Imperial College London

Dr T Ben Britton

Faculty of EngineeringDepartment of Materials

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 2634b.britton Website

 
 
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Location

 

B301Bessemer BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

101 results found

Wang S, Kalacska S, Maeder X, Michler J, Giuliani F, Ben Britton Tet al., 2019, The effect of delta-hydride on the micromechanical deformation of a Zr alloy studied by in situ high angular resolution electron backscatter diffraction, Publisher: PERGAMON-ELSEVIER SCIENCE LTD

Working paper

Hielscher R, Bartel F, Britton TB, 2019, Gazing at crystal balls: Electron backscatter diffraction pattern analysis and cross correlation on the sphere, Ultramicroscopy, Vol: 207, Pages: 1-11, ISSN: 0304-3991

We present spherical analysis of electron backscatter diffraction (EBSD) patterns with two new algorithms: (1) band localisation and band profile analysis using the spherical Radon transform; (2) orientation determination using spherical cross correlation. These new approaches are formally introduced and their accuracies are determined using dynamically simulated patterns. We demonstrate their utility with an experimental dataset obtained from ferritic iron. Our results indicate that the analysis of EBSD patterns on the sphere provides an elegant method of revealing information from these rich sources of crystallographic data.

Journal article

Foden A, Collins DM, Wilkinson AJ, Britton TBet al., 2019, Indexing Electron Backscatter Diffraction Patterns with a Refined Template Matching Approach, Publisher: Elsevier BV

Working paper

Hielscher R, Bartel F, Britton TB, Gazing at crystal balls - Electron backscatter diffraction indexing and cross correlation on a sphere, Ultramicroscopy, ISSN: 0304-3991

We present spherical analysis of electron backscatter diffraction (EBSD)patterns with two new algorithms: (1) pattern indexing utilising a sphericalRadon transform and band localisation; (2) pattern indexing with directspherical cross correlation on the surface of the sphere, with refinement.These new approaches are formally introduced and their accuracies aredetermined using dynamically simulated patterns. We demonstrate their utilitywith an experimental dataset obtained from ferritic iron. Our results indicatethat analysis of EBSD patterns on the surface of a sphere provides a valuablemethod of unlocking information from these rich sources of crystallographicdata.

Journal article

Wang S, Kalácska S, Maeder X, Michler J, Giuliani F, Britton Tet al., The effect of δ-hydride on the micromechanical deformation of Zircaloy-4 studied by in situ high angular resolution electron backscatter diffraction, Scripta Materialia, ISSN: 1359-6462

Zircaloy-4(Zr-1.5%Sn-0.2%Fe-0.1%Cr wt%)is usedas nuclear fuel cladding materials and hydride embrittlementis amajor failure mechanism. To explore the effect of δ-hydrideon plastic deformation and performance of Zircaloy-4, in situhigh angular resolution electron backscatter diffraction(HR-EBSD)was used to quantify stress andgeometrically necessarydislocation(GND)density during bending tests of hydride-free and hydride-containingsingle crystalZircaloy-4 microcantilevers. Results suggest that while the stress applied was accommodated by plastic slip in the hydride-free cantilever,the hydride-containing cantilever showedprecipitation-induced GND pile-up at hydride-matrix interfacepre-deformation, andconsiderable locally-increasing GNDdensity under tensile stressupon plastic deformation.

Journal article

Britton B, Jackson C, Wade J, 2019, The reward and risk of social media for academics, Nature Reviews Chemistry, ISSN: 2397-3358

Journal article

Wallis D, Hansen LN, Britton TB, Wilkinson AJet al., High-angular resolution electron backscatter diffraction as a new tool for mapping lattice distortion in geological minerals, Journal of Geophysical Research. Solid Earth, ISSN: 2169-9356

