An alignment algorithm using coherent twin boundaries as internal reference in 3D-EBSD.

A three-dimensional (3D) microstructural volume is reconstructed from a stack of two-dimensional sections which was obtained by serial sectioning coupled with electron back scattering diffraction (EBSD) mapping of a 316L austenitic stainless steel. A new alignment algorithm named linear translation by minimising the indicator (LTMI) is proposed to reduce the translational misalignments between adjacent sections by referencing to coherent twin boundaries which are flat and lying on {111} planes. The angular difference between the measured orientation of a flat twin boundary and that of the {111} plane is used as an indicator of the accuracy of the alignment operations. This indicator is minimised through linear translations of the centroids of triangular facets, which constitute grain boundaries at a distance not restricted by the in-plane step size of the EBSD maps. And hence the systematic trend in the translational misalignments can be effectively reduced. The LTMI alignment procedure proposed herein effectively corrects the misalignments remained by other methods on a 3D-EBSD data prepared using serial sectioning methods. The accuracy in distinguishing between coherent and incoherent twin boundaries is significantly improved.

Employing Constrained Nonnegative Matrix Factorization for Microstructure Segmentation.

Materials characterization using electron backscatter diffraction (EBSD) requires indexing the orientation of the measured region from Kikuchi patterns. The quality of Kikuchi patterns can degrade due to pattern overlaps arising from two or more orientations, in the presence of defects or grain boundaries. In this work, we employ constrained nonnegative matrix factorization to segment a microstructure with small grain misorientations, (<1∘), and predict the amount of pattern overlap. First, we implement the method on mixed simulated patterns-that replicates a pattern overlap scenario, and demonstrate the resolution limit of pattern mixing or factorization resolution using a weight metric. Subsequently, we segment a single-crystal dendritic microstructure and compare the results with high-resolution EBSD. By utilizing weight metrics across a low-angle grain boundary, we demonstrate how very small misorientations/low-angle grain boundaries can be resolved at a pixel level. Our approach constitutes a versatile and robust tool, complementing other fast indexing methods for microstructure characterization.

Simultaneous mapping of cathodoluminescence spectra and backscatter diffraction patterns in a scanning electron microscope.

Electron backscatter diffraction and cathodoluminescence are complementary scanning electron microscopy modes widely used in the characterisation of semiconductor films, respectively revealing the strain state of a crystalline material and the effect of this strain on the light emission from the sample. Conflicting beam, sample and detector geometries have meant it is not generally possible to acquire the two signals together during the same scan. Here, we present a method of achieving this simultaneous acquisition, by collecting the light emission through a transparent sample substrate. We apply this combination of techniques to investigate the strain field and resultant emission wavelength variation in a deep-ultraviolet micro-LED. For such compatible samples, this approach has the benefits of avoiding image alignment issues and minimising beam damage effects.

Formation of {111} oriented domains during the sputtering epitaxy growth of (001) oriented Iridium films.

In the wafer-scale growth of Ir(001) on yttria-stabilized zirconia (YSZ) by magnetron sputtering epitaxy two kinds of {111} oriented domains are observed. One consists of sharp 'fjord'-shaped features in which four 90° alternated rotational variants of {111} are possible and the second one consists of islands with less defined shapes in which eight 45° alternated rotational variants can be found. Their formation occurs directly at the Ir/YSZ interface along incoherent grain boundaries, likely nucleating at local defects of the YSZ surface. In order to avoid these misoriented domains, process separation and proper etching pretreatment of the wafers both before and between the sputtering processes have been found to be the key strategy for achieving reproducibility and overall better material quality.

Development of an Alternative Manufacturing Technology for Niobium Components.

