I12-JEEP: Joint Engineering, Environmental and Processing
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Yuanbo T.
Tang
,
Chinnapat
Panwisawas
,
Benjamin M.
Jenkins
,
Junliang
Liu
,
Zhao
Shen
,
Enrico
Salvati
,
Yilun
Gong
,
Joseph N.
Ghoussoub
,
Stefan
Michalik
,
Bryan
Roebuck
,
Paul A. J.
Bagot
,
Sergio
Lozano-Perez
,
Chris R. M.
Grovenor
,
Michael P.
Moody
,
Alexander M.
Korsunsky
,
David M.
Collins
,
Roger C.
Reed
Diamond Proposal Number(s):
[23674]
Open Access
Abstract: A supersaturated 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 phase. The response of the material to a heat treatment therefore requires new understanding at the fundamental level, since the first population of precipitate forms upon heating, in contrast to cooling from homogenisation above the 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 volume fraction with temperature. The first structural changes were detected at an unexpectedly low temperature of 445 °C. Second, the temperature for nucleation and its sensitivity to heating rate was studied using an electrical resistivity method. Then, the 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 precipitate distribution upon heating.
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Jan 2023
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E02-JEM ARM 300CF
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[23408, 27236, 28846, 28480]
Open Access
Abstract: Understanding the effects of fast neutrons on high-temperature superconductors is of growing importance as new compact fusion reactors rely on these materials to generate the high magnetic fields needed to confine the plasma. The critical temperature of the most promising candidate material for small-scale fusion devices, rare-earth barium cuprate, is known to decrease monotonically with radiation dose, indicating the generation of lattice defects everywhere in the material. Here, we use high-energy-resolution X-ray absorption spectroscopy to probe how the local environment around the copper atoms is influenced by point defects induced by He+ ion irradiation in the oxygen sublattice. Density functional theory calculations are used to interpret spectral features and we find clear evidence that ion irradiation significantly disrupts the bonding environment around the copper atoms in the copper-oxygen planes responsible for superconductivity in this compound. We propose the generation of a specific Frenkel defect that is consistent with our experimental results. Our results challenge previous assumptions in the literature that irradiation produces point defects only in the chain sites. In addition, we show that partial recovery is possible by annealing at modest temperatures, which may have implications for the operation of superconducting fusion magnets.
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Aug 2022
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Abstract: Superconducting windings will be necessary in future fusion reactors to generate the strong magnetic fields needed to confine the plasma, and these superconducting materials will inevitably be exposed to neutron damage. It is known that this exposure results in the creation of isolated damage cascades, but the presence of these defects alone is not sufficient to explain the degradation of macroscopic superconducting properties and a quantitative method is needed to assess the subtle lattice damage in between the clusters.
We have studied REBCO coated conductors irradiated with neutrons to a cumulative dose of 3.3×1022 n*m−2 that show a degradation of both Tc and Jc values, and use HRTEM analysis to show that this irradiation introduces ∼10 nm amorphous collision cascades. In addition we introduce a new method for the analysis of these images to quantify the degree of lattice disorder in the apparently perfect matrix between these cascades. This method utilises Fast Fourier and Discrete Cosine Transformations of a statistically-relevant number of HRTEM images of pristine, neutron-irradiated, and amorphous samples, and extracts the degree of randomness in terms of entropy values. Our results show that these entropy values in both mid-frequency band FFT and DCT domains correlate with the expected level of lattice damage, with the pristine samples having the lowest and the fully amorphous regions the highest entropy values. Our methodology allows us to quantify ‘invisible’ lattice damage to and correlate these values to the degradation of superconducting properties, and also has relevance for a wider range of applications in the field of electron microscopy where small changes in lattice perfection need to be measured.
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Dec 2021
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[21686]
Abstract: Li1+xAlxGe2-x(PO4)3 (LAGP) thin films have been grown on sapphire substrates by RF magnetron sputtering and post annealing. The effects of varying sputtering parameters such as power and pressure were studied, and the deposited films were characterized to investigate how the ionic conductivity values depend on the microstructure. The composition of as-sputtered films was found to be more strongly influenced by power than the pressure. The films deposited at lower powers, which results in lower deposition rates, have compositions similar to that of the target. Heating the substrates during deposition is found to minimise the formation of pinhole defects in films subsequently annealed at higher temperatures. Post annealing leads to a gradual transformation from the as-sputtered amorphous phase to crystalline LAGP thin films. At high annealing temperatures (above 700 °C) both porosity and the GeO2 impurity phase appear in the films and result in lower ionic conductivities. We have optimised the processing conditions to achieve ionic conductivities in excess of 10−4 Scm−1 and activation energies as low as 0.31 eV in films only 1 μm thick, suggesting that LAGP could offer attractive properties as a thin film battery electrolyte material.
