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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Effects of V addition on recrystallization resistance of 7150 aluminum alloy after simulative hot deformation

The effects of different V contents (0.01 to 0.19 wt.%) on the recrystallization resistance of 7150 aluminum alloys during post-deformation heat treatment were investigated. The microstructural evolutions at as-cast, as-homogenized conditions and after post-deformation annealing were studied using optical, scanning electron and transmission electron microscopes and using the electron backscattered diffraction technique. The precipitation of Al{sub 21}V{sub 2} dispersoids was observed in alloys containing 0.11 to 0.19 wt.% V after homogenization. The dispersoids were mainly distributed in the dendrite cells, and the precipitate-free zones occurred in the interdendritic regions and near grain boundaries. V addition could significantly enhance the recrystallization resistance during post-deformation annealing, particularly in the presence of a great number of Al{sub 21}V{sub 2} dispersoids. Recrystallized grain growth was effectively restricted because of the dispersoid pinning effect. The alloy containing 0.15 wt.% V exhibited the highest recrystallization resistance amongst all V-containing alloys studied. - Highlights: • Investigated the effect of V level on microstructure and flow stress of 7150 alloys • Characterized microstructures using optical microscopy, SEM, TEM and EBSD • Described the precipitation behavior of V-dispersoids in the dendritic structure • Studied the V effect on recrystallization resistance during post heat treatment • V addition greatly enhanced the recrystallization resistance during annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Research Update: Reactively sputtered nanometer-thin ZrN film as a diffusion barrier between Al and boron layers for radiation detector applications

In this paper, optimization of the process flow for PureB detectors is investigated. Diffusion barrier layers between a boron layer and the aluminum interconnect can be used to enhance the performance and visual appearance of radiation detectors. Few nanometers-thin Zirconium Nitride (ZrN) layer deposited by reactive sputtering in a mixture of Ar/N{sub 2}, is identified as a reliable diffusion barrier with better fabrication process compatibility than others. The barrier properties of this layer have been tested for different boron layers deposited at low and high temperatures with extensive optical microscopy analyses, electron beam induced current, SEM, and electrical measurements. This study demonstrated that spiking behavior of pure Al on Si can be prevented by the thin ZrN layer thus improving the performance of the radiation detectors fabricated using boron layer.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of T6 heat treatment on the microstructural and mechanical properties of Al–Si–Cu–Mg alloys

In this communication, it is aimed to optimize the conditions for T6 heat treatment of permanent die cast Al–Si–Cu–Mg alloys. Various solutionizing temperatures, aging treatments and soaking times were used to improve / modify the mechanical properties of presently studied alloys. Formation mechanism of the particles was understood by carrying out optical microscopy and energy dispersive X–ray (EDX) spectroscopy measurements. Spherical particles of alloys were studied for their microstructural properties using scanning electron microscopy (SEM). Microhardness test was performed to investigate their mechanical properties. Dependence of cluster formation and microhardness of the alloys on the adequate solutionizing temperature, aging treatment and soaking time has been discussed in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2004

Two-Photon Fluorescence Microscopy Developed for Microgravity Fluid Physics

Recent research efforts within the Microgravity Fluid Physics Branch of the NASA Glenn Research Center have necessitated the development of a microscope capable of high-resolution, three-dimensional imaging of intracellular structure and tissue morphology. Standard optical microscopy works well for thin samples, but it does not allow the imaging of thick samples because of severe degradation caused by out-of-focus object structure. Confocal microscopy, which is a laser-based scanning microscopy, provides improved three-dimensional imaging and true optical sectioning by excluding the out-of-focus light. However, in confocal microscopy, out-of-focus object structure is still illuminated by the incoming beam, which can lead to substantial photo-bleaching. In addition, confocal microscopy is plagued by limited penetration depth, signal loss due to the presence of a confocal pinhole, and the possibility of live-cell damage. Two-photon microscopy is a novel form of laser-based scanning microscopy that allows three-dimensional imaging without many of the problems inherent in confocal microscopy. Unlike one-photon microscopy, it utilizes the nonlinear absorption of two near-infrared photons. However, the efficiency of two-photon absorption is much lower than that of one-photon absorption because of the nonlinear (i.e., quadratic) electric field dependence, so an ultrafast pulsed laser source must typically be employed. On the other hand, this stringent energy density requirement effectively localizes fluorophore excitation to the focal volume. Consequently, two-photon microscopy provides optical sectioning and confocal performance without the need for a signal-limiting pinhole. In addition, there is a reduction in photo-damage because of the longer excitation wavelength, a reduction in background fluorescence, and a 4 increase in penetration depth over confocal methods because of the reduction in Rayleigh scattering.

