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15 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2 [Next/Last]

Instruments / Technical Area	Publication Details	Published
E02-JEM ARM 300CF	The mechanism of twin thickening and the elastic strain state of TWIP steel nanotwins Thomas W. J. Kwok , T. P. Mcauliffe , A. K. Ackerman , B. H. Savitzky , M. Danaie , C. Ophus , D. Dye Materials Science And Engineering: A 324 DOI: 10.1016/j.msea.2023.145005 Diamond Proposal Number(s): [18770] Open Access Show Abstract ▼ Abstract: A Twinning Induced Plasticity (TWIP) steel with a nominal composition of Fe-16.4Mn-0.9C-0.5Si-0.05Nb-0.05V was deformed to an engineering strain of 6%. The strain around the deformation twins were mapped using the 4D-STEM technique. Strain mapping showed a large average elastic strain of approximately 6% in the directions parallel and perpendicular to the twinning direction. However, the large average strain comprised of several hot spots of even larger strains of up to 12%. These hot spots could be attributed to a high density of sessile Frank dislocations on the twin boundary and correspond to shear stresses of 1–1.5 GPa. The strain and therefore stress fields are significantly larger than other materials known to twin and are speculated to be responsible for the early thickness saturation of TWIP steel nanotwins. The ability to keep twins extremely thin helps improve grain fragmentation, i.e. the dynamic Hall-Petch effect, and underpins the large elongations and strain hardening rates in TWIP steels.	Apr 2023
	Robust measurements of functional material properties using in situ 4D-STEM Colin Ophus , Michele Conroy , Mohsen Danaie , Benjamin H. Savitzky , Alexander Rakowski , Abigail Ackerman , Steven E. Zeltmann , Jim Ciston , Andrew M Minor , David Dye Microscopy And Microanalysis 28, 2312 - 2313 Microscopy & Microanalysis 2022: P09 - Insights into Phase Transitions in Functional Materials by in situ/operando TEM: Experiment Meets Theory DOI: 10.1017/S1431927622008881 Show Abstract ▼ Abstract: Conventional scanning transmission electron microscopy (STEM) imaging experiments record only a few values per probe position, generating bright field or dark field images, consisting of unscattered or scattered electrons respectively. The contrast in these images is highly sensitive to changes in local structure and the resolution is sufficient to resolve individual atoms. Unfortunately, many real-world samples in materials science studies are too thick or too complex to easily measure the structural properties of interest in this manner. An alternative to conventional STEM imaging is to use a high-speed direct electron detector, which records a full image (2D data) of the diffracted electron probe scanned over the sample (2D grid of positions), producing a four-dimensional measurement known as 4D-STEM. These 4D-STEM measurements of millions of diffraction patterns are extremely rich in information, but require efficient and robust software in order to measure sample properties. We have developed the py4DSTEM open source analysis toolkit to perform these analyses.	Aug 2022
E02-JEM ARM 300CF	In situ analysis of nm-scale alpha formation in titanium alloys A. K. Ackerman , C. Ophus , M. Danaie , P. Karamched , A. J. Knowles , A. Wilkinson , D. Rugg , D. Dye Microscopy And Microanalysis 25, 1490 - 1491 Microscopy & Microanalysis 2019: P01 - In situ TEM Characterization of Dynamic Processes During Materials Synthesis and Processing DOI: 10.1017/S1431927619008183 Diamond Proposal Number(s): [18190]	Aug 2019
I15-Extreme Conditions	The effect of pressure on hydrogen solubility in Zircaloy-4 H. E. Weekes , D. Dye , J. E. Proctor , D. Smith , C. Simionescu , T. J. Prior , M. R. Wenman Journal Of Nuclear Materials DOI: 10.1016/j.jnucmat.2019.07.012 Diamond Proposal Number(s): [11823, 11658] Show Abstract ▼ Abstract: The effect of pressure on the room temperature solubility of hydrogen in Zircaloy-4 was examined using synchrotron X-ray diffraction on small ground flake samples in a diamond anvil cell at pressures up to 20.9 GPa. Different combinations of hydrogen level/state in the sample and of pressure transmitting medium were examined; in all three experiments, it could be concluded that pressure resulted in the dissolution of δ hydrides and that interstitial hydrogen seemingly retards the formation of ω Zr. A pressure of around 9 GPa was required to halve the hydride fraction. These results imply that the effect of pressure is thermodynamically analogous to that of increasing temperature, but that the effect is small. The results are consistent with the volume per Zr atom of the α, δ and ω phases, with the bulk moduli of α and δ, and with previous measurements of the hydrogen site molar volumes in the α and δ phases. The results are interpreted in terms of their implication for our understanding of the driving forces for hydride precipitation at crack tips, which are in a region of hydrostatic tensile stress on the order of 1.5 GPa.	Jul 2019
