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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Microchemical analysis of the SCS-6 silicon carbide fiber

A detailed quantitative study of the microstructural variation of chemical composition of chemically vapor-deposited commercial SiC SCS-6 fiber is presented. Chemical etching and various electron-optical techniques including SEM, TEM, scanning Auger microscopy, AES, and parallel electron energy loss spectroscopy are used to analyze the chemical composition of the as-received fiber. In addition, some results on stereology of the high-temperature annealed fiber are presented. The results show that the carbon-to-silicon atom ratio in the SiC layers decreases in a stepwise fashion from about 3:2 to about 1:1 in going from the innermost layer to the outermost layer.

Ning, Xian-Jie↗
NASA NTRS2014

Multi-Scale Computational Modeling of Two-Phased Metal Using GMC Method

A multi-scale computational model for determining plastic behavior in two-phased CMSX-4 Ni-based superalloys is developed on a finite element analysis (FEA) framework employing crystal plasticity constitutive model that can capture the microstructural scale stress field. The generalized method of cells (GMC) micromechanics model is used for homogenizing the local field quantities. At first, GMC as stand-alone is validated by analyzing a repeating unit cell (RUC) as a two-phased sample with 72.9% volume fraction of gamma'-precipitate in the gamma-matrix phase and comparing the results with those predicted by finite element analysis (FEA) models incorporating the same crystal plasticity constitutive model. The global stress-strain behavior and the local field quantity distributions predicted by GMC demonstrated good agreement with FEA. High computational saving, at the expense of some accuracy in the components of local tensor field quantities, was obtained with GMC. Finally, the capability of the developed multi-scale model linking FEA and GMC to solve real life sized structures is demonstrated by analyzing an engine disc component and determining the microstructural scale details of the field quantities.

nickel alloys↗
DOE OSTI2018

Automated defect analysis in electron microscopic images

Electron microscopy and defect analysis are a cornerstone of materials science, as they offer detailed insights on the microstructure and performance of a wide range of materials and material systems. Building a robust and flexible platform for automated defect recognition and classification in electron microscopy will result in the completion of analysis orders of magnitude faster after images are recorded, or even online during image acquisition. Automated analysis has the potential to be significantly more efficient, accurate, and repeatable than human analysis, and it can scale with the increasingly important methods of automated data generation. Herein, an automated recognition tool is developed based on a computer vison–based approach; it sequentially applies a cascade object detector, convolutional neural network, and local image analysis methods. We demonstrate that the automated tool performs as well as or better than manual human detection in terms of recall and precision and achieves quantitative image/defect analysis metrics close to the human average. The proposed approach works for images of varying contrast, brightness, and magnification. Furthermore, these promising results suggest that this and similar approaches are worth exploring for detecting multiple defect types and have the potential to locate, classify, and measure quantitative features for a range of defect types, materials, and electron microscopic techniques.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Nonlinear size dependent analysis and effectiveness of nanocrystalline micro/nanogyroscopes

Vibratory micro/nanogyroscopes made of nanocrystalline silicon have a complex microstructure consisting of grains, voids, and interface material phases. Given that the length scale of such inertial sensors is close to the size of the grains themselves, classical continuum mechanics theories are no longer adequate to accurately model the dynamic behaviors of these sensors. In this work, the couple stress and surface elasticity are incorporated to the governing equations of an electrically-actuated, amplitude-based, capacitive sensing cantilever gyroscope to obtain a comprehensive model of the nano-system. Then, the impact of the size dependent effects on the nonlinear dynamic behavior of the gyroscope is investigated by studying its performance for gyroscopes ranging in size from the micro-to the nano-scale. The present numerical study shows that the additional stiffness contributions from the couple stress and surface elasticity and changes in scale cause significant changes in the frequency response, nonlinear behaviors, and sensitivity of the gyroscope to the rotation rates. Furthermore, this numerical analysis demonstrates the importance of accounting for size dependent effects for micro/nanogyroscopes in order to avoid any deterioration of the effectiveness of the gyroscope operability.

