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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Electronic structure and properties of magnetic defects in Co(1+x)Al(1-x) and Fe(1+x)Al(1-x) alloys

CoAl and FeAl compounds are developed along two directions. Magnetic susceptibility and specific heat at low temperature on (NiCo)Al and (CoFe)Al ternary alloys are in good agreement with band calculations. Results on magnetization and specific heat under field at low temperature on nonstoichiometric compounds show clearly the importance of the nearest neighbor effects. In the case of CoAl, the isolated cobalt atoms substituting aluminum are characterized by a Kondo behavior, and, for FeAl, the isolated extra iron atoms are magnetic and polarize the matrix. Moreover, for the two compounds, clusters of higher order play a considerable part in the magnetic properties for CoAl, these clusters also seem to be characterized by a Kondo behavior, for FeAl, these clusters whose moment is higher than in the case of isolated atoms, could be constituted of excess parts of iron atoms.

Abbe, D.↗
NASA NTRS1984

The physical metallurgy of mechanically-alloyed, dispersion-strengthened Al-Li-Mg and Al-Li-Cu alloys

Powder processing of Al-Li-Mg and Al-Li-Cu alloys by mechanical alloying (MA) is described, with a discussion of physical and mechanical properties of early experimental alloys of these compositions. The experimental samples were mechanically alloyed in a Szegvari attritor, extruded at 343 and 427 C, and some were solution-treated at 520 and 566 C and naturally, as well as artificially, aged at 170, 190, and 210 C for times of up to 1000 hours. All alloys exhibited maximum hardness after being aged at 170 C; lower hardness corresponds to the solution treatment at 566 C than to that at 520 C. A comparison with ingot metallurgy alloys of the same composition shows the MA material to be stronger and more ductile. It is also noted that properly aged MA alloys can develop a better combination of yield strength and notched toughness at lower alloying levels.

Gilman, P. S.↗
NASA NTRS1992

Oxygen-induced Al surface segregation in Al(x)Ga(1-x)As and the effect of Y overlayers on the oxidation of the Y/Al(x)Ga(1-x)As interface

The oxidation of Al(x)Ga(1-x)As (x = 0.15, AlGaAs) was studied by AES and XPS at 350 C and different oxygen exposures (up to 5 x 10 exp 4 L). Also studied were the effects of yttrium overlayers (theta = 3 ML) on the oxidation of the AlGaAs surface. Substantial oxygen-induced Al surface segregation has been observed for both yttriated and nonyttriated AlGaAs surfaces which increased with increasing oxygen exposure. Also observed is a significant Y-enhanced oxidation of the AlGaAs surface. Oxidation of the yttriated AlGaAs surface was found to be a factor of 4 greater than that of the nonyttriated surface. Also, while oxidation of the nonyttriated AlGaAs yielded mainly Al2O(x) (x less than 3) and only little Ga2O3, the yttriated AlGaAs surface oxide layer was principally Ga2O3 and stoichiometric Al2O3. However, both the yttriated and nonyttriated surfaces were found to contain metallic As within the oxide layer.

Mesarwi, A.↗
NASA NTRS1999

Numerical Analysis of Temperature Gradients and Interface Shape During Directional Solidification of Al and Al-Cu Alloy Under Microgravity Conditions

Numerical modeling was undertaken to analyze the influence of radial thermal gradient on solid/liquid (s/1) interface shape and convection patterns during solidification of pure Al and Al-4 wt% Cu alloy. The objective of the numerical task was to predict the influence of convective velocity on an insoluble particle near a s/l interface. These predictions would then be used to define the minimum gravity level (g) required to investigate the fundamental physics of interaction between a particle and a s/I interface. To satisfy this objective, steady state calculations were performed for different gravity levels and orientations with the gravity vector. ne furnace configuration used in this analysis is the proposed International Space Station Furnace, Quench Module Insert (QMI) 1. Results from a thermal model of the furnace core were used as initial boundary conditions for solidification modeling. General model of binary alloy solidification was based on the finite element code FIDAP. It was found that for the worst case orientation of 90 degrees with the gravity vector and a g level of 10(exp -4)g(sub o) (g(sub o) = 9.8 m/s(exp 2)) the dominant forces acting on the particle would be the fundamental drag and interfacial forces.

