to the penetration of hydrogenic species), so the characteristic layered microstructure arising from the original manufacturing process is very important in determining the overall oxidation behaviour.
Xenon plasma focussed ion beam preparation of an Al-6XXX alloy sample for atom probe tomography including analysis of an α-Al(Fe,Mn)Si dispersoid
Famelton JR, Hughes GM, Williams CA, Barbatti C, Moody MP, Bagot PAJ
August 2021
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Journal article
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Materials Characterization
A Xe plasma Focussed Ion Beam instrument was used to prepare in-situ specimens for Atom Probe Tomography from a bulk sample of an aluminium 6XXX alloy. The nature and distribution of precipitates and solute clusters observed in the alloy are not observed to differ between standard electropolishing methods and Xe plasma preparation. Enabled by site specific specimen preparation, analysis of an α-Al(Fe,Mn)Si dispersoid shows segregation at the phase boundary and in the shell of the dispersoid.
Atom Probe Tomography of a Cu-doped TiNiSn Thermoelectric Material: Nanoscale Structure and Optimisation of Analysis Conditions
Henry H, Halpin J, Popuri S, Daly L, Bos J-W, MOODY M, MacLaren D, BAGOT P
July 2021
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Journal article
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Microscopy and Microanalysis
Extending Estimating Hydrogen Content in Atom Probe Tomography Experiments Where H2Molecule Formation Occurs
Meier M, Jones M, Felfer P, Moody M, Haley D
July 2021
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Journal article
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Microscopy and Microanalysis
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.
Structural and compositional analysis of (InGa)(AsSb)/GaAs/GaP Stranski-Krastanov quantum dots.
Gajjela RSR, Hendriks AL, Douglas JO, Sala EM, Steindl P, Klenovský P, Bagot PAJ, Moody MP, Bimberg D, Koenraad PM
June 2021
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Journal article
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Light, science & applications
We investigated metal-organic vapor phase epitaxy grown (InGa)(AsSb)/GaAs/GaP Stranski-Krastanov quantum dots (QDs) with potential applications in QD-Flash memories by cross-sectional scanning tunneling microscopy (X-STM) and atom probe tomography (APT). The combination of X-STM and APT is a very powerful approach to study semiconductor heterostructures with atomic resolution, which provides detailed structural and compositional information on the system. The rather small QDs are found to be of truncated pyramid shape with a very small top facet and occur in our sample with a very high density of ∼4 × 10<sup>11</sup> cm<sup>-2</sup>. APT experiments revealed that the QDs are GaAs rich with smaller amounts of In and Sb. Finite element (FE) simulations are performed using structural data from X-STM to calculate the lattice constant and the outward relaxation of the cleaved surface. The composition of the QDs is estimated by combining the results from X-STM and the FE simulations, yielding ∼In<sub>x</sub>Ga<sub>1 - x</sub>As<sub>1 - y</sub>Sb<sub>y</sub>, where x = 0.25-0.30 and y = 0.10-0.15. Noticeably, the reported composition is in good agreement with the experimental results obtained by APT, previous optical, electrical, and theoretical analysis carried out on this material system. This confirms that the InGaSb and GaAs layers involved in the QD formation have strongly intermixed. A detailed analysis of the QD capping layer shows the segregation of Sb and In from the QD layer, where both APT and X-STM show that the Sb mainly resides outside the QDs proving that Sb has mainly acted as a surfactant during the dot formation. Our structural and compositional analysis provides a valuable insight into this novel QD system and a path for further growth optimization to improve the storage time of the QD-Flash memory devices.
Nanoindentation in multi-modal map combinations: A Correlative Approach to Local Mechanical Property Assessment
Magazzeni C, Gardner H, Howe I, Gopon P, Waite J, Rugg D, Armstrong D, Wilkinson A
June 2021
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Journal article
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https://doi.org/10.1557/s43578-020-00035-y
A method is presented for the registration and correlation of intrinsic
property maps of materials, including data from nanoindentation hardness,
Electron Back-Scattered Diffraction (EBSD), Electron Micro-Probe Analysis
(EPMA). This highly spatially resolved method allows for the study of
micron-scale microstructural features, and has the capability to rapidly
extract correlations between multiple features of interest from datasets
containing thousands of datapoints. Two case studies are presented in
commercially pure (CP) titanium: in the first instance, the effect of crystal
anisotropy on measured hardness and, in the second instance, the effect of an
oxygen diffusion layer on hardness. The independently collected property maps
are registered us-ing affine geometric transformations and are interpolated to
allow for direct correlation. The results show strong agreement with trends
observed in the literature, as well as providing a large dataset to facilitate
future statistical analysis of microstructure-dependent mechanisms.
cond-mat.mtrl-sci
Nanocluster evolution and mechanical properties of ion irradiated T91 ferritic-martensitic steel
The oxidation properties of a family of novel polycrystalline Ni-based superalloys with varying Ti:Nb ratio have been studied, which has shown a correlation between increasing titanium content and accelerated oxidation kinetics. High-resolution characterization of microstructure and chemistry was carried out on the resultant oxide layers using SEM/EDX and Atom Probe Tomography to precisely locate Ti segregation within chromia scales, in order to identify a potential mechanism to explain this correlation. Despite some spread in the data, levels of Ti dissolved in the chromia oxide scales showed little correlation with the nominal Ti concentration or the oxidation properties of each alloy, indicating that oxidation rates are not reliant on dopant levels within bulk chromia. A number of grain boundaries within the oxide scale were targeted for APT analysis, as these are known to act as short-circuit diffusion paths. Segregation of Ti, Nb and Ta to oxide grain boundaries was observed, suggesting that ion transport rates may instead be mediated by dopants present at grain boundaries rather than dissolved within the bulk.
Re-examining the role of nuclear fusion in a renewables-based energy mix
Nicholas TEG, Davis TP, Federici F, Leland J, Patel BS, Vincent C, Ward SH
February 2021
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Journal article
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Energy Policy
Fusion energy is often regarded as a long-term solution to the world's energy needs. However, even after solving the critical research challenges, engineering and materials science will still impose significant constraints on the characteristics of a fusion power plant. Meanwhile, the global energy grid must transition to low-carbon sources by 2050 to prevent the worst effects of climate change. We review three factors affecting fusion's future trajectory: (1) the significant drop in the price of renewable energy, (2) the intermittency of renewable sources and implications for future energy grids, and (3) the recent proposition of intermediate-level nuclear waste as a product of fusion. Within the scenario assumed by our premises, we find that while there remains a clear motivation to develop fusion power plants, this motivation is likely weakened by the time they become available. We also conclude that most current fusion reactor designs do not take these factors into account and, to increase market penetration, fusion research should consider relaxed nuclear waste design criteria, raw material availability constraints and load-following designs with pulsed operation.
Atom Probe Tomography for Isotopic Analysis: Development of the 34S/32S System in Sulfides
Gopon P, Douglas JO, Meisenkothen F, Singh J, London AJ, Moody MP
January 2021
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Journal article
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Microscopy and Microanalysis
Using a combination of simulated data and pyrite isotopic reference materials, we have refined a methodology to obtain quantitative δ34S measurements from atom probe tomography (APT) datasets. This study builds on previous attempts to characterize relative 34S/32S ratios in gold-containing pyrite using APT. We have also improved our understanding of the artifacts inherent in laser-pulsed APT of insulators. Specifically, we find the probability of multi-hit detection events increases during the APT experiment, which can have a detrimental effect on the accuracy of the analysis. We demonstrate the use of standardized corrected time-of-flight single-hit data for our isotopic analysis. Additionally, we identify issues with the standard methods of extracting background-corrected counts from APT mass spectra. These lead to inaccurate and inconsistent isotopic analyses due to human variability in peak ranging and issues with background correction algorithms. In this study, we use the corrected time-of-flight single-hit data, an adaptive peak fitting algorithm, and an improved deconvolution algorithm to extract 34S/32S ratios from the S2+ peaks. By analyzing against a standard material, acquired under similar conditions, we have extracted δ34S values to within ±5% (1% = 1 part per thousand) of the published values of our standards.
