Electron Backscatter Diffraction for Investigating Lithium-Ion Electrode Particle Architectures
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25 ENERGY STORAGE↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Metallographic Preparation of Space Shuttle Reaction Control System Thruster Electron Beam Welds for Electron Backscatter Diffraction
A Space Shuttle Reaction Control System (RCS) thruster failed during a firing test at the NASA White Sands Test Facility (WSTF), Las Cruces, New Mexico. The firing test was being conducted to investigate a previous electrical malfunction. A number of cracks were found associated with the fuel closure plate/injector assembly (Fig 1). The firing test failure generated a flight constraint to the launch of STS-133. A team comprised of several NASA centers and other research institutes was assembled to investigate and determine the root cause of the failure. The JSC Materials Evaluation Laboratory was asked to compare and characterize the outboard circumferential electron beam (EB) weld between the fuel closure plate (Titanium 6Al-4V) and the injector (Niobium C-103 alloy) of four different RCS thrusters, including the failed RCS thruster. Several metallographic challenges in grinding/polishing, and particularly in etching were encountered because of the differences in hardness, ductility, and chemical resistance between the two alloys and the bimetallic weld. Segments from each thruster were sectioned from the outboard weld. The segments were hot-compression mounted using a conductive, carbon-filled epoxy. A grinding/polishing procedure for titanium alloys was used [1]. This procedure worked well on the titanium; but a thin, disturbed layer was visible on the niobium surface by means of polarized light. Once polished, each sample was micrographed using bright field, differential interference contrast optical microscopy, and scanning electron microscopy (SEM) using a backscatter electron (BSE) detector. No typical weld anomalies were observed in any of the cross sections. However, areas of large atomic contrast were clearly visible in the weld nugget, particularly along fusion line interfaces between the titanium and the niobium. This prompted the need to better understand the chemistry and microstructure of the weld (Fig 2). Energy Dispersive X-Ray Spectroscopy (EDS) was used to confirm the chemical composition of the variations in contrast in these areas. Niobium alloys generally require exposure to more aggressive chemical reagents than titanium alloys for etching because of niobium s chemical resistance; therefore, the titanium portion of the sample was etched first. A five second immersion in Kroll s reagent revealed a general microstructure on the titanium portion of the sample; however, the titanium heat affected zone closest to the weld, was over-etched due to higher concentrations of refined grains and an increase in eta-phase. The Kroll s etchant also revealed some microstructure in the weld nugget itself; the niobium portion of the sample remained unetched.
Martinez, James↗
Electron Backscatter Diffraction Analysis of Additively Manufactured Steel Grains.
Abstract not provided.
Schnebly, Landon↗
Electron Backscatter Diffraction of Low Symmetry Metals and Alloys
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36 MATERIALS SCIENCE↗
Effect of Dry Electropolishing on the Electron Backscatter Diffraction Mapping of Dissimilar Titanium Welds
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Schnebly, Landon Flake↗
An Electron Backscatter Diffraction (EBSD)-Based Automated Tool for Ceramic Capacitor Grain Size Analysis
Ceramic capacitors continue to be recurring problem parts for NASA, despite best efforts to screen out potential defects and failures through environmental and electrical testing and nondestructive inspection techniques such as acoustic microscopy. The physical properties of ceramic capacitors necessitates thin dielectric layers capable of withstanding significant electric fields. Any defects in those ceramic layers can result in reduced insulation resistance failure modes including short circuit failures, so the quality and consistency of the dielectric material is critical. The size of the individual ceramic grains in the dielectric material is a critical parameter. However, judging “grain size” is not so simple—in a single capacitor there can be wide variation in grain sizes observed. It is theorized that by studying the grain size distributions of “known good” and “known bad” lots of capacitors, some conclusions could be drawn that would allow us to better predict to the reliability of future lots based on grain size distributions. The initial goal of this effort was to find or develop an automated tool that could inspect a capacitor and return grain size distribution results.
Robert Hodson↗
Crystallographic analysis in the Scanning electron microscope: Electron backscatter diffraction.
Abstract not provided.
Michael, Joseph R.↗
Sample mount for electron backscatter diffraction
A sample mount having a bottom surface, a front surface, and a second portion is disclosed. The first portion is perpendicular to the bottom surface. The second portion has an external surface and an internal surface and extends from the first portion to form a 70-degree angle relative to the bottom surface. The sample mount may also have a top surface, an opening extending through the second portion of the front surface, and a receiving area configured to receive a sample, wherein the top surface presents an unimpeded path between the sample and an SEM pole piece. The sample mount may include a spring-loaded handle configured to push the sample against the internal surface of the second portion of the front surface, wherein pushing the sample against the internal surface places the sample at the 70-degree angle relative to the bottom surface.