Analysis of distortions of the crystal lattice within individual mineralgrains is central to the investigation of microscale processes that control andrecord tectonic events. These distortions are generally combinations of latticerotations and elastic strains, but a lack of suitable observational techniqueshas prevented these components being mapped simultaneously and routinely inearth science laboratories. However, the technique of high-angular resolutionelectron backscatter diffraction (HR-EBSD) provides the opportunity tosimultaneously map lattice rotations and elastic strains with exceptionalprecision, on the order of 0.01 degree for rotations and 10-4 in strain, usinga scanning electron microscope. Importantly, these rotations and latticestrains relate to densities of geometrically necessary dislocations andresidual stresses. Recent works have begun to apply and adapt HR-EBSD togeological minerals, highlighting the potential of the technique to provide newinsights into the microphysics of rock deformation. Therefore, the purpose ofthis overview is to provide a summary of the technique, to identify caveats andtargets for further development, and to suggest areas where it offers potentialfor major advances. In particular, HREBSD is well suited to characterising theroles of different dislocation types during crystal plastic deformation and tomapping heterogeneous internal stress fields associated with specificdeformation mechanisms/microstructures or changes in temperature, confiningpressure, or applied deviatoric stress. These capabilities make HR-EBSD aparticularly powerful new technique for analysing the microstructures ofdeformed geological materials.

Journal article

Gianola DS, Britton TB, Zaefferer S, 2019, New techniques for imaging and identifying defects in electron microscopy, MRS Bulletin, Vol: 44, Pages: 450-458, ISSN: 0883-7694

Defects in crystalline solids control the properties of engineered and natural materials, and their characterization focuses our strategies to optimize performance. Electron microscopy has served as the backbone of our understanding of defect structure and their interactions, owing to beneficial spatial resolution and contrast mechanisms that enable direct imaging of defects. These defects reside in complex microstructures and chemical environments, demanding a combination of experimental approaches for full defect characterization. In this article, we describe recent progress and trends in methods for examining defects using scanning electron microscopy platforms. Several emerging approaches offer attractive benefits, for instance, in correlative microscopy across length scales and in in situ studies of defect dynamics.

Journal article

Wang S, Giuliani F, Britton TB, 2019, Microstructure and formation mechanisms of δ-hydrides in variable grain size Zircaloy-4 studied by electron backscatter diffraction, Acta Materialia, Vol: 169, Pages: 76-87, ISSN: 1359-6454

Microstructure and crystallography of δ phase hydrides in as-received fine grain and ‘blocky alpha’ large grain Zircaloy-4 (average grain size ∼11 μm and >200 μm, respectively) were examined using electron backscatter diffraction (EBSD). Results suggest that the matrix-hydride orientation relationship is {0001} α ||{111} δ ;<112¯0> α ||<110> δ for all the cases studied. The habit plane of intragranular hydrides and some intergranular hydrides has been found to be {101¯7} of the surrounding matrix. The morphology of intergranular hydrides can vary depending upon the angle between the grain boundary and the hydride habit plane. The misfit strain between α-Zr and δ-hydride is accommodated mainly by high density of dislocations and twin structures in the hydrides, and a mechanism of twin formation in the hydrides has been proposed. The growth of hydrides across grain boundaries is achieved through an auto-catalytic manner similar to the growth pattern of intragranular hydrides. Easy collective shear along <11¯00> makes it possible for hydride nucleation at any grain boundaries, while the process seems to favour grain boundaries with low (<40°) and high (>80°) c-axis misorientation angles. Moreover, the angle between the grain boundary and the adjacent basal planes does not influence the propensity for hydride nucleation.

Journal article

Moutona I, Breen AJ, Wang S, Chang Y, Szczepaniak A, Kontis P, Stephenson LT, Raabe D, Herbig M, Britton TB, Gault Bet al., 2019, Quantification challenges for atom probe tomography of hydrogen and deuterium in zircaloy-4, Microscopy and Microanalysis, Vol: 25, Pages: 481-488, ISSN: 1431-9276

Analysis and understanding of the role of hydrogen in metals is a significant challenge for the future of materials science, and this is a clear objective of recent work in the atom probe tomography (APT) community. Isotopic marking by deuteration has often been proposed as the preferred route to enable quantification of hydrogen by APT. Zircaloy-4 was charged electrochemically with hydrogen and deuterium under the same conditions to form large hydrides and deuterides. Our results from a Zr hydride and a Zr deuteride highlight the challenges associated with accurate quantification of hydrogen and deuterium, in particular associated with the overlap of peaks at a low mass-to-charge ratio and of hydrogen/deuterium containing molecular ions. We discuss possible ways to ensure that appropriate information is extracted from APT analysis of hydrogen in zirconium alloy systems that are important for nuclear power applications.

Journal article

Wang S, Giuliani F, Britton T, 2019, Variable temperature micropillar compression to reveal <a> basal slip properties of Zircaloy-4, Scripta Materialia, Vol: 162, Pages: 451-455, ISSN: 1359-6462

Zircaloy-4 is widely used as nuclear fuel cladding materials, where it is important to understand the mechanical properties between room temperature and reactor operating temperatures (around 623 K). To aid in this understanding, we have performed compression tests on micropillars aligned to activate <a> basal slip across this temperature range. Engineering analysis of the results indicates that the plastic yield follows a thermally activated constitutive law. We also observe the nature of the slip bands formed on the side surface of our pillars and see characteristic ‘bulging’ that tends to localise as temperature increases.

Journal article

Winkelmann A, Ben Britton T, Nolze G, 2019, Constraints on the effective electron energy spectrum in backscatter Kikuchi diffraction, Publisher: AMER PHYSICAL SOC

Working paper

Jun T-S, Maeder X, Bhowmik A, Guillonneau G, Michler J, Giuliani F, Britton TBet al., 2019, The role of β-titanium ligaments in the deformation of dual phase titanium alloys, Materials Science and Engineering: A, Vol: 746, Pages: 394-405, ISSN: 0921-5093

Multiphase titanium alloys are critical materials in high value engineeringcomponents, for instance in aero engines. Microstructural complexity isexploited through interface engineering during mechanical processing to realisesignificant improvements in fatigue and fracture resistance and strength. Inthis work, we explore the role of select interfaces using in-situmicromechanical testing with concurrent observations from high angularresolution electron backscatter diffraction (HR-EBSD). Our results aresupported with post mortem transmission electron microscopy (TEM). Usingmicro-pillar compression, we performed in-depth analysis of the role of select{\beta}-titanium (body centred cubic) ligaments which separate neighbouring{\alpha}-titanium (hexagonal close packed) regions and inhibit the dislocationmotion and impact strength during mechanical deformation. These results shedlight on the strengthening mechanisms and those that can lead to strainlocalisation during fatigue and failure.

Journal article

Gu T, Gourlay C, Britton T, 2019, Evaluating creep deformation in controlled microstructures of Sn-3Ag-0.5Cu solder, Journal of Electronic Materials, Vol: 48, Pages: 107-121, ISSN: 0361-5235

The reliability of solder joints is affected significantly by thermomechanical properties such as creep and thermal fatigue. In this work, the creep of directionally solidified (DS) Sn-3Ag-0.5Cu wt.% (SAC305) dog-bone samples (gauge dimension: 10 × 2 × 1.5 mm) with a controlled <110> or <100> fibre texture is investigated under constant load testing (stress level: ∼ 30 MPa) at a range of temperatures from 20°C to 200°C. Tensile testing is performed and the secondary creep strain rate and the localised strain gradient are studied by two-dimensional optical digital image correlation (2-D DIC). The dominating creep mechanisms and their temperature dependence are explored at the microstructural scale using electron backscatter diffraction (EBSD), which enables the understanding of the microstructural heterogeneity of creep mechanisms at different strain levels, temperatures and strain rates. Formation of subgrains and the development of recrystallization are observed with increasing strain levels. Differences in the deformation of β-Sn in dendrites and in the eutectic regions containing Ag3Sn and Cu6Sn5 are studied and related to changes in local deformation mechanisms.