Due to their physical and mechanical properties, niobium products are used in the nuclear power industry, chemical industry, electronics, medicine and in the defence industry. Traditional manufacturing technology for these products is characterized by long production cycles and significant material losses during their surface machining. This paper presents the results of a study on the fabrication of niobium products by Spark Plasma Sintering (SPS). Structural and mechanical tests were conducted on the products obtained, as well as a comparative analysis with the properties of products obtained using traditional technology. Based on the analysis of the test results obtained, recommendations were made for the sintering of Nb powders. It was found that the optimum temperature for sintering the powder is 2000 °C as the density of the material obtained is close to the theoretical density. The microstructure obtained is comparable to samples obtained by the traditional method after recrystallization annealing. Samples obtained according to the new technology are characterized by higher mechanical properties Rp0.2 and Rm and the highest hardness.

Synergistic Thermal and Electron Wind Force-Assisted Annealing for Extremely High-Density Defect Mitigation.

This study investigates the effectiveness of combined thermal and athermal stimuli in mitigating the extremely high-density nature of dislocation networks in the form of low-angle grain boundaries in FeCrAl alloy. Electron wind force, generated from very low duty cycle and high current density pulses, was used as the athermal stimulus. The electron wind force stimulus alone was unable to remove the residual stress (80% low-angle grain boundaries) due to cold rolling to 25% thickness reduction. When the duty cycle was increased to allow average temperature of 100 °C, the specimen could be effectively annealed in 1 min at a current density of 3300 A/mm2. In comparison, conventional thermal annealing requires at least 750 °C and 1.5 h. For specimens with 50% thickness reduction (85% low-angle grain boundaries), the electron wind force was again unable to anneal the defects even at 3300 A/mm2 current density and average temperature of 100 °C. Intriguingly, allowing average concurrent temperature of 200 °C eliminated almost all the low-angle grain boundaries at a current density of 700 A/mm2, even lower than that required for the 25% thickness reduced specimens. Comprehensive electron and X-ray diffraction evidence show that alloys with extremely high defect density can be effectively annealed in less than a minute at approximately 200 °C, offering a substantial improvement over conventional high-temperature annealing.

Quaternary Zinc Alloys with Magnesium, Calcium and Strontium after Hydrostatic Extrusion-Microstructure and Its Impact on Mechanical and Corrosion Properties.

The development of bioabsorbable implants from Zn alloys is one of the main interests in the new generation of biomaterials. The main drawbacks of Zn-based materials are their insufficient mechanical properties. In the presented studies, a quaternary alloy composed of zinc with magnesium (0.2-1 wt. %), calcium (0.1-0.5 wt. %) and strontium (0.05-0.5 wt. %) was prepared by gravity casting followed by hot extrusion and then by hydrostatic extrusion. Microstructural characterization using scanning electron microscopy (SEM) and X-ray diffraction (XRD) phase analysis was performed. The mechanical properties were examined, using static tensile tests. Corrosion properties were analyzed using immersion tests. Samples were immersed in Hanks' solution (temperature = 37 °C, pH = 7.4) for 14 days. All alloys were subjected after corrosion to SEM observations on the surface and cross-section. The corrosion rate was also calculated. The microstructure of the investigated quaternary alloy consists of the α-Zn grains and intermetallic phases Mg2Zn11, CaZn13 and SrZn13 with different grain sizes and distribution, which impacted both mechanical and corrosion properties. Thanks to the alloying by the addition of Mg, Ca, and Sr and plastic deformation using hydrostatic extrusion, outstanding mechanical properties were obtained along with improvement in uniformity of corrosion rate.

Ultrasonic characterization of microstructural changes due to static recrystallization and grain growth in Inconel 625 and Inconel 718 superalloys.