42 ENGINEERING↗
DOE OSTI2020

Quantification of silicon carbide grain structure in TRISO fuel by BSE image analysis

The grain structure of the silicon carbide (SiC) layer in tristructural-isotropic (TRISO) fuels has commonly been qualified in fuel specifications based on a qualitative comparison to visual standards to ensure undesirable microstructure are not produced. This approach is inherently dependent on subjective judgement and provides limited data for analysis or comparison. An alternative method to rapidly quantify (i.e., provide a numeric measure of) the grain structure of the SiC layer in TRISO fuels has been developed. This method relies on the identification of silicon carbide grain boundaries based on brightness variation in backscattered electron (BSE) images through the application of automated image processing algorithms. The speed with which the requisite BSE imaging and analysis may be completed enables the practical use of this method on an industrial scale as a part of qualifying TRISO fuel to meet a given specification on silicon carbide grain structure, which is an important parameter for TRISO fuel performance. The method is benchmarked by comparison to prior Electron-Backscattered Diffraction (EBSD) results for TRISO particles from the Advanced Gas Reactor (AGR) program.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Effect of microstructure on fatigue crack propagation in additive manufactured nickel-based superalloy Haynes 282: an experiment and crystal plasticity study

Haynes 282 is a γ' precipitation-strengthened nickel-based superalloy known for its exceptional high-temperature creep resistance and excellent fabricability. Recent advancements in powder-bed fusion-based additive manufacturing (PBF-AM) have enabled the fabrication of Haynes 282 with accurate, site-specific control of the grain orientation and morphology at the microscale. This ability opens up new avenues for microstructure design, to improve the material’s fatigue crack resistance and service life. This paper investigates the fatigue crack growth behavior of hybrid microstructure Haynes 282 fabricated via PBF-AM. Previous experiments revealed a higher crack propagation rate in the coarse columnar-grained microstructural regions when compared against fine-grained areas. Here, a strain gradient crystal plasticity model was adapted to study the fracture-related mechanical fields at the crack tip in the two microstructures. The simulation results showed a consistent influence of grain structure and texture on crack propagation, as was seen in the experiment. The model analysis revealed higher crack propagation driving force along crack direction in the coarse-grained sharply textured microstructure and higher driving force for crack kinking in fine-grained more diffusely textured microstructure, which is ascribed to the combined effect of yield stress, hardening rate, texture and grain morphology. The presented modeling approach will facilitate the development of the AM-based accurate microstructure design by deepening the fundamental study in AM-specific microstructure-properties relations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

The Impact of Furnace-Testing on the Microstructure of an Irradiated U-Mo Fuel Plate

The Material Management and Minimization Program (formerly known as the Reduced Enrichment for Research and Test Reactor Program) is responsible for converting research reactors that use highly enriched uranium (HEU) fuels to ones that use low-enriched uranium (LEU) fuels. As part of the development of LEU fuels, a variety of irradiation experiments are being conducted using the Advanced Test Reactor. In addition to the reactor tests, there is interest in generating information about the transient behavior of irradiated fuel plates. For example, it is of interest to determine the temperature at which a blister will form on the surface of a fuel plate, due to fission gas release from the fuel meat, for a particular fuel plate design. Since in-pile testing to determine the 'blister threshold' (the temperature where a blister forms on the surface of a fuel plate) in plate-type fuel is very difficult and expensive and has historically been deemed impractical for fuel qualification testing, an out-of-pile 'blister test' has been developed and employed. This post-irradiation blister anneal test was developed as a conservative simulation of in-pile behavior and has been routinely used for many research reactor fuel designs currently in use. In this test, the irradiated fuel plate is inserted into a furnace at a given temperature, soaked for a period of time, and removed for inspection. If no visible blisters appear, the furnace temperature is increased, and the plate is soaked and inspected again. This process continues until blisters are observed. Recently, a section from an irradiated U-7Mo dispersion fuel plate with Al-4043 matrix, which has a nominal composition of 4.81Si-0.20Fe-0.14Ti-0.16Cu-0.01Cr 0.01Mn-bal Al, was tested in a furnace located in the Hot Fuel Examination Facility, located at the Idaho National Laboratory, up to 500 deg. C, at which point blisters were observed on the surface of the fuel plate section. A sample near the blistered region of the fuel plate section was then characterized using scanning electron (SEM) and transmission electron microscopy (TEM). This paper discusses the results of this characterization and how they compare to those generated for a similar sample characterized after fabrication but before irradiation and for a sample characterized after irradiation but before furnace testing. One goal of this work is to identify the changes in the microstructure during blister testing that contribute to the eventual release of fission gas that results in the development of blisters. SEM analysis of the furnace-tested sample showed that in some locations of the U-7Mo particles, Al-4043 matrix constituents (primarily Si) had penetrated the microstructure along grain boundaries. This provided potential pathways for increased fission gas migration in the fuel meat microstructure during the furnace heating process. Some attack of these boundaries was also observed in the as-fabricated U-7Mo/Al-4043 sample, but there appeared to be additional attack during the furnace annealing. Besides the changes observed in grain boundary features, the TEM analysis showed that the fission gas bubbles that are typically present in the intra-granular regions of the as-irradiated U-7Mo microstructure as a fission gas bubble superlattice had changed in size, morphology, and distribution. The result of this may be an increase in the mobility of the fission gas in intra-granular regions of the fuel. The complete implications of the changes in fission gas morphology and distribution in the fuel meat microstructure and their impact on blistering continues to be investigated. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Crystallographic and Compositional Analysis of impurity phase: U2MoSi2C in UMo Alloys

