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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 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Thixotropic spectra and Ashby-style charts for thixotropy

There is no universal model for thixotropy, and comparing thixotropic effects between different fluids is a subtle yet challenging problem. We introduce a generalized (model-insensitive) framework for comparing thixotropic properties based on thixotropic spectra. A superposition of exponential stress modes distributed over thixotropic time scales is used to quantify buildup and breakdown times and mode strengths in response to step-change input. This mathematical framework is tested with several experimental step-shear rate data on colloidal suspensions. Low-dimensional metrics based on moments of the distribution reveal characteristic average thixotropic properties, which are visualized on Ashby-style diagrams. This method outlines a framework for describing thixotropy across a diverse range of microstructures, supporting scientific studies as well as material selection for engineering design applications.

Mechanics↗
DOE OSTI2022

Numerical modeling of ion transport and adsorption in porous media: A pore-scale study for capacitive deionization desalination

In this report a pore-scale model is presented to simulate the dynamic ion transport and adsorption processes in porous electrodes used for capacitive deionization (CDI). The Stokes equation governing water flow is solved using the lattice Boltzmann method and Nernst-Planck equation describing ion transport is solved using the finite volume method. The ion adsorption process is considered at the surface of carbon electrodes. After validation against analytical solutions and published results, the model is used to study the coupled water flow, ion transport and adsorption in both two-dimensional and three-dimensional porous CDI electrodes at the pore scale. The effect of electrode microstructure, electrical potential and flow velocity on the adsorption processes is quantitatively investigated, and the relative importance of various parameters is determined. The presented model can be a powerful numerical tool to quantitatively analyze ion transport and adsorption in porous electrodes, and may provide useful information for the design and optimization of CDI electrodes and operating conditions for desired desalination efficiency, water throughput and cost.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

Review: mechanical behavior of metal/ceramic interfaces in nanolayered composites—experiments and modeling

In this study, recent experimental and modeling studies in nanolayered metal/ceramic composites are reviewed, with focus on the mechanical behaviors of metal/nitrides interfaces. The experimental and modeling studies of the slip systems in bulk TiN are reviewed first. Then, the experimental studies of interfaces, including co-deformation mechanism by micropillar compression tests, in situ TEM straining tests for the dynamic process of the co-deformation, thickness-dependent fracture behavior, and interrelationship among the interfacial bonding, microstructure, and mechanical response, are reviewed for the specific material systems of Al/TiN and Cu/TiN multilayers at nanoscale. The modeling studies reviewed cover first-principles density functional theory-based modeling, atomistic molecular dynamics simulations, and mesoscale modeling of nanolayered composites using discrete dislocation dynamics. The phase transformation between zinc-blende and wurtzite AlN phases in Al/AlN multilayers at nanoscale is also reviewed. Finally, a summary and perspective of possible research directions and challenges are given.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Gradient nanostructuring via compositional means

Nanocrystalline metals are inherently unstable against thermal and mechanical stimuli, commonly resulting in significant grain growth. Also, while these metals exhibit substantial Hall-Petch strengthening, they tend to suffer from low ductility and fracture toughness. With regard to the grain growth problem, alloying elements have been employed to stabilize the microstructure through kinetic and/or thermodynamic mechanisms. And to address the ductility challenge, spatially-graded grain size distributions have been developed to facilitate heterogeneous deformation modes: high-strength at the surface and plastic deformation in the bulk. In the present work, we combine these two strategies and present a new methodology for the fabrication of gradient nanostructured metals via compositional means. Here, we have demonstrated that annealing a compositionally stepwise Pt-Au film with a homogenous microstructure results in a film with a spatial microstructural gradient, exhibiting grains which can be twice as wide in the bulk compared to the outer surfaces. Additionally, phase-field modeling was employed for the comparison with experimental results and for further investigation of the competing mechanisms of Au diffusion and thermally induced grain growth. This fabrication method offers an alternative approach for developing the next generation of microstructurally stable gradient nanostructured films.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Additive friction stir deposition of SS316: Effect of process parameters on microstructure evolution

