497 29
between these two crystal structures. Both applications add
an important new tool to the SEM. The SEM now has the
capability to study the morphology of a sample through
either secondary or backscattered electron imaging, the
chemistry through energy dispersive spectrometry and the
crystallography of the sample by electron channeling con-
trast imaging and EBSD. EBSD techniques have recently
been developed that allow both the elastic and plastic strains
present in a microstructure to be determined and this has
been called high resolution EBSD or HREBSD. A more use-
ful description would be high angular resolution EBSD. This
technique is beyond the scope of this chapter (Wilkinson
et al. 2006 ).
Microtexture is a term that means a population of indi-
vidual orientations that are usually related to some feature of
the sample microstructure. A simple example of this is the
relationship of the individual grain size to grain orientation.
The concept of microtexture may also be extended to include
the misorientation between grains, often termed the meso-
texture. It is now possible using EBSD to collect and analyze
thousands of orientations per minute, thus allowing excellent
statistics in various distributions. The ability to link texture
and microstructure has enabled significant progress in the
understanding of recrystallization, grain boundary structure
and properties, grain growth and many other important
physical phenomena.
The identification of phases in the SEM has usually been
obtained by determining the composition of the phase and
then inferring the identity of the phase. This technique is
subject to the inherent inaccuracies in quantitative analysis
in the SEM using EDS or WDS. In addition, this technique is
not useful when one is attempting to identify a phase that has
multiple crystal structures, but only one composition. A
good example of this concern is TiO 2 , with three different
crystal structures. Another important technological problem
is the identification of austenite in ferrite in engineering
steels. Austenite has a face centered cubic crystal structure
and ferrite is body centered cubic and both phases may have
very similar chemistries.
Improved resolution for EBSD has been achieved by uti-
lizing thin samples that allow the transmission and diffrac-
tion of electrons using accelerating voltages (20–30 kV)
achievable in the SEM. The patterns generated in this way
have very similar characteristics to EBSD but are formed in
transmission mode and thus, due to the thin sample, have
much improved spatial resolution as compared to EBSD per-
formed on bulk samples. Transmission Kikuchi diffraction
(TKD) allows the microtexture of ultrafine grained crystal-
line materials to be studied (Keller and Geiss 2012 ; Trimby
2012 ).
In order to best use EBSD, it is helpful if the reader has
some knowledge of crystallography and how crystallography
is represented. There are a number of excellent books on this
subject (McKie and McKie 1986 ; Rousseau 1998 ). This mod-
ule will first describe the origin of the EBSD pattern in the
SEM. The detectors or cameras used to detect EBSD patterns
will be described. As sample preparation is critical to the suc-
cess of an EBSD investigation, it is important to understand
the methods needed to produce samples of appropriate qual-
ity. Finally, details of the actual experiment and the resulting
output will be discussed.. Fig. 29.9 Inverse pole figure map of ZnO crystals
ab. Fig. 29.10 EBSD of a dual phase steel that contains both austenite
and ferrite. EBSD of multiphase samples can discriminate phases with
different crystal structures. a This is a band contrast map, basically a mea-
sure of the pattern sharpness, which accurately reflects the grain struc-
ture of the sample. b Orientation map of the austenite phase while the
ferrite is shown in the underlying band contrast image (Bar = 200 μm)
29.2 · Electron Backscatter Diffraction in the Scanning Electron Microscope