Characterisation of nano-scale precipitates in BOR60 irradiated T91 steel using atom probe tomography
Developing Atom Probe Tomography to Characterize Sr-Loaded Bioactive Glass for Bone Scaffolding
Ren Y, Autefage H, Jones JR, Stevens MM, Bagot PAJ, Moody MP
January 2021
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Journal article
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Microscopy and Microanalysis
In this study, atom probe tomography (APT) was used to investigate strontium-containing bioactive glass particles (BG-Sr10) and strontium-releasing bioactive glass-based scaffolds (pSrBG), both of which are attractive biomaterials with applications in critical bone damage repair. We outline the challenges and corresponding countermeasures of this nonconductive biomaterial for APT sample preparation and experiments, such as avoiding direct contact between focussed ion beam micromanipulators and the extracted cantilever to reduce damage during liftout. Using a low imaging voltage (≤3 kV) and current (≤500 pA) in the scanning electron microscope and a low acceleration voltage (≤2 kV) and current (≤200 pA) in the focussed ion beam prevents tip bending in the final stages of annular milling. To optimize the atom probe experiment, we considered five factors: total detected hits, multiple hits, the background level, the charge-state ratio, and the accuracy of the measured compositions, to explore the optimal laser pulse for BG-Sr10 bioactive glass. We show that a stage temperature of 30 K, 200-250 pJ laser pulse energy, 0.3% detection rate, and 200 kHz pulse rate are optimized experimental parameters for bioactive glass. The use of improved experimental preparation methods and optimized parameters resulted in a 90% successful yield of pSrBG samples by APT.
Observation of Mn-Ni-Si-rich Features in Thermally-Aged Model Reactor Pressure Vessel Steels
JENKINS B, Styman P, Riddle N, BAGOT P, MOODY M, Smith G, Hyde J
January 2021
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Journal article
|
Scripta Materialia
Quantifying the effect of oxygen on micro-mechanical properties of a near-alpha titanium alloy
Gardner HM, Gopon P, Magazzeni CM, Radecka A, Fox K, Rugg D, Wade J, Armstrong DEJ, Moody MP, Bagot PAJ
Microstructural understanding of the oxidation of an austenitic stainless steel in high-temperature steam through advanced characterization
SHEN Z, Tweddle D, YU H, He G, Varambhia A, KARAMCHED P, HOFMANN F, WILKINSON A, MOODY M, Zhang L, LOZANO-PEREZ S
August 2020
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Journal article
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Acta Materialia
New insights into the oxidation mechanisms of a ferritic-martensitic steel in high-temperature steam
SHEN Z, Chen K, Yu H, JENKINS B, Ren Y, Saravanan N, He G, Luo X, BAGOT P, MOODY M, Zhang L, LOZANO-PEREZ S
August 2020
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Journal article
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Acta Materialia
The Effects of Chemistry Variations in New Nickel-Based Superalloys for Industrial Gas Turbine Applications
Sulzer S, Hasselqvist M, Murakami H, Bagot P, Moody M, Reed R
June 2020
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Journal article
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Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
© 2020, The Author(s). Industrial gas turbines (IGT) require novel single-crystal superalloys with demonstrably superior corrosion resistance to those used for aerospace applications and thus higher Cr contents. Multi-scale modeling approaches are aiding in the design of new alloy grades; however, the CALPHAD databases on which these rely remain unproven in this composition regime. A set of trial nickel-based superalloys for IGT blades is investigated, with carefully designed chemistries which isolate the influence of individual additions. Results from an extensive experimental characterization campaign are compared with CALPHAD predictions. Insights gained from this study are used to derive guidelines for optimized gas turbine alloy design and to gauge the reliability of the CALPHAD databases.
A More Holistic Characterisation Of Internal Interfaces In A Variety of Materials via Complementary Use Of Transmission Kikuchi Diffraction and Atom Probe Tomography
Jenkins BM, Douglas JO, Gardner HM, Tweddle D, Kareer A, Karamched PS, Riddle N, Hyde JM, Bagot PAJ, Robert Odette G, Moody MP
June 2020
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Journal article
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Applied Surface Science
Element segregation and α2 formation in primary α of a near-α Ti-alloy
Dichtl C, Zhang Z, Gardner H, Bagot P, Radecka A, Dye D, Thomas M, Sandala R, da Fonseca JQ, Preuss M
Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada
Interfaces play critical roles in materials and are usually both structurally and compositionally complex microstructural features. The precise characterization of their nature in three-dimensions at the atomic scale is one of the grand challenges for microscopy and microanalysis, as this information is crucial to establish structure-property relationships. Atom probe tomography is well suited to analyzing the chemistry of interfaces at the nanoscale. However, optimizing such microanalysis of interfaces requires great care in the implementation across all aspects of the technique from specimen preparation to data analysis and ultimately the interpretation of this information. This article provides critical perspectives on key aspects pertaining to spatial resolution limits and the issues with the compositional analysis that can limit the quantification of interface measurements. Here, we use the example of grain boundaries in steels; however, the results are applicable for the characterization of grain boundaries and transformation interfaces in a very wide range of industrially relevant engineering materials.
interfaces, steel, atom probe tomography, coupled solute drag
Using alpha hulls to automatically and reproducibly detect edge clusters in atom probe tomography datasets
Jenkins BM, London AJ, Riddle N, Hyde JM, Bagot PAJ, Moody MP
Nanoscale analysis of ion irradiated ODS 14YWT ferritic alloy
Auger M, Hoelzer DT, Field KG, MOODY MP
Edited by:
Was, GS
January 2020
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Journal article
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Journal of Nuclear Materials
In this work, the nanoscale microstructure of an advanced oxide dispersion strengthened (ODS) 14YWT ferritic alloy (SM13 heat) with nominal composition Fe-14Cr-3W-0.4Ti-0.3Y2O3 (wt. %) has been characterized by atom probe tomography (APT) before and after ion irradiation with 70 MeV Fe9+ ions at 450oC to a total dose of 21 dpa. A detailed solute cluster analysis of APT data reveals that, in the manufacturing process, larger nanoparticles form in or close to the grain boundaries respective to those inside grains. The evolution of the nanoparticles after irradiation seems to be related to their location, as a higher increase in the number density and in the Y:Ti ratio is observed for the nanoparticles in or close to grain boundaries. APT analysis also shows Cr, W and C segregation to grain boundaries enhanced by the irradiation. A previous study of this same alloy before and after irradiation reports that the mechanical properties do not seem to be affected, but the microstructure was not investigated to confirm. The present work confirms little microstructural evolution after irradiation in this 14YWT alloy, indicating tolerance at the given irradiation conditions.
14YWT, ODS alloys, Atom probe tomography, Ion irradiation, Clusters
Decoration of voids with rhenium and osmium transmutation products in neutron irradiated single crystal tungsten
A Nanoscale Investigation of Carlin-Type Gold Deposits: An Atom-Scale Elemental and Isotopic Perspective
GOPON P, DOUGLAS JO, Auger M, HANSEN LN, WADE J, Cline JS, Robb LJ, MOODY MP
Edited by:
Meinert, L
September 2019
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Journal article
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Economic Geology
Carlin-type gold deposits are one of the most important gold mineralization styles in the world. Despite their economic importance and the large volume of work that has been published, there remain crucial questions regarding their metallogenesis. Much of this uncertainty is due to the cryptic nature of the gold occurrence, with gold occurring as dispersed nanoscale inclusions within host pyrite rims that formed on earlier formed barren pyrite cores. The small size of the gold inclusions has made determining their nature within the host sulfides and the mechanisms by which they precipitated from the ore fluids particularly problematic.
