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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Fractographic analysis of gaseous hydrogen induced cracking in 18Ni maraging steel

Electron microscope fractographic analysis supplemented an extensive study of the kinetics of gaseous hydrogen assisted cracking in 18Ni maraging steel. Temperature determined the crack path morphology in each steel which, in turn, was directly related to the temperature dependence of the crack growth rate. Crack growth in the low temperature regime proceeded along prior austenite grain boundaries. Increasing the temperature above a critical value produced a continuously increasing proportion of transgranular quasi-cleavage associated with lath martensite boundaries. The amount of transgranular cracking was qualitatively correlated with the degree of temperature-induced deviation from Arrhenius behavior. Fractographic observations are interpreted in terms of hypothesized mechanisms for gaseous hydrogen embrittlement. It is concluded that hydrogen segregation to prior austenite and lath martensite boundaries must be considered as a significant factor in developing mechanisms for gaseous embrittlement of high strength steels.

Gangloff, R. P.↗
NASA NTRS1982

RF sputtered silicon and hafnium nitrides: Properties and adhesion to 440C stainless steel

Silicon nitride and hafnium nitride coatings were deposited by reactive RF sputtering on oxidized and unoxidized 440C stainless steel substrates. Sputtering was done in mixtures of argon and nitrogen gases from pressed powder silicon nitride and from hafnium metal targets. Depositions were at two background pressures, 8 and 20 mtorr, and at two different fractions (f) of nitrogen in argon, 0.25 and 0.60, for hafnium nitride and at f = 0.25 for silicon nitride. The coatings and the interface between the coating and substrates were investigated by X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray analysis and Auger electron spectroscopy. A Knoop microhardness of 1650 + or - 100 kg/sq mm was measured for hafnium nitride and 3900 + or - 500 kg/sq mm for silicon nitride. The friction coefficients between a 440C rider and the coatings were measured under lubricated conditions. Scratch test results demonstrate that the adhesion of hafnium nitride to both oxidized and unoxidized 440C is superior to that of silicon nitride. Oxidized 440C is found to have increased adhesion, to both nitrides, over that of unoxidized 440C.

Grill, A.↗
NASA NTRS1984

RF sputtered silicon and hafnium nitrides as applied to 440C steel

Silicon nitride and hafnium nitride coatings were deposited on oxidized and unoxidized 440C stainless steel substrates. Sputtering was done in mixtures of argon and nitrogen gases from pressed powder silicon nitride and from hafnium metal targets. The coatings and the interface between the coating and substrate were investigated by X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray analysis and Auger electron spectroscopy. Oxide was found at all interfaces with an interface width of at least 600 A for the oxidized substrates and at least 300 A for the unoxidized substrates. Scratch test results demonstrate that the adhesion of hafnium nitride to both oxidized and unoxidized 440C is superior to that of silicon nitride. Oxidized 440C is found to have increased adhesion, to both nitrides, over that of unoxidized 440C. Coatings of both nitrides deposited at 8 mtorr were found to have increased adhesion to both oxidized and unoxidized 440C over those deposited at 20 mtorr.

Grill, A.↗
NASA NTRS1983

RF-sputtered silicon and hafnium nitrides - Properties and adhesion to 440C stainless steel

Silicon nitride and hafnium nitride coatings were deposited by reactive RF sputtering on oxidized and unoxidized 440C stainless steel substrates. Sputtering was done in mixtures of argon and nitrogen gases from pressed powder silicon nitride and from hafnium metal targets. Depositions were at two background pressures, 8 and 20 mtorr, and at two different fractions (f) of nitrogen in argon, 0.25 and 0.60, for hafnium nitride and at f = 0.25 for silicon nitride. The coatings and the interface between the coating and substrates were investigated by X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray analysis and Auger electron spectroscopy. A Knoop microhardness of 1650 + or 100 kg/sq mm was measured for hafnium nitride and 3900 + or 500 kg/sq mm for silicon nitride. The friction coefficients between a 440C rider and the coatings were measured under lubricated conditions. Scratch test results demonstrate that the adhesion of hafnium nitride to both oxidized and unoxidized 440C is superior to that of silicon nitride. Oxidized 440C is found to have increased adhesion, to both nitrides, over that of unoxidized 440C.

