Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Single Crystal”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Fatigue behavior of a single-crystal superalloy

A single-crystal superalloy, PWA 1480 is under consideration as a replacement material for the turbine blades of the high pressure fuel turbopump (HPFTP) of the space shuttle main engine (SSME). Three separate experimental programs were conducted to characterize the fatigue behavior of this alloy. Fatigue tests were conducted at room temperature (in air) and at 1000 F (in vacuum) on smooth specimens machined from both cast bars and slabs. The data from all of these programs are consolidated to provide a broader characterization of the fatigue behavior of the single crystal PWA 1480. The zero-mean-stress fatigue relationships are expressed in terms of stress range versus cyclic life lines on log-log plots. Characterization of the fatigue behavior of (001) oriented PWA 1480 single crystal under conditions of tensile mean stress was performed by using the unified approach proposed by Heidmann. In this approach the fatigue life is modified by a mean stress parameter so that a single life relationship can be used to represent both zero and tensile mean stress data.

Kalluri, Sreeramesh↗
DOE OSTI2021

MBE growth and donor doping of coherent ultrawide bandgap AlGaN alloy layers on single-crystal AlN substrates

Single-crystal Aluminum Nitride (AlN) crystals enable the epitaxial growth of ultrawide bandgap Al(Ga)N alloys with drastically lower extended defect densities. Here, we report the plasma-MBE growth conditions for high Al-composition AlGaN alloys on single-crystal AlN substrates. An AlGaN growth guideline map is developed, leading to pseudomorphic Al x Ga 1–x N epitaxial layers with x ~0.6–1.0 Al contents at a growth rate of ~0.3 μm/h. These epitaxial layers exhibit atomic steps, indicating step flow epitaxial growth, and room-temperature band edge emission from ~4.5 to 5.9 eV. Growth conditions are identified in which the background impurity concentrations of O, C, Si, and H in the MBE layers are found to be very near or below detection limits. An interesting Si segregation and gettering behavior is observed at the epitaxial AlGaN/AlN heterojunction with significant implications for the formation and transport of 2D electron or hole gases. Well-controlled intentional Si doping ranging from ~2 × 10 17 to 3 × 10 19 atoms/cm 3 is obtained, with sharp dopant density transition profiles. In Si-doped Al 0.6 Ga 0.4 N epilayers, a room-temperature free electron concentration of ~3 × 10 19 /cm 3 , an electron mobility of ~27 cm 2 /V s, and an n-type resistivity of ~7.5 m Ω cm are obtained. Here, the implications of these findings on electronic and photonic devices on single-crystal AlN substrates are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A sensitivity analysis of twinning crystal plasticity finite element model using single crystal and poly crystal Zircaloy

The popularity of crystal plasticity finite element method (CPFEM) models is increasing due to their ability to predict the mechanical response of crystalline materials such as metals and metal alloys more accurately than traditional continuum mechanics models. This is since the crystal plasticity models consider the effect of atomic structure, microstructural morphology, and properties of individual grains. These CPFEM models use a large number of material parameters in order to capture the mesoscale physics which comes with the downside of the tedious calibration process. In this paper, a CPFEM code was developed to include the twinning induced grain reorientation and subsequent crystallographic slip for HPC material. The developed code is incorporated in a large-scale, parallelized nonlinear solver WARP3D. Further, a sensitivity analysis with respect to 22 material parameters was then conducted using single crystal and polycrystal representative volume element (RVE) of Zircaloy material. Loading was applied along five different crystallographic orientations for single crystal RVE and along three directions namely, rolling (RD), transverse (TD), and normal (ND) direction for polycrystal RVE. Results obtained from the sensitivity analysis were used for the calibration of material parameters for Zircaloy. Finally, developed code along with calibrated material parameters was used to investigate the effect of the hydride phase formation in Zircaloy which is a typical case observed for nuclear applications. It was found that the volume fraction of the hydride phase has a significant impact on the mechanical properties of Zircaloy.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Lithium ions in the van der Waals gap of Bi{sub 2}Se{sub 3} single crystals

