Publications
130 results found
Jiang J, Yang J, Zhang T, et al., 2015, On the mechanistic basis of fatigue crack nucleation in Ni superalloy containing inclusions using high resolution electron backscatter diffraction, Acta Materialia, Vol: 97, Pages: 367-379, ISSN: 1873-2453
A series of interrupted three-point bend low-cycle fatigue tests were carried out on a powder metallurgy FHG96 nickel superalloy sample containing non-metallic inclusions. High resolution electron backscatter diffraction (HR-EBSD) was used to characterise the distribution and evolution of geometrically necessary dislocation (GND) density, residual stress and total dislocation density near a non-metallic inclusion. A systematic study of room temperature cyclic deformation is presented in which slip localisation, cyclic hardening, ratcheting and stabilisation occur, through to crack formation and microstructurally-sensitive propagation. Particular focus is brought to bear at the inclusion–matrix interface. Complex inhomogeneous deformation structures were directly observed from the first few loading cycles, and these structures were found not to vary significantly with increasing number of cycles. A clear link was observed between crack nucleation site and microstructurally-sensitive growth path and the spatially-resolved sites of extreme values of residual stress and GND density.
Zhang T, Jiang J, Shollock BA, et al., 2015, Slip localization and fatigue crack nucleation near a non-metallic inclusion in polycrystalline nickel-based superalloy, Materials Science and Engineering A: Structural Materials: Properties, Microstructure and Processing, Vol: 641, Pages: 328-339, ISSN: 1873-4936
Fatigue crack nucleation at a non-metallic agglomerate inclusion has been studied by high spatial resolution Digital Image Correlation (HR-DIC) and high angular resolution Electron Backscatter Diffraction (HR-EBSD). Spatial and temporal characterization and correlation of deformation with underlying microstructures has been performed, with distributions of plastic strain measured from HR-DIC; and residual stress and density of geometrically necessary dislocations (GND) measured from HR-EBSD. Initial residual stress and GND fields, as a consequence of differing thermal expansivities in the metallic and oxide phases, localized around the agglomerate have been quantified using HR-EBSD. The localization of the pre-existing stress and dislocation states appear to lead to early onset of plasticity upon subsequent mechanical loading. Heterogeneous distributions of plastic strain have been observed in the course of the fatigue test by HR-DIC. Crack nucleation via agglomerate/nickel interface decohesion and particle fracture has been demonstrated and this is correlated with the elevation in strain and dislocation density. The measurements of residual stress, strain, and dislocation density provide key information for the mechanisms of fatigue cracking and the development of damage nucleation criteria in these material systems.
Guo Y, Collins DM, Tarleton E, et al., 2015, Measurements of stress fields near a grain boundary: exploring blocked arrays of dislocations in 3D, Acta Materialia, Vol: 96, Pages: 229-236, ISSN: 1873-2453
The interaction between dislocation pile-ups and grain boundaries gives rise to heterogeneous stress distributions when a structural metal is subjected to mechanical loading. Such stress heterogeneity leads to preferential sites for damage nucleation and therefore is intrinsically linked to the strength and ductility of polycrystalline metals. To date the majority of conclusions have been drawn from 2D experimental investigations at the sample surface, allowing only incomplete observations. Our purpose here is to significantly advance the understanding of such problems by providing quantitative measurements of the effects of dislocation pile up and grain boundary interactions in 3D. This is accomplished through the application of differential aperture X-ray Laue micro-diffraction (DAXM) and high angular resolution electron backscatter diffraction (HR-EBSD) techniques. Our analysis demonstrates a similar strain characterization capability between DAXM and HR-EBSD and the variation of stress intensity in 3D reveals that different parts of the same grain boundary may have different strengths in resisting slip transfer, likely due to the local grain boundary curvature.
