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At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Understanding the Effect of Electrochemical Properties and Microstructure on the Microgalvanic Corrosion of Mg Alloys via Phase-Field Simulations

In this work, we apply a phase-field model to gain insights into the corrosion behavior of Mg alloys. Specifically, we study the effect of electrochemical properties of the materials and their environment and the spatial distribution of second phases in a magnesium alloy. To this end, we perform sensitivity analyses in which we separately vary the exchange current density and corrosion potential of the second phase, as well as the electrolyte conductivity. We describe the effects of these parameters on the corrosion current and the resulting corrosion-front morphology. We also confirm that the ratio between the Wagner length, calculated for the anodic phase, and the initial width of the anodic domain is a good predictor of the morphological characteristic of the corroding surface. In addition, we examine the effect of the microstructure on the corrosion behavior in both 2D and 3D systems by varying the shape, size, and distribution of the second-phase regions. Our findings provide insights into the influence of the two-phase microstructure on the corrosion behavior in a magnesium alloy.

Electrochemistry↗
DOE OSTI2019

Fundamental Relationship of Microstructure and Ionic Conductivity of Amorphous LLTO as Solid Electrolyte Material

All-solid-state Li-ion batteries (ASSLiB) attracted lots of attention mainly due to their higher safety compared with commercial Li-ion batteries. The research of solid electrolyte is critical for the development of ASSLiB, and among all the candidates of solid electrolyte materials, amorphous Lithium Lanthanum Titanate Oxide (LLTO) is promising because of its outstanding electrochemical stability up to 12V. However, the fundamental relationship among the ionic conductivity, microstructure, and mechanism of Li ion transport is still unrevealed. In this study, both amorphous LLTO thin film and LLTO powder were successfully prepared by sol-gel process. In order to determine the relationship between microstructure and ionic conductivity, various annealing time at 500°C were applied. This work shows that the ionic conductivity increases from 2.32 × 10 -8 S/cm to 9.01 × 10 -6 S/cm with the annealing time before LLTO starts to crystallize and decreases back to ~1.6 × 10 -9 S/cm after the formation of crystal phase. The absolute value of difference is close to 3 orders of magnitude. Furthermore, the morphology of the thin film changes accordingly, solvent evaporation, surface refinement and crystallization phases would occur sequentially, and this indicates that there is an optimal synthesis condition for the LLTO film. However, the changes of structure, morphology and ionic conductivity does not affect activation energy. This will help researchers to find optimized synthesis condition of amorphous LLTO and potentially search for and design other solid electrolyte materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Kinetic Simulations of Microstructural Evolution (KSOME)

"Kinetic simulations of microstructural evolution" (KSOME) is an object Kinetic Monte Carlo (OMKC) simulation code. It is developed to simulate microstructural evolution in materials during irradiation. KSOME is developed from ground up with priority given to the flexibility, ease of upgradability, and computation efficiency, in that order. With previously developed simulation codes, various processes (more precisely, the diffusion-reaction processes) that can occur in a system were hardwired into the code. Hence, to perform higher fidelity simulations, a significant coding effort was required every time to incorporate either a more accurate description of existing processes or new processes. With KSOME, the necessity for frequent code upgrades whenever there is a need to perform higher fidelity simulations is either eliminated or reduced significantly. In KSOME, the categories of various diffusion-reaction processes and the data-management system are hardwired, while the execution of the diffusion-reaction processes specific to a system is specified via input files. In the present version of KSOME, the analytical expression required to calculate defect interaction radii are inputted via a text file. However, the ability to parse mathematical expressions from a text file can be extended to input the analytical expression to calculate other defect properties; including the expressions to calculate the change in the migration barriers of mobile defects due to long-range interaction with extended defects

