Electron Backscatter Diffraction Experiments Research Articles

Quantitative characterization of Zr60700 alloy plate rolling in different directions based on electron back-scatter diffraction

Fully annealed Zr60700 alloy plates with a thickness of 15 mm were rolled at 15%, 30%, 45%, 60%, and 75% thickness reductions, and the rolling paths were unidirectional rolling (UR) and cross-rolling (CR), respectively. Electron back-scatter diffraction (EBSD) experiments revealed that the texture developed gradually towards the basal texture with increased thickness reduction. Severe orientation hardening enhanced the deformation resistance of the CR sample, resulting in a higher grain size than the UR sample. The plastic deformation during the rolling process was dominated by dislocation slip. The results of the prediction based on the Schmid factor (SF) and the calculation based on the in-grain misorientation axis (IGMA) showed that the prismatic <a> slip was the primary deformation mode in the early stages of the UR and CR processes. With the increase in thickness reduction, the basal <a> and pyramidal <c+a> slip played an increasingly important role. Compared with the UR process, the CR process was more accessible to activate the basal <a> slip and more conducive to forming the basal texture. Mechanical tests showed that the CR samples exhibited higher isotropy than the as-received and UR samples.

Nanoscale speckle patterning for combined high‐resolution strain and orientation mapping of environmentally sensitive materials

AbstractScanning electron microscopy‐based high‐resolution digital image correlation (HRDIC) is now an established technique, providing full‐field strain and displacement measurement at the microscale. Techniques for generating speckle patterns for sub‐micron strain mapping can often be either substrate dependent or rely on applying aggressive conditions which may alter the microstructure of interest or damage the substrate in highly sensitive materials. We detail a modification of a methodology successfully applied in the literature to allow its use with metallic materials that are particularly sensitive to the corrosive media, such as copper‐base alloys. Nanometre‐thick silver films, applied with physical vapour deposition, are remodelled using NaBr in non‐aqueous isopropanol, replacing the aqueous solution of NaCl in the original method, forming a uniform dispersion of silver islands highly suitable for digital image correlation (DIC) measurement. The entire procedure is performed at ambient temperature. We find that the DIC pattern is suitably electron transparent to allow electron backscatter diffraction (EBSD) measurements without pattern removal, producing diffraction patterns of sufficient quality for cross‐correlation based high‐angular resolution EBSD. This property facilitates simultaneous EBSD and DIC mapping experiments, providing deeper insights into the kinematics of plastic deformation in crystalline materials. Sub‐100 nm islands are achieved through control of the sputter coating parameters, resulting in DIC cross‐correlation subwindows of 140 nm with a 50% overlap. This resolution is sufficient to capture the fine detail of strain localisation phenomena during plastic deformation, demonstrated here with a case study in CuCrZr, a precipitation‐hardened heat sink material for application in nuclear fusion components. Here, we extract full‐field displacement data with DIC and corresponding orientation information using EBSD without the need for pattern removal.

Effect of recrystallization degree on properties of passive film of super ferritic stainless steel S44660

Abstract The effect of the recrystallization degree on the properties of passive films formed in 0.1 M HNO3 solution for super ferritic stainless steel S44660 was examined in this study. The initial specimens, in their cold-rolled state, showed a high dislocation density, as observed through electron backscatter diffraction (EBSD) experiments. Analysis of potentiodynamic polarization (PDP) curves and electrochemical impedance spectroscopy (EIS) measurements suggested that with the increase of recrystallization degree, the corrosion current density reduced and the corrosion potential increased. As revealed by Mott–Schottky analysis, the passive film showed a dual structure of n-type and p-type semiconductors, with the carrier density of the passive film decreasing as the recrystallization degree increased. X-ray photoelectron spectroscopy (XPS) provided insights into the film composition, indicating that the Fe2O3 and Cr2O3 content, which improved the stability of the passive film, increased with the degree of recrystallization. In summary, the increase in recrystallization degree reduced the number of defects in the microstructure, thereby creating favorable conditions for the formation of highly protective passive films. The passive film formed after complete recrystallization exhibited enhanced corrosion resistance.