This study combines high-resolution electron probe microanalysis (EPMA) with atom probe tomography (APT) to constrain whether the gold occurs as nanospheres or is dispersed within the Carlin pyrites. APT offers the unique capability of obtaining major, minor, trace, and isotopic chemical information at near-atomic spatial resolution. We use this capability to investigate the atomic-scale distribution of trace elements within Carlin type pyrite rims, as well as the relative differences of sulfur isotopes within the rim and core of gold-hosting pyrite.
We show that gold within a sample from the Turquoise Ridge deposit (Nevada) occurs within arsenian pyrite overgrowth (rims) that formed on a pyrite core. Furthermore, this As-rich rim does not contain nanonuggets of gold and instead contains dispersed lattice-bound Au within the pyrite crystal structure. The spatial correlation of gold and arsenic within our samples is consistent with increased local arsenic concentrations that enhanced the ability of arsenian pyrite to host dispersed gold (Kusebauch et al., 2019). We hypothesize that point defects in the lattice induced by the addition of arsenic to the pyrite structure facilitate the dissemination of gold. The lack of gold nanospheres in our study is consistent with previous work showing that dispersed gold in arsenian pyrite can occur in concentrations up to ~1:200 (gold/arsenic). We also report a method for determining the sulfur isotope ratios from atom probe data sets of pyrite (±As) that illustrates a relative change between the pyrite core and its Au and arsenian pyrite rim. This spatial variation confirms that the observed pyrite core-rim structure is due to two-stage growth involving a sedimentary core and hydrothermal rim, as opposed to precipitation from an evolving hydrothermal fluid.
Combined APT, TEM and SAXS characterisation of nanometre-scale precipitates in titanium alloys
Dear F, Kontis P, Gault B, Ilavsky J, Gardner H, Bagot P, Moody M, Rugg D, Dye D
August 2019
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Journal article
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Microscopy and Microanalysis
An in-situ approach for preparing atom probe tomography specimens by xenon plasma-focused ion beam
BAGOT P, Gardner H, MOODY M
July 2019
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Journal article
|
Ultramicroscopy
Insight into the impact of atomic- and nano-scale indium distributions on the optical properties of InGaN/GaN quantum well structures grown on m -plane freestanding GaN substrates
Tang F, Zhu T, Fu WY, Oehler F, Zhang S, Griffiths JT, Humphreys C, Martin TL, Bagot PAJ, Moody MP, Patra SK, Schulz S
Identification of colloidal silica polishing induced contamination in silicon
Tweddle D, Hamer P, Shen Z, Moody MP, Wilshaw PR
June 2019
|
Journal article
|
MATERIALS CHARACTERIZATION
Silicon, Polishing, Contamination, Atom probe tomography, Correlative microscopy
Atom probe tomography of carbides in Fe-Cr-(W)-C steels
Gramlich ARM, Auger M, Schneider A, MOODY MP
Edited by:
Scheffler, UT
May 2019
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Journal article
|
Steel Research International
In this study, Fe‐Cr‐C and Fe‐Cr‐W‐C alloys are characterized using atom probe tomography. The alloys have been heat treated at 1070 °C for 30 min and subsequently at 780 °C for various time periods. Carbide formation is observed at each state. Cr‐C precipitates smaller than 5 nm in radius for short heat treatment times and larger than 50 nm for heat‐treatment times greater than 1000 s are observed. It is found that the phase interface moves during the first time period at an almost constant speed. Later on the velocity of the phase interface decreases. Furthermore, kinetic assumptions for carbide growth from a previous theoretical study have been verified. As expected, a decrease of the microhardness with increasing aging time is detected which is caused by martensite tempering. The aim of this study is to measure the change in chemical compositions across phase interfaces between matrix and precipitates to obtain a better understanding of the precipitation process.
Atom probe tomography, Carbides, Ferritic-martensitic steels, Precipitations
Characterization of the crack initiation and propagation in Alloy 600 with a cold-worked surface
SHEN Z, Chen K, Tweddle D, He G, Arioka K, LOZANO-PEREZ S
May 2019
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Journal article
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Corrosion Science
Partitioning of Ti and Kinetic Growth Predictions on the Thermally Grown Chromia Scale of a Polycrystalline Nickel-Based Superalloy
Pedrazzini S, Rowlands BS, Turk A, Parr IMD, Hardy MC, Bagot PAJ, Moody MP, Galindo-Nava E, Stone HJ
May 2019
|
Journal article
|
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
A gas-phase reaction cell for modern Atom Probe systems
HALEY DANIEL, McCarrol I, MOODY M, BAGOT P
April 2019
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Journal article
|
Microscopy and Microanalysis
Atom Probe Tomography Investigations of Microstructural Evolution in an Aged Nickel Superalloy for Exhaust Applications
Gardner H, Pedrazzini S, Douglas JO, De Lille D, Moody MP, Bagot PAJ
April 2019
|
Journal article
|
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
DF-Fit : A robust algorithm for detection of crystallographic information in Atom Probe Tomography data
HALEY DJ, MOODY M, BAGOT P
April 2019
|
Journal article
|
Microscopy and Microanalysis
Long-term trends in child maltreatment in England and Wales: A time series analysis of official record data from 1858 to 2016
DEGLI ESPOSTI M, HUMPHREYS DK, Jenkins BM, Gasparrini A, POOLEY S, Eisner M, BOWES L
March 2019
|
Journal article
|
Lancet Public Health
Modeling and simulation in atom probe tomography
Larson DJ, Moody MP
March 2019
|
Journal article
|
MATERIALS CHARACTERIZATION
Effect of Nb and Fe on damage evolution in a Zr-alloy during proton and neutron irradiation
Francis E, Babu RP, Harte A, Martin TL, Frankel P, Jädernäs D, Romero J, Hallstadius L, Bagot PAJ, Moody MP, Preuss M
Using spherical indentation to measure the strength of copper-chromium-zirconium
Cackett AJ, Lim JJH, Klupś P, Bushby AJ, Hardie CD
December 2018
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Journal article
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Journal of Nuclear Materials
Precipitation hardened CuCrZr will be used in heat-sink components in the ITER tokomak and is a primary candidate for EU DEMO. The measurement of mechanical properties of irradiated CuCrZr using conventional, standardised techniques is difficult due to the challenges involved in working with radioactive material and the relatively large specimen size required. Spherical nano-indentation offers a technique to measure stress-strain properties from far smaller volumes than conventional tests. In this work, CuCrZr has been heat-treated at different temperatures to vary the Cr precipitate size and spacing. Spherical nano-indentation using multiple tip radii was then used to produce stress-strain curves for all samples, from which values of initial flow stress were calculated. It was found that there was a strong indentation size effect (ISE) in the stress required to initiate plasticity, however at higher indentation strains the flow stress became constant for tip radii, R, ≥8 μm. This suggests that at the initiation of plastic deformation the ISE is dominated by dislocation source activation but in later stages the interaction with microstructural material length-scales dominate the measured mechanical strength. The mechanical response of these small-scale tests is governed by multiple mechanisms, which convolute interpretation of data and must be considered when measuring the effects of irradiation on the mechanical properties.