Nandipati, Giridhar [Pacific Northwest National La↗
DOE OSTI2025

Laser Powder Bed Fusion Microstructure Surrogate Model

SAND2025-11467O The Laser Powder Bed Fusion (LPBF) Microstructure Surrogate Model is a machine-learning-based tool. It predicts statistics of microstructures that are produced by the LPBF additive manufacturing process. It includes a series of codes for training, testing, and analyzing the model as well as utility scripts for handling data. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Moser, Daniel [Sandia National Lab. (SNL-CA), Live↗
DOE OSTI2016

Demonstration of acceleration of relativistic electrons at a dielectric microstructure using femtosecond laser pulses

Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. Achieving the desired GV m –1 accelerating gradients is possible only with laser pulse durations shorter than ~1 ps. In this Letter, we present, to the best of our knowledge, the first demonstration of acceleration of relativistic electrons at a dielectric microstructure driven by femtosecond duration laser pulses. Furthermore, using this technique, an electron accelerating gradient of 690±100 MV m –1 was measured—a record for dielectric laser accelerators.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Dissipation of radiation energy in concentrated solid-solution alloys: Unique defect properties and microstructural evolution

The effort to develop metallic alloys with increased structural strength and improved radiation performance has focused on the incorporation of either solute elements or microstructural inhomogeneities to mitigate damage. The recent discovery and development of single-phase concentrated solid-solution alloys (SP-CSAs) has prompted fundamental questions that challenge established theories and models currently applicable to conventional alloys. Here, the current understanding of electronic and atomic effects, defect evolution, and microstructure progression suggests that radiation energy dissipates in SP-CSAs at different interaction strengths via energy carriers (electrons, phonons, and magnons). Modification of electronic- and atomic-level heterogeneities and tailoring of atomic transport processes can be realized through tuning of the chemical complexity of SP-CSAs by the selection of appropriate elements and their concentrations. Fundamental understanding of controlling energy dissipation via site-to-site chemical complexity reveals new design principles for predictive discovery and guided synthesis of new alloys with targeted functionalities, including radiation tolerance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

3-D reconstruction and microstructural characterization of neutron-irradiated U-10Zr fuel using FIB-SEM serial sectioning

Herein, focused ion beam-scanning electron microscopy serial sectioning was applied to characterize the three-dimensional (3-D) porosity and phase regions of a neutron-irradiated U-10 wt% Zr fuel. The specimen was removed from an intermediate radial region of a fuel pin irradiated to 5.7 at.% burn-up. Backscattered electron imaging and energy-dispersive spectroscopy were performed on each serial section, allowing for the characterization of microstructural morphology and composition. Porosity size followed a lognormal distribution, ranging from 1.46 × 10 –4 to 25.58 µm 3 with a total porosity volume fraction of 13.02%. Distinctive microstructural regions were identified by composition and porosity: (1) a Zr-rich region with an average composition of 28.4 wt% Zr and a local porosity fraction of 6.88%, and (2) a U-rich region with an average composition of 97.0 wt% U and a local porosity fraction of 14.11%; subdivided into U-rich—high porosity (16.68%) and U-rich—low porosity (8.04%) regions. The detailed 3-D compositional and porosity regions can improve nuclear fuel performance codes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

FFT-based model for irradiated aggregate microstructures in concrete

The concrete biological shield of light water reactors is exposed to neutron and gamma irradiation throughout its lifetime, which results in the long-term degradation of the concrete’s mechanical properties. Under neutron irradiation, the concrete’s aggregates are subjected to radiation-induced volumetric expansion (RIVE), which strongly depends on the mineral content of the aggregate and exhibits the largest expansion in silicate-bearing minerals. In this work, the authors used the fast Fourier transform-based code Microstructure-Oriented Scientific Analysis of Irradiated Concrete (MOSAIC) in 2D to model the expansion of five different aggregates provided by the Japan Concrete Aging Management Program (JCAMP). Comparable rock specimens were irradiated at the JEEP-II test reactor. The model uses realistic aggregate microstructure reconstruction based on high-resolution characterization images. The model accounts for anisotropic RIVE, thermal expansion, and the associated initiation and propagation of damage. The RIVE models are calibrated based on expansion data in the literature. The authors assume that damage occurs exclusively at interfaces between the particles that compose an aggregate and that these interfaces also exhibit swelling. Using a micromechanical model, the evolution of Young’s modulus with RIVE is calculated for each aggregate and compared with Russian irradiation data. The modeled linear expansion agrees well with the experimentally measured expansion. Furthermore, the model also predicts that anisotropic RIVE and thermal expansion result in an earlier onset of damage with neutron fluence than in the isotropic case.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructure development in a cold worked SRF Nb sheet undergoing 700°C-900°C/3h heat treatments.

