Backscatter Kikuchi Diffraction Research Articles

Mapping of lattice distortion in martensitic steel—Comparison of different evaluation methods of EBSD patterns

To visualize the varying tetragonal distortions in high carbon martensitic steels by EBSD, two different approaches have been applied on backscattered Kikuchi diffraction (BKD) patterns. A band-edge refinement technique called Refined Accuracy (RA) (Oxford Instruments) is compared with a technique called Pattern Matching (PM), which optimizes the fit to a simulated BKD signal. RA distinguishes between hypothetical phases of different fixed c/a, while PM determines a best fitting continuous c/a by projective transformation of a master pattern. Both techniques require stored BKD patterns.The sensitivity of the c/a-determination was tested by investigating the microstructure of a ferritic steel with an expected c/a=1. The influence of the Kikuchi pattern noise on c/a was compared for a single or 40 averaged frames per measuring point, and turned out to be not significant. The application of RA and PM on the martensitic microstructure delivered qualitatively similar maps of c/a. The comparison of RA and PM shows that RA is suitably fast and precise during mapping the martensite c/a ratio in analyses of high carbon martensite, especially for fast initial surveys. As RA leads quantitatively to higher noise in c/a, the PM analysis can be used for higher precision results.

Use of electron backscatter diffraction patterns to determine the crystal lattice. Part 1. Where is the Bragg angle?

The derivation of a crystal structure and its phase-specific parameters from a single wide-angle backscattered Kikuchi diffraction pattern requires reliable extraction of the Bragg angles. By means of the first derivative of the lattice profile, an attempt is made to determine fully automatically and reproducibly the band widths in simulated Kikuchi patterns. Even under such ideal conditions (projection centre, wavelength and lattice plane traces are perfectly known), this leads to a lattice parameter distribution whose mean shows a linear offset that correlates with the mean atomic number Z of the pattern-forming phase. The consideration of as many Kikuchi bands as possible reduces the errors that typically occur if only a single band is analysed. On the other hand, the width of the resulting distribution is such that higher image resolution of diffraction patterns, employing longer wavelengths to produce wider bands or the use of higher interference orders is less advantageous than commonly assumed.

Nanoscale twinning in Fe–Mn–Al–Ni martensite: a backscatter Kikuchi diffraction study

Iron-based Fe-Mn-Al-Ni shape-memory alloys are of rather low materials cost and show remarkable pseudoelastic properties. To further understand the martensitic transformation giving rise to the pseudoelastic properties, different Fe-Mn-Al-Ni alloys have been heat treated at 1473 K and quenched in ice water. The martensite, which is formed from a body-centred cubic austenite, is commonly described as face-centered cubic (f.c.c.), even though there are also more complex, polytypical descriptions of martensite. The presently studied backscatter Kikuchi diffraction (BKD) patterns have been evaluated, showing a structure more complex than simple f.c.c. This structure can be described by nanoscale twins, diffracting simultaneously in the exciting volume. The twinned structure shows a tetragonal distortion, not uncommon for martensite in spite of the lack of interstitial elements. These features are evaluated by comparing the measured BKD patterns with dynamically simulated ones.

Manual measurement of angles in backscattered and transmission Kikuchi diffraction patterns.

A historical tool for crystallographic analysis is provided by the Hilton net, which can be used for manually surveying the crystal lattice as it is manifested by the Kikuchi bands in a gnomonic projection. For a quantitative analysis using the Hilton net, the projection centre as the relative position of the signal source with respect to the detector plane needs to be known. Interplanar angles are accessible with a precision and accuracy which is estimated to be ≤0.3°. Angles between any directions, e.g. zone axes, are directly readable. Finally, for the rare case of an unknown projection-centre position, its determination is demonstrated by adapting an old approach developed for photogrammetric applications. It requires the indexing of four zone axes [uvw] i in a backscattered Kikuchi diffraction pattern of a known phase collected under comparable geometric conditions.

Constraints on the effective electron energy spectrum in backscatter Kikuchi diffraction

Electron Backscatter Diffraction (EBSD) is a technique to obtain microcrystallographic information from materials by collecting large-angle Kikuchi patterns in the scanning electron microscope (SEM). An important fundamental question concerns the scattering-angle dependent electron energy distribution which is relevant for the formation of the Kikuchi diffraction patterns. Here we review the existing experimental data and explore the effective energy spectrum that is operative in the generation of backscatter Kikuchi patterns from silicon. We use a full pattern comparison of experimental data with dynamical electron diffraction simulations. Our energy-dependent cross-correlation based pattern matching approach establishes improved constraints on the effective Kikuchi pattern energy spectrum which is relevant for high-resolution EBSD pattern simulations and their applications.