Journal article

Tong VS, Knowles AJ, Dye D, Ben Britton Tet al., 2019, Rapid electron backscatter diffraction mapping: Painting by numbers, Materials Characterization, Vol: 147, Pages: 271-279, ISSN: 1044-5803

Microstructure characterisation has been greatly enhanced through the use of electron backscatter diffraction (EBSD), where rich maps are generated through analysis of the crystal phase and orientation in the scanning electron microscope (SEM). Conventional EBSD analysis involves raster scanning of the electron beam and serial analysis of each diffraction pattern in turn. For grain shape, crystallographic texture, and microstructure analysis this can be inefficient. In this work, we present Rapid EBSD, a data fusion approach combining forescatter electron (FSE) imaging with static sparse sampling of EBSD patterns. We segment the FSE image into regions of similar colour (i.e. phase and crystal orientation) and then collect representative EBSD data for each segmented region. This enables microstructural assessment to be performed at the spatial resolution of the (fast) FSE imaging whilst including orientation and phase information from EBSD analysis of representative points. We demonstrate the Rapid EBSD technique on samples of a cobalt based superalloy and a strained dual phase titanium alloy, comparing the results with conventional analysis. Rapid EBSD is advantageous for assessing grain size distributions in time-limited experiments.

Journal article

Birch R, Wang S, Tong VS, Britton TBet al., 2019, The effect of cooling rate and grain size on hydride microstructure in Zircaloy-4, Journal of Nuclear Materials, Vol: 513, Pages: 221-225, ISSN: 0022-3115

We explore the distribution, morphology and structure of zirconium hydrides formed using different cooling rates through the solid state Zr+[H] → Zr + hydride transus, in fine and blocky alpha Zircaloy-4. We observe that cooling rate and grain size control the phase and distribution of hydrides formed. The blocky alpha (coarse grain, > 200 μm) Zircaloy-4, has a smaller grain boundary area to grain volume ratio and this significantly affects nucleation and growth of hydrides as compared to fine grain size (∼11 μm) material.

Journal article

Britton TB, Tong V, Hickey J, Foden A, Wilkinson Aet al., 2018, AstroEBSD: exploring new space in pattern indexing with methods launched from an astronomical approach, Journal of Applied Crystallography, Vol: 51, Pages: 1525-1534, ISSN: 0021-8898

Electron backscatter diffraction (EBSD) is a technique used to measure crystallographic features in the scanning electron microscope. The technique is highly automated and readily accessible in many laboratories. EBSD pattern indexing is conventionally performed with raw electron backscatter patterns. These patterns are software processed to locate the band centres (and sometimes edges) from which the crystallographic index of each band is determined. Once a consistent index for many bands is obtained, the crystal orientation with respect to a reference sample and detector orientation can be determined and presented. Unfortunately, because of challenges related to crystal symmetry, there are limited available pattern-indexing approaches and this has probably hampered open development of the technique. In this article, a new method of pattern indexing is presented, based upon a method with which satellites locate themselves in the night sky, and its effectiveness is systematically demonstrated using dynamical simulations and real experimental patterns. The benefit of releasing this new algorithm as open-source software is demonstrated when this indexing process is utilized, together with dynamical solutions, to provide some of the first accuracy assessments of an indexing solution. In disclosing a new indexing algorithm, and software processing toolkit, the authors hope to open up EBSD developments to more users. The software code and example data are released alongside this article for third party developments.

Journal article

Breen AJ, Mouton I, Lu W, Wang S, Szczepaniak A, Kontis P, Stephenson LT, Chang Y, da Silva AK, Liebscher C, Raabe D, Britton TB, Herbig M, Gault Bet al., 2018, Atomic scale analysis of grain boundary deuteride growth front in Zircaloy-4, Scripta Materialia, Vol: 156, Pages: 42-46, ISSN: 1359-6462

Zircaloy-4 (Zr-1.5%Sn-0.2%Fe-0.1%Cr wt%) was electrochemically charged with deuterium to create deuterides and subsequently analysed with atom probe tomography and scanning transmission electron microscopy to understand zirconium hydride formation and embrittlement. At the interface between the hexagonal close packed (HCP) α-Zr matrix and a face centred cubic (FCC) δ deuteride (ZrD1.5–1.65), a HCP ζ phase deuteride (ZrD0.25–0.5) has been observed. Furthermore, Sn is rejected from the deuterides and segregates to the deuteride/α-Zr reaction front.

