Serial Sectioning Procedure Research Articles

Numerical Procedure of Three-Dimensional Reconstruction of Ferrite-Pearlite Microstructure Data from SEM/EBSD Serial Sectioning

Preparation of a reliable 3D digital material representation model, for further finite element formability calculations, based on series of 2D images from serial sectioning procedure is the main goal of the paper. Within the work series of 2D SEM/SE2 images of a ferrite-pearlite microstructure were accompanied by an EBSD investigation to clearly identify the morphology of both constituents. Then, based on such input data, a dedicated 3D reconstruction algorithm was developed to recreate complete volumetric information about the investigated microstructure. The algorithm is an extension of the previously developed approach operating only on a binary type data. Developed modifications to the data preparation stage, image spatial adjustments, features identification, interpolation and finally reconstruction are presented. As a result, a detailed 3D microstructure representation, that broadens the capabilities of 2D imaging techniques, was obtained and used as an input for the 3D finite element mesh discretization.

Study of the Grain Size Distribution during Preheating Period Prior to the Hot Deformation in AISI 316L Austenitic Stainless Steel

Grain size and its distribution is the dominant microstructure feature of austenitic stainless steels. These characteristics considerably affect the mechanical properties of the steels. The distribution of grain size during preheating prior to the hot deformation has the main effect on the uniform distribution of the strain interior of the grains and, consequently, on the homogeneous development of processes such as static, dynamic, and metadynamic recrystallization in the material. The grain size distribution can be expressed using the Jensen–Gundersen point method along with the commonly-cited distribution functions such as the lognormal, gamma, Weibull, Louat, or Hilert relations. In this study, 3D Monte Carlo Potts method was employed for predicting grain growth kinetics and relevant grain size distribution during annealing process to describe which distribution function is dominant. To validate simulation results, the serial sectioning procedure was performed on AISI 316L cylindrical samples annealed at 1200°C for 5, 10, and 15 min. Results show that grain number densities (GND) affect the grain size distribution, in which at the relatively low GNDs, the lognormal function and at the higher ones, the gamma function are realized. Moreover, a new method for the grain size standard deviation statement via the lognormal distribution is introduced.

Initiation sites for cracks developed from pits in a shot-peened 12Cr martensitic stainless steel

A serial sectioning procedure was carried out on a shot-peened 12Cr martensitic stainless steel to determine the location of fatigue crack initiation sites from pits of varying depth. Multiple cracks, including fully-developed cracks (surface-breaking cracks extending beyond the pit base) and non-fully-developed cracks, were observed for pits of depth greater than 70μm. If the longest crack at each side of the pit was assumed to be the dominant crack, most dominant cracks did not initiate from the pit base despite a propensity for macro-stress and strain localisation to the pit base. These results indicate that common assumptions about crack initiation from pits in shot-peened steel can be misleading. Knowledge of the location of crack initiation sites and how the crack develops is required to characterise the mechanical driving force for the crack prior to attainment of a fully-developed crack.

Five-Parameter Grain Boundary Determination in Annealed Ferrite Structure Using Electron Backscatter Diffraction and Serial Sectioning Technique

The SEM/electron back scattered diffraction and serial sectioning procedure have been used to study the five parameter description of grain boundaries in a polygonal ferrite microstructure of 9Cr-1Mo steel. A routine has been evolved to correlate the successive images of a selected region and determine the grain boundary plane morphology. The relative misorientation of the crystallites, in terms of misorientation angle-axis (ω,ȓ), the grain boundary inclination angles [azimuth (γ) and polar (β) angles], and the crystallographic description of the two meeting planes have been studied and compared with random distribution. The low-angle boundaries are found to be persistently present in higher amounts after the grain growth induced by extended annealing.

A 3D numerical and experimental investigation of microstructural alterations around non-metallic inclusions in bearing steel

Non-metallic inclusions such as sulfides and oxides are byproducts of steel manufacturing process. When a component is subjected to repetitive loading, fatigue cracks can emanate from these inclusions due to stress concentrations that happen because of mismatch in elastic–plastic properties of inclusions and matrix. In certain applications such as gears and bearings, crack initiation from inclusions is accompanied with microstructural alteration. This paper employs a numerical as well an experimental approach to investigate these microstructural changes which are so-called “butterfly wings”. A 3D finite element model was developed to obtain the stress distribution in a domain subjected to Hertzian loading with an embedded non-metallic inclusion. A formerly introduced 2D model based on continuum damage mechanics (CDM) was developed to simulate the butterfly wing formation in 3D. Wingspan-to-inclusion ratios were observed at different cross sections following an analytical serial sectioning procedure. A closed form solution was suggested for the wingspan-to-observed-inclusion-diameter ratio and the results were corroborated with the data available in the open literature. On the experimental front, nonmetallic inclusions inside a sample made of bearing steel was detected using ultrasonic inspection method. Rolling contact fatigue (RCF) tests were run on the specimen and post-failure serial sectioning was conducted to understand the 3D shape of butterflies formed around an inclusion detected by ultrasound. Comparison of experimental and numerical serial sectioning of the wings showed a close correlation in the butterfly wings geometry.

