I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[24084]
Abstract: Microstructure-informed crystal plasticity finite element models have shown great promise in predicting plastic and creep deformation in polycrystalline materials. These models can provide substantial insight into the design, fabrication and lifetime assessment of critical metallic components during operation, for instance, in thermal power plants. However, to correctly incorporate damage prediction into models, the microstructural strain simulated at the grain level must be accurately predicted with suitable validation. For this reason, a 3D X-ray Diffraction (3DXRD) experiment was carried out on 316H stainless steel, a material commonly used in thermal power plants, to obtain the per-grain strain response during plastic and creep deformation at 550°C. Several hundred grains within a probed X-ray volume were tracked and measured whilst loading in-situ, obtaining per-grain centre-of-mass positions, crystallographic orientations, and average lattice strain over individual grains. These data were used to calibrate a crystal plasticity model to study the plastic and creep deformation using macroscopic stress-strain and stress-relaxation data. Subsequently, the model was used to predict the average elastic strain in different grains during the cyclic creep experiment, which was validated by 3DXRD datasets. The model results reveal that {100} or {311} grain families are strongly sensitive to microstructure, thereby a polycrystal model that describes specific orientation and neighbourhood characteristics is essential to predict the local response of these grain families. Whereas, self-consistent models are suitable for {110} and {111} grain families. This study shows that only with a suitable calibration of subsurface grain behaviour, crystal plasticity models reveal grain characteristic-dependent micromechanical behaviour.
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Aug 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[29061]
Open Access
Abstract: The mechanisms that govern a previously unexplained hardening effect of a single phase Cu-30wt%Zn
-brass after heating have been investigated. After cold-work, the alloy possesses an increased yield strength and hardening rate only when heat treated to temperatures close to 220 °C, and is otherwise softer. Crystallographic texture and microstructure, explored using electron backscatter diffraction (EBSD), describe the deformation heterogeneity including twin development, as a function of heat treatment. When heated, an increased area fraction of deformation twins is observed, with dimensions reaching a critical size that maximises the resistance to dislocation slip in the parent grains. The effect is shown to dominate over other alloy characteristics including short range order, giving serrated yielding during tensile testing which is mostly eliminated after heating. In-situ X-ray diffraction during tensile testing corroborates these findings; dislocation-related line broadening and lattice strain development between as worked and heated
-brass is directly related to the interaction between the dislocations and the population of deformation twins. The experiments unambiguously disprove that other thermally-induced microstructure features contribute to thermal hardening. Specifically, the presence of recrystallised grains or second phases do not play a role. As these heat treatments match annealing conditions subjected to
-brass during deformation-related manufacturing processes, the results here are considered critical to understand, predict and exploit, where appropriate, any beneficial process-induced structural behaviour.
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Aug 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
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Kai
Zhang
,
Tim
Wigger
,
Rosa
Pineda
,
Simon A.
Hunt
,
Ben
Thomas
,
Thomas
Kwok
,
David
Dye
,
Gorka
Plata
,
Jokin
Lozares
,
Inaki
Hurtado
,
Stefan
Michalik
,
Michael
Preuss
,
Peter D.
Lee
,
Mohammed A.
Azeem
Diamond Proposal Number(s):
[23749]
Abstract: Microstructure evolution during high-strain rate and high-temperature thermo-mechanical processing of a 44MnSiV6 microalloyed steel is investigated using in situ synchrotron high-energy powder X-ray diffraction. The conditions selected replicate a newly developed near solidus high-strain rate process designed for reducing raw material use during the hot processing of steels. High temperatures (exceeding 1300 °C) and high strain rate
= 9 s-1 processing regimes are explored. The lattice strains and dislocation activity estimated from diffraction observations reveal that the microstructure evolution is primarily driven by dynamic recrystallisation. A steady-state stress regime is observed during deformation, which develops due to intermittent and competing work hardening and recovery processes. The texture evolution during the heating, tension, shear deformation and cooling stages is systematically investigated. The direct observation of phase evolution at high-temperature and high-strain rate deformation enables a comprehensive understanding of new manufacturing processes and provides deep insights for the development of constitutive models for face-centred cubic alloys.
