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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Skyrmion Emergence Mediated by Antiferromagnetic Interlayer Exchange Coupling

Skyrmions are considered as topologically protected magnetic textures; they are covering a large area of applications. In this work, we studied using micromagnetic simulations the emergence of skyrmions in a nanodisk stacked in a FM/NM/FM multilayer system. We show how the skyrmion is formed through the antiferromagnetic interlayer exchange coupling (IEC). We also show the impact of the IEC on skyrmion size in both layers. We try as a conclusion to identify the range of IEC where skyrmions could exist in such systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Petro-mineralogical Studies of the Paleoproterozoic Phosphorites in the Sonrai basin, Lalitpur District, Uttar Pradesh, India

The Paleoproterozoic phosphorites constitute an economically significant component of the Sonrai basin of Lalitpur district. These are associated with ferruginous shale, ironstone, limestone and quartz breccia. Petro-mineralogical studies of samples of the phosphorites, using X-ray diffractometry and scanning electron microscopy, reveal that the collophane (carbonate-fluorapatite) is the dominant phosphate mineral. Calcite, dolomite, quartz, mica and haematite are the dominant gangue constituents. The phosphate minerals occur as oolites mutually replaced by carbonate and silica. The presence of iron oxides has been found in most of the thin sections. There is meagre evidence of organic matter in the form of filaments of microbial phosphate laminae in the samples of phosphorite. The mineral assemblages, their texture and various forms in these phosphorites may be due to some environmental vicissitudes followed by replacement processes and biogenic activities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Sb[subscript 2]Te[subscript 3] and Bi[subscript 2]Te[subscript 3] Thin Films Grown by Room-Temperature MBE

Sb{sub 2}Te3 and Bi{sub 2}Te3 thin films were grown on SiO{sub 2} and BaF{sub 2} substrates at room temperature using molecular beam epitaxy. Metallic layers with thicknesses of 0.2 nm were alternately deposited at room temperature, and the films were subsequently annealed at 250 C for 2 h. x-Ray diffraction and energy-filtered transmission electron microscopy (TEM) combined with high-accuracy energy-dispersive x-ray spectrometry revealed stoichiometric films, grain sizes of less than 500 nm, and a texture. High-quality in-plane thermoelectric properties were obtained for Sb{sub 2}Te3 films at room temperature, i.e., low charge carrier density (2.6 x 10{sup 19} cm{sup -3}, large thermopower (130 {micro}V K{sup -1}), large charge carrier mobility (402 cm{sup 2} V{sup -1} s{sup -1}), and resulting large power factor (29 {micro}W cm{sup -1} K{sup -2}). Bi{sub 2}Te3 films also showed low charge carrier density (2.7 x 10{sup 19} cm{sup -3}), moderate thermopower (-153 {micro}V K{sup -1}), but very low charge carrier mobility (80 cm{sup 2} V{sup -1} s{sup -1}), yielding low power factor (8 {micro}W cm{sup -1} K{sup -2}). The low mobilities were attributed to Bi-rich grain boundary phases identified by analytical energy-filtered TEM.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Geometric Limitation and Tensile Properties of Wire and Arc Additive Manufacturing 5A06 Aluminum Alloy Parts

Wire and arc additive manufacture (WAAM), as an emerging and promising technology of metal additive manufacturing, it lacks of experimental works to clarify the feature of geometrical configuration, microstructure and tensile properties, which can be used for further evaluating whether the as-deposited part can be used directly, and providing design reference for structure optimization. Taking 5A06 aluminum alloy additive manufacturing for example, in this paper, the geometric limitation and tensile property criteria are characterized using experimental method. The minimum angle and curvature radius that can be made by WAAM are 20° and 10 mm when the layer width is 7.2 mm. It shows isotropy when loading in build direction and perpendicular one. When loading in the direction of parallel and perpendicular to texture orientation, the tensile properties are anisotropic. The difference between them is 22 MPa.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Corrosion Behavior of Nano-/Ultrafine-Grained Al-0.2 wt.% Sc Alloy Produced by Accumulative Roll Bonding (ARB)