Journal article

Lan B, Britton TB, Jun T-S, Gan W, Hofmann M, Dunne F, Lowe Met al., 2018, Direct volumetric measurement of crystallographic texture using acoustic waves, Acta Materialia, Vol: 159, Pages: 384-394, ISSN: 1359-6454

Crystallographic texture in polycrystalline materials is often developed as preferred orientation distribution of grains during thermo-mechanical processes. Texture dominates many macroscopic physical properties and reflects the histories of structural evolution, hence its measurement and control are vital for performance optimisation and deformation history interogation in engineering and geological materials. However, exploitations of texture are hampered by state-of-the-art characterisation techniques, none of which can routinely deliver the desirable non-destructive, volumetric measurements, especially at larger lengthscales. Here we report a direct and general methodology retrieving important lower-truncation-order texture and phase information from acoustic (compressional elastic) wave speed measurements in different directions through the material volume (avoiding the need for forward modelling). We demonstrate its deployment with ultrasound in the laboratory, where the results from seven representative samples are successfully validated against measurements performed using neutron diffraction. The acoustic method we have developed includes both fundamental wave propagation and texture inversion theories which are free from diffraction limits, they are arbitrarily scalable in dimension, and can be rapidly deployed to measure the texture of large objects. This opens up volumetric texture characterisation capabilities in the areas of material science and beyond, for both scientific and industrial applications.

Journal article

Luan Q, Britton TB, Jun T, 2018, Strain rate sensitivity in commercial pure titanium: the competition between slip and deformation twinning, Materials Science and Engineering: A, Vol: 734, Pages: 385-397, ISSN: 0921-5093

Titanium alloys are widely used in light weight applications such as jet engine fans, where their mechanical performance under a range of loading regimes is important. Titanium alloys are mechanically anisotropic with respect to crystallographic orientation, and remarkably titanium creeps at room temperature. This means that the strain rate sensitivity (SRS) and stress relaxation performance are critical in predicting component life. In this work, we focus on systematically exploring the macroscopic SRS of Grade 1 commercially pure titanium (CP Ti) with varying grain sizes and texture using uniaxial compression. Briefly, we find that Ti samples had positive SRS and samples compressed along the sheet rolling direction (RD) (i.e. soft grains dominant) were less rate sensitive than bars compressed along the sheet normal direction (ND) (i.e. hard grains dominant). We attribute this rate sensitivity to the relative activity of slip and twinning. Within the grain size range of ~ 317 ±7 μm, we observe an increase in the rate sensitivity, where volume fraction of {101 ̅2}<101 ̅1> T1 tensile twins was low, and the twin width at different strain rates were similar. These observations imply that the macroscopic rate sensitivity is controlled by the ensemble behaviour of local deformation processes: the amount of slips accumulated at grain boundaries affects the SRS, which is grain size and texture dependent. We hope that this experimental study motivates mechanistic modelling studies using crystal plasticity, including strain rate sensitivity and twinning, to predict the performance of titanium alloys.

Journal article

Niania M, Podor R, Britton TB, Li C, Cooper SJ, Svetkov N, Skinner S, Kilner Jet al., 2018, In situ study of strontium segregation in La<inf>0.6</inf>Sr<inf>0.4</inf>Co<inf>0.2</inf>Fe<inf>0.8</inf>O<inf>3- δ</inf>in ambient atmospheres using high-temperature environmental scanning electron microscopy, Journal of Materials Chemistry A, Vol: 6, Pages: 14120-14135, ISSN: 2050-7496

Samples of the solid oxide fuel cell cathode material La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF) were annealed using High-Temperature Environmental Scanning Electron Microscopy (HT-ESEM) from room temperature to 1000 °C in atmospheres of pure oxygen, pure water and ambient lab air. Image series of each heat treatment were taken where microstructural changes were observed and compared between samples. Strontium segregation rate was found to be significantly increased in the presence of pure water as compared to pure O2and ambient air. Electron backscattered diffraction (EBSD) was performed in order to assess the effect of crystal orientation on particle formation and surface sensitive chemical analysis techniques were used to determine the chemical changes at the grain surface as a result of the different heat treatments. It was shown that crystal orientation affected the nature and growth rate of strontium-based particles, however, due to the pseudo-symmetry of La0.6Sr0.4Co0.2Fe0.8O3-δ, precise crystal orientation relationships could not be determined. The chemical composition of the grain surface was found to be approximately equal under each atmosphere.