Jiang J, Ben Britton T, Wilkinson AJ, 2015, The orientation and strain dependence of dislocation structure evolution in monotonically deformed polycrystalline copper, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 69, Pages: 102-117, ISSN: 0749-6419
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- Citations: 72
Britton TB, Dunne FP, Wilkinson AJ, 2015, On The Mechanistic Basis of Deformation at the Microscale in Hexagonal Close Packed Metals, Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 471, ISSN: 1471-2946
This is an overview of micromechanical deformation mechanisms in hexagonal close-packed metals. We start with an in-depth discussion of single-crystal behaviour concerning crystallographic slip, plastic anisotropy and deformation twinning. We move on to discuss some complexities involved in polycrystalline deformation and modelling approaches, focusing on rate effects in titanium alloys that are thought to play a significant role in dwell fatigue. We finish our review with a brief commentary on current understanding and state-of-the-art techniques, and outline some key areas where further study is recommended.
Jiang J, Britton TB, Wilkinson AJ, 2015, Evolution of intragranular stresses and dislocation densities during cyclic deformation of polycrystalline copper, Acta Materialia, Vol: 94, Pages: 193-204, ISSN: 1873-2453
Tong V, Jiang J, Wilkinson AJ, et al., 2015, The effect of pattern overlap on the accuracy of high resolution electron backscatter diffraction measurements, Ultramicroscopy, Vol: 155, Pages: 62-73, ISSN: 0304-3991
High resolution, cross-correlation-based, electron backscatter diffraction (EBSD) measures the variation of elastic strains and lattice rotations from a reference state. Regions near grain boundaries are often of interest but overlap of patterns from the two grains could reduce accuracy of the cross-correlation analysis. To explore this concern, patterns from the interior of two grains have been mixed to simulate the interaction volume crossing a grain boundary so that the effect on the accuracy of the cross correlation results can be tested. It was found that the accuracy of HR-EBSD strain measurements performed in a FEG-SEM on zirconium remains good until the incident beam is less than 18 nm from a grain boundary. A simulated microstructure was used to measure how often pattern overlap occurs at any given EBSD step size, and a simple relation was found linking the probability of overlap with step size.
Weekes HE, Vorontsov VA, Dolbnya IP, et al., 2015, In situ micropillar deformation of hydrides in Zircaloy-4, Acta Materialia, Vol: 92, Pages: 81-96, ISSN: 1873-2453
Deformation of hydrided Zircaloy-4 has been examined using in situ loading of hydrided micropillars in the scanning electron microscope and using synchrotron X-ray Laue microbeam diffraction. Results suggest that both the matrix and hydride can co-deform, with storage of deformation defects observed within the hydrides, which were twinned. Hydrides placed at the plane of maximum shear stress showed deformation within the hydride packet, whilst packets in other pillars arrested the propagation of shear bands. X-ray Laue peak broadening, prior to deformation, was associated with the precipitation of hydrides, and during deformation plastic rotation and broadening of both the matrix and hydride peaks were observed. Post-mortem TEM of the deformed pillars has indicated a greater density of dislocations associated with the precipitated hydride packets, while the observed broadening of the hydride electron diffraction spots further suggests that plastic strain gradients were induced in the hydrides by compression.
