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Angus Wilkinson

Professor Angus Wilkinson
Joint Head of Department, Professor of Materials

Department of Materials
University of Oxford
16 Parks Road
Oxford OX1 3PH

Tel: +44 1865 273737 (HoD Office)
Tel: +44 1865 273792 (Room 110.20.04)
Tel: +44 1865 273777 (reception)
Fax: +44 1865 273764

Micromechanics Group Website

Summary of Interests

My group is concerned with the mechanical behaviour of materials, mostly metals and alloys, at the microstructural level. We are at the forefront of developing the SEM based EBSD technique for mapping stress distributions at high spatial resolution. Other techniques used extensively within the group are nano-indentation, micro-cantilever bend testing and micro-pillar compression testing, digital image correlation and dislocation-based modelling. We aim to help improve mechanistic understanding of deformation, fracture and fatigue processes in metals and alloys. Currently we are working on Ti, Cu, Ni, Fe-Cr and W based alloys.

Current Research Projects

High Resolution EBSD - Mapping Strain, Lattice Rotation and Dislocation Density
Prof Angus J Wilkinson, Dr Phani Karamched, Tomohito Tanaka
We are continuing to develop the cross-correlation based analysis of electron back scatter diffraction (EBSD) patterns that was pioneered by the group for mapping elastic strain tensors at high spatial resolution. Current interests are (i) overcoming the ‘reference pattern problem’, by using pattern simulations, (ii) improving the calibration of detector geometry and optical distortions, and, (iii) increasing spatial resolution by moving to TKD geometries. The method is being applied to a wide range of materials systems including internal stresses in metals (particularly current focus on martensitic steel), semiconductors (III-V nitrides) and geological materials (olivine).  

Micromechanical Testing of Ti Alloys
Dr J Gong, Dr A. J. Wilkinson
We are using FIB to cut micron scale cantilevers in polycrystalline Ti alloy samples. The cantilevers are then tested in bending using a nanoindenter. The load-displacement data is analysed using crystal plasticity finite element simulations to extract elastic constants (Young’s modulus) and plastic flow properties (critical resolved shear stress). We are examining the effects of alloying additions and the presence of beta phase on the CRSS of the various slip systems in near alpha alloys. We are also investigating the effects of individual grain boundaries on plastic deformation. (Funded by EPSRC with support from Rolls Royce)

Fundamentals of cyclic deformation and fatigue crack initiation
Prof Angus J Wilkinson, Dr Jicheng Gong, Arutyun Arutyunyan, Christopher Magazzeni
Fatigue is a pervasive failure mode that threatens structural integrity in many industrial sectors.  In polycrystals grain-grain interactions lead to inter- and intra-granular inhomogeneity in the dislocation density and residual stress distributions. Characterising the evolution of this patterning during cycling is key to understanding strain localisation and subsequent crack initiation.  We have developed ultrasonic based fatigue testing of miniaturised samples allowing accelerated testing out to the gigacycle regime with optical microscopy monitoring of the entire stressed region.  We are using this to (i) explore both fundamental aspects of crack initiation and short fatigue crack growth in Ti alloys, and (ii) probe fatigue lives in locally modified microstructures near linear friction welds in Ti alloys.  Results will be used to guide development of crystal plasticity models and fatigue indicator parameters.

Local stress fields and deformation generated by twinning and martensitic phase transformation
Dr A. J. Wilkinson
Deformation twinning makes a sizeable contribution to the plastic deformation of many bcc and hcp metals and alloys.  The twinning shear strain is often very large, and consequently leads to very high, but localised, stresses within the surrounding matrix.  Further plastic flow through dislocation motion can occur in the matrix so as to relax the high stresses and accommodate some of the twinning strain. Furthermore deformation twinning is often cited as a mechanicsm leading to fracture initiation.  Martensitic phase transformations have some similarity with deformation twinning though hydrostatic strains can be caused in addition to shearing.  In this project the new cross-correlation based EBSD method will be used to map elastic strains (ie stresses) and lattice rotations around deformation twins and martensite laths.  The following interactions will be studied: twin-grain boundary, twin-dislocation slip, twin-crack and twin-twin.  The project will concentrate on fundamental aspect of these processes using various model material systems.