Journal article

Britton TB, Goran D, Tong VS, 2018, Space rocks and optimising scanning electron channelling contrast, Materials Characterization, Vol: 142, Pages: 422-431, ISSN: 1044-5803

Forescatter electron imaging is a popular microscopy technique, especially for scanning electron microscopes equipped with an electron backscatter diffraction detector. In principal, this method enables qualitative imaging of microstructure but quantitative assessment can be limited due to limited information about the contrast afforded. In this work, we explore forescatter electron imaging and demonstrate that imaging can be optimised for topographic, phase, and subtle orientation contrast imaging through appropriate sample and detector positioning. We demonstrate the relationship between imaging modes using systematic variation in detector positioning and compare this with pseudo-forescatter electron images, obtained from image analysis of diffraction patterns, to explore and confirm image contrast modes. We demonstrate these contrast mechanisms on a map obtained from a sample of the Gibeon meteorite.

Journal article

Niania M, Podor R, Britton TB, Li C, Cooper SJ, Svetkov N, Skinner S, Kilner Jet al., 2018, Correction: In situ study of strontium segregation in La<inf>0.6</inf>Sr<inf>0.4</inf>Co<inf>0.2</inf>Fe<inf>0.8</inf>O<inf>3- δ</inf>in ambient atmospheres using high-temperature environmental scanning electron microscopy (J. Mater. Chem. A (2018) DOI: 10.1039/c8ta01341a), Journal of Materials Chemistry A, Vol: 6, Pages: 14464-14464, ISSN: 2050-7488

© 2018 The Royal Society of Chemistry. Correction for 'In situ study of strontium segregation in La0.6Sr0.4Co0.2Fe0.8O3-δin ambient atmospheres using high-temperature environmental scanning electron microscopy' by Mathew Niania et al., J. Mater. Chem. A, 2018, DOI: 10.1039/c8ta01341a. The authors regret that the name of the first author of ref. 37 was displayed as "F. Pisigkin". The correct name should be "F. Piskin". The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

Journal article

Knowles A, Tea-Sung J, Bhowmik A, Jones N, Britton TB, Giuliani F, Stone H, Dye Det al., 2018, Data on a new beta titanium alloy system reinforced with superlattice intermetallic precipitates, Data in Brief, Vol: 17, Pages: 863-869, ISSN: 2352-3409

The data presented in this article are related to the research article entitled “a new beta titanium alloy system reinforced with superlattice intermetallic precipitates” (Knowles et al., 2018) [1]. This includes data from the as-cast alloy obtained using scanning electron microscopy (SEM) and x-ray diffraction (XRD) as well as SEM data in the solution heat treated condition. Transmission electron microscopy (TEM) selected area diffraction patterns (SADPs) are included from the alloy in the solution heat treated condition, as well as the aged condition that contained < 100 nm B2 TiFe precipitates [1], the latter of which was found to exhibit double diffraction owing to the precipitate and matrix channels being of a similar width to the foil thickness (Williams and Carter, 2009) [2]. Further details are provided on the macroscopic compression testing of small scale cylinders. Of the micropillar deformation experiment performed in [1], SEM micrographs of focused ion beam (FIB) prepared 2 µm micropillars are presented alongside those obtained at the end of the in-situ SEM deformation as well as videos of the in-situ deformation. Further, a table is included that lists the Schmidt factors of all the possible slip systems given the crystal orientations and loading axis of the deformed micropillars in the solution heat treated and aged conditions.