Structural transformation behavior of oxide scale during coiling of 0.9 wt% Cr-containing high-strength steel

The phase transformation mechanism of oxide scale on the surfaces of chromium (Cr)-free carbon steel and 0.9 wt% Cr-containing steel at different coiling temperatures and cooling rates was studied using thermal simulation and electron backscattering diffraction experiments. The results showed that the eutectoid transformation of both the steel followed the “C” curve relationship. The Cr-containing steel had a larger eutectoid transformation area fraction than the Cr-free carbon steel. The nose tip temperature of the eutectoid transformation of the oxide scale on the surfaces of Cr-free carbon steel and 0.9 wt% Cr-containing steel were 420∼510 °C and 420–480 °C, respectively. For the 0.9 wt% Cr-containing steel, the proportion of Σ3 and Σ13b grain boundaries in cubic Fe3O4 increased, followed by a decrease, when the coiling temperature decreased from 610 to 410 °C. The Σ3 and Σ13b grain boundaries of the Fe3O4 low-dimensional coincident site lattice had the highest proportion for 510 °C coiling temperature. The low-dimensional coincident site lattice grain boundaries could be used to enhance crack resistance and improve the oxide scale on the steel plate surface.

Temperature dependent deformation behavior and texture evolution in AA6082 aluminum alloy: An integrated experimental and crystal plasticity simulation approach

This research provides a comprehensive analysis of the texture and temperature dependent deformation behavior of the aluminum alloy AA6082. The study is performed using a combination of experimental deformation tests and computational simulations using a crystal plasticity (CP) framework. The primary objective is to identify the critical influence of temperature on local stress states and dislocation density within the material during tensile tests. From an experimental perspective, the study employs ex-situ deformation tests and subsequent electron backscatter diffraction (EBSD) data in combination with energy dispersive x-ray spectrometer (EDS) analysis at 200 °C and 400 °C. The experimental EBSD data are adopted, preprocessed and converted into a geometry file for the numerical simulations. On the computational front, a dislocation density-based material model is adopted for CP simulations. The physical and fitting parameters of the model are calculated, adopted from the literature, or calibrated by comparing the global simulation results with experimental stress-strain observations under uniaxial tensile load at room temperature, 200 °C and 400 °C. Empirical functions for solid solution strengthening, dislocation density, fitting parameters controlling mean free path and dislocation annihilation have been derived that can be used to quickly interpolate them for any intermediate temperature. These functions combined with other model parameters can now be used for temperature-dependent CP modeling of AA6082. The isothermal grain-scale simulation and ex-situ experimental results confirmed a noteworthy texture transformation at higher temperatures, characterized by a reduction in the primary Cube orientation and its transition into a Copper orientation due to the stretching process. The correlation between the experimental results and the simulations on macro- and micro-scales is reasonable, indicating the accuracy and effectiveness of the CP approach in predicting the temperature dependent deformation behavior and texture evolution in aluminum alloys.

A Comprehensive Material Model for the Super-Duplex Stainless Steel SAF2507 in a Welding Environment

The aim of this work is to describe a reliable methodology for determining parameters of a material model suitable for implementation in a welding simulation using the finite element method (FEM). The adopted methodology employs a multi-scale approach integrating a microstructure evolution model, a representative volume element (RVE) calibrated through experimental methods, including a thermal–mechanical simulator, and electron backscatter diffraction (EBSD) experiments. The result is a complete material model, which covers thermal, mechanical and metallurgical material models for SAF2507 (EN 1.4410), that shows promising results and was successfully implemented in finite element (FE) code. A direct comparison of experimental and calculated results shows a deviation of up to 12% for the phase fraction of austenite and 25% for the mean grain diameter of ferrite.

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.