Xian JW, Belyakov SA, Britton TB, et al., 2015, Heterogeneous nucleation of Cu<sub>6</sub>Sn<sub>5</sub> in Sn-Cu-Al solders, JOURNAL OF ALLOYS AND COMPOUNDS, Vol: 619, Pages: 345-355, ISSN: 0925-8388
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- Citations: 46
Xian JW, Belyakov SA, Britton TB, et al., 2015, Heterogeneous Nucleation of Bulk Cu<sub>6</sub>Sn<sub>5</sub> in Sn-Ag-Cu-Al and Sn-Cu-Al Solders, IEEE 65th Electronic Components and Technology Conference (ECTC), Publisher: IEEE, Pages: 2241-2247, ISSN: 0569-5503
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- Citations: 1
Wilkinson AJ, Tarleton E, Vilalta-Clemente A, et al., 2014, Measurement of probability distributions for internal stresses in dislocated crystals, APPLIED PHYSICS LETTERS, Vol: 105, ISSN: 0003-6951
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- Citations: 28
Speller SC, Dudin P, Fitzgerald S, et al., 2014, High-resolution characterization of microstructural evolution in Rb<i><sub>x</sub></i>Fe<sub>2-<i>y</i></sub>Se<sub>2</sub> crystals on annealing, PHYSICAL REVIEW B, Vol: 90, ISSN: 2469-9950
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- Citations: 18
Armstrong DEJ, Britton TB, 2014, Effect of dislocation density on improved radiation hardening resistance of nano-structured tungsten–rhenium, Materials Science and Engineering A - Structural Materials Properties Microstructure and Processing, Vol: 611, Pages: 388-393, ISSN: 0921-5093
Rolled tungsten 5 wt% rhenium sheet has been annealed to produce two microstructures. As received with a high dislocation density, measured using HR-EBSD, and pancake shaped grains with a thickness of ≈200 nm and annealed with equiaxed grains with average grain size of ≈90 µm and low dislocation density. Both materials were ion implanted with 2 MeV W+ ions to damage levels of 0.07, 0.4, 1.2 and 13 displacements per atom (dpa). Nanoindentation was used to measure change in hardness after implantations. While irradiation induced hardening is seen to saturate in the as received material at an increase of 0.4 GPa at 0.4 dpa, the relative hardness change is over four time higher in the annealed material (1.3 GPa) and saturation does not occur by 13 dpa. These differences in radiation response are due to the increased sinks for damage in the as received microstructure in the form of dislocation networks. This is advantageous for use of such nanostructured tungsten sheet in composite materials for structural applications as they will have improved radiation resistance as compared to bulk tungsten products. As well as showing the danger of using idealized microstructures for radiation damage studies.
Guo Y, Britton TB, Wilkinson AJ, 2014, Slip band-grain boundary interactions in commercial-purity titanium, Acta Materialia, Vol: 76, Pages: 1-12, ISSN: 1873-2453
The interaction between slip bands and grain boundaries in commercial-purity titanium was examined using cross-correlation-based electron backscatter diffraction. At a low strain level, three types of interactions were observed: blocked slip band with stress concentration; slip transfer; and blocked slip band with no stress concentration. The stress concentration induced by the blocked slip band was fitted with Eshelby’s theoretical model, from which a Hall–Petch coefficient was deduced. It was found that the Hall–Petch coefficient varies with the individual grain boundary. We investigated the geometric alignment between the slip band and various slip systems to the neighbouring grain. Stress concentration can be induced by the blocked slip band if the slip system is poorly aligned with 〈a〉 prismatic, pyramidal or basal slip systems in the neighbouring grain. Transfer of slip across the boundary occurs when there is good alignment on 〈a〉 prismatic or 〈a〉 pyramidal slip systems. Other stress-relieving mechanisms are possible when the best alignment is not with the slip system that has the lower critical resolved shear stress.
Rugg D, Britton TB, Gong J, et al., 2014, In-service materials support for safety critical applications - A case study of a high strength Ti-alloy using advanced experimental and modelling techniques, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 599, Pages: 166-173, ISSN: 0921-5093
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- Citations: 23
Wilkinson AJ, Britton TB, Jiang J, et al., 2014, A review of advances and challenges in EBSD strain mapping, 13th European Workshop of the European-Microbeam-Analysis-Society on Modern Developments and Applications in Microbeam Analysis (EMAS), Publisher: IOP PUBLISHING LTD, ISSN: 1757-8981
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- Citations: 37
Britton TB, Jiang J, Clough R, et al., 2013, Assessing the precision of strain measurements using electron backscatter diffraction - Part 2: Experimental demonstration, ULTRAMICROSCOPY, Vol: 135, Pages: 136-141, ISSN: 0304-3991
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- Citations: 17