The corrosion behavior of the Al-0.2 wt.% Sc alloy fabricated by the accumulative roll bonding (ARB) process in a 3.5 wt.% NaCl solution was studied using the electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The effect of the microstructural parameters, such as dislocation density, texture, grain boundary, and lattice strain, on the corrosion behavior was also investigated in this study. The results demonstrated that the ARB process can significantly improve the corrosion resistance and modify the corrosion potential to attain higher positive potentials. In addition, the pitting corrosion changed into the lateral spreading of the pits at the seventh and tenth cycles of the ARB process with average grain size of 410 and 370 nm, respectively. The change in the fraction of the high-angle grain boundary during the ARB process is the most important parameter regarding the variation in corrosion type. The average grain size of 410 nm in seventh cycle, as the optimum average grain size, demonstrated the highest corrosion resistance.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Microstructure and Mechanical Properties of Cast Al-5Zn-2Mg Alloy Subjected to Equal-Channel Angular Pressing

In the present work, cast Al-5Zn-2Mg alloy was processed through equal-channel angular pressing (ECAP) in route B{sub C} up to four number of passes. Microstructure and mechanical properties were investigated on processed and unprocessed materials. In cast condition, the material was composed of dendritic structure. After homogenization treatment, large-sized grains were observed. After ECAP processing, significant grain refinement was observed. After ECAP processing, high-density dislocations and high degree of misorientation between the grains were observed. In cast material, rod-shaped precipitates were observed, while, after ECAP processing, spherical-shaped precipitates were observed. ECAP processing leads to a noticeable improvement in the mechanical properties of the material. After four passes, 122% improvement in the microhardness and 135% improvement in the ultimate tensile strength of the material were observed. After three passes, a slight decrease in the mechanical properties was observed. This is attributed to the dissolution of the metastable η′ phase, annihilation of dislocations, dynamic recrystallization and texturing during ECAP processing. Brittle fracture mode was observed in tensile testing cast and homogenized samples. After ECAP processing, fracture mode was changed into shear fracture mode.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Three-Dimensional Additively Manufactured Microstructures and Their Mechanical Properties

Metal additive manufacturing (AM) allows for the freeform creation of complex parts. However, AM microstructures are highly sensitive to the process parameters used. Resulting microstructures vary significantly from typical metal alloys in grain morphology distributions, defect populations and crystallographic texture. AM microstructures are often anisotropic and possess three-dimensional features. These microstructural features determine the mechanical properties of AM parts. Here, we reproduce three “canonical” AM microstructures from the literature and investigate their mechanical responses. Stochastic volume elements are generated with a kinetic Monte Carlo process simulation. A crystal plasticity-finite element model is then used to simulate plastic deformation of the AM microstructures and a reference equiaxed microstructure. Results demonstrate that AM microstructures possess significant variability in strength and plastic anisotropy compared with conventional equiaxed microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Shock and Microstructural Characterization of the α-ω Phase Transition in Titanium Crystals