Wieliczka, David M.↗
Multimodal Analysis of Spatially Heterogeneous Microstructural Refinement and Softening Mechanisms in Three-Pass Friction Stir Processed Al4Si Alloy
Multiple thermally and thermomechanically induced microstructural refinement mechanisms can be activated in metallic alloys when subjected to solid phase processing methods such as friction stir processing (FSP). In this work, we provide detailed descriptions of the relationship between region-specific microstructural refinement mechanisms and the variation in microhardness, through a systematic and multimodal microstructural characterization of an FSP-processed 75% cold-rolled Al-4 at.% Si model binary alloy. Spatially resolved high-energy synchrotron X-ray diffraction, electron backscattered diffraction, and scanning transmission electron microscopy were used to understand the spatially heterogeneous microstructural evolution due to FSP. Results provide insights into how mechanisms such as static recovery, static recrystallization, dynamic recovery and recrystallization, geometric and continuous dynamic recrystallization, and particle-stimulated static or dynamic grain nucleation may occur heterogeneously in the microstructure as a function of the distance from the stir zone in processed alloys, directly influencing the degree of softening. The systematic analysis of microstructures and hardness in the FSP-processed model binary alloy given in this work highlights the rich microstructural domains that can be uniquely harnessed through solid phase processing of metallic alloys.
Al4Si, Friction Stir Processing, Geometric Dynamic↗
Examining the multi-scale complexity and the crystallographic hierarchy of isothermally treated bainitic and martensitic structures
In this work, differences and similarities between bainitic and martensitic structures obtained by isothermal heat treatments such as austempering, quench and partitioning (Q&P) and quench and tempering (Q&T), are investigated by multiple techniques including X-ray diffraction, electron backscatter diffraction, scanning and transmission electron microscopy and atom probe tomography. Additionally, results reveal that analogous lath-like ferritic structures with similar austenite content can be achieved by adjusting the isothermal holding temperature. However, certain variability in hardness is recorded, which is consistent with differences on the precipitation state revealed by the nano-scale examination of the structure, and with dissimilar crystallographic size distribution of ferritic grains.
36 MATERIALS SCIENCE↗
Alloying effects on deformation induced microstructure evolution in copper
In this work, we investigated the effects of alloying elements on plastic deformation and microstructure evolution in polycrystalline copper (Cu) and Cu alloyed with 1 wt. % lead (Cu-1 %Pb). These materials were selected due to the size mismatch between Cu and Pb, with the latter forming precipitates at grain boundaries. Multi-modal characterization techniques, including neutron diffraction, electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), along with finite element simulations were employed to study the deformation behavior across multiple length scales. While both Cu and Cu-1%Pb exhibited similar macroscale response and final deformation textures, both dislocation line profile analysis and TEM revealed increased dislocation density in deformed Cu-1%Pb specimens. The presence of lead precipitates also significantly affected local plastic deformation during compression, with their influence diminishing with increasing strain. These results demonstrate the complex relationships between alloying elements, plastic deformation, microstructural evolution, and material behavior under load. The insights gained from this multi-scale and multi-technique approach contribute to the fundamental understanding of microstructural evolution in immiscible alloys and are valuable for tailoring the properties of structural materials for specific engineering applications.
36 MATERIALS SCIENCE↗
Multimodal microscopy of extended defects in β-Ga 2 O 3 (010) EFG crystals
Beta-phase gallium oxide (β-Ga 2 O 3 ) has attracted attention in recent years as a potentially low cost, large area substrate and active layer material for high power, high temperature power electronics and sensing devices. However, growth of β-Ga 2 O 3 crystals is complicated by easily activated (100) and (001) cleavage planes, the presence of low angle grain boundaries (LAGBs) and twins, and the potential formation of polycrystalline grains. In this study, β-Ga 2 O 3 crystals were grown by the edge-defined film-fed growth technique with an (010) principal face. Two crystals with apparently randomly formed high angle grain boundaries (HAGBs) were selected and analyzed by electron backscatter diffraction, electron channeling contrast imaging, and cathodoluminescence to investigate the nature of the LAGBs and the source of the HAGB formation. It was discovered that planar LAGBs lying parallel to the (010) plane exist in the region immediately preceding the start of an HAGB. Increased misorientation across the LAGB was observed, approaching the initiation of a new grain. We present multimodal microscopy characterization, correlating misorientation and variation in optoelectronic properties with LAGBs and the associated dislocations.
