3D EBSD Research Articles

Influence of grain boundary plane distribution on ionic conductivity in yttria-stabilized zirconia sintered at elevated temperatures

The paper investigates electrical properties of fully stabilized zirconia, which is widely applied as a solid electrolyte in electrochemical devices such as solid oxide fuel cells. High ionic conductivity of these materials is crucial for effective operating of the devices; however, grain boundary resistivity limits conductivity in polycrystalline ceramics. Thus, optimisation of the microstructure of zirconia is necessary from an application point of view. Based on three-dimensional electron backscatter diffraction (3D EBSD) data, the research employed a complex impedance spectroscopy to establish a correlation between microstructure of cubic zirconia sinters and their conductivity. Samples with different levels of anisotropy in grain boundary plane parameters were investigated. The obtained results indicate that the conduction of ions through the grain boundaries is higher in the sample with the higher representation of the near-(001) grain boundaries. Such a relationship suggests that an over-representation of low-energy grain boundaries in zirconia polycrystals leads to an increase of ionic conductivity.

Influence of Sintering Conditions on Anisotropy of Grain Boundary Networks and Microstructure Topology in Yttria-Stabilized Zirconia

The paper presents original data of 3D EBSD orientation maps collected for 13 Yttria-Stabilized Zirconia (YSG) samples, sintered at different temperatures for different times. The largest map contains 18,833 grains and 64,506 grain boundaries. These data allowed for the analysis of grain boundary networks, based on all 5 macroscopic parameters and some topological studies of microstructures. Grain boundaries having the (001) and (111) boundary planes are favored and disfavored respectfully in all YSZ samples. The anisotropy appears to be stronger if grains are larger. However, large grains themselves do not imply strong anisotropy. Symmetric boundaries are slightly more frequent in YSZ compared to random boundaries, but despite some premises, the evidence for over-representation of 180 deg-tilt boundaries is still too weak. Distributions of the number of faces per grain and mean number of faces per grain are similar to those reported for metals, and there is a close-to-linear correlation between the number of faces and grain size.Graphical

Slip localization behavior at triple junctions in nickel-base superalloys

Incipient slip localization in the vicinity of hundreds of grain boundary triple junctions (TJs) in a lightly deformed nickel-base superalloy IN718 is studied using a combination of three-dimensional (3D) crystal plasticity finite element (CPFE) modeling, high resolution digital image correlation (HR-DIC) and 3D electron back-scatter diffraction tomography (3D EBSD). A 3D reconstruction method enables identification of thousands of TJs and correspondence of any observed slip bands with their originating TJ lines below the specimen surface. We present a large-scale CPFE model of the experimental 3D microstructure composed of high-fidelity representation of the TJ lines and the boundaries and interiors of the parent grains and use it to calculate the local micromechanical response and slip activity of all TJs at the onset of macroscopic yielding. Statistical analysis of the calculated quantities reveal TJs develop larger stress concentration and grain-average re-orientation than grain interiors and grain boundaries, however no substantial differences in cumulative slip were found among these microstructural regions. We find that TJs with observed slip bands generate lower grain-average re-orientation, fewer active slip systems, and more localized slip on a single system than those without. The distinctions in the reorientation and slip activity are stronger in TJs that experience more intense slip.

A 3D characterization of equiaxed grains induced by mediated nucleation in additively manufactured Inconel 718

In additive manufacturing of Ni-based alloy IN718, what causes Icosahedral Short-Range Order (ISRO) or iQC mediated nucleation of equiaxed grains is still not understood. In order to have a better comprehension of the microstructure formation, a more comprehensive characterization both on grain structure and chemical heterogeneities must be achieved. In this work, a scanning electron microscope equipped with a focused ion beam (FIB) allowed to perform a 3D EDS chemical analysis and EBSD orientation mapping of the volume in an equiaxed grain zone. After the 3D reconstruction of the equiaxed grains has been performed, grain-to-grain orientation analysis allowed to analyze multiple twin boundaries orientation relationships in a volume containing hundreds of grains. Chemical mapping using EDS allowed to identify TiC inclusions from which a five-fold symmetry axis seem to emerge, indicating a potential nucleation site. Such areas were analyzed in transmission electron microscopy (TEM) to investigate the different present phases. The nucleation sequence and potential origin of mediated nucleation are further discussed, opening new prospects for grain refinement in additively manufactured nickel-based alloys.