Grill, A.↗
NASA NTRS1991

Parallel electric fields detected via conjugate electron echoes during the Echo 7 sounding rocket flight

Electron detectors on the Echo 7 active sounding rocket experiment measured 'conjugate echoes' resulting from artificial electron beam injections. Analysis of the drift motion of the electrons after a complete bounce leads to measurements of the magnetospheric convection electric field mapped to ionospheric altitudes. The magnetospheric field was highly variable, changing by tens of mV/m on time scales of as little as hundreds of millisec. While the smallest-scale magnetospheric field irregularities were mapped out by ionospheric conductivity, larger-scale features were enhanced by up to 50 mV/m in the ionosphere. The mismatch between magnetospheric and ionspheric convection fields indicates a violation of the equipotential field line condition. The parallel fields occurred in regions roughly 10 km across and probably supported a total potential drop of 10-100 V.

Nemzek, R. J.↗
NASA NTRS1982

Equipment Analysis

Magnavox Government & Electronics Company originally used the NASTRAN program in the design stage of heavy aluminum fixtures for vibration testing. Program also used to compare the resonant frequencies of the circuitry to predict whether failures may occur because of high vibration levels. The company engineers can then make design alterations to improve the equipment's vibration resistance. Method allows Magnavox to insure reliability and reduce any possibility of vibration-caused failure in critical defense products they manufacture. Magnavox uses another COSMIC software package called GENOPTICS in the development of a Digital Optical Recorder, and also in research and development of other optical systems. This enables use of an optically recorded disc to store and retrieve digital data. It is reported that this program provides accurate results and that its use saved six man-months of time that would have been needed to develop a comparable software package.

Source record↗
DOE OSTI2018

Liquid metal embrittlement in laser lap joining of TWIP and medium-manganese TRIP steel: The role of stress and grain boundaries

Highlights: • This work shows liquid metal embrittlement in externally loaded laser lap welding. • Results confirmed a direct relation between external load and LME susceptibility. • TWIP steel showed a higher LME susceptibility compared to medium-Mn TRIP steel. • Results indicated stress-assisted diffusion of Zn into austenite grain boundaries. • High angle grain and Σ3 twinning boundaries play major role in Zn penetration. - Abstract: High-Manganese austenite-containing steels with superior combination of strength and ductility have shown potential for enhancement of passenger safety and body-in-white (BIW) weight reduction. Even though Zn-coated austenitic steels have improved corrosion resistance, they are highly susceptible to liquid metal embrittlement (LME) during welding. The present work is aimed to address LME susceptibility during restrained laser lap joining of high-Mn twinning induced plasticity (TWIP) and medium-Mn transformation induced plasticity (MMn-TRIP) steels. Electron probe micro-analysis (EPMA) results showed that stress-assisted diffusion of Zn into the austenite grain boundaries and further liquid Zn formation by a peritectic reaction lead to grain boundary decohesion. Electron backscatter diffraction (EBSD) results demonstrated that high angle and special grain boundaries are prone to Zn-penetration within the heat-affected-zone (HAZ). Additionally, LME sensitivity was observed to be highly dependent on the magnitude of applied stress.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Comparative X-Ray Absorption Analysis of the Spectrum of Vacant Electronic States in Cobalt and Nickel Tetraphenylporphyrin Complexes

The energy distributions and the properties of the lower vacant electronic states in cobalt and nickel tetraphenylporphyrin complexes CoTPP and NiTPP are studied by X-ray absorption spectroscopy. Quasimolecular analysis of the experimental absorption spectra measured in the region of the 2p and 1s ionization thresholds of complexing metal atoms, as well as the 1s thresholds of ligand atoms (nitrogen and carbon), is based on the comparison of the corresponding spectra with each other and with the spectra of the simplest nickel porphyrin NiP. It has been established that, despite a general similarity of the spectra of nitrogen and carbon in CoTPP and NiTPP, the fine structure of the 2p and 1s absorption spectra of cobalt and nickel atoms are radically different. The observed differences in the spectra of cobalt and nickel are associated with the features of the energy distribution of vacant 3d electron states. The presence in CoTPP of the partially filled valence 3db{sub 2g} molecular orbital (MO) results in the appearance in the cobalt spectra of a low-energy band, which is absent in the spectrum of nickel in NiTPP and leads to a doublet structure of transitions to b{sub 1g} and e{sub g} MOs due to the exchange interaction between 3d electrons in partially filled 3db{sub 2g} and 3db{sub 1g} or 3de{sub g} MOs. The spectrum of vacant states in CoTPP differs from that in NiTPP also due to the smaller energy distance between 3db{sub 1g} and e{sub g} MOs and the different positions of nonbonding MOs with the C2p character of the porphine ligand.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Characterization and Failure Analysis of 650-V Enhancement-Mode GaN HEMT for Cryogenically Cooled Power Electronics

