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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Modeling the strength and ductility of magnesium alloys containing nanotwins

Magnesium alloys have been receiving much attention recently as potential lightweight alternatives to steel for automotive and other applications, but the poor formability of these alloys at low temperatures has limited their widespread adoption for automotive applications. Recent work with face centered cubic (FCC) materials has shown that introduction of twins at the nanometer scale in ultra-fine grained FCC polycrystals can provide significant increase in strength with a simultaneous improvement in ductility. This objective of this work is to explore the feasibility of extending this concept to hexagonal close packed (HCP) materials, with particular focus on using this approach to increase both strength and ductility of magnesium alloys. A crystal plasticity based finite element (CPFE) model is used to study the effect of varying the crystallographic texture and the spacing between the nanoscale twins on the strength and ductility of HCP polycrystals. Deformation of the material is assumed to occur by crystallographic slip, and in addition to the basal and prismatic slip systems, slip is also assumed to occur on the {1 0 -1 1} planes that are associated with compression twins in these materials. The slip system strength of the pyramidal systems containing the nanotwins is assumed to be much lower than the strength of the other systems, which is assumed to scale with the spacing between the nanotwins. The CPFE model is used to compute the stress-strain response for different microstrucrutral parameters, and a criterion based on a critical slip system shear strain and a critical hydrostatic stress is used to compute the limiting strength and ductility, with the ultimate goal of identifying the texture and nanotwin spacing that can lead to the optimum values for these parameters.

Gorti, Sarma B↗
DOE OSTI2015

When the Desert Beetle Met the Carnivorous Plant: A Perfect Match for Droplet Growth and Shedding

Phase change of vapor followed by coalescence and transport on ubiquitous bumped or curved surfaces is of fundamental importance for a wide range of phenomena and applications from water condensation on cold beverage bottles, to fogging on glasses and windshields, self-cleaning by jumping droplets, weathering, self-assembly, desalination, latent heat transfer, etc. Over the past decades, many attempts to understand and control the droplet growth dynamics and shedding of condensates on textured surfaces have focused on finding the role of micro/nanotexture combined with wettability. In particular, inspired by the Namib desert beetle bump structure, studies tested the effect of topography on the preferential condensation. However, like the preferential condensation observed on flat surfaces, hybrid wettability rather than texture plays a major role; the role of bump topography on local preferential condensation has been unexplored and still not clearly understood. In addition, given that not only facilitating the droplet growth but also transporting the condensed droplets toward the desired reservoir is essential to make fresh sites for renucleation and regrowth of the droplets for enhancing condensation efficiency, the current hybrid-wettability- based design is not efficient to transport the condensates due to the high contact angle hysteresis created by highly wettable pinning points. Here we show that beetle-inspired bump topography leads faster localized condensation and transport of water. Employing simple analytic and more complicated numerical calculations, we reveal the detailed role of topography and predict the focused diffusion flux based on the distortion of concentration gradient around convex surface topography. We experimentally demonstrate the systematic understanding on the unseen effect of topographical parameters on faster droplet growth dynamics on various bump geometries. Further rational design of asymmetric topography and synergetic combination with slippery coating simultaneously enable both faster droplet growth and transport for applications including efficient water condensation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Super-surface selective nanomembranes providing simultaneous high permeation flux and high selectivity

Superhydrophobic membrane structures having a beneficial combination of throughput and a selectivity. The membrane structure can include a porous support substrate; and a membrane layer adherently disposed on and in contact with the porous support substrate. The membrane layer can include a nanoporous material having a superhydrophobic surface. The superhydrophobic surface can include a textured surface, and a modifying material disposed on the textured surface. Methods of making and using the membrane structures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Machining induced fissures in relation to microstructure of sintered U3Si2 fuel pellets

