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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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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Microstructural Analysis of Irradiated U-Mo Fuel Plates: Recent Results

Microstructural characterization of irradiated dispersion and monolithic RERTR fuel plates using scanning electron microscopy (SEM) is being performed in the Electron Microscopy Laboratory at the Idaho National Laboratory. The SEM analysis of samples from U-Mo dispersion fuel plates focuses primarily on the behavior of the Si that has been added to the Al matrix to improve the irradiation performance of the fuel plate and on the overall behavior of fission gases (e.g., Xe and Kr) that develop as bubbles in the fuel microstructure. For monolithic fuel plates, microstructural features of interest, include those found in the U-Mo foil and at the U-Mo/Zr and Zr/6061 Al cladding interfaces. For both dispersion and monolithic fuel plates, samples have been produced using an SEM equipped with a Focused Ion Beam (FIB). These samples are of very high quality and can be used to uncover some very unique microstructural features that are typically not observed when characterizing samples produced using more conventional techniques. Overall, for the dispersion fuel plates with matrices that contained Si, narrower fuel/matrix interaction layers are typically observed compared to the fuel plates with pure Al matrix, and for the monolithic fuel plates microstructural features have been observed in the U-10Mo foil that are similar to what have been observed in the fuel particles found in U-Mo dispersion fuels. Most recently, more prototypic monolithic fuel samples have been characterized and this paper describes the microstructures that have been observed in these samples.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Microstructural Analysis and Transport Resistances of Low-Platinum-Loaded PEFC Electrodes

In this study, we present microstructural characterization for polymer electrolyte fuel cell (PEFC) cathodes with low platinum loadings (low-PGM). The characterization results are used to quantify the contribution of mass transport resistances to cell voltage losses observed in polarization curve data. Three-dimensional pore morphology and ionomer distribution are resolved using nano-scale X-ray computed tomography (nano-CT). Electrode structural properties are reported along with analysis of the impact of microstructure on the effective charge and reactant transport properties. These characterizations are incorporated with a two-dimensional multi-physics model that accounts for energy, charge, and mass transport along with the effect of liquid water flooding. Defining a total mass transport resistance for the whole polarization curve, contributions of transport mechanisms are identified. Analysis of the experimental polarization curves at different operating pressures and temperatures indicates that the mass transport resistance in the cathode is dominated by the transport processes in the electrode. It is shown that flooding in the electrode is a major contributor to transport losses especially at elevated operating pressures while the pressure-independent resistance at the catalyst surface due to transport through the ionomer film plays a significant role, especially at low temperatures and low catalyst loading. In addition, by performing a parametric study for varying catalyst loadings, the importance of electrode roughness (i.e, electrochemically-active surface area/geometric electrode area) in determining the mass transport losses is highlighted.

25 ENERGY STORAGE↗
DOE OSTI2014

X-ray microstructural analysis of nanocrystalline TiZrN thin films by diffraction pattern modeling

A detailed microstructural characterization of nanocrystalline TiZrN thin films grown at different substrate temperatures (T{sub S}) was carried out by X-ray diffraction (XRD). Total diffraction pattern modeling based on more meaningful microstructural parameters, such as crystallite size distribution and dislocation density, was performed to describe the microstructure of the thin films more precisely. This diffraction modeling has been implemented and used mostly to characterize powders, but the technique can be very useful to study hard thin films by taking certain considerations into account. Nanocrystalline films were grown by using the cathodic pulsed vacuum arc technique on stainless steel 316L substrates, varying the temperature from room temperature to 200 °C. Further surface morphology analysis was performed to study the dependence of grain size on substrate temperature using atomic force microscopy (AFM). The crystallite and surface grain sizes obtained and the high density of dislocations observed indicate that the films underwent nanostructured growth. Variations in these microstructural parameters as a function of T{sub S} during deposition revealed a competition between adatom mobility and desorption processes, resulting in a specific microstructure. These films also showed slight anisotropy in their microstructure, and this was incorporated into the diffraction pattern modeling. The resulting model allowed for the films' microstructure during synthesis to be better understood according to the experimental results obtained. - Highlights: • Mobility and desorption competition generates a critical temperature. • A microstructure anisotropy related to the local strain was observed in thin films. • Adatom mobility and desorption influence grain size and microstrain.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Computer vision in microstructural analysis

The following is a laboratory experiment designed to be performed by advanced-high school and beginning-college students. It is hoped that this experiment will create an interest in and further understanding of materials science. The objective of this experiment is to demonstrate that the microstructure of engineered materials is affected by the processing conditions in manufacture, and that it is possible to characterize the microstructure using image analysis with a computer. The principle of computer vision will first be introduced followed by the description of the system developed at Texas A&M University. This in turn will be followed by the description of the experiment to obtain differences in microstructure and the characterization of the microstructure using computer vision.

Srinivasan, Malur N.↗
DOE OSTI2018

Microstructure Analysis and Rheological Behavior of Magnesium Alloys at Semi-solid Temperature Range

Microstructure and rheological properties of AZ91 and Elektron 21 magnesium alloys in semi-solid state were studied. Differential scanning calorimetry revealed significant differences in melting range in analyzed materials. Isothermal annealing for 5, 30 and 80 min, in semi-solid range, corresponding to 50 and 70% of solid fraction, showed slower microstructure coarsening kinetics in Elektron 21 due to the presence of Zr- and RE-enriched precipitations. Ostwald ripening and coalescence resulted in decrease in grains density with increasing annealing time and temperature. Hardness after annealing showed overall tendency to diminish with soaking time probably due to the growth of average grain size. Rheological analysis showed tendency to lower the value of dynamic viscosity coefficient as shear rate rise, which confirmed non-Newtonian flow behavior. The highest values of dynamic viscosity coefficient were obtained for alloy AZ91.

36 MATERIALS SCIENCE↗
DOE OSTI2020

MATBOX (Microstructure Analysis Toolbox) [SWR-20-76]

MATBOX is a MATLAB application for performing various microstructure-related tasks including microstructure numerical generation, image filtering and microstructure segmentation, microstructure characterization, result three-dimensional visualization and result correlation, and microstructure meshing. MATBOX was originally developed to analyze electrode microstructures for lithium ion batteries; however, the algorithms provided by the toolbox are widely applicable to other heterogeneous materials. The toolbox provides a user-friendly experience thanks to a Graphic-User Interface.

Usseglio Viretta, Francois↗
DOE OSTI2013

Chemical selective microstructural analysis of thin film using resonant x-ray reflectivity

Strong modulations of the reflected x-ray intensities near the respective absorption edges of the constituent materials promise to determine layer composition of thin film structures along with spectroscopic like information. Near the absorption edge, the orders of magnitude more contrast beyond the pure electron density distributions of materials find an approach to overcome the low density difficulty of the conventional x-ray reflectivity technique. These aspects are explained by experimental studies on partially decomposed boron nitride thin films. Chemical composition profile is determined from free surface to the embedded buried layer with depth resolution in nanometer scale. The results of resonant reflectivity for chemical analysis are correlated with depth dependent x-ray photo electron spectroscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Three-dimensional microstructural analysis of fragmentation behavior of platelet Al3Ti particles in Al-Al3Ti composite deformed by equal-channel angular pressing

