The electron backscatter diffraction (EBSD) is the method widely used in materials science, nowadays. In past twenty years the instrumentation underwent extensive progress and the EBSD became standard laboratory technique. Significant progress in the instrumentation, the development of modern high resolution scanning electron microscopes and dual beam microscopes, as well as the fast EBSD detectors still offers the new possibilities of application of EBSD method for studying of various types of modern and perspective materials.
The Kikuchi pattern formation in Transmission Electron Microscope (TEM) was first observed and explained in 1928 by S. Kikuchi [1]. It was immediately found that the Kikuchi pattern is a powerful tool for the crystal orientation determination because “The Kikuchi diffraction pattern is a projection of the geometry of the crystal lattice from a volume of specimen in which this geometry is constant, or nearly so (Kikuchi [1]).” In 1932 Meibon and Rupp observed high angle Kikuchi patterns from “reflected” electrons. Venables and Harland observed electron backscatter patterns in the Scanning Electron Microscope equipped with 30 mm diameter fluorescent imaging screen and television camera. This method allowed examination of specimens and the measurement of crystal orientation at high spatial resolution, which was significantly improved by the use of field emission gun scanning electron microscopes. The first on-line working (automated) EBSD systems were developed in 1980. In 1993 the Orientation Imaging Microscopy (OIM) or orientation mapping was established. The on-line orientation determination from the EBSD patterns is computationally time-consuming task, however within the last decades the EBSD technique underwent a great boom as a consequence of the computers hardware improvements and progresses in the scanning electron microscopes technique, as well.
The EBSD is surface sensitive method. Measured information come from the depth of several tenths of nm, depending on the measured material atomic number (the penetration depth of electrons decreases with increasing atomic number). The spatial resolution of the EBSD depends on the used electron microscope type (used electron source). In the case of scanning electron microscope equipped with field emission cathode it is in order of ~10 nm.
Two types of information are essentially held by the electron backscatter patterns. First is the Kikuchi pattern quality measure and the second is the orientation of irradiated volume. The Kikuchi pattern quality information, can be used for determination of the crystal “perfection”, estimation of the crystal defects types and its densities because the presence of the lattice defects in irradiated volume has in general in consequence decrease of the Kikuchi pattern “sharpness” (blurring of the Kikuchi pattern). However, the Kikuchi pattern quality is strongly influenced by the specimen surface preparation. The surface area is in most cases of samples highly defective (from production or sample processing). The Kikuchi pattern from poorly prepared specimen is therefore not sharp and this effect correlates with influence of the lattice defects and imperfections. Therefore, the determination of the lattice defects and densities can be done only quasi-quantitatively.
More interesting information about the investigated specimen are provided by the orientation of each infinitesimal measured sample volume which can be calculated from respective Kikuchi pattern. From the orientation map we can obtain information on the specimen morphology, grains and sub-grains shapes and grain and sub-grain size distributions. Measured orientation information allows us to calculate the misorientation [2] between different measured points and to describe the properties and the character of grain boundaries (GBs), to quantify fractions of high/low angle grain boundaries, observe and investigate occurrence of special grain boundaries (for instance CSL grain boundaries).
Orientation information yields the details on the preferred orientation of crystallites, where we are not restricted to the measurements of distribution of one (or several) lattice planes in different direction in sample, which is the case of texture measurements using the X-ray diffraction, but we simply determine the distribution of all possible crystal orientations in given direction in sample.
Measured orientation data can be used for calculation of the orientation distribution function (ODF) or misorientation distribution function (MODF). In specimen containing more phases, quantitative (volume averaged) phase analysis can be done, and above described details can be constructed for each individual phase present in sample. Moreover, we can investigate mutual orientation dependences between different phases in the specimen.
The possibilities and advantages of several different program packages for measurement, data processing and evaluation will be discussed in the talk. The particular EBSD results will be demonstrated for various type of investigated materials – severally plastically deformed (SPD) materials, hardmetals, cermets, ceramics, thin coatings, single crystalline samples and epitaxial thin films.