Micromechanical testing
Dr David E.J. Armstrong, Dr Jicheng Gong, Prof Angus J. Wilkinson
The project develops new methods of testing mechanical properties at the micron scale, using a combination of focussed ion beam machining (to produce specimens) and atomic force microscopy / nanoindentation (to test them). The methods are applied to testing thin films, ion-irradiated layers, interfaces and properties of individual grains and grain boundaries in alloys. A newly-commissioned machine will enable tests to be perfomed in the temperature range -50 to +750C. Supported by EPSRC and CCFE Culham (Junior Research Fellowship at St Edmund Hall: D. Armstrong)

Brittle-ductile transitions in BCC metals for fusion power applications
Dr D.E.J. Armstrong, Dr. E. Tarleton, Professor S.G. Roberts, Dr. A.J. Wilkinson, Professor S.L. Dudarev*
The project investigates the brittle-to-ductile transition in tungsten and iron-chromium alloys up to 12%Cr (all these metals are the basis for proposed fusion power plant alloys). Pre-cracked miniature bend specimens of single crystals and polycrystalline materials are fracture tested in the temperature range 77 - 450K. The effect of dislocation motion around the crack tips on fracture stress is examined, and modelled using dynamic-dislocation simulations. Funded by EPSRC and CCFE. (*EURATOM/CCFE)

6 public active projects

Research Publications


?a? Prismatic, ?a? basal, and ?c+a? slip strengths of commercially pure Zr by micro-cantilever tests
J Gong, TB Britton, MA Cuddihy, FPE Dunne, AJ Wilkinson
Acta Materialia (2015) vol. 96, 249-257

Measurements of stress fields near a grain boundary: Exploring blocked arrays of dislocations in 3D
Y Guo, DM Collins, E Tarleton, F Hofmann, J Tischler, W Liu, R Xu, AJ Wilkinson, TB Britton
Acta Materialia (2015) vol. 96, 229-236

On the mechanistic basis of deformation at the microscale in hexagonal close-packed metals
TB Britton, FPE Dunne, AJ Wilkinson
Proceedings of the Royal Society A (2015) vol. 471, 20140881

Evolution of intragranular stresses and dislocation densities during cyclic deformation of polycrystalline copper
J Jiang, TB Britton, AJ Wilkinson
Acta Materialia (2015) vol. 94, 193-204

The effect of pattern overlap on the accuracy of high resolution electron backscatter diffraction measurements
V Tong, , J Jiang, AJ Wilkinson, TB Britton
Ultramicroscopy (2015) vol. 155, 62-73

Using transmission Kikuchi diffraction to study intergranular stress corrosion cracking in type 316 stainless steels
M Meisnar, A Vilalta-Clemente, A Gholinia, Michael Moody, AJ Wilkinson, N Huin, S Lozano-Perez
Micron (2015) vol. 75, 1-10

The orientation and strain dependence of dislocation structure evolution in monotonically deformed polycrystalline copper
J Jiang, TB Britton and AJ Wilkinson
International Journal of Plasticity (2015) vol. 69, 102-117

A synchrotron X-ray diffraction study of in situ biaxial deformation
DM Collins, M Mostafavi, RI Todd, T Connolley and AJ Wilkinson
Acta Materialia (2015) vol. 90, 46-58

A discrete dislocation plasticity study of the micro-cantilever size effect
E Tarleton, DS Balint, J Gong, and AJ Wilkinson
Acta Materialia (2015) vol. 88, 271-282



Measurement of probability distributions for internal stresses in dislocated crystals
AJ Wilkinson, E Tarleton, A Vilalta-Clemente, J Jiang, TB Britton, and DM Collins
Applied Physics Letters (2014) vol. 105, 181907

?c + a? Dislocations in deformed Ti–6Al–4V micro-cantilevers
R Ding, J Gong, AJ Wilkinson, IP Jones
Acta Materialia (2014) vol. 76 127-134

Slip band–grain boundary interactions in commercial-purity titanium
Y Guo, TB Britton and AJ Wilkinson
Acta Materialia (2014) vol. 76 1-12

Simulation of deformation twins and their interactions with cracks
A Stoll and AJ Wilkinson
Computational Materials Science (2014) vol. 89 224-232

In-service materials support for safety critical applications – a case study of a high strength Ti-alloy using advanced experimental and modelling techniques
D Rugg, TB Britton, J Gong, AJ Wilkinson, PAJ Bagot
Materials Science and Engineering A (2014), vol. 559 166-173