Solid state nature of additive friction stir deposition (AFSD) additive manufacturing process is very advantageous in terms of defect formation and microstructural refinement in the material. Current study presents the process optimization, microstructural evolution and kinetics of recrystallization for AFSD deposited low stacking fault energy material - SS316. As deposited microstructure shows equiaxed ultra fine grains with an average grain size of ~5.0 ± 0.5 μm. Shear deformation at high temperature during processing leads to the operation of restoration mechanisms. Observation of necklace type microstructure in the as deposited SS316 is attributed to discontinuous dynamic recrystallization during processing. Recrystallization kinetics of the AFSD SS316 is characterized using Johnson-Mehl-Avarami-Kolmogorov (JMAK) model. Deformation – thermal cycling during AFSD process resulted in inconsistent recrystallization kinetics. Variation in strain, strain rate and temperature during processing with processing parameters result in varying microstructure and tool wear. Further, high strength-ductility combination and sustained work hardening in as deposited SS316 appear to arise from transformation and twinning during deformation, leading to the formation of hierarchical twins and martensitic phase after deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Magnetic Properties of Exchange-Coupled Co{sub 72}Pt{sub 28}/Pt/Co{sub 81}Ir{sub 19} Composite Media for Perpendicular Magnetic Recording

In this work, we report the investigation of microstructure and magnetic properties of the Co{sub 72}Pt{sub 28}/Pt/Co{sub 81}Ir{sub 19} exchange-coupled composite (ECC) media using soft-layer (SL) of Co{sub 81}Ir{sub 19} with negative magnetocrystalline anisotropy (MA). Our TEM images show that the hard-layer (HL) exhibits a columnar type microstructure with well-isolated grains and the exchange-coupled SL with hcp-structure show the same texture. Strong coupling of the two layers have been evidenced by the magnetic characterization for all the studied films with Pt inter-layer thickness ranging from 0 to 2 nm. Importantly, these ECC media films have much lower coercivities and much higher thermal stabilities in the favor of high-density magnetic recording.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Experimental Study on the Hot Deformation Characterization of Low-Carbon Nb-V-Ti Microalloyed Steel

X80 steel, as typical low-carbon Nb-V-Ti microalloyed steel, is getting more and more attention in oil and gas transmission pipeline manufacturing. In this paper, the hot deformation behavior of X80 steel has been investigated. Hot compression tests of the steel were conducted under different temperatures and strain rates. Based on the experimental data, the flow stress constitutive equations were established. It is found that the hot deformation activation energy of this steel is higher than C-Mn and low-carbon steel. Then, the kinetics model and grain size model of dynamic recrystallization were developed according to the flow curves and the optical microstructures. In addition, the processing maps were developed to analyze the workability of X80 steel at elevated temperature. The analysis results show that the optimum processing window is at the temperature of 1300-1473 K and the strain rate of 0.01-10 s{sup −1}. The microstructure observation indicates that the optimum processing parameters are applicable to the tested steel.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Improved Thermal Conductivity of a Potting Material for High-Power Fast Warm-Up Cathodes

With higher power, frequency and longer life of microwave tubes, cathode heater assembly is being modified to enhance the warm-up performance and reliability, which are governed by ceramics thermal conductivity, electrical resistivity and shrinkage. In present work, a potting material with a high thermal conductivity of 22.14 W/(m K) and low linear shrinkage of 5.5% was prepared using two kinds of alumina powders with different size and morphology. Aqueous slurries were produced for centrifugal casting. The highest solid loading slurries with 70 vol.% were obtained. Green body with relative density above 70% was easily made from slurries using centrifugal casting. Relative sintered density reached 86.75% maximum without any sintering aids. Rheological behavior of slurries, potting microstructure, sintering shrinkage and thermal conductivity were analyzed. Continuous particle distribution, series and parallel models were used to guide the powders proportion and explain the thermal conductivity. The potting material thermal conductivity experimental data agreed with the series and parallel models when the weight parameter ξ was between 0.3 and 0.5.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Crystalline Loading of Lipophilic Coenzyme Q10 Pharmaceuticals within Conjugated Carbon Aerogel Derivatives

