Brian Welk

Nature of the interfaces between the constituent phases in the high entropy alloy CoCrCuFeNiAl

The interfaces between the phase separated regions in the dendritic grains of laser-deposited samples of the high entropy alloy CoCrCuFeNiAl have been studied using aberration-corrected analytical (scanning) transmission electron microscopy ((S)TEM). The compositional variations have been determined using energy dispersive x-ray spectroscopy (EDS) in (S)TEM. It was found that between B2, consisting mainly of Al, Ni, Co, and Fe, and disordered bcc phase, consisting mainly of Cr and Fe, there is a transition region, approximately 1.5 nm in width, over which the chemical composition changes from the B2 to that of the bcc phase. The crystal structure of this interfacial region is also B2, but with very different sublattice occupancy than that of the adjacent B2 compound. The structural aspects of the interface between the ordered B2 phase and the disordered bcc phase have been characterized using high angle annular dark-field (HAADF) imaging in STEM. It has been determined that the interfaces are essentially coherent, with the lattice parameters of the two B2 regions and the disordered bcc phase being more or less the same, the uncertainty arising from possible relaxations from the proximity of the surfaces of the thin foils used in imaging of the microstructures. Direct observations show that there is a planar continuity between all three constituent phases.

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.

Characterizing Sub-lattice Occupancies in B2 Phases in High Entropy Metallic Alloys using Atomic Resolution STEM-XEDS Mapping

In the recent past, there has been considerable emphasis placed on the exploration of high entropy alloys (HEA). These alloys have been defined as ones with five or more, essentially equal atomic concentrations [1, 2]. CoCrCuFeNiAl is an example of an HEA alloy which mainly consists of two phases, namely ordered B2 and disordered bcc. Although this alloy has been the subject of much study and its microstructures characterized using a number of techniques, only recently has aberration-corrected (S)TEM coupled with x-ray energy dispersive spectroscopy (XEDS), involving large collection angles (ChemiSTEMTM), been applied [3]. In this latter study, it was found that, between the B2, consisting mainly of Al, and Ni, Co, and Fe, and disordered bcc phases, consisting mainly of Cr and Fe, there is a transition region, approximately 1.5nm in width, over which the chemical composition changes from the B2 to that of the bcc phase. The crystal structure of this interfacial region is also B2, but with a significantly different sub-lattice occupancy than that of the adjacent B2 compound. In these B2 phases with very differing compositions, and hence sub-lattice compositions, the intensities of both atomic columns in HAADF images and superlattice reflections in diffraction patterns may vary considerably [3]. The origin of these intensity differences is of interest. For example, when the difference in the intensities of atomic columns in each of the sub-lattices is small, this may be interpreted as either the average compositions of the sub-lattices being similar, and/or being a reduced degree of order of the B2 compound. It is obvious that in order to be able to understand the behavior of these alloys, it is necessary that the degree of order be known. The first of these possibilities may be assessed by making direct measurements of the sub-lattice composition, while the second possibility, degree of ordering, may be assessed by plotting these compositions on an ordering tie-line diagram [4]. The current study involves the direct measurement of sub-lattice compositions.

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.

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 of High Entropy Alloys Using Super-X EDS Characterization

High entropy alloys (HEA), more recently referred to as compositionally complex alloys (CCA), are a new group of alloys receiving a great deal of attention because of the potentially remarkable balance of properties they are expected to exhibit. They offer new pathways to lightweighting in structural applications, new alloys for intermediate and elevated temperature components, and new magnetic materials[1,2]. To realize their potential, however, requires considerable alloy development that will rely on application of integrated computational materials (science and) engineering (ICME), which requires accurate computational models predicting their performance in addition to a detailed knowledge of, for example, their deformation mechanisms. Often, these alloys consist of a mixture of ordered and disordered phases, and because of the compositional complexity, it is necessary to know the nature (i.e., degree of order, site occupancy, and presence of anti-site defects) in the ordered phases if effective models of the deformation behavior are to be developed[3]. These various metrics require accurate compositional measurements at the atomic scale.

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.

A Hybrid Metal-to-Composite Joint Fabricated Through Additive Manufacturing Processes

Devices and machines which perform additive manufacturing (adding material in a layer-wise or bead-wise manner to produce complex structure rather than removing material through machining) are maturing and entering the commercial market. While small prototype parts are routinely made using these devices, a number of industries, including biomedical and aerospace, are considering using these techniques for production parts. New materials which take advantage of the unique capability of additive manufacturing are beginning to evolve. Hybridization of materials at smaller scales now becomes possible with the precision of additive manufacturing devices. However, the fundamentals of structural performance of materials that can be produced by these methods are still to be explored and understood..The current effort focuses on characterizing and describing the fundamental processing of hybrid materials produced using a combination of laser sintering of metals combined with polymer infusion of advanced carbon fabric. Ultimately, the work seeks to develop a fundamental understanding of the structural mechanics of these novel graphite-metal materials produced through hybrid processes. By understanding development and location of weak structural planes, effects of voids and discontinuities, load transfer from nano to macro scale, reinforcement distribution, gradients in properties, and effects of residual stress, a complete materials design process beginning with structural requirements and ending with material and process selection can be developed.This paper will summarize the first experimental steps taken to process and fabricate a metal-to-composite hybrid joint using a combination of additive manufacturing and conventional composite processes. Experimental conditions are described and morphology of the resulting hybrids is discussed. Future plans for testing are described.Copyright