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Aug 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[27571]
Open Access
Abstract: Using synchrotron X-ray diffraction, tomography and machine-learning enabled phase segmentation strategy, we have studied under operando conditions the nucleation, co-growth and dynamic interplays among the dendritic and multiple intermetallic phases of a typical recycled Al alloy (Al5Cu1.5Fe1Si, wt.%) in solidification with and without ultrasound. The research has revealed and elucidated the underlying mechanisms that drive the formation of the very complex and convoluted Fe-rich phases with rhombic dodecahedron and 3D skeleton networks (the so-called Chinese-script type morphology). Through statistical microstructural analyses and numerical modelling of the ultrasound melt processing, the research has demonstrated that a short period of ultrasound processing of just 7s in the liquid state is able to reduce the average size of the α-Al dendrites and the Fe-containing intermetallic phases by ∼5 times compared to the cases without ultrasound. This work has provided more new insights on quantitatively understanding of the formation of convoluted morphology of intermetallic phases in 4D domain and the beneficial effects of applying ultrasound to recycled Al alloys, which are directly relevant to industrial practice.
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Aug 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[19251]
Open Access
Abstract: The augmentation of mechanical properties of reduced activation ferritic martensitic steels through the introduction of creep resistant nano-oxide particles produces a class of oxide dispersion strengthened steels, which have attracted significant interest as candidates for first wall supporting structural materials in future nuclear fusion reactors. In the present work, the effect of temperature on the elastic properties and micro-mechanics of 0.3 wt% Y2O3 oxide dispersion strengthened steel EUROFER97 is investigated using synchrotron high energy X-ray diffraction in-situ tensile testing at elevated temperatures, alongside the non-oxide strengthened base steel as a point of comparison. The single crystal elastic constants of both steels are experimentally determined through analysis of the diffraction peaks corresponding to specific grain families in the polycrystalline samples investigated. The effect of temperature on the evolving dislocation density and character in both materials is interrogated, providing insight into deformation mechanisms. Finally, a constitutive flow stress model is used to evaluate the factors affecting yield strength, allowing the strengthening contribution of the oxide particles to be assessed, and correlation between the thermally driven microstructural behaviour and macroscopic mechanical response to be determined.
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Apr 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[7665]
Open Access
Abstract: Deformation behavior of multicomponent metallic glasses are determined by the evolution of the short- and medium-range order (SRO and MRO) structures. A precise understanding of how different atom species rearrange themselves in different stress states is still a great challenge in materials science and engineering. Here, we report a systematic and synergetic research of using electron microscopy imaging, synchrotron X-ray total scattering plus empirical potential structure refinement (EPSR) modelling to study in situ the deformation of a commercial multicomponent metallic glassy alloy (Zr41.2Ti13.8Cu12.5Ni10Be22.5). Systematic and comprehensive analyses on the characteristics of the SRO and MRO structures and the decoupled 15 partial PDFs at each stress level reveal quantitatively how the SRO and MRO structures evolution in 3D space in the tensile and compressive states. The results show that the Zr-centred atom clusters have a low degree of icosahedra and are the preferred atom clusters to rearrange themselves under the tensile and compressive stresses, and the Zr-Zr pair is the dominant atom pair in controlling the initiation of shear bands and the subsequent propagation. The evolution of the MRO clusters under different stress states are realised by changing the connection modes between the Zr-centred atom clusters. The coordinated changes of both bond angles and bond lengths of the Zr-centred clusters are the dominant factors in accommodating the tensile or compressive elastic stresses. While other solute-centred MRO clusters only play a minor role in the atomic structure evolution.
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Apr 2024
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James A. D.
Ball
,
Claire
Davis
,
Carl
Slater
,
Himanshu
Vashishtha
,
Mohammed
Said
,
Louis
Hébrard
,
Florian
Steinhilber
,
Jonathan P.
Wright
,
Thomas
Connolley
,
Stefan
Michalik
,
David M.
Collins
Open Access
Abstract: A novel complex-phase steel alloy is conceived with a deliberately unstable austenite, , phase that enables the deformation-induced martensitic transformations (DIMT) to be explored at low levels of plastic strain. The DIMT was thus explored, in-situ and non-destructively, using both far-field Three-Dimensional X-ray Diffraction (3DXRD) and Electron Back-Scatter Diffraction (EBSD). Substantial martensite formation was observed under 10 % applied strain with EBSD, and many
ɛ
grain formation events were captured with 3DXRD, indicative of the indirect transformation of martensite via the reaction
ɛ
. Using
ɛ
grain formation as a direct measurement of grain stability, the influence of several microstructural properties, such as grain size, orientation and neighbourhood configuration, on stability have been identified. Larger grains were found to be less stable than smaller grains. Any grains oriented with {100} parallel to the loading direction preferentially transformed with lower stresses. Parent
ɛ
-forming grains possessed a neighbourhood with increased ferritic/martensitic volume fraction. This finding shows, unambiguously, that the nearby presence of and promotes
ɛ
formation in neighbouring grains. The minimum strain work criterion model for
ɛ
variant prediction was also evaluated, which worked well for most grains. However,
ɛ
-forming grains with a lower stress were less well predicted by the model, indicating crystal-level behaviour must be considered for accurate
ɛ
formation. The findings from this work are considered key for the future design of alloys where the deformation response can be controlled by tailoring microstructure and local or macroscopic crystal orientations.
