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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Eutectic superalloys strengthened by aligned delta, Ni3Cb lamellae, gamma-prime, Ni3Al precipitates and reduced interlamellar spacing.

Monovariant eutectic alloys, located on the liquidus trough between the binary eutectic gamma, Ni - delta, Ni3Cb and the ternary eutectic gamma, Ni - gamma-prime, Ni3Al - delta, Ni3Cb, were identified which permitted the production of aligned lamellae within a nickel solid solution matrix containing the precipitate gamma-prime. These alloys exhibited great insensitivity in their composite microstructures to solidification parameters such as growth rate temperature gradient, and were found to be remarkably uniform in composition along their length.

Lemkey, F. D.↗
NASA NTRS1973

Mechanical properties of electron-beam-melted molybdenum and dilute Mo-Re alloys.

Study of Mo-Re alloys aimed at examining the effects of small rhenium additions on the low-temperature ductility of molybdenum and determining the mechanical properties of dilute Mo-Re alloys. The results obtained indicate that high-purity Mo-Re alloys have ductile-brittle transition temperatures considerably lower than those for unalloyed molybdenum and that rhenium promotes normal solid-solution strengthening in molybdenum at elevated temperatures.

Klopp, W. D.↗
NASA NTRS1966

Stabilization of Tungsten-Uranium Dioxide Composites Under Thermal Cycling Conditions

Uranium losses during thermal cycling of tungsten - uranium dioxide composites to 2500° C in flowing purified hydrogen for specimens initially containing 35 volume percent uranium dioxide were reduced by the use of thorium dioxide, calcium oxide, or yttrium oxide as additives in solid solution with the uranium dioxide. The effectiveness of the additives decreased in the order yttrium oxide, calcium oxide, and thorium dioxide. Stabilization of uranium dioxide by calcium oxide or yttrium oxide can be explained in part on the basis of the introduction of oxygen vacancies into the fluorite lattice and the associated lowered partial molar free energy of oxygen. The difference in the effectiveness of calcium oxide and yttrium oxide is discussed, and a possible explanation of the observed behavior is proposed. Of the concentrations of yttrium oxide tested (i.e., 2. 5, 5, and 10 mole percent), 10 mole percent of yttrium oxide was the most effective in pre­ venting loss of uranium from composities.

Gluyas, Richard E.↗
NASA NTRS1973

Eutectic superalloys strengthened by sigma, Ni3CB lamellae and gamma prime, Ni3Al precipitates

By means of a screening and solidification optimization study of certain alloys located on the gamma-sigma liquidus surface within the Ni-Cb-Cr-Al system, alloys with high temperature properties superior to those of all known superalloys were defined. One alloy, Ni - 19.7w/o Cb - 6.0w/o Cr - 2.5w/o Al, directionally solidified at 3 cm/hr met or exceeded each program goal. A second alloy, Ni-21.75 w/o Cb-2.55 w/o Al, although deficient in its inherent oxidation resistance, met the other program goals and combined a remarkable insensitivity of composite microstructure to solidification parameters with excellent low temperature toughness. This investigation demonstrated that useful properties for gas turbine airfoil application have been achieved by reinforcing a strong and tough gamma solid solution matrix containing precipitated gamma prime by a lamellar intermetallic compound Ni3 Cb having greater strength at elevated temperature.

Lemkey, F. D.↗
NASA NTRS1974

Effect of long-time, elevated-temperature exposures to vacuum and lithium on the properties of a tantalum alloy, T-111

The effect of long-term, elevated-temperature vacuum and lithium exposures on the mechanical properties of T-111 (Ta-8W-2Hf) is determined. Exposure conditions were for 1000 hours at 980 or 1315 C, 5000 hours at 1315 C, and a duplex temperature exposure of 1000 hours at 980 C plus 4000 hours at 1040 C. The exposures resulted in reduced tensile and creep strengths of the T-111 in the 900 to 1100 C temperature range where a dynamic strain-age-strengthening mechanism is operative in this alloy. This strength reduction was attributed to the depletion of oxygen from solid solution in this alloy.

Buzzard, R. J.↗
NASA NTRS1973

Grain boundary mobility in anion doped MgO

Certain anions OH(-), F(-) and Gl(-) are shown to enhance grain growth in MgO. The magnitude of their effect decreases in the order in which the anions are listed and depends on their location (solid-solution, second phase) in the MgO lattice. As most anions exhibit relatively high vapor pressures at sintering temperatures, they retard densification and invariably promote residual porosity. The role of anions on grain growth rates was studied in relation to their effect on pore mobility and pore removal; the atomic process controlling the actual rates was determined from observed kinetics in conjunction with the microstructural features. With respect to controlling mechanisms, the effects of all anions are not the same. OH(-) and F(-) control behavior through creation of a defect structure and a grain boundary liquid phase while Cl(-) promotes matter transport within pores by evaporation-condensation. Studies on an additional anion, S to the minus 2nd power gave results which were no different from undoped MgO, possibly because of evaporative losses during hot pressing. Hence, the effect of sulphur is negligible or undetermined.

Kapadia, C. M.↗
NASA NTRS1973

Epitaxial growth of III-V compounds for electroluminescent light sources

The epitaxial growth techniques used in the fabrication of III-V compound electroluminescent devices are reviewed. Both vapor and liquid phase epitaxial techniques are discussed, including the applications of these techniques to well established materials as well as newer materials. The state of the art of light-emitting devices fabricated from members of the III-V compounds and their solid solutions is also reviewed.

Chu, T. L.↗
NASA NTRS1974

The effects of composition on mechanical properties of W-4Re-Hf-C alloys

Studies were made of the effects of alloy composition on the mechanical behavior of as-worked W-4Re-Hf-C alloys containing up to about 0.8 mol % Hfc. Extracted second-phase particles were analyzed and related to alloy composition and creep strength. While strengthening is attributed to HfC particles, the presence of excess hafnium or carbon (above the calculated amounts for stoichiometric HfC) in swaged W-4Re-Hf-C alloys generