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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Numerical case study of the aerosol–cloud interactions in warm boundary layer clouds over the eastern North Atlantic with an interactive chemistry module

The presence of warm boundary layer stratiform clouds over the eastern North Atlantic (ENA) region is commonly influenced by the Azores High, especially during the summer season. To investigate comprehensive aerosol–cloud interactions, this study employs the Weather Research and Forecasting model coupled with a chemistry component (WRF-Chem), incorporating aerosol chemical components that are relevant to the formation of cloud condensation nuclei (CCN) and accounting for aerosol spatiotemporal variation. This study focuses on aerosol indirect effects, particularly the long-range transport of aerosols, in the ENA region under three different weather regimes: a ridge with a surface high-pressure system, a post-trough with a surface high-pressure system, and a weak trough. The WRF-Chem simulations conducted at a near-large-eddy scale offer valuable insights into the model's performance, especially in terms of its ability to use high spatial resolution to capture mesoscale cloud features across various weather regimes. Our result shows that introducing 5 times more aerosols to either non-precipitating or precipitating clouds significantly increases ambient CCN numbers, resulting in, to varying degrees, higher liquid water path (LWP) values. The substantial aerosol–cloud interaction especially occurs in the precipitating clouds and demonstrates the susceptibility of the LWP to changes in CCN under different regimes. Conversely, thin, non-rain clouds at the edges of a cloud system are prone to evaporation, exhibiting an aerosol drying effect. The aerosols released during this process transition back to the accumulation mode, facilitating future activation. This dynamic behavior is not adequately represented in prescribed-aerosol simulations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Domain wall and interphase boundary motion in (1−x)Bi(Mg{sub 0.5}Ti{sub 0.5})O{sub 3}–xPbTiO{sub 3} near the morphotropic phase boundary

Electric field-induced changes in the domain wall motion of (1−x)Bi(Mg{sub 0.5}Ti{sub 0.5})O{sub 3}–xPbTiO{sub 3} (BMT-xPT) near the morphotropic phase boundary (MPB) where x = 0.37 (BMT-37PT) and x = 0.38 (BMT-38PT), are studied by means of synchrotron x-ray diffraction. Through Rietveld analysis and profile fitting, a mixture of coexisting monoclinic (Cm) and tetragonal (P4mm) phases is identified at room temperature. Extrinsic contributions to the property coefficients are evident from electric-field-induced domain wall motion in both the tetragonal and monoclinic phases, as well as through the interphase boundary motion between the two phases. Domain wall motion in the tetragonal and monoclinic phases for BMT-37PT is larger than that of BMT-38PT, possibly due to this composition's closer proximity to the MPB. Increased interphase boundary motion was also observed in BMT-37PT. Lattice strain, which is a function of both intrinsic piezoelectric strain and elastic interactions of the grains (the latter originating from domain wall and interphase boundary motion), is similar for the respective tetragonal and monoclinic phases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Large-eddy simulations of the Northeastern US coastal marine boundary layer

In this study, large eddy simulations (LES) of offshore boundary layers near the Nantucket coast are performed using Nalu-Wind. The marine boundary layer conditions are chosen to match the predominantly unstable and neutral conditions measured by the Cape Wind platform. The appropriate domain, resolution, and boundary condition settings required for the LES are established through this work. Differences between stable and unstable cases are found in the wind speed profiles, averaged statistics, and wind spectra, and explained in terms of stratification effects.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1980

Boundary-fitted coordinates for regions with highly curved boundaries and reentrant boundaries

A procedure was developed using the differential equation approach for generating boundary fitted coordinates for regions with highly curved boundaries as well as reentrant boundaries, such as those encountered in breaking surface waves. The resulting coordinates are nearly orthogonal and can provide adequate resolution even in the reentrant region. Consistent treatment of end boundaries and the use of a systematic initialization scheme and advanced implicit numerical solution techniques make the procedure highly efficient. The method developed for implicit enforcement of the periodicity boundary condition should be beneficial in the analysis of turbomachinery flow applications.