Bulk Nb for TESLA shaped SRF cavities is a mature technology, with high gradient (>35 MV/m) and high Q cavities (>1010, ~2K) routinely fabricated. Significant advances are in order to push Q?s to 1011 (~2K), and involve modifications to the sub-surface Nb layers by impurity doping (N, O). In order to achieve the lowest surface resistance any trapped flux needs to be expelled for cavities to reach high Q?s. There is clear evidence that cavities fabricated from polycrystalline sheets meeting current specifications require higher temperatures beyond 800oC leads to better flux expulsion, and hence improves Q. Recently, cavities fabricated with a non-traditional Nb sheet with initial cold work due to cold rolling expelled flux better after 800°C/3h heat treatment than cavities fabricated using fine-grain polycrystalline Nb sheets. Here, we analyze the microstructure development in Nb from the vendor supplied cold work non-annealed sheet that was fabricated into an SRF cavity as a function of heat treatment building upon the methodology development to analyze microstructure being developed by the FSU-MSU-UT-Austin- JLAB collaboration. The results indicate correlation between full recrystallization and better flux expulsion.

Balachandran, S.↗
DOE OSTI2013

Hybrid models for the simulation of microstructural evolution influenced by coupled, multiple physical processes

Most materials microstructural evolution processes progress with multiple processes occurring simultaneously. In this work, we have concentrated on the processes that are active in nuclear materials, in particular, nuclear fuels. These processes are coarsening, nucleation, differential diffusion, phase transformation, radiation-induced defect formation and swelling, often with temperature gradients present. All these couple and contribute to evolution that is unique to nuclear fuels and materials. Hybrid model that combines elements from the Potts Monte Carlo, phase-field models and others have been developed to address these multiple physical processes. These models are described and applied to several processes in this report. An important feature of the models developed are that they are coded as applications within SPPARKS, a Sandiadeveloped framework for simulation at the mesoscale of microstructural evolution processes by kinetic Monte Carlo methods. This makes these codes readily accessible and adaptable for future applications.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Observation of 690 MV m -1 Electron Accelerating Gradient with a Laser-Driven Dielectric Microstructure

Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. In this work, experimental results are presented of relativistic electron acceleration with 690±100 MVm -1 gradient. This is a record-high accelerating gradient for a dielectric microstructure accelerator, nearly doubling the previous record gradient. To reach higher acceleration gradients the present experiment employs 90 fs duration laser pulses.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Enhancing Electrophoretic Display Lifetime: Thiol-Polybutadiene Evaporation Barrier Property Response to Network Microstructure