I15-Extreme Conditions	On the high-pressure phase stability and elastic properties of β -titanium alloys D. Smith , O. P. J. Joris , A. Sankaran , H. E. Weekes , D. Bull , T. J. Prior , D. Dye , D. Errandonea , J. E. Proctor Journal Of Physics: Condensed Matter 29 DOI: 10.1088/1361-648X/aa60b6 Diamond Proposal Number(s): [8724] Show Abstract ▼ Abstract: We have studied the compressibility and stability of different β-titanium alloys at high pressure, including binary Ti–Mo, Ti–24Nb–4Zr–8Sn (Ti2448) and Ti–36Nb–2Ta–0.3O (gum metal). We observed stability of the β phase in these alloys to 40 GPa, well into the ω phase region in the P–T diagram of pure titanium. Gum metal was pressurised above 70 GPa and forms a phase with a crystal structure similar to the η phase of pure Ti. The bulk moduli determined for the different alloys range from 97 ± 3 GPa (Ti2448) to 124 ± 6 GPa (Ti–16.8Mo–0.13O).	Apr 2017
I12-JEEP: Joint Engineering, Environmental and Processing	Revealing dendritic pattern formation in Ni, Fe and Co alloys using synchrotron tomography M. A. Azeem , P. D. Lee , A. B. Phillion , S. Karagadde , P. Rockett , R. C. Atwood , L. Courtois , K. M. Rahman , D. Dye Acta Materialia DOI: 10.1016/j.actamat.2017.02.022 Diamond Proposal Number(s): [11074] Show Abstract ▼ Abstract: The microstructural patterns formed during liquid to solid phase transformations control the properties of a wide range of materials. We developed a novel methodology that allows in situ quantification of the microstructures formed during solidification of high temperature advanced alloys. The patterns formed are captured in 4D (3D plus time) using a methodology which exploits three separate advances: a bespoke high temperature environment cell; the development of high X-ray contrast alloys; and a novel environmental encapsulation system. This methodology is demonstrated on Ni, Fe, and Co advanced alloy systems, revealing dendritic pattern formation. We present detailed quantification of microstructural pattern evolution in a novel high attenuation contrast Co-Hf alloy, including microstructural patterning and dendrite tip velocity. The images are quantified to provide 4D experimental data of growth and coarsening mechanisms in Co alloys, which are used for a range of applications from energy to aerospace.	Feb 2017
I12-JEEP: Joint Engineering, Environmental and Processing	Hydride reorientation in Zircaloy-4 examined by in situ synchrotron X-ray diffraction Hannah Weekes , Nicholas Jones , Trevor Lindley , David Dye Journal Of Nuclear Materials 478, 32 - 41 DOI: 10.1016/j.jnucmat.2016.05.029 Diamond Proposal Number(s): [8755] Show Abstract ▼ Abstract: The phenomenon of stress-reorientation has been investigated using in situ X-ray diffraction during the thermomechanical cycling of hydrided Zircaloy-4 tensile specimens. Results have shown that loading along a sample’s transverse direction (TD) leads to a greater degree of hydride reorientation when compared to rolling direction (RD)-aligned samples. The elastic lattice micro-strains associated with radially oriented hydrides have been revealed to be greater than those oriented circumferentially, a consequence of strain accommodation. Evidence of hydride redistribution after cycling, to α-Zr grains oriented in a more favourable orientation when under an applied stress, has also been observed and its behaviour has been found to be highly dependent on the loading axis. Finally, thermomechanical loading across multiple cycles has been shown to reduce the difference in terminal solid solubility of hydrogen during dissolution (TSSD,H) and precipitation (TSSP,H).	Sep 2016