Minor impurity elements in metallic nuclear materials can critically influence the microstructural evolution and mechanical properties, making it crucial to understand the structure, composition and distribution of the impurity phases. Using Transmission Electron Microscopy, Atom Probe Tomography and ab-initio calculations we provide the atomic scale crystallographic structural and compositional analysis of a new impurity phase: U2MoSi2C in an important nuclear fuel U-10Mo alloy. We identify the new phase to have tetragonal symmetry with lattice parameters of a=6.67Å, c=4.33Å, and space group P4/mbm (No.127). Ab-initio calculations were performed to verify structural stability and to perform atom positions refinement.

Kovarik, Libor↗
DOE OSTI2019

A Multi-Layer Composite Based on the 3Ni–Al System Produced by a Combined Deformation Treatment

Using combined deformation processing, including preliminary mechanical activation followed by consolidation via high-pressure torsion, a multi-layer nanocomposite based on nickel and aluminum is manufactured. The influence of the duration of mechanical activation on its microstructure parameters is investigated by the X-ray diffraction analysis and scanning and transmission electron microscopy. It is found out that nanostructuring of the multi-layer nanocomposite during its manufacture ensures the formation of a high density of phase and grain boundaries. It is shown that this structural transformation is accompanied by an intense strengthening effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Effect of Grain Refining on Properties of a Cast Superaustenitic Stainless Steel

The goal of this study was to evaluate the industrial performance of cast high-alloy superaustenitic 19Cr-17Ni-6Mo stainless steel by refining the as-cast structure. A grain-refined, as-cast structure was achieved by the in situ inoculation with titanium nitrides (TiN) co-precipitated on previously formed spinel (MgAl{sub 2}O{sub 4}) inclusions, thus promoting heterogeneous nucleation of austenite during solidification. A homogenization heat treatment of the casting did not provide significant changes of the as-cast grain macrostructure in either the base or grain-refined steels. However, it was found that a combination of inoculation with heat treatment is an effective way of reducing interdendritic segregation. The industrial performance which includes the mechanical properties, corrosion resistance, and machinability was evaluated in the heat-treated condition for both base and inoculated steels. Tensile testing revealed improvements in ultimate tensile strength, ductility, and yield strength of the inoculated steel. The room-temperature impact properties exhibited a slight decrease in average impact energy but showed reduced variability in the inoculated steel compared to the base steel. The machining results showed that the inoculated steel had a slight improvement in machinability. The inoculated steel exhibited a lower corrosion rate but showed an increase in mass loss due to pitting. The changes in steel performance were linked to microstructure and nonmetallic inclusion families obtained by automated ASPEX SEM/EDX analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Creep Behavior and Phase Equilibria in Model Precipitate Strengthened Alumina-Forming Austenitic Alloys

