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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Defect Production and Microstructural Feature Impact for Radiation Damage in Additively Manufactured 316 Stainless Steel

This milestone presents multi-scale modeling research results for additively manufactured 316 stainless steel. A combination of phase field, cluster dynamics, molecular dynamics, and density functional theory with machine learning is used, allowing for predictions of radiation-driven microstructural evolution in additively manufactured 316 stainless steel over a range of temperatures, damage rates, neutron spectra, and microstructures, and supporting the development of combined ion and neutron irradiation for material qualification. Informed by ion irradiation and neutron irradiation results across the Advanced Materials and Manufacturing Technologies program, we investigate the unique aspects of radiation-driven microstructure evolution in additively manufactured 316 stainless steel. In particular, we focus on understanding the impact of carbon concentration (varying, for example, between the 316L and 316H standards) on void formation; radiation-induced segregation at dislocation cells and grain boundaries; and the evolution of dislocation loops and network dislocation populations. We find that the unique characteristics of the additively manufactured microstructures must be accounted for in understanding the evolution of dislocation populations under thermal and irradiation conditions, such as the variation in sink strengths arising due to the variation in dislocation density. We also find that the radiation-induced segregation of Cr and Ni to grain boundaries and cell walls differs due to the differences in their defect sink biases. We also find that increasing the Ni content can slow vacancy diffusion, which may provide a mechanism for the observed reduction in transient swelling rate for austenitic Fe-Cr-Ni alloys with increasing Ni content. In addition, ion irradiations have shown that increasing carbon content in 316 SS results in a larger population of smaller voids, suggesting reduced vacancy diffusion. Our results show that the carbon content of additively manufactured 316 SS has a significant impact on the migration rate of defect clusters. The presence of carbon atoms results in carbon-vacancy trapping, significantly reducing the diffusion rate of vacancies. Carbon atoms may also be trapped near the surface of a void, which may reduce void growth by trapping vacancies that diffuse toward the void.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Vulnerable window of yield strength for swelling-driven fracture of phase-transforming battery materials

Abstract Despite numerous experimental and theoretical investigations of the mechanical behavior of high-capacity Si and Ge Li-ion battery anodes, our basic understanding of swelling-driven fracture in these materials remains limited. Existing theoretical studies have provided insights into elasto-plastic deformations caused by large volume change phase transformations, but have not modeled fracture explicitly beyond Griffith’s criterion. Here, we use a multi-physics phase-field approach to model self-consistently anisotropic phase transformation, elasto-plastic deformation, and crack initiation and propagation during lithiation of Si nanopillars. Our computational results reveal that fracture occurs within a “vulnerable window” inside the two-dimensional parameter space of yield strength and fracture energy and highlight the importance of taking into account the surface localization of plastic deformation to accurately predict the magnitude of tensile stresses at the onset of fracture. They further demonstrate how the increased robustness of hollow nanopillars can be understood as a direct effect of anode geometry on the size of this vulnerable window. Those insights provide an improved theoretical basis for designing next-generation mechanically stable phase-transforming battery materials undergoing large volume changes.

25 ENERGY STORAGE↗
DOE OSTI2024

Identifying Topological Defects in Lamellar Phases through Contour Analysis of Complex Wave Fields

Lamellar phases frequently contain structural imperfections that significantly affect their behaviors and properties. Our previous research successfully reconstructed real-space configurations of defective lamellar phases from diffuse scattering patterns, indicating the presence of phase vortices as a potential method for identifying topological defects disrupting the smectic ordering. Here, this report presents a mathematical framework using regularized wave fields to represent defective lamellar structures in real space. Phase singularities, resulting from the interference of random waves and indicating lamellar order disruption, are identified through a contour integral. These wave fields, derived from coherent scattering in reciprocal space, were validated via computational benchmarks analyzing small-angle neutron scattering data from AOT surfactant solutions, facilitating further statistical analysis of the defects. Our study highlights the potential to extract meaningful information about topological defects in lyotropic phases by inversely analyzing experimentally measured two-point static correlations. Our method allows for detailed structural analysis of various lyotropic phases, both particulate and nonparticulate, in their quiescent states and facilitates quantitative investigation of defects’ role in phase transitions. By integrating small-angle scattering, deep learning, and vortex tangle analysis, our comprehensive approach shows promise in addressing complex challenges in the structural analysis of soft matter systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Field-Induced Spin-Modulated Transitions in Epitaxial (001) BiFeO{sub 3} Films