Insertion/extraction of lithium ions into/from Bi{sub 2}Se{sub 3} crystals was investigated by means of cyclic voltammetry. The process of insertion is reflected in the appearance of two bands on voltammograms at {approx}1.7 and {approx}1.5 V, corresponding to the insertion of Li{sup +} ions into octahedral and tetrahedral sites of the van der Waals gap of these layered crystals. The process of extraction of Li{sup +} ions from the gap results in the appearance of four bands on the voltammograms. The bands 1 and 2 at {approx}2.1 and {approx}2.3 V correspond to the extraction of a part of Li{sup +} guest ions from the octahedral and tetrahedrals sites and this extraction has a character of a reversible intercalation/deintercalation process. A part of Li{sup +} ions is bound firmly in the crystal due to the formation of negatively charged clusters of the (LiBiSe{sub 2}.Bi{sub 3}Se{sub 4}{sup -}) type. A further extraction of Li{sup +} ions from the van der Waals gap is associated with the presence of bands 3 and 4 placed at {approx}2.5 and {approx}2.7 V on the voltammograms as their extraction needs higher voltage due to the influence of negative charges localized on these clusters. -- Graphical abstract: Insertion/extraction of lithium ions into/from Bi{sub 2}Se{sub 3} layered crystals was investigated by cyclic voltammetry. The extraction of Li{sup +} results in the appearance of four bands on the voltammograms. The first two bands have a character of a reversible process. A part of Li{sup +} ions is bound firmly in the crystal due to the formation of negatively charged clusters of the (LiBiSe{sub 2}.Bi{sub 3}Se{sub 4}{sup -}) type. Their extraction needs higher voltage due to the negative charge. Display Omitted

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

In Situ TEM and AFM Investigation of Morphological Controls during the Growth of Single Crystal BaWO4

Barium tungstate (BaWO4) is a widely investigated inorganic optical material due to its attractive emission properties. Because those properties strongly depend on crystal structure and morphology, numerous approaches to controlling growth have been pursued. However, an understanding of the growth mechanisms that lead to the wide range of morphologies obtained to date is largely lacking, and most attempts to develop that understanding have been based on post-growth analyses. Significantly, such analyses have led to the conclusion that certain BaWO4 crystal morphologies result from a nonclassical growth process of oriented attachment. In this work, we systematically varied the morphology of BaWO4 crystals by adjusting the relative concentrations of solute, water, and ethanol. We then explored the growth mechanism leading to the observed range of morphologies through in situ TEM and in situ AFM. We find that even the most complex BaWO4 morphologies occur through purely classical growth mechanisms largely controlled by the content of solute and ethanol. The latter acts as an impurity to poison growth at low concentrations and low solute levels, but leads to development of growth instabilities and eventual dendritic growth at high alcohol and moderate solute concentrations by driving up the supersaturation. These findings also highlight the necessity of in situ experiments to interpret ex situ observations of crystal growth and decipher the controlling mechanisms.

Liu, Lili↗
DOE OSTI2016

Growth, structural, optical, thermal and mechanical properties of cytosinium hydrogen selenite: A novel nonlinear optical single crystal

Highlights: • Growth of bulk single crystals of cytosinium hydrogen selenite (CHS) is reported. • Dielectric constant of CHS is measured as a function of Frequency and temperature. • Lower cut off value of UV–vis-NIR spectrum of CHS crystal is observed at 210 nm. • Meyer’s index value of CHS crystal calculated identifies it as a soft material. • Powder SHG efficiency of CHS is about 1.5 times that of KDP crystal. - Abstract: A novel nonlinear optical single crystal of cytosinium hydrogen selenite was grown from aqueous solution of cytosinium hydrogen selenite by slow solvent evaporation method at room temperature. The structural properties of grown crystal have been studied by single crystal and powder X-ray diffraction analysis. Presence of various functional groups was identified from Fourier transform infrared spectroscopy. The optical transmittance and absorbance spectra were recorded by UV–vis-NIR spectrometer and the grown crystal possesses good transparency in the entire visible region. The dielectric constant and dielectric loss of the crystal were calculated as a function of frequency at different temperatures. The mechanical strength of the cytosinium hydrogen selenite crystal was estimated using Vicker’s microhardness tester. Etch patterns of the cytosinium hydrogen selenite crystal were obtained using distilled water as etchant for different etching time. Second harmonic generation efficiency tested using Nd:YAG laser is about 1.5 times that of KDP.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Evolution of structure in Na{sub 0.5}Bi{sub 0.5}TiO{sub 3} single crystals with BaTiO{sub 3}