Hydrogen Embrittlement of Pre-Cathodically Hydrogen Charged Inconel 718 Fabricated via Selective Laser Melting: Fracture and Crack Propagation via 3D EBSD

Hydrogen Embrittlement of Pre-Cathodically Hydrogen Charged Inconel 718 Fabricated via Selective Laser Melting: Fracture and Crack Propagation via 3D EBSD

Multi-scale three-dimensional analysis on local arrestability of intergranular crack in high-strength martensitic steel

The present study investigated the local arrestability of intergranular crack in high-strength martensitic steel through multi-scale three-dimensional (3D) analysis using X-ray computed tomography and focused ion beam machining (FIB)-scanning electron microscopy (SEM) serial sectioning combined with electron backscattering diffraction (3D EBSD). Macroscopic analysis using X-ray computed tomography demonstrated discontinuous propagation of the intergranular cracks, indicating local arrest of the crack propagation. An analysis of the opening displacement of each crack component revealed that the resolved normal stress was not the only factor determining the intergranular crack propagation path. The relationship between the microstructure and local crack-arrestability was microscopically analyzed using FIB-SEM serial sectioning. The 3D EBSD analysis clearly suggested that the crack propagations were arrested at the low-angle grain boundary plane segments and at the grain boundary triple junctions surrounded by relatively large martensite variants. Moreover, the larger martensite variants around grain boundaries contributed to the plastic accommodation of stress concentration and promoted crack-tip blunting. We propose that increasing the fraction of low-angle grain boundary plane segments as well as that of large martensite variants existing around grain boundaries can enhance local crack-arrestability and retard intergranular fracture of high-strength martensitic steels.

Five dimensional grain boundary distribution for yttria stabilized zirconia based on experimentally determined macroscopic boundary parameters

Distributions showing the frequencies of occurrence of grain boundaries as functions of their 5 macroscopic boundary parameters have been computed for a set of yttria-stabilized zirconia samples sintered at different conditions and thus having different grain sizes. For this purpose, datasets containing both grain misorientation and boundary plane parameters have been collected by the means of the 3D EBSD technique. Then, the 5-parameter distributions have been computed using the approach based on kernel density estimation. A few top peaks are visible in all of the obtained distributions. Their heights exceed the level of the random distribution by at least about 3 multiples of the corresponding statistical errors. The list of favored grain boundaries includes the Σ3/(111) and Σ11/(11¯3) boundaries, as well as the boundaries having both the boundary plane (100) and misorientation by 10∘ to 37∘ about the [100] axis.The largest of the collected dataset containing 64,506 distinct grain boundaries, and being probably the largest dataset of this kind ever collected for zirconia, allowed to study e.g. rare boundaries like those with high Σ misorientations about the [110] axis.

Slip localization in Inconel 718: A three-dimensional and statistical perspective

The slip localization behavior of the polycrystalline nickel base superalloy Inconel 718 during monotonic tensile loading at room temperature, is investigated for the first time in relation to the 3D microstructure. Multi-modal data merging tools are used to recombine high resolution digital image correlation (HR-DIC) data with 3D electron back-scatter diffraction tomography (3D EBSD), over a wide region of interest. This procedure enables reconstruction of the slip band planes in the 3D microstructure. Statistical analyses conducted over 500 individual slip bands reveal strong correlations between their location and specific microstructure configurations. In particular, over half of the slip bands emanate from triple junction lines (3D lines defined by the junction of three crystals). Moreover, the most intense and longest slip bands, which would become critical fatigue crack nucleation sites during cyclic loading, are located close and parallel to particular annealing twin boundaries and are simultaneously connected to triple junction lines. Crystal plasticity finite elements calculations are performed on the experimental microstructure to identify the slip activity that results in the formation of high intensity slip bands (localized plasticity) or zones of high lattice rotation (non-localized plasticity) in these particular microstructure regions.

