I11-High Resolution Powder Diffraction
I12-JEEP: Joint Engineering, Environmental and Processing
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Kay
Song
,
Guanze
He
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Abdallah
Reza
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Tamas
Ungar
,
Phani
Karamched
,
David
Yang
,
Ivan
Tolkachev
,
Kenichiro
Mizohata
,
Stephen P.
Thompson
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Eamonn T.
Connolly
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Robert C.
Atwood
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Stefan
Michalik
,
David E. J.
Armstrong
,
Felix
Hofmann
Diamond Proposal Number(s):
[28444, 32094]
Open Access
Abstract: Severe plastic deformation changes the microstructure and properties of steels, which may be favourable for their use in structural components of nuclear reactors. In this study, high-pressure torsion (HPT) was used to refine the grain structure of Eurofer-97, a ferritic/martensitic steel. Electron microscopy and X-ray diffraction were used to characterise the microstructural changes. Following HPT at room temperature to a maximum shear strain of 230, the average grain size reduced by a factor of ~30, with a marked increase in high-angle grain boundaries. Dislocation density also increased by more than one order of magnitude. The thermal stability of the deformed material was investigated via in-situ annealing during synchrotron X-ray diffraction. This revealed substantial recovery between 450 K – 800 K. Irradiation with 20 MeV Fe-ions to ~0.1 dpa caused a 20% reduction in dislocation density compared to the as-deformed material. However, HPT deformation prior to irradiation only had a minor effect in mitigating the irradiation-induced reductions in thermal diffusivity and surface acoustic wave velocity of the material. Microstructural and material property changes are dominated by deformation compared to irradiation. In light of this, the benefits of using HPT to improve the irradiation resistance of Eurofer-97 are limited. These results provide a multi-faceted view of the changes in ferritic/martensitic steels due to severe plastic deformation, and how these changes can be used to alter material properties.
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Jul 2024
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DIAD-Dual Imaging and Diffraction Beamline
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Himanshu
Vashishtha
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Parastoo
Jamshidi
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Anastasia
Vrettou
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Anna
Kareer
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Michael
Goode
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Hans
Deyhle
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Andrew
James
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Sharif
Ahmed
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Christina
Reinhard
,
Moataz M.
Attallah
,
David M.
Collins
Diamond Proposal Number(s):
[28029]
Open Access
Abstract: This study explores cardiovascular stents fabricated using laser powder bed fusion (LPBF) which is an emerging method to offer patient-specific customisable parts. Here, the shape memory alloy NiTi, in a near equiatomic composition, was investigated to deconvolve the material response from macroscopic component effects. Specifically, stress-geometry interactions were revealed, in-situ, for a minaturised cardiovascular stent subjected to an externally applied cylindrical stress whilst acquiring synchrotron X-ray imaging and diffraction data. The approach enabled the collection of spatially resolved micromechanical deformation data; the formation of stress-induced martensite and R-phase was evident, occurring in locations near junctions between stent ligaments where stress concentrations exist. In the as-fabricated condition, hardness maps were obtained through nanoindentation, demonstrating that the localised deformation and deformation patterning is further controlled by porosity and microstructural heterogeneity. Electron backscatter diffraction (EBSD) supported these observations, showing a finer grain structure near stent junctions with higher associated lattice curvature. These features, combined with stress concentrations when loaded will initiate localised phase transformations. If the stent was subjected to repeated loading, representing in-vivo conditions, these regions would be susceptible to cyclic damage through transformation memory loss, leading to premature component failure. This study highlights the challenges that must be addressed for the post-processing treatment of LPBF-processed stents for healthcare-related applications.
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Jul 2024
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Open Access
Abstract: The ability to characterise the three-dimensional microstructure of multiphase materials is essential for understanding the interaction between phases and associated materials properties. Here, laboratory-based diffraction-contrast tomography (lab-based DCT), a recently-established materials characterization technique that can determine grain phases, morphologies, positions and orientations in a voxel-based reconstruction method, was used to map part of a dual-phase steel alloy sample. To assess the resulting microstructures that were produced by the lab-based DCT technique, an electron backscatter diffraction (EBSD) map was collected within the same sample volume. To identify the two-dimensional (2D) slice of the three-dimensional (3D) lab-based DCT reconstruction that best corresponded to the 2D EBSD map, a novel registration technique based solely on grain-averaged orientations was developed – this registration technique requires very little a priori knowledge of dataset alignment and can be extended to other techniques that only recover grain-averaged orientation data such as far-field 3D X-ray diffraction microscopy. Once the corresponding 2D slice was identified in the lab-based DCT dataset, comparisons of phase balance, grain size, shape and texture were performed between lab-based DCT and EBSD techniques. More complicated aspects of the microstructural morphology such as grain boundary shape and grains less than a critical size were poorly reproduced by the lab-based DCT reconstruction, primarily due to the difference in resolutions of the technique compared with EBSD. However, lab-based DCT is shown to accurately determine the centre-of-mass position, orientation, and size of the large grains for each phase present, austenite and martensitic ferrite. The results reveals a complex ferrite grain network of similar crystal orientations that are absent from the EBSD dataset. Such detail demonstrates that lab-based DCT, as a technique, shows great promise in the field of multi-phase material characterization.