In this paper, a multicrystal comprised of a small number of large crystals of high-purity titanium and a [ 0001 ] oriented high-purity single crystal titanium sample were shock loaded using gas gun plate impact experiments. Tests were performed at stresses above the &#x03B1;<!-- α --> &#x2212;<!-- - --> &#x03C9;<!-- ω --> phase transition stress (for high-purity polycrystalline specimens) to observe the behavior of oriented crystals under similar conditions. Post-mortem characterization of the shocked microstructure was conducted on the single crystal sample to measure textures, and quantify phases and twinning. The apparent activation of plastic and transformation mechanisms was dependent upon crystal orientation. Specifically, the [ 0001 ] crystal showed a higher Hugoniot elastic limit than the [ 10 1 &#x00AF;<!-- ¯ --> 0 ] or [ 3 1 &#x00AF;<!-- ¯ --> 4 &#x00AF;<!-- ¯ --> 4 ] orientations. The slope of velocity as a function of time was lower in the [ 0001 ] orientation than the other orientations during plastic deformation, indicating sluggish transformation kinetics for the α to ω phase transition for the [ 0001 ] oriented crystal. Finally, microtexture measurements of a recovered [ 0001 ] oriented single crystal revealed the presence of retained ω phase after unloading, with orientations of the constituent phase fractions indicative of the forward α→ω transition, rather than the reverse ω→α transition, suggesting that the material never achieved a state of 100% ω phase.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Predicting intragranular misorientation distributions in polycrystalline metals using the viscoplastic self-consistent formulation

In a recent paper, we reported the methodology to calculate intragranular fluctuations in the instantaneous lattice rotation rates in polycrystalline materials within the mean-field viscoplastic self-consistent (VPSC) model. Here, this paper is concerned with the time integration and subsequent use of these fluctuations to predict orientation-dependent misorientation distributions developing inside each grain representing the polycrystalline aggregate. To this end, we propose and assess two approaches to update the intragranular misorientation distribution within the VPSC framework. To illustrate both approaches, we calculate intragranular misorientations in face-centered cubic polycrystals deformed in tension and plane-strain compression. These predictions are tested by comparison with corresponding experiments for polycrystalline copper and aluminum, respectively, and with full-field calculations. It is observed that at sufficiently high strains some grains develop large misorientations that may lead to grain fragmentation and/or act as driving forces for recrystallization. Finally, the proposed VPSC-based prediction of intragranular misorientations enables modeling of grain fragmentation, as well as a more accurate modeling of texture using a computationally efficient mean-field approach, as opposed to computationally more expensive full-field approaches.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Surface and subsurface characterization of laser-interference structured Ti6Al4V

Ti6Al4V specimens were exposed to high-energy laser pulses of 1.24 J/cm 2 fluences per pulse using a two-beam optical configuration to attain laser-interference. In addition to the formation of periodic surface textures by laser-interference, scanning electron microscope (SEM) images demonstrated several microstructural changes on the surface processed. Moreover, the surface and subsurface of Ti6Al4V specimens were characterized for the as-received and laser-interference processed conditions using x-ray photoelectron spectroscopy (XPS) and electron energy dispersive spectroscopy (EDS). The XPS data showed that this laser technique is effective at removal of surface contaminants for Ti6Al4V. The XPS analysis also revealed the formation of an oxy-nitride layer on the laser treated material. Finally, the microstructure analysis indicates that grain refinement, dendrite and twin structures were found near the surface due to laser processing.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Impact load-induced micro-structural damage and micro-structure associated mechanical response of concrete made with different surface roughness and porosity aggregates

The relationship between the nature of micro damage under impact loading and changes in mechanical behavior associated with different microstructures is studied for concretes made with two different coarse aggregates having significant differences mainly in roughness and porosity - sintered fly ash and uncrushed gravel. A range of techniques including X-ray diffraction, digital image analysis, mercury porosimetry, X-ray computed tomography, laser surface profilometry and scanning electron microscopy were used to characterize the aggregates and micro-structures. The concrete prepared with lightweight aggregates was stronger in compression than the gravel aggregate concrete due to enhanced hydration as a result of internal curing. In the lightweight concrete, it was deduced that an inhomogeneous micro-structure led to strain incompatibilities and consequent localized stress concentrations in the mix, leading to accelerated failure. The pore structure, compressibility, and surface texture of the aggregates are of paramount importance for the micro-cracking growth.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Sr immobilization in irradiated Portland cement paste exposed to carbonation

