Publications
131 results found
Xu Y, Gu T, Xian J, et al., 2022, Multi-scale plasticity homogenization of Sn–3Ag-0.5Cu: From β-Sn micropillars to polycrystals with intermetallics, Materials Science and Engineering: A, Vol: 855, Pages: 1-15, ISSN: 0921-5093
The mechanical properties of β-Sn single crystals have been systematically investigated using a combined methodology of micropillar tests and rate-dependent crystal plasticity modelling. The slip strength and rate sensitivity of several key slip systems within β-Sn single crystals have been determined. Consistency between the numerically predicted and experimentally observed slip traces has been shown for pillars oriented to activate single and double slip. Subsequently, the temperature-dependent, intermetallic-size-governing behaviour of a polycrystal β-Sn-rich alloy SAC305 (96.5Sn–3Ag-0.5Cu wt%) is predicted through a multi-scale homogenization approach, and the predicted temperature- and rate-sensitivity reproduce independent experimental results. The integrated experimental and numerical approaches provide mechanistic understanding and fundamental material properties of microstructure-sensitive behaviour of electronic solders subject to thermomechanical loading, including thermal fatigue.
Fang N, Birch R, Britton TB, 2022, Optimizing broad ion beam polishing of zircaloy-4 for electron backscatter diffraction analysis, Publisher: Elsevier
Microstructural analysis with electron backscatter diffraction (EBSD)involves sectioning and polishing to create a flat and preparation-artifactfree surface. The quality of EBSD analysis is often dependant on this step, andthis motivates us to explore how broad ion beam (BIB) milling can be optimisedfor the preparation of zircaloy-4 with different grain sizes. We systematicallyexplore the role of ion beam angle, ion beam voltage, polishing duration andpolishing temperature and how this changes the surface roughness and indexingquality. Our results provide a method to routinely prepare high-qualityZircaloy-4 surfaces, and methods to optimise BIB polishing of other materialsfor high-quality EBSD studies.
Huang C, Kyvelou P, Zhang R, et al., 2022, Mechanical testing and microstructural analysis of wire arc additively manufactured steels, Materials and Design, Vol: 216, ISSN: 0264-1275
Wire arc additive manufacturing (WAAM) is a metal 3D printing method that allows the cost-effective and efficient production of large-scale elements, and has thus gained great interest from architects and structural engineers. Integration of this novel technology into the construction industry, however, requires the development of a clear understanding of the mechanical behaviour of WAAM materials. To this end, a comprehensive experimental study into the mechanical properties and microstructure of WAAM plates made of normal- and high-strength steels has been undertaken and is reported herein. A total of 137 as-built and machined tensile coupons were tested, extracted in various directions relative to the print layer orientation from WAAM plates of two nominal thicknesses, built using different deposition strategies. Theinfluence of the geometric undulations inherent to the WAAM process and deposition strategy on the resulting mechanical properties was investigated. Microstructural characterisation was also performed by means of optical microscopy (OM) and electron backscatter diffraction (EBSD). The WAAM normal-strength steel plates exhibited a principally ferritic-pearlitic microstructure, while the WAAM high-strength steel plates displayed a mixed microstructure featuring ferrite, bainite and martensite. The EBSD analysis revealed a weak crystallographic texture, which explained the observed mechanical properties being almost isotropic. No significant differences in tensile properties were observed with the different deposition strategies, except for some variation in ductility. The geometric undulations of the as-built coupons resulted in some reduction in effective mechanical properties and a degree of anisotropy. Overall, the examined WAAM material exhibited consistent mechanical properties, a Young’s modulus comparable to conventionally-produced steel plates, marginally lower strength, reflecting the slower cooling conditions than is customary, and good
Birch R, Benjamin Britton T, 2022, Effective structural unit analysis in hexagonal close-packed alloys - reconstruction of parent beta microstructures and crystal orientation post-processing analysis, JOURNAL OF APPLIED CRYSTALLOGRAPHY, Vol: 55, Pages: 33-45, ISSN: 1600-5767
Jun T-S, Bhowmik A, Maeder X, et al., 2021, In-situ diffraction based observations of slip near phase boundaries in titanium through micropillar compression, MATERIALS CHARACTERIZATION, Vol: 184, ISSN: 1044-5803
- Author Web Link
- Cite
- Citations: 3