In order to evaluate the feasibility of newly developed gallium nitride (GaN) devices in a cryogenically cooled converter, this article characterizes a 650-V enhancement-mode GaN high-electron mobility transistor (GaN HEMT) at cryogenic temperatures. The characterization includes both static and dynamic behaviors. The results show that this GaN HEMT is an excellent device candidate to be applied in cryogenic-cooled applications. For example, transconductance at cryogenic temperature (93 K) is 2.5 times higher than one at room temperature (298 K), and accordingly, peak di / dt during turn-on transients at cryogenic temperature is around 2 times of that at room temperature. Moreover, the ON-resistance of the channel at the cryogenic temperature is only one-fifth of that at room temperature. The corresponding explanations of performance trends at cryogenic temperatures are also given from the view of semiconductor physics. In addition, several device failures were observed during the dynamic characterization of GaN HEMTs at cryogenic temperatures. Additionally, the ultrafast switching speed-induced high di / dt and dv / dt at cryogenic temperatures amplify the negative effects of parasitics inside the switching loop. Based on failure waveforms, two failure modes were classified, and detailed failure mechanisms caused by ultrafast switching speed are given in this article.

42 ENGINEERING↗
DOE OSTI2018

Effect of initial orientation on dynamic recrystallization of a zirconium alloy during hot deformation

Highlights: • The dynamic recrystallization process is enhanced by the operation of slip. • Continuous dynamic recrystallization is promoted by the rotation of grains. • Texture induced hardening hides the softening induced by dynamic recrystallization. - Abstract: The present study investigated the influence of the initial orientation on the dynamic recrystallization (DRX) behavior of a Zr-1Sn-0.3Nb alloy. A hot-rolled and annealed Zr sheet was compressed along two directions: along the normal direction so that the grains' -axis was nearly parallel to the loading direction (0° sample) and along the transverse direction so that the grains' -axis was nearly perpendicular to the loading direction (90° sample). The samples were compressed at 700 °C at a strain rate of 1 s{sup −1}. The microstructures at different strains were characterized by the electron backscatter diffraction (EBSD) technique, and conventional dislocation analysis using transmission electron microscope (TEM) was performed. A threshold value of grain orientation spread (GOS) equaled to 5° was used to distinguish the dynamically recrystallized grains from the deformed matrix. The results revealed that the DRX behavior strongly depended on the initial orientation. The Schmid factor analysis and TEM observation confirmed that pyramidal slip operated from the first stage of deformation in the 0° sample but not in the 90° sample. For the 0° sample, in the early and medium stages of deformation, due to the high stored energy caused by the operation of pyramidal slip, DDRX was mainly contributed to the formation of new fine grains. However, in the later stage of deformation, the DRX mechanism changed from DDRX to CDRX. In the 90° sample, although DDRX featured by grain boundary bulging occurred, the main DRX mechanism was CDRX in the whole deformation processing. Moreover, texture induced hardening in the early stage of deformation hides the softening induced by DDRX.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Study of shot noise in photoresists for extreme ultraviolet lithography through comparative analysis of line edge roughness in electron beam and extreme ultraviolet lithography

In this paper, the influence of the absorption shot noise on line edge roughness (LER) of photoresists for extreme ultraviolet (EUV) lithography is studied experimentally through the comparative analysis of LER obtained by EUV (92 eV photons) and 100 keV e-beam lithography. Techniques for performing EUV and e-beam lithography with a matched image log slope for a fair comparison of LER values are described. Measurements of absorption of 100 keV electrons estimated through a transmissive electron energy loss spectroscopy measurement with a 120 keV electron beam showed that despite having access to core levels in the material (e.g., 284 eV edge in carbon), these electrons mostly just excite the energy levels less than 100 eV in the resist, with a mean deposited energy of 35 eV. By combining the incident flux and the absorption probabilities, the absorbed quanta for patterning of 50 nm half-pitch line/space features was found to be similar between the two patterning technologies.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Human alpha A-crystallin missing N-terminal domain poorly complexes with filensin and phakinin