An evaporation barrier is required to enhance the lifetime of electrophoretic deposition (EPD) displays. As EPD functions on the basis of reversible deposition and resuspension of colloids suspended in a solvent, evaporation of the solvent ultimately leads to device failure. Incorporation of a thiol-polybutadiene elastomer into EPD displays enabled display lifetime surpassing six months in counting and catalyzed rigid display transition into a flexible package. Final flexible display transition to mass production compels an electronic-ink approach to encapsulate display suspension within an elastomer shell. Final thiol-polybutadiene photosensitive resin network microstructure was idealized to be dense, homogeneous, and expose an elastic response to deformation. Research at hand details an approach to understanding microstructural change within display elastomers. Polybutadiene-based resin properties are modified via polymer chain structure, with and without added aromatic urethane methacrylate difunctionality, and in measuring network response to variation in thiol and initiator concentration. Dynamic mechanical analysis results signify that cross-linked segments within a difunctionalized polybutadiene network were on average eight times more elastically active than that of linked segments within a non-functionalized polybutadiene network. Difunctionalized polybutadiene samples also showed a 2.5 times greater maximum elastic modulus than non-functionalized samples. Hybrid polymer composed of both polybutadiene chains encompassed TE-2000 stiffness and B-1000 elasticity for use in encapsulating display suspension. Later experiments measured kinetic and rheological response due to alteration in dithiol cross-linker chain length via real time Fourier transform infrared spectroscopy and real-time dynamic rheology. Distinct differences were discovered between dithiol resin systems, as maximum thiol conversion achieved in short and long chain length dithiols was 86% and 11%, respectively. Oscillatory real-time rheological experiments confirmed a more uniform network to better dissipate applied shear in short chain length dithiol systems, as long chain length dithiols relayed a steep internal stress build-up due to less cross-links and chain entanglements. Thorough understanding of network formation aids the production of a stronger and impermeable elastomeric barrier for preservation of EPD displays.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Initial Assessment of X-Ray Computer Tomography image analysis for material defect microstructure

The original development work leading to this report was focused on the non destructive three-dimensional (3-D) characterization of nuclear graphite as a means to better understand the nature of the inherent pore structure. The pore structure of graphite and its evolution under various environmental factors such as irradiation, mechanical stress, and oxidation plays an important role in their observed properties and characteristics. If we are to transition from an empirical understanding of graphite behavior to a truly predictive mechanistic understanding the pore structure must be well characterized and understood. As the pore structure within nuclear graphite is highly interconnected and truly 3-D in nature, 3-D characterization techniques are critical. While 3-D characterization has been an excellent tool for graphite pore characterization, it is applicable to a broad number of materials systems over many length scales. Given the wide range of applications and the highly quantitative nature of the tool, it is quite surprising to discover how few materials researchers understand and how valuable of a tool 3-D image processing and analysis can be. Ultimately, this report is intended to encourage broader use of 3 D image processing and analysis in materials science and engineering applications, more specifically nuclear-related materials applications, by providing interested readers with enough familiarity to explore its vast potential in identifying microstructure changes. To encourage this broader use, the report is divided into two main sections. Section 2 provides an overview of some of the key principals and concepts needed to extract a wide variety of quantitative metrics from a 3-D representation of a material microstructure. The discussion includes a brief overview of segmentation methods, connective components, morphological operations, distance transforms, and skeletonization. Section 3 focuses on the application of concepts from Section 2 to relevant materials at Idaho National Laboratory. In this section, image analysis examples featuring nuclear graphite will be discussed in detail. Additionally, example analyses from Transient Reactor Test Facility low-enriched uranium conversion, Advanced Gas Reactor like compacts, and tristructural isotopic particles are shown to give a broader perspective of the applicability to relevant materials of interest.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Prediction of Thermal Transport Properties of Materials with Microstructural Complexity

This project aims at overcoming the major obstacle standing in the way of progress in dynamic multiscale simulation, which is the lack of a concurrent atomistic-continuum method that allows phonons, heat and defects to pass through the atomistic-continuum interface. The research has led to the development of a concurrent atomistic-continuum (CAC) methodology for multiscale simulations of materials microstructural, mechanical and thermal transport behavior. Its efficacy has been tested and demonstrated through simulations of dislocation dynamics and phonon transport coupled with microstructural evolution in a variety of materials and through providing visual evidences of the nature of phonon transport, such as showing the propagation of heat pulses in single and polycrystalline solids is partially ballistic and partially diffusive. In addition to providing understanding on phonon scattering with phase interface and with grain boundaries, the research has contributed a multiscale simulation tool for understanding of the behavior of complex materials and has demonstrated the capability of the tool in simulating the dynamic, in situ experimental studies of nonequilibrium transient transport processes in material samples that are at length scales typically inaccessible by atomistically resolved methods.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure-sensitive Crystal Viscoplasticity for Ni-base Superalloys Targeting Long-term Creep-Fatigue Interaction Modeling