Multiscale in-situ observations of the micro- and nanostructure of a PH 13-8 Mo maraging steel during austenitization

The aim of the present work is to elaborate on the microstructural evolution of a PH 13-8 Mo maraging steel during austenitization by using multiscale in-situ techniques, which range from high-temperature electron backscatter diffraction and high-energy X-ray diffraction to high-temperature transmission electron microscopy. In order to supplement these in-situ experiments, samples quenched from different temperatures after isochronal heating are subjected to an in-depth microstructural characterization by means of atom probe tomography.The results indicate diffusion-dominated kinetics for the α’ to γ transformation in the investigated heating rate range. Moreover, high-temperature electron backscatter diffraction experiments confirm the occurrence of the austenite memory effect. In addition to the inheritance of grain size and crystallographic orientation of the prior austenite grains, a lath-like substructure remains in austenite, which consists of thermally stable, geometrically necessary dislocations. It is suggested that these dislocations play the key role for enabling recrystallization at higher temperatures without prior cold deformation. This phenomenon is evidenced for the first time in a PH 13-8 Mo maraging steel. However, it is believed that excessive amounts of carbides at austenite grain boundaries or an alteration of the dislocation structure could impede this abnormal recrystallization.

Indexing high-noise electron backscatter diffraction patterns using convolutional neural network and transfer learning

The crystal orientation indexing method based on Hough transform has many “zero solution” points when indexing the crystal orientation of materials, especially those with large strains. We propose an efficient and migratable indexing method for fast and autonomous crystal orientations indexing of experimental electron backscatter diffraction (EBSD) patterns of various crystal structures by transfer learning. To better evaluate the performance of the model, the performance of the model was assessed both quantitatively based on the numerical metrics and qualitatively through the Inverse Pole Figure (IPF). The results of indexing high-noise nickel EBSD patterns show that the CNN-based indexing method could not only obtain an acceptable indexing accuracy (a mean disorientation error of 1.77° for retraining and 2.31° for transfer learning), but also reasonably index the “zero solution” points remained in the Hough transform-based indexing method. And the results of indexing other materials by transfer learning show that the CNN has strong knowledge migration capability. In addition, the interpretability of the CNN was investigated by visualizing feature maps of each convolutional layer, and the sensitivity analysis of the CNN was realized by testing masked images.

Mechanical behavior of austenitic stainless steels produced by wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is an innovative technology with the potential to drive the transformation and upgrading of metallic manufacturing industry and construction sector. The advantages of WAAM technology in rapid manufacturing, design freedom, and energy saving have attracted attentions in the construction field. This research study focuses on investigating the microstructural and mechanical behavior of austenitic stainless steels produced by wire arc additive manufacturing through test programs. The stainless steel plates were first additively manufactured using cold metal transfer technology with three types of feedstock wires (ER304, ER308L, ER316L). Tensile coupon specimens and microstructural observation samples were extracted from the WAAM plates. The electron backscatter diffraction (EBSD) experiments were conducted to identify and analyze the microstructures of the WAAM austenitic stainless steels. Five test orientations, namely θ = 0˚, 30˚, 45˚, 60˚, 90˚ relative to the printing layer direction, were designed to investigate the mechanical properties anisotropy. Two types of specimen surface condition (milled type and as-built type) were considered to assess the impact of geometric undulation. The geometric features of the as-built specimens were obtained using 3D laser scanning. A total of 60 tensile tests with the aid of digital image correlation (DIC) system were conducted to obtain the stress–strain responses of the WAAM austenitic stainless steels. The mechanical properties anisotropy of the WAAM austenitic stainless steels was analyzed in detail.

Local strength of bainitic and ferritic HSLA steel constituents understood using correlative electron microscopy and microcompression testing

HSLA steels with different polygonal ferrite and granular bainite contents resulting from two different cooling rates were investigated. Micropillar compression tests, electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) experiments were performed to reveal microscopic strength differences and their origin. The obtained results indicate that a higher cooling rate caused a smaller granular bainite substructure size and a higher dislocation density for both ferrite and bainite. In addition, the critical resolved shear stress (CRSS) values for both phases were found to be higher for the faster cooling process. This is ascribed to the increased dislocation density for faster cooling rather than the grain size as will be discussed in the manuscript. Interestingly, the macroscopic yield strength can be closely estimated by the CRSS obtained from micropillar compression considering the corresponding phase fractions. The achieved results can be used in future as input variables for crystal plasticity models.

Phenomenological understanding of kappa-carbides on strengthening mechanism of low-density steel

We elucidate here the phenomenological understanding of deformation mechanisms over a wide range of strain rates (5.5 × 10–4s–1 to 5.5 × 10–1s–1) based on the evolution of microstructure. Atom probe tomography (APT), transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) experiments were conducted to reveal the spatial distribution of precipitates and microstructure evolution. The ordered kappa-carbides were characterised by a layered-type structure, which made it difficult for dislocations to by-pass kappa-carbides in the same layer individually and the corresponding strengthening mechanism was cutting mechanism. Dislocations and microbands evolution analysis shows that compared to dislocations, slip band width was the key factor that governed the strength of the experimental steel at different strain rates.

Adaptable physics-based super-resolution for electron backscatter diffraction maps

In computer vision, single-image super-resolution (SISR) has been extensively explored using convolutional neural networks (CNNs) on optical images, but images outside this domain, such as those from scientific experiments, are not well investigated. Experimental data is often gathered using non-optical methods, which alters the metrics for image quality. One such example is electron backscatter diffraction (EBSD), a materials characterization technique that maps crystal arrangement in solid materials, which provides insight into processing, structure, and property relationships. We present a broadly adaptable approach for applying state-of-art SISR networks to generate super-resolved EBSD orientation maps. This approach includes quaternion-based orientation recognition, loss functions that consider rotational effects and crystallographic symmetry, and an inference pipeline to convert network output into established visualization formats for EBSD maps. The ability to generate physically accurate, high-resolution EBSD maps with super-resolution enables high-throughput characterization and broadens the capture capabilities for three-dimensional experimental EBSD datasets.

Advanced in-situ experimental techniques for characterization of deformation mechanisms in magnesium alloys

A combination of advanced in-situ experimental techniques, comprised of neutron diffraction, acoustic emission (AE), and in-situ electron backscattered diffraction (EBSD) was selected to provide extensive insight into the deformation behavior of magnesium alloys based on their mutual complementarity. The potential and limitations of these techniques were shown and discussed in the scope of the study of the influence of the crystallographic texture influence on the activity of individual deformation mechanisms in a hot-rolled sheet of the AZ31 magnesium alloy. The neutron diffraction experiments coupled with a recording of the AE signal allowed monitoring of the twinning activity and the evolution of its dynamics from nucleation toward twin growth. The AE suggested microplastic behavior, which was confirmed by the lattice strain evolution analysis for the sample compressed in the sheet normal direction. The in-situ EBSD experiments provided direct observation of the deformed microstructure, including the formation of twinning bands and the transition from twin nucleation to growth with progressing strain, being in very good agreement with the indirect neutron diffraction and AE measurements. Furthermore, the subsequent analysis of the EBSD maps enabled the quantification of the twinned volume fraction and its qualitative comparison with the evolution measured by neutron diffraction. The EBSD-based slip trace analysis revealed a notable non-Schmid basal activity and offered insight into the mechanisms accommodating strain once the twinning was exhausted.

Effects of chemical segregation on ductility-anisotropy in high strength Fe-Mn-Al-C lightweight austenitic steels

