Serial Sectioning Experiments Research Articles

Dictionary Indexing of Electron Back-Scatter Diffraction Patterns: a Hands-On Tutorial

Dictionary indexing of electron back-scatter patterns was recently proposed as an alternative to the commercially available indexing packages. In this tutorial paper, we describe in detail the various steps that need to be taken to successfully complete an indexing run on an arbitrary data set. We provide three toy data sets for the reader to experiment with: poly-crystalline nickel with several different acquisition conditions, orthorhombic forsterite, and a single slice from a large serial sectioning experiment on a Ni-based superalloy. The data files and all files produced by the indexing routine are made available as Supplementary Material (https://doi.org/10.1184/R1/7792505).

Topology characteristics of three-dimensional grains in polycrystalline materials

The quantitative microstructural analysis in recrystallized pure iron is carried out by serial sectioning experiment coupled with three-dimensional (3-D) grain reconstruction technique. The full 3-D morphology of 16254 pure iron grains, which is the largest experimental 3-D grain dataset to date, is obtained. It is shown that the peak and the mean of the grain face number distribution were 10 and 13.5, respectively. For individual grains, the average trends that the highest and lowest face classes exhibited the highest affinity for mutual contact but the lowest affinity for contact with themselves are experimentally confirmed by 3-D pure iron grains. The pure iron grains are observed to have much more three-edged faces than Monte Carlo grains, resulting in relatively higher average dispersions of the grain edge distribution.

Analysis on topological grain forms via large-scale serial sectioning experiment and Monte Carlo simulation

Topological forms of three-dimensional grains were investigated by means of large-scale serial sectioning experiment (16,254 pure iron grains) and Monte Carlo-Potts model simulation (150,428 simulation grains). Noticeable topological bias among pure iron grains, Monte Carlo grains and other type of cells is observed in terms of the most frequent grain forms. Moreover, Monte Carlo structure has lower average dispersion for edge distributions of grains than pure iron microstructure, Poisson-Voronoi structure and isolated convex polyhedra, which indicates that some differences in kinetics or evolution processes may play a role in such topological differentiation.

3D reconstruction and characterization of carbides in Ni-based high carbon alloy in a FIB-SEM system

Abstract Dual beam focused ion beam scanning electron microscopes (FIB-SEMs) are well suited for characterizing micron and submicron size microstructural features in three dimensions throughout a serial-sectioning experiment. In this article, a FIB-SEM instrument was used to collect morphological, crystallographic, and chemical information for an Ni–Ta–Al–Cr alloy of high carbon content. The alloy has been designed to have excellent tribological properties at elevated temperatures. The morphology, spatial distribution, scale, and degree of interconnection of primary carbides in the Ni–Ta–Al–Cr–C alloy was assessed via serial sectioning in a casting cross-section. The 3D reconstructions showed that the primary carbides and dendrites were forming a dendrite surrounded by primary carbide network over the entire cross-section. Additionally, the morphology and spatial distribution of secondary carbides after heat treatment was determined.

Experimental measurement of surface strains and local lattice rotations combined with 3D microstructure reconstruction from deformed polycrystalline ensembles at the micro-scale

AbstractThis article describes a new approach to characterize the deformation response of polycrystalline metals using a combination of novel micro-scale experimental methodologies. An in-situ scanning electron microscope (SEM)-based tension testing system was used to deform micro-scale polycrystalline samples to modest and moderate plastic strains. These tests included measurement of the local displacement field with nm-scale resolution at the sample surface. After testing, focused ion beam serial sectioning experiments that incorporated electron backscatter diffraction mapping were performed to characterize both the internal 3D grain structure and local lattice rotations that developed within the deformed micro-scale test samples. This combination of experiments enables the local surface displacements and internal lattice rotations to be directly correlated with the underlying 3D polycrystalline microstructure, and such information can be used to validate and guide further development of modeling and simulation methods that predict the local plastic deformation response of polycrystalline ensembles.

Equivalent Elastic Property of Cast Aluminum Alloy around Clustered Shrinkage Pores

The mechanical properties of the clustered shrinkage pores in high-pressure die cast aluminum alloy ADC12 were evaluated through the serial sectioning experiment and the image-based finite element analyses. We have investigated the effect of pores on the fatigue strength, and found a mechanical significance of the clustered shrinkage pores, which considerably undermines the fatigue strength of die cast aluminum alloys. In this study, we constructed twenty three unit cell models for the homogenization analysis based on the three-dimensional image of a clustered shrinkage pore. From the homogenization analysis and uniaxial extension analysis, we obtained the equivalent elastic constants and the micro stress concentration factor as a function with respect to the porosity volume fraction.

A framework for automated analysis and simulation of 3D polycrystalline microstructures.: Part 1: Statistical characterization

This is the first of a two-part paper aimed at developing a robust framework for the collection, quantification and simulation of 3D polycrystalline microstructures. Serial-sectioning methods are used to generate data that characterize the microstructural morphology and crystallography of grains. The microstructure simulation model and codes take as input a series of electron backscatter diffraction (EBSD) patterns from the serial-sectioning experiments. Robust statistical analysis of the grain-level microstructures in 3D is conducted in this part of this paper. This analysis can provide necessary information for modeling and simulation efforts in the form of a highly refined and unbiased description of specific features, such as the distribution of grain size, shape and orientation.