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Aug 2023
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[27903]
Open Access
Abstract: High strength AA7xxx are attractive for use in the automotive industry, offering significant strength/weight benefits. These alloys are often used in tempers that require long ageing times of several hours. Pre-ageing has been proposed to be effective in suppressing natural ageing, and reducing the total ageing time by integrating the final ageing step into the paint bake cycle. However, the precipitate evolution during the pre-ageing and subsequent paint bake processes remains to be fully understood. In the present work, the pre-ageing process was studied for AA7075 over a wide range of temperatures and times. Small angle X-ray scattering (SAXS) was used as the main technique to investigate the precipitate evolution during the pre-ageing, natural ageing and paint bake, with the support from transmission electron microscopy (TEM) and isothermal calorimetry. For the first time, the results show that 8 h pre-ageing at 80 °C can produce a microstructure consisting of GP zones with an average radius of approximately
0.9 nm, which remains stable up to at least 7 months. After a short paint bake process, 94% of the T6 hardness can be obtained by uniformly distributed precipitates with an average radius of approximately
2.6 nm. The final size and strengthening effect of the precipitates after 20 min baking is found to be insensitive to the heating rate, which has not been reported previously. The present results further suggest this process is robust for industrial application.
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Apr 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[25682]
Open Access
Abstract: The crystallographic texture development during processing of dual-phase Ti alloys like Ti-6Al-4 V is of fundamental technological importance. However, measuring texture in both phases in these materials is a significant challenge because of the spatial inhomogeneity of the texture and low volume fraction of the minority β-phase at room temperature. Here we demonstrate how synchrotron X-ray diffraction can be used to overcome these difficulties and measure texture and texture variation in hot-rolled samples in a reproducible manner. The texture in hot-rolled Ti-64 was calculated from 2D synchrotron diffraction patterns obtained along different directions. The data was analysed using MAUD, which is based on Rietveld refinement of the diffracted intensities, and using a Fourier series based analysis method, that extracts intensities directly from the 2D diffraction patterns, and then uses the open-source software MTEX to fit an orientation distribution function (ODF). By comparing the results with faithful EBSD measurements, we show that the Fourier series method produces much more accurate texture measurements, especially for the minority β-phase. We also show that a minimum of 2, and preferably 3, different measurement orientations are needed to fully represent the texture. This implies that measurements of texture which rely on diffraction data from a single sample orientation, like in fast in-situ studies or spatially resolved measurements, can only provide qualitative information and must be interpreted with care.
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Mar 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[25467]
Abstract: Tracking texture evolution during in situ loading is critical to understand and simulate the dynamic behaviour of microstructure in polycrystalline materials, yet conventional texture quantification methods are sometimes restricted due to various factors, such as acquisition time, sample environment and complex setup. To address this, a novel approach to extract texture information from single shot Time-Of-Flight neutron diffraction pattern has been developed. Another texture analysis approach based on single shot synchrotron X-ray diffraction has also been demonstrated. The effectiveness of two methods is assessed for polycrystalline Nickel-based superalloy polycrystalline samples possessing different textures. Both methods feature a moderate acquisition time of ~10 min and 30 s respectively, as well as a simplified setup which allows adding complex sample environments and the use of additional equipment. Comparison with the referential EBSD texture suggests that both approaches achieve a satisfactory match, though some details of the complex contour profiles in inverse pole figures may be missing. Besides that, a novel metric has been proposed to quantify the matching quality of pole figures. By employing the EPSC modelling approach, it is shown that the texture deviation due to the technique chosen for its evaluation exerts a subtle influence on th macro- and mesoscale simulation results, highlighting the significance of this approach for underpinning robust computational modelling.
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Apr 2022
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B16-Test Beamline
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Diamond Proposal Number(s):
[12827]
Abstract: We investigate local deformation within a dual-phase Ti6242 alloy by considering the interaction between α orientation (i.e., slip system) and the presence of β phase (i.e., fraction and morphology), and the corresponding evolution of stored dislocations. In situ micropillar compression combined with microLaue diffraction and high angular resolution electron backscatter diffraction (HR-EBSD) shows that the high rate of geometrically necessary dislocation (GND) accumulation was observed in basal-slip oriented pillar, while easy formation of glide step with minimal GND accumulation was found in prism-slip oriented pillar. The difference is explained due to the role of the phase boundary for these slip configurations, where local stress concentrations can arise even in pillar with easy slip orientation (i.e., prism slip) if the phase boundary acts as a barrier to slip and results in inhomogeneity of local deformation. This study reveals significance of β phase in potentially modulating the local dislocation based hardening and hence local stress states within Ti polycrystalline aggregate.