Highlights: • In vitro complexes between αA, its deletion mutants with filensin and phakinin was determined. • Complexes were determined following ultracentrifugation and by electron microscopic methods. • N-terminal domain of αA-crystallin is needed to form complex with filensin and phakinin in vitro. The aim of this study was to determine relative importance of N-terminal domain and C-terminal extension of αA-crystallin during their in vitro complex formation with phakinin and filensin (the two lens-specific intermediate filament [IF] proteins). Cloned phakinin, filensin and vimentin were purified under a denaturing conditions by consecutive DEAE-cellulose-, hydroxyapatite- and Sephadex G-75-column chromatographic methods. WTαA-crystallin, αA-NT (N-terminal domain [residue number 1–63])-deleted and αA-CT (C-terminal terminal extension [residue number 140–173]-deleted), were cloned in pET 100 TOPO vector, expressed in BL-21 (DE3) cells using 1% IPTG, and purified using a Ni{sup 2+}-affinity column. The following two in vitro methods were used to determine complex formation of WT-αA, αA-NT, or αA-CT with phakinin, filensin or both phakinin plus filensin together: an ultracentrifugation sedimentation (centrifugation at 80,000 × g for 30 min at 20 °C) followed by SDS-PAGE analysis, and an electron microscopic analysis. In the first method, the individual control proteins (WT-αA, αA-NT and αA-CT crystallin species) remained in the supernatant fractions whereas phakinin, filensin, and vimentin were recovered in the pellet fractions. On complex formation by individual WT-αA-, αA-NT or αA-CT-species with filensin, phakinin or both phakinin and filensin, WT-αA and αA-CT were recovered in the pellet fraction with phakinin, filensin or both filensin and phakinin, whereas αA-NT remained mostly in the supernatant, suggesting its poor complex formation property. EM-studies showed filamentous structure formation between WT-αA and αA-CT with phakinin or filensin, or with both filensin and phakinin together but relatively poor filamentous structures with αA-NT. Together, the results suggest that the N-terminal domain of αA-crystallin is required during in vitro complex formation with filensin and phakinin.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Understanding Formation of Irradiation-Induced Defects through 4D-STEM, Electron Tomography, and WBDF-STEM

A major challenge in advancing nuclear materials for next-generation fission and proposed fusion reactors is to comprehensively understand the formation of irradiation-induced defects. Here it is essential to correlate the evolution of irradiation-induced defects and the degradation of mechanical properties, as they collectively dictate the material's lifespan and ensure nuclear safety. Scanning transmission electron microscopy (STEM) based techniques have emerged as indispensable tools for irradiation-induced defect characterization, offering high spatial resolution imaging and chemical analysis, such as electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS). These techniques have been effectively used to obtain an atomic-scale view of the defect structure. Recent advances in electron microscopy, particularly in 4D-STEM, offer detailed insight into microstructural evolution by capturing full 2D diffraction patterns at every pixel position. Using high-speed direct electron detectors, this technology generates a four-dimensional dataset, overcoming the limitations of traditional STEM imaging.

36 MATERIALS SCIENCE↗
NASA NTRS2018

Results of the Aerosol Sampling Experiment on the International Space Station

The indoor air quality of the International Space Station (ISS), in terms of particulate matter, has been assessed through a sampling experiment that collected airborne debris for return to Earth. The Aerosol Sampling Experiment took place on ISS in December 2016 and January 2017, with sample return in February 2017. For redundancy, two different aerosol samplers collected particles in two size ranges spanning from 10 nm to hundreds of micrometers. Multiple analysis techniques have been used to characterize the particles, such as reflective light microscopy, manual scanning electron microscopy (SEM) analysis (secondary and backscattered imaging) with energy dispersive spectroscopy (EDS) x-ray analysis, computer controlled scanning electron microscopy (CCSEM) and Raman spectroscopy. Sampling took place in five locations on ISS, with the greatest deposition of particles in Node 3, followed by Node 1, the US Lab and Node 2. The PMM had very few airborne particles, as expected, owing to the lack of human presence. A large proportion of the sampled material consisted of fibers from clothing. Many particles had complex morphologies or contained multiple metals in a carbonaceous matrix. Metal particles were analyzed for each sampling location in terms of both weight and number percent, with 27 heavy metals detected. Fiberglass and TiO2 particles were present in every location. Quantitative analysis results are presented, and where possible, particle emission sources are identified with the intention to fuel discussions on mitigation.