Understanding irradiation-induced nanoprecipitation in zirconium alloys using parallel TEM and APT
Harte A, Babu RP, Hirst CA, Martin TL, Bagot PAJ, Moody MP, Frankel P, Romero J, Hallstadius L, Darby EC, Preuss M
November 2018
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Journal article
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JOURNAL OF NUCLEAR MATERIALS
Nano precipitation, Transmission electron microscopy, Atom probe tomography, Zirconium, Irradiation
Atom probe tomography analysis of the reference zircon gj-1: An interlaboratory study
Exertier F, La Fontaine A, Corcoran C, Piazolo S, Belousova E, Peng Z, Gault B, Saxey DW, Fougerouse D, Reddy SM, Pedrazzini S, Bagot PAJ
Microstructural and mechanical characterisation of Fe-14Cr-0.22Hf alloy fabricated by spark plasma sintering
Auger MA, Huang Y, Zhang H, Jones CA, Hong Z, moody MP, Roberts SG, Grant PS
Edited by:
Yartys, VA
September 2018
|
Journal article
|
Journal of Alloys and Compounds
Fe-14Cr pre-alloyed powder and pure Hf powder were mechanically alloyed to produce powder with nominal composition Fe-14Cr-0.22Hf (wt. %) that was consolidated by the spark plasma sintering (SPS) technique in order to investigate the ability of Hf to produce a nanometric dispersion of oxide particles in a ferritic matrix. Comprehensive microstructural and mechanical characterisation of the as-milled powder and the consolidated material was performed using electron microscopy, X-ray diffraction, atom probe tomography and indentation techniques. It was shown that Hf additions can effectively produce, by internal oxidation, a fine scale dispersion of Hf-O nanoparticles in the consolidated material. A uniform grain structure was produced in the alloy. Although the nanoparticle dispersion was not homogeneous at the finest scale, the resulting dispersion strengthening contributed significantly to the hardness. According to these results, internal oxidation of reactive elements rather than direct addition of oxides may offer additional opportunities in the design and development of oxide dispersion strengthened steels.
Powder metallurgy, Hafnium, ODS steels, SPS, TEM, APT
Atom probe Tomography of fast-diffusing impurities and the effect of gettering in multicrystalline silicon
August 2018
|
Journal article
|
AIP Conference Proceedings
Interpreting Atom Probe Data from Oxide-Metal Interfaces.
McCarroll I, Scherrer B, Felfer P, Moody MP, Cairney JM
August 2018
|
Journal article
|
Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada
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.
Microstructure evolution of T91 irradiated in the BOR60 fast reactor
Jiao Z, Taller S, Field K, Yeli G, Moody MP, Was GS
A family of novel polycrystalline Ni-based superalloys with varying Ti:Nb ratios has been created using computational alloy design techniques, and subsequently characterized using atom probe tomography and electron microscopy. Phase chemistry, elemental partitioning, and γ′ character have been analyzed and compared with thermodynamic predictions created using Thermo-Calc. Phase compositions and γ′ volume fraction were found to compare favorably with the thermodynamically predicted values, while predicted partitioning behavior for Ti, Nb, Cr, and Co tended to overestimate γ′ preference over the γ matrix, often with opposing trends vs Nb concentration.
Extending Continuum Models for Atom Probe Simulation
Haley DJ, Bagot PAJ, Moody M
February 2018
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Journal article
|
Materials Characterization
Nanoscale structural and chemical analysis of F-implanted enhancement-mode InAlN/GaN heterostructure field effect transistors
Tang F, Lee KB, Guiney I, Frentrup M, Barnard JS, Divitini G, Zaidi ZH, Martin TL, Bagot PA, Moody MP, Humphreys CJ, Houston PA
,
et al
January 2018
|
Journal article
|
JOURNAL OF APPLIED PHYSICS
Effect of alloying elements on microstructural evolution in oxygen content controlled Ti-29Nb-13Ta-4.6Zr (wt. %) alloys for biomedical applications during aging
Haley DJ, Honma T, Arafeh A, Nakai M, Ninomii N, Moody MP
January 2018
|
Journal article
|
Materials Science and Engineering A: Structural Materials: Properties, Microstructure and Processing
Correlative atomic scale characterisation of secondary carbides in M50 bearing steel
Hopkin SE, Danaie M, Guetard G, Rivera-Diaz-del-Castillo P, Bagot PAJ, Moody MP
Specimen preparation methods for elemental characterisation of grain boundaries and isolated dislocations in multicrystalline silicon using atom probe tomography
Lotharukpong C, Tweddle D, Martin TL, Wu M, Grovenor CRM, Moody MP, Wilshaw PR
September 2017
|
Journal article
|
MATERIALS CHARACTERIZATION
Atom probe tomography, Focused ion beam, Grain boundaries, Isolated dislocations, Multicrystalline silicon
On the microtwinning mechanism in a single crystal superalloy
Barba D, Alabort E, Pedrazzini S, Collins DM, Wilkinson AJ, Bagot PAJ, Moody MP, Atkinson C, Jérusalem A, Reed RC
A nexus between 3D atomistic data hybrids derived from atom probe microscopy and computational materials science: A new analysis of solute clustering in Al-alloys
Atom probe analysis of ex-situ gas-charged stable hydrides
Haley DJ, Moody M, Bagot P
April 2017
|
Journal article
|
Microscopy and Microanalysis
Automated Atom-By-Atom Three-Dimensional (3D) Reconstruction of Field Ion Microscopy Data.
Dagan M, Gault B, Smith GDW, Bagot PAJ, Moody MP
April 2017
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Journal article
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Microsc Microanal
An automated procedure has been developed for the reconstruction of field ion microscopy (FIM) data that maintains its atomistic nature. FIM characterizes individual atoms on the specimen's surface, evolving subject to field evaporation, in a series of two-dimensional (2D) images. Its unique spatial resolution enables direct imaging of crystal defects as small as single vacancies. To fully exploit FIM's potential, automated analysis tools are required. The reconstruction algorithm developed here relies on minimal assumptions and is sensitive to atomic coordinates of all imaged atoms. It tracks the atoms across a sequence of images, allocating each to its respective crystallographic plane. The result is a highly accurate 3D lattice-resolved reconstruction. The procedure is applied to over 2000 tungsten atoms, including ion-implanted planes. The approach is further adapted to analyze carbides in a steel matrix, demonstrating its applicability to a range of materials. A vast amount of information is collected during the experiment that can underpin advanced analyses such as automated detection of "out of sequence" events, subangstrom surface displacements and defects effects on neighboring atoms. These analyses have the potential to reveal new insights into the field evaporation process and contribute to improving accuracy and scope of 3D FIM and atom probe characterization.
3D reconstruction, atomic resolution, crystal defects, field ion microscopy
Comparing the Consistency of Atom Probe Tomography Measurements of Small-Scale Segregation and Clustering Between the LEAP 3000 and LEAP 5000 Instruments.
Martin TL, London AJ, Jenkins B, Hopkin SE, Douglas JO, Styman PD, Bagot PAJ, Moody MP
April 2017
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Journal article
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Microsc Microanal
The local electrode atom probe (LEAP) has become the primary instrument used for atom probe tomography measurements. Recent advances in detector and laser design, together with updated hit detection algorithms, have been incorporated into the latest LEAP 5000 instrument, but the implications of these changes on measurements, particularly the size and chemistry of small clusters and elemental segregations, have not been explored. In this study, we compare data sets from a variety of materials with small-scale chemical heterogeneity using both a LEAP 3000 instrument with 37% detector efficiency and a 532-nm green laser and a new LEAP 5000 instrument with a manufacturer estimated increase to 52% detector efficiency, and a 355-nm ultraviolet laser. In general, it was found that the number of atoms within small clusters or surface segregation increased in the LEAP 5000, as would be expected by the reported increase in detector efficiency from the LEAP 3000 architecture, but subtle differences in chemistry were observed which are attributed to changes in the way multiple hit detection is calculated using the LEAP 5000.
atom probe tomography, clustering, detector efficiency, small-scale segregation, steel
Detecting Clusters in Atom Probe Data with Gaussian Mixture Models.