Zhang R, Buchanan C, Matilainen V-P, et al., 2021, Mechanical properties and microstructure of additively manufactured stainless steel with laser welded joints, Materials and Design, Vol: 208, Pages: 1-20, ISSN: 0264-1275
Powder bed fusion (PBF) is a commonly employed metal additive manufacturing (AM) process in which components are built, layer-by-layer, using metallic powder. The component size is limited by the internal build volume of the employed PBF AM equipment; the fabrication of components larger than this volume therefore requires mechanical joining methods, such as laser welding. There are, however, very limited test data on the mechanical performance of PBF metal with laser welded joints. In this study, the mechanical properties of PBF built 316L stainless steel parts, joined together using laser welding to form larger components, have been investigated; the microstructure of the components has also been examined. 33 PBF 316L stainless steel tensile coupons, with central laser welds, welded using a range of welding parameters, and with coupon half parts built in two different orientations, were tested. The porosity, microhardness and microstructure of the welded coupons, along with the widths of the weld and heat-affected zone (HAZ), were characterised. The PBF base metal exhibited a typical cellular microstructure, while the weld consisted of equiaxed, columnar and cellular dendrite microstructures. Narrow weld regions and HAZs were observed. The PBF base metal was found to have higher proof and ultimate strengths, but a similar fracture strain and a lower Young’s modulus, compared with conventionally manufactured 316L stainless steel. The strengths were dependent on the build direction – the vertically built specimens showed lower proof strengths than the horizontal specimens. The laser welds generally exhibited lower microhardness, proof strengths and fracture strains than the PBF base metal which correlated with the observed structure. This work has demonstrated that PBF built parts can be joined by laser welding to form larger components and provided insight into the resulting strength and ductility.
Liu Y, Adande S, Britton TB, et al., 2021, Cold dwell fatigue analyses integrating crystal-level strain rate sensitivity and microstructural heterogeneity, International Journal of Fatigue, Vol: 151, Pages: 1-19, ISSN: 0142-1123
Cold dwell fatigue remains an important life-limiting factor in aircraft engine titanium alloys. Microstructure-level creep and stress accumulation during each loading cycle are controlled by strain rate sensitivity. Here, an integrated experimental and computational framework is used to link crystal-level slip properties to microstructure-sensitive cold dwell debit of a forged rotor graded Ti-6Al-4V alloy. Slip strengths and anisotropic strain rate sensitivities are extracted from micro-pillar compression tests for different slip systems, incorporated within α+β microstructurally-faithful polycrystal representations. Dwell and non-dwell cyclic loading in alloy Ti-6Al-4V are investigated for two differing microstructures, and the cycles to failure predicted based solely on the crystal c-axis tensile strength, and the dwell debit quantified. The dwell effect is predicted to diminish to zero below a peak applied stress of about 790 MPa in the alloy studied.
Britton B, Carter J, Korey M, et al., 2021, Material Goals Towards Equity Along the STEM and LGBTQIA plus Spectra, JOM, ISSN: 1047-4838
Bilsland C, Barrow A, Britton TB, 2021, Correlative statistical microstructural assessment of precipitates and their distribution, with simultaneous electron backscatter diffraction and energy dispersive X-ray spectroscopy, Materials Characterization, Vol: 176, Pages: 1-10, ISSN: 1044-5803
Modern engineering alloys have bespoke microstructures, where features such as precipitates are used to control properties. In many Ni-based alloys, carbo-nitride precipitates are introduced to strengthen and improve performance. These precipitates can be distributed throughout the microstructure and niobium rich carbides are often found at grain boundaries. In this work, we used combined energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) to characterise the population of these precipitates. Processing of the EDS signal is used to label the Mo/Nb-rich precipitates, and their size and location are measured from maps using a circular Hough transform. This label map is combined with the grain boundary network (from EBSD analysis). Statistical analysis, using ANOVA testing, reveals differences in chemistry between carbides found in Ni-rich matrix grain interiors, on random high angle boundaries and on special boundaries (Σ3 and Σ9). These results are compared between wrought and power metallurgy product forms. These distributions are discussed in the context of their performance within demanding environments, such as reactor core internals.