Alterations in the ground state of thin (001) films of a BiFeO{sub 3} (BFO)-type multiferroic in a magnetic field are studied theoretically, with changes in the energy of induced anisotropy taken into account. The anisotropy vs. field phase diagrams identifying the stability regions of homogeneous antiferromagnetic states and the regions of emergence of spatially modulated antiferromagnetic states are constructed for three mutually orthogonal orientations of applied magnetic field. We show that, as the magnetic field decreases, the transformation of a homogeneous phase into a spatially modulated state occurs at the instability point of the homogeneous state via gradual emergence of the conical phase that transforms into a planar cycloid with the decreasing magnetic field. A multiferroic film grown on a (001) substrate develops considerable anisotropy of the energy of spatially modulated state, depending on the modulation orientation. Meanwhile, cycloids with different orientations undergo the transitions from incommensurate phase into the homogeneous state differently: either the conical cycloid is formed followed by its collapse into the homogeneous state or an unlimitedly growing domain of the homogeneous phase is formed within the flat cycloid. Examples of field-induced changes in magnetization, with changes in spin states taken into account, are provided. These results are of value in practical applications of multiferroic strain engineering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Intermittent Defect Fluctuations in Oxide Heterostructures

Abstract The heterogeneous nature, local presence, and dynamic evolution of defects typically govern the ionic and electronic properties of a wide variety of functional materials. While the last 50 years have seen considerable efforts into development of new methods to identify the nature of defects in complex materials, such as the perovskite oxides, very little is known about defect dynamics and their influence on the functionality of a material. Here, the discovery of the intermittent behavior of point defects (oxygen vacancies) in oxide heterostructures employing X‐ray photon correlation spectroscopy is reported. Local fluctuations between two ordered phases in strained SrCoO x with different degrees of stability of the oxygen vacancies are observed. Ab‐initio‐informed phase‐field modeling reveals that fluctuations between the competing ordered phases are modulated by the oxygen ion/vacancy interaction energy and epitaxial strain. The results demonstrate how defect dynamics, evidenced by measurement and modeling of their temporal fluctuations, give rise to stochastic properties that now can be fully characterized using coherent X‐rays, coupled for the first time to multiscale modeling in functional complex oxide heterostructures. The study and its findings open new avenues for engineering the dynamical response of functional materials used in neuromorphic and electrochemical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Integrated Simulation Framework for Additively Manufactured Ti-6Al-4V: Melt Pool Dynamics, Microstructure, Solid-State Phase Transformation, and Microelastic Response

In this work, to accelerate the establishment of fundamental understanding of the additive manufacturing (AM) process and its influence on microstructural evolution and related properties, we develop a multiphysics and multiscale modeling framework that integrates: (1) a high-fidelity powder-scale three-dimensional simulation of transient heat transfer and melt flow dynamics, (2) cellular automaton simulation of solidification grain structure and texture, (3) phase-field modeling of precipitation and dissolution of second-phase precipitate during repeated thermal cycles, and (4) microstructure-based micro- and mesoscopic elastic response calculation. Using Ti-6Al-4V as a model system, we demonstrate the application of the integrated framework to simulate complex microstructure evolution during a single-track laser powder bed fusion process and the associated mechanical response. Our modeling framework successfully captures the solidification β grain structure as a function of laser power and scanning speed, α precipitation upon subsequent cooling with different rates, and elastic response of the resulting (α + β) two-phase microstructure. The key features of solidification and second-phase precipitate microstructures, and their dependence on processing parameters, agree well with existing experimental observations. Finally, the established modeling framework is generally applicable to other metallic materials fabricated by AM.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fluid-enhanced surface diffusion controls intraparticle phase transformations

Phase transformations driven by compositional change require mass flux across a phase boundary. In some anisotropic solids, however, the phase boundary moves along a non-conductive crystallographic direction. One such material is Li X FePO 4 , an electrode for lithium-ion batteries. With poor bulk ionic transport along the direction of phase separation, it is unclear how lithium migrates during phase transformations. Here, we show that lithium migrates along the solid/liquid interface without leaving the particle, whereby charge carriers do not cross the double layer. X-ray diffraction and microscopy experiments as well as ab initio molecular dynamics simulations show that organic solvent and water molecules promote this surface ion diffusion, effectively rendering Li X FePO 4 a three-dimensional lithium-ion conductor. Phase-field simulations capture the effects of surface diffusion on phase transformation. Lowering surface diffusivity is crucial towards supressing phase separation. In conclusion, this work establishes fluid-enhanced surface diffusion as a key dial for tuning phase transformation in anisotropic solids.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Strong Landau-quantization effects in high-magnetic-field superconductivity of a two-dimensional multiple-band metal near the Lifshitz transition