Electron Channeling Contrast Imaging of Defects in III-Nitride Semiconductors
C Trager-Cowan et al
Microscopy and Microanalysis (2014) vol. 20 1024-1025

Comparison of Techniques for Strain Measurements in CuInSe2 Absorber Layers of Thin-film Solar Cells
N Schäfer et al
Microscopy and Microanalysis (2014) vol. 20 1464-1465

A review of advances and challenges in EBSD strain mapping
AJ Wilkinson, TB Britton, J Jiang and PS Karamched
IOP Conf. Ser.: Mater. Sci. Eng. (2014) vol. 55 012020



Evolution of dislocation density distributions in copper during tensile deformation
J Jiang, TB Britton, AJ Wilkinson
Acta Materialia (2013), vol. 61, 7227–7239

Assessing the precision of strain measurements using electron backscatter diffraction - Part 1: Detector assessment
TB Britton, J Jiang, R Clough, E Tarleton, AI Kirkland, AJ Wilkinson
Ultramicroscopy (2013) vol. 135, 126–135

Assessing the precision of strain measurements using electron backscatter diffraction - Part 2: Experimental Demonstration
TB Britton, J Jiang, R Clough, E Tarleton, AI Kirkland, AJ Wilkinson
Ultramicroscopy (2013) vol. 135, 136-141

Probing Deformation and Revealing Microstructural Mechanisms with Cross-Correlation-Based, High-Resolution Electron Backscatter Diffraction
TB Briton, J Jiang, PS Karamched, AJ Wilkinson
JOM (2013) vol. 65, 1245-1253

Electron Backscatter Diffraction: An Important Tool for Analyses of Structure–Property Relationships in Thin-Film Solar Cells
D Abou-Ras, J Kavalakkatt, M Nichterwitz, N Schäfer, S Harndt, AJ Wilkinson, K Tsyrulin, H Schulz, F Bauer
JOM (2013) vol. 65, 1222-1228

Mapping type III intragranular residual stress distributions in deformed copper polycrystals
J Jiang, TB Briton, AJ Wilkinson
Acta Materialia (2013), vol. 61, 5895–5904

Direct detection of electron backscatter diffraction patterns
AJ Wilkinson, G Moldovan, TB Britton, A Bewick, R Clough, and AI Kirkland
Physical Review Lettters (2013), vol. 111, 065506 

Effect of sliding speed and counterface properties on the tribo-oxidation of brush seal material under dry sliding conditions
MR Thakare, JF Mason, AK Owen, DRH Gillespie, AJ Wilkinson, G Franceschini
Tribology International (2013) available online 18 February 2013

Controlling the Orientation, Edge Geometry and Thickness of Chemical Vapor Depostion Graphene
AT Murdock, A Koos, TB Britton, L Houben, T Batten, T Zhang, AJ Wilkinson, RE Dunin-Borkowski, CE Lekka, N Grobert
ACS Nano, (2013), vol. 7 ,1351–1359

Measurement of geometrically necessary dislocation density with high resolution electron backscatter diffraction: Effects of detector binning and step size
J Jiang, TB Britton and AJ Wilkinson
Ultramicroscopy, (2013), vol. 125, 1-9


click here for full list of publications


Projects Available

Advanced Diffraction Analysis in the SEM (EBSD and ECCI)
Prof Angus J Wilkinson

Electron back scatter diffraction (EBSD) is now a ubiquitous tool for the characterisation of crystalline materials (grain orientations, phase identification, strain mapping).  Electron channelling contrast imaging (ECCI) on the other hand is a method for imaging and characterising lattice defects (dislocations, stacking faults) that has slowly reached a level where it is now robust and reliable in producing impressive defect images.  
This project will continue our development of these methods and exploitation of the synergies between them by combining ECCI images of indivual defects with quantification of the resulting stress fields by HR-EBSD.  The availability of good pattern and image simulations based on dynamical diffraction theory, and the possibility of advanced direct electron detection systems opens up new possibilities opportunities.  