Bune, Andris V.↗
NASA NTRS2004

Elevated Temperature Deformation of Fe-39.8Al and Fe-15.6Mn-39.4Al

The elevated temperature compressive properties of binary Fe-39.8 at % Al and Fe-15.6Mn-39.4Al have been measured between 1000 and 1300 K at strain rates between 10(exp 7) and 10(exp 3)/ s. Although the Mn addition to iron aluminide did not change the basic deformation characteristics, the Mn-modified alloy was slightly weaker. In the regime where deformation of FeAl occurs by a high stress exponent mechanism (n = 6), strength increases as the grain size decreases at least for diameters between approx. 200 and approx. 10 microns. Due to the limitation in the grain size-flow stress-temperature-strain rate database, the influence of further reductions of the grain size on strength is uncertain. Based on the appearance of subgrains in deformed iron aluminide, the comparison of grain diameters to expected subgrain sizes, and the grain size exponent and stress exponent calculated from deformation experiments, it is believed that grain size strengthening is the result of an artificial limitation on subgrain size as proposed by Sherby, Klundt and Miller.

Whittenberger, J. Daniel↗
NASA NTRSDate not supplied

Mineralogical and Al-Mg Isotopic Study of Fine-Grained Ca-Al-Rich Inclusions

Fine-grained Ca-Al-rich inclusions (FGIs) in carbonaceous chondrites are interpreted as aggregates of nebular gas-solid condensates that escaped significant melting.Thus far, a small number of FGIs from CV3 chondrites have been analyzed, showing a range of (26Al/27Al)0=~5.4×10−5to ~3.4×10−5.These values are similar to (26Al/27Al)0inferred from coarse-grained, igneous CAIs (CGIs) from CV3 chondrites.This observed spread in (26Al/27Al)0values indicates the CAI formation over an extended time period. However, more analyses are needed to determine if the FGIs formed continuously over a significant time period or by multiple episodic events of nebular condensation. In this study, we present high-precision Al-Mg isotopic data of FGIs from reduced CV3 chondrites to better constrain their formation timescale relative to CGIs in CV3 chondrites, as well as to smaller FGIs in CO3 chondrites. This isotopic study is coordinated with a FIB/TEM study to elucidate the origin and nature of FGIs in the petrologic and mineralogical context.

J Han↗
NASA NTRS1988

Al(0.3)Ga(0.7)As / Al(0.05)Ga(0.95)As light-emitting diodes on GaAs-coated Si substrates grown by liquid phase epitaxy

Al(0.3)Ga(0.7)As/Al(0.05)Ga(0.95)As double-heterostructure light-emitting diodes (LEDs) were successfully grown for the first time by liquid phase epitaxy on a GaAs-coated Si substrate that was prepared by a sequential process of migration-enhanced epitaxy and molecular beam epitaxy. The edge-emitting LEDs had diode ideality factors of 1.54 at a forward-biased voltage higher than 0.9 V and external quantum efficiencies of 0.0033 W/A per facet. This efficiency is 50 times higher than the previously reported value, and is on the same order as that of AlGaAs homojunction LEDs fabricated on the GaAs substrates by liquid phase epitaxy.

Sakai, Shiro↗
NASA NTRS1989

Solution chemistry effects on the stress corrosion cracking behavior of alloy 2090 (Al-Li-Cu) and alloy 2024 (Al-Cu-Mg)

The SCC initiation behavior of alloys 2090 and 2024 is examined in various NaCl-based environments. The pre-exposure and bulk/local solution chemistry effects discovered by Holroyd et al. (1986) are investigated, with emphasis on the effect of bulk solution chemistries and atmospheric CO2 on the occluded cell environment and the role of the occluded environment in the crack initiation and early-stage propagation processes. It was found that constant immersion in NaCl does not promote SCC in alloy 2090 or alloy 2024. Upon removal from NaCl, SCC is quickly facilitated, but only in the presence of atmospheric CO2. The need for CO2 is attributed to an increase in carbonate concentrations, eventually allowing passivation of blunted fissures by precipitation of Li2CO3. It is inferred that any effects due to aging are small in magnitude, relative to the effects of subtle changes in the bulk/local solution chemistries.

Moran, James P.↗