Fischer, David G.↗
DOE OSTI2014

Improving properties of Mg with Al–Cu additions

The present work reports improvement in tensile properties of the Mg matrix reinforced with micron-sized copper–aluminum particulate hybrids. The Al–Cu particulate hybrids were incorporated into the Mg matrix through powder metallurgy method. The synthesized alloys exhibited homogeneously dispersed Mg{sub 2}Cu particles in the matrix, therefore leading to a 110% increase in yield strength (221 MPa) and a 72% enhancement in ultimate tensile strength (284 MPa) by addition of 1.0 wt.%Al–0.6 wt.%Cu particle hybrids. Optical microscopy, scanning election microscopy, transmission electron microscopy and X-ray diffraction were used to investigate the microstructure and intermetallic phases of the synthesized alloys. - Highlights: • Mg matrix is reinforced with Al–Cu particulate hybrids. • Powder metallurgic method is used to fabricate the alloys. • Tensile strength and ductility were increased simultaneously.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Formation of conductive copper lines by femtosecond laser irradiation of copper nitride film on plastic substrates

In this paper, we report a simple method to form conductive copper lines by scanning a single-beam femtosecond pulse laser on a plastic substrate covered with copper nitride (Cu{sub 3}N) film. The Cu{sub 3}N films were prepared by DC magnetron sputtering in the presence of an Ar + N{sub 2} atmosphere at 100 °C. The influence of the laser power and scanning speed on the formed copper line width, surface features, and morphology was analyzed by means of optical microscopy, X-ray diffraction, non-contact 3D profilometer, and scanning electron microscopy. The experimental results demonstrate that low laser power and low scanning speed favor the formation of uniform and flat Cu lines. After process optimization, copper lines with a width less than 5 μm were obtained, which provides an attractive application prospect in the field of flexible electronic devices.

36 MATERIALS SCIENCE↗
NASA NTRS2021

Melt Pool Imaging using a Configurable Architecture Additive Testbed System

This paper describes the inline (coaxial to laser) near infrared (NIR) camera sensor on the Configurable Architecture Additive Testbed (CAAT). The CAAT is an instrument that provides the capability to investigate laser based additive manufacturing (AM) processes and is configured for the metal powder bed fusion process. A low cost NIR camera is radiometrically calibrated to obtain coaxial, inline, imagery of laser generated melt pools. The camera capabilities, system optical path, and the uncertainty in the temperature measurement from NIR surface area scans on a bare titanium alloy plate are presented and discussed. The surface radiance measurements are compared to optical microscopy images of the melt pool width and depth. A metallic additive manufacturing process thermal model is developed in order to predict thermal distributions during laser scanning. The predicted thermal distributions by the model for different configurations are compared to the coaxial NIR measurements and discussed.

Additive manufacturing↗
DOE OSTI2015

Growth of large naphthalene and anthracene single-crystal sheets at the liquid–air interface

The growth of organic single crystals of naphthalene (C{sub 10}H{sub 8}) and anthracene (C{sub 14}H{sub 10}) at the liquid‒air interface from a mixture of solvents has been investigated. The growth technique used in the study makes it possible to obtain single-crystal sheets up to 10 mm in size for 24 h. The surface morphology and structure of the crystals have been analyzed by optical microscopy and X-ray diffraction. C{sub 10}H{sub 8} and C{sub 14}H{sub 10} single crystals grow coplanarly along the (001) plane. A thermodynamic model of the flat-crystal nucleus formation at the liquid‒air interface, based on the analysis of the change in the free Gibbs energy, is considered.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Current status of post-irradiation examination for the ATF-1 irradiation

A series of irradiations, referred to as the ATF series, is currently underway to evaluate the feasibility of different Accident Tolerant Fuels for commercial light water reactors. For initial screening, concepts consisting of an uranium bearing phase and cladding were irradiated in stainless steel capsules. These tests provide screening data among concepts to ensure viability of a fuel form going forward and can provide some initial data on fuel performance particularly information about fuel-cladding interaction and fuel behavior at operating temperatures and fission densities. Screening concepts are under irradiation or planned for irradiation at the Advanced Test Reactor of Idaho National Laboratory for a number of industrial partners (AREVA, GE, Westinghouse) and national laboratories (Los Alamos National Laboratory, Oak Ridge National Laboratory). Baseline PIE will be performed on all irradiated rodlets and will consist of visual examinations, neutron radiography, gamma spectrometry, dimensional inspections, fission gas analysis, optical microscopy, and chemical analysis. Additional evaluations may also be performed. The first capsules have arrived at the hot cell for initial post-irradiation examination. Results from initial examinations are presented along with example results from equivalent exams on similar fuel. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Fabrication of advanced accident tolerant U-Si fuel forms