Classification and Diagnostic Investigation in Inflammatory Myopathies: A Study of 99 Patients

Insights into the pathogenesis of inflammatory myopathies have led to new diagnostic methods. The aims of our study were (1) to evaluate the consequences of using the classification of Amato/European Neuromuscular Centre Workshop (ENMC) compared to that of Bohan and Peter; and (2) to evaluate any diagnostic benefit in using an extended pathological investigation. From a consecutive retrospective database, we evaluated 99 patients for classification. Patients with inclusion body myositis (IBM) were classified according to Griggs, et al. In addition to routine stainings and immunohistochemistry, a multilevel serial sectioning procedure was performed on paraffin-embedded material, to identify scarce pathological findings. Classification according to Bohan and Peter could be performed for 83 of the 99 patients, whereas only 60 patients met the Amato/ENMC criteria, the latter resulting in the following diagnostic groups: IBM (n = 18), nonspecific myositis (n = 14), polymyositis (n = 12), dermatomyositis (n = 10), dermatomyositis sine dermatitis (n = 5), and immune-mediated necrotizing myopathy (n = 1). Most of the Amato/ENMC diagnostic groups harbored patients from several of the Bohan and Peter groups, which included a substantial group lacking proximal muscle weakness. The serial sectioning procedure was essential for classification of 9 patients (15%), and led to a more specific diagnosis for 13 patients (22%) according to Amato/ENMC. The classification of Amato/ENMC was more restrictive, forming groups based on clinical criteria and specified myopathological findings, which clearly differed from the groups of the Bohan and Peter classification. An extended pathological investigation increased the diagnostic yield of a muscle biopsy and highlights the quantity and specificity of certain pathological findings.

A Direct and Quantitative Three-Dimensional Reconstruction of the Internal Structure of Disordered Mesoporous Carbon with Tailored Pore Size

A new technique that allows direct three-dimensional (3D) investigations of mesopores in carbon materials and quantitative characterization of their physical properties is reported. Focused ion beam nanotomography (FIB-nt) is performed by a serial sectioning procedure with a dual beam FIB-scanning electron microscopy instrument. Mesoporous carbons (MPCs) with tailored mesopore size are produced by carbonization of resorcinol-formaldehyde gels in the presence of a cationic surfactant as a pore stabilizer. A visual 3D morphology representation of disordered porous carbon is shown. Pore size distribution of MPCs is determined by the FIB-nt technique and nitrogen sorption isotherm methods to compare both results. The obtained MPCs exhibit pore sizes of 4.7, 7.2, and 18.3 nm, and a specific surface area of ca. 560 m(2)/g.

Tomographic Spectral Imaging with Multivariate Statistical Analysis: Comprehensive 3D Microanalysis

A comprehensive three-dimensional (3D) microanalysis procedure using a combined scanning electron microscope (SEM)/focused ion beam (FIB) system equipped with an energy-dispersive X-ray spectrometer (EDS) has been developed. The FIB system was used first to prepare a site-specific region for X-ray microanalysis followed by the acquisition of an electron-beam generated X-ray spectral image. A small section of material was then removed by the FIB, followed by the acquisition of another X-ray spectral image. This serial sectioning procedure was repeated 10-12 times to sample a volume of material. The series of two-spatial-dimension spectral images were then concatenated into a single data set consisting of a series of volume elements or voxels each with an entire X-ray spectrum. This four-dimensional (three real space and one spectral dimension) spectral image was then comprehensively analyzed with Sandia's automated X-ray spectral image analysis software. This technique was applied to a simple Cu-Ag eutectic and a more complicated localized corrosion study where the powerful site-specific comprehensive analysis capability of tomographic spectral imaging (TSI) combined with multivariate statistical analysis is demonstrated.

Three-dimensional analysis of porous BaTiO3 ceramics using FIB nanotomography.

