Backscatter Kikuchi Patterns Research Articles

Recent Developments in Automated Crystal Orientation Mapping (ACOM) - Quantitative Evaluation and Graphical Representation of Individual Grain Orientation Data

A system is presented which performs fully unattendedly the measurement of the crystal orientations of individual grains using the automated interpretation of Backscatter Kikuchi Patterns (BKP). The features which are necessary to scan a selected area of the specimen surface with a high spatial resolution are described Several possibilities for a quantitative evaluating of the acquired orientation data and their representation by pseudo-colored maps are shown. A simple estimate of the quality of BKD pattern yields information on the degree of deformation or recrystallization. Methods of quantitative stereological and statistical evaluation of the acquired data are demonstrated. The local texture of small selected areas can be investigated and be described by its statistical functions which are calculated from the achieved orientation data.

Determination of the Grain Boundary Misorientation for the Analysis of the Discontinuous Ordering Reaction in Fe-50 at. % Co

The discontinuous ordering (DO) reaction represents the mechanism of atomic ordering in alloys at such low temperatures, at which the mobility of atoms in the bulk of the alloy can be neglected and the ordering process occurs only in the regions swept by migrating grain boundaries (GBs). In order to study the relationship between the grain boundary crystallography and the kinetics of the DO reaction in the Fe-50 at.% Co alloy, the orientations of all the grains in a 8x4 mm 2 sample have been determined in the scanning electron microscope by an automated analysis of the backscattered Kikuchi patterns, and the crystallographic orientation image of the sample has been constructed. With the help of this image, completed by a light microscopy map of the sample, all GBs have been numbered sequentially and the maximal width of the ordered phase has been determined in the light microscope (LM) for each individual GB. Afterwards, the misorientation parameters for all GBs investigated in the LM have been determined (totally 226 GBs). Such a procedure allowed us to establish a relationship between the rate of the DO reaction at individual GBs and their misorientation parameters. The data are presented as the dependencies of the GB migration rate on the misorientation angles around the axis close to the low-index , and axes. It is shown that the GBs close to the special Σ3 , Σ19 , Σ9 , Σ11 , Σ5 , Σ13 and Σ17 misorientations (here Σ is the inverse density ofthe coincidence sites) exhibit a low DO rate. This is interpreted in terms of a decreased diffusivity in the special GBs. At the same time, GBs with a misorientation angle slightly below the value of 46.6° for the special Σ19 boundary exhibit the highest DO rate. A model is suggested which establishes a relationship between DO rate, diffusivity and mobility of the GB.

A CCD Camera System for the Acquisition of Backscatter Kikuchi Patterns on an SEM

A CCD Camera System for the Acquisition of Backscatter Kikuchi Patterns on an SEM

The Characterisation of Microtexture by Orientation Mapping

For a complete description of a material's microstructure the morphology as well as the distributions of chemical elements and of crystal lattice orientations must be known. While morphology is a standard issue of electron microscopy, and element distributions can be mapped readily using an EDX appliance, crystal lattice orientations in the bulk surface are accessible in routine work only recently [1, 2]. Backscatter Kikuchi patterns (BKP), also termed electron backscattering patterns (EBSP), are widely used for the determination of individual grain orientations in the surface of bulk polycrystals.

The Determination of Local Texture by Electron Diffraction–A Tutorial Review

Electron diffraction methods are briefly reviewed for the determination of individual grain orientations and for the measurement of SAD pole figures. The standard techniques of orientation determination grain by grain using a TEM are the interpretation of selected area electron spot and microbeam Kikuchi diffraction patterns. Electron-transparent thin samples are required. Specimen regions smaller than 500 nm or 10 nm in diameter, respectively, can be studied. Alternatively, quantitative pole figures can be measured using a TEM from selected areas down to 0.5 μm in diameter.The orientations of grains in a bulk sample are obtained with an SEM from backscatter Kikuchi patterns or from (selected area) channelling patterns. Spatial resolution is approximately 1 μm or 5 μm, respectively.Individual grain orientation and pole figure measurements can be performed on-line by interfacing the electron microscope with a computer. In contrast to X-ray or neutron diffraction, electron microscopes give the means to image microstructural details at high resolution as well as to study crystal texture of exactly the same specimen region by electron diffraction.

Boron and Hydrogen in NI3AL: Part II. Mechanical Testing of Bicrystals

AbstractTo provide a sensitive measurement of the effect of boron segregation on the strength and ductility of Ni3A1 grain boundaries, bicrystal tensile tests were performed on small specimens of boron doped Ni76A124 cut from extremely large-grained boules. Five specimens with the same “random” or low-symmetry grain boundary (disorientations measured by means of backscattered Kikuchi patterns) and two specimens with a second random grain boundary were tested in quenched and slow-cooled conditions. Duplicate tests performed in a low (7 ppm) water-vapor environment showed that the fracture mode and the stress and strain at fracture are altered by environmental embrittlement at individual, partially strengthened grain boundaries.

Abnormal grain growth in textured FeAl intermetallics

Abnormal grain growth has been observed in powder processed, hot extruded, B2 FeAl alloys which display significant wire textures. This study uses X-ray inverse pole figures and electron backscatter diffraction patterns to examine the relationship between the texture and this abnormal grain growth. Texture analysis has been performed on samples heat treated at various temperatures both above and below the critical temperature for abnormal grain growth initiation. The powder processed samples initially have a strong «111å wire texture which is generally retained after heat treatments of up to 1000 °C. At heat treatments of 1050 °C and higher this texture disappears and instances of abnormal grain growth are observed. In contrast to the powder alloys, abnormal grain growth has not been observed in cast and extruded FeAl alloys. Backscattered Kikuchi patterns have been used to determine the micro-texture of the alloys so that the relationship between the initial wire texture and the abnormal grain growth may be examined. The results of the texture and micro-texture analysis are discussed in light of current theoretical models for grain growth.

Computer-Aided TEM- and SEM-based individual orientation techniques for recrystalllzation studies in commercial aluminum alloys

Commercial production of aluminum alloy sheet for beer and beverage cans critically depends on the control of plastic anisotropy which affects earing behavior. The final cold rolling texture is responsible for the 45° earing. Plastic anisotropy of the product is minimized by promoting the {001} <100> cube texture during upstream hot rolling and annealing. Hence, the origin of cube texture in light of the nucleation and growth aspects of the recrystallization process has been the subject of research for several decades. Since recrystallization is a local event, electron microscopy has been used in this investigation to shed light on its mechanism. In particular, computer-aided analysis of Kikuchi patterns from the TEM and Backscattered Kikuchi Patterns from the SEM have been used for studying the crystallographic nature of recrystallization nuclei and their orientation relationship to the deformed matrix from which they originate.