'Five-parameter' analysis of grain boundary networks by electron backscatter diffraction

This paper describes state‐of‐the‐art analysis of grain boundary populations by EBSD, with particular emphasis on advanced, nonstandard analysis. Data processing based both on misorientation alone and customised additions which include the boundary planes are reviewed. Although commercial EBSD packages offer comprehensive data processing options for interfaces, it is clear that there is a wealth of more in‐depth data that can be gleaned from further analysis. In particular, determination of all five degrees of freedom of the boundary population provides an exciting opportunity to study grain boundaries by EBSD in a depth that was hitherto impossible. In this presentation we show ‘five‐parameter’ data from 50 000 boundary segments in grain boundary engineered brass. This is the first time that the distribution of boundary planes has been revealed in a grain boundary engineered material.     

Visualization of grain subdivision by analysing the misorientations within a grain using electron backscatter diffraction

The misorientation relative to the average orientation of a grain and the point-to-point relative misorientation along a line across a moderately cold deformed grain, calculated from an electron backscatter diffraction (EBSD) dataset, are analysed in detail by visualizing both the misorientation angle and the misorientation axis. The significance of monitoring the misorientation axis is illustrated by an example of a grain subdivided into a misorientation band structure. A new technique to visualize the subdivision structure by assigning colours to misorientations in such a way that the contrast is maximized within a grain is introduced and discussed. Furthermore, some methods for grain boundary reconstruction from EBSD datasets are compared with the map of the confidence index in order to provide a validation of the accuracy of these methods.     

Crystallographic analysis of facets using electron backscatter diffraction

Applications of electron backscatter diffraction (EBSD), also known as backscatter Kikuchi diffraction in the scanning electron microscope (SEM) are first and foremost microtexture and grain boundary misorientation analysis on a single polished section in the specimen. A more subtle and revealing approach to analysis of these data is to use EBSD to probe the orientations of planar surfaces, i.e. facets, which bound crystals. These surfaces include: • grain or phase boundaries • fractures • cracks It is of great interest to know the crystallography of such facets since it provides a key to understanding the physical properties of them.
As far as investigation methodology is concerned, surfaces or facets associated with polycrystals are of two types: exposed or unexposed. Exposed facets, such as a fracture surface, can be viewed directly in the SEM, whereas unexposed facets, such as a grain boundary, are usually revealed as an etched trace on a polished surface. Photogrammetric methods can be used to obtain the positional orientation of an exposed facet, and the crystallographic orientation is obtained either directly from the surface or by indirect sectioning. Calibrated sectioning is required to obtain the equivalent parameters for an internal surface. The present paper compares the methods for obtaining and interpreting the crystallography of facets, with illustrations from several materials.     

Novel combination of orientation measurements and transmission microscopy for experimental determination of grain boundary miller indices in silicon and other semiconductors

The determination of grain boundary planes in multicrystalline material has only been restricted to transmission electron microscope investigations (Jang et al., 1992; Elgat et al., 1985) or to metallograpical investigations of the grain boundary (Randle et al., 1993). The first method is expensive, and both are complex and time consuming in grain boundary preparation. This paper proposes the determination of grain boundary planes in semiconductor wafer by a combined application of Electron Back Scatter Diffraction and Infrared Transmission Microscopy. In particular, the new method is demonstrated with directional solidificated multicrystalline silicon.     

Backscattered electron imaging and electron backscattered diffraction in the study of bacterial attachment to titanium alloy structure

The application of secondary electron (SE) imaging, backscattered electron imaging (BSE) and electron backscattered diffraction (EBSD) was investigated in this work to study the bacterial adhesion and proliferation on a commercially pure titanium (cp Ti) and a Ti6Al4V alloy (Ti 64) with respect to substrate microstructure and chemical composition. Adherence of Gram‐positive Staphylococcus epidermidis 11047 and Streptococcus sanguinis GW2, and Gram‐negative Serratia sp. NCIMB 40259 and Escherichia coli 10418 was compared on cp Ti, Ti 64, pure aluminium (Al) and vanadium (V). The substrate microstructure and the bacterial distribution on these metals were characterised using SE, BSE and EBSD imaging. It was observed that titanium alloy‐phase structure, grain boundaries and grain orientation did not influence bacterial adherence or proliferation at microscale. Adherence of all four strains was similar on cp Ti and Ti 64 surfaces whilst inhibited on pure Al. This work establishes a nondestructive and straight‐forward statistical method to analyse the relationship between microbial distribution and metal alloy structure.     