Three-dimensional (3D) data represent the basis for reliable quantification of complex microstructures. Therefore, the development of high-resolution tomography techniques is of major importance for many materials science disciplines. In this paper, we present a novel serial sectioning procedure for 3D analysis using a dual-beam FIB (focused ion beam). A very narrow and reproducible spacing between the individual imaging planes is achieved by using drift correction algorithms in the automated slicing procedure. The spacing between the planes is nearly of the same magnitude as the pixel resolution on scanning electron microscopy images. Consequently, the acquired stack of images can be transformed directly into a 3D data volume with a voxel resolution of 6 x 7 x 17 nm. To demonstrate the capabilities of FIB nanotomography, a BaTiO3 ceramic with a high volume fraction of fine porosity was investigated using the method as a basis for computational microstructure analysis and the results compared with conventional physical measurements. Significant differences between the particle size distributions as measured by nanotomography and laser granulometry indicate that the latter analysis is skewed by particle agglomeration/aggregation in the raw powder and by uncertainties related to calculation assumptions. Significant differences are also observed between the results from mercury intrusion porosimetry (MIP) and 3D pore space analysis. There is strong evidence that the ink-bottle effect leads to an overestimation of the frequency of small pores in MIP. FIB nanotomography thus reveals quantitative information of structural features smaller than 100 nm in size which cannot be acquired easily by other methods.

A Three-Dimensional Finite Element Scheme to Investigate the Apparent Mechanical Properties of Trabecular Bone

A computational technique is described for investigating the apparent mechanical properties of trabecular bone based on tissue geometry obtained from the marching cubes volume rendering scheme. Using this scheme, a 3D representation of the trabecular bone was extracted from two-dimensional cross-sections of the tissue originating from a quantitative serial sectioning procedure. Surface information consists of node coordinates and polygon connectivity in a 3D space. A custom, adaptive mesh generation technique using a normal offset was used to prepare 3D finite element volume meshes (4-node tetrahedral elements) of variable mesh density from the extracted surface geometry. Nine target mesh resolutions (32 µm to 107 µm ) were examined for a (1·5 mm × 1·5 mm × 2 mm) volume of trabecular bone. A mesh density of 50,000 elements/mm3 of bone tissue was found to be adequate for convergence of apparent (bulk) modulus for 1 % uniaxial compression. For this convergent case, the maximum local normal compressive tissue stress was 400 MPa which was six hundred-fold greater than the computed apparent stress. Variation in the apparent modulus was less than 5% when Poisson's ratio values were varied between 0·1 and 0·4. Poisson's ratio values greater than 0·4 had a more marked effect on the apparent modulus. Based upon these results, approximately 1 million, 4-node tetrahedral elements are required to analyze a continuum scale model of trabecular bone (5 mm cube).

Rotation cryotomy: Medical and scientific value of a new serial sectioning procedure

Preparation of thin serial sections for comparative macromorphologic investigations has always represented a grave technical problem, especially in the case of regions in which bone as well as soft tissue are to be documented within their natural relations to each other in any desired sectional plane. Non-decalcified specimens up to the size of a whole cadaver are embedded in physiologic medium, precisely positioned, and deep-frozen to a specimen-ice block. A newly developed device, working on the basis of blades rotating at high speed, allows quick, successive removal of sections from the surface of the specimen block, with a thickness of each section infinitely variable between 0.1 and 5 mm. Following each cut, the new surface of the block can be documented photographically or on videotape for macromorphologic evaluation. So far more than 1,000 human, animal, and botanical specimens have been sectioned and evaluated with this method. In none of the cases were specimens damaged. Furthermore, any desired sectional plane could be adjusted; consequently a definite correlation between these sections and previous sonography, magnetic resonance (MR), or computed tomography (CT) images could be established. As serial cryosectioning becomes available to a far wider circle of medical and natural scientists, high-quality results should be obtained at lower costs. © 1996 Wiley-Liss, Inc.

Three-dimensional studies of neurons in the lateral geniculate nucleus of the rat: I. Organelle organization in the perikaryon and its proximal branches

The results of a two- and three-dimensional study of the content of perikarya and proximal branches from neurons in the rat lateral geniculate body are reported. Techniques for the serial sectioning procedure and the serial analysis are outlined. The two neurons analysed three-dimensionally were elliptoid, multipolar with modified bipolarity, uninucleated, uninucleolated and uniciliated with a variety of organelles dispersed in the cytoplasm. Most organellesvariety of organelles dispersed in the cytoplasm. Most organelles were quantitatively analysed with respect to morphological dimensions. The cellular membranes were of particularly impressive dimensions. An almost complete, quantitatively integrated, structural view at the organelle level is given for the analysed parts of the neurons. Mitochondria, Golgi complexes and cytoplasmic dense bodies were abundant in the middle of the perikarya, while α-cytomembranes and free ribosomes had their highest concentrations at the poles of the perikarya. Also, mitochondria and cytoplasmic dense bodies were observed in relatively high concentrations in the proximal branches. The results are evaluated and discussed in relation to technique, conventional two-dimensional analysis and some biochemical data available for similar parts of neurons.