This report introduces a new temperature-dependent, microstructure-sensitive crystal viscoplasticity model for single-crystal Ni-base superalloys. The model predicts the material response of the single-crystal components in the hot gas path sections of industrial gas turbines. The influence of changes in the microstructure that occur with aging in service, critical to predicting long-term creep-fatigue interactions, is embedded into the model through the γ' precipitate morphology evolution. The model is calibrated to predict the experimental response of CMSX-8, a lower cost variant of the second generation single-crystal superalloy CMSX-4. In addition, the experimentally-measured creep-fatigue and thermomechanical fatigue behavior of CMSX-8 is reported.

03 NATURAL GAS↗
DOE OSTI2018

Controlling microstructure in deposits fabricated using powder blown direct energy deposition technique

The overall goal of this collaboration is to develop technologies to control grain morphology and microstructures of Inconel 718 components additively manufactured through the Direct Energy Deposition (DED) process (Identical to the LENS (laser engineered net shaping) processes) and to achieve equiaxed or near equiaxed grain structures. The phase1 technical collaboration was used to fabricate Inconel 718 builds with different process parameters, pre heat and scan strategies. The results were then rationalized using computational heat transfer and solidification models. Microstructural characterization showed that the aspect ratio of the grains can be reduced to less than 1.5, and that control of the grain sizes to within 50-100 μm could be potentially obtained by using an external source to preheat the substrate to 400 ̊C. Heat transfer models coupled with solidification models were used to rationalize the results which show that preheating lowered the temperature gradient thereby resulting in moving towards the equiaxed region of the columnar to equiaxed transition (CET) curve. The results demonstrate that higher preheat temperatures could be potentially used to obtain a truly equiaxed structure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Laser Intensity Profile Effects on the Solidification Microstructure of Ti-6Al-4V and Ti-5553

Traditional machining of Ti-6Al-4V and Ti-5Al-5Mo-5V-3Cr (Ti-5553) is challenging due to high chemical reactivity, adiabatic shear band formation, and material cost. Titanium is attractive because of its high tensile strength, low density, corrosion resistance, and ability to withstand extreme temperatures. Selective Laser Melting (SLM) is capable of manufacturing geometrically complicated parts at a lower expense. Exceptional tolerances can be obtained with properly tuned processing parameters. Alterations on scan parameters permit microstructure and melt pool control. Single track laser melting experiments were performed on Ti-6Al-4V and Ti- 5553 using elliptical intensity profiles. Results show that maintaining constant energy density but increasing power results in a melt pool failing to penetrate the substrate for Ti-5553. Increasing laser energy density increases melt pool width and can increase powder bed denudation. Comparing Ti64 and Ti-5553 microstructures contributes to a better understanding of rapid solidification in titanium.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanical properties and microstructure characterization of unirradiated Eurofer-97 steel variants for the EUROfusion project

To understand the microstructure and mechanical property degradation of various Eurofer-97 steel variants being neutron irradiated at HFIR up to 2.5 and 20 dpa for the EUROfusion programme, it is necessary to develop a general understanding of these steels in non-irradiated form. In this context, room temperature mechanical property evaluation tests and multi-length scale microstructure characterization of the different Eurofer-97 steel variants: H, I, J, K, L, M, N, O, P and reference E series steels, was performed at ORNL. Mechanical tests consisted of Vickers hardness indentation measurements, uniaxial tensile tests and fracture toughness tests.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