Improving the precision of orientation measurements from technical materials via EBSD pattern matching

We use pattern matching of experimental and dynamically simulated backscattered Kikuchi diffraction (BKD) patterns to increase the orientation precision of electron backscatter diffraction (EBSD) measurements. In order to quantify the improvement in orientation precision, we analyze the experimental distribution of the kernel average misorientation (KAM) angles. We find that for the same raw data, i.e. the same EBSD data acquisition time budget, the pattern matching approach improves the KAM resolution by an order of magnitude compared to orientation data delivered from the conventional Hough-transform based data analysis. This quantitative improvement enables us to interpret small orientation changes in plastically deformed materials which are hidden in noisy orientation data delivered from the reference EBSD system.As an application example, we analyze a ferritic-martensitic steel (P92) sample before and after low-cycle fatigue (LCF) loading (±0.3% strain) at 620 °C. Whereas the low precision of the EBSD orientation data from the manufacturer software does not allow a reliable discrimination of the gradually changing microstructure, we find very clear systematic differences of the local microstructure after the pattern matching orientation refinement of the initial, raw pattern data. For the investigated P92 sample, the KAM-angle histograms are well described by two log-normal distributions indicating the already tempered and the remaining and mostly untempered martensite.

Electron backscatter diffraction beyond the mainstream

We present special applications of electron backscatter diffraction (EBSD) which aim to overcome some of the limitations of this technique as it is currently applied in the scanning electron microscope. We stress that the raw EBSD signal carries additional information which is useful beyond the conventional orientation determination. The background signal underlying the backscattered Kikuchi diffraction (BKD) patterns reflects the chemical composition and surface topography but also contains channeling‐in information which is used for qualitative real‐time orientation imaging using various backscattered electron signals. A significantly improved orientation precision can be achieved when dynamically simulated pattern are matched to the experimental BKD patterns. The breaking of Friedel's rule makes it possible to obtain orientation mappings with respect to the point‐group symmetries. Finally, we discuss the determination of lattice parameters from individual BKD patterns. Subgrain structure in a single quartz grain. The increased noise level in the left map reflects the lower precision of a standard orientation determination using band detection by the Hough transform. The right map results from the same experimental raw data after orientation refinement using a pattern matching approach. The colors correspond an adapted inverse pole figure color key with a maximum angular deviation of about 2° from the mean orientation.

Kikuchi bandlet method for the accurate deconvolution and localization of Kikuchi bands in Kikuchi diffraction patterns

In order to retrieve crystallographic information from an electron backscatter Kikuchi diffraction pattern, its Kikuchi bands have to be localized. One of the main reasons for the limited precision of the present Kikuchi band localization methods is that the diffuse edges of a Kikuchi band are convoluted by many other Kikuchi bands that intersect them. To improve the localization accuracy, Kikuchi bands have to be deconvoluted. In this article, a new method for the deconvolution and localization of Kikuchi bands is presented. The deconvolution is based on the fact that, in a Kikuchi pattern, there are a number of Kikuchi bands that are not parallel to the bands that intersect them. It is performed in Fourier space. After deconvolution, localization is carried out by a quantitative shape analysis of the intensity profiles of the deconvoluted Kikuchi bands. Using the introduced method, for a real electron backscatter Kikuchi diffraction pattern with 45° half capture angle and 0.12° per pixel maximum scale factor, the characteristic hyperbolic features of the Kikuchi bands can be localized with a precision of better than 0.1° in reflection angle.

Orientation microscopy with fast EBSD

Automated backscatter Kikuchi diffraction in the SEM is about to become a tool for process and quality control. Mandatory requirements for these applications are a high speed and provisions to enable re-examination of the results at any time. Means and motivation for high speed electron backscattering diffraction are discussed. Separate acquisition and store of pattern sequences in an unprocessed data format, followed by offline calculation of the grain orientations, has many advantages over online orientation microscopy. With actually >1000 acquired patterns per second it is significantly faster than conventional electron backscattering diffraction. The data can be examined again using the original backscatter Kikuchi sequences, and the presence of a priori unknown phases can be checked for. Online pattern solving, as a dual task, is optional.

High-Speed Orientation Microscopy with Offline Solving Sequences of EBSD Patterns

A high speed in acquisition of backscatter Kikuchi patterns (BKP) and solving the stored raw patterns offline has many advantages over online EBSD. No compromise is made between speed and reliability. Automated backscatter Kikuchi diffraction in the scanning electron microscope (SEM) is about to become a tool for process and quality control. Mandatory requirements for these applications are measures to enable re-examination of the results at any time and a high speed. Therefore, fast acquisition of pattern sequences and off¬line indexing will soon become standard. Online pattern solving is optional, but at the disadvantage of reduced speed and reliability.

