A special mechanism for the generation of the vibrations creates optimum energy transmission to the specimen. The preparation is conducted very gently to obtain a polished surface without deformation. In this way grain shape and size, recrystallized and non-recrystallized areas, type of grain boundaries and the local texture (in this case shown in the form of pole figures separated for deformed and recrystallized areas) can be easily detected and quantified. recrystallized grains) appear in identical colors while grains with internal orientation gradients reveal changing colors. In the crystal orientation map similar colors mean similar crystallographic directions pointing towards the sample normal. Thomas)įigure 3 illustrates the microstructure of a partially recrystallized IF steel 6 as seen by electron channeling contrast and by COM. d) (111) pole figures of the deformed and recrystallized partition of the sample, showing that recrystallization strongly supports crystal orientations with (111) || ND (center of pole figure). Grain boundaries with misorientation larger than 15° are marked as black lines. c) Crystal direction map indicating the crystal directions pointing parallel to the sample normal direction (ND). b) Diffraction pattern quality map of the observed area. a) Electron channeling contrast image obtained with the backscattered electron (BSE) detector from the untilted sample. Example of ACOM on a microstructure of a partially recrystallized IF steel. A typical result acquired by COM is illustrated in Figure 3.įigure 3. Measurement and pattern analysis time is usually in the order of 50 to 200 patterns per second. For COM, the electron beam is moved stepwise over the sample and at every position a pattern is obtained and measured. The detection of band position and the following analysis is performed by fully automated and commercially available software. Setup of sample and detector within a scanning electron microscope (SEM). Patterns are obtained by using a detector which consists of a phosphor screen detected by a highly light-sensitive camera placed in close distance to the sample (20 to 40 mm) as is illustrated in Figure 2.įigure 2. Finally, the crystal orientation and phase can be measured from indexed bands. Exposure time 7 s, with background subtraction.Įach of the bands match a set of lattice planes in the crystal and from the angles between the bands and from their width the Miller indices of these lattice planes can be established. High-resolution EBSD pattern from an as-cast niobium sample (915 x 915 pixel). Figure 1 shows a typical pattern: It contains bright bands (the so-called Kikuchi bands), on a comparatively strong background.įigure 1. 4.Įlectron backscatter diffraction patterns which are acquired from bulk samples have many similarities with Kikuchi diffraction patterns acquired from thin foils in the transmission electron microscope (TEM). A detailed overview of this state-of-the-art method is given by the book of Schwartz et al. Sample preparation typically is less complicated than TEM and consists of accurate chemical, mechanical or ion-assisted polishing with the aim of creating a plane surface free of any defects. no thin foils as in the case of TEM are needed, with an adequately high spatial resolution of around 50 nm. The EBSD technique permits observation of bulk samples, i.e. Using dedicated software, even specifics of the atomic lattice 2 and residual stresses 3 may be determined. Also, EBSD can be used to examine the structure of crystals, i.e. The resulting crystal orientation maps offer a wealth of information on the sample, including type and distribution of different phases, size, shape and defect condition of grains, type and position of grain boundaries, local crystal orientation and misorientation distribution (texture) and many more. Using this data, the microstructure of the scanned area can be recreated. The automatic analysis of these EBSD patterns yields, for every scan point, the crystallographic orientation and phase and a value representing the quality of the diffraction pattern. The COM technique is based on the repeated acquisition of electron diffraction patterns acquired from every point of a scan grid on a flat surface of a steeply inclined sample in the SEM. It applies computer algorithms for the automated analysis of the diffraction patterns. Specifically, the emergence of computer algorithms for the completely automated analysis of diffraction patterns has pushed the method to evolve into a new kind of scanning microscopy technique, known as “orientation imaging microscopy, OIM” 1 or “crystal orientation microscopy/mapping, COM”. In the field of scanning electron microscopy (SEM), the electron backscatter diffraction (EBSD) method has developed into a robust tool for the crystallographic analysis of materials.
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