Highlights: • Particle distribution in ECAPed Al-Al{sub 3}Ti composite depends on material flow of matrix. • Fragmentation of Al{sub 3}Ti particles by ECAP occurs along twin boundary in the particles. • Al{sub 3}Ti particles in the composite fragment after twin deformation of the particles. - Abstract: The fragmentation of platelet Al{sub 3}Ti particles in an Al-Al{sub 3}Ti composite by equal-channel angular pressing (ECAP) is investigated using three-dimensional (3D) microstructural evaluation and crystallography. The Al-Al{sub 3}Ti composite comprises coarse platelet Al{sub 3}Ti particles in an α-Al matrix. The ECAP of this composite is performed for up to 4 passes under processing routes A, B{sub c}, and C. Route B{sub c} produces the smallest Al{sub 3}Ti particle fragments in comparison with the fragments produced under routes A and C. This is because that route B{sub c} produces the largest number of shearing directions and shearing planes. Platelet Al{sub 3}Ti particle fragments in the specimen deformed by ECAP under route A are homogeneously distributed along the deformation axis. In contrast, in the specimens deformed by four ECAP passes under routes B{sub c} and C, the Al{sub 3}Ti particle fragments are gathered into several groups. The fragment groups have a length similar to the initial length of the platelet Al{sub 3}Ti particles. These spatial distributions of particle fragments can be explained by material flow of α-Al matrix during ECAP. Moreover, from 3D microstructural evaluation and crystallographic analysis of the Al{sub 3}Ti particle fragments, it is found that the Al{sub 3}Ti particles are preferentially fragmented on the twin boundary plane of {112}{sub Al3Ti}. Therefore, it is concluded that fragmentation of a platelet Al{sub 3}Ti particle by ECAP occurs along the twin boundary plane after twin deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructural analysis of laser weld fusion zone in Haynes 282 superalloy

Analytical electron microscopy and spectroscopy analyses of the fusion zone (FZ) microstructure in autogenous laser beam welded Haynes 282 (HY 282) superalloy were performed. The micro-segregation patterns observed in the FZ indicate that Co, Cr and Al exhibited a nearly uniform distribution between the dendrite core and interdendritic regions while Ti and Mo were rejected into the interdendritic liquid during the weld solidification. Transmission electron diffraction analysis and energy dispersive X-ray microanalysis revealed the second phase particles formed along the FZ interdendritic region to be Ti-Mo rich MC-type carbide particles. Weld FZ solidification cracking, which is sometimes associated with the formation of {gamma}-{gamma}' eutectic in {gamma}' precipitation strengthened nickel-base superalloys, was not observed in the HY 282 superalloy. Modified primary solidification path due to carbon addition in the newly developed superalloy is used to explain preclusion of weld FZ solidification cracking in the material. - Highlights: Black-Right-Pointing-Pointer A newly developed superalloy was welded by CO{sub 2} laser beam joining technique. Black-Right-Pointing-Pointer Electron microscopy characterization of the weld microstructure was performed. Black-Right-Pointing-Pointer Identified interdendritic microconstituents consist of MC-type carbides. Black-Right-Pointing-Pointer Modification of primary solidification path is used to explain cracking resistance.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Microstructural analysis of solar cell welds

Parallel-gap resistance welding of silicon solar cells with copper interconnects results in complex microstructural variations that depend on the welding variables. At relatively low heat input solid-state welds are produced. At medium heat the Ag-Cu eutectic forms resulting in a braze joint. High heat produces a fusion weld with complete melting of the silver layer on the silicon solar cell. If the silicon is also melted, cracking occurs in the silicon cell below the weld nugget. These determinations were made using light microscopy, microprobe, and scanning electron microscopy analyses.

Moore, T. J.↗
DOE OSTI2016

Coordinated U–Pb geochronology, trace element, Ti-in-zircon thermometry and microstructural analysis of Apollo zircons