Zelenty J, Dahl A, Hyde J, Smith GDW, Moody MP
April 2017
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Journal article
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Microsc Microanal
Accurately identifying and extracting clusters from atom probe tomography (APT) reconstructions is extremely challenging, yet critical to many applications. Currently, the most prevalent approach to detect clusters is the maximum separation method, a heuristic that relies heavily upon parameters manually chosen by the user. In this work, a new clustering algorithm, Gaussian mixture model Expectation Maximization Algorithm (GEMA), was developed. GEMA utilizes a Gaussian mixture model to probabilistically distinguish clusters from random fluctuations in the matrix. This machine learning approach maximizes the data likelihood via expectation maximization: given atomic positions, the algorithm learns the position, size, and width of each cluster. A key advantage of GEMA is that atoms are probabilistically assigned to clusters, thus reflecting scientifically meaningful uncertainty regarding atoms located near precipitate/matrix interfaces. GEMA outperforms the maximum separation method in cluster detection accuracy when applied to several realistically simulated data sets. Lastly, GEMA was successfully applied to real APT data.
Nanoscale Stoichiometric Analysis of a High-Temperature Superconductor by Atom Probe Tomography
Pedrazzini S, London AJ, Gault B, Saxey D, Speller S, Grovenor CRM, Danaie M, Moody MP, Edmondson PD, Bagot PAJ
April 2017
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Journal article
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Microscopy and Microanalysis
Single-Ion Deconvolution of Mass-Peak Overlaps for Atom Probe Microscopy
London A, haley D, moody MP
April 2017
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Journal article
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Microscopy and Microanalysis
Due to the intrinsic evaporation properties of the material studied, insufficient mass-resolving power and lack of knowledge of the kinetic energy of incident ions, peaks in the atom probe mass-to-charge spectrum can overlap and result in incorrect chemical measurements. Contributions to these peak overlaps can be deconvoluted globally, by simply examining adjacent peaks combined with knowledge of natural isotopic abundances. However, this strategy does not account for the fact that the relative contributions to this convoluted signal can often vary significantly in different regions of the analysis volume; e.g. across interfaces and within clusters. Some progress has been made with spatially localised deconvolution in cases where the discrete microstructural regions can be easily identified within the reconstruction, but this means no further point-cloud analyses are possible. Hence, we present an ion-by-ion methodology where the chemical identity of each ion, normally obscured by peak overlap, is resolved by examining the isotopic abundance of their immediate surroundings. The resulting peak-deconvoluted data is a point cloud and can be analysed with any existing tools. We will present the detailed case studies and discussion of the limitations of this new technique.
Direct Observation of Individual Hydrogen Atoms at Trapping Sites in a Ferritic Steel
Haley D, Cheng Y, Moody M, London AJ, Bagot P, Wepf RA, Gerstl SSA, Rainforth WM, Sweeney F
March 2017
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Journal article
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Science
Sequential nucleation of phases in a 17-4PH steel: Microstructural characterisation and mechanical properties
We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.
An Atom Probe Tomography study of site preference and partitioning in a nickel-based superalloy
Bagot PAJ, Douglas JO, Pedrazzini SP, Crudden DJ, Martin TL, Moody MP, Reed RC
February 2017
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Journal article
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Acta Materialia
Ion-irradiation Induced Clustering in W-Re-Ta, W-Re and W-Ta alloys: an Atom Probe Tomography and Nanoindentation Study
Armstrong DEJ, roberts S, smith G, moody M, beck C, Bagot P
February 2017
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Journal article
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Acta Materialia
On the composition of microtwins in a single crystal nickel-based superalloy
Barba D, Pedrazzini S, Vilalta Clemente A, Wilkinson AJ, Moody MP, Bagot PAJ, Jerusalem A, Reed RC
January 2017
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Journal article
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Scripta Materialia
Correlative analysis is performed using atom probe tomography and high resolution transmission Kikuchi diffraction techniques on microtwins of ∼10 nm thickness, in a ⟨011⟩-orientated single crystal superalloy crept at 800 °C and 650 MPa. Composition profiles across the microtwins and microtwin-parent boundaries are presented. Enrichment of microtwin-parent interfaces by approximately 2 at.% Cr and 1 at.% Co within the γ′-phase is found; no compositional variations of other elements – Ta, Nb, Mo, W – are detected. Our results provide unique insights into the mechanism of microtwin formation and the likely influence of alloy composition on deformation kinetics.
The effect of boron on oxide scale formation in a new polycrystalline superalloy
Kontis P, Pedrazzini S, Gong Y, Bagot PAJ, Moody MP, Reed RC
Erratum: Corrigendum to “A mechanistic study of the temperature dependence of the stress corrosion crack growth rate in SUS316 stainless steels exposed to pressurized water reactor primary water” (Acta Mater. (2016) 114 (15–24))
Meisnar M, Vilalta-Clemente A, Moody M, Arioka K, Lozano-Perez S
A mechanistic study of the temperature dependence of the stress corrosion crack growth rate in SUS316 stainless steels exposed to PWR primary water
Lozano-Perez S, Meisnar M, Vilalta-Clemente A, Moody M, Arioka K
August 2016
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Journal article
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Acta Materialia
Effect of the milling atmosphere on the microstructure and mechanical properties of a ODS Fe-14Cr model alloy
Auger MA, de Castro V, Leguey T, Lozano-Perez S, Bagot PAJ, Moody MP, Roberts SG
August 2016
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Journal article
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Materials Science & Engineering A
A systematic study has been undertaken to assess how the milling atmosphere, in the processing of an ODS steel with nominal composition Fe-14Cr-0.3Y2O3 (wt. %), will affect the microstructure and mechanical properties of the resultant alloys. Batches of the steel were manufactured by a powder metallurgy route incorporating mechanical alloying, hot isostatic pressing, forging and heat treatment. Hydrogen or helium atmospheres were used in the mechanical alloying, with all other processing parameters remaining identical. Transmission electron microscopy (TEM) and Atom Probe Tomography (APT) show that both milling atmospheres promote a homogeneous dispersion of Y-rich nanoparticles in the final alloys, being smaller when milling in H. Previously reported mechanical characterisation of these alloys shows better mechanical response at high temperature for the alloy milled in a H. This can be justified by the presence of smaller Y-rich nanoparticles together with the absence of bubbles, observed in the alloy milled in He.
ODS steels, Powder metallurgy, Milling atmosphere, TEM, APT
Green semipolar III-nitride light-emitting diodes grown by limited area epitaxy
The performance of multiple quantum well green and yellow semipolar light-emitting diodes (LEDs) is limited by relaxation of highly strained InGaN-based active regions and the subsequent formation of nonradiative defects. Limited area epitaxy was used to block glide of substrate threading dislocations and to reduce the density of misfit dislocations (MDs) directly beneath the active region of (2021) LEDs. Devices were grown and fabricated on a 1D array of narrow substrate mesas to limit the MD run length. Reducing the mesa width from 20 μm to 5 μm lowered the density of basal plane and non-basal plane MDs on the mesas and limited the number of defect-generating dislocation intersections. This improvement in material quality yielded a 73% enhancement in peak external quantum efficiency for the devices with the narrowest mesas compared to the devices with the widest mesas.
Optimisation of sample preparation and analysis conditions for atom probe tomography characterisation of low concentration surface species
Douglas JO, Bagot PAJ, Johnson BC, Jamieson DN, Moody MP
Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour
Martin TL, Moody MP, Bagot PAJ, Smith GDW, Scott T, Coe C, Morrall P
July 2016
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Journal article
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Scientific Reports
Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour.