As uranium silicide (U3Si2) becomes a more desired fuel replacement for uranium dioxide in light water reactors, it is import to understand the fabrication process. Moreover, it is important to understand how the as-sintered microstructure of the fuel pellet affects the final product; uranium silicide fuel pellets are currently fabricated using a powder metallurgy process. Pellet quality and integrity is a concern as any unwanted defects may cause adverse irradiation behavior. Thus, pellets need to remain relatively free of defects (surface chipping, cracking, undesired microstructure, etc.) in order to be placed into a fuel assembly. Recently, it was observed that uranium silicide fuel pellets developed surface fissures on the machined surface after a centerless grinding process. Initial observations indicate a relation between microstructure and machining induced fissures; in essence, fissures on the machined surface are only observed in pellets containing a non-uniform texture (fine grains surrounding coarse grains). Experiments have been focused on determining the cause(s) of the non-uniform texture. Once the cause was determined and grain size was reproduced, samples with a coarse-grained microstructure, along with samples containing a fine-grained microstructure were centerless ground to confirm the relation between surface fissures and microstructure. Samples were also subjected to microscopic analysis, grain size analysis, and x-ray diffraction (XRD).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Super-surface selective nanomembranes providing simultaneous high permeation flux and high selectivity

Superhydrophobic membrane structures having a beneficial combination of throughput and a selectivity. The membrane structure can include a porous support substrate; and a membrane layer adherently disposed on and in contact with the porous support substrate. The membrane layer can include a nanoporous material having a superhydrophobic surface. The superhydrophobic surface can include a textured surface, and a modifying material disposed on the textured surface. Methods of making and using the membrane structures.

42 ENGINEERING↗
DOE OSTI2015

Methods to fabricate variations in porosity of lithium ion battery electrode films

A method and apparatus for forming lithium-ion batteries and battery cell components, and more specifically, to a system and method for fabricating such batteries and battery cell components using deposition processes that form three-dimensional porous structures are provided. One method comprises texturing a conductive substrate by calendering the conductive substrate between opposing wire mesh structures, forming a first layer of cathodically active material having a first porosity on the surface of the textured conductive substrate, and forming a second layer of cathodically active material having a second porosity on the first layer, wherein the second porosity is greater than the first porosity.

25 ENERGY STORAGE↗
DOE OSTI2019

EBSD characterization of metallic nuclear fuel

Grain structure and texture are important in all materials as they influence most mechanical properties. In particular for nuclear materials texture can influence material properties important for reactor performance, such as swelling, yield stress, fracture toughness etc. Moreover such data are of primary importance to develop and validate physics-based models for nuclear fuels based on microstructure evolution during irradiation (e.g. MARMOT). Scanning Electron Microscopy (SEM) coupled with Electron Back Scatter Diffraction (EBSD) has been proven as an effective technique for evaluating grain size, shape, and orientation. However it has been seldom used for nuclear fuels. This has been mostly related to difficulties in handling and preparing such materials for EBSD analyses. Particularly challenging remains sample preparation for metallic irradiated fuels, as they are prone to rapid oxidation. Indeed EBSD analyses require the elimination of any surface defect or oxide layer as the signal arise from 50-100 nm depth in the material. At Idaho National Laboratory (INL) great effort has focused in developing techniques to obtain suitable surfaces for EBSD analyses. In this paper the first results from EBSD analyses obtained from a wide range of nuclear materials will be presented. Sample analyzed included fresh U, U-Zr, Pu-Zr , and U-Mo, including some irradiated fuel.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Electron Beam Powder Bed Fusion Additive Manufacturing of Refractory Metals

The processing of refractory metals via additive manufacturing (AM) presents an opportunity to fabricatecomponents not possible through traditional powder metallurgy techniques. However, processing via AM isextremely challenging and there exist a host of technological limitations still unaddressed. Molybdenumand tungsten are two materials of particular interest for nuclear energy generation applications. Themajority of existing work on the processing of these materials is focused on laser powder bed fusion whereasa smaller body of work exists for electron beam melting AM. In general, material with acceptable densitycan be obtained via both routes however cracking is much more difficult to mitigate against. Strongcrystallographic fiber textures have been observed across a range of refractory systems. In this work wepresent our recent findings on electron beam melting AM of pure tungsten and molybdenum. Wedemonstrate that defect-free material can be obtained in both systems with appropriate processing. Strongbuild direction crystallographic texture fibers are observed in both systems. In molybdenum the fibertexture has direct impact on the resulting tensile behavior. These results demonstrate that electron beamAM is a suitable technology for processing these difficult to fabricate materials.