Here, we present the results of a coordinated SIMS U–Pb, trace element, Ti-in-zircon thermometry, and microstructural study of 155 lunar zircons separated from Apollo 14, 15, and 17 breccia and soil samples that help resolve discrepancies between the zircon data, the lunar whole rock history and lunar magma ocean crystallization models. The majority of lunar grains are detrital fragments, some nearly 1 mm in length, of large parent crystals suggesting that they crystallized in highly enriched KREEP magmas. The zircon age distributions for all three landing sites exhibit an abundance of ages at ~4.33 Ga, however they differ in that only Apollo 14 samples have a population of zircons with ages between 4.1 and 3.9 Ga. These younger grains comprise only 10% of all dated lunar zircons and are usually small and highly shocked making them more susceptible to Pb-loss. These observations suggest that the majority of zircons crystallized before 4.1 Ga and that KREEP magmatism had predominantly ceased by this time. We also observed that trace element analyses are easily affected by contributions from inclusions (typically injected impact melt) within SIMS analyses spots. After filtering for these effects, rare-earth element (REE) abundances of pristine zircon are consistent with one pattern characterized by a negative Eu anomaly and no positive Ce anomaly, implying that the zircons formed in a reducing environment. This inference is consistent with crystallization temperatures based on measured Ti concentrations and new estimates of oxide activities which imply temperatures ranging between 958 ± 57 and 1321 ± 100 °C, suggesting that zircon parent magmas were anhydrous. Together, the lunar zircon ages and trace elements are consistent with a ≤300 My duration of KREEP magmatism under anhydrous, reducing conditions. We also report two granular texture zircons that contain baddeleyite cores, which both yield 207 Pb– 206 Pb ages of 4.33 Ga. These grains are our best constraints on impact ages within our sample population, and suggest at least one large impact is contemporaneous with the most common time of magmatic zircon formation on the Moon’s crust visited by the Apollo missions.

58 GEOSCIENCES↗
DOE OSTI2024

Microstructure analysis and machinability of additively manufactured A205 aluminum with heat treatments

A205 aluminum is one of the few high-strength aluminum alloys discovered for additive manufacturing (AM). The microstructure and heat treatment effects of AM A205 vary from those of its cast form, indicating possible differences in machinability during post-processing. Here, the objective of this research is to determine these variations of AM A205 and their effects on machinability using the cast condition as the baseline. As built and two heat-treated conditions (solution treatment and age hardening) were applied and compared in terms of their microstructures, micro-hardness, and machinability including vibration, specific cutting energy, chip morphology, and surface finish. The effects of print orientations on machinability were tested as well and found to be insignificant. AM as built had a higher hardness and slightly better machinability than its cast as built cast counterpart due to a smaller grain size (1 µm vs. 15 µm), eutectic θ-Al 2 Cu lattice and a fine, homogeneous TiB 2 distribution. The solution treatment dissolved this θ-Al 2 Cu lattice and increased the grain size (3 µm) which decreased the hardness, increased the ductility seen in the chips, and reduced the overall machinability. The presence of θ’-Al 2 Cu precipitates improved the machinability of aged AM A205. In addition, it was found that A205 exhibited both ductile and brittle behavior depending on the cutting speed, thus producing different machinability. The speed dependency is related to the material condition and heat treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructural Analysis of Powder Metallurgy Tool Steels in the Context of Abrasive Wear Behavior: A New Computerized Approach to Stereology

The present work describes a new methodology designed to characterize the microstructures of tool steels containing carbide hard phases, with the focus set on their abrasive wear resistance. A series of algorithms were designed and implemented in MATLAB® to (i) recognize each of the features of interest, (ii) measure relevant quantities and (iii) characterize each of the phases and the alloy in function of attributes usually neglected in wear description applications: size distribution, shape and contiguity of the hard phases. The new framework incorporates new parameters to describe each one of these attributes, as observed in SEM micrographs. All three aforementioned stages contain novel contributions that can be potentially beneficial to the field of materials design in general and to the field of alloy design for severely abrasive environments in particular. Models of known geometry and micrographs of different powder metallurgy steels were analyzed, and the obtained results were compared with the obtained by the linear intercept method. The relation between the new parameters and the ones available in the scientific literature is also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Automated Grain Boundary (GB) Segmentation and Microstructural Analysis in 347H Stainless Steel Using Deep Learning and Multimodal Microscopy