The formation of ordered clusters in Ti-7Al and Ti-6Al-4V
Bagot PAJ, Moody M, Martin T
June 2016
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Journal article
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Acta Materialia
Continuous and discontinuous precipitation in Fe-1 at.%Cr-1 at.%Mo alloy upon nitriding; crystal structure and composition of ternary nitrides
Moody MP
May 2016
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Journal article
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Philosophical Magazine
The microstructure of non-polar a-plane (11 2 0) InGaN quantum wells
field evaporation, field ionization, atom probe tomography (APT), molecular dissociation
On the effect of boron on grain boundary character in a new polycrystalline superalloy
Kontis P, Yusof HAM, Pedrazzini S, Danaie M, Moore KL, Bagot PAJ, Moody MP, Grovenor CRM, Reed RC
January 2016
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Journal article
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Acta Materialia
The role of boron in conferring the grain boundary character in a new polycrystalline superalloy suitable for power generation applications is considered. One boron-free and three boron-containing variants are studied using a suite of high resolution characterisation techniques including atom probe tomography (APT), high resolution secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). The primary effect of boron addition is the suppression of Cr-rich M23C6 carbide and the formation instead of the Cr-rich M5B3 boride. The SIMS analysis indicates that the boride particles are distributed fairly uniformly along the grain boundaries, of length up to 500 nm along the grain boundary. The substantial majority of the boron added resides in the form of these M5B3 borides; some boron segregation is found at the γ′/M5B3 interfaces but interfaces of other forms - such as γ/γ′, γ/M5B3, γ/MC and γ′/MC - show no significant segregation. Creep testing indicates that the optimum boron content in this alloy is 0.05 at.%.
Advances in atom probe tomography instrumentation: Implications for materials research
Moody MP, Vella A, Gerstl SSA, Bagot PAJ
January 2016
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Journal article
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MRS Bulletin
A series of recent instrumental advances have facilitated the application of atom probe tomography (APT) to the characterization of an increasingly wide range of materials and devices. Whereas APT was previously mostly limited to the analysis of alloys, advances in areas such as laser pulsing and detectors have enabled characterization of semiconductors and brittle materials. Most recently, ultraviolet laser pulsing has facilitated the analysis of materials previously considered not viable for the atom probe, such as minerals and large bandgap insulator materials. The development of in situ gas reaction cells fully integrated in atom probe instruments has enabled the characterization of surface reactions of materials exposed to highly controlled environments. Finally, current work toward an integrated cryo-Transfer system is anticipated to create new directions for APT research.
Insights into microstructural interfaces in aerospace alloys characterised by atom probe tomography
Martin TL, Radecka A, Sun L, Simm T, Dye D, Perkins K, Gault B, Moody MP, Bagot PAJ
January 2016
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Journal article
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Materials Science and Technology (United Kingdom)
Atom probe tomography (APT) is becoming increasingly applied to understand the relationship between the structure and composition of new alloys at the micro- And nanoscale and their physical properties. Here, we use APT datasets from two modern aerospace alloys to highlight the detailed information available from APT analysis, along with potential pitfalls that can affect data interpretation. The interface between two phases in a Ti-6Al-4V alloy is used to illustrate the importance of parameter choice when using proximity histograms or concentration profiles to characterise interfacial chemistry. The higher number density of precipitates and large number of constituent elements in a maraging steel (F1E) present additional challenges such as peak overlaps that vary across the dataset, along with inhomogeneous interface chemistries.
Oxidation behaviour of a next generation polycrystalline Mn containing Ni-based superalloy
A prototype next-generation superalloy containing 1 at.% Mn was oxidised in air at 800 °C for 100 h, and compared with a commercial Ni-based superalloy. The oxide scale consisted of a multi-phase layered structure measured by Atom Probe Tomography as uppermost NiCr2Mn2O4, followed by an inhomogeneous mix of Cr2O3, spinel MnCr2O4 and rutile (Ti,Cr)O2. The Mn did not form a homogeneous, surface passivating oxide layer. Despite this, the alloy showed a 3 × reduction of oxide thickness compared to a commercial polycrystalline Ni-based superalloy.
Structural, electronic, and optical properties of m -plane InGaN/GaN quantum wells: Insights from experiment and atomistic theory
Schulz S, Tanner DP, O'Reilly EP, Caro MA, Martin TL, Bagot PAJ, Moody MP, Tang F, Griffiths JT, Oehler F, Kappers MJ, Oliver RA
,
et al
December 2015
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Journal article
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Physical Review B - Condensed Matter and Materials Physics
In this paper we present a detailed analysis of the structural, electronic, and optical properties of an m-plane (In,Ga)N/GaN quantum well structure grown by metal organic vapor phase epitaxy. The sample has been structurally characterized by x-ray diffraction, scanning transmission electron microscopy, and 3D atom probe tomography. The optical properties of the sample have been studied by photoluminescence (PL), time-resolved PL spectroscopy, and polarized PL excitation spectroscopy. The PL spectrum consisted of a very broad PL line with a high degree of optical linear polarization. To understand the optical properties we have performed atomistic tight-binding calculations, and based on our initial atom probe tomography data, the model includes the effects of strain and built-in field variations arising from random alloy fluctuations. Furthermore, we included Coulomb effects in the calculations. Our microscopic theoretical description reveals strong hole wave function localization effects due to random alloy fluctuations, resulting in strong variations in ground state energies and consequently the corresponding transition energies. This is consistent with the experimentally observed broad PL peak. Furthermore, when including Coulomb contributions in the calculations we find strong exciton localization effects which explain the form of the PL decay transients. Additionally, the theoretical results confirm the experimentally observed high degree of optical linear polarization. Overall, the theoretical data are in very good agreement with the experimental findings, highlighting the strong impact of the microscopic alloy structure on the optoelectronic properties of these systems.
From solid solution to cluster formation of Fe and Cr in α-Zr
Burr PA, Wenman MR, Gault B, Moody MP, Ivermark M, Rushton MJD, Preuss M, Edwards L, Grimes RW
December 2015
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Journal article
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Journal of Nuclear Materials
To understand the mechanisms by which the re-solution of Fe and Cr additions increase the corrosion rate of irradiated Zr alloys, the solubility and clustering of Fe and Cr in model binary Zr alloys was investigated using a combination of experimental and modelling techniques - atom probe tomography (APT), x-ray diffraction (XRD), thermoelectric power (TEP) and density functional theory (DFT). Cr occupies both interstitial and substitutional sites in the α-Zr lattice; Fe favours interstitial sites, and a low-symmetry site that was not previously modelled is found to be the most favourable for Fe. Lattice expansion as a function of Fe and Cr content in the α-Zr matrix deviates from Vegard's law and is strongly anisotropic for Fe additions, expanding the c-axis while contracting the a-axis. Matrix content of solutes cannot be reliably estimated from lattice parameter measurements, instead a combination of TEP and APT was employed. Defect clusters form at higher solution concentrations, which induce a smaller lattice strain compared to the dilute defects. In the presence of a Zr vacancy, all two-atom clusters are more soluble than individual point defects and as many as four Fe or three Cr atoms could be accommodated in a single Zr vacancy. The Zr vacancy is critical for the increased apparent solubility of defect clusters; the implications for irradiation induced microstructure changes in Zr alloys are discussed.
Imaging of radiation damage using complementary field ion microscopy and atom probe tomography
Dagan M, Hanna LR, Xu A, Roberts SG, Smith GDW, Gault B, Edmondson PD, Bagot PAJ, Moody MP
December 2015
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Journal article
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Ultramicroscopy
Radiation damage in tungsten and a tungsten-tantalum alloy, both of relevance to nuclear fusion research, has been characterized using a combination of field ion microscopy (FIM) imaging and atom probe tomography (APT). While APT provides 3D analytical imaging with sub-nanometer resolution, FIM is capable of imaging the arrangements of single atoms on a crystal lattice and has the potential to provide insights into radiation induced crystal damage, all the way down to its smallest manifestation - a single vacancy. This paper demonstrates the strength of combining these characterization techniques. In ion implanted tungsten, it was found that atomic scale lattice damage is best imaged using FIM. In certain cases, APT reveals an identifiable imprint in the data via the segregation of solute and impurities and trajectory aberrations. In a W-5 at%Ta alloy, a combined APT-FIM study was able to determine the atomic distribution of tantalum inside the tungsten matrix. An indirect method was implemented to identify tantalum atoms inside the tungsten matrix in FIM images. By tracing irregularities in the evaporation sequence of atoms imaged with FIM, this method enables the benefit of FIM's atomic resolution in chemical distinction between the two species.