Ductile Fe-Mn-Al-C lightweight steels offer great potential as high specific strength materials for weight critical applications. In the present work, very high yield (∼1 GPa) and ultimate tensile strength levels (∼1.5 GPa) were obtained along the rolling and transverse directions of Fe-30Mn-8.5Al-0.9Si-0.9C-0.5Mo (wt.%), with high tensile elongation to failure of ∼35%. This excellent mechanical behavior was attributed to the nanoscale, ordered κ-carbide precipitates formed during aging after rolling. However, tensile ductility was not isotropic through all directions of the rolled plate. In particular, the ductility was consistently lower than 5% true strain along the normal direction. Upon detailed microstructural investigations, micro-scale lamellar chemical micro-segregation bands were detected, which caused the observed anisotropic embrittlement along certain plate directions. These bands resulted in low failure strains along the normal direction since it is oriented perpendicular to these chemical segregation bands, resulting in a failure type reminiscent of delamination-induced cleavage fracture. Chemical segregation causes an inhomogeneous κ-carbide precipitate distribution upon aging, producing more pronounced mechanical anisotropy after peak-aging as compared to the solution heat treated samples. Surprisingly, deformation twinning was observed after tensile deformation of solution-heat treated specimens via electron-backscatter diffraction experiments, which is anomalous for a high stacking fault energy (SFE) material. It was proposed that chemical micro-segregation promotes locally different SFE regions, leading to deformation twinning in this nominally high SFE material. Overall, this work demonstrates the effects of chemical segregation on mechanical properties and microstructural evolution in a high performance, lightweight Fe-Mn-Al-C steel.

Microstructure Evolution Mechanism of Ultra-Thin Dual Phase Magnesium-Lithium Alloy during Asymmetric Warm Rolling.

Magnesium–lithium alloy is the lightest metal alloy material so far, and the ultra-thin plate is also one of the main trends in the future development of Mg-Li alloy. In order to explore how to prepare LZ91 ultra-thin Mg-Li alloy, this topic adopts the combination of the finite element method (FEM) and visco-plastic self-consistent (VPSC) calculation, electron back-scattered diffraction (EBSD) and tensile experiment, and uses the asymmetric warm rolling process to realize the processing of ultra-thin LZ91 Mg-Li alloy plate with a thickness of 0.25 mm. The experimental results show that the maximum basal texture strengths of 1 mm initial plate and 0.25 mm ultra-thin rolled plate are 36.02 mud and 29.19 mud, respectively. The asymmetric warm rolling process not only reduces the basal texture strength but also significantly refines the grains. The tensile strength and yield strength of 0.25 mm ultra-thin rolled plate along the rolling direction reached 206.8 MPa and 138.4 MPa, respectively. This has a positive effect on the mechanical properties of subsequent materials. VPSC results show that the base slip is the main factor in Mg-Li alloy asymmetric warm rolling, and a large number of tensile twinning are initiated due to the coordinated deformation of the body-centered cubic (BCC) phase, which is beneficial to improve the plastic deformation capacity of Mg-Li alloy.

Crystal plasticity simulation of in-grain microstructural evolution during large deformation of IF-steel

High-resolution three-dimensional crystal plasticity simulations are used to investigate deformation heterogeneity and microstructure evolution during cold rolling of interstitial free (IF-) steel. A Fast Fourier Transform (FFT)-based spectral solver is used to conduct crystal plasticity simulations using a dislocation-density-based crystal plasticity model. The in-grain texture evolution and misorientation spread are consistent with experimental results obtained using electron backscatter diffraction (EBSD) experiments. The crystal plasticity simulations show that two types of strain localization features develop during the large strain deformation of IF-steel. The first type forms band-like areas with large strain accumulation that appear as river patterns extending across the specimen. In addition to these river-like patterns, a second type of strain localization with rather sharp and highly localized in-grain shear bands is identified. These localized features are dependent on the crystallographic orientation of the grain and extend within a single grain. In addition to the strain localization, the evolution of in-grain orientation gradients, misorientation features, dislocation density, kernel average misorientation, and stress in major texture components are discussed.

In Situ Observation of Tensile Deformation of Ti-22Al-25Nb Alloy and Characterization of Deformation in α2 Phase