Preparation of metallic samples for electron backscatter diffraction and its influence on measured misorientation

Preparation of specimens for electron backscatter diffraction has to be done with great care to ensure a high indexing fraction from high-quality patterns. Despite the amount of published and recommended preparation methods for different materials, detailed information about the preparation parameters are either missing, or different preparation methods are recommended for one material. The aim of this contribution is to compare the application of several preparation techniques on different metallic samples to determine a suitable preparation method for high-quality electron backscatter diffraction measurements for a variety of alloys. From the results obtained, polishing with an oxide polishing suspension is the most appropriate preparation method for the materials and preparation methods investigated. Furthermore, the influence of mechanical polishing as well as of oxide polishing suspension polishing on misorientation is found to be negligible for misorientation angles greater than 1°. In the course of this study the absolute indexing reproducibility of the EBSD-system employed was determined to be 1.18° with respect to the misorientation angle θ.     

Scanning electron microscopy and transmission electron microscopy in situ studies of grain boundary migration in cold-deformed aluminium bicrystals

The crystallography of recrystallization has been investigated in channel‐die deformed pure aluminium bicrystals with {100}<011>/{110}<001> orientations. The microstructural and microtextural changes during the early stages of recrystallization were followed by systematic local orientation measurements using scanning and transmission electron microscopes. In particular, orientation mapping combined with in situ sample heating was used to investigate the formation and growth of new grains at very early stages of recrystallization. Grain boundary migration and ‘consumption’ of the as‐deformed areas was always favoured along directions parallel to the traces of the {111} slip planes that had been most active during deformation.     

High-angle triple-axis specimen holder for three-dimensional diffraction contrast imaging in transmission electron microscopy

Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90° ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils.     

Five-parameter grain boundary analysis of a grain boundary–engineered austenitic stainless steel

Two different grain boundary engineering processing routes for type 304 austenitic stainless steel have been compared. The processing routes involve the application of a small level of strain (5%) through either cold rolling or uni-axial tensile straining followed by high-temperature annealing. Electron backscatter diffraction and orientation mapping have been used to measure the proportions of Σ3ⁿ boundary types (in coincidence site lattice notation) and degree of random boundary break-up, in order to gain a measure of the success of the two types of grain boundary engineering treatments. The distribution of grain boundary plane crystallography has also been measured and analyzed in detail using the five-parameter stereological method. There were significant differences between the grain boundary population profiles depending on the type of deformation applied.     

Electron backscatter diffraction of grain and subgrain structures — resolution considerations

Characterization of microstructures containing small grains or low-angle grain boundaries by electron backscattered diffraction (EBSD) is limited by the spatial and angular resolution limits of the technique. It was found that the best effective spatial resolution (60 nm) for aluminium alloys in a tungsten-filament scanning electron microscope (SEM) was obtained for an intermediate probe current which provided a compromise between pattern quality and specimen interaction volume. The same specimens and EBSD equipment when used with a field-emission gun SEM showed an improvement in spatial resolution by a factor of 2–3. For characterizing low-angle boundary microstructures, the precision of determining relative orientations is a limiting factor. It was found that the orientation noise was directly related to the probe current and this was interpreted in terms of the effect of probe current on the quality of the diffraction patterns.     

金相图像的晶界恢复与重建

针对定量金相分析中金相图像的晶界恢复与重建以及数学形态学在图像处理中的特殊作用,从理论上证明了传统膨胀运算对图像灰度连续性的影响及影响程度与结构元素尺寸的关系,并对传统的膨胀运算的定义做了改进,据此提出了多尺度测地膨胀算法并以此恢复和重建金相图像的晶界.首先依据改进的膨胀运算对金相图像进行预处理;然后用多尺度迭代腐蚀和...     