Ghia, U.↗
DOE OSTI2016

Phonon scattering by dislocations at grain boundaries in polycrystalline Bi 0.5 Sb 1.5 Te 3

Reducing lattice thermal conductivity ( κ l ) of a thermoelectric material is one of the most popular strategies to improve its thermoelectric performance. Particularly, many efforts have been focused on decreasing grain size to effectively scatter low‐frequency phonons by boundary scattering. In addition to the boundary scattering, we have recently demonstrated that dense arrays of dislocations formed in grain boundaries can further reduce the κ l by dislocation scattering at room temperature and above. In order to closely examine the effect of the dislocation scattering, the κ l of polycrystalline Bi 0.5 Sb 1.5 Te 3 samples with and without dislocations were measured at low temperature ( T < 200 K). Because other phonon scattering mechanisms like Umklapp and point‐defect scatterings are not dominant at low temperature, we clearly show the presence of the dislocation scattering in the sample with the dislocations by successfully describing its low temperature experimental κ l with a theoretical model.

Kim, Hyun‐Sik↗
DOE OSTI2018

Grain boundary engineering to control the discontinuous precipitation in multicomponent U10Mo alloy

Grain boundaries in metallic alloys often play a crucial role, not only in determining the mechanical properties or thermal stability of alloys, but also in dictating the phase transformation kinetics during thermomechanical processing. We demonstrate that locally stabilized structure and compositional segregation at grain boundaries—“grain boundary complexions”—in a complex multicomponent alloy can be modified to influence the kinetics of cellular transformation during subsequent thermomechanical processing. Using aberration-corrected scanning transmission electron microscopy and atom probe tomography analysis of a metallic nuclear fuel highly relevant to worldwide nuclear non-proliferation efforts —uranium-10 wt% molybdenum (U-10Mo) alloy, new evidence for the existence of grain boundary complexion is provided. We then modified the concentration of impurities dissolved in Υ-UMo grain interiors and/or segregated to Υ-UMo grain boundaries by changing the homogenization treatment, and these effects were used used to retard the kinetics of cellular transformation during subsequent sub-eutectoid annealing in this U-10-Mo alloy during sub-eutectoid annealing. Thus, this work provided insights on tailoring the final microstructure of the U-10Mo alloy, which can potentially improve the irradiation performance of this important class of alloy fuels.

Devaraj, Arun (ORCID:0000000313146212)↗
DOE OSTI2023

Atomic Diffusion, Segregation, and Grain Boundary Migration in Nickel-Based Alloys from Molecular Dynamics Simulations

Grain boundary diffusion and metal mobility in alloys control material performance in many applications and yet remain poorly understood at a mechanistic level. With advances in accessible time and length scales for computational molecular simulations, and recent force field developments, we now possess tools to help unravel those mechanisms. Using large-scale molecular dynamics simulations, here we examined vacancy-mediated diffusion processes in Ni-5Cr alloy with low and high-energy grain boundaries. We show that atomic diffusion inside the grain boundary plane is about four times higher than bulk diffusion, at any temperature, and exhibits a typical Arrhenius behavior with a very small energy barrier (0~.8 eV for Cr and 0.7 eV for Ni within 1300-1600 K). Additionally, the fastest diffusing species inverts; Cr diffusion was faster than Ni in the bulk but slower in the grain boundaries. This is attributed to the creation of high cohesive energy clusters of Cr at the grain boundary. Grain boundary migration was also observed to be temperature dependent and appears to be two times higher in the 5% Cr alloy than in pure Ni, highlighting the important role of the alloying element on grain boundary motion.

Simonnin, Pauline GN↗
DOE OSTI2016

YSZ thin films with minimized grain boundary resistivity

In recent years, interface engineering of solid electrolytes has been explored to increase their ionic conductivity and improve the performance of solid oxide fuel cells and other electrochemical power sources. It has been observed that the ionic conductivity of epitaxially grown thin films of some electrolytes is dramatically enhanced, which is often attributed to effects (e.g. strain-induced mobility changes) at the heterophase boundary with the substrate. Still largely unexplored is the possibility of manipulation of grain boundary resistivity in polycrystalline solid electrolyte films, clearly a limiting factor in their ionic conductivity. Here in this paper, we report that the ionic conductivity of yttria stabilized zirconia thin films with nano-columnar grains grown on a MgO substrate nearly reaches that of the corresponding single crystal when the thickness of the films becomes less than roughly 8 nm (smaller by a factor of three at 500 °C). Using impedance spectroscopy, the grain boundary resistivity was probed as a function of film thickness. The resistivity of the grain boundaries near the film–substrate interface and film surface (within 4 nm of each) was almost entirely eliminated. This minimization of grain boundary resistivity is attributed to Mg 2+ diffusion from the MgO substrate into the YSZ grain boundaries, which is supported by time of flight secondary ion mass spectroscopy measurements. We suggest grain boundary “design” as an attractive method to obtain highly conductive solid electrolyte thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Segregation-induced ordered superstructures at general grain boundaries in a nickel-bismuth alloy