In many metallic materials such as Inconel superalloys, the microstructure and grain size play an important role in their mechanical and physical properties and could impact the performance during long-term service at the operational temperature. Therefore, on-site detection of the microstructural transformation (such as recrystallization and grain growth) is of primary importance from a structural integrity point of view. Nondestructive evaluation methods such as the ultrasonic attenuation measurement offer a unique advantage that they can be used to evaluate the microstructure evolution of a component during fabrication or service operation. Nondestructive determination of the grain size could help predict the mechanical behavior of the component. In this study, the measured attenuation coefficient was fitted to a theoretical attenuation model to establish the grain size, which shows a strong quantitative agreement with the grain size determined from Electron Backscatter Diffraction (EBSD) analysis. Furthermore, the EBSD texture results confirmed the existence of a recrystallization temperature region previously established using hardness measurements. This experimental evidence demonstrates that ultrasonic attenuation can predict the grain transformation that could occur during material processing or operational service.

A Study of the Internal Deformation Fields and the Related Microstructure Evolution during Thermal Fatigue Tests of a Single-Crystal Ni-Base Superalloy.

Ni-base superalloys operate in harsh service conditions where cyclic heating and cooling introduce deformation fields that need to be investigated in detail. We used the high-angular-resolution electron backscatter diffraction method to study the evolution of internal stress fields and dislocation density distributions in carbides, dendrites, and notch tips. The results indicate that the stress concentrations decay exponentially away from the notch, and this pattern of distribution was modified by the growth of cracks and the emission of dislocations from the crack tip. Crack initiation follows crystallographic traces and is weakly correlated with carbides and dendrites. Thermal cycles introduce local plasticity around carbides, the dendrite boundary, and cracks. The dislocations lead to higher local stored energy than the critical value that is often cited to induce recrystallization. No large-scale onset of recrystallization was detected, possibly due to the mild temperature (800 °C); however, numerous recrystallized grains were detected in carbides after 50 and 80 cycles. The results call for a detailed investigation of the microstructure-related, thermally assisted recrystallization phenomenon and may assist in the microstructure control and cooling channel design of turbine blades.

Epitaxial Metal Electrodeposition Controlled by Graphene Layer Thickness.

Control over material structure and morphology during electrodeposition is necessary for material synthesis and energy applications. One approach to guide crystallite formation is to take advantage of epitaxy on a current collector to facilitate crystallographic control. Single-layer graphene on metal foils can promote "remote epitaxy" during Cu and Zn electrodeposition, resulting in growth of metal that is crystallographically aligned to the substrate beneath graphene. However, the substrate-graphene-deposit interactions that allow for epitaxial electrodeposition are not well understood. Here, we investigate how different graphene layer thicknesses (monolayer, bilayer, trilayer, and graphite) influence the electrodeposition of Zn and Cu. Scanning transmission electron microscopy and electron backscatter diffraction are leveraged to understand metal morphology and structure, demonstrating that remote epitaxy occurs on mono- and bilayer graphene but not trilayer or thicker. Density functional theory (DFT) simulations reveal the spatial electronic interactions through thin graphene that promote remote epitaxy. This work advances our understanding of electrochemical remote epitaxy and provides strategies for improving control over electrodeposition.

An Investigation of the Anisotropic Mechanical Properties of Additive-Manufactured 316L SS with SLM.

Selective laser melting (SLM) forms specimens that often exhibit anisotropic mechanical properties. Most existing research only explains that the mechanical properties of specimens perpendicular to the build direction are superior to those parallel to the build direction. In this paper, the mechanical properties of SLM 316L SS specimens with different surfaces and different directions are compared. Finally, it was found that the mechanical properties of specimens on Face 3 are stronger than those on Face 1 and Face 2, while the mechanical properties of specimens on Face 1 and Face 2 are similar. For specimens in different directions on the same surface, the mechanical properties of Face 1 and Face 2 exhibit clear anisotropy, while the mechanical properties of Face 3 tend to be isotropic. In this paper, the EBSD technique was used to analyze the specimens. It was found that the anisotropy of the mechanical properties of Face 1 and Face 2 are attributed to the presence of texture and columnar crystals in the sample. This paper can provide accurate and reliable material performance data for the practical application of SLM 316L SS, thereby guiding the optimization of engineering design and manufacturing processes.