We investigate the onset of superconductivity in a magnetic field for a clean two-dimensional multiple-band superconductor in the vicinity of the Lifshitz transition when one of the bands is very shallow. Due to the small number of carriers in this band, the quasiclassical Werthamer-Helfand approximation breaks down and Landau quantization has to be taken into account. We found that the transition temperature T C2 ( H ) has giant oscillations and is resonantly enhanced at the magnetic fields corresponding to the matching of the chemical potential with the Landau levels in the shallow band. This enhancement is especially pronounced for the lowest Landau level. As a consequence, the reentrant superconducting regions in the temperature-field phase diagram emerge at low temperatures near the magnetic fields at which the shallow-band Landau levels cross the chemical potential. The specific behavior depends on the relative strength of the intraband and interband pairing interactions and the reentrance is most pronounced in the purely interband coupling scenario. The reentrant behavior is suppressed by the Zeeman spin splitting in the shallow band; the separated regions disappear already for very small spin-splitting factors. On the other hand, the reentrance is restored in the resonance cases when the spin-splitting energy exactly matches the separation between the Landau levels. As a result, the predicted behavior may be realized in the gate-tuned FeSe monolayer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Cubic hastatic order in the two-channel Kondo-Heisenberg model

Materials with non-Kramers doublet ground states naturally manifest the two-channel Kondo effect, as the valence fluctuations are from a non-Kramers doublet ground state to an excited Kramers doublet. Here, the development of a heavy Fermi liquid requires a channel-symmetry-breaking spinorial hybridization that breaks both single and double time-reversal symmetry, and is known as hastatic order. Motivated by cubic Pr-based materials with $Γ$ 3 non-Kramers ground state doublets, this paper provides a survey of cubic hastatic order using the simple two-channel Kondo-Heisenberg model. Hastatic order necessarily breaks time-reversal symmetry, but the spatial arrangement of the hybridization spinor can be either uniform (ferrohastatic) or break additional lattice symmetries (antiferrohastatic). The experimental signatures of both orders are presented in detail, and include tiny conduction electron magnetic moments. Interestingly, there can be several distinct antiferrohastatic orders with the same moment pattern that break different lattice symmetries, revealing a potential experimental route to detect the spinorial nature of the hybridization. We employ an SU( N ) fermionic mean-field treatment on square and simple cubic lattices, and examine how the nature and stability of hastatic order varies as we vary the Heisenberg coupling, conduction electron density, band degeneracies, and apply both channel and spin symmetry breaking fields. In conclusion, we find that both ferrohastatic and several types of antiferrohastatic orders are stabilized in different regions of the mean-field phase diagram, and evolve differently in strain and magnetic fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ceramics Based on Powder Mixtures Containing Calcium Hydrogen Phosphates and Sodium Salts (Na{sub 2}CO{sub 3}, Na{sub 4}P{sub 2}O{sub 7}, and NaPO{sub 3})

Ceramic materials in the Na{sub 2}O–CaO–P{sub 2}O{sub 5} system have been produced using powder mixtures containing calcium hydrogen phosphates (monetite/brushite: CaHPO{sub 4}/CaHPO{sub 4} ∙ 2H{sub 2}O) and sodium salts (Na{sub 2}CO{sub 3} ∙ H{sub 2}O, Na{sub 4}P{sub 2}O{sub 7} ∙ 10H,O, and NaPO{sub 3}). These salts were used as precursors to the following high-temperature phases: Сa{sub 2}P{sub 2}O{sub 7}, Na{sub 2}O, Na{sub 4}P{sub 2}O{sub 7}, and NaPO{sub 3}. The amount of the salts in the powder mixtures was such that the oxide composition of the ceramics corresponded to 10 mol % sodium oxide for each mixture in the Na{sub 2}O–CaO–P{sub 2}O{sub 5} system. The powder mixtures were prepared using mechanical activation in acetone, which was accompanied by monetite rehydration to brushite. X-ray diffraction characterization showed that, after firing, the phase composition of the ceramics produced from the powder mixtures thus prepared lay in the Сa{sub 2}P{sub 2}O{sub 7}–NaCaPO{sub 4}–Na{sub 2}СaP{sub 2}O{sub 7}–Са(РО{sub 3}){sub 2} phase field. The resultant ceramic materials contain biocompatible and bioresorbable phases and can be recommended for bone implant fabrication.