A framework for automated 3D microstructure analysis & representation

Over the past 5 years there have been significant advances in developing serial-sectioningmethods that provide quantitative data describing the structure and crystallography of grain-level microstructures in three dimensions (3D). The subsequent analysis and representation of this information can provide modeling and simulation efforts with a highly-refined and unbiased characterization of specific microstructural features. For example, the grain structure and crystallography of an engineering alloy could be characterized and then translated directly into a 3D volume mesh for subsequent Finite Element Analysis. However, this approach requires a multitude of data sets in order to appropriately sample the intrinsic heterogeneity observed in typical microstructures. One way to circumvent this issue is to develop computation tools that create synthetic microstructures that are statistically-equivalent to the measured structure. This study will discuss the development of software programs that take as input a series of Electron Backscatter Diffraction Patterns from a serial sectioning experiment, and output a robust statistical analysis of the 3D data, as well as generate a host of synthetic structures which are analogous to the real microstructure. Importantly, the objective of this study is to provide a framework towards complete microstructure representation that is consistent with quantifiable experimental data.

Microstructure analysis of rheoformed AZ91 alloy produced by rotating magnetic fields

AZ91 magnesium alloy was rheoformed using rotating magnetic fields (RMFs) after isothermal near-liquidus treatment. Thixotropic microstructures obtained at different temperatures were characterized in detail and linked to the corresponding volume solid fraction, and serial sectioning experiments were performed to construct three-dimensional morphologies of clusters consisting of conglutinated primary grains. The experimental results indicated that incompact structure agglomerating a few primary solid particles was observed within structures of low solid fraction, while a reduction in the castings’ forming temperature and so increasing the fraction of primary solid phase brought out interaction among the primary particles within vigorously stirring melt, and thus caused slide and plastic deformation between or among the neighboring solid particles. In contrast with structure with low solid fraction, this slide and plastic deformation resulted in differently morphological 3D structures welded together with much more solid particles. Moreover, the increase in solid fraction mainly lied on the formation of new particles.

Three-Dimensional Microstructural Characterization Using Focused Ion Beam Tomography

AbstractThis article reviews recent developments and applications of focused ion beam (FIB) microscopes for three-dimensional (3D) materials characterization at the microscale through destructive serial sectioning experiments. Precise ion milling—in combination with electron-optic—based imaging and surface analysis methods—can be used to iteratively section through metals, ceramics, polymers, and electronic or biological materials to reveal the true size, shape, and distribution of microstructural features. Importantly, FIB tomographic experiments cover a critical size-scale gap that cannot be obtained with other instrumentation. The experiments encompass material volumes that are typically larger than 1000 μm3, with voxel dimensions approaching tens of nanometers, and can contain structural, chemical, and crystallographic information. This article describes the current state of the art of this experimental methodology and provides examples of specific applications to 3D materials characterization.

3D microstructural characterization of nickel superalloys via serial-sectioning using a dual beam FIB-SEM

Abstract Dual beam focused ion beam-scanning electron microscopes are well suited for characterizing micron and sub-micron size microstructural features in three dimensions via serial-sectioning procedures. Importantly, these commercially-available instruments can be used to collect morphological, crystallographic, and chemical information throughout a serial-sectioning experiment. Selected examples are shown to demonstrate these capabilities.

Morphological development of solidification structures under forced fluid flow: experimental observation

Morphological evolution of solidification structures in stirred Sn-15Pb (wt-%) alloy has been investigated using various stirrer geometries and stirring intensities. A serial sectioning experiment was carried out to evaluate the actual morphology of the solid formed in three dimensions, and illustrated that microstructural observation from a single two-dimensional section may be inconclusive in many cases. Based on experimental observation it is proposed that the morphological evolution can be explained as a growth phenomenon. Different solidification structures observed under melt stirring conditions can be explained on the basis of the effect of fluid flow characteristics on diffusion geometry around the growing solid. It has been shown that a low intensity laminar flow produces a dendritic structure; particle rotation under shear flow produces a rosette morphology, and intense turbulent flow produces fine and compact solidification structures.

The effect of undercooling on the cellular precipitation reaction in Cu-3 Pct Ti

The effect of undercooling on the morphology of the cellular precipitation reaction in Cu-3 Pct Ti is examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and serial sectioning experiments. The reaction front formed at small undercooling, which exhibits strong faceting of the precipitate growth interfaces, gradually changes with increasing undercooling to a smoothly curved reaction front with concave precipitate growth interfaces and convex grain boundary segments. This concealment of the faceted reaction front appears to be due to the rapid accumulation of growth ledges with increasing undercooling. This study also indicates that the cellular precipitation reaction, at small undercooling, is initiated by Widmanstatten precipitation. At larger undercoolings, a second mechanism is responsible for cellular genesis. Finally, contrary to accepted models of colony development, serial sectioning experiments show that nucleation of additional lamellae may occur at the faces of existing lamellae, from where they extend laterally to achieve the characteristic interlamellar spacing for that temperature.

Deformation and fracture in directionally solidified Co-CoAl eutectic

The effect of growth defects known as lamellar terminations on the yielding and fracture behaviour of Co-CoAl eutectic single crystals was studied using tensile tests and finite-element modelling. The yield strength and strain to fracture were found to decrease with increasing termination density. Observations of deformed surfaces and serial sectioning experiments on fractured tensile specimens revealed that crack initiation during the fracture process was enhanced by the presence of lamellar terminations. The fracture surfaces were found to have a staircase-type appearance, which indicated that the final fracture process was discontinuous with a step-wise propagation from one CoAl lamella to adjacent CoAl lamellae. A computer simulation was conducted to determine the stress distributions about lamellar terminations in model microstructures, since the experimental results suggested that the lamellar terminations behaved as stress concentrations in the microstructure. The finite-element calculation confirmed that lamellar terminations can influence the yielding process; the stress at which the first slip system was activated was found to decrease with increasing termination density.