Guo Y, Zong C, Britton TB, 2021, Development of local plasticity around voids during tensile deformation, Materials Science and Engineering: A, Vol: 814, Pages: 1-13, ISSN: 0921-5093
Voids can limit the life of engineering components. This motivates us to understand local plasticity around voids in a nickel base superalloy combining experiments and simulations. Single crystal samples were deformed in tension with in-situ high angular resolution electron back scatter diffraction to probe the heterogeneous local stress field under load; the reference stress is informed by crystal plasticity finite element simulations. This information is used to understand the activation of plastic deformation around the void. Our investigation indicates that while the resolved shear stress would indicate slip activity on multiple slip systems, slip is reduced to specific systems due to image forces and forest hardening. This study rationalizes the observed development of plastic deformation around the void, aiding in our understanding of component failure and engineering design.
Emmanuel M, Gavalda-Diaz O, Sernicola G, et al., 2021, Fracture energy measurement of prismatic plane and Σ2 boundary in cemented carbide, JOM, Vol: 73, Pages: 1589-1596, ISSN: 1047-4838
The grain boundary network of WC in WC-Co is important, as cracks often travel intergranularly. This motivates the present work, where we experimentally measure the fracture energy of Σ2 twist grain boundaries between WC crystals using a double cantilever beam (DCB) opened with a wedge under displacement control in a WC-10wt%Co sample. The fracture energy of this boundary type was compared with cleaving {101 ̅0} prismatic planes in a WC single crystal. Fracture energies of 7.04 ± 0.36 Jm-2 and 3.57 ± 0.28 Jm-2 were measured for {101 ̅0} plane and Σ2 twist boundaries respectively.
Ball P, Britton TB, Hengel E, et al., 2021, Gender issues in fundamental physics: Strumia’s bibliometric analysis fails to account for key confounders and confuses correlation with causation, Quantitative Science Studies, Vol: 2, Pages: 263-272
McAuliffe TP, Bantounas I, Reynolds LR, et al., 2021, Quantitative precipitate classification and grain boundary property control in Co/Ni-base superalloys, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, Vol: 52, Pages: 1649-1664, ISSN: 1073-5623
A correlative approach is employed to simultaneously assess structure and chemistry of (carbide and boride) precipitates in a set of novel Co/Ni-base superalloys. Structure is derived from electron backscatter diffraction (EBSD) with pattern template matching, and chemistry obtained with energy dispersive X-ray spectroscopy (EDS). It is found that the principal carbide in these alloys is Mo and W rich with the M6C structure. An M2B boride also exhibiting Mo and W segregation is observed at B levels above approximately 0.085 at. pct. These phases are challenging to distinguish in an SEM with chemical information (EDS or backscatter Z-contrast) alone, without the structural information provided by EBSD. Only correlative chemical and structural fingerprinting is necessary and sufficient to fully define a phase. The identified phases are dissimilar to those predicted using ThermoCalc. We additionally perform an assessment of the grain boundary serratability in these alloys, and observe that significant amplitude is only obtained in the absence of pinning intergranular precipitates.