EBSD 기법을 이용한 Gamma TiAl의 마이크로 조직파괴에 관한 연구

A backscatter Kikuchi diffraction attachment to an SEM enables the convenient investigation of grain orientations on bulk or micro surface. Their relation to micro?structural features gives insight into many aspects of anisotropic materials properties. In micro area such as Micro Electro Mechanical Systems(MEMS) devices is required in order to improve understanding of how they may be expected to perform upon the micro?scale. Electro Back Scatter Diffraction (EBSD) helps us to find uniform area as MEMS material. The γ-TiAl has two different lamellar structures γ/α₂?Ti3Al phase which have shows {111} γ//{0001}α₂ plane indexing. The micro?size testing specimen was successfully made by this structural relation. Interlamellar structure specimen averagely show 20~25% lower fracture toughness value compare with translamellar specimens. Moreover micro fracture surface and micro crack progress were observed.

Use of EBSD to identify phases in interdendrite region of a cast Zn–Al‐based alloy (ZA27)

Electron backscattered Kikuchi diffraction methodology was used to identify phases in the interdendrite region of an alloy ZA27. Two Zn-rich hexagonal close-packed structure phases eta and epsilon phases were distinguished using predetermined lattice parameters of the phases. In relation to studies of scanning electron microscopy and X-ray diffraction, electron backscattered diffraction results revealed that the Al-rich precipitates of the alpha phase were from decomposition of the eta'(T), and the four-phase transformation: alpha+epsilon--> T'+eta, had occurred in the epsilon phase after ageing at 150 degrees C for 8 h.

On the formation mechanisms, spatial resolution and intensity of backscatter Kikuchi patterns

The present paper is divided into two main sections. In the first, the formation mechanisms of backscatter Kikuchi patterns (BKP) are discussed on the basis of measurements on the sharpness of Kikuchi lines and on the spatial, that means the lateral and depth resolution of the technique. We propose that thermal diffuse scattering is the important incoherent scattering mechanism involved in pattern formation. This mechanism is not considered in the classical description of the origin of backscattered electrons in the scanning electron microscope (SEM) which is why there is in some important points no agreement between classical Monte-Carlo-type electron trajectory simulations and experimental results. We assume that the energy spectrum of the backscattered electrons shows, similar to the spectra in transmission electron microscopy, a sharp zero-loss peak. In the second section, we discuss the intensity of Kikuchi bands in BKP. It is shown that the kinematical theory gives—of course—not the correct intensities, but that these intensities are, on the other hand, not too far off the experimental ones. We subsequently introduce a simple intensity correction procedure that is based on the two-beam dynamical theory, originally proposed by Blackman for transmission electron diffraction patterns. It is shown by examples of diffraction patterns of niobium and silicon that this procedure leads to satisfying results, once two unknown variables (a universal constant and the exit depth of the electrons) have been empirically fit. It is assumed that in the future, this correction will improve the possibilities of phase identification by backscatter Kikuchi diffraction patterns.

Automated Crystal Orientation Measurement by backscatter Kikuchi diffraction

We’ve built this digital research platform to provide academics everywhere with fast, stable and secure digital access to our library of over 110,000 scholarly books and 800,000 journal articles. We’ve tested the platform in close cooperation with leading academic institutions. If you have any questions or you notice something doesn’t quite work as it should, please visit our <a href="/publishing/faq?lang=en" class="text-primary">Help/FAQ</a> page and let us know.

Electron backscattered Kikuchi diffraction technique: for a better understanding of epitaxial superconducting film growth on buffered Ni (RABiTS) tapes

A reel-to-reel MOCVD system has been designed to synthesize high quality YBCO coated tapes on Ni RABiTS (Rolling Assisted Biaxially Textured Substrates). Special buffer layer stackings have been deposited to improve the quality of the superconductor. Several buffer layers architectures rose in dense YBCO films with a similar texture, but fluctuations in critical current densities (Jc) were measured. Therefore, a more accurate and detailed measurement method such as Electron Backscattered Kikuchi Diffraction (BKD) has been used to assess the crystalline quality of the stackings. The studied sequence here was NiW /NiO /YSZ /CeO2 /YBCO. The grain and the subgrain structure as well as their size and disorientation have been analysed for each layer. First on Ni tape, secondly on the protecting NiO (200) buffer layer, then on the following CeO2 (200) film. Finally, unpublished BKD diagrams of the subsequent YBCO (001) films have been reported here. The grain evolution has been successfully studied showing the buffer layer effect on the grain growth. In this work we highlight the correlation between the misorientation of the grains (inducing NiO (111) growth and cracks) and the grain boundary morphology (size, grooves). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Phase discrimination by automated BKD.