Quantification of oxide particle composition in model oxide dispersion strengthened steel alloys
Oxide dispersion strengthened ferritic steels (ODS) are being considered for structural components of future designs of fission and fusion reactors because of their impressive high-temperature mechanical properties and resistance to radiation damage, both of which arise from the nanoscale oxide particles they contain. Because of the critical importance of these nanoscale phases, significant research activity has been dedicated to analysing their precise size, shape and composition (Odette et al., Annu. Rev. Mater. Res. 38 (2008) 471-503 [1]; Miller et al., Mater. Sci. Technol. 29(10) (2013) 1174-1178 [2]). As part of a project to develop new fuel cladding alloys in India, model ODS alloys have been produced with the compositions, Fe-0.3Y2O3, Fe-0.2Ti-0.3Y2O3 and Fe-14Cr-0.2Ti-0.3Y2O3. The oxide particles in these three model alloys have been studied by APT in their as-received state and following ion irradiation (as a proxy for neutron irradiation) at various temperatures. In order to adequately quantify the composition of the oxide clusters, several difficulties must be managed, including issues relating to the chemical identification (ranging and variable peak-overlaps); trajectory aberrations and chemical structure; and particle sizing. This paper presents how these issues can be addressed by the application of bespoke data analysis tools and correlative microscopy. A discussion follows concerning the achievable precision in these measurements, with reference to the fundamental limiting factors.
Using transmission Kikuchi diffraction to study intergranular stress corrosion cracking in type 316 stainless steels
Meisnar M, Vilalta-Clemente A, Gholinia A, Moody M, Wilkinson AJ, Huin N, Lozano-Perez S
August 2015
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Journal article
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Micron
Transmission Kikuchi diffraction (TKD), also known as transmission-electron backscatter diffraction (t-EBSD) is a novel method for orientation mapping of electron transparent transmission electron microscopy specimen in the scanning electron microscope and has been utilized for stress corrosion cracking characterization of type 316 stainless steels. The main advantage of TKD is a significantly higher spatial resolution compared to the conventional EBSD due to the smaller interaction volume of the incident beam with the specimen.Two 316 stainless steel specimen, tested for stress corrosion cracking in hydrogenated and oxygenated pressurized water reactor chemistry, were characterized via TKD. The results include inverse pole figure (IPFZ) maps, image quality maps and misorientation maps, all acquired in very short time (
A combined approach for deposition and characterization of atomically engineered catalyst nanoparticles
Yang Q, Joyce DE, Saranu S, Hughes GM, Varambhia A, Moody MP, Bagot PAJ
July 2015
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Journal article
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Catalysis, Structure and Reactivity
The structure and composition of catalytic silver nanoparticles (Ag-NPs) fabricated through a novel gas condensation process has been characterized by Scanning Electron Microscopy (SEM) and Atom Probe Tomography (APT). SEM was used to confirm the number density and spatial distribution of Ag-NPs deposited directly onto standard silicon microposts used for APT experiments. Depositing nanoparticles (NPs) directly by this method eliminates the requirement for focussed ion beam (FIB) liftout, significantly decreasing APT specimen preparation time and enabling far more NPs to be examined. Furthermore, by encapsulating deposited particles before final FIB sharpening, the APT reconstruction methodologies have been improved over prior attempts, as demonstrated by comparison to the SEM data. Progress in these areas is vital to enable large-scale catalyst research efforts using APT, a technique, which offers significant potential to examine the detailed atomic-scale chemistry in a wide variety of catalytic NPs.
Atom probe tomography of stress corrosion crack tips in SUS316 stainless steels
An atom probe tomography study of the oxide-metal interface of an oxide intrusion ahead of a crack in a polycrystalline Ni-based superalloy
Kitaguchi HS, Moody MP, Li HY, Evans HE, Hardy MC, Lozano-Perez S
March 2015
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Journal article
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Scripta Materialia
Intergranular oxide intrusions formed ahead of a crack in a Ni-based superalloy at 650 °C have been examined using three-dimensional atom probe tomography. Of two scans undertaken, a thin (∼5 nm) alumina layer was observed next to the alloy substrate in one, overlaid by a chromia layer. In the second, chromia penetrated to the alloy interface. The chromia layer contained Ti in solution as well as discrete particles of TiO2.
Indium clustering in a -plane InGaN quantum wells as evidenced by atom probe tomography
Tang F, Zhu T, Oehler F, Fu WY, Griffiths JT, Massabuau FCP, Kappers MJ, Martin TL, Bagot PAJ, Moody MP, Oliver RA
February 2015
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Journal article
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Applied Physics Letters
Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown sample. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane sample pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering.
Atomically resolved tomography to directly inform simulations for structure-property relationships.
Microscopy encompasses a wide variety of forms and scales. So too does the array of simulation techniques developed that correlate to and build upon microstructural information. Nevertheless, a true nexus between microscopy and atomistic simulations is lacking. Atom probe has emerged as a potential means of achieving this goal. Atom probe generates three-dimensional atomistic images in a format almost identical to many atomistic simulations. However, this data is imperfect, preventing input into computational algorithms to predict material properties. Here we describe a methodology to overcome these limitations, based on a hybrid data format, blending atom probe and predictive Monte Carlo simulations. We create atomically complete and lattice-bound models of material specimens. This hybrid data can then be used as direct input into density functional theory simulations to calculate local energetics and elastic properties. This research demonstrates the role that atom probe combined with theoretical approaches can play in modern materials engineering.
Thermal-mechanical fatigue behaviour of a new single crystal superalloy: Effects of Si and Re alloying
Abstract The thermal-mechanical fatigue (TMF) behaviour of a new single crystal superalloy suitable for power generation applications is considered. Effects of alloying with either Si or Re are elucidated. Out-of-phase TMF is emphasised, although to clarify the effects arising some static creep deformation tests are also carried out. A significant Si-effect is found: a modest addition of 0.25 wt.% Si increases the TMF life by a factor of 2. A greater lower temperature yield stress and thinner slip bands traversing the γ′-phase - with a concomitant greater resistance to recrystallisation and cracking along them - contribute to the enhanced TMF performance promoted by Si alloying. Alloying with Re, whilst improving the creep behaviour more markedly than Si, does not have such a strong effect on TMF life. The results provide insights into the composition/performance relationships relevant to the TMF performance of single crystal superalloys.
Oxidation and Surface Segregation Behavior of a Pt-Pd-Rh Alloy Catalyst
Bagot PAJ, Kruska K, Haley D, Carrier X, Marceau E, Moody MP, Smith GDW
November 2014
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Journal article
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Journal of Physical Chemistry C
Platinum gauze catalysts are used extensively in the production of nitric acid from ammonia, where they are subject to harsh operating conditions combining elevated temperatures and oxidizing environments. These cause significant loss of metal species as volatile oxides. How different metallic species behave in these environments at a fundamental, atomic-scale level is not well understood. In this work, we study the early stages of oxidation of a Pt-Rh-Pd gauze at temperatures of 873-1273 K. Using a combination of advanced experimental methods, we explore how the oxidation behavior can strongly influence the surface and near-surface gauze microstructure. We show that Rh and Pd can segregate on different areas of the same surface and discuss how such atomic migration can be linked to mechanisms of metal loss from such alloys.