Abstract Creep-rupture behavior and microstructural response in alumina-forming austenitic (AFA) alloys with two different precipitation strengthening mechanisms, “Laves-phase + M 23 C 6 carbide” and “coherent L1 2 γ′-Ni 3 (Al,Ti),” were explored as “model” cases of multi-phase, multi-scale heat-resistant AFA alloys for 650–750°C use. These alloys will be used to guide and verify computational alloy design and life-prediction modeling under an on-going eXtremeMAT project through the Office of Fossil Energy and Carbon Management, US Department of Energy. Computational thermodynamics were used to design and predict the amounts of strengthening and deteriorating secondary phases at 750°C. Creep-rupture lives of the alloys tested at 750°C and 100 MPa were in a range of 4000–9000 h, and the microstructure at the gage/grip after creep-rupture testing was compared with isothermally aged alloys for 1500 h, as well as the calculated phases. Detailed microstructure characterization includes phase identification, volume fraction measurement, and compositional analysis, which were correlated with the creep-rupture properties. High-temperature oxidation resistance was also screened and compared with commercial, chromia-forming heat-resistant steels. These model alloys also provide the basis for further design and optimization of next generation AFA alloys with improved creep resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Myna: Connecting powder bed fusion build data to simulation tools for digital twin applications

Additive manufacturing (AM), as a digital process, can generate a detailed digital thread linking a part’s design and manufacturing to its operational performance. As AM systems advance, an increasing amount of process data is stored in manufacturing databases. In principle, this data can be utilized by simulation-based digital twin approaches, such as real-time process control and asynchronous post-processing guidance. However, few tools currently exist for systematically integrating digital thread data with computational tools. Here, in this study, we propose a software package, called Myna, for connecting data from powder bed fusion processes to simulation tools. The utility of such a platform is demonstrated using build data from the Oak Ridge National Laboratory Manufacturing Demonstration Facility “Peregrine v2023-10” public dataset to automatically configure and run 54 semi-analytical 3DThesis melt pool simulations, 78 numerical Additive FOAM melt pool simulations, and 3 ExaCA microstructure simulations. The simulated, spatially registered microstructures are then compared directly with electron backscatter diffraction characterization of the corresponding as-built part locations. The resulting simulated microstructure showed variation as a function of process parameters, particularly stripe width; however, the experimental data had little variation between the microstructure texture and grain size resulting from different processing conditions. Analysis of the discrepancies suggest that it is possible a two-phase ferritic-austenitic solidification model is needed to accurately predict grain size and texture for certain stainless steel 316L feedstock compositions under powder bed fusion conditions, providing direction for future research. As illustrated here, due to the number and complexity of the simulations involved in AM process-structure–property predictions, automated methods to connect process data and simulations will remain necessary tools for testing hypotheses and implementing digital twin applications.

Knapp, Gerald L. [Oak Ridge National Laboratory (O↗
DOE OSTI2015

Parametric models for samples of random functions

A new class of parametric models, referred to as sample parametric models, is developed for random elements that match sample rather than the first two moments and/or other global properties of these elements. The models can be used to characterize, e.g., material properties at small scale in which case their samples represent microstructures of material specimens selected at random from a population. The samples of the proposed models are elements of finite-dimensional vector spaces spanned by samples, eigenfunctions of Karhunen–Loève (KL) representations, or modes of singular value decompositions (SVDs). The implementation of sample parametric models requires knowledge of the probability laws of target random elements. Numerical examples including stochastic processes and random fields are used to demonstrate the construction of sample parametric models, assess their accuracy, and illustrate how these models can be used to solve efficiently stochastic equations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Fabrication and microstructures of functional gradient SiBCN–Nb composite by hot pressing

A functional gradient material with five layers composed of SiBCN ceramic and niobium (Nb) was prepared successfully by hot pressing. The phase composition, morphology features and microstructures were investigated in each layer of the gradient material. The Nb-containing compounds involving NbC, Nb{sub 6}C{sub 5}, Nb{sub 4}C{sub 3}, Nb{sub 5}Si{sub 3} and NbN increase with the volume fraction of Nb increasing in the sub-layer. They are randomly scattered (≤ 25 vol.% Nb), then strip-like, and finally distribute continuously (≥ 75 vol.% Nb). The size of BN(C) and SiC grains in Nb-containing layers is larger than in 100% SiBCN layer due to the loss of the capsule-like structures. No distinct interfaces form in the transition regions indicating the gradual changes in phase composition and microstructures. - Highlights: • A functional gradient SiBCN–Nb material was prepared successfully by hot pressing. • Phase composition, morphology features and microstructures were investigated. • Thermodynamic calculation was used to aid in the phase analysis. • No distinct interfaces form typical of the functional gradient material.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effect of Zn doping on structural, magnetic and dielectric properties of LaFeO{sub 3} synthesized through sol–gel auto-combustion process