Automated backscatter Kikuchi diffraction in the SEM enables rapid discrimination of phases and the automated acquisition of phase-distribution maps at sub-micron resolution, if the phases belong to different Laue groups and/or if their lattice constants are significantly different. The acquired database can be further used for quantitative determination of phase contents, for construction of crystal orientation maps, for characterization of grain and phase boundaries, for crystal texture analysis on a grain-specific level by calculating pole figures and orientation density functions separately for each phase, and for orientation stereology in general. Pattern-quality maps provide a clear reproduction of the microstructure on a meso-scale level.

Review Electron backscatter Kikuchi diffraction in the scanning electron microscope for crystallographic analysis

The technique of electron backscatter Kikuchi diffraction patterns (BKDPs) in the scanning electron microscope is reviewed. The paper focuses mainly on the crystallographic applications of the technique, including discussions on point group and space group determination and strain analysis. Orientation microscopy is discussed but not reviewed. The geometrical configurations of BKDPs are reviewed in detail and the relationship between BKDPs and the technique of electron channelling patterns (ECPs) is explored briefly. Essential crystallography is discussed and methods of analysis of BKDPs to extract crystallographic information are analyzed in detail. Some important characteristics of diffraction contrast in BKDPs are analyzed with respect to the geometry of the technique, the dynamical theory of electron diffraction and crystallographic applications. Examples of the use of theoretical contrast in pattern interpretation are provided. Anomalous effects in BKDPs are analyzed in detail and ways of identifying anomalous contrast in practice are discussed. BKDPs included in the paper are zincblende (ZnS), silicon, germanium, GaAs, chalcopyrite (CuFeS2, TaTe4 and Er2Ge2O7.

EBSD of Zn-rich phases in Zn–Al-based alloys

Based on microstructure characterization, electron back-scatter Kikuchi diffraction (EBSD) methodology was used on a multi-phase alloy ZnAl4Cu11 (in wt.%). Electron back-scatter Kikuchi diffraction patterns (EBSDPs) were produced from the bulk Zn–Al-based alloy specimen using solely mechanical polishing instead of mechanical and electro-polishing. Both EBSDs of the Zn-rich hexagonal close-packed structure (hcp) phases of ε and η were distinguished for the first time using pre-determined lattice parameters of these phases as the computer database for the multi-phase alloy. These two procedures were practical developments of EBSD technology in the study of crystalline orientation and phase identification.

The microstructure of submicrometer wide planar-reactive ion etched versus trench-damascene AlCu lines

The microstructure was measured for AlCu lines, formed using either a traditional planar metal subtractive etch process or a newly developed hot AlCu-trench-damascene process. It was found that 0.35 μm wide damascene AlCu lines formed a large grained bamboo microstructure with little or no Al (111) texture. The local crystallographic texture was measured in a scanning electron microscope using electron backscatter pattern analysis often referred to as backscatter Kikuchi diffraction. Damascene structures consisted of AlCu films deposited at greater than 400 °C onto Ti or Ti/TiN into preformed amorphous SiO2 trenches, 0.3–5.0 μm wide by 0.4 μm deep, followed by aluminum chemical mechanical polishing to remove the metal overburden. Standard planar metal control samples consisted of blanket Al or AlCu films deposited onto either an amorphous SiO2 substrate or onto SiO2/Ti/TiN substrates, followed by subtractive etching to define 0.45–10 μm wide lines as well as large (e.g., 10×10 μm2) pads. The planar metal samples exhibited either little change or a slight strengthening of their (111) fiber texture with decreasing line width; this was in sharp contrast to the damascene films in which a marked weakening in the (111) fiber texture with decreasing line width was found. In addition a trimodal (111) texture distribution developed in trenches where TiAl3 intermetallic formed. The role of intermetallic formation (TiAl3), elevated (&amp;gt;400 °C) AlCu deposition temperature, large bamboo grain size, local AlCu crystallographic texture and differences in sidewall coverage between subtractive etched and trench-damascene processed AlCu on film microstructure are examined.

Microtexture studies of lead scandium tantalate ceramics

Crystallographic orientations of various samples of polycrystalline lead scandium tantalate, Pb2ScTaO6, abbreviated PST, were investigated by the technique of backscatter Kikuchi diffraction pattern (BKDP) in the scanning electron microscope (SEM). The samples were processed under different conditions. Several hundreds of crystal orientations in the bulk ceramics were examined by BKDPs and the results were plotted in microtexture pole- and inverse pole-figures for determination of the average and local preferred orientations. These results were compared with crystallographic information obtained using X-ray diffraction (XRD). In addition, local textures in certain selected regions in the PST ceramics were also determined.