Journal article

Britton TB, Hickey JLR, 2018, Understanding deformation with high angular resolution electron backscatter diffraction (HR-EBSD), EMAS 2017 Workshop - 15th European Workshop on Modern Developments and Applications in Microbeam Analysis & IUMAS-7 Meeting - 7th Meeting of the International union of Microbeam Analysis Societies, Publisher: IOP Publishing, ISSN: 1757-8981

High angular resolution electron backscatter diffraction (HR-EBSD) affords an increase in angular resolution, as compared to 'conventional' Hough transform based EBSD, of two orders of magnitude, enabling measurements of relative misorientations of 1 x 10−4 rads (~ 0.006°) and changes in (deviatoric) lattice strain with a precision of 1 x 10−4. This is achieved through direct comparison of two or more diffraction patterns using sophisticated cross-correlation based image analysis routines. Image shifts between zone axes in the two-correlated diffraction pattern are measured with sub-pixel precision and this realises the ability to measure changes in interplanar angles and lattice orientation with a high degree of sensitivity. These shifts are linked to strains and lattice rotations through simple geometry. In this manuscript, we outline the basis of the technique and two case studies that highlight its potential to tackle real materials science challenges, such as deformation patterning in polycrystalline alloys.

Conference paper

Bhowmik A, Britton TB, Lee J, Liu W, Jun T-S, Sernicola G, Karimpour M, Balint D, Giuliani Fet al., 2017, Deformation behaviour of [001] oriented MgO using combined in-situ nano-indentation and micro-Laue diffraction, Acta Materialia, Vol: 145, Pages: 516-531, ISSN: 1359-6454

We report a coupled in-situ micro-Laue diffraction and nano-indentation experiment, with spatial and time resolution, to investigate the deformation mechanisms in [001]-oriented single crystal MgO. Crystal plasticity finite element modelling was applied to aid interpretation of the experimental observations of plasticity. The Laue spots showed both rotation and streaking upon indentation that is typically indicative of both elastic lattice rotation and plastic strain gradients respectively in the material. Multiple facets of streaking of the Laue peaks suggested plastic slip occurring on almost all the {101}-type slip planes oriented 45° to the sample surface with no indication of slip on the 90° {110} planes. Crystal plasticity modelling also supported these experimental observations. Owing to asymmetric slip beneath the indenter, as predicted by modelling results and observed through Laue analysis, sub-grains were found to nucleate with distinct misorientation. With cyclic loading, the mechanical hysteresis behaviour in MgO is revealed through the changing profiles of the Laue reflections, driven by reversal of plastic strain by the stored elastic energy. Crystal plasticity simulations have also shown explicitly that in subsequent loading cycles after first, the secondary slip system unloads completely elastically while some plastic strain of the primary slip reverses. Tracking the Laue peak movement, a higher degree of lattice rotation was seen to occur in the material under the indent, which gradually decreased moving laterally away. With the progress of deformation, the full field elastic strain and rotation gradients were also constructed which showed opposite lattice rotations on either sides of the indent.

Journal article

Wallis D, Hansen LN, Britton TB, Wilkinson AJet al., 2017, Dislocation interactions in olivine revealed by HR-EBSD, Journal of Geophysical Research, Vol: 122, Pages: 7659-7678, ISSN: 0148-0227

Interactions between dislocations potentially provide a control on strain rates produced by dislocation motion during creep of rocks at high temperatures. However, it has been difficult to establish the dominant types of interactions and their influence on the rheological properties of creeping rocks due to a lack of suitable observational techniques. We apply high-angular resolution electron backscatter diffraction (HR-EBSD) to map geometrically necessary dislocation (GND) density, elastic strain, and residual stress in experimentally deformed single crystals of olivine. Short-range interactions are revealed by cross-correlation of GND density maps. Spatial correlations between dislocation types indicate that non-collinear interactions may impede motion of proximal dislocations at temperatures of 1000°C and 1200°C. Long-range interactions are revealed by autocorrelation of GND density maps. These analyses reveal periodic variations in GND density and sign, with characteristic length-scales on the order of 1–10 μm. These structures are spatially associated with variations in elastic strain and residual stress on the order of 10-3 and 100 MPa, respectively. Therefore, short-range interactions generate local accumulations of dislocations, leading to heterogeneous internal stress fields that influence dislocation motion over longer length-scales. The impacts of these short- and/or long-range interactions on dislocation velocities may therefore influence the strain rate of the bulk material, and are an important consideration for future models of dislocation-mediated deformation mechanisms in olivine. Establishing the types and impacts of dislocation interactions that occur across a range of laboratory and natural deformation conditions will help to establish the reliability of extrapolating laboratory-derived flow laws to real Earth conditions.

