Experimental Techniques


Our group use a wide range of experimental techniques, a few of which we have been developing within the team which are listed here.

Developing research techniques:

Ni-EBSD-Pattern
Example diffraction pattern from a Ni-Superalloy

High angular resolution electron backscatter diffraction (HR-EBSD)

Conventional EBSD compares diffraction patterns with a look up table (LUT), through some clever analysis routines, to extract crystal orientation with very good precision (0.5 degrees). This is routinely used worldwide to extract maps of crystal orientation, grain morphology and texture in a wide range of material systems.

High resolution EBSD builds upon this technique using image correlation to improve the precision significantly, enabling measurement of residual elastic strain i.e. residual stress (1x10-4 in strain) and lattice high rotation (0.006 degrees). We use maps of residual strain gradients to extract stored (geometrically necessary) dislocation content and explore microstructural heterogeneity in exquisite detail.

We have an in-house set of software codes developed by our team within matlab. We actively collaborate with Professor Angus Wilkinson and and his team in Oxford, as well as the commercial team behind CrossCourt (BLGVantage).

Thanks to the hard work an active research field, this technique is widely used in the nuclear, aerospace, and semiconductor industries to improve product performance and component life.

NEW! --> Slides from the 2017 EMAS tutorial talk available here.

Slides from the M&M 2016 FIG Meeting are now available.

Notes from RMS EBSD 2016 workshop are now available. Notes from the MAS EBSD 2016 workshop are now available.

If you are interested in EBSD & orientations - check out our open access EBSD tutorial paper & associated matlab + python codes

High spatial resolution digital image correlation (HR-DIC)

Digital image correlation involves comparison of a series of video images from deforming samples. These images are compared using sophisticated software algorithms to extract the total (surface) deformation gradient tensor.

We use this technique across a range of length and time scales, using optical and scanning electron microscopy, to generate maps of strain across a range of lengthscales suited towards our engineering and science problem.

We have an in-house set of software codes developed by our team within matlab. This enables precise understanding of the correlation routine and optimisation of our results towards our particular research question.

Image of slip bands in Ni - from Jiang, J., Zhang, T., Dunne, F.P.E., and Britton T.B. Deformation compatibility in a single crystalline Ni superalloy Proceedings of the Royal Society A (2016)
http://dx.doi.org/10.1098/rspa.2015.0690
 
Pillars-Indenter

Micropillars ready to be indented for in situ mechanical testing. Each pillars is ~2 micrometers in diameter

In situ micromechanical testing

We have been utilising an Alemnis micro- / nano- indenter housed within a very high performance scanning electron microscope (Zeiss Auriga-40) to enable localised testing of material performance combined with real-time observation of the deformation mechanisms. 

We routinely measure properties such as elastic performance, yield, strain rate sensitivity, and failure of a range of materials. We are developing new insight into strain rate sensitivity and fracture through innovative design of sample geometries and complementary analysis with finite element modelling methods.

We have also been taking our experimental testing rigs to high energy X-ray facilities to perform in situ Laue microdiffraction to probe the internal microstructure of materials during mechanical loading.

Tutorial Lectures:

These lectures form part of the post graduate EM lecture course at Imperial College London.
SEM Tutorial

SEM (2016 notes)

  • Resolution limits
  • Electron interactions
  • Sources
  • Depth of field
  • Image formation
  • Alignment
  • Sample preparation

http://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxleHBtaWNyb21lY2hhbmRjaGFyfGd4OjE0YmE5MTYzMjY4MTU5Yw

FIB (2016 Notes)

  • Why ions?
  • Ion channelling / blocking
  • FIB set up
  • Damage
  • Sectioning
  • Lamella prep



EBSD Tutorial PDF

EBSD (2016 Notes)

  • Brief introduction & history
  • Orientation determination
  • Map generation
  • Tips & tricks
EDS Tutorial

EDS/EDX (2016 Notes)

  • EDX fundamentals
  • Formation of K, L and M lines
  • Peak overlap
  • Detector overview - including SDD operation
  • SEM vs (S)TEM
  • Resolution limits
  • Tips & tricks