Austenitic 347H stainless steel offers superior mechanical properties and corrosion resistance required for extreme operating conditions such as high temperature. The change in microstructure due to composition and process variations is expected to impact material properties. Identifying microstructural features such as grain boundaries thus becomes an important task in the process-microstructure-properties loop. Applying convolutional neural network (CNN)-based deep learning models is a powerful technique to detect features from material micrographs in an automated manner. In contrast to microstructural classification, supervised CNN models for segmentation tasks require pixel-wise annotation labels. However, manual labeling of the images for the segmentation task poses a major bottleneck for generating training data and labels in a reliable and reproducible way within a reasonable timeframe. Microstructural characterization especially needs to be expedited for faster material discovery by changing alloy compositions. Here, in this study, we attempt to overcome such limitations by utilizing multimodal microscopy to generate labels directly instead of manual labeling. We combine scanning electron microscopy images of 347H stainless steel as training data and electron backscatter diffraction micrographs as pixel-wise labels for grain boundary detection as a semantic segmentation task. The viability of our method is evaluated by considering a set of deep CNN architectures. We demonstrate that despite producing instrumentation drift during data collection between two modes of microscopy, this method performs comparably to similar segmentation tasks that used manual labeling. Additionally, we find that naïve pixel-wise segmentation results in small gaps and missing boundaries in the predicted grain boundary map. By incorporating topological information during model training, the connectivity of the grain boundary network and segmentation performance is improved. Finally, our approach is validated by accurate computation on downstream tasks of predicting the underlying grain morphology distributions which are the ultimate quantities of interest for microstructural characterization.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis and Microstructural Analysis of Magnetic CaFe{sub 0.5}Co{sub 0.5}O{sub 3−δ} Using Rietveld Method

Perovskite cobaltates are widely recognized as potential candidates for their applications in magnetic and magnetoresistive applications. In this report, pseudo-magnetic CaFe{sub 0.5}Co{sub 0.5}O{sub 3−δ} was synthesized at ambient pressure. Various calcinations, heating times, and sintering temperatures were applied in order to achieve the optimized conditions. The optimal sintering temperature with excellent phase and microstructure was found at ∼1050 °C using CaCO{sub 3} as precursor. Rietveld analysis was carried out to solve and refine the XRD pattern of the final specimens. The sample with excellent refined values was solved in orthorhombic phase and pbcm space group. From the SEM and EDS analysis, the excellent grain growth with high densification and ABO{sub 3} structure was confirmed respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Microstructure analysis for chemical interaction between cesium and SUS 316 steel in fast breeder reactor application

In this study the corrosion products on a surface after cesium corrosion examination at 650 deg. C for 100 hrs were characterized by TEM observation around the corroded area on the surface in order to understand the corrosion mechanism of cesium fission product for cladding materials in fast reactor. The experimental results suggest the main corrosion mechanism occurred in the process of the separation of cesium chromate and metal (Fe, Ni). The main reaction of corrosion process was considered to be equation, 2Cs + 7/2 O{sub 2} + 2Cr {yields} Cs{sub 2}Cr{sub 2}O{sub 7}(L). (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1990

High-temperature deformation and microstructural analysis for Si3N4-Sc2O3

It was indicated that Si3N4 doped with Sc2O3 may exhibit high temperature mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High temperature deformation of samples was studied by characterizing the microstructures before and after deformation. It was found that elements of the additive, such as Sc and O, exist in small amounts at very thin grain boundary layers and most of them stay in secondary phases at triple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. Deformation of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent deformation resistance of the samples at high temperature can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.

Cheong, Deock-Soo↗
NASA NTRS1992

High-temperature deformation and microstructural analysis for silicon nitride-scandium(III) oxide

It was indicated that Si3N4 doped with Sc2O3 may exhibit high temperature mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High temperature deformation of samples was studied by characterizing the microstructures before and after deformation. It was found that elements of the additive, such as Sc and O, exist in small amounts at very thin grain boundary layers and most of them stay in secondary phases at tripple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. Deformation of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent deformation resistance of the samples at high temperature can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.

Cheong, Deock-Soo↗