Quasi-In Situ Observation of the Microstructural Response during Fatigue Crack Growth of Friction Stir Welded AA2024-T4 Joint.

The reliability of friction stir welded joints is a critical concern, particularly given their potential applications in the aerospace manufacturing industry. This study offers a quasi-in situ observation of the microstructural response during fatigue crack growth (FCG) of a friction stir welded AA2024-T4 joint, aiming to correlate fatigue crack growth behavior with mechanical properties investigated using electron backscatter diffraction (EBSD). Notched compact tension (CT) specimens corresponding to the morphology of the stir zone (SZ), advancing side (AS), and retreating side (RS) were meticulously designed. The findings indicate that the welding process enhances the joint's resistance to fatigue crack growth, with the base metal exhibiting a shorter fatigue life (i.e., ~105 cycles) compared to the welding zones (SZ ~ 3.5 × 105 cycles, AS ~ 2.5 × 105 cycles, and RS ~ 3.0 × 105 cycles). Crack propagation occurs within the stir zone, traversing refined grains, which primarily contribute to the highest fatigue life and lowest FCG rate. Additionally, cracks initiate in AS and RS, subsequently expanding into the base metal. Moreover, the study reveals a significant release of residual strain at the joint, particularly notable in the Structural-CT-RS (Str-CT-RS) sample compared to the Str-CT-AS sample during the FCG process. Consequently, the FCG rate of Str-CT-AS is higher than that of Str-CT-RS. These findings have significant implications for improving the reliability and performance of aerospace components.

Three-Dimensional Columnar Microstructure Representation Using 2D Electron Backscatter Diffraction Data for Additive-Manufactured Haynes®282®.

This study provides a methodology for exploring the microstructural and mechanical properties of the Haynes®282® alloy produced via the Powder Bed Fusion-Electron Beam (PBF-EB) process. Employing 2D Electron Backscatter Diffraction (EBSD) data, we have successfully generated 3D representations of columnar microstructures using the Representative Volume Element (RVE) method. This methodology allowed for the validation of elastic properties through Crystal Elasticity Finite Element (CEFE) computational homogenization, revealing critical insights into the material behavior. This study highlights the importance of accurately representing the grain morphology and crystallographic texture of the material. Our findings demonstrate that created virtual models can predict directional elastic properties with a high level of accuracy, showing a maximum error of only ~5% compared to the experimental results. This precision underscores the potential of our approach for predictive modeling in Additive Manufacturing (AM), specifically for materials with complex, non-homogeneous microstructures. It can be concluded that the results uncover the intricate link between microstructural features and mechanical properties, underscoring both the challenges encountered and the critical need for the accurate representation of grain data, as well as the significance of achieving a balance in EBSD area selection, including the presence of anomalies in strongly textured microstructures.

Dislocation Hardening in a New Manufacturing Route of Ferritic Oxide Dispersion-Strengthened Fe-14Cr Cladding Tube.

The microstructure evolution associated with the cold forming sequence of an Fe-14Cr-1W-0.3Ti-0.3Y2O3 grade ferritic stainless steel strengthened by dispersion of nano oxides (ODS) was investigated. The material, initially hot extruded at 1100 °C and then shaped into cladding tube geometry via HPTR cold pilgering, shows a high microstructure stability that affects stress release heat treatment efficiency. Each step of the process was analyzed to better understand the microstructure stability of the material. Despite high levels of stored energy, heat treatments, up to 1350 °C, do not allow for recrystallization of the material. The Vickers hardness shows significant variations along the manufacturing steps. Thanks to a combination of EBSD and X-ray diffraction measurements, this study gives a new insight into the contribution of statistically stored dislocation (SSD) recovery on the hardness evolution during an ODS steel cold forming sequence. SSD density, close to 4.1015 m-2 after cold rolling, drops by only an order of magnitude during heat treatment, while geometrically necessary dislocation (GND) density, close to 1.1015 m-2, remains stable. Hardness decrease during heat treatments appears to be controlled only by the evolution of SSD.