Xu Z, Britton B, Guo Y, 2021, Casting voids in nickel superalloy and the mechanical behaviour under room temperature tensile deformation, Materials Science and Engineering A: Structural Materials: Properties, Microstructure and Processing, Vol: 806, Pages: 1-10, ISSN: 0921-5093
The microstructure of a second-generation nickel base superalloy is studied using X-ray computed tomography (XCT) and scanning electron microscopy (SEM). The as-cast material contains 0.15 (±0.001) vol% voids and these are distributed in the inter-dendritic region. The volume fraction of the voids increases to 0.21 (±0.001) vol% after tensile deformation. Surface observations show evidence of dislocation emissions from the void surface, a mechanism possibly facilitates the expansion of the voids and contributes to the increased void volume fraction. Phenomenological parameters such as stress triaxiality, often believed to control void growth, are investigated through crystal plasticity simulation and compared with literature reported data. The results indicate weak correlation between stress triaxiality and void growth, but this may be possibly due to the lack of data at higher level of plastic deformation, which is limited by the ductility of the material. The distribution of the stress triaxiality field within the sample is heterogeneous and the peak of the triaxiality field is a function of the ratio between notch diameter and sample width. A smaller notch diameter to sample width ratio tend to distribute the triaxiality peaks towards the centre of the sample but also lead to higher strain localisation, an effect that results in early sample failure.
Mouton I, Chang Y, Chakraborty P, et al., 2021, Hydride growth mechanism in zircaloy-4: Investigation of the partitioning of alloying elements, Materialia, Vol: 15, Pages: 1-11, ISSN: 2589-1529
The long-term safety of water-based nuclear reactors relies in part on the reliability of zirconium-based nuclear fuel cladding. Yet the progressive ingress of hydrogen during service makes zirconium alloys subject to delayed hydride cracking. Here, we use a combination of electron back-scattered diffraction and atom probe tomography to investigate specific microstructural features from the as-received sample and in the blocky-α microstructure, before and after electrochemical charging with hydrogen/deuterium followed by a low temperature heat treatment at 400 °C for 5 h followed by furnace cooling at a rate of 0.5 °C/min. Specimens for atom probe were prepared at cryogenic temperature to avoid the formation of spurious hydrides. We report on the compositional evolution of grains and grain boundaries over the course of the sample's thermal history, as well as the ways the growth of the hydrides modifies locally the composition and the structure of the alloy. We observe a significant amount of deuterium left in the matrix, even after the slow cooling and growth of the hydrides. Stacking faults form ahead of the growth front and the segregation of Sn at the hydride/matrix interface and on these faults. We propose that this segregation may facilitate further growth of the hydride. Our systematic investigation enables us discuss how the solute distribution affects the evolution of the alloy's properties during its service lifetime.
D'Elia E, Mottura A, Britton TB, et al., 2021, Developing a materials world: an analysis of UK HE data, Publisher: Center for Open Science
Despite being a catalyst for progress, Materials Science and Engineering is relatively unknown as an undergraduate discipline in the UK. By analysing UK data published by the Universities and Colleges Admissions System (UCAS) and the United Kingdom's Higher Education Statistics Agency (HESA), we explore how applications to study and uptake of
Tong VS, Ben Britton T, 2021, TrueEBSD: Correcting spatial distortions in electron backscatter diffraction maps, Ultramicroscopy, Vol: 221, Pages: 1-8, ISSN: 0304-3991
Electron backscatter diffraction (EBSD) in the scanning electron microscope is routinely used for microstructural characterisation of polycrystalline materials. Maps of EBSD data are typically acquired at high stage tilt and slow scan speed, leading to tilt and drift distortions that obscure or distort features in the final microstructure map. In this paper, we describe TrueEBSD, an automatic postprocessing procedure for distortion correction with pixel-scale precision. Intermediate images are used to separate tilt and drift distortion components and fit each to a physically-informed distortion model. We demonstrate TrueEBSD on three case studies (titanium, zirconium and hydride containing Zr), where distortion removal has enabled characterisation of otherwise inaccessible microstructural features.