Also see homepages: Angus Wilkinson

Grain Boundary Sliding and Superplasticity
Prof Angus J Wilkinson and Prof Richard I Todd

Grain boundary sliding is an important deformation mechanism in the creep and superplastic regimes.  It is clear that sliding happens more readily on some boundaries than others but the links between grain boundary character and resistance to sliding have not been established.  In polycrystals grain boundary sliding is generally thought to be accompanied by other accommodation processes such as diffusion, or dislocation mediated plasticity. 
This project will use state of the art micro-mechanical testing methods to probe properties of individual grain boundaries isolated in FIB-machined micron scale test pieces.  This uncouples grain boundary sliding from other accommodation processes and through testing many boundaries will link behaviour to structural characteristics of the boundaries.  Similarly, diffusional creep processes may be studied on isolated boundaries under well-controlled stress gradients.  The work on individual grain boundaries will be augmented by experiments on bulk polycrystalline samples.  In particular, we would build on initial success in using diffraction contrast tomography to follow in 3-D and in the interior of polycrystals during superplastic flow the relative motion and neighbour grain switching events that must occur.

Also see homepages: Richard Todd Angus Wilkinson

Strains Induced by Hydride Formation in Zirconium
Prof Angus J Wilkinson, Dr Ed Tarleton, and Dr David E J Armstrong

In service temperature cycling of nuclear fuel cladding can lead to repeated sequences of precipitation and dissolution of hydrides in zirconium based alloys. During the transformation from hydrogen in solid solution to the hydride phase there is a considerable volume expansion. This project will explore the links between nucleation sites, hysteresis between temperatures for precipitation and dissolution, the stress field and local plasticity induced by the transformation strain and the precipitation morphology. The following techniques will be used: high resolution EBSD, digital image correlation of SEM images, in situ thermal cycling, finite element based-crystal plasticity simulations. This project will be carried out in close conjunction with Rolls Royce and other partner Universities within the HexMat flagship EPSRC programme (

Also see homepages: Edmund Tarleton Angus Wilkinson

Dislocation based modelling of engineering alloys
E Tarleton and Prof A J Wilkinson

You will be part of a small dynamic team developing state of the art computational models which are used to simulate a range of micro mechanical tests and microscopy data. This project focuses on simulating delayed hydride cracking in Zr alloys as used in compact nuclear reactors for submarine propulsion. You will simulate the coupled mechanical/hydrogen diffusion process within a discrete dislocation plasticity framework. This will involve developing a FEM code to solve the H diffusion equation, and coupling this with a discrete dislocation plasticity code to simulate dislocation-hydrogen interactions. The majority of the coding will be in Matlab, with the opportunity to learn and use C and CUDA to accelerate the code.

The project will link to experimental work within the wider Materials for Fusion and Fission Power group and may involve interaction with Rolls Royce (Marine).


Also see homepages: Edmund Tarleton Angus Wilkinson

Understanding High Temperature Small Scale Mechanical Performance of Materials for Nuclear Fusion
Dr D.E.J. Armstrong, Dr E. Tarleton, Professor A.J. Wilkinson,

Future nuclear power systems, both fission and fusion, rely on the development of materials which can withstand some of the most extreme engineering environments. These include temperatures up to 1500oC, high fluxes of high energy neutrons and effects of gaseous elements produced by transmutation and implantation from the plasmas. Due to efforts to minimise the production of nuclear waste by such reactors the elements which may be used in structural components is limited and in many cases there is a lack of understanding of the basic deformation processes occur in ether pure materials or alloys and importantly how these are affected by temperature, radiation damage and gas content. This project will build upon the expertise in the MFFP and Micromechanics groups on high temperature mechanical testing at the micro and nano-scale. Facilities include two high temperature nanoindenters (-50oC to 950oC), high temperature microhardness (RT to 1500oC) and dedicated FIB-SEM and FEG-SEM with EBSD as well as state of the art computer codes for strain gradient crystal plasticity finite element modelling and discrete dislocation plasticity modelling. Both nanoindentation, micro-compression and micro-bend experiments will be used to study plastic deformation, fracture and creep in a range of novel high temperature materials (likely Fe, SiC or Zr based) with potential for use in future fusion reactors. HR-EBSD and AFM will be used to study deformation structures produced during testing and to inform strain gradient crystal plasticity finite element and discrete dislocation models. This will allow for a fuller understanding of the underlying physics of deformation in these materials both before and after irradiation or gas implantation. Strong links will be made to activities within the Culham Centre for Fusion Energy.

Also see homepages: David Armstrong Edmund Tarleton Angus Wilkinson

Also see a full listing of New projects available within the Department of Materials.