Failure mechanisms data analysis during tension of additively manufactured Ti-6Al-4V alloy reinforced with nano-zirconia particles: Investigations of the crack path.

The data presented here aim to show how to analyze crack propagation of a novel metallic matrix composite of Ti-6Al-4V reinforced with 1 wt.% nano-yttria-stabilized zirconia processed by laser powder bed fusion technology. The data was acquired via microstructural observations and electron backscatter diffraction (EBSD) analyses after the quasistatic tensile tests at room temperature. The overall crack path configuration based on the fracture surface observation by scanning electron microscopy (SEM) was first operated, presenting two main regions: (i) local inclined planes (hereafter denoted as "stair-like"), and (ii) region in accordance with the theoretical mode I fracture plane. Thereafter, a series of EBSD data set on a surface obtained after longitudinal cut off operation on one failed piece was conducted at three distinct positions: (i) in the stair-like configuration region, (ii) in the mode I fracture region, and (iii) in the region where the crack path made his transition between these two mechanisms. Since the EBSD data sets were not prone to any post-processing filtering operation, comparison of the observed mechanism with other Ti-6Al-4V alloy processed by additive manufacturing (AM) technology can be easily carried out.

Diffraction-Based Multiscale Residual Strain Measurements.

Modern analytical tools, from microfocus X-ray diffraction (XRD) to electron microscopy-based microtexture measurements, offer exciting possibilities of diffraction-based multiscale residual strain measurements. The different techniques differ in scale and resolution, but may also yield significantly different strain values. This study, for example, clearly established that high-resolution electron backscattered diffraction (HR-EBSD) and high-resolution transmission Kikuchi diffraction (HR-TKD) [sensitive to changes in interplanar angle (Δθθ)], provide quantitatively higher residual strains than micro-Laue XRD and transmission electron microscope (TEM) based precession electron diffraction (PED) [sensitive to changes in interplanar spacing (Δdd)]. Even after correcting key known factors affecting the accuracy of HR-EBSD strain measurements, a scaling factor of ∼1.57 (between HR-EBSD and micro-Laue) emerged. We have then conducted "virtual" experiments by systematically deforming an ideal lattice by either changing an interplanar angle (α) or a lattice parameter (a). The patterns were kinematically and dynamically simulated, and corresponding strains were measured by HR-EBSD. These strains showed consistently higher values for lattice(s) distorted by α, than those altered by a. The differences in strain measurements were further emphasized by mapping identical location with HR-TKD and TEM-PED. These measurements exhibited different spatial resolution, but when scaled (with ∼1.57) provided similar lattice distortions numerically.

Accurate and fast localization of EBSD pattern centers for screen moving technology.

The authors of this study develop an accurate and fast method for the localization of the pattern centers (PCs) in the electron backscatter diffraction (EBSD) technique by using the model of deformation of screen moving technology. The proposed algorithm is divided into two steps: (a) Approximation: We use collinear feature points to obtain the initial value of the coordinates of the PC and the zoom factor. (b) Subdivision: We then construct a deformation function containing the three parameters to be solved, select a large region for global registration, use the inverse compositional Gauss-Newton (ICGN) to optimize the objective function, and obtain the results of iteration of the PC and the zoom factor. The proposed algorithm was applied to simulated patterns, and yielded an accuracy of measurement of the PCs that was better than 4.6×10-6 of their resolution while taking only 0.2 s for computations. Moreover, the proposed algorithm has a large radius of convergence that makes it robust to the initial estimate. We also discuss the influence of factors of mechanical instability on its results of calibration during the insertion of the detector, and show that errors in measurements caused by the tilt motion of the camera are related only to the tilt angle of its motion and the detector distance, and are unrelated to the distance moved by it.

Correction of step size dependency in local misorientation obtained by EBSD measurements: Introducing equidistant local misorientation.

