A new EBSD indexing method with enhanced grain boundary indexing performance using a three-dimensional parameter space.

Electron backscatter diffraction (EBSD) is a technique used to measure crystallographic features in the scanning electron microscope. The technique is highly automated and readily accessible in many laboratories. EBSD pattern indexing is conventionally performed with raw electron backscatter patterns. These patterns are software processed to locate the band centres (and sometimes edges) from which the crystallographic index of each band is determined. Once a consistent index for many bands is obtained, the crystal orientation with respect to a reference sample and detector orientation can be determined and presented. Unfortunately, because of challenges related to crystal symmetry, there are limited available pattern-indexing approaches and this has probably hampered open development of the technique. In this article, a new method of pattern indexing is presented, based upon a method with which satellites locate themselves in the night sky, and its effectiveness is systematically demonstrated using dynamical simulations and real experimental patterns. The benefit of releasing this new algorithm as open-source software is demonstrated when this indexing process is utilized, together with dynamical solutions, to provide some of the first accuracy assessments of an indexing solution. In disclosing a new indexing algorithm, and software processing toolkit, the authors hope to open up EBSD developments to more users. The software code and example data are released alongside this article for third party developments.

Self-supporting thin Yttria Stabilized Zirconia (YSZ) ceramics electrolytes have been prepared by laser machining. They are carved from a sintered YSZ plate to shape a 20 µm thick and 8 mm in diameter central region, surrounded by an unprocessed 150 µm thick supporting zone. Scanning Electron Microscopy (SEM) and Electron BackScattering Diffraction (EBSD) studies confirmed that the strains produced by the laser processing are small and limited to only one or two layers of YSZ grains (~5 µm). SEM and Transmission Electron Microscopy (TEM) have been also used to characterize the surface of the membrane. It is corrugated and coated with YSZ nanoparticles as a result of the laser plasma deposition. Electrochemical characterization by Impedance Spectroscopy (EIS) showed that this surface morphology improves the electrical performance of the membrane slightly but clearly, reducing the cathode polarization resistance by about 5% in the 650-850 ºC range.

Investigation of microstructure and thermal expansion behaviour of a functionally graded YSZ/IN718 composite produced by laser-powder bed fusion

The increasing interest in nanostructured materials has raised the need for high spatial resolution orientation mapping and large‐scale quantitative characterisation of such microstructures. Because Electron Back Scatter Diffraction (EBSD) does not achieve such high spatial resolution on bulk samples, these kind of studies are often done using a Transmission Electron Microscope (TEM). However, TEM‐based orientation mapping techniques suffer from small field of view. As a result, Transmission Kikuchi Diffraction (TKD) in Scanning Electron Microscope (SEM) was developed as a technique capable of delivering the same type of results as EBSD but with a spatial resolution improved by up to one order of magnitude [1,2]. TKD analysis is conducted on an electron transparent sample using the same hardware and software as for EBSD system. But when using conventional EBSD geometry, the transmitted patterns (TKP) are captured by a vertical phosphor screen with a considerable loss of signal and with strong distortions induced by gnomonic projection. Also, with standard TKD detector configuration, most of the transmitted signal does not reach the phosphor screen and results in lower quality patterns which can have negative effect in the measurement quality. The limitations of such non‐optimal sample‐detector geometry can be overcome by an on‐axis detection system. With a horizontal phosphor screen placed underneath the sample, the transmitted signal is captured where it is the strongest and TKPs will have minimal distortions. Using low probe currents, the spatial resolution can be increased and the beam‐induced specimen drift reduced as compared to standard TKD detector configuration [3]. The improved stability and high spatial resolution allow the user to conduct large‐area TKD orientation mapping. Using a partially recrystallized ultrafine stainless steel sample, we will demonstrate that statistical data can be obtained for the quantitative characterisation of nanostructured materials in the SEM (figure 1).