Graphical abstract: - Highlights: • We have synthesized the samples of LaFe{sub 1−x}Zn{sub x}O{sub 3} (0 ≤ x ≤ 0.3) using sol–gel auto-combustion process. • The doping of Zn{sup 2+} hugely enhances the dielectric constant (ε′) and it shows a colossal value. • The parent compound LaFeO{sub 3} does not show any relaxation peak, but the substitution of Zn at Fe{sup 3+} site brings the relaxation in the system. • The system shows a peak behavior thereby giving the Debye like dipolar relaxation response. - Abstract: We have studied the structural and dielectric properties of nano-crystalline LaFe{sub 1−x}Zn{sub x}O{sub 3} (0 ≤ x ≤ 0.3) pervoskite samples synthesized through sol–gel auto-combustion technique. X-ray diffraction and FTIR spectroscopy are used to confirm the single phase characteristics. Microstructural features are investigated using scanning electron microscope and compositional analysis is performed through energy dispersive spectroscopy. The average grain sizes, calculated from the Scherrer formula, lie in the range below 30 nm. The hysteresis (M-H) curves display a weak magnetic order and a shift in the hysteresis loops. Dielectric response has been discussed, in the framework of “universal dielectric response” model. The value of dielectric constant (ε′) increases drastically on Zn doping. The dielectric loss factor (ε″) shows Debye like dipolar relaxation behavior. The observed peaks in loss factor (ε″) are attributed to the fact that a strong correlation between the conduction mechanism and the dielectric behavior exists in ferrites.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Optical and Structural Properties of High-Efficiency Epitaxial Cu(In,Ga)Se 2 Grown on GaAs

Photovoltaic devices based on Cu(In,Ga)Se 2 (CIGS) usually employ polycrystalline thin films as the absorber layer. This is because, to date, the highest conversion efficiencies have been attained with polycrystalline CIGS films. Recently, Nishinaga et al. presented an epitaxial CIGS thin-film solar cell grown on a GaAs (100) substrate with a conversion efficiency of 20.0%. In this contribution, we study the optical and structural properties of this high-efficiency epitaxial film, along with others with different compositions using cathodoluminescence spectrum imaging and transmission electron microscopy. A comparison of the high-efficiency epitaxial film and a traditional polycrystalline film with a similar global composition reveals significant differences in microstructure and uniformity of emission properties despite similar performance. The analysis of epitaxial films with a higher gallium concentration indicates that the emission characteristics and nature of extended defects in epitaxial CIGS films are strongly dependent on the gallium content. The results presented here provide evidence that, with further optimization, photovoltaic conversion efficiencies of epitaxial CIGS films could exceed those of polycrystalline CIGS.

14 SOLAR ENERGY↗
DOE OSTI2019

Sol–gel based synthesis and enhanced processability of MAX phase Cr 2 GaC

MAX phases are typically prepared by high-temperature (oftentimes high-pressure) solid-state methods. In this paper, we report a new wet chemistry based synthesis technique starting from an aqueous solution of metal nitrates and citric acid to prepare MAX phase Cr 2 GaC. This solution-processable precursor mixture has the potential to be easily scaled, painted, printed or fabricated onto supports – an advantage that is demonstrated by the formation of hollow carbon microspheres which are decorated with Cr 2 GaC particles. A small amount of chromium carbide and oxide remains in the product, however, the amount of the latter can be reduced by a larger excess in citric acid in the precursor gel. The transformation mechanism of the initial amorphous gel into highly crystalline and anisotropic MAX phase particles is investigated by detailed thermal analysis. Transmission electron microscopy studies are conducted to elucidate the microstructure of the sol–gel-prepared particles as well as the decorated hollow microspheres. From magnetic susceptibility measurements, the density of states at the Fermi level is deduced reflecting the quality of the Pauli paramagnet Cr 2 GaC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