The structural, dielectric, and piezoelectric properties of Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}-x mol. %BaTiO{sub 3} (NBT-x%BT) crystals have been investigated. The dielectric and piezoelectric properties of NBT-x%BT were enhanced near x = 5–7. High resolution synchrotron x-ray powder diffraction studies revealed the presence of a phase boundary between monoclinic (Cc) and tetragonal (P4bm) phases near x = 5–7, where the dielectric and piezoelectric properties were enhanced.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Demonstration of Single-Crystal Self-Seeded Two-Color X-Ray Free-Electron Lasers

A scheme for generating two simultaneous hard-x-ray free-electron laser pulses with a controllable difference in photon energy is described and then demonstrated using the self-seeding setup at the Linac Coherent Light Source (LCLS). The scheme takes advantage of the existing LCLS equipment, which allows two independent rotations of the self-seeding diamond crystal. The two degrees of freedom are used to select two nearby crystal reflections, causing two wavelengths to be present in the forward transmitted seeding x-ray pulse. The free-electron laser system must support amplification at both desired wavelengths.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Correlated Single-Crystal Electronic Absorption Spectroscopy and X-ray Crystallography at NSLS Beamline X26-C

The research philosophy and new capabilities installed at NSLS beamline X26-C to support electronic absorption and Raman spectroscopies coupled with X-ray diffraction are reviewed. This beamline is dedicated full time to multidisciplinary studies with goals that include revealing the relationship between the electronic and atomic structures in macromolecules. The beamline instrumentation has been fully integrated such that optical absorption spectra and X-ray diffraction images are interlaced. Therefore, optical changes induced by X-ray exposure can be correlated with X-ray diffraction data collection. The installation of Raman spectroscopy into the beamline is also briefly reviewed. Data are now routinely generated almost simultaneously from three complementary types of experiments from the same sample. The beamline is available now to the NSLS general user population.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2017

Growth of EuO single crystals at reduced temperatures

Single crystals of (Eu 1-x Ba x )O have been grown in a molten barium-magnesium metal flux at temperatures up to 1000 °C, producing single crystals of (Eu 1-x Bax)O with barium doping levels ranging from x = 0.03 to x = 0.25. Magnetic measurements show that the ferromagnetic Curie temperature T C correlates with the Ba doping levels, and a modified Heisenberg model was used to describe the stoichiometry dependence of T C . Extrapolation of the results indicates that a sample with Ba concentration of x = 0.72 should have a T C of 0 K, potentially producing a quantum phase transition in this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The role of non-covalent interactions on CO bulk oxidation on Pt single crystal electrodes in alkaline electrolytes

The role of non-covalent interaction between both non-specifically adsorbed hydrated K+, Li+ and Ba2+ cations (M+) and hydroxyl species (M+-OHad) as well as underpotentially deposited Cu adatoms and OHad (Cuupd-OHad) on bulk CO oxidation (COb) is investigated on Pt(111) and Pt(100) in alkaline solutions. The effect of Cuupd-OHad on COb oxidation is observed almost at the reversible potential for CO oxidation, signaling that Cuupd-induced adsorption of OHad activates COb oxidation at very low over potentials. In contrast, the effect of M+-OHad was found to be strongly dependent on the surface coverage of OHad on Pt; e.g., while no effect is found when the surface is pre-covered by adsorbed CO (COad), a discernable effect is observed on OHad pre-covered Pt surface.

Kodama, Kensaku↗