Five Dimensional Grain Boundary Distribution for Yttria Stabilized Zirconia Based on Experimentally Determined Macroscopic Boundary Parameters

Distributions showing the frequencies of occurrence of grain boundaries as functions of their 5 macroscopic boundary parameters have been computed for a set of yttria-stabilized zirconia samples sintered at different conditions and thus having different grain sizes. For this purpose, datasets containing both grain misorientation and boundary plane parameters have been collected by the means of the 3D EBSD technique. Then, the 5-parameter distributions have been computed using the approach based on kernel density estimation. A few top peaks are visible in all of the obtained distributions. Their heights exceed the level of the random distribution by at least about 3 multiples of the corresponding statistical errors. The list of favored grain boundaries includes the Σ3/(111) and Σ11/(1‾13) boundaries, as well as the boundaries having both the boundary plane (100) and misorientation by 10° to 37° about the [100] axis.

Integrated three-dimensional characterization of reactive phase formation and coarsening during isothermal annealing of metastable Zn–3Mg–4Al eutectic

Microstructural instabilities associated with a metastable lamellar eutectic when exposed to an elevated temperature were analyzed in a Zn−3Mg−4Al alloy as a model system. X-ray diffraction and scanning electron microscopy showed that annealing at a temperature 43 K below the equilibrium eutectic temperature converted the metastable ternary MgZn2/η-Zn/β-ZnAl eutectic to a stable mixture of Mg2Zn11/η-Zn/α-Al. 3D EBSD suggested that supersaturation of η-Zn with Mg and Al eased difficulties in nucleation of Mg2Zn11 and α-Al at the MgZn2/η-Zn phase interfaces. Quasi-in-situ X-ray nanotomography revealed that a reactive diffusion process prevailed in an early stage of annealing leading to rapid consumption of MgZn2 for growth of Mg2Zn11 and concomitant thinning and pinch-off of η-Zn lamellae. The reactive diffusion process also brought about significant and quantifiable changes in the topological characteristics of the η-Zn phase at remarkably shorter time scales compared to Rayleigh instability and Ostwald ripening mechanisms. The present results provide fresh insights on the short-term annealing effects on metastable eutectics, with relevance to structural evolution in additive manufacturing.

Laguerre tessellations and polycrystalline microstructures: a fast algorithm for generating grains of given volumes

ABSTRACT We present a fast algorithm for generating Laguerre diagrams with cells of given volumes, which can be used for creating RVEs of polycrystalline materials for computational homogenisation, or for fitting Laguerre diagrams to EBSD or XRD measurements of metals. Given a list of desired cell volumes, we solve a convex optimisation problem to find a Laguerre diagram with cells of these volumes, up to any prescribed tolerance. The algorithm is built on tools from computational geometry and optimal transport theory which, as far as we are aware, have not been applied to microstructure modelling before. We illustrate the speed and accuracy of the algorithm by generating RVEs with user-defined volume distributions with up to 20,000 grains in 3D. We can achieve volume percentage errors of less than 1% in the order of minutes on a standard desktop PC. We also give examples of polydisperse microstructures with bands, clusters and size gradients, and of fitting a Laguerre diagram to 3D EBSD measurements of an IF steel.

Analysis of polycrystalline microstructure of AlMgSc alloy observed by 3D EBSD

The aim of this paper is to evaluate an ambitious imaging experiment and to contribute to the methodology of statistical inference of the three-dimensional microstructure of polycrystalline materials. The microstructure of the considered Al-3Mg-0.2Sc alloy was investigated by three-dimensional electron backscattered diffraction (3D-EBSD), i.e., tomographic imaging with xenon plasma focused ion beam (Xe-FIB) alongside EBSD. The samples were subjected to severe plastic deformations by equal channel angular dressing (ECAP) and annealed subsequently prior to the mapping. First we compared the misorientation level needed for a reliable segmentation of grains distinguishing between conventional evaluation of two-dimensional cuts and the 3D data set. Then, using methods of descriptive spatial statistics, various morphological characteristics of a large number of grains were analyzed, as well as the crystallographic texture and the spatial distribution of grain boundaries. According to the results stated so far in the literature, an even microstructure was expected, nevertheless local inhomogeneities in grains and grain boundaries with regard to their size, texture and spatial distribution were observed and justified.