Xu Y, Gu T, Xian J, et al., 2021, Intermetallic size and morphology effects on creep rate of Sn-3Ag-0.5Cu solder, International Journal of Plasticity, Vol: 137, ISSN: 0749-6419
The creep behaviour of directionally solidified SAC305 (96.5Sn-3Ag-0.5Cu wt%) alloy has been investigated with integrated particle matrix composite (PMC) crystal plasticity modelling and quantitative experimental characterisation and test. In this manuscript, the mechanistic basis of creep rate dependence is shown to be influenced by plastic strain gradients, and the associated hardening due to geometrically necessary dislocation (GND) density. These gradients are created due to heterogenous deformation at the Sn phase and intermetallic compound (IMCs) boundaries. The size and distribution of IMCs is important, as finer and well dispersed IMCs leading to higher creep resistance and lower creep rates, and this agrees with experimental observations. This understanding has enabled the creation of a new microstructurally homogenized model which captures this mechanistic link between the GND hardening, the intermetallic size, and the corresponding creep rate. The homogenised model relates creep rates to the microstructure found within the solder alloy as they evolve in service, when ageing and coarsening kinetics are known.
Gu T, Gourlay CM, Britton TB, 2021, The role of lengthscale in the creep of Sn-3Ag-0.5Cu solder microstructures, Journal of Electronic Materials, Vol: 50, Pages: 926-938, ISSN: 0361-5235
Creep of directionally solidified Sn-3Ag-0.5Cu wt.% (SAC305) samples with near-<110> orientation along the loading direction and different microstructural lengthscale is investigated under constant load tensile testing and at a range of temperatures. The creep performance improves by refining the microstructure, i.e. the decrease in secondary dendrite arm spacing (λ2), eutectic intermetallic spacing (λe) and intermetallic compound (IMC) size, indicating a longer creep lifetime, lower creep strain rate, change in activation energy (Q) and increase in ductility and homogeneity in macro- and micro-structural deformation of the samples. The dominating creep mechanism is obstacle-controlled dislocation creep at room temperature and transits to lattice-associated vacancy diffusion creep at elevated temperature (TTM > 0.7 to 0.75). The deformation mechanisms are investigated using electron backscatter diffraction and strain heterogeneity is identified between β-Sn in dendrites and β-Sn in eutectic regions containing Ag3Sn and Cu6Sn5 particles. The size of the recrystallised grains is modulated by the dendritic and eutectic spacings; however, the recrystalised grains in the eutectic regions for coarse-scaled samples (largest λ2 and λe) is only localised next to IMCs without growth in size.
Ball P, Hengel E, Moriarty P, et al., 2021, Gender issues in fundamental physics: Strumia's bibliometric analysis fails to account for key confounders and confuses correlation with causation, Quantitative Science Studies, Vol: 2, Pages: 1-10, ISSN: 2641-3337
Alessandro Strumia recently published a survey of gender differences in publications and citations in high-energy physics (HEP). In addition to providing full access to the data, code, and methodology, Strumia (2020) systematically describes and accounts for gender differences in HEP citation networks. His analysis points both to ongoing difficulties in attracting women to high-energy physics and an encouraging—though slow—trend in improvement.
McAuliffe TP, Dye D, Britton TB, 2020, Spherical-angular dark field imaging and sensitive microstructural phase clustering with unsupervised machine learning., Ultramicroscopy, Vol: 219, Pages: 1-11, ISSN: 0304-3991
Electron backscatter diffraction is a widely used technique for nano- to micro-scale analysis of crystal structure and orientation. Backscatter patterns produced by an alloy solid solution matrix and its ordered superlattice exhibit only extremely subtle differences, due to the inelastic scattering that precedes coherent diffraction. We show that unsupervised machine learning (with principal component analysis, non-negative matrix factorisation, and an autoencoder neural network) is well suited to fine feature extraction and superlattice/matrix classification. Remapping cluster average patterns onto the diffraction sphere lets us compare Kikuchi band profiles to dynamical simulations, confirm the superlattice stoichiometry, and facilitate virtual imaging with a spherical solid angle aperture. This pipeline now enables unparalleled mapping of exquisite crystallographic detail from a wide range of materials within the scanning electron microscope.