The local misorientation, known as KAM, is affected by both the step size (representing the spacing of measurement points applied in orientation measurements) and the point distance (indicating the distance between the points used in the misorientation calculation). The point distance can be increased by selecting surrounding points that are far from the target point. This study proposed the concept of an equidistant local misorientation, for which surrounding points at the same point distance from the target point were selected to calculate misorientation. An arbitrary point distance can be set for the equidistant local misorientation regardless of the step size. The changes in equidistant local misorientation for various point distances were calculated for the crystal orientation datasets obtained with different step sizes and measurement grids (square or hexagonal) using Type 316 stainless steel specimens, in which plastic strain of about 5 % was induced. It was shown that the equidistant local misorientation was identical regardless of the step size and measurement grid when the same point distance was used. Then, it was concluded that the difference in the local misorientation which emanated from the difference in step size could be corrected by employing the equidistant local misorientation. Increasing the point distance improved the signal-to-noise (S/N) ratio in the mapping data of the equidistant local misorientation. However, the results suggested that the maximum point distance for enhancing the S/N ratio should be within 30 % of the average grain size. On the other hand, decreasing the step size by keeping the point distance constant was found not to improve the S/N ratio, while it enhanced the spatial resolution of the mapping data.

Microstructure and crystallographic texture data in modern giant clam shells (Tridacna squamosa and Hippopus hippopus).

This article provides novel data on the microstructure and crystallographic texture of modern giant clam shells (Tridacna squamosa and Hippopus hippopus) from the Coral Triangle region of northeast Borneo. Giant clams have two aragonitic shell layers-the inner and outer shell layer. This dataset focuses on the inner shell layer as this is well preserved and not affected by diagenetic alteration. To prepare samples for analysis, shells were cut longitudinally at the axis of maximum growth and mounted onto thin sections. Data collection involved scanning electron microscopy (SEM) to determine microstructure and SEM based electron backscatter diffraction (EBSD) for quantitative measurement of crystallographic orientation and texture. Post-acquisition reanalysis of saved EBSD patterns to optimize data quality included changing the number of reflectors and band detection mode. We provide EBSD data as band contrast images and colour-coded orientation maps (inverse pole figure maps). Crystallographic co-orientation strength obtained with multiple of uniform density (MUD) values are derived from density distributed pole figures of indexed EBSD points. Raw EBSD data files are also given to ensure repeatability of the steps provided in this article and to allow extraction of further crystallographic properties for future researchers. Overall, this dataset provides 1. a better understanding of shell growth and biomineralization in giant clams and 2. important steps for optimizing data collection with EBSD analyses in biogenic carbonates.

A simple, static and stage mounted direct electron detector based electron backscatter diffraction system.

To engineer the next generation of advanced materials we must understand their microstructure, and this requires microstructural characterization. This can be achieved through the collection of high contrast, data rich, and insightful microstructural maps. Electron backscatter diffraction (EBSD) has emerged as a popular tool available within the scanning electron microscope (SEM), where maps are realized through the repeat capture and analysis of Kikuchi diffraction patterns. Typical commercial EBSD systems require large and sophisticated detectors that are mounted on the side of the SEM vacuum chamber which can be limiting in terms of widespread access to the technique. In this work, we present an alternative open-hardware solution based upon a compact EBSD system with a simple, static geometry that uses an off-the-shelf direct electron detector co-mounted with a sample. This simple stage is easy to manufacture and improves our knowledge of the diffraction geometry significantly. Microscope and detector control is achieved through software application programming interface (API) integration. After pattern capture, analysis of the diffraction patterns is performed using open-source analysis within AstroEBSD. To demonstrate the potential of this set up, we present two simple EBSD experiments using a line scan and area mapping. We hope that the present system can inspire simpler EBSD system design for widespread access to the EBSD technique and promote the use of open-source software and hardware in the workflow of EBSD experiments.