36 MATERIALS SCIENCE↗
DOE OSTI2017

An Atomistic Introduction to Orientation Relations Between Phases in the Face-centered Cubic to Body-centered Cubic Phase Transition in Iron and Steel

We establish an atomistic view of the high- and low-temperature phases of iron/steel as well as some elements of the phase transition between these phases on cooling. In particular we examine the 4 most common orientation relationships between the high temperature austenite and low-temperature ferrite phases seen in experiment. With a thorough understanding of these relationships we are prepared to set up various atomistic simulations, using techniques such as Density Functional Theory and Molecular Dynamics, to further study the phase transition, in particular, quantities needed for Phase Field Modeling, such as the free energies of bulk phases and the phase transition front propagation velocity.

36 MATERIALS SCIENCE↗
NASA NTRS1977

Redetermination of the Fe-rich portion of the Fe-Ni-Co phase diagram

The iron rich portion of the Fe-Ni-Co ternary diagram was determined at four temperatures. The phase boundaries and tie-lines of the (alpha + gamma) phase field were measured by analyzing the alpha and gamma phases with an electron microprobe. Grain boundary allotrimorphs of the alpha phase were observed in the polished and etched sections of samples which were step cooled from the gamma phase into the (alpha + gamma) region. Widmanstaetten-type microstructures composed of gamma-precipitates were observed in samples which were directly heated from room temperature into the (alpha + gamma) region.

Widge, S.↗
NASA NTRS1995

Low velocity opposed-flow frame spread in a transport-controlled environment DARTFire

The overall objectives of the DARTFire project are to uncover the underlying physics and increase understanding of the mechanisms that cause flames to propagate over solid fuels against a low velocity of oxidizer flow in a low-gravity environment. Specific objectives are (1) to analyze experimentally observed flame shapes, measured gas-phase field variables, spread rates, radiative characteristics, and solid-phase regression rates for comparison with previously developed model prediction capability that will be continually extended, and (2) to investigate the transition from ignition to either flame propagation or extinction in order to determine the characteristics of those environments that lead to flame evolution. To meet the objectives, a series of sounding rocket experiments has been designed to exercise several of the dimensional, controllable variables that affect the flame spread process over PMMA in microgravity, i.e., the opposing flow velocity (1-20 cm/s), the external radiant flux directed to the fuel surface (0-2 W/cm(exp 2)), and the oxygen concentration of the environment (35-70%). Because radiative heat transfer is critical to these microgravity flame spread experiments, radiant heating is imposed, and radiant heat loss will be measured. These are the first attempts at such an experimental control and measurement in microgravity. Other firsts associated with the experiment are (1) the control of the low velocity, opposed flow, which is of the same order as diffusive velocities and Stefan flows; (2) state-of-the-art quantitative flame imaging for species-specific emissions (both infrared and ultraviolet) in addition to novel intensified array imaging to obtain a color image of the very dim, low-gravity flames.

West, Jeff↗
DOE OSTI2016

Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching

Electric-field modulation of magnetism in strain-mediated multiferroic heterostructures is considered a promising scheme for enabling memory and magnetic microwave devices with ultralow power consumption. However, it is not well understood how electric-field-induced strain influences magnetic relaxation, an important physical process for device applications. Here, we investigate resonant magnetization dynamics in ferromagnet/ferroelectric multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct strain states provided by electric-field-induced ferroelectric phase transition. The strain not only modifies magnetic anisotropy but also magnetic relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic Gilbert damping by electric field, which is attributed to strain-induced tuning of spin-orbit coupling. By contrast, a small but measurable change in extrinsic linewidth broadening is attributed to inhomogeneous ferroelastic domain switching during the phase transition of the PMN-PT substrate.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Ultrasonic oscillatory two-phase flow in microchannels