Fernandez-Zelaia, Patxi↗
DOE OSTI2012

Structural Characterization of Nb Films Deposited by ECR Plasma Energetic Deposition on Crystalline Insulators

An energetic condensation thin film coating technique with an electron cyclotron resonance (ECR) induced plasma ion source is used to deposit Nb thin films on crystalline insulating substrates, such as a-plane and c-plane sapphire (Al2O3) and on magnesium oxide, MgO (100), (110) and (111). Heteroepitaxial Nb films were produced by ECR deposition with regulated substrate temperature. The residual resistance ratio (RRR) of about 1 micron thick films reach unprecedented values (350 - 450) on (11-20) sapphire substrates. The epitaxial relationship of Nb/crystalline substrate is found to be strongly influenced by the substrate bias voltage (adding to the initial Nb+ kinetic energy), the substrate crystalline orientation, and heating conditions. At low substrate temperature, the Nb films demonstrated non-epitaxial crystalline textures, revealed by XRD Pole Figure technique and Electron Backscattering Diffraction (EBSD). The texture might be caused by ?Volmer-Weber? growth mode, i.e. island growth, at low surface adatom mobility. This study shows that the film?s crystal structural character has great impact on its RRR/Tc value, which in turn is related to the electron-mean-free-path of radio-frequency superconductivity. The knowledge learned from this research sheds some light on how to coat low-defect density Nb thin films on SRF cavity-preferred metallic substrates, such as Cu.

Zhao, X.↗
DOE OSTI2023

Defect Characterization of Monocrystalline Silicon Solar Cells with Polysilicon Passivated Contact Using Electrically-Detected Magnetic Resonance (EDMR) Spectroscopy

As the c-Si based solar cell efficiencies are approaching over 26%, it is becoming critical to characterize the low concentrations of the defects – as low as 10^10-10^11 cm-3 (for e.g., iron contamination in high-lifetime Ga-doped wafers3 and n-type wafers), and further reduce them. Also, atomistic level understanding of the mechanisms of the low concentration process-induced-defects and reliability limiting defects (such as light and elevated temperature induced degradation, surface passivation degradation) is needed to design the mitigation strategies. The conventional characterization techniques are limited due to their detection limitations. Some of the techniques based on lifetime spectroscopies can still be used for low concentration characterization however, they are based on estimations and theoretical models and hence, indirect and cannot fully reveal information about the microscopic mechanism of the defects. Thus, we present the application of an ultrasensitive magnetic resonance-based technique for the direct spectroscopic detection of the defects in Si PV - electrically detected magnetic resonance (EDMR). In this work, we aim to focus on establishing a process flow for fabrication of minicells with (miniature replica of the larger-area cells) and setting up the routine for EDMR measurements on them with the EDMR instrumentation capability at NREL. For the EDMR measurements, sample size is limited by the dimensions of sample holder tube (width less than 3.2 mm, active area - 20 mm). Thus, we have designed c-Si based minicells with polysilicon (poly-Si) passivated contacts same as the larger-area cells that we fabricate in our group at NREL. We also modified our minicell process flow for fabricating the textured minicells for preserving the texture during processing and taking care of the laser-ablation edge damage which can significantly affect the performance of such small devices. We have achieved comparable performance on these newly fabricated minicells as that of our 4 cm2 devices with same structure (comparable VOC, JSC, FF). We also conducted EDMR measurements on the minicells and observed a distinct EDMR signal at g-value ~2.005 at temperatures 30K and above, as shown in Fig. 2. We associate this signal to the presence of silicon dangling bonds based on the g-value. We also observed an EDMR signal at g-value ~1.998 at temperature ~5K. The origin of this signal is still being investigated. Thus, we show the proof of concept of minicells and EDMR measurements with which we now aim to study some of the unknown defects in silicon solar cell devices.

EDMR↗
DOE OSTI2018

Native Plants in Floodplain in Controlling Hg Flux into East Fork Poplar Creek of Oak Ridge - 18166