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Oct 2020
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[20528, 23235]
Abstract: We have investigated the microstructural and crystallographic evolution of nanocrystalline zirconia under heavy ion irradiation using in-situ transmission electron microscopy (TEM) and have studied the atomic configurations of defect clusters using aberration-corrected scanning transmission electron microscopy (STEM). Under heavy ion irradiation the monoclinic-ZrO2 is observed to transform into cubic phase, stabilised by the strain induced by irradiation-induced defect clusters. We suggest that the monoclinic-to-cubic transformation is martensitic in nature with an orientation relationship identified to be (100)m∥(100)c and [001]m∥[001]c. By increasing the damage dose, both the formation of voids and irradiation-induced grain growth were observed. A model for the formation of voids is proposed, taking defect interactions into consideration. The study has also demonstrated that high resolution orientation mapping by transmission Kikuchi diffraction (TKD) combined with in-situ irradiation in a TEM is a powerful method to probe the mechanisms controlling irradiation-induced processes, including grain boundary migration, phase transformations and texture evolution.
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Oct 2020
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Abstract: The production of persistent-mode joints between Nb–Ti conductors remains an important problem in the field of superconducting magnets. Several researchers have demonstrated spot welding (resistance welding) as a technique capable of yielding superconducting joints directly between Nb–Ti filaments. In this study, the characteristic microstructural features associated with spot-welded joints between both multifilamentary and monofilamentary Nb–Ti wires are presented. Some initial measurements of the current-carrying ability of a monofilamentary joint have also been made by a novel magnetic technique. The suitability of spot welding for commercial magnet manufacture is discussed.
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Apr 2016
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I11-High Resolution Powder Diffraction
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Abstract: We have used glancing-incident angle X-ray diffraction (GIXRD) to study the stability of oxide nanoclusters in an Fe–14Cr–0.2Ti–0.3Y2O3 ODS alloy. High dose self-ion irradiation produces damaged layers a few hundred nanometres deep normally requiring time-consuming, site-specific techniques to study them. We have shown that GIXRD provides an effective way to study the damage depth profile by varying the incident angle, and that the Y2Ti2O7 nanoclusters in these alloys are disrupted by high dose irradiation at temperatures from 150 to 973 K.
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Jan 2016
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[6547, 7528]
Abstract: Three model ODS alloys (Fe–0.3Y2O3, Fe–0.2Ti–0.3Y2O3 and Fe–14Cr–0.2Ti–0.3Y2O3) were prepared by ball milling and then hot extrusion to study the effect of Ti and Cr on the size, distribution, crystal structure and composition of the nano-oxide particles. All alloys were characterized by high resolution transmission electron microscopy (HRTEM), atom probe tomography (APT) and synchrotron-X-ray diffraction (S-XRD) to determine the distribution, structure and composition of the oxide nanoparticles samples. The median particle sizes were 9.6 nm, 7.7 nm and 3.7 nm for the Fe–Y2O3, Fe–Ti–Y2O3 and Fe–Cr–Ti–Y2O3 alloys, respectively, so the presence of Ti resulted in a significant reduction in oxide particle diameter and the addition of Cr gave a further reduction in size. In the Fe–0.3Y2O3 alloy, the particles are found to be bcc Y2O3, whereas in the other two alloys (Fe–Ti–0.3Y2O3 and Fe–Cr–Ti–Y2O3), the oxide particles were found to be structurally consistent with both orthorhombic Y2TiO5 and fcc Y2Ti2O7. Detailed APT studies showed Cr shells around oxide particles of all sizes in the Fe–Cr–Ti–Y2O3 alloy, that a range of cluster compositions are present and that the particle chemistry varies with cluster size. We show that the addition of Cr has a strong effect on both the size and stoichiometry of the particles.
