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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Three phase crystallography and solute distribution analysis during residual austenite decomposition in tempered nanocrystalline bainitic steels

Interphase carbide precipitation due to austenite decomposition was investigated by high resolution transmission electron microscopy and atom probe tomography in tempered nanostructured bainitic steels. Results showed that cementite (θ) forms by a paraequilibrium transformation mechanism at the bainitic ferrite–austenite interface with a simultaneous three phase crystallographic orientation relationship. - Highlights: • Interphase carbide precipitation due to austenite decomposition • Tempered nanostructured bainitic steels • High resolution transmission electron microscopy and atom probe tomography • Paraequilibrium θ with three phase crystallographic orientation relationship.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Strain partition and rupture analysis of notched tensile multilayered steel specimens

Highlights: • In situ SEM tensile experiments were performed to investigate the fracture processes. • In situ synchrotron x-ray diffraction were carried out to study the microscopic deformation in MLS steel. • The changing trends of the strain in the austenite layer and martensitic layer have been revealed. - Abstract: Multilayered steel composites consisting of alternating martensitic and austenite layers were successfully fabricated with a combination of high strength and ductility. In situ SEM tensile experiments were performed to investigate the fracture processes. Results indicated that the martensitic layer distributed between two ductile austenite layers has better deformation ability, and the dimple fracture mode dominated the fracture of the whole specimen. In situ synchrotron microbeam X-ray diffraction experiments were carried out to study the microscopic deformation in austenitic layer and martensitic layer ahead of notch root under incremental tensile loading. Results indicated that for austenite layer, the maximum strain is located in the middle of the layer at the lower applied load. When at the higher applied load, larger strain is concentrated on the notch root. For martensitic layer, uniform strain is distributed at the region at the lower applied load, with increasing the applied load, small strain appears in the middle of martensitic layer. However, the variation in the strain in the martensitic layer is relatively smaller, which is actually affected by both the notch and the ferrite content in the martensitic layer. The changing trends of the strain in the austenite layer and martensitic layer can still show the better combination of brittle martensitic phase and ductile austenite phase.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Medium range order and structural relaxation in As–Se network glasses through FSDP analysis

Synchrotron X-ray diffraction and neutron scattering studies are performed on As–Se glasses in two states: as-prepared (rejuvenated) and aged for ~27 years. The first sharp diffraction peak (FSDP) obtained from the structure factor data as a function of composition and temperature indicates that the cooperative processes that are responsible for structural relaxation do not affect FSDP. The results are correlated with the composition dependence of the complex heat capacity of the glasses and concentration of different structural fragments in the glass network. The comparison of structural information shows that density fluctuations, which were thought previously to have a significant contribution to FSDP, have much smaller effect than the cation–cation correlations, presence of ordered structural fragments or cage molecules.

glass transitions↗
DOE OSTI2018

Automated Algorithms for Band Gap Analysis from Optical Absorption Spectra

As high-throughput combinatorial experimental methods become more common, the technical challenge is shifting from producing materials to dealing with increasingly large datasets. One of the most important metrics to determine suitability of semiconductor materials for various applications is the band gap. This paper discusses automated algorithms for determining band gaps from optical absorption spectra. The algorithms are applied to a database of 34,313 optical absorption spectra, and selected results are compared to published theoretical and experimental band gap data from 16 materials sets. The best algorithm determines the band gaps with an accuracy of 0.37 eV for direct- and 0.93 eV for indirect band gaps for >20,000 spectra.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Exploring the Impact of Nuclear Data Uncertainties in Ultra-high Resolution Gamma Spectroscopy for Isotopic Analysis Using Approximate Bayesian Computation

High purity germanium (HPGe) currently provides the highest readily available resolution gamma detection for a broad range of radiation measurements, but microcalorimetry is a developing option that has considerably higher resolution even than HPGe. Superior microcalorimetry resolution offers the potential to better distinguish closely spaced X-rays and gamma-rays, a common challenge for the low energy spectral region near 100 keV from special nuclear materials, and the higher signal-to-background ratio also confers an advantage in detection limit. As microcalorimetry continues to develop, it is timely to assess the impact of uncertainties in detector and item response functions and in basic nuclear data, such as branching ratios and half-lives, used to interpret spectra in terms of the contributory radioactive isotopes. We illustrate that a new inference option known as approximate Bayesian computation (ABC) is effective and convenient both for isotopic inference and for uncertainty quantification for microcalorimetry. The ABC approach opens a pathway to new and more powerful implementations for practical applications than currently available.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Texture analysis of AGR program matrix materials

We report the fuel form for high-temperature gas-cooled reactors consists of tristructural isotropic (TRISO) particles embedded in a matrix of graphite flake and carbonized resin. The process of overcoating particles prior to compacting yields a circumferential orientation of the graphite flake surrounding the TRISO particles, which is modified to varied extents when overcoated particles are pressed into the final fuel form. As graphite is highly anisotropic, the texture may impact the properties and performance of the fuel. Ellipsometry was used to measure the texture of the matrix for fueled compacts and unfueled “matrix-only” samples. Results indicated local texture related to the spherical particles in compacts associated with overcoating versus a more linear layered structure in “matrix-only” samples.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