Low-density aerogel materials currently are being considered for applications in controlling the rate of release for small-molecule pharmaceuticals in vivo. In particular, silica (SiO2) aerogels are an intriguing platform for controlling both the absolute amount of drug loading, but also the crystalline state of small molecule pharmaceuticals has been shown to affect drug release kinetics. To date, loading silica aerogel materials with crystalline pharmaceuticals typically require dissolving small molecules in a supercritical solvent (i.e., CO2) before drying to recover the aerogel/drug composite. Here we demonstrate a simple and low-cost method for controlling the crystallinity of the model drug coenzyme Q10 (CoQ10) within carbon aerogel materials by rationally controlling the chemical microstructure of the aerogel to exhibit ?-conjugated (sp2) chemical bonding. In particular, both pyrolyzed graphene and nanodiamond aerogels exhibit enhanced intrinsic drug loading capacity and CoQ10 crystallinity over a broad range of sp2 surface-curvature. In contrast, amorphous carbon aerogel materials are observed to load CoQ10 pharmaceuticals with strictly amorphous microstructure.

Lim, Mathew↗
DOE OSTI2018

Moisture transport and sorption in cement based materials containing slag or silica fume

This paper presents the moisture dependency of moisture transport and moisture fixation in mortars with OPC, slag and silica fume. Water vapor desorption isotherms were measured with gravimetric methods and the moisture dependency of moisture transport was investigated with cup-tests. The results show an ongoing evolution of water vapor desorption isotherms from eight months to four years. The evolution is more pronounced for mortars containing slag. The results also show that there is a significant difference in moisture dependency of the moisture transport properties above 70% relative humidity; some mortars exhibit a clear moisture dependency in moisture transport whereas others do not. At a relative humidity below 70%, the water to binder ratio is more decisive for moisture transport than the type of binder. These results are of value for service-life models, where they represent important input data, and for understanding the evolution of the microstructure at later ages.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The application of synchrotron micro-computed tomography to characterize the three-dimensional microstructure in irradiated nuclear fuel

This research demonstrated the first time that synchrotron X-ray micro-computed tomography (μ-CT) was utilized to analyze the three-dimensional (3-D) morphology of the microstructure of irradiated nuclear fuel. Both absorption contrast and propagation-based phase contrast enhanced μ-CT techniques were evaluated. Porosity and phase region volumes were determined in neutron irradiated uranium 10 wt.% zirconium (U-10Zr) using propagation-based phase contrast enhanced μ-CT. Volumes were determined by image processing software and algorithms, with the porosity volume subsequently compared to the ASTM E562 method. The 3-D porosity of a small region (~ 8 x 10 5 µm 3 ) located in the intermediate fuel redistribution zone that was removed via a focused ion beam was determined to be 7.2% via image processing. A detailed 3-D analysis of the porosity with respect to volume and morphology was provided. Five growth stages of pore evolution were observed including: nucleation, growth, coalescence, interconnected porosity, and extended/interconnected porosity. Four distinct phase regions were identified, including the pores, via both absorption contrast and propagation-based phase contrast enhanced μ-CT. A quantitative comparison of fuel swelling between this localized microscopic U-10Zr fuel region, previously irradiated in the Fast Flux Test Facility, and historic U-10Zr fuels irradiated in the Experimental Breeder Reactor-II (EBR-II) was conducted. It was determined that for similar burnups, the localized swelling in this microscopic fuel region was 7.7%, which was approximately one-half of the value of the macroscopic swelling reported in EBR-II irradiated fuel. With the advent of new specimen preparation tools for irradiated materials, as well as advances in characterization techniques, researchers can now obtain previously inaccessible microstructural insight into irradiated fuels. This possibility naturally lends itself to improved fuel performance models for the nuclear community.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Formation and self-organization of void superlattices under irradiation: A phase field study