Experimental and numerical investigations are performed to provide an assessment of the transport behavior of an ultrasonic oscillatory two-phase flow in a microchannel. The work is inspired by the flow observed in an innovative ultrasonic fabric drying device using a piezoelectric bimorph transducer with microchannels, where a water-air two-phase flow is transported by harmonically oscillating microchannels. The flow exhibits highly unsteady behavior as the water and air interact with each other during the vibration cycles, making it significantly different from the well-studied steady flow in microchannels. Here, the computational fluid dynamics (CFD) modeling is realized by combing the turbulence Reynolds-averaged Navier-Stokes (RANS) k – ω model with the phase-field method to resolve the dynamics of the two-phase flow. The numerical results are qualitatively validated by the experiment. Through parametric studies, we specifically examined the effects of vibration conditions (i.e., frequency and amplitude), microchannel taper angle, and wall surface contact angle (i.e., wettability) on the flow rate through the microchannel. The results will advance the potential applications where oscillatory or general unsteady microchannel two-phase flows may be present.

42 ENGINEERING↗
DOE OSTI2025

Metallothionein expression in Eastern mosquitofish ( Gambusia holbrooki ) exposed to 137 Cs and lead: implications for using metallothionein as a metal exposure biomarker

Given the range of threats facing aquatic ecosystems, it is critical we have monitoring tools to quickly and efficiently identify stressors within ecosystems. Metallothionein’s (MTs) are a group of proteins widely used as biomarkers of metal exposure; however, their suitability has been questioned due to their influenceable nature and ability to be induced by various stressors. Through our study, we sought to (1) evaluate induction of MT in eastern mosquitofish (Gambusia holbrooki) exposed to a radionuclide ( 137 Cs) and metal (Pb), (2) assess the influence of in situ 137 Cs pre-exposure on Pb-induced MT expression, and (3) quantify changes in MT concentrations during Pb depuration. We conducted our experiment in three phases using mosquitofish as a model species: Phase I—pre-exposure to 137 Cs in the field, Phase II—exposure to Pb in the lab immediately following 137 Cs exposure, and Phase III—depuration in the laboratory. We quantified MT concentrations over time and assessed differences among treatments. We did not find in situ exposure of mosquitofish to 137 Cs to induce MT, nor did pre-exposure to 137 Cs appear to influence induction of MT following Pb exposure. Metallothionein was rapidly induced in mosquitofish following Pb exposure; however, MT induction was also observed in control fish. Additionally, there was no apparent relationship between MT and Pb body burdens. During depuration, we found MT concentrations to be highly variable among fish demonstrating no clear response. Furthermore, our study demonstrates the high variability exhibited by MT, the need for further validation of MT as a metal exposure biomarker, and the value in additional research on these proteins under varying exposure scenarios, particularly environmentally realistic concentrations.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1986

Near-field testing of the 5-meter model of the tetrahedral truss antenna

This report documents the technical results from near-field testing of the General Dynamics 5-meter model of the tetrahedral truss antenna at the Martin Marietta Denver Aerospace facility. A 5-meter square side of the tetrahedral served as the perimeter of the antenna, and a mesh surface and extensive surface contouring cord network was used to create a parabolic aperture shape to within an rms accuracy of 30 mils or better. Pattern measurements were made with offset feed systems radiating at frequencies of 7.73, 11.60, 2.27, and 4.26 (all in GHz). This report discusses the method of collecting the data, system measurement accuracy, the test data compiled, and diagostics and isolation of causes of pattern results. The technique of using near-field phase for measuring surface mechanical tolerances is included. Detailed far field antenna patterns and their implications are provided for all tests conducted.

Kefauver, Neill↗
NASA NTRS1990

Experiment design and operations

The objectives, design, and field operations of the First ISLSCP Field Experiment (FIFE) are described. The simultaneous acquisition of satellite, atmosphere, and surface data, and the understanding of the processes governing surface energy and mass exchange and how these are manifested in satellite-resolution radiometric data are identified as the specific objectives of the field-phase experiment. The central issues concerning the design of the field experiment are considered: the size of the site, the duration of the experiment, and the location of the site; it is noted that the Konza Prairie National Reserve was selected as the focus of the study. Field operations in 1987 and 1989 are discussed, and it is pointed out that a data set is available now from a single combined repository to all FIFE investigators, and that scientists can test models and algorithms on scales consistent with satellite observations and with enough supporting data on finer scales.

Sellers, P. J.↗