Meyer, Marit E.↗
DOE OSTI2020

Detection of coherent optical phonons in a thin bismuth film by ultrafast electron diffraction

Coherent dynamics of lattice oscillations in a ∼20-nm-thick film obtained by thermal sputtering of bismuth is studied using ultrashort electron bunches synchronised with femtosecond laser pulses irradiating the sample. The Fourier analysis of ultrafast electron diffraction (UED) data shows that the observed modulation of the signal is due to the ensemble of modes corresponding to optical phonons with frequencies of approximately 3, 6 and 9 THz. A conclusion is made that these peaks correspond to the manifestation of the bismuth A{sub 1g} mode (three-terahertz peak), as well as its first and second overtones, which is probably due to quantum confinement in a 20-nm Bi nanostructure. The possibility of a detailed study of the quantum-size effect in bismuth with the help of a transmission UED is analysed. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Designing Quaternary and Quinary Refractory-Based High-Entropy Alloys: Statistical Analysis of Their Lattice Distortion, Mechanical, and Thermal Properties

The rapid evolution in materials science has resulted in a significant interest in high-entropy alloys (HEAs) for their unique properties. This study focuses on understanding both quaternary and quinary body-centered cubic (BCC) of 12 refractory-based HEAs, and on analysis of their electronic structures, lattice distortions, mechanical, and thermal properties. A comprehensive assessment is undertaken by means of density functional theory (DFT)-based first principles calculations. It is well known that multiple constituents lead to notable lattice distortions, especially in quinary HEAs. This distortion, in turn, has significant implications on the electronic structure that ultimately affect mechanical and thermal behaviors of these alloys such as ductility, lattice thermal conductivity, and toughness. Our in-depth analysis of their electronic structures revealed the role of valence electron concentration and its correlation with bond order and mechanical properties. Local lattice distortion (LD) was investigated for these 12 HEA models. M1 (WTiVZrHf), M7 (TiZrHfW), and M12 (TiZrHfVNb) have the highest LD whereas the models M3 (MoTaTiV), M5 (WTaCrV), M6 (MoNbTaW), and M9 (NbTaTiV) have the less LD. Furthermore, we investigated the thermal properties focusing on Debye temperature (ΘD), thermal conductivity (κ), Grüneisen parameter (γα), and dominant phonon wavelength (λdom). The NbTaTiV(M9) and TiVNbHf(M10) models have significantly reduced lattice thermal conductivities (κL). This reduction is due to the mass increase and strain fluctuations, which in turn signify lattice distortion. The findings not only provide an understanding of these promising materials but also offer guidance for the design of next-generation HEAs with properties tailored for potential specific applications.

Materials Science↗
NASA NTRS1978

Time delay occultation data of the Helios spacecraft for probing the electron density distribution in the solar corona

S-band time delay measurements were collected from the spacecraft Helios A and B during three solar occultations in 1975/76 within heliocentric distances of about 3 and 215 earth radius in terms of range, Doppler frequency shift, and electron content. Characteristic features of measurement and data processing are described. Typical data sets are discussed to probe the electron density distribution near the sun (west and east limb as well) including the outer and extended corona. Steady-state and dynamical aspects of the solar corona are presented and compared with earth-bound-K-coronagraph measurements. Using a weighted least squares estimation, parameters of an average coronal electron density profile are derived in a preliminary analysis to yield electron densities at r = 3, 65, 215 earth radius. Transient phenomena are discussed and a velocity of propagation v is nearly equal to 900 km/s is determined for plasma ejecta from a solar flare observed during an extraordinary set of Helios B electron content measurements.

Edenhofer, P.↗