Wang S, Giuliani F, Britton T, 2020, Slip-hydride interactions in Zircaloy-4: Multiscale mechanical testing and characterisation, Acta Materialia, Vol: 200, Pages: 537-550, ISSN: 1359-6454
The interactions between δ-hydrides and plastic slip in a commercial zirconium alloy, Zircaloy-4, under load were studied using in situ secondary electron microscope (SEM) micropillar compression tests of single crystal samples and ex situ digital image correlation (DIC) macroscale tensile tests of polycrystalline samples. The hydrides decorate near basal planes in orientation, and for micropillars orientated for 〈a〉 basal slip localised shear at the hydride–matrix interface is favoured over slip in α-Zr matrix due to a lower shear stress required. In contrast, for pillars oriented for 〈a〉 prismatic slip the shear stress needed to trigger plastic slip within the hydride is slightly higher than the critical resolved shear stress (CRSS) for the 〈a〉 prismatic slip system. In this case, slip in the hydride is likely achieved through 〈110〉-type shear which is parallel to the activated 〈a〉-type shear in the parent matrix. At a longer lengthscale, these results are used to inform polycrystalline samples analysed using high spatial resolution DIC. Here localised interface shear remains to be a significant deformation path which can both cause and be caused by matrix slip on planes closely-oriented to the phase boundaries. Matrix slip on planes nearly perpendicular to the adjacent hydride–matrix interfaces can either result in plastic slip within the hydrides or get arrested at the interfaces, generating local stress concentration. Through these mechanisms, the presence of δ-hydrides leads to enhanced strain localisation in Zircaloy-4 early in the plastic regime.
Gu T, Tong V, Gourlay C, et al., 2020, In-situ study of creep in Sn-3Ag-0.5Cu solder, Acta Materialia, Vol: 196, Pages: 31-43, ISSN: 1359-6454
The creep behaviour and microstructural evolution of a Sn-3Ag-0.5Cu wt% sample with a columnar microstructure have been investigated through in-situ creep testing under constant stress of 30 MPa at ~298 K. This is important, as 298 K is high temperature within the solder system and in-situ observations of microstructure evolution confirm the mechanisms involved in deformation and ultimately failure of the material. The sample has been observed in-situ using repeat and automatic forescatter diode and auto electron backscatter diffraction imaging. During deformation, polygonisation and recrystallisation are observed heterogeneously with increasing strain, and these correlate with local lattice rotations near matrix-intermetallic compound interfaces. Recrystallised grains have either twin or special boundary relationships to their parent grains. The combination of these two imaging methods reveal grain 1 (loading direction, LD, 10.4° from [100]) deforms less than the neighbour grain 2 (LD 18.8° from [110]), with slip traces in the strain localised regions. In grain 2, (10)[001] slip system is observed and in grain 1 (10)[1]/2 and (110)[11]/2 slip systems are observed. Lattice orientation gradients build up with increasing plastic strain and near fracture recrystallisation is observed concurrent with fracture.
Dessolier T, McAuliffe T, Hamer WJ, et al., 2020, Effect of high temperature service on the complex through-wall microstructure of centrifugally cast HP40 reformer tube, Publisher: arXiv
Centrifugally cast reformer tubes are used in petrochemical plants forhydrogen production. Due to the conditions of hydrogen production, reformertubes are exposed to high temperature which causes creep damage inside themicrostructure. In this study, two different ex-service HP40 alloy reformertubes which come from the same steam reformer unit have been compared bymicrostructural characterisation performed at a range of length scales from mmto um. Analyses performed by EBSD (Electron Backscatter Diffraction), EDS(Energy Dispersive X-ray Spectroscopy) and PCA (Principal Component Analysis)show that both tubes have similar microstructural constituents, with thepresence of an austenitic matrix and M23C6, G phase and M6C carbides at thegrain boundaries. Even if both tubes have a similar microstructure, one tubedue to it localisation inside the steam reformer unit presents a region withmore micro cracks which may indicate that this tube have accumulated more creepdamage than the other one.