The use of combined cathodoluminescence and EBSD analysis: a case study investigating grain boundary migration mechanisms in quartz

Grain boundary migration is an important mechanism of microstructural modification both in rocks and in metals. Combining detailed cathodoluminescence (CL) and electron backscatter diffraction (EBSD) analysis offers the opportunity to relate directly changes in crystallographic orientation to migrating boundaries. We observe the following features in naturally heated quartz grains from the thermal aureole of the Ballachulish Igneous Complex (Scotland, U.K.): (a) propagation of substructures and twin boundaries in swept areas both parallel and at an angle to the growth direction, (b) development of slightly different crystallographic orientations and new twin boundaries at both the growth interfaces and within the swept area and (c) a gradual change in crystallographic orientation in the direction of growth. All these features are compatible with a growth mechanism in which single atoms are attached and detached both at random and at preferential sites, i.e. crystallographically controlled sites or kinks in boundary ledges. Additionally, strain fields caused by defects and/or trace element incorporation may facilitate nucleation sites for new crystallographic orientations at distinct growth interfaces but also at continuously migrating boundaries. This study illustrates the usefulness of combined CL and EBSD in microprocess analysis. Further work in this direction may provide detailed insight into both the mechanism of static grain growth and the energies and mobilities of boundaries in terms of misorientation and grain boundary plane orientation.     

Low angle boundary migration of shot‐peened pure nickel investigated by electron channeling contrast imaging and electron backscatter diffraction

Study on recrystallization of deformed metal is important for practical industrial applications. Most of studies about recrystallization behavior focused on the migration of the high‐angle grain boundaries, resulting in lack of information of the kinetics of the low angle grain boundary migration. In this study, we focused on the migration of the low angle grain boundaries during recrystallization process. Pure nickel deformed by shot peening which induced plastic deformation at the surface was investigated. The surface of the specimen was prepared by mechanical polishing using diamond slurry and colloidal silica down to 0.02 μm. Sequential heat treatment under a moderate annealing temperature facilitates to observe the migration of low angle grain boundaries. The threshold energy for low angle boundary migration during recrystallization as a function of misorientation angle was evaluated using scanning electron microscopy techniques. A combination of electron channeling contrast imaging and electron backscatter diffraction was used to measure the average dislocation density and a quantitative estimation of the stored energy near the boundary. It was observed that the migration of the low angle grain boundaries during recrystallization was strongly affected by both the stored energy of the deformed matrix and the misorientation angle of the boundary. Through the combination of electron channeling contrast imaging and electron backscatter diffraction, the threshold stored energy for the migration of the low angle grain boundaries was estimated as a function of the boundary misorientation.     

Progressive steps in the development of electron backscatter diffraction and orientation imaging microscopy

Ten years ago electron backscatter diffraction (EBSD) became available to a wider group active in materials research. This paper highlights some of the more significant developments in camera technology and software developments that have arisen since then. The use of slow‐scan charge couple device cameras for phase identification and rapid determination of orientation image micrographs is reviewed. The current limiting spatial resolution of the technique is shown to be less than 10 nm. A procedure for improving lattice spacing measurement by utilizing the full resolution of the camera is described with experimental measurements on silicon and nickel showing relative errors of plus/minus 3%. An investigation of partially recrystallized aluminium shows how the recrystallized fraction can be extracted with confidence but that the mapping of substructure in the highly deformed regions is questionable. Phase identification is described for complex cases in which the phase data tabulated in standard databases do not correspond to what is observed in the EBSD patterns. Phase mapping in a complex mineral in which chemical data and EBSD data are collected simultaneously is shown to be improved by recording both the chemical and the EBSD data into computer memory and proceeding with the phase discrimination and orientation measurement in off‐line analysis.     

