J.M. Sosa

Development and application of MIPAR™: a novel software package for two- and three-dimensional microstructural characterization

Three-dimensional microscopy has become an increasingly popular materials characterization technique. This has resulted in a standardized processing scheme for most datasets. Such a scheme has motivated the development of a robust software package capable of performing each stage of post-acquisition processing and analysis. This software has been termed Materials Image Processing and Automated Reconstruction (MIPAR™). Developed in MATLAB™, but deployable as a standalone cross-platform executable, MIPAR™ leverages the power of MATLAB’s matrix processing algorithms and offers a comprehensive graphical software solution to the multitude of 3D characterization problems. MIPAR™ consists of five modules, three of which (Image Processor, Batch Processor, and 3D Toolbox) are required for full 3D characterization. Each module is dedicated to different stages of 3D data processing: alignment, pre-processing, segmentation, visualization, and quantification.With regard to pre-processing, i.e., the raw-intensity-enhancement steps that aid subsequent segmentation, MIPAR’s Image Processor module includes a host of contrast enhancement and noise reduction filters, one of which offers a unique solution to ion-milling-artifact reduction. In the area of segmentation, a methodology has been developed for the optimization of segmentation algorithm parameters, and graphically integrated into the Image Processor. Additionally, a 3D data structure and complementary user interface has been developed which permits the binary segmentation of complex, multi-phase microstructures. This structure has also permitted the integration of 3D EBSD data processing and visualization tools, along with support of additional algorithms for the fusion of multi-modal datasets. Finally, in the important field of quantification, MIPAR™ offers several direct 3D quantification tools across the global, feature-by-feature, and localized classes.

Three-dimensional characterisation of the microstructure of an high entropy alloy using STEM/HAADF tomography

Abstract The microstructure of a high entropy alloy with composition of Mo0.5Al1Nb1Ta0.5Ti1Zr1 (the digits refer to molar volumes) has been characterised directly in three dimensions using TEM dark field (DF) imaging and by recording tilt pair micrographs using STEM high angle annular DF (HAADF) imaging. The microstructure contains disordered bcc precipitates that appeared as orthogonal stacks of plate-like features. A tapered needle sample was prepared in a focused ion beam/SEM and was used to acquire a 180° tomographic dataset of STEM/HAADF images in 2° increments. The tilt series images were registered, and the algebraic reconstruction technique was used to reconstruct the three-dimensional microstructure. The bcc precipitates were segmented using a combinative approach involving two threshold techniques. The precipitates were then visualised using commercial software, which revealed surprisingly the existence of both cuboidal and plate-like morphologies. Colouring each precipitate according to its morphology (determined using the omega-2 moment invariant) revealed a precipitate arrangement where plate-like features appeared parallel to each cuboid face.

Revealing Transformation and Deformation Mechanisms in NiTiHf and NiTiAu High Temperature Shape Memory Alloys Through Microstructural Investigations

Shape memory alloys (SMAs) are ‘smart’ materials which are able to change their shape in response to changes in temperature. This unusual behavior arises from a solid-state phase transformation, which can be utilized to generate force. These extraordinary properties have made them of great interest to the automotive and aerospace industries for potential light-weight solid-state actuator applications. An actuator is any mechanism which converts energy, such as heat or electricity, into motion. SMAs outshine traditional actuating systems such as pneumatics, hydraulics, and DC motors due to their remarkably high power-to-weight ratios [1]. By replacing heavy conventional actuating systems, they offer the possibility of higher reliability, lighter weight and increased capability while lowering space and power consumption. This will lead to improved efficiency and reduced emissions, particularly in aircraft. There is currently a drive toward developing SMAs which can be used in high temperature environments, for applications such as fuel control valves within jet engines [2].

MIPAR™: 2D and 3D Image Analysis Software Designed by Materials Scientists, for All Scientists

Many software programs have been developed independently for 2D and 3D image analysis, both commercial and open source. However, few, if any, can equip users with extensive toolsets for 2D and 3D materials characterization in a single package. To this end, Materials Image Processing and Automated Reconstruction (MIPAR) has been developed. MIPAR is based on an app-suite construction. The apps were designed as standalone programs, each suited for different tasks, but each capable of communication with the others. This paper will discuss the capabilities and purpose of each of these salient applications, as well as describe MIPAR’s typical 2D and 3D characterization workflows.

Correlative 3D Imaging and Characterization of Human Dentine

3D characterization [1, 2] is of particular importance in the study of mineralized tissues such as teeth and bones due to the presence of channels, pores and features that span millimeter, micrometer and nanometer length scales. The major component in human teeth, by weight and volume, is dentine. This hydrated hard tissue encloses the central pulp and has microscopic channels, dentineal tubules that radiate from the pulp to the cementum on the surface of the dentine that connects with the hard outer enamel. The permeability provided by these tubules can cause dental hypersensitivity. The object of our current work is to understand how treatments for dental hypersensitivity act on these tubules.