McGilvery C, Jiang J, Rounthwaite N, et al., 2020, Characterisation of carbonaceous deposits on diesel injector nozzles, Fuel: the science and technology of fuel and energy, Vol: 274, Pages: 1-9, ISSN: 0016-2361
Diesel injector nozzles are highly engineered components designed to optimise delivery of fuel into the combustion chamber of modern engines. These components contain narrow channels to enhance spray formation and penetration, hence mixing and combustion. Over time, these injectors can become clogged due to fouling by carbonaceous deposits which may affect the long-term performance of a diesel engine. In this paper we explore the chemical composition and structure of deposits formed within the nozzle at the nanometre scale using electron microscopy. We focus on comparing deposits generated using a chassis dynamometer-based test with Zn fouled fuel with a DW10B dirty up test. We have developed and applied a method to precisely section the deposits for ‘top view’ scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis of the morphology and relative accumulation of deposits formed during chassis dynamometer and engine based dirty-up tests. We extend this analysis to finer length scales through lift-out of ~70 nm thick electron transparent cross section foils, including both the metal substrate and deposit, using focussed ion beam (FIB) machining. These foils are analysed using scanning transmission electron microscopy (STEM) and STEM-EDS. These thin foils reveal thin-film growth and chemical stratification of Zn, C, O and other elements in the organic deposit layers developed during growth on the steel substrate during industry standard fouling tests.
Britton TB, Jackson CA-L, Wade J, 2020, The reward and risk of social media for academics, Publisher: Center for Open Science
We are three academics who are active on social media. We explore the motivations for and benefits of engaging with social media, as well as its costs and risks. Overall, we believe this engagement to be a net benefit for us, our employers and for wider society.
Kyvelou P, Slack H, Daskalaki Mountanou D, et al., 2020, Mechanical and microstructural testing of wire and arc additively manufactured sheet material, Materials and Design, Vol: 192, ISSN: 0264-1275
Wire and arc additive manufacturing (WAAM) is a method of 3D printing that enables large elements to be built, with reasonable printing times and costs. There are, however, uncertainties relating to the structural performance of WAAM material, including the basic mechanical properties, the degree of anisotropy, the influence of the as-built geometry and the variability in response. Towards addressing this knowledge gap, a comprehensive series of tensile tests on WAAM stainless steel was conducted; the results are presented herein. As-built and machined coupons were tested to investigate the influence of the geometrical irregularity on the stress-strain characteristics, while material anisotropy was explored by testing coupons produced at different angles to the printing orientation. Non-contact measurement techniques were employed to determine the geometric properties and deformation fields of the specimens, while sophisticated analysis methods were used for post processing the test data. The material response revealed a significant degree of anisotropy, explained by the existence of a strong crystallographic texture, uncovered by means of electron backscatter diffraction. Finally, the effective mechanical properties of the as-built material were shown to be strongly dependent on the geometric variability; simple geometric measures were therefore developed to characterise the key aspects of the observed behaviour.
Pedrazzini S, Pek ME, Ackerman AK, et al., 2020, Influence of powder-bed temperature on the microstructure and mechanical properties of Ti-6Al-4V produced by selective laser melting, Publisher: arXiv
Advanced characterisation techniques were used on LPBF Ti-6Al-4V samplesproduced on a heated base plate. When the substrate temperature is 100{\deg}Cthe elongation is 6\%, which increases and peaks at 10\% at 570{\deg}C, thensharply decreases to zero ductility at 770{\deg}C. At 100{\deg}C, a heavilystrained and twinned microstructure, primarily composed of {\alpha}+{\alpha}',was observed and it was comparable to asbuilt microstructures obtained byconventional LPBF methods. At higher temperatures, twins are no longer presentand instead nano-scale {\beta} precipitates are observed within {\alpha}' and{\alpha}, as well as dislocation networks (570{\deg}C) and tangles(770{\deg}C). Solute segregation at crystal defects was observed in allpre-heating conditions. Al and V segregation at microtwins was observed in the100{\deg}C sample, reporting for the first time `selective' and mutuallyexclusive Al- and V-rich regions forming in adjacent twins. V segregation atdislocations was observed in the 570{\deg}C and 770{\deg}C samples, consistentwith the higher preheating temperatures. High O contents were measured in allsamples but with apparent opposing effects. At 100{\deg}C and 570{\deg}C wasestimated to be below the critical threshold for O embrittlement and locallyaids in maintaining a strength high by solid solution strengthening, whereas at770{\deg}C it was above the threshold, therefore failing in a brittle fashion.Based on these observations, the initial increase in ductility from 100{\deg}Cto 570{\deg}C is attributed to a reduction in microtwins and the dislocationnetworks acting as `soft barriers' for slip within a coarser microstructure.The lack of ductility at 770{\deg}C was attributed to local soluteredistribution causing dislocation pinning and an increase of O content in thissample.