Journal article

Sernicola G, Giovannini T, Patel P, Kermode J, Balint D, Britton TB, Giuliani Fet al., 2017, In situ stable crack growth at the micron scale, Nature Communications, Vol: 8, ISSN: 2041-1723

Grain boundaries typically dominate fracture toughness, strength, slow crack growth of ceramics. To improve these properties through mechanistically informed grain boundary engineering, precise measurement of the mechanical properties of individual boundaries is essential, although this is rarely achieved due to its complexity. Here we present a new approach to characterise the fracture energy at the lengthscale of individual grain boundaries and demonstrate this capability with measurement of the surface energy of silicon carbide (SiC) single crystals. We perform experiments using an in situscanning electron microscopy based double cantilever beam test, thus enabling viewing and measurement of stable crack growth directly. These experiments correlate well with our density functional theory (DFT) calculations of the surface energy of the same SiC plane. Subsequently, we measure the fracture energy for a bi-crystal of SiC, diffusion bonded with a thin glassy layer. These measurements ultimately promote microstructural engineering of novel and advanced ceramics.

Journal article

Jing Y, Su D, Yue X, Britton T, Jiang Jet al., 2017, The development of high strength brazing technique for Ti-6Al-4V using TiZrCuNi amorphous filler, Materials Characterization, Vol: 131, Pages: 526-531, ISSN: 1044-5803

The brazing joint of the Ti-6Al-4V alloy was produced with a designed brazing filler alloy and the optimized brazing temperature which is lower than the β-phase transformation of the matrix. The strength and the ductility of brazing joined Ti-6Al-4V samples were evaluated by conventional tensile tests with a DIC 2D–strain field measurement. The Widmanstätten microstructure with no voids or cracks or intermetallic compounds was found throughout the joint with a width of β-lamellar as ~ 1 μm. Due to the fine acicular α-Widmanstätten and β-lamellar, and the uniformly diffused filler elements throughout the entire joint, the strength of the joint was as much as the matrix. In addition, the hardness test results agreed well with the tensile strength tests. All fractures occurred in the matrix rather than the brazing joints. Furthermore, the maximum local tensile strain was measured as 20% in the matrix, while under the same stress, the brazing joint only reached 6.3% tensile plastic strain. Thus, the mechanical properties of the joint with the associated microstructure demonstrated that a successful brazing filler alloy has been developed for the Ti-6Al-4V alloy.

Journal article

Knowles AJ, Jun T-S, Bhowmik A, Jones NG, Giuliani F, Britton TB, Stone HJ, Dye Det al., 2017, A new beta titanium alloy system reinforced with superlattice intermetallic precipitates, Scripta Materialia, Vol: 140, Pages: 71-75, ISSN: 1872-8456

Titanium alloys traditionally lack a nm-scale intermetallic precipitate that can be exploited for age-hardening from solid solution. Here such a strengthening concept is developed in the Ti-Fe-Mo system, with it being found that a high temperature β (bcc A2) single-phase field for homogenisation can be obtained, which following ageing (750 °C/80 h) precipitated B2 TiFe <100 nm in size. The orientation relationship was found to be ⟨100⟩A2//⟨100⟩B2, {100}A2//{100}B2, with a misfit of −6.1%. The alloy was found to be very hard (HV0.5 = 6.4 GPa) and strong (σy, 0.2 = 1.9 GPa) with a density of 6.68 g cm−3. TEM observation and micropillar deformation showed that the precipitates resist dislocation cutting.

Journal article

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