Self-organized patterns, realized in non-equilibrium processes, have been widely observed in physics and chemistry. As a powerful tool to create far-from-equilibrium environments, irradiation produces a variety of types of defects, which can self-organize through physical interactions and chemical reactions. Such a process becomes complicated especially when both thermodynamics and kinetics play critical roles in pattern formation. Here, we explore the formation and self-organization mechanism of void superlattices in metals and alloys under irradiation through phase field modeling and simulations. For the first time, three different formation mechanisms of void superlattices are clearly distinguished according to their thermodynamic origin and reaction kinetics. It is discovered that the characteristic length and symmetry of an emerging superlattice is determined by the interplay of the thermodynamic driving force and the kinetic anisotropy of the system. Through parametric study, the effects of kinetic coefficients, such as atomic mobility and irradiation dose rate, on the nucleation, growth, coarsening, coalescence, and ordering of voids are systematically investigated. The theoretical model developed in this work may provide guidelines for designing desired self-organized microstructures under irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Impact of carbonation on leaching of constituents from a cementitious waste form for treatment of low activity waste at the DOE Hanford site

Carbonation can be a major aging process during disposal of alkaline cementitious waste forms and can impact constituent leaching by changes in material alkalinity, pore structure, and controlling mineral phases. The effect of carbonation on the leaching of major and trace constituents from Cast Stone, a cementitious waste form developed to treat high salt content low activity waste, was studied through a combination of leaching experiments and reactive transport simulations. Diffusive transport of constituents in the waste form was evaluated using reactive transport modeling of diffusion-controlled leaching test results and a geochemical speciation model derived from pH-dependent leaching. Comparisons between Cast Stone materials aged under nitrogen, air, and 2% carbon dioxide in nitrogen showed that carbonation impacts solubility, physical retention and observed diffusivity of major and trace constituents. Carbonation under 2% CO 2 decreased the diffusion-controlled leaching of chromium by two orders of magnitude. Finally, modeling results suggest that carbonation may also decrease solubility of technetium while changes to microstructure by carbonation increases effective diffusivity of constituents in Cast Stone.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

The hierarchical structure of organic mixed ionic–electronic conductors and its evolution in water

Polymeric organic mixed ionic–electronic conductors underpin several technologies in which their electrochemical properties are desirable. These properties, however, depend on the microstructure that develops in their aqueous operational environment. We investigated the structure of a model organic mixed ionic–electronic conductor across multiple length scales using cryogenic four-dimensional scanning transmission electron microscopy in both its dry and hydrated states. Four-dimensional scanning transmission electron microscopy allows us to identify the prevalent defects in the polymer crystalline regions and to analyse the liquid crystalline nature of the polymer. The orientation maps of the dry and hydrated polymers show that swelling-induced disorder is mostly localized in discrete regions, thereby largely preserving the liquid crystalline order. Therefore, the liquid crystalline mesostructure makes electronic transport robust to electrolyte ingress. Furthermore, this study demonstrates that cryogenic four-dimensional scanning transmission electron microscopy provides multiscale structural insights into complex, hierarchical structures such as polymeric organic mixed ionic–electronic conductors, even in their hydrated operating state.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Simulating the Fracture of Notched Mortar Beams through Extended Finite-Element Method and Peridynamics

This paper simulates fracture in notched mortar beams under three-point bending using extended finite element method (XFEM) and peridynamics. A three-phase microstructure (i.e., cement paste, aggregates, and paste-aggregate interface) is used for constitutive modeling of the mortar to obtain the elastic properties for simulation. In the XFEM approach, the simulated homogenized elastic modulus is used along with the total fracture energy of the cement mortar in a damage model to predict the fracture response of the mortar including crack propagation and its fracture parameters (Mode I stress intensity factor, K IC and critical crack tip opening displacement, CTOD C ). The damage model incorporates a maximum principal stress-based damage initiation criteria and a traction-separation law for damage evolution. In the peridynamics approach, a bond-based model involving a prototype microelastic brittle (PMB) material model is used. The elastic properties and fracture energy release rates are used as inputs in the PMB model, along with the choice of peridynamic horizon size. Comparison with experimental fracture properties ( K IC , CTOD C ) as well as crack propagation paths from digital image correlation show that both the approaches yield satisfactory results, particularly for K IC and crack extension. Furthermore, both these methods can be adopted for fracture simulation of cement-based materials.