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Sep 2015
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I11-High Resolution Powder Diffraction
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Hongtao
Zhang
,
Yina
Huang
,
Huanpo
Ning
,
Ceri A.
Williams
,
Andrew
London
,
Karl
Dawson
,
Zuliang
Hong
,
Michael
Gorley
,
Chris
Grovenor
,
Gordon J.
Tatlock
,
Steve G.
Roberts
,
Michael J.
Reece
,
Haixue
Yan
,
Patrick
Grant
Diamond Proposal Number(s):
[7528]
Open Access
Abstract: Ferritic steels strengthened with Ti–Y–O nanoclusters are leading candidates for fission and fusion reactor components. A Fe–14Cr–0.4Ti + 0.25Y2O3 (14YT) alloy was fabricated by mechanical alloying and subsequently consolidated by spark plasma sintering (SPS). The densification of the 14YT alloys significantly improved with an increase in the sintering temperature. Scanning electron microscopy and electron backscatter diffraction revealed that 14YT SPS-sintered at 1150 °C under 50 MPa for 5 min had a high density (99.6%), a random grain orientation and a bimodal grain size distribution (<500 nm and 1–20 μm). Synchrotron X-ray diffraction patterns showed bcc ferrite, Y2Ti2O7, FeO, and chromium carbides, while transmission electron microscopy and atom probe tomography showed uniformly dispersed Y2Ti2O7 nanoclusters of <5 nm diameter and number density of 1.04 × 1023 m−3. Due to the very much shorter consolidation times and lower pressures used in SPS compared with the more usual hot isostatic pressing routes, SPS is shown to be a cost-effective technique for oxide dispersion strengthened (ODS) alloy manufacturing with microstructural features consistent with the best-performing ODS alloys.
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Apr 2015
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I06-Nanoscience
I10-Beamline for Advanced Dichroism
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M. D.
Watson
,
L. J.
Collins-Mcintyre
,
L. R.
Shelford
,
A. I.
Coldea
,
D.
Prabhakaran
,
S. C.
Speller
,
T.
Mousavi
,
C. R. M.
Grovenor
,
Z.
Salman
,
S. R.
Giblin
,
G.
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[7345]
Open Access
Abstract: Breaking the time reversal symmetry of a topological insulator, for example by the presence of magnetic ions, is a prerequisite for spin-based electronic applications in the future. In this regard Mn-doped Bi2Te3 is a prototypical example that merits a systematic investigation of its magnetic properties. Unfortunately, Mn doping is challenging in many host materials—resulting in structural or chemical inhomogeneities affecting the magnetic properties. Here, we present a systematic study of the structural, magnetic and magnetotransport properties of Mn-doped Bi2Te3 single crystals using complimentary experimental techniques. These materials exhibit a ferromagnetic phase that is very sensitive to the structural details, with TC varying between 9 and 13 K (bulk values) and a saturation moment that reaches 4.4(5) μB per Mn in the ordered phase. Muon spin rotation suggests that the magnetism is homogeneous throughout the sample. Furthermore, torque measurements in fields up to 33 T reveal an easy axis magnetic anisotropy perpendicular to the ab-plane. The electrical transport data show an anomaly around TC that is easily suppressed by an applied magnetic field, and also anisotropic behavior due to the spin-dependent scattering in relation to the alignment of the Mn magnetic moment. Hall measurements on different crystals established that these systems are n-doped with carrier concentrations of ~ 0.5–3.0 × 1020 cm−3. X-ray magnetic circular dichroism (XMCD) at the Mn L2,3 edge at 1.8 K reveals a large spin magnetic moment of 4.3(3) μB/Mn, and a small orbital magnetic moment of 0.18(2) μB/Mn. The results also indicate a ground state of mixed d4–d5–d6 character of a localized electronic nature, similar to the diluted ferromagnetic semiconductor Ga1−xMnxAs. XMCD measurements in a field of 6 T give a transition point at T ≈ 16 K, which is ascribed to short range magnetic order induced by the magnetic field. In the ferromagnetic state the easy direction of magnetization is along the c-axis, in agreement with bulk magnetization measurements. This could lead to gap opening at the Dirac point, providing a means to control the surface electric transport, which is of great importance for applications.
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Oct 2013
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