A New Polycrystalline Co-Ni Superalloy
Knop M, Mulvey P, Ismail F, Radecka A, Rahman KM, Lindley TC, Shollock BA, Hardy MC, Moody MP, Martin TL, Bagot PAJ, Dye D
October 2014
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Journal article
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JOM
In 2006, a new-ordered L12 phase, Co3(Al,W), was discovered that can form coherently in a face-centered cubic (fcc) A1 Co matrix. Since then, a community has developed that is attempting to take these alloys forward into practical applications in gas turbines. A new candidate polycrystalline Co-Ni γ/γ′ superalloy, V208C, is presented that has the nominal composition 36Co-35Ni-15Cr-10Al-3W-1Ta (at.%). The alloy was produced by conventional powder metallurgy superalloy methods. After forging, a γ′ fraction of ~56% and a secondary γ′ size of 88 nm were obtained, with a grain size of 2.5 μm. The solvus temperature was 1000°C. The density was found to be 8.52 g cm−3, which is similar to existing Ni alloys with this level of γ′. The alloy showed the flow stress anomaly and a yield strength of 920 MPa at room temperature and 820 MPa at 800°C, similar to that of Mar-M247. These values are significantly higher than those found for either conventional solution and carbide-strengthened Co alloys or the γ/γ′ Co superalloys presented in the literature thus far. The oxidation resistance, with a mass gain of 0.08 mg cm−2 in 100 h at 800°C, is also comparable with that of existing high-temperature Ni superalloys. These results suggest that Co-based and Co-Ni superalloys may hold some promise for the future in gas turbine applications.
Restoring the lattice of Si-based atom probe reconstructions for enhanced information on dopant positioning
Estimating the physical cluster-size distribution within materials using atom-probe.
Stephenson LT, Moody MP, Gault B, Ringer SP
September 2011
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Journal article
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Microsc Res Tech
A limiting characteristic of the atom-probe technique is the nondetection of ions and this embodies a significant "missing information" problem in investigations of atomic clustering phenomena causing difficulty in the interpretation of any atom-probe experiment. It is shown that the measurable cluster-size distribution can be modeled by a mixed binomial distribution. A deconvolution method based upon expectation-maximization (EM) algorithm is presented to obtain the original physical distribution from an efficiency-degraded distribution, thereby providing means to calculate accurate cluster number densities from atom probe results. The accuracy of this restoration was predominantly dependent upon the detector efficiency and was proved to be highly accurate in the case of conventional atom-probe detector efficiencies (ε = 57%). Such considerations and measures are absolutely necessary when the number density of clusters and small precipitates is in any way regarded as important. We conclude that limitations in detector efficiency are more limiting for cluster-finding analyses via atom-probe techniques than spatial resolution issues, and therefore the current endeavors for improving detector technologies are well found.
atom probe tomography, clustering analysis, disordered solids, solute clustering
Direct observation of local potassium variation and its correlation to electronic inhomogeneity in (Ba1-xKx)Fe2As 2 pnictide
Yeoh WK, Gault B, Cui XY, Zhu C, Moody MP, Li L, Zheng RK, Li WX, Wang XL, Dou SX, Sun GL, Lin CT
Solute clustering is increasingly recognised as a significant characteristic within certain material systems that can be tailored to the optimization of bulk properties and performance. Atom probe tomography (APT) is emerging as a powerful tool for the detection of these nanoscale features; however, complementary to experiment, precise and efficient characterization algorithms are required to identify and characterise these nanoclusters within the potentially massive three-dimensional atomistic APT datasets. In this study, a new three-dimensional Markov field (3DMF) cluster identification algorithm is proposed. The algorithm is based upon an analysis of the direct atomic neighbourhood surrounding each atom, and the only input parameter required utilises known crystallographic properties of the system. Further, an array of statistical approaches has been developed and applied with respect to the results generated by the 3DMF algorithm including: an SN statistic, a two-tailed z-test, a difference measure, the ξ2 test, and a direct evaluation of the Warren-Cowley parameter for short-range ordering. Finally, the methodologies have been applied to the characterization of the nanostructural evolution of an Al-1.1Cu-0.5Mg (at.%) alloy subjected to a variety of heat treatments.
Spatial resolution in atom probe tomography
Gault B, Moody MP, De Geuser F, La Fontaine A, Stephenson LT, Haley D, Ringer SP
Statistical tools for the local electrode atom probe
Moody MP, Stephenson LT, Ringer SP
August 2006
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Journal article
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Microscopy and Microanalysis
Numerical study of the accuracy and efficiency of various approaches for Monte Carlo surface hopping calculations
Herman MF, Moody MP
August 2005
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Journal article
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Journal of Chemical Physics
A one-dimensional, two-state model problem with two well-separated avoided crossing points is employed to test the efficiency and accuracy of a semiclassical surface hopping technique. The use of a one-dimensional model allows for the accurate numerical evaluation of both fully quantum-mechanical and semiclassical transition probabilities. The calculations demonstrate that the surface hopping procedure employed accounts for the interference between different hopping trajectories very well and provides highly accurate transition probabilities. It is, in general, not computationally feasible to completely sum over all hopping trajectories in the semiclassical calculations for multidimensional problems. In this case, a Monte Carlo procedure for selecting important trajectories can be employed. However, the cancellation due to the different phases associated with different trajectories limits the accuracy and efficiency of the Monte Carlo procedure. Various approaches for improving the accuracy and efficiency of Monte Carlo surface hopping procedures are investigated. These methods are found to significantly reduce the statistical sampling errors in the calculations, thereby increasing the accuracy of the transition probabilities obtained with a fixed number of trajectories sampled.
Globally uniform semiclassical surface-hopping wave function for nonadiabatic scattering
Herman MF, El Akramine O, Moody MP
April 2004
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Journal article
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Journal of Chemical Physics
A globally uniform time-dependent semiclassical wave function is presented for nonadiabatic scattering. This wave function, motivated by the globally uniform semiclassical wave function of Kay, takes the form of a surface-hopping expansion. It has all the important numerical advantages over the primitive formulation. The globally uniform wave function does not have caustic singularities and avoid a root search for trajectories obeying double-ended boundary conditions required by the primitive calculation.
Monte Carlo simulation methodology of the ghost interface theory for the planar surface tension
Moody MP, Attard P
January 2004
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Journal article
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Journal of Chemical Physics
The ghost interface technique was derived along with an extensive analysis of long-range potential truncation correction procedures. It has been shown to provide an accurate route to the surface. It also represented an important conceptual breakthrough in terms of visualizing and understanding the liquid-vapor interface. An approximate linear dependence was observed as the surface tension decreases with rising vapor supersaturation.
Phase corrected higher-order expression for surface hopping transition amplitudes in nonadiabatic scattering problems
Moody MP, Ding F, Herman MF
December 2003
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Journal article
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Journal of Chemical Physics
A new surface hopping solution developed specifically for the case where the Born-Oppenheimer electronic coordinates are dominated by two states is presented. This new approach offers a significant increase in computational efficiency.
Curvature-Dependent Surface Tension of a Growing Droplet
Homogeneous nucleation of droplets from a supersaturated vapor phase
Moody MP, Attard P
October 2002
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Journal article
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Journal of Chemical Physics
The process of homogeneous droplet nucleation was studied for infinite- and finite-sized systems using a constrained free energy approach that invokes uniform density profiles and an infinitely sharp interface. By making further approximations, the classical nucleation theory of Becker and Doring was derived. The theory was numerically evaluated using an accurate parameterization of the Lennard-Jones equation of state. Results were given for the constrained Helmholtz free energy, the energy barrier to spontaneous nucleation, and the critical radius. It was found that the translational contribution to the energy of formation had a negligible effect on the estimation of the critical radius and on the magnitude of the activation energy.
Curvature dependent surface tension from a simulation of a cavity in a Lennard-Jones liquid close to coexistence
Moody MP, Attard P
November 2001
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Journal article
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Journal of Chemical Physics
The behavior of the surface tension of a liquid close to coexistence surrounding a small cavity was examined. The contact density profile was used by two separate means to evaluate the surface tension. Evidence was obtained that this profile is a good model for the planar liquid-vapor interface.