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Dec 2021
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[21081, 24233]
Abstract: Soft porous matter is commonly encountered in artificial tissue applications, pharmaceuticals delivery systems and in cosmetic and food products. These materials are typically opaque and tend to deform under very small levels of shear; this makes the characterization of their microstructure very challenging, particularly in the native state. Air-in-oil systems (oleofoams) are an emerging type of soft material with promising applications in cosmetics and foods, which contain air bubbles stabilized by Pickering fat crystals dispersed in a liquid oil phase. Synchrotron radiation X-ray computed tomography (SR - XCT) is a non-invasive, non-destructive technique increasingly used to investigate multiphasic, porous materials, owing to its high flux which enables sub-micron resolution and significant statistics at rapid acquisition speed. While the penetration of high energy X-rays can provide high resolution images and allows the reconstruction of the 3D structure of samples, the experimental setup and measuring parameters need to be carefully designed to avoid sample deformation or beam damage.
In this work, a robust methodology for investigating the 3D microstructure of soft, porous matter was developed. Sample preparation and experimental setup were chosen to allow synchrotron tomographic analysis of soft oleofoams with a low melting point (<30 °C). In particular, the use of cryogenic conditions (plunge-freeze in liquid nitrogen) provided stability against melting during the acquisition. Additionally, an image processing workflow was designed for analysing the 3D microstructure of the samples using ImageJ. Hence, the size and shape distribution of the air phase, as well as the thickness of the continuous gel phase could be determined for samples with significantly different microstructures (fresh vs. heated). Furthermore, the use of time-resolved X-ray radiography (XRR) allowed to study dynamic changes in the microstructure of the samples during thermal destabilization, visualizing bubble coalescence and growth in optically opaque foam samples with a sub-second timescale.
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Aug 2021
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[20527]
Open Access
Abstract: Hybrid metal extrusion & bonding (HYB) is a joining method that enables solid-state bonding by combining addition of aluminium filler material through continuous extrusion with pressure exerted by a rotating steel tool. This work presents mechanical and microstructural characterisation of a second generation HYB butt joint of aluminium alloy 6082 and structural steel S355. The ultimate tensile strength was measured to be in the range of 184–220 MPa, which corresponds to 60–72% joint efficiency. Digital image correlation analysis of the strain development during tensile testing revealed that root cracks formed, before the final fracture ran close to the aluminium-steel interface. A significant amount of residual aluminium was found on the steel fracture surface, especially in regions that experienced higher pressure during joining. Scanning and transmission electron microscopy revealed that the bond strength could be attributed to a combination of microscale mechanical interlocking and a discontinuous nanoscale interfacial Al-Fe-Si intermetallic phase layer. Analysis of scanning electron diffraction data acquired in a tilt series, indicated that the polycrystalline intermetallic phase layer contained the cubic αc phase. The results give insight into the bonding mechanisms of aluminium-steel joints and into the performance of HYB joints, which may be used to better understand and further develop aluminium-steel joining processes.
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Nov 2020
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Open Access
Abstract: A typical heat treatment for a low alloy steel will often involve a quenching heat treatment step, in which the steel is cooled from high temperatures to trigger austenite decomposition. The particular cooling rate during the quenching step can have a marked influence on the phase transformations taking place, and the resulting steel microstructure and mechanical properties. Although methods such as dilatometry have been available for many decades to characterise continuous-cooling transformation (CCT) behaviour in steels, the use of in situ synchrotron X-ray diffraction (SXRD) to elucidate CCT behaviour in a systematic way has not been reported.
In this work, we measure the CCT behaviours of two pressure vessel steels in situ using simultaneous dilatometry and SXRD. Both steels are subject to austenitisation followed by quenching at a range of cooling rates. On comparing results from SXRD and dilatometry, it is found that recorded starts of transformations appear to be in good agreement. However, calculations of phase fractions derived from dilatometry data significantly overestimate the fraction of ferrite that forms in comparison to SXRD when the formation involves the partitioning of carbon. This happens for two reasons: first, because the method to extract ferrite volume fractions from dilatometry data generally ignores the presence of any retained austenite at low temperatures, and second, because analyses of dilatometry data do not account for the expansion of the austenite during transformation due to enrichment in carbon. This enrichment leads to an increase in strain, and the standard analysis method falsely attributes this increase to ferrite formation, thereby overestimating it. The results highlight that caution must be exercised when interpreting the results of dilatometry, since levels of ferrite (especially diffusively-formed) and retained austenite are important quantities for the prediction of mechanical behaviour, and they are not readily quantified by the analysis of dilatometry data alone.
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May 2020
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