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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

dc and microwave performance of a 0.1-micron gate InAs/In(0.52)Al(0.48)As MODFET

The performance characteristics of 0.1-micron gate InAs/In(0.52)Al(0.48)As MODFETs grown by molecular beam epitaxy are measured and analyzed. The transistors are characterized by measured g sub m (max) = 840 mS/mm, f sub T = 128 GHz, and a very high current carrying capability, e.g., I sub dss = 934 mA/mm at V sub gs = 0.4 V and V sub ds = 2.7 V. The value of f sub T is estimated from extrapolation of the current gain (H21) at a -6-dB/octave rolloff. This is the first report on the microwave characteristics of an InAs-channel MODFET and establishes the superiority of this heterostructure system.

Yang, D.↗
NASA NTRS1990

Ductility enhancement from interface dislocation sources in a directionally solidified beta + gamma + gamma-prime Ni-Fe-Al composite alloy

A directionally solidified beta + gamma + gamma-prime Ni-Fe-Al in situ composite alloy of composition Ni50Fe30Al20 has been used to investigate the effect of a plastically soft second phase on the mechanical behavior of a B2 ordered intermetallic alloy. This material exhibits extensive plasticity during compressive deformation at room temperature and fails in shear with extensive gamma + gamma-prime lamellar or rod pullout. The material also exhibits about 10 percent tensile elongation to fracture at room temperature, with final fracture that includes substantial necking of the gamma + gamma-prime lamellae or rods. Observation of slip lines and dislocation substructures discloses that the normally brittle beta matrix undergoes extensive plasticity in order to deform compatibly with the more ductile gamma phase. The plasticity of the beta matrix is accomplished by the generation of glissile dislocations into the beta matrix from the beta/gamma interface region and is enhanced because of a favorable beta-gamma orientation relationship for slip transfer. Ductility enhancement from interface-generated mobile dislocations generated from beta-gamma interfaces is compared to that observed in film-coated beta-NiAl single crystals and FeAl polycrystals.

Larsen, M.↗
NASA NTRS1992

Bose-Einstein correlations in Si + Al and Si + Au collisions at 14.6A GeV/c

The E802 Spectrometer at the Brookhaven Alternating Gradient Synchrotron has been used to measure the correlation in relative momentum between like-sign pions emitted in central Si + Al and Si + Au collisions at 14.6A GeV/c. Data are presented in terms of the correlation function for both identified pi(-) and pi(+) pairs near the nucleon-nucleon center-of-mass rapidity. All parametrizations of the correlation function are consistent with a spherically symmetric source of rms radius 3.5 +/- 0.4 fm and lifetime fm/c.

Abbott, T.↗
NASA NTRS1992

Combustion synthesis of ceramic-metal composite materials - The TiC-Al2O3-Al system

Combustion synthesis was applied for producing ceramic-metal composites with reduced levels of porosity, by allowing an excess amount of liquid metal, generated by the exothermic reaction during synthesis, to infiltrate the pores. It is shown that this method, when applied to TiC-Al2O3 system, led to a decreased level of porosity in the resulting TiC-Al2O3-Al product, as compared with that of TiC-Al2O3 system. This in situ procedure is more efficient than the two-stage conventional processes (i.e., sintering followed by liquid metal infiltration), although there are limitations with respect to total penetration of the liquid metal and maintaining a stable propagation of the combustion reaction.

Feng, H. J.↗
NASA NTRS1992

Low cost, SPF aluminum cryogenic tank structure for ALS

Past production work has shown that cryogenic tank structure for the Shuttle Booster Rockets and the Titan system have very high life cycle costs for the fuel tank structure. The tanks are machined stiffener-skin combination that are subsequently formed into the required contour after machining. The material scrap rate for these configurations are usually high, and the loss of a tank panel due to forming or heat treatment problems is very costly. The idea of reducing the amount of scrap material and scrapped structural members has prompted the introduction of built-up structure for cryogenic tanks to be explored on the ALS program. A build-up structure approach that has shown improvements in life cycle cost over the conventional built-up approach is the use of superplastically formed (SPF) stiffened panels (reducing the overall part count and weight for the tank) resistance spot welded (RSW) to outer tank skin material. The stiffeners provide for general stability of the tank, while the skin material provides hoop direction continuity for the loads.