This study explores the combined effect of edge profile design and ceramic particle reinforcement on the microstructure, mechanical performance, and corrosion resistance of friction stir welding (FSW) of AA6061 aluminum alloys. Two edge geometries, straight edge (STE) and square-wave edge (SQE), were used for welding both unreinforced and yttria-stabilised zirconia (YSZ)-reinforced AA6061 plates. Electron backscatter diffraction (EBSD) analysis revealed that the square-edge configuration and YSZ addition significantly refined the grain structure and enhanced dynamic recrystallization (DRX). Notably, the AA6061-YSZ-SQE sample exhibited the highest fraction of high-angle grain boundaries and the finest average grain size. Scanning electron microscope (SEM) results indicated that YSZ particles contributed to improved refinement and uniform distribution of precipitates through mechanisms like Zener pinning and particle-stimulated nucleation. AA6061-YSZ-SQE showed the highest hardness and tensile strength, owing to square-edge interlocking and YSZ reinforcement, offering superior strength with acceptable ductility. Corrosion testing demonstrated that square-edge reinforced specimens showed excellent electrochemical performance and resistance to localised corrosion. The AA6061-YSZ-SQE specimens exhibited the most positive corrosion potential, the highest pitting potential, and the least surface damage, showing superior passivation and stability.

Relationship between cracks and microstructures in APS YSZ coatings at elevated temperatures

Advanced analysis on growth mechanisms of thermally grown oxide at elevated temperature for thermal barrier coatings

Segmentation-crack structured yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying (APS) using a Triplex Pro™-200 gun. In this work, free-standing coating specimens (~700 μm) were isothermally heat-treated in air from 1200 to 1600 °C for 24 h and at 1550 °C for 20 to 100 h, respectively. The thermal aging behaviors such as microstructures, phase compositions, grain growth and mechanical properties were characterized via scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and a Vickers hardness test. The results indicated that the as-sprayed coatings mainly consisted of metastable tetragonal (t′-YSZ) phase, but the t′-YSZ gradually partitioned into equilibrium tetragonal (t-YSZ) and cubic (c-YSZ) phases due to yttrium diffusion during thermal exposure, and with an improvement in temperature, the c-YSZ may retain or transform into another yttrium-rich tetragonal (t″-YSZ) phase. The transformation of t-YSZ to monoclinic phase (m-YSZ) has occurred after 1550 °C/40 h heat treatment, and the content of the m-YSZ phase increased with the prolongation of the thermal exposure time. The variations of Vickers hardness have a correlation with pores healing and grain growth, which might be attributed to the coating sintering and m-YSZ phase formation. Furthermore, the growth pattern of the grains was investigated in detail. In service, cracks and pores proceeded along the grain boundaries, especially surrounding the small grains. It is conducive to the engineering application of TBCs fabricated with the Triplex Pro™-200 gun.

Thermal stability of yttria-stabilized zirconia (YSZ) and YSZ-Al2O3 coatings

Dark‐field (DF) imaging can be performed by selecting a specific diffracted beam in the selected area diffraction pattern in conventional transmission electron microscope (CTEM) or in the convergent beam electron diffraction pattern in scanning transmission electron microscopy (STEM) mode [1]. The resultant micrograph provides high intensity of the objects in the probed volume that diffract in this particular direction. In contrast, dark‐field micrographs can be obtained in STEM mode by capturing the signal from a specific range of scattering angles, with the most representative example being the high‐angle annular dark‐field imaging (HAADF) [2]. This leads to a contrast mostly based on atomic number differences between the different objects analysed [3]. These techniques were developed originally for CTEM and STEM. Because DF based on scattering angles is technically easy to obtain in a scanning electron microscope (SEM) by collecting the transmitted/diffracted signals with an electron detector below the thin specimen, it has been implemented in SEMs seriously since several years. This permitted taking advantage of the high contrast and low beam damage obtained at low accelerating voltages STEM in the SEM is now routinely achieved with a spatial resolution close to 1 nm in field‐emission SEMs [4]. Despite these new possibilities, DF imaging only based on diffracted beams has not been achieved yet in a SEM. The mostly used diffraction technique in the SEM has been, since the discovery of Venables [5], electron backscatter diffraction (EBSD) which has a spatial resolution of roughly 20‐30 nm and which needs a limited bulk surface preparation compared to CTEM or STEM. EBSD is assumed to be related to the electron channeling pattern (ECP) diffraction technique by the reciprocity theorem [6], although its angular resolution is, at this time, limited by the pixel resolution of the acquisition equipment. Figure 1 is a comparison between an ECP and an EBSP acquired at 20 kV from a [001] (001) silicon wafer. In this work, pseudo‐Kikuchi patterns (EBSP) recorded via EBSD were stored and reprocessed by reporting pixels or clusters of pixels intensities from a specific location in a reference EBSP to reconstruct the final image (EBSD map). A resulting micrograph (called EBSD‐DF image) was produced with a direct link to the diffracted beams in the EBSP and hence, to the crystallography of the sample, i.e., a DF image. The origin of the contrast is then similar to that of electron channeling contrast image (ECCI) as shown in Figure 2, in which EBSD‐DF micrographs of an indented compressed iron specimen with different reflections are displayed. However, the post‐acquisition processing is an invaluable advantage over ECCI because it allows generating multiple micrographs at the same time with only one set of EBSPs recorded in a beam raster fashion. This opens new ways of extracting and using the information contained in each EBSP and the main applications, at this point, are understanding deformation behaviors and interpretation [7] of channeling contrast [8].

