Oral Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

Transmission Kikuchi diffraction versus thin-section electron back-scattering diffraction: Advantages and limitations (#50)

Azdiar A. Gazder 1 , Khalil I. Elkhodary 2 , David R.G. Mitchell 1 , Ahmed A. Saleh 3
  1. Electron Microscopy Centre, University of Wollongong, Wollongong, New South Wales 2500, Australia
  2. Department of Mechanical Engineering, The American University in Cairo, New Cairo, Cairo 11835, Egypt
  3. School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, New South Wales 2522, Australia

The transmission Kikuchi diffraction (TKD) technique combines the routine quantitative capability of the automated orientation imaging technique while approaching the spatial and angular resolution of a transmission electron microscope operating in scanning-transmission and diffraction modes. This is achieved by minimising the interaction volume between the electron beam and electron transparent samples; which in turn reduces the lateral spread of the electron beam.

However, TKD suffers from several limitations. Sensitivity to the thickness of the electron transparent region leads to high sample attrition rates. Defocussing caused by the wedge profile of electro-polished samples limits the size of the TKD maps. The position of the pattern centre and differences in the diffraction characteristics and the TKD pattern quality at boundary regions compared to grain interiors can lead to uncertainties in indexing. Additionally, since the TKD pattern originates from at/near the bottom surface of the electron transparent region, there is an inherent ambiguity with respect to the through thickness location of microstructural features; particularly when mapping multi-phase and/or precipitate containing materials.

While most routine electron back-scattering diffraction (EBSD) work provides statistical orientation information, the spatial and angular resolutions are typically limited by the interaction volume between the electron beam and bulk samples. On the other hand, the reduced interaction volume proffered by electron transparent or thin-section samples can readily leveraged in conventional scanning EBSD mode to return relatively large area orientation maps that approach the spatial and angular resolution of the TKD technique. This technique is less sensitive to the sample thickness, is conducted using the conventional EBSD geometry and microscope settings and negates the uncertainty in the location of microstructural features.

Various steel based examples will be presented to showcase the application, advantages and limitations of the TKD and thin-section EBSD techniques.