14 SOLAR ENERGY↗
Microstructural, Oxidation, and Mechanical Behavior of NbTi-Based Refractory Alloys with 5 to 10 Pct Co, Cr, and Ni Additions
NbTi-based refractory alloys with additions of Co, Cr, and Ni represent an interesting medium-entropy alloy system with potential for protective oxide film formation, high strength, and ductility. This study investigates the microstructural evolution, oxidation behavior, and mechanical properties of NbTi-based alloys containing 5 to 10 at. pct Co, Cr, and Ni. CALPHAD predictions suggest that this composition range can be heat treated to obtain a predominantly body-centered cubic matrix phase. Mechanical properties, including microhardness, yield strength, maximum strength, and specific strength are evaluated through isothermal compression tests conducted between room temperature and 800 °C. The oxidation kinetics of these alloys are assessed through discontinuous oxidation tests. Parabolic oxidation kinetics were observed for NbTi–10Ni and NbTi–5Co, while linear oxidation kinetics were found for NbTi–10Cr and NbTi–10(CoCrNi). Microstructures and oxide layers are characterized using X-ray diffraction, electron backscatter diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. All alloys exhibit significant mechanical softening between room temperature and 800 °C, with elastic-perfectly plastic flow observed at 800 °C. The addition of 10 pct Cr to NbTi resulted in two BCC phases up to 1050 °C, conflicting with CALPHAD predictions of a single-phase solid solution at this temperature, and resulting in higher flow stress at 800 °C. NbTi–10(CoCrNi) exhibited the lowest flow stress at 800 °C despite having more ‘cocktail effect’ potential and insufficient molar fractions of Co, Cr, or Ni to form a desirable protective oxide film.
36 MATERIALS SCIENCE↗
Rapid grain refinement and compositional homogenization in a cast binary Cu50Ni alloy achieved by friction stir processing
Friction stir processing (FSP) has been increasingly adopted for joining and processing materials in automotive, aerospace and industrial construction. During FSP a dynamic competition between high-speed shear deformation and deformation-induced heating brings about a complex competition between multiple dynamic microstructural evolution mechanisms making it difficult to predict the microstructural evolution pathway. Hence, improved understanding of microstructural evolution mechanisms during FSP can be beneficial for continued growth in the adoption of FSP for demanding applications of future. Towards this goal, this study uses a model binary Cu – 50 at.% Ni alloy to clarify the effect of single and double pass FSP on the microstructural evolution of a coarse grained and compositionally heterogeneous cast microstructure. High energy synchrotron X-ray diffraction, electron backscatter diffraction, and nanoindentation are used to clarify the microstructural evolution due to FSP. The process of compositional homogenization of as-cast segregations is studied by energy dispersive spectroscopy and atom probe tomography. Our results show that a single fast FSP pass at 30 mm.s -1 produces a 100 µm deep layer of submicrometric and hall-petch hardened CuNi grains. The initial cast compositional heterogeneities in a micrometric scale is rapidly transformed to nano-sized domains, mainly confined at grain boundaries. Double pass FSP increases the penetration depth of the processed layer and leads to a 2.9 times grain growth relative to single pass FSP. Grain fragmentation, discontinuous dynamic recrystallization, grain growth, and twinning mechanisms are discussed. In conclusion, these results highlight the value of FSP for ultrafast grain refinement and compositional homogenization of cast alloys.
36 MATERIALS SCIENCE↗
The Measurement of Grain Size by Electron Beam Backscattered Diffraction
The method of electron back-scatter diffraction provides an analytic means to identify crystalline phase and the grain size of structural materials. The need to utilize imaging parameters consistent with revealing the contributing microstructural scale is often overlooked through packaged imaging scripts. It is shown that imaging parameters consistent with a post processing assessment of low misorientation angles between boundaries are achievable as using pixel sizes on the order of 10 1 nm.
36 MATERIALS SCIENCE↗
Critical differences between electron beam melted and selective laser melted Ti-6Al-4 V
Effective optimization of the production of Ti-6Al-4 V using AM requires a fundamental understanding of the relative importance of different microstructural features to the deformation and failure mechanisms, particularly features that vary between production methods. In this study, the tensile response and deformation mechanisms of electron beam melted (EBM) AM Ti-6Al-4 V material loaded in different orientations and produced using various powder sizes were compared to those of selective laser melted (SLM) AM Ti-6Al-4 V material. The density and morphology of pores, phase fractions, prior-β grains, and defect microstructures were evaluated using scanning electron microscopy, X-ray computed tomography, electron backscatter diffraction, and transmission electron microscopy before and after deformation. The results were used to evaluate the relative importance of each feature on strengthening, deformation, and failure initiation mechanisms. Results focused primarily on coarse-powder EBM materials indicated that phase distribution and defect density were most influential for determining material yield strength as well as maximum possible strain to failure. Porosity was lower overall in EBM Ti-6Al-4 V than in SLM, allowing for occasional increases in part strain to failure, but remained a limiting factor determining overall part ductility.
36 MATERIALS SCIENCE↗