A critical review of orientation microscopy in SEM and TEM

Abstract

Orientation microscopy (OM) refers to techniques for reconstruction of microstructures based on the spatially resolved measurement of individual crystallographic phases and orientations. This review gives an overview on different techniques of OM in the scanning and transmission electron mi-croscope. All rely on the automated evaluation of electron diffraction patterns. The most popular technique is based on electron backscatter diffraction (EBSD) in the SEM. In the TEM several techniques are available which are based on either Kikuchi diffraction patterns, spot diffraction patterns with and without electron precession, or reconstructed spot diffraction patterns. Each technique is introduced in detail. Subsequently the techniques are critically compared with respect to their spatial and angular resolution, their robustness in terms of orientation determination and questions of practical applicability for materials science. One point discussed in detail is the spatial resolution. It is shown that the spatial resolution, i.e. the volume from which the diffraction information is generated, is not very different for the SEM and TEM techniques. For this and other reasons we argue that the EBSD technique is in many cases the best suited method for OM. In those cases where it is not (e.g. investigations on truly nanocrystal-line materials, beam sensitive samples) it is the spot diffraction method combined with electron precession and template matching for orientation determination which offers the best resolution and robustness. The Kikuchi pattern technique in the TEM is only reasonably used when highest angular resolution is to be achieved, e.g. for lattice constant determination.

Combining structural and chemical information at the nanometer scale by correlative transmission electron microscopy and atom probe tomography

“…The spatial resolution of the NBD orientation mapping is limited by the combination of several effects, namely, the spot size of the focused electron beam, the convergence angle and the sample thickness [42], it can reach values down to 1 nm [27,32]. For indexing of the NBD patterns, alignment of a certain zone axis with respect to the incident beam is not required.…”

Microstructure of adiabatic shear bands in Ti6Al4V

“…Crystals that light up in each DF image are in a Bragg condition. By using the intensities of each pixel in the complete stack of DF images, the spot diffraction pattern from a small region can be reconstructed [36,37]. This region can ultimately go down to the pixel size of the DF image.…”

“…In the present case a stack of dark field images is recorded by precession and using the most prominent diffraction rings appearing in the present material. Virtual diffraction patterns from smaller regions can then be reconstructed with the conical dark field TEM technique [36,37]. Fig.…”

An EBSD Study of the Deformation of Service-Aged 316 Austenitic Steel

“…The experimental results showed that the evolution of low angle misorientations with the increase in plastic strain was well represented by including a misorientation range of 2°-15° (see section 3.5) and the angular resolution of an EBSD system which uses a Hough transform to detect lines in the patterns is less than 1° [31] , so with proper EBSD system optimization it is possible to determine all misorientations above 2° absolutely. For these reasons a misorientation of 2° was taken as the lower limit of a subgrain boundary while misorientations >15° were regarded as high angle boundaries [17,22,[32][33][34] .…”