Anton, Claire E.↗
NASA NTRS1992

User's manual for the ALS base heating prediction code, volume 2

The Advanced Launch System (ALS) Base Heating Prediction Code is based on a generalization of first principles in the prediction of plume induced base convective heating and plume radiation. It should be considered to be an approximate method for evaluating trends as a function of configuration variables because the processes being modeled are too complex to allow an accurate generalization. The convective methodology is based upon generalizing trends from four nozzle configurations, so an extension to use the code with strap-on boosters, multiple nozzle sizes, and variations in the propellants and chamber pressure histories cannot be precisely treated. The plume radiation is more amenable to precise computer prediction, but simplified assumptions are required to model the various aspects of the candidate configurations. Perhaps the most difficult area to characterize is the variation of radiation with altitude. The theory in the radiation predictions is described in more detail. This report is intended to familiarize a user with the interface operation and options, to summarize the limitations and restrictions of the code, and to provide information to assist in installing the code.

Reardon, John E.↗
NASA NTRS1992

Solidification kinetics and metastable phase formation in binary Ti-Al

Electromagnetic levitation was used to solidify near-equiatomic alloys of Ti-Al at various bulk undercoolings. Detailed thermal histories were acquired during experiments using optical pyrometry with sampling rates as fast as 500 KHz. Solidification and other high-temperature transformation pathways were deduced from the thermal data and microstructural analysis. Recalescence rise times were employed to determine semiquantitative primary solidification kinetics for the different phases. Primary beta solidification was observed at compositions well into the equilibrium alpha regime; this is presented as part of a near-equiatomic nucleation domain diagram that shows the primary solidification phase that results for each combination of nucleation temperature and composition. Solidification kinetics are faster for primary beta than they are for primary alpha. For undercoolings less than about 150 K, the primary solidification kinetics are about an order of magnitude slower for gamma than for alpha.

Anderson, C. D.↗
NASA NTRS1993

Formation of a metastable ferromagnetic tau phase during containerless melt processing in Mn-Al-C alloys

This paper reports the production of a metastable ferromagnetic tau phase directly from the melt in Mn(0.55)Al(0.433)C(0.017), using a containerless processing method involving levitation melting followed by quenching. Using the results from differential thermal analysis measurements and an analysis of the phase equilibria, it was found that the minimum amount of undercooling level required for ferromagnetic metastable tau phase formation in this alloy was Delta T = 87 K. The attainment of this undercooling may be facilitated by the application of containerless melt processing.

Kim, Y. J.↗
NASA NTRS1993

An analysis of the frequency limitations of an Al(x)Ga(1-x)As/GaAs optical modulator

An analysis is made of the frequency response of an Al(x)Ga(1-x)As/GaAs optical modulator operating at a wavelength of 0.83 micron and utilizing the linear-optic effect in a Mach-Zehnder configuration. It is shown that, in semiconductor modulators, electroabsorption should be taken into account in optimizing the frequency response of the device. It is also shown that, by incorporating an insulator (a semiconductor with a large band gap) between the metallic electrode and the channel, the capacitance of the electroabsorptive modulator can be kept low at a reasonable value under the worst conditions.

Tabib-Azar, M.↗
NASA NTRS1993

Liquidus temperatures in the Ti-Al system

Liquidus temperatures were determined for the titanium-aluminum system at compositions ranging from 41 to 62 at. pct Al. The measurements were obtained by inducing solidification of slightly undercooled melts under containerless processing conditions using electromagnetic levitation. Absolute temperatures were determined by optical pyrometry in combination with independent measurements of spectral emissivities by laser polarimetry. The present liquidus temperatures are in agreement with two sets of literature values and are consistent with a set of solid-state literature data. These values exceed those selected in one recent proposed phase diagram revision by about 30 K and are as much as 40 to 60 K higher than those in another proposed revision.