The room temperature tensile deformation of Ti-22Al-25Nb alloy with an equiaxed α2 phase microstructure and the activated slip system of α2 particles were investigated by a combination of in situ tensile tests and electron backscatter diffraction experiments. The results demonstrate that only a few wide and long slip bands occur in the B2 matrix in the initial stage of yielding. With the tensile displacement increases, a large number of slip bands, including multiple- and cross-slip bands, appear in the B2 matrix and the distance between two adjacent slip bands decreases significantly. Meanwhile, the movement of the slip bands is hindered by the α2 particles and the B2 grain boundaries, and the slip bands appear only in a small number of the α2 particles. From the beginning of the tensile process to the final fracture, there are lots of α2 particles without slip bands. The slip bands penetrate the needle-like lamellar O phase without changing the slip direction. Compared with the α2 particles, the hindering effect of needle-like O phases on the motion of the slip bands is quite small. The microcracks nucleated at the α2/B2 phase boundaries or within the α2 particles, and microcracks propagated along the α2/B2 phase boundaries or across the α2 particles. The fracture surface shows the quasi-cleavage feature, which contains a large number of small and shallow dimples on planar facets. The analysis indicates that the plastic deformation of the alloy is mainly contributed by the B2 phase. For room temperature tensile deformation of α2 phase, there are three types of slip systems that can be activated, including the prism &lt;a&gt; type slip, the basal &lt;a&gt; type slip and the pyramidal &lt;a+c&gt; type slip. The prism &lt;a&gt; type slip is most likely to be activated, followed by the basal &lt;a&gt; type slip and finally the pyramidal &lt;a+c&gt; type slip. In addition, the critical resolved shear stress (CRSS) for the pyramidal &lt;a+c&gt; type slip is the highest among the three types of slip systems. Therefore, the deformation in the α2 phase is mainly contributed by the prism &lt;a&gt; type slip and the basal &lt;a&gt; type slip.

Effect of the anisotropy of martensitic transformation on ferrite deformation in Dual-Phase steels

The volume increase and shape change during austenite to martensite transformation in dual-phase (DP) steels are largely accommodated in the microstructure by the deformation of the surrounding ferrite matrix. Accurate estimation of transformation-induced deformation of ferrite via experiments and modeling is essential for predicting the subsequent mechanical behavior of DP steels. This study aims to illustrate the disadvantages of simplifying the anisotropic transformation deformation of martensite to isotropic dilatation for modeling the transformation-induced deformation of ferrite. A novel methodology is developed comprising sequential experimental and numerical research on DP steels to quantify transformation-induced strains in ferrite. This methodology combines the results of prior austenite grain reconstruction, phenomenological theory of martensite crystallography and electron backscatter diffraction (EBSD) orientation data to estimate variant-specific transformation deformation. Subsequently, by comparison of full-field micromechanical calculation results on a virtual DP steel microstructure with experimental EBSD kernel average misorientation and geometrically necessary dislocation measurement results it is shown that neglecting the shear deformation associated with the martensitic transformation leads to significant underestimation in the prediction of transformation-induced strains in ferrite.

Multiscale mechanical consequences of ocean acidification for cold-water corals

Ocean acidification is a threat to deep-sea corals and could lead to dramatic and rapid loss of the reef framework habitat they build. Weakening of structurally critical parts of the coral reef framework can lead to physical habitat collapse on an ecosystem scale, reducing the potential for biodiversity support. The mechanism underpinning crumbling and collapse of corals can be described via a combination of laboratory-scale experiments and mathematical and computational models. We synthesise data from electron back-scatter diffraction, micro-computed tomography, and micromechanical experiments, supplemented by molecular dynamics and continuum micromechanics simulations to predict failure of coral structures under increasing porosity and dissolution. Results reveal remarkable mechanical properties of the building material of cold-water coral skeletons of 462 MPa compressive strength and 45–67 GPa stiffness. This is 10 times stronger than concrete, twice as strong as ultrahigh performance fibre reinforced concrete, or nacre. Contrary to what would be expected, CWCs retain the strength of their skeletal building material despite a loss of its stiffness even when synthesised under future oceanic conditions. As this is on the material length-scale, it is independent of increasing porosity from exposure to corrosive water or bioerosion. Our models then illustrate how small increases in porosity lead to significantly increased risk of crumbling coral habitat. This new understanding, combined with projections of how seawater chemistry will change over the coming decades, will help support future conservation and management efforts of these vulnerable marine ecosystems by identifying which ecosystems are at risk and when they will be at risk, allowing assessment of the impact upon associated biodiversity.