Prospective advanced accident tolerant UN-USi fuel forms for light-water reactors are being studied at Los Alamos National Laboratory. In this paper we present a recent effort to fabricate and characterize U{sub 3}Si{sub 5} and UN-U{sub 3}Si{sub 5} fuel. The U{sub 3}Si{sub 5} is prepared by arc-melting stoichiometric amounts of uranium and silicon metals. The arc melting process consists of cutting U metal plate into small pieces that can be placed in a tri-arc furnace for melting. The material is slowly heated until a uniform melt of the U and Si is achieved. The fabrication of the U{sub 3}Si{sub 5} pellets followed a conventional cold-press and sinter process. As for the fabrication of UN-U{sub 3}Si{sub 5}, the uranium nitride (UN) feedstock powder was synthesized using carbothermic reduction nitridation. The UN is milled and sieved to sub-74 μm. The UN was mixed with EBS (ethylene bis-stearamide) and milled for 45 minutes. The UN-EBS was combined with 10 wt.% U{sub 3}Si{sub 5} powder (equivalent to 15 vol.% in UN) and additional EBS. The fabrication of the UN-U{sub 3}Si{sub 5} pellets followed a conventional cold-press and sinter process similar to that used to fabricate the U{sub 3}Si{sub 5} pellets. A sample UN-U{sub 3}Si{sub 5} pellet was cross-sectioned, ground, and polished for optical microscopy. The UN and U{sub 3}Si{sub 5} phases are apparent as well as pores and micro-cracks. The affect of micro-cracking on fuel performance is unknown and should be assessed during post-irradiation examination.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Effect of Chemical Composition on the Microstructure and Properties of the Ag-Ga-Ge Alloys

This study presents a comparison of thermodynamically calculated phase compositions of Ag-Ga-Ge alloys at fixed temperatures with phase analysis results of alloys annealed at respective temperatures. Three isothermal sections of the Ag-Ga-Ge system at 25, 100 and 300 °C have been extrapolated using optimized thermodynamic parameters from the literature. An experimental analysis of the microstructure was carried out using optical microscopy, scanning electron microscopy and energy-dispersive spectrometry. Results obtained by x-ray powder diffraction methods (identified phases and lattice parameters) were compared with the results of the predicted phase equilibria. Good overall agreement between experimental and calculated values was obtained. The Brinell hardness and electrical conductivity of selected alloys were measured and obtained results were analyzed with respect to their overall compositions and phase constituents.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Polystyrene/MoS{sub 2}@oleylamine nanocomposites

The effects of adding different concentrations of MoS{sub 2}@oleylamine nano particles on the thermal and mechanical properties of polystyrene (PS) nanocomposites have been investigated. X-ray diffraction and optical microscopy were used to characterize the morphology of the resulting nanocomposites. The thermal stability of the nanocomposites has been characterized by thermogravimetric analysis. It has been found that the MoS{sub 2}@oleylamine nanoparticles have a good compatibility with the PS matrix forming homogeneous dispersion even at high concentrations. The PS/MoS{sub 2}@oleylamine nanocomposites showed enhanced thermal stability in comparison with neat polystyrene.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Near- and far-field measurements of phase-ramped frequency selective surfaces at infrared wavelengths

Near- and far-field measurements of phase-ramped loop and patch structures are presented and compared to simulations. The far-field deflection measurements show that the phase-ramped structures can deflect a beam away from specular reflection, consistent with simulations. Scattering scanning near-field optical microscopy of the elements comprising the phase ramped structures reveals part of the underlying near-field phase contribution that dictates the far-field deflection, which correlates with the far-field phase behavior that was expected. These measurements provide insight into the resonances, coupling, and spatial phase variation among phase-ramped frequency selective surface (FSS) elements, which are important for the performance of FSS reflectarrays.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Carbon impurities on graphene synthesized by chemical vapor deposition on platinum

We report nanocrystalline carbon impurities coexisting with graphene synthesized via chemical vapor deposition on platinum. For certain growth conditions, we observe micron-size island-like impurity layers which can be mistaken for second graphene layers in optical microscopy or scanning electron microscopy. The island orientation depends on the crystalline orientation of the Pt, as shown by electron backscatter diffraction, indicating growth of carbon at the platinum surface below graphene. Dark-field transmission electron microscopy indicates that in addition to uniform single-crystal graphene, our sample is decorated with nanocrystalline carbon impurities with a spatially inhomogeneous distribution. The impurity concentration can be reduced significantly by lowering the growth temperature. Raman spectra show a large D peak, however, electrical characterization shows high mobility (∼8000 cm{sup 2}/Vs), indicating a limitation for Raman spectroscopy in characterizing the electronic quality of graphene.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Identification of sigma and chi phases in duplex stainless steels