Comparison of segmentation of 2D and 3D EBSD measurements in polycrystalline materials

Comparison of segmentation of 2D and 3D EBSD measurements in polycrystalline materials

Correlative Microscopy Observation (3D EBSD + APT + TEM) on Intergranular Corrosion Behaviors in 316L Stainless Steel

Correlative Microscopy Observation (3D EBSD + APT + TEM) on Intergranular Corrosion Behaviors in 316L Stainless Steel

On the alignment of 3D EBSD data collected by serial sectioning technique

Three-dimensional Electron Back Scattering Diffraction (3D-EBSD) is a technique for microstructure characterization that works by sequential sectioning via mechanical polishing, Focused Ion Beam (FIB) milling or layer ablation by laser. In this technique, consecutive steps of sample preparation and EBSD measurement are employed to extract 2D-EBSD sections and to reconstruct the 3D microstructure. The 3D data collected by the serial sectioning technique, suffer from misalignment between the adjacent sections. In the present work, serial sectioning by mechanical polishing was employed to collect 3D EBSD data of a dual-phase (DP) steel sample. A previously developed algorithm based on the minimization of misorientation between the neighboring sections was utilized to accurately align the consecutive sections. The reconstructed microstructure was then used to validate the accuracy of the alignment algorithm. The results show that the alignment procedure has successfully improved the reconstructed 3D microstructure and produced reconstructed sections, which in terms of microstructural parameters (i.e. grain size and morphology), image quality and kernel average misorientation distribution resemble the results of a directly measured EBSD experiment and can be used to differentiate the 3D morphology and crystallography of martensite from ferrite in DP steels.

Three-dimensional Analysis and Reconstruction of Additively Manufactured Materials in the Cloud-Based BisQue Infrastructure

A microstructure analytics and 3D reconstruction software package, DREAM.3D, was integrated as a module into a cloud-based platform, BisQue. Parallelization of DREAM.3D module executions and the ability to parameterize pipeline variables over a range of values have led to insights about the grain segmentation misorientation tolerance in TriBeam-collected 3D EBSD datasets of additively manufactured materials with complex anisotropic microstructures. Furthermore, a comparison in grain size measurements was made between standard 2D metallographic slices and 3D measures using BisQue’s parallelized DREAM.3D module executions. The direction of cloud-based data infrastructure and the prospects for impact in material science are also discussed.

3D EBSD Analysis of Hydrogen Induced Cracking in Pipeline Steel Using Serial Section Broad Ion Beam Tomography

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Analysing single twinning events in Mg-6Zn using nanoindentation

The present work addresses the challenge of estimating the twin thickening stresses. Single twinning events were captured in solution treated and peak-aged Mg-6Zn alloy subjected to {101¯0} nanoindentation. Markedly different responses of twinning to aging are seen compared to slip. 3D EBSD and high resolution EBSD are combined with crystal plasticity finite element modelling to fully characterize the twinning event. A model is then derived to allow us to estimate the influence of alloying with Zn and peak aging on the stresses required for twin thickening using the depth of the pop-in and the nanoindentation hardness before twinning. The stress for twin thickening increases from 6 MPa to 26 MPa and 74 MPa with an error of ± 10% due to the addition of solute Zn and the presence of particles formed during peak aging respectively.

Automated 3D EBSD for metallic powders

Metallic powders are commonly used in additive manufacturing processes. While their post-process consolidated properties are widely studied, there is little research on the properties of the powders prior to consolidation. Understanding the powder characteristics before use in additive manufacturing processes could lead to fine-tuning properties of additively manufactured materials. The three-dimensional grain structure of metals can be useful in predicting their properties and microstructure. Powder particles are much smaller and more difficult to fixture and polish than their bulk counterparts, hence typical protocols are difficult to use when serially sectioning them. This method describes a recommendation as to how to fixture, mill, and image metallic powder particles using a Xe P-FIB to mill and take EBSD measurements. It is based on milling and imaging techniques used for bulk materials, but with the specific advantage of how to fixture the powder sample. Our modifications include:•the method of fixturing the specimen to the holder.•the method of protecting the sample during milling.

Novel Setup for High Performance Simultaneous 3D EBSD and 3D EDS Acquisition

Novel Setup for High Performance Simultaneous 3D EBSD and 3D EDS Acquisition