MIPAR™: 2D and 3D Image Analysis Software Designed for Materials Scientists, by Materials Scientists

Many software programs have been developed independently for 2D and 3D image analysis, both commercial and open source. However, few, if any, can equip users with extensive toolsets for 2D and 3D materials characterization in a single package. To this end, Materials Image Processing and Automated Reconstruction (MIPAR) has been developed. MIPAR is based upon a modular (i.e. appsuite) construction. The apps were designed as standalone programs, each suited for different tasks, but each capable of communication with the others. This paper will discuss the capabilities and purpose of each of these salient applications, as well as describe MIPAR’s typical 2D and 3D characterization workflows.

Characterizing Atomic Ordering in Intermetallic Compounds Using X-ray Energy Dispersive Spectroscopy in an Aberration-Corrected (S)TEM

Intermetallic compounds have been the subject of considerable interest as structural and functional materials in a wide range of applications. They are used as engineered materials themselves or as second phase components in high performance applications. It is important that these materials be fully characterized to permit effective alloy development to meet the requisite balance of properties for a given application. One important parameter is the degree to which these compounds are ordered. This is particularly important in a new series of materials known as high entropy alloys (HEA), or compositionally complex alloys (CCA), which contain typically four to six alloying elements, each at or near to equi-atomic concentrations. Many of these CCAs contain an intimate mixture of a disordered bcc phase and an ordered phase with the B2 crystal structure. These ordered phases contain reasonable concentrations of many of the alloying elements in the alloy, and so it is of interest to know how the elements are partitioned to the two sublattices in the ordered structure and to what degree anti-site defects are tolerated, i.e., what is the degree of order in these compounds. An approach to the determination of this latter parameter has been afforded by the combination of aberration-corrected S(TEM) instruments, where electron probe sizes less than interatomic spacings may be achieved coupled with x-ray energy dispersive spectrometers (XEDS) making use of silicon drift detectors(SDD) and large collection angles. This approach has been adopted in the present research, making use of an FEI ThemisTM instrument equipped with Super-XTM XEDS. Experimentally, the compositions of the individual sublattices are determined from spatially-resolved XEDS measurements and subsequent data analysis, and these compositions are plotted onto an Ordering Tie-Line diagram[1], from which the degree of order is deduced.

Microstructural Characterization of a Fe-25Mn-3Al-3Si TWIP–TRIP Steel

1. Interdisciplinary Materials Science, Vanderbilt University, Nashville TN, USA 2. Microscopy and Microanalytical Sciences, PO Box 7103, Oak Ridge, TN, USA 3. Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO, USA 4. Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA 5. Materials Science and Engineering, The Ohio State University, Columbus, OH, USA 6. Max-Planck-Institut für Eisenforschung, Max-Planck-Straβe 1, Düsseldorf, Germany

Super-X XEDS STEM Tomography of y' Precipitates in the LSHR Nickel Superalloy

Electron tomography has been proposed to be advantageous for reconstructing sub-micron precipitates in nickel superalloys. However, not every type of electron image provides the necessary contrast for high fidelity tomographic reconstruction. The γʹ′ precipitates in Low Solvus High Refractory (LSHR) form coherently with the matrix and exhibit limited atomic number contrast relative to the matrix when imaged with traditional transmission (TEM) and scanning transmission electron microscopy (STEM) bright field/dark field imaging. Previous research has shown that energy filtered TEM (EFTEM) has displayed successfully γʹ′ morphologies based off the Cr-L3,2 edge[1,2]. However, EFTEM is hindered by poor signal to noise during image collection requiring prohibitive acquisition times. X-ray energy dispersive spectroscopy (XEDS) in STEM offers a robust method to collect a wide range of compositional information and enables spectral image (SI) collection that permits post-processing analysis of multiple elemental species. The primary objective of the work to be presented was to use Super-XTM XEDS in STEM to acquire compositional maps of LSHR to produce tomographic reconstructions that accurately depict γʹ′ precipitates within a dual-microstructure heat treatment (DMHT) gradient [3] as shown in Figure 1(a). Chromium is a significant component of the LSHR alloy at 12.3 wt% and segregates to the γ matrix, therefore chromium XEDS SI can provide strong contrast between the γʹ′ precipitates and the chromium-rich matrix. The XEDS SI shown in Figure 1(b) was used for the full precipitate reconstruction as displayed in Figure 1(c). The DMHT gradient contains a range of intricate γʹ′ morphologies that have proven difficult to characterize with two-dimensional methods. Three-dimensional characterization not only provides the morphology of the γʹ′, but will also permit more accurate microstructural metrics for inputs for integrated computational materials (ICME) models.

MIPAR™: 2D and 3D Microstructural Characterization Software Designed for Materials Scientists, by Materials Scientists

1. Center for the Accelerated Maturation of Materials, Department of Materials Science and Engineering, The Ohio State University, 1305 Kinnear Rd., Columbus, OH 43212 Stereology, the science of estimating three-dimensional quantities from two-dimensionally acquired measurements, has historically been the sole technique for microstructural quantification [1]. Over the last decade and a half, 3D characterization has begun to replace stereology with direct-3D quantification. As data acquisition techniques continue to advance, the need for more materials science-orientated analytical 2D and 3D software has become evident.