Bhowmik A, Lee J, Adande S, et al., 2020, Investigating spatio-temporal deformation in single crystal Ni-based superalloys using in-situ diffraction experiments and modelling, Materialia, Vol: 9, Pages: 1-14, ISSN: 2589-1529
In this study, we perform a detailed analysis of room temperature deformation of a [100]–orientated singlecrystal Ni-based superalloy, CMSX-4 micropillar, using a combinatorial and complimentary characterisation approach of micro-Laue diffraction coupled with post-deformation microscopy and crystal plasticity modelling.Time-resolved micro-Laue data indicated that deformation was initiated by activation of multiple slip (after 5%engineering strain) which led to the generation of a plastic strain accumulation accompanied by a two-foldincrease in the dislocation density within the micropillar. Subsequent to that, slip occurred primarily on two systems (11̄1)[101] and (111)[1̄01] with the highest Schmid factor in the single crystal micropillar thereby resultingin little accumulation of unpaired GNDs during a major part of the loading cycle, upto 20% strain in this case.Finite element crystal plasticity modelling also showed good agreement with the experimental analyses, wherebysignificant strains were found to develop in the above slip systems with a localisation near the centre of themicropillar. Post-deformation transmission electron microscopy study confirmed that deformation was mediatedthrough a/2<110> dislocations on {111} planes in the 𝛾-phase, while high stress levels led to shearing of the 𝛾′precipitates by a/2<110> partials bounding an anti-phase boundary free to glide on the {111} planes. Duringthe deformation of the single crystal micropillar, independent rotations of the 𝛾 and 𝛾′ phases were quantified byspatially resolved post-deformation micro-Laue patterns. The degree of lattice rotation in the 𝛾-phase was higherthan that in the 𝛾′-phase.
McAuliffe TP, Foden A, Bilsland C, et al., 2020, Advancing characterisation with statistics from correlative electron diffraction and X-ray spectroscopy, in the scanning electron microscope., Ultramicroscopy, Vol: 211, Pages: 1-16, ISSN: 0304-3991
The routine and unique determination of minor phases in microstructures is critical to materials science. In metallurgy alone, applications include alloy and process development and the understanding of degradation in service. We develop a correlative method, exploring superalloy microstructures, which are examined in the scanning electron microscope (SEM) using simultaneous energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD). This is performed at an appropriate length scale for characterisation of carbide phases' shape, size, location, and distribution. EDS and EBSD data are generated using two different physical processes, but each provide a signature of the material interacting with the incoming electron beam. Recent advances in post-processing, driven by 'big data' approaches, include use of principal component analysis (PCA). Components are subsequently characterised to assign labels to a mapped region. To provide physically meaningful signals, the principal components may be rotated to control the distribution of variance. In this work, we develop this method further through a weighted PCA approach. We use the EDS and EBSD signals concurrently, thereby labelling each region using both EDS (chemistry) and EBSD (crystal structure) information. This provides a new method of amplifying signal-to-noise for very small phases in mapped regions, especially where the EDS or EBSD signal is not unique enough alone for classification.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.