Britton TB, Jiang J, Clough R, et al., 2013, Assessing the precision of strain measurements using electron backscatter diffraction - part 1: Detector assessment, ULTRAMICROSCOPY, Vol: 135, Pages: 126-135, ISSN: 0304-3991
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- Citations: 32
Jiang J, Britton TB, Wilkinson AJ, 2013, Evolution of dislocation density distributions in copper during tensile deformation, ACTA MATERIALIA, Vol: 61, Pages: 7227-7239, ISSN: 1359-6454
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- Citations: 199
Ben Britton T, Jiang J, Karamched PS, et al., 2013, Probing Deformation and Revealing Microstructural Mechanisms with Cross-Correlation-Based, High-Resolution Electron Backscatter Diffraction, JOM, Vol: 65, Pages: 1245-1253, ISSN: 1047-4838
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- Citations: 21
Jiang J, Britton TB, Wilkinson AJ, 2013, Mapping type III intragranular residual stress distributions in deformed copper polycrystals, ACTA MATERIALIA, Vol: 61, Pages: 5895-5904, ISSN: 1359-6454
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- Citations: 40
Wilkinson AJ, Moldovan G, Britton TB, et al., 2013, Direct Detection of Electron Backscatter Diffraction Patterns, PHYSICAL REVIEW LETTERS, Vol: 111, ISSN: 0031-9007
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- Citations: 37
Britton TB, Holton I, Meaden G, et al., 2013, High angular resolution electron backscatter diffraction: measurement of strain in functional and structural materials, Microscopy and Analysis, Vol: 27
The performance of crystalline materials is dominated by the nature of elastic strains and defects. The interaction of stress fields and defects, such as dislocations, and microstructure at the meso-scale isof significant importance. We discuss and explore applications of the high angular resolution electron backscatter (HR-EBSD) technique, which is capable of resolving elastic strains and defect populations withhigh fidelity and high spatial resolution, which enables us to probe the behaviour of materials and link structure to properties. Our examples span the realms of functional and structural materials, including silicon,germanium and titanium.
Jiang J, Britton TB, Wilkinson AJ, 2013, Measurement of geometrically necessary dislocation density with high resolution electron backscatter diffraction: Effects of detector binning and step size, ULTRAMICROSCOPY, Vol: 125, Pages: 1-9, ISSN: 0304-3991
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- Citations: 195
Murdock AT, Koos A, Ben Britton T, et al., 2013, Controlling the Orientation, Edge Geometry, and Thickness of Chemical Vapor Deposition Graphene, ACS NANO, Vol: 7, Pages: 1351-1359, ISSN: 1936-0851
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- Citations: 164
Britton TB, Wilkinson AJ, 2012, Stress fields and geometrically necessary dislocation density distributions near the head of a blocked slip band, ACTA MATERIALIA, Vol: 60, Pages: 5773-5782, ISSN: 1359-6454
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- Citations: 152
Speller SC, Britton TB, Hughes GM, et al., 2012, Microstructural analysis of phase separation in iron chalcogenide superconductors, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, Vol: 25, ISSN: 0953-2048
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- Citations: 48
Britton TB, Wilkinson AJ, 2012, High resolution electron backscatter diffraction measurements of elastic strain variations in the presence of larger lattice rotations, ULTRAMICROSCOPY, Vol: 114, Pages: 82-95, ISSN: 0304-3991
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- Citations: 136
Seal JR, Britton TB, Wilkinson AJ, et al., 2012, Characterizing Slip Transfer In Commercially Pure Titanium Using High Resolution Electron Backscatter Diffraction (HR-EBSD) and Electron Channeling Contrast Imaging (ECCI), Microscopy and Microanalysis, Vol: 18, Pages: 702-703, ISSN: 1431-9276
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- Citations: 7
Britton TB, Wilkinson AJ, 2012, Strains, Planes and EBSD in Materials Science, Materials Today, Vol: 15, Pages: 366-376
Electron back scatter diffraction (EBSD) has made an impressive impact on the characterization of materials by directly linking microstructure and crystallographic texture to provide very rich and quantitative datasets which in many instances have forced us to rethink how microstructure should be defined and analyzed. In this article we try to first give a very basic idea of how an EBSD map is obtained and what the data produced is like. We then give a brief history detailing some of the more major steps in developing the technique to what it is today. Finally, we explore two advanced and exciting technique areas of strain mapping and 3D microscopy and demonstrate how the EBSD technique continues to evolve to tackle new applications and bolster our materials characterization toolbox.
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