Electron backscatter diffraction (EBSD) is a powerful tool to automatically and quantitatively characterize the orientation of grains and phases of ceramic and composite materials [1]. EBSD ultra‐fast pattern acquisition, i.e., patterns streaming to hard disk (HD) and later pattern indexing, becomes an interesting technique to investigate a series of large‐scale ceramic, which can quickly provide phase distribution information for further improving ceramic production. However at the same time, it becomes more and more important to handle the huge offline EBSD raw data efficiently and correctly. In this project, we already reported the EBSD characterisation results of the polymorphs of a solid state sintered silicon carbide component based on Densitec 15, a ready to press powder‐made by Saint Gobain Ceramic Materials AS [2]. The pre‐sintered powder was produced using the Acheson process and would typically consist of the 4H‐ and 6H‐polytypes, with small amounts of 3C and sometimes traces of 15R. The offline EBSD raw data collection was carried out in a Hitachi SU‐6600 FESEM and the patterns were acquired by using NORDIF UF‐1100 EBSD detector and written directly to HD. The previous results only identified 4H‐ and 6H‐phases in the sample, consistent with the expected transformation of 3C‐crystals that takes place at temperatures significantly lower than the sintering temperature of 2110°C. In this abstract further detailed phase identification of silicon carbide 3C by the new developed NORDIF EBSD Extraction Software is carried out. Figure 1 is the overview for the new developed NORDIF EBSD Extraction Software, where the indexed phase map of the present silicon carbide sample shows partly on the right part of the figure. Offline EBSD indexing reveals that the content of the silicon carbide 3C phase is below 0.5% in the sample. By using the point analysis tool (+) in the program, the individual EBSD patterns from the silicon carbide 3C phase can be retrieved from HD with auto contrast and background subtraction corrections. Representative 3C‐SiC EBSD patterns shown in Fig. 2 together with the corresponding internal coordinations (x,y), where the pattern (6,59) is exactly the same retrieved pattern shown that in Fig. 1. Further detailed 3C‐SiC pattern indexing is performed. Under the system optimized calibration settings, the best confidence indexes (CIs) in Fig. 2 are all below 0.03, and the representative indexing result shows in Fig. 3. As checking back and comparing that in Fig. 1, it can be concluded that the indexed 0.5% 3C‐SiC phases are mostly located at the boundaries among different grains, phases and pores, which resulted those EBSD patterns mis‐indexed as 3C‐SiC phase. Offline EBSD together with its Extraction Software is hence an excellent tool to study not only the crystallographic texture and phase distribution, but also fully confirmed that the 3C‐SiC recrystallisation and phase transformations processes taking place during sintering of ceramic materials. It also reveals that the present EBSD Extraction Software is good practice to carefully view the offline EBSD raw data before applying further processing algorithms.