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Dec 2023
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[13488]
Open Access
Abstract: In this paper, we used synchrotron X-ray radiography and tomography to study in operando conditions the growth dynamics of the primary Al3Ni intermetallic phases in an Al-15wt%Ni alloy in the solidification process with magnetic pulses of up to 1.5 T. The real-time observations clearly revealed the growth dynamics of the intermetallics in time scale from millisecond to minutes, including phase growth instability, side branching, fragmentation and orientation alignment under different magnetic fluxes. A multiphysics numerical model was also developed to calculate time-evolved Lorentz forces and stresses acting on the Al3Ni phases and the nearby melt. The differential forces between the growing Al3Ni phases and the nearby melt can create slip dislocations at the growing crystal front which can be further developed into nm and μm crystal steps for initiating phase branching. Furthermore, the magnitudes of the shear stresses are strongly related to the size, morphological and geometric features of the growing Al3Ni phases. Dependent on the magnitude of the shear stresses, phase fragmentation could occur in a single pulse period or in multiple pulse periods via fatigue mechanism. The combined real-time experimental observation and modelling work allowed us to elucidate some of the long-time debated hypotheses concerning intermetallic phases growth instability and phase fragmentation in pulse magnetic fields.
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Dec 2023
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Open Access
Abstract: Metastable β-Ti alloys based on the binary Ti-Nb system can exhibit a stress induced transformation to the α″ phase allowing superelasticity and shape memory behaviours but they are also susceptible to the formation of the hexagonal ω phase. The presence of ω is widely reported to prevent the α″ transformation, and in certain forms embrittles the material. Most studies characterise the ω phase ex situ and only observation of the ω phase is used to predict its stability. This approach ignores different potential formation mechanisms and results in an ambiguous picture of its true stability. Here, through the use of in situ synchrotron X-ray diffraction we establish the true nature of the α″ and athermal ω phase transformations with respect to both temperature and composition in a series of cold rolled Ti-Nb alloys which initially contained both α″ and ω. Across the range of studied alloys, the α″ start temperature was always found to be above the ω start temperature but both phases were observed to grow simultaneously contradicting previous reports. In addition, the ω start temperature in all alloys was found to be ≤ 10˚C indicating that the ω present in the initial microstructures was metastable. These observations contradict a vast swathe of the conclusions drawn from ex situ data regarding the stability of the ω phase and categorically show that observation of this phase alone cannot be used to establish its stability and the relevant thermodynamic temperature, ωs.
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Oct 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Fan
Wu
,
Thomas
Flint
,
Renan M.
Kindermann
,
Matthew J.
Roy
,
Lu
Yang
,
Stuart
Robertson
,
Zhaoxia
Zhou
,
Michael
Smith
,
Pratheek
Shanthraj
,
Paul
English
,
Robert
Atwood
,
Wajira
Mirihanage
Diamond Proposal Number(s):
[24149]
Open Access
Abstract: The evolving interface forms between two different liquids during dissimilar welding can critically influence the development of the as-solidified microstructure and determine the mechanical properties of the joint. To investigate the interface evolution mechanisms during arc welding, time-resolved X-radiography was employed. The observations reveal the formation of transient finger-like protrusions at the dissimilar liquid interface prior to a brief, quasi-steady state. The analysis of the experimental observations using the magneto-thermal-hydrodynamic numerical simulations confirms that the quasi-steady state involves the formation of a short-lived solid phase, which alters the regular mixing during the process. Analysis of the in-situ experimental observations elucidate the interactions between thermal, momentum, electromagnetic and compositional fields which determine mechanisms of formation of the liquid interface instabilities and the melt pool shape. Based on the analysis, we extended our study to offer practical enhancement for dissimilar welding through offsetting the heat source.
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Aug 2023
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