Cement based materials are widely used as binding matrices for radionuclides in low and intermediate level waste management applications. We studied the effect of irradiation and carbonation under atmospheric condition on the leaching of Sr from Portland cement paste. Samples were exposed to gamma irradiation or subjected to thermal treatment under either inert or atmospheric conditions. Leaching tests were performed and supplemented by post-leaching characterization including local chemical analysis (LA-ICPMS) crystallographic analysis (XRD), and EPMA imaging. The combination of these methods enabled us to link between the crystallography, texture and composition of the treated samples and their ability to retain Sr ions. Results show that carbonation was the main factor determining the retention of Sr ions, whereas irradiation did not have a significant effect. Moreover, carbonation has a positive effect on the retention of Sr ions in the matrix with the formation of a carbonated zone.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

PyProcar: A Python library for electronic structure pre/post-processing

The PyProcar Python package plots the band structure and the Fermi surface as a function of site and/or s,p,d,f - projected wavefunctions obtained for each k-point in the Brillouin zone and band in an electronic structure calculation. This can be performed on top of any electronic structure code, as long as the band and projection information is written in the PROCAR format, as done by the VASP and ABINIT codes. PyProcar can be easily modified to read other formats as well. This package is particularly suitable for understanding atomic effects into the band structure, Fermi surface, spin texture, etc. PyProcar can be conveniently used in a command line mode, where each one of the parameters define a plot property. In the case of Fermi surfaces, the package is able to plot the surface with colors depending on other properties such as the electron velocity or spin projection. Furthermore, the mesh used to calculate the property does not need to be the same as the one used to obtain the Fermi surface. A file with a specific property evaluated for each k-point in a k-mesh and for each band can be used to project other properties such as electron–phonon mean path, Fermi velocity, electron effective mass, etc. Another existing feature refers to the band unfolding of supercell calculations into predefined unit cells.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Edaphic controls on soil organic carbon stocks in restored grasslands

Cultivation of undisturbed soils dramatically depletes organic carbon stocks at shallow depths, releasing a substantial quantity of stored carbon to the atmosphere. Restoration of native ecosystems can help degraded soils rebuild a portion of the depleted soil organic matter. However, the rate and magnitude of soil carbon accrual can be highly variable from site to site. Thus, a better understanding of the mechanisms controlling soil organic carbon stocks is necessary to improve predictions of soil carbon recovery. We measured soil organic carbon stocks and a suite of edaphic factors in the upper 10 cm of a series of restored tallgrass prairies representing a range of drainage conditions. Our findings suggest that factors related to soil organic matter stabilization mechanisms (texture, polyvalent cations) were key predictors of soil organic carbon, along with variables that influence plant and microbial biomass (available phosphorus, pH) and soil moisture. Exchangeable soil calcium was the strongest single predictor, explaining 74% of the variation in soil organic carbon, followed by clay content,which explained 52% of the variation. Our results demonstrate that the cumulative effects of even relatively small differences in these edaphic properties can have a large impact on soil carbon stocks when integrated over several decades.

Calcium↗
DOE OSTI2022

Understanding syringeability and injectability of high molecular weight PEO solution through time-dependent force-distance profiles

Opioid medications play a vital role in treating moderate to severe pain. Unfortunately, many drug misusers and abusers attempt to alter the formulations or properties of these drugs by manipulation, (e.g., crushing, chewing, smoking, snorting, injecting). The intravenous (IV) route is most dangerous to abusers, as the drugs directly enter the circulatory system and produce intense euphoria. To obtain a full understanding of the impact of syringe factors (e.g., needle gauge size, needle length, syringe barrel size), on the ease of injection, we undertook a comprehensive assessment of syringeability and injectability of manipulated abuse-deterrent formulations (ADFs). A texture analyzer-based testing method was developed for the measurement of the resistance force of pulling, holding, and pushing phases of injections. Results showed that the finer needle gauge sizes required higher injection force to withdraw drug solutions. In addition, the syringed liquid volume was highly dependent on needle gauge size, holding time, and sample viscosity. In most cases, a lower needle gauge number and a longer holding time increased the syringed volume. Needle length was highly correlated to injection force (R 2 = 0.99). Using longer needles to inject drug solution requires greater force. Furthermore, large barrel size was correlated to pushing force (R 2 = 0.99); thus, increasing the difficulty of pushing the plunger of a large syringe with one hand. Lastly, relationships between injection force, sample viscosity, and testing conditions were elucidated using a mathematical model, which could be used in the future to assess and predict injection force of solution samples.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Microstructure and high temperature properties of tungsten processed via electron beam melting additive manufacturing