The aim of this work is to find out the most suitable method for detecting and analyzing accurately the formation conditions of secondary phases, particularly Sigma-phase (σ-phase) and Chi-phase (χ-phase) in duplex stainless steels (UNS S32205 and UNS S32750). The microstructure was characterized after a solution annealing at 1080 °C followed by an isothermal heating at 830 °C for different time ranges, ranging from 1 min to 9 h, in order to enlighten the controversial point concerning the mechanism of χ-phase nucleation in relation with the σ-phase. Etched samples were observed using optical microscopy (MO), and scanning electron microscopy (FESEM) with a backscattered electron detector (BSE) was used on unetched samples. Compositional microanalysis (EDS) was carried out for identifying the different phases present in the steels. Sigma phase was easily observed using different etching procedures, whereas χ-phase was only clearly detected with FESEM–BSE on unetched samples. The compositional analyses showed that the molybdenum content in χ-phase almost doubles the content of this element in σ-phase, and as a result the kinetics of nucleation and growth were also found to be remarkably faster when the alloy content in the steel is higher. In addition, chromium nitrides and carbides were also observed to precipitate as a result of the heat treatments and, in the case of the chromium nitrides, they act as a favorable site for the nucleation of σ-phase and χ-phase. - Highlights: • Microscopy was used on heat treated duplex steels for microstructure identification. • FESEM–BSE observation on unetched samples provided the best contrast between phases. • Analyses of carbides, nitrides, chi and sigma phases were possible by EDS and WDS. • Chromium nitrides act as favorable site for the nucleation of chi and sigma phases. • Secondary phases nucleation kinetics are faster in superduplex than in duplex steels.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Design and development of liquid filled polymeric fibers with flexure rate viscoelastic properties

The design and development of a novel category of bi-component polymeric fibers, made of a polymeric sheath and a liquid core is described. To understand and to analyze the flow of molten polymer and liquid within a spin pack, we built a macroscale analogon where co-flow of polymer and liquid is investigated systematically. The macroscale analogon is composed of a glass cylinder with a finite length and a coaxial capillary. The inner fluid flows in the capillary and at its outlet meets the outer fluid flowing inside the glass cylinder. The fluids are pumped into the setup using pressurized bottles with controlled flow rates. A high-speed camera is placed in front of the glass cylinder to record the transient and the steady flow of the two phases and the morphology of their interface during co-flow. We systematically analyzed the combination of various fluids and different injection channel geometries, and used these findings to design a customized spin pack. Extrusion trials with molten polymers and specific liquids resulted in the production of liquid filled polymeric fibers (LFF) with different amounts of liquid from 3% to 33%vol. and diameters from 150μm to 1mm. Fiber morphology has been investigated with the help of optical microscopy and computer tomography, in order to analyze both surface and core morphology. Mechanical characterization of fibers has been carried out with special care to the damping capacity of such fibers using two different methods: two point bending tests to evaluate the energy dissipation of fibers upon bending at low frequency values (0.005-0.5Hz), and analysis of vibration reduction to determine the quality factor at the resonance frequency of the 1{sup st} and 3{sup rd} vibration mode.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Visibility of two-dimensional layered materials on various substrates

For the investigation of 2D layered materials such as graphene, transition-metal dichalcogenides, boron nitride, and their heterostructures, dedicated substrates are required to enable unambiguous identification through optical microscopy. A systematic study is conducted, focusing on various 2D layered materials and substrates. The simulated colors are displayed and compared with microscopy images. Additionally, the issue of defining an appropriate index for measuring the degree of visibility is discussed. For a wide range of substrate stacks, layer thicknesses for optimum visibility are given along with the resulting sRGB colors. Further simulations of customized stacks can be conducted using our simulation tool, which is available for download and contains a database featuring a wide range of materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Application of gamma-ray radiography and gravimetric measurements after accelerated corrosion tests of steel embedded in mortar

The accelerated corrosion by the impressed current technique is widely used in studies of concrete durability since it has the advantage that tests can be carried out within reasonable periods of time. In the present work the relationship between the applied current density and the resulting damage on the reinforcing steel, by applying optical microscopy, scanning electron microscopy, gamma-ray radiography and gravimetric measurements, was studied by means of the implementation of accelerated corrosion tests on reinforced mortar. The results show that the efficiency of the applied current is between 1 and 77%, regardless of the applied current density, the water/cement ratio and the mortar cover depth of the specimens. The results show the applicability of the gamma-ray radiography technique to detect localized corrosion of steel rebars in laboratory specimens.

36 MATERIALS SCIENCE↗