Anderson, C. D.↗
NASA NTRS1993

Transformation to Ni5Al3 in a 63.0 at. pct Ni-Al alloy

Microstructures of 63 at. pct P/M Ni-Al alloys with a composition close to the stoichiometry of the Ni5Al3 phase were investigated using homogenized and quenched specimens aged at low temperatures for various times. Results of analyses of XRD data and electron microscopy observations were used for quantitative phase analysis, performed to calculate the (NiAl + Ni5Al3)/Ni5Al3 phase boundary locations. The measured lattice parameters of Ni5Al3 phase formed at 823, 873, and 923 K indicated an increase in tetragonality of the phase with increasing nickel content.

Khadkikar, P. S.↗
NASA NTRS1993

Secondary and tertiary dendrite arm spacing relationships in directionally solidified Al-Si alloys

Secondary, lambda sub 2, and tertiary, lambda sub 3, dendrite arm spacings have been measured from Al-Si alloys which were directionally solidified as functions of growth velocity, V, temperature gradient, G, and composition, Co. Both lambda sub 2 and lambda sub 3 decreased as the imposed growth velocity and silicon concentrations were increased, and for each function a systematic variance in the rate was seen. Complications with measuring secondary arm spacings are shown and it was found that the tertiary arm data agree much better with coarsening theory, the implication being that lambda sub 3, when measurable, is a more representative and reliable measure of the solidification history than lambda sub 2.

Grugel, R. N.↗
NASA NTRS1993

Composition dependence of superconductivity in YBa2(Cu(3-x)Al(x))O(y)

Eleven different compositions in the system YBa2(Cu(3-x)Al(x))O(y) (x = 0 to 0.3) have been synthesized and characterized by electrical resistivity measurements, powder X-ray diffraction, and scanning electron microscopy. The superconducting transition temperature T sub c (onset) was almost unaffected by the presence of alumina due to its limited solubility in YBa2Cu3O(7-x). However, T sub c(R = 0) gradually decreased, and the resistive tails became longer with increasing Al2O3 concentration. This was probably due to formation of BaAl2O4 and other impurity phases from chemical decomposition of the superconducting phase by reaction with Al2O3.

Bansal, N. P.↗
NASA NTRS1993

Formation of deoxidization products in iron ingot by the addition of Al, Si, and/or Mn (M-5)

The objective of this work is to examine the morphology, composition, and distribution of deoxidation products in iron and iron-10 percent Ni alloy ingots. The deoxidation agents Si, Mn, Al, and their mixtures are selected to investigate the formation mechanism of the deoxidation products and to compare the differences of oxide formation among these agents in microgravity. After the experiment in space, the tested specimens are going to be analyzed by the use of the latest physical and/or chemical analytical equipment, and the information obtained will be a great help for the comprehension of the formation of oxide inclusion in steel for practical purposes, and also for the study of the solidification mechanism theory in the theoretical field.

Fukazawa, Akira↗
NASA NTRS1993

The influence of a microgravity environment on the dendritic morphology during directional solidification of hypoeutectic Al-Si alloys

NASA grant NAGW-2540 provided the opportunity to evaluate and extend ongoing studies of directionally solidified Al-Si alloys. Microstructural development was further characterized in terms of solidification processing parameters; novel relationships between processing and development of dendrite trunk diameters and tertiary dendrite arm spacings were found. This has resulted in three publications (one in print, one in press, and one in review). Microstructural development under conditions of controlled acceleration during directional solidification has been investigated; this has culminated in a Master's degree and will be submitted for publication. The above work not only contributes to our understanding of solidification phenomena but also defines the processing parameters for a successful microgravity experiment while providing a data base to which mu g samples can be unequivocally compared and evaluated.

Grugel, Richard N.↗
NASA NTRS1993

ALS engine propellant effector system

This report summarizes analysis, design, and experimental testing done on the propellant effector (valve plus electromechanical actuator) for the Advanced Launch System (ALS) main engine.

Faulkner, Colin↗
NASA NTRS1993

ALS engine controller system

This report summarizes analysis and design done on the controller system for the Advanced Launch System (ALS) main engine.

Payne, Roger↗