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Oxford Micromechanics Group

The Oxford Micromechanics Group are interested in how materials (engineered and naturally occurring) respond, at the microstructural level, to externally applied loading - mechanical, thermal, and/or environmental (chemical, irradiation).  The complex patterning of local stress and strain distributions and how they evolve, and are linked to particular aspects of the microstructure, provides many fascinating intellectual challenges.  Technical impact comes from building sound understanding and models of how materials fail.  This is central to setting safe performance windows, and developing new alloys and microstructures with greater capability.
Our centre of mass is in the Department of Materials, but we also span across to the Department of Engineering Science and Department of Earth Science.  We work on a range of materials systems including those for nuclear, aerospace, and automotive sectors, as well minerals.  We also have made significant contributions to development of new testing and characterisation methods allowing us to gain new insights. 

Papers & Pre-prints

  • Tension-compression asymmetry of slip in Ti-6Al

    Roberts, W, Gong, J, Wilkinson, AJ, Tarleton, E
    2020
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    Journal article
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    SCRIPTA MATERIALIA
    < c plus a > slip, Ti-6Al, Tension compression asymmetry, Crystal plasticity, CRSS

  • On the assessment of creep damage evolution in nickel-based superalloys through correlative HR-EBSD and cECCI studies

    Sulzer, S, Li, Z, Zaefferer, S, Hafez Haghighat, SM, Wilkinson, A, Raabe, D, Reed, R
    2020
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    Journal article
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    Acta Materialia
    © 2019 The evolution of dislocation density with creep strain in single-crystal superalloys is studied quantitatively using high-resolution electron backscatter diffraction (HR-EBSD) and electron channelling contrast imaging under controlled diffraction conditions (cECCI). Data regarding dislocation density/structure is measured for deformation at 900 °C and 450 MPa up to ≈ 1% plastic strain. Effects of chemical composition are elucidated via three purpose-designed superalloys of differing rhenium and ruthenium contents. The evidence indicates that dislocation avalanching is already prevalent at plastic strains of ≈ 0.1%; thereafter, an exponential decay in the dislocation multiplication rate is indicative of self-hardening due to dislocation constriction within the matrix channels, as confirmed by the imaging. The results are rationalised using discrete dislocation dynamics modelling: a universal dislocation evolution law emerges, which will be useful for alloy design efforts.

  • Dislocation density distribution at slip band-grain boundary intersections

    Guo, Y, Collins, DM, Tarleton, E, Hofmann, F, Wilkinson, AJ, Ben Britton, T
    2020
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    Journal article
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    ACTA MATERIALIA
    High-energy X-ray diffraction, Slip transmission, Geometrically necessary dislocations, Disconnections, Grain boundary ledge

  • Surface Evolution of Lithium Titanate upon Electrochemical Cycling Using a Combination of Surface Specific Characterization Techniques

    Rikarte, J, Acebedo, B, Vilalta-Clemente, A, Bonilla, F, Wilkinson, AJ, Galceran, M, Lousa, A, Rubio-Zuazo, J, Muñoz-Márquez, MÁ
    2020
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    Journal article
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    Advanced Materials Interfaces
    © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Among the electrodes for Li-ion batteries, Li4Ti5O12 (LTO) stands out as anode owing to its stability and safety, in part ascribed to its low surface reactivity. However, the overlayer formation on the LTO surface upon electrochemical cycling is reported in recent years; a rough surface layer of electrochemically inactive α-Li2TiO3 on top of the LTO (111) surface is suggested on the grounds of scanning probe techniques and theoretical ab initio calculations which would negatively strike on the battery performance. Hence the investigation of the LTO surface evolution is key to achieve more stable and safer Li-ion batteries. LTO (111) thin film electrodes are used as model system where a variety of surface specific characterization techniques are applied to unveil the surface behavior of LTO in Li-ion batteries. In contrast with previous studies, with the help of high-resolution transmission electron microscopy and synchrotron-based surface X-ray diffraction, α-Li2TiO3 is found to be a surface preparation product. Of special importance is the use of high-resolution electron backscatter diffraction to report an increase on the LTO surface strain upon electrochemical cycling which can have a critical effect in long cycling performance of LTO that is always considered a zero-strain material.
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