There is considerable interest in the adoption of additive manufacturing for processing refractory metals. The layer-wise fabrication approach enables opportunities for producing complex geometries which cannot be otherwise be achieved via powder metallurgy. However, the processing science is still in its nascent stages and structure–property relations are relatively unexplored. Fundamental research is needed to further develop the technology and enable the fabrication of refractory metals for high temperature applications. Here we focus on the processing of pure tungsten using electron beam melting additive manufacturing. Experimentally we develop a suitable processing window for achieving high density crack free material. Microstructural analysis reveals that the microstructure generally consists of a columnar structure with a (111) build direction fiber preference, although, fiber switching was observed. Process induced deformation is believed to drive the formation of subgrains whose boundaries exhibit a high dislocation density. Additionally, high temperature tensile testing reveals that the material exhibits excellent properties closer to that of annealed tungsten. Significant mechanical anisotropy was observed to be present which is likely driven by strong crystallographic texture.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Room-temperature MBE deposition, thermoelectric properties, and advanced structural characterization of binary Bi[subscript 2]Te[subscript 3] and Sb[subscript 2]Te[subscript 3] thin films

Sb{sub 2}Te{sub 3} and Bi{sub 2}Te{sub 3} thin films were grown at room temperature on SiO{sub 2} and BaF{sub 2} substrates using molecular beam epitaxy. A layer-by-layer growth was achieved such that metallic layers of the elements with 0.2 nm thickness were deposited. The layer structure in the as-deposited films was confirmed by X-ray diffraction and was seen more clearly in Sb{sub 2}Te{sub 3} thin films. Subsequent annealing was done at 250 C for 2 h and produced the Sb{sub 2}Te{sub 3} and Bi{sub 2}Te{sub 3} crystal structure as confirmed by high-energy X-ray diffraction. This preparation process is referred to as nano-alloying and it was demonstrated to yield single-phase thin films of these compounds. In the thin films a significant texture could be identified with the crystal c axis being almost parallel to the growth direction for Sb{sub 2}Te{sub 3} and tilted by about 30{sup o} for Bi{sub 2}Te{sub 3} thin films. In-plane transport properties were measured for the annealed films at room temperature. Both films yielded a charge carrier density of about 2.6 x 10{sup 19} cm{sup -3}. The Sb{sub 2}Te{sub 3} films were p-type, had a thermopower of +130 {micro}V K{sup -1}, and surprisingly high mobilities of 402 cm{sup 2} V{sup -1} s{sup -1}. The Bi{sub 2}Te{sub 3} films were n-type, showed a thermopower of -153 {micro}V K{sup -1}, and yielded significantly smaller mobilities of 80 cm2 V{sup -1} s{sup -1}. The chemical composition and microstructure of the films were investigated by transmission electron microscopy (TEM) on cross sections of the thin films. The grain sizes were about 500 nm for the Sb{sub 2}Te{sub 3} and 250 nm for the Bi{sub 2}Te{sub 3} films. In the Bi{sub 2}Te{sub 3} thin film, energy-filtered TEM allowed to image a Bi-rich grain boundary phase, several nanometers thick. This secondary phase explains the poor mobilities of the Bi{sub 2}Te{sub 3} thin film. With these results the high potential of the nano-alloying deposition technique for growing films with a more complex layer architecture is demonstrated.

36 MATERIALS SCIENCE↗