I12-JEEP: Joint Engineering, Environmental and Processing	The behaviour of Gum Metal (Ti-36Nb-2Ta-3Zr-0.3O wt.%) during superelastic cycling Nicholas Jones , Vassili Vorontsov , David Dye Proceedings of the 13th World Conference on Titanium DOI: 10.1002/9781119296126.ch154 Diamond Proposal Number(s): [6701] Show Abstract ▼ Abstract: Metastable beta titanium alloys, such as Gum Metal (Ti-36Nb-2Ta-3Zr-0.3O wt.%), have received significant attention from the biomedical field over the last decade due to their low elastic modulus. Despite initial skepticism, it is now widely accepted that these alloys undergo a stress-induced transformation when subjected to an applied load, forming an orthorhombic martensite phase within the beta matrix. The reversible nature of this trans formation gives rise to super elasticity, which is of significant interest for engineering applications outside of the biomedical industry. However, little is known as to the stability of the super elastic behaviour with respect to repeated load cycling. Here the response of Gum Metal during super elastic cycling was studied in situ, using high energy synchrotron diffraction. The material was observed to accumulate permanent damage with every cycle and the critical stress required for transformation decreased. The diffraction data was used to track the evolution of the martensite phase, both as a function of applied stress and cycle number. The martensite that formed was highly textured, with two independent orientations observed on each Debye-Scherrerring. These orientations formed at different applied stress es and had different volume fractions at the peak stress. The volume fraction at the peak stress of all martensite orientations increased with cycling, which is believed to increase the defect concentration in the material and hence influence the deformation behaviour.	May 2016
B16-Test Beamline	Using coupled micropillar compression and micro-Laue diffraction to investigate deformation mechanisms in a complex metallic alloy Al13Co4 Ayan Bhowmik , Igor Dolbnya , Thomas Britton , Nicholas Jones , Giorgio Sernicola , Claudia Walter , Peter Gille , David Dye , William Clegg , Finn Giuliani Applied Physics Letters 108 DOI: 10.1063/1.4944486 Diamond Proposal Number(s): [8179] Open Access Show Abstract ▼ Abstract: In this study, we have used in-situ micro-Laue diffraction combined with micropillar compression of focused ion beam milled Al13Co4 complex metallic alloy to investigate the evolution of deformation in Al13Co4. Streaking of the Laue spots shows that the onset of plastic flow occurs at stresses as low as 0.8 GPa, although macroscopic yield only becomes apparent at 2 GPa. The measured misorientations, obtained from peak splitting, enable the geometrically necessary dislocation density to be estimated as 1.1 × 1013 m−2.	Mar 2016
I12-JEEP: Joint Engineering, Environmental and Processing	Characterisation of short fatigue cracks in titanium alloy IMI 834 using X-ray microtomography Tamara Chapman , Kristina Kareh , Matthias Knop , Thomas Connolley , P. D. Lee , Mohammed Azeem , D. Rugg , Trevor Lindley , David Dye Acta Materialia 99, 49 - 62 DOI: 10.1016/j.actamat.2015.07.069 Diamond Proposal Number(s): [8942] Show Abstract ▼ Abstract: A first attempt at the three-dimensional evaluation of naturally initiated surface connected and internal fatigue cracks is presented. Fatigue crack initiation and growth in air and vacuum environments have been investigated through X-ray microtomography in air and vacuum environments at elevated temperatures (350 °C), accompanied by post-mortem electron microscopy of the fracture surfaces. In vacuum (<<10−5 mbar), multiple internal and surface-connected crack initiation was observed, but only the surface-connected cracks grew. In contrast, fewer cracks formed in air, these were mostly surface-connected and all were observed to grow. In all instances the initiation features were associated with globular primary αα. An improved fatigue life was found in vacuum, which was mostly a consequence of delayed initiation, but was also due to slower fatigue crack propagation. The non-propagation of internal cracks was taken to imply that even the good laboratory vacuum obtained here was insufficient to simulate the conditions obtained for an internal crack in a component. The crack shape evolved towards a semi-circular shape a/c=1a/c=1 in air during fatigue crack growth, whilst the vacuum cracks remained semi-elliptical (a/c≃1.4a/c≃1.4). This was taken to imply that oxide-induced crack closure played a role in fatigue crack growth in air.	Oct 2015

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