The properties of materials change, sometimes catastrophically, as alloying elements and impurities accumulate preferentially at grain boundaries. Studies of bicrystals show that regular atomic patterns often arise as a result of this solute segregation at high-symmetry boundaries, but it is not known whether superstructures exist at general grain boundaries in polycrystals. In bismuth-doped polycrystalline nickel, we found that ordered, segregation-induced grain boundary superstructures occur at randomly selected general grain boundaries, and that these reconstructions are driven by the orientation of the terminating grain surfaces rather than by lattice matching between grains. This discovery shows that adsorbate-induced superstructures are not limited to special grain boundaries but may exist at a variety of general grain boundaries, and hence they can affect the performance of polycrystalline engineering alloys.

Science & Technology - Other Topics↗
DOE OSTI2023

Flexible Boundary Design for a Chattanooga Microgrid Powered by Landfill Solar Photovoltaic and Battery Storage

Landfill based microgrids powered by renewable energy aid reliability and resiliency while promoting environmental and energy justice. This paper aims to design a flexible boundary algorithm for a proposed Chattanooga landfill microgrid with the ability to shrink or expand its boundaries based on the available power from the solar PV and battery storage. This helps to improve resiliency unlike the conventional fixed boundary microgrids. The flexible boundary algorithm determines the combination and switching status of the intellirupter ® which changes the microgrid boundaries to achieve power balance by dropping or energizing specific load sections. Finally, the microgrid with flexible boundary was simulated in MATLAB/Simulink and performed satisfactorily when tested under various scenarios.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

Grain boundary phases in bcc metals

We report a computational discovery of novel grain boundary structures and multiple grain boundary phases in elemental body-centered cubic (bcc) metals represented by tungsten, tantalum and molybdenum. While grain boundary structures created by the γ-surface method as a union of two perfect half crystals have been studied extensively, it is known that the method has limitations and does not always predict the correct ground states. Here, we use a newly developed computational tool, based on evolutionary algorithms, to perform a grand-canonical search of a high-angle symmetric tilt and twist boundaries in tungsten, and we find new ground states and multiple phases that cannot be described using the conventional structural unit model. We use molecular dynamics (MD) simulations to demonstrate that the new structures can coexist at finite temperature in a closed system, confirming these are examples of different grain boundary phases. The new ground state is confirmed by first-principles calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Exploration of the mechanisms of temperature-dependent grain boundary mobility: Search for the common origin of ultrafast grain boundary motion

The temperature dependence of grain boundary mobility is complex, varied, and rarely fits ideal Arrhenius behavior. This work presents a series of case studies of planar grain boundaries in a model FCC system that were previously demonstrated to exhibit a variety of temperature-dependent mobility behaviors. It is demonstrated that characterization of the mobility versus temperature plots is not sufficient to predict the atomic motion mechanism of the grain boundaries. Herein, the temperature-dependent motion and atomistic motion mechanisms of planar grain boundaries are driven by a synthetic, orientation-dependent, driving force. The systems studied include CSL boundaries with Σ values of 5, 7, and 15, including both symmetric and asymmetric boundaries. These boundaries represent a range of temperature-dependent trends including thermally activated, antithermal, and roughening behaviors. Examining the atomic-level motion mechanisms of the thermally activated boundaries reveals that each involves a complex shuffle, and at least one atom that changes the plane it resides on. The motion mechanism of the antithermal boundary is qualitatively different and involves an in-plane coordinated shuffle that rotates atoms about a fixed atom lying on a point in the coincident site lattice. Furthermore, this provides a mechanistic reason for the observed high mobility, even at low temperatures, which is due to the low activation energy needed for such motion. However, it will be demonstrated that this mechanism is not universal, or even common, to other boundaries exhibiting non-thermally activated motion. This work concludes that no single atomic motion mechanism is sufficient to explain the existence of non-thermally activated boundary motion.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Evolution of grain boundary character distributions in alloy 825 tubes during high temperature annealing: Is grain boundary engineering achieved through recrystallization or grain growth?