The identification of crystallographic phases in the scanning electron microscope (SEM) has been limited by the lack of a simple way to obtain electron diffraction data of an unknown while observing the microstructure of the specimen. With the development of charge coupled device (CCD)-based detectors, backscattered electron Kikuchi patterns, alternately referred to as electron backscattered diffraction (EBSD) patterns, can be easily collected. Previously, EBSD has been limited to crystallographic orientation studies due to the poor pattern quality collected with video rate detector systems. With CCD detectors, a typical EBSD can now be acquired from a micron or submicron sized crystal using an exposure time of 1–10 s with an accelerating voltage of 10–40 kV and a beam current as low as 0.1 nA. Crystallographic phase analysis using EBSD is unique in that the properly equipped SEM permits high magnification images, EBSDs, and elemental information to be collected from bulk specimens. EBSD in the SEM has numerous advantages over other electron beam-based crystallographic techniques. The large angular view (∼70°) provided by EBSD and the ease of specimen preparation are distinct advantages of the technique. No sample preparation beyond what is commonly used for SEM specimens is required for EBSD.

Determination of the structure and orientation of nanometer-sized precipitates in matrix materials via transmission diffraction signals emitted by bulk samples in the Scanning Electron Microscope

Since the first automated electron backscatter diffraction (EBSD) results were attained 22 years ago, EBSD has become a common characterization technique in materials laboratories around the world. This has led to advancements and new understanding in not just crystallography but also in microstructural evolution, phase transformations, defects and dislocations, mechanical behavior, failure, and other materials phenomena. As a complement to scanning electron microscopy (SEM), EBSD is accessible and available to many researchers with little additional sample preparation. With improvements to both SEM and EBSD, it is now possible to analyze large areas for statistically significant data, and as precision increases, higher resolutions and smaller length scales have become accessible. EBSD analyses are also being combined with other characterization and analysis techniques to provide new insights. Although EBSD has matured and measurements have become more commonplace, new techniques, applications, and approaches continue to be introduced regularly. This collection of articles focuses on the versatility of EBSD in the range of materials systems presented, as well as on new techniques and applications of EBSD for materials characterization. Examples of the combination of EBSD with other characterization techniques include the supplementation and enhancement of EBSD data by transmission electron microscopy (TEM), atomic force microscopy (AFM), and electron channeling contrast imaging. Novel approaches to strain measurements, and the analysis of stacking faults, defects, and dislocations are also presented. The versatility of EBSD is demonstrated in the range of materials systems represented in these articles; EBSD analyses of conventional polycrystalline metals and alloys, novel lightweight alloys, second phase precipitates, and the complex structures of thin film solar cells are presented. The article from D. Abou-Ras and his co-workers provides an overview of the application of EBSD on thin-film solar cells. Of particular interest is the integration of EBSD results with several scanning probe microscopy techniques for correlating properties critical to photovoltaic performance with the crystallographic orientation aspects of the observed microstructures. I. Gutierrez-Urrutia, S. Zaefferer, and D. Raabe have reviewed a novel application of EBSD for imaging crystal defects, such as dislocations, cells, and stacking faults. EBSD is used to determine the optimal diffraction conditions for electron channeling contrast imaging to elucidate dislocation substructures similar to those observed using conventional TEM diffraction. Z. Chen and C.J. Boehlert combine EBSD with AFM to quantify deformation in an AZ31 magnesium alloy, noting that grain boundary sliding has a significant contribution. In the article by T. Ben Britton and colleagues, elastic strains are measured using highresolution, cross-correlation-based EBSD, presenting three examples of this exciting technique. Finally, Seiichi Suzuki presents a systematic overview of the transmission EBSD technique, which provides very high spatial resolution in orientation mapping. This collection of articles represents just a sampling of the new and exciting data being collected using EBSD, while also covering a breadth of work that illustrates both the utility and the potential of this important technique. As advancements continue to be made, we anticipate EBSD to fuel further innovative studies and bring exciting results in crystallography, microstructural evolution, materials processing, and microstructure quantification for years to come.

A new characterization approach for studying relationships between microstructure and creep damage mechanisms of uranium dioxide