High-temperature electron backscatter diffraction and scanning electron microscopy imaging techniques: in-situ investigations of dynamic processes

In-situ heating experiments have been conducted at temperatures of approximately 1200 K utilising a new design of scanning electron microscope, the CamScan X500. The X500 has been designed to optimise the potential for electron backscatter diffraction (EBSD) analysis with concomitant in-situ heating experimentation. Features of the new design include an inclined field emission gun (FEG) column, which affords the EBSD geometrical requirement of a high (typically 160 degrees) angle between the incoming electron beam and specimen surface, but avoids complications in heating-stage design and operation by maintaining it in a horizontal orientation. Our studies have found that secondary electron and orientation contrast imaging has been possible for a variety of specimen materials up to a temperature of at least 900 degrees C, without significant degradation of imaging quality. Electron backscatter diffraction patterns have been acquired at temperatures of at least 900 degrees C and are of sufficient quality to allow automated data collection. Automated EBSD maps have been produced at temperatures between 200 degrees C and 700 degrees C in aluminium, brass, nickel, steel, quartz, and calcite, and even at temperatures >890 degrees C in pure titanium. The combination of scanning electron microscope imaging techniques and EBSD analysis with high-temperature in-situ experiments is a powerful tool for the observation of dynamic crystallographic and microstructural processes in metals, semiconductor materials, and ceramics.     

Extending the limit of atomic level grain boundary structure imaging using high-resolution electron microscopy

It has been possible to image ∑ = 21/[111]21.8° tilt boundaries in thin Au films and to deduce their atomic arrangements. These results represent an electron microscopic resolution level of 1.43 Å, attainable with a small amount of image processing, which produces interpretable structure images. This substantial improvement over other recent grain boundary studies, which required about 1.9–2.0 Å resolution, clearly demonstrates that many more tilt grain boundary orientations are now accessible instead of a limited subset.     

Characterization of crystallographic properties of SMC poly Si using electron backscattered diffraction

Crystallographic properties of silicide mediated crystallization (SMC) polycrystalline silicon (poly Si) and excimer laser annealing (ELA) poly Si were studied by electron backscattered diffraction. Large‐grain sized poly Si with a large fraction of low‐angle grain boundaries was acquired by SMC, and small‐grain sized poly Si with high‐angle grain boundaries especially around 60° was acquired by ELA. The thin film transistor (TFT) device characteristics were investigated in view of short‐range crystallinity (pattern quality) and long‐range crystallinity (misorientation distribution) of the specimens. Short‐range crystallinity did not significantly affect the TFT device characteristics, and long‐range crystallinity considering the low energy level of special boundaries could be better related to the TFT device characteristics of poly Si.     

Study of dynamic grain growth by electron microscopy and EBSD

The effect of hot deformation on fully recrystallized aluminium–copper alloys (Al-4wt%Cu and Al-33wt%Cu) with different volume fractions of CuAl₂ has been studied. The alloys are Zener pinned systems with different superplastic properties. Strain-induced grain growth, observed in both alloys, was quantitatively estimated by means of electron microscopy and EBSD and compared with the rate of static grain growth. Surface marker observations and in situ hot-deformation experiments combined with EBSD were aimed at clarifying the mechanisms responsible for the changes in the deformed microstructures. A sequence of secondary and backscattered electron images and EBSD maps was obtained during in situ SEM deformation with different testing conditions. Overlaying EBSD maps for the Al-4wt%Cu with channelling contrast images showed that grain boundary motion occurred during deformation, creating a layered structure and leading to an increase in size of some grains and shrinkage of others. Of a particular interest are results related to behaviour of CuAl₂ in superplastic Al-33wt%Cu during deformation, including several problems with the use of EBSD in this alloy.     

In situ transmission electron microscopy studies and real-time digital imaging

A newly designed CCD camera has been utilized for real-time and static image acquisitions. The performance of the camera is demonstrated for heating/cooling in-situ TEM experiments performed on a commercial high strength aluminium alloy using a double tilt heating holder. The real-time digital imaging capability of the new camera should facilitate the in-situ TEM that is now re-establishing itself as a strategic tool for materials characterization.