Grain boundary engineering (GBE) of nickel-based alloy 825 tubes was carried out with different cold drawing deformations by using a draw-bench on a factory production line and subsequent annealing at various temperatures. The microstructure evolution of alloy 825 during thermal-mechanical processing (TMP) was characterized by means of the electron backscatter diffraction (EBSD) technique to study the TMP effects on the grain boundary network and the evolution of grain boundary character distributions during high temperature annealing. The results showed that the proportion of ∑ 3{sup n} coincidence site lattice (CSL) boundaries of alloy 825 tubes could be increased to > 75% by the TMP of 5% cold drawing and subsequent annealing at 1050 °C for 10 min. The microstructures of the partially recrystallized samples and the fully recrystallized samples suggested that the proportion of low ∑ CSL grain boundaries depended on the annealing time. The frequency of low ∑ CSL grain boundaries increases rapidly with increasing annealing time associating with the formation of large-size highly-twinned grains-cluster microstructure during recrystallization. However, upon further increasing annealing time, the frequency of low ∑ CSL grain boundaries decreased markedly during grain growth. So it is concluded that grain boundary engineering is achieved through recrystallization rather than grain growth. - Highlights: •The grain boundary engineering (GBE) is applicable to 825 tubes. •GBE is achieved through recrystallization rather than grain growth. •The low ∑ CSL grain boundaries in 825 tubes can be increased to > 75%.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Meso-scale anisotropic hydrogen segregation near grain-boundaries in polycrystalline nickel characterized by EBSD/SIMS

To study anisotropic hydrogen segregation and diffusion in nickel polycrystalline, Secondary Ion Mass Spectrometry (SIMS) and Electron Back Scattered Diffraction (EBSD) are integrated to investigate hydrogen distribution around grain boundaries. Hydrogen distribution in pre-charged samples were correlated with grain boundary character by integrating high-resolution grain microstructure from EBSD inverse pole figure map and low-resolution hydrogen concentration profile map from SIMS. This multimodal imaging instrumentation shows that grain boundaries in nickel can be categorized into two families based on behavior of hydrogen distribution crossing grain boundary: the first one includes random grain boundaries with fast hydrogen diffusivity, showing a sharp gap for hydrogen concentration profile cross the grain boundaries. The second family are special Σ3n grain boundaries with low hydrogen diffusivity, showing a smooth gradient of hydrogen concentration cross the grain boundary. Heterogeneous hydrogen distributions due to grain boundary family revealed by SIMS/EBSD on mesoscale further validate the recent hydrogen permeation data and anisotropic ab-initio calculations in nanoscale. The results highlight the fact that grain boundaries character impacts hydrogen distribution significantly.

Electron Back Scattered Diffraction↗
DOE OSTI2023

Grain Boundary Plane Measurement Using Transmission Electron Microscopy Automated Crystallographic Orientation Mapping for Atom Probe Tomography Specimens

Abstract Grain boundaries are critical in determining the properties of materials, including mechanical stability, conductivity, and corrosion resistance. The specific properties of materials depend not only on the misorientation of the crystals, the three most commonly characterized parameters, but also on the angle of the grain boundary plane between the two crystals, the final two parameters in the five-parameter macroscopic description of the grain boundary. The method presented here allows for the direct measurement of all five parameters of the grain boundary in a transmission electron microscopy specimen of various morphologies. This is especially applicable to atom probe specimens, where only a single-tilt axis is generally available, allowing the crystallographic description to be matched to the detailed chemical data available in the atom probe tomography. This method provides a platform for efficient grain boundary analysis in unique samples, saving operator time and allowing for ease of acquisition and interpretation in comparison with traditional electron diffraction methods.

Materials Science↗