42 ENGINEERING↗
DOE OSTI2018

Investigating deformation and mesoscale void creation in HMX based composites using tomography based grain scale FEM

The microstructure of plastic bonded explosives (PBXs) significantly affects their macroscale mechanical characteristics. Imaging and modeling of the mesoscale constituents allows for a detailed examination of the deformation of mechanically loaded PBXs. In this study, a pair of explosive HMX crystals were bound with an HTPB based polymer binder and imaged using micro Computed Tomography ($µ$CT). Delamination of the polymer binder from the crystals was induced via macro-scale application of a tensile load. Cohesive parameters for simulation of the crystal/binder interface were determined by comparing numerical and experimental results of the delamination of this bi-crystal system. Simulations showed macro-scale plastic behavior is accommodated through both crystal-binder delamination and plastic deformation of the binder itself. Imaging and simulation of this bi-crystal system demonstrated the complex interplay of material constitutive behavior and grain-scale geometry. Successful parameterization of this relatively simple mechanical system is a step toward a better understanding void nucleation in similarly composed polycrystalline composites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Physics-based model of irradiation creep for ferritic materials under fusion energy operation conditions

Irradiation creep is known to be an important process for structural materials in nuclear environments, potentially leading to creep failure at temperatures where thermal creep is generally negligible. While there is a great deal of data for irradiation creep in steels and zirconium alloys in light water reactor conditions, much less is known for first wall materials under fusion energy conditions. Lacking suitable fusion neutron sources for detailed experimentation, modeling, and simulation can help bridge the dose-rate and spectral-effects gap and produce quantifiable expectations for creep deformation of first wall materials under standard fusion conditions. In this paper, we develop a comprehensive model for irradiation creep created from merging a crystal plasticity representation of the dislocation microstructure and a defect evolution simulator that accounts for the entire cluster dimensionality space. Both approaches are linked by way of a climb velocity that captures dislocation-biased defect absorption and a dislocation strengthening term that reflects the accumulation of defect clusters in the system. Here, we carry out our study in Fe under first wall fusion reactor conditions, characterized by a fusion neutron spectrum with average recoil energies of 20 keV and a damage dose rate of ≈3×10 –7 dpa/s at temperatures between 300 and 800 K.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Laser Weld Geometry and Microstructure of Cast Uranium-6 wt% Niobium Alloy

Laser welding was performed on a U6 wt% Nb uranium alloy using a 400W solid state laser with welding speeds from 20 to 2,500 mm/s. This speed range spanned melt pool sizes from traditional welding to surface modification and additive manufacturing. With increasing scan speed, the ratio of weld length relative to depth and width increased, with melt pool lengths being more than 5x greater than the width and 10x greater than the depth at the highest speeds. Keyhole mode welds were shown to occur at low speeds, while conduction mode welds occurred at 700 mm/s or higher as the weld depth dropped off more rapidly than width at higher speeds. Microstructures that form at the boundary between the fusion zone and base metal were observed to have a nonconventional appearance consisting of interpenetrating dark and light contrast phases before cells or dendrites appear. Dendrites with secondary arms form from this boundary in keyhole welds and refine to no visible secondary arms near the weld center. Primary and secondary dendrite arms, where present, were shown to refine in size inversely with cooling rate raised to the 0.465 and 0.376 powers respectively. Dendrites were largely absent from the conduction mode welds at higher speeds, and were replaced by a banded microstructure, that appears to form by an oscillatory solidification front mechanism.

36 MATERIALS SCIENCE↗