Legacy Hg contamination has been identified as the highest priority clean-up risk on the Oak Ridge Reservation (ORR) by the Department of Energy Office of Environmental Management (DOE-EM), Tennessee Department of Environment and Conservation (TDEC), and the US Environmental Protection Agency (EPA). During the 1950's and early 1960's, elemental mercury (Hg) was used to produce enriched Li isotope at the Y-12 National Security Complex (Y-12 Plant) for manufacturing components of various nuclear weapons systems. It is estimated that 350,000 kg of Hg was released to the environment contaminating facilities, soil, sediment, surface water, and groundwater within the boundaries of the Y-12 Plant and the downstream environment (i.e., East Fork Poplar Creek, EFPC). EFPC is a 23-km stream where the headwaters start in the Y-12 Plant, flows through the city of Oak Ridge, and empties into the Clinch River. Although various remediation efforts have reduced Hg fluxes from the Y-12 Plant over the last 25 years, the Hg concentration in water continue to exceed both the regulatory limit (51 ng/L) and the remediation goal (200 μg/L). Perennial grasses as floodplain plants have been successfully employed to control surface runoff and stabilize the floodplain. Hg has been strongly bound to particles suspended with surface runoff. Miscanthus grass is a perennial, tall grass that is adjusted to coarse, fine and medium textured soils. Although it grows best in deep, well-drained floodplain soils it is tolerant of poor to excessive well-drained soils, has an extensive tolerance for acidic to alkaline soils, and tolerates soil textures ranging from sand to clay. These long tangled root systems can reach moisture more deeply than other grasses during drought thus anchoring the plant into the soil. The fine appearance and branching hairs grow to form a dense mat that helps improve soil structure by increasing porosity and adding organic material that helps to bind soil particles together. In compacted or clay soils, spreading roots increase soil porosity by creating fractures in soil aggregates allowing water to penetrate deeper within the subsoil. This study showed that DOE remediation significantly reduced residual Hg to be <400 mg/kg in floodplain. However the residual Hg was mostly present in non-cinnabar mercury which is more bioavailable than cinnabar. The current study also found that Hg transfer flux from floodplain soils through surface soils with trees and grasses under natural rainfall events was an average of 0.28±0.15 μg/L, which was similar to the Hg concentrations in water of EFPC as reported by ORNL. Total Hg concentrations and Hg and speciation in floodplain soils were strongly affected by particle size distribution. Fine particles had higher Hg concentrations rich in cinnabar Hg. Clay particles contained as high as 2000-1600 mg/kg Hg with most Hg as cinnabar Hg, while coarse particles contained less total Hg, dominated by non-cinnabar Hg. Hg speciation in floodplain soil strongly controls its solubility, mobility, and bioavailability in both terrestrial/ aquatic ecosystems and downstream Hg concentrations. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Incorporating dynamic recrystallization into a crystal plasticity model for high-temperature deformation of Ti-6Al-4V

During hot deformation of (α + β) titanium alloys, the simultaneous action of strain and temperature in the (α + β) regime facilitates dynamic recovery, dynamic recrystallization (DRX), and phase transformations via non-equilibrium paths. DRX is manifested in the form of fine recrystallized α or β grains. Here, in the present study, a two-phase crystal plasticity finite element framework (CP-DRX) has been developed which incorporates DRX kinetics into the crystal plasticity (CP) model to predict the flow characteristics of Ti-6Al-4V alloys during thermo-mechanical processing. The CP slip system parameters, as well as elastic properties from both α and β phases of Ti, are calibrated for different strain rate conditions. An EBSD-informed two-phase microstructure representation has been utilized in the CP-DRX framework to explore the time-dependent evolution of DRX microstructure and crystal orientation for different strain rate conditions. The proposed CP-DRX can capture the evolution of crystal orientation and plastic flow stress–strain response of polycrystalline Ti-6Al-4V during the deformation process. Furthermore, the proposed model is able to capture the softening behavior, observed in average stress–strain response from experiments performed using a Gleeble thermomechanical simulator and predict the recrystallization texture.

(α+ β)-Titanium (Ti) Alloys↗
DOE OSTI2022

Nanoscale trace-element zoning in pyrite framboids and implications for paleoproxy applications

Pyrite framboids (spherical masses of nanoscale pyrite) are among the earliest textures of pyrite to form in sediments. It has been proposed that their trace-element (TE) contents can be used to track the TE composition of the water column in which they formed. However, it is not clear how these TEs are associated with the framboidal pyrite grains. For instance, it is important to know whether they are incorporated uniformly or are enriched in different regions of the framboid. Here, we used high-resolution scanning transmission electron microscopy to identify chemical zoning within pyrite framboids. We found that initial, nanoscale pyrite euhedral crystals, which make up the volumetric majority of the framboids, are covered/infilled by later pyrite that templates on the earlier pyrite. Further, this later pyrite is enriched in TEs, suggesting that many TEs are incorporated in pyrite relatively late (during early diagenesis; not in the water column). This observation suggests that although chemical analyses of pyrite framboids may provide ocean-water chemistry trends through time, the details are complex. Specifically, the TEs found in pyrite may be linked to adsorption onto organic matter, detrital material, and authigenic minerals such as Fe- and Mn-oxide phases followed by desorption in the sediments or release via dissolution and incorporation into pyrite as overgrowths on the initial nanoscale euhedral crystals that make up framboids. While the use of pyrite chemistry to understand past ocean conditions remains promising, and even diagenetic additions may not preclude the utility of pyrite for reconstructing ancient ocean conditions, care must be taken in interpretations because the end concentration may be influenced by diagenesis.

58 GEOSCIENCES↗
DOE OSTI2012

SOLID STATE JOINING OF MAGNESIUM TO STEEL

Friction stir welding and ultrasonic welding techniques were applied to join automotive magnesium alloys to steel sheet. The effect of tooling and process parameters on the post-weld microstructure, texture and mechanical properties was investigated. Static and dynamic loading were utilized to investigate the joint strength of both cast and wrought magnesium alloys including their susceptibility and degradation under corrosive media. The conditions required to produce joint strengths in excess of 75% of the base metal strength were determined, and the effects of surface coatings, tooling and weld parameters on weld properties are presented.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unconventional Anomalous Hall Effect in Hexagonal Polar Magnet Y 3 Co 8 Sn 4

A rare realization of unconventional anomalous Hall effect (UAHE) both below and above the magnetic transition temperature (T C ) in a hexagonal noncentrosymmetric magnet Y 3 Co 8 Sn 4 , using a combined experimental and ab initio calculations. Occurrence of such UAHE is mainly attributed to the reciprocal ($\mathscr{KS}$) topology (i.e., the presence of topological Weyl points at/near the Fermi level), along with some contribution from the topological magnetic texture (at low temperatures), as inferred from the measured field-dependent ac susceptibility. The effect of UAHE on the measured transport behavior however evolves differently with temperature above and below T C = 53 K, suggesting different physical mechanism responsible in the two phases. A unique planar ferrimagnetic ordering is found to be the most stable state with ab-plane as the easy plane below T C . The simulated net magnetization and the moment per Co atom agrees fairly well with the experimentally measured values. A reasonably large anomalous Hall conductivity (AHC) is also observed in both the phases (above and below T C ) of the present compound, which is again not so ubiquitous. In conclusion, the results underscore the family of R 3 Co 8 Sn 4 (R = rare earth) polar magnets as a compelling backdrop for exploring the synergy of magnetism and topological non-trivial electronic states, pivotal for spintronic applications.

Density functional theory calculations↗
DOE OSTI2019

Thermal Cycling and Ratchet Growth of TATB and PBX 9502

The irreversible volume expansion, or ratchet growth, of TATB and PBX 9502 (95 weight% TATB) compactions has been quantified over a wide range of thermal cycles. While the precise TATB texture distributions of these specimen sets are likely different from each other, we believe they are consistent within each set, as the expansion data show reproducibility and consistency. These data provide a baseline characterization of the ratchet growth phenomenon in these materials. The increased expansion that comes with changes in the temperature range of the cycles is quantified, repeated hot cycles growing far more than cold. For thermal cycles above ambient where the temperature range is increased in subsequent cycles, the growth of a given cycle is shown to be dictated by previously-established growth trajectories, and the specimen will grow according to the growth potential associated with the temperature range of the present cycle. Alternating hot-cold cycles greatly enhances the cold-cycle contributions as compared to the growth of cold cycles alone. These “rules” of ratchet growth are first established, then observed to hold true for more complex sequences of hot and cold cycles. Finally, a simple equation is used to parameterize the response of individual data sets.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2018

Temperature-Dependent Magnetic Properties of Electrodeposited CoPtP Alloy Nanowires

CoPtP alloy nanowires, ~ 200 nm in diameter, have been prepared by the electrodeposition method into the pores of a porous anodic aluminum oxide template. X-ray diffraction pattern shows that the wires consist of a mixture of fcc and hcp phases with CoPt (002) and CoPt (221) texture. The coercivity was found to be 1150 Oe at 50 K and 760 Oe at 300 K, when the field was applied parallel to the wire axis. The temperature dependence of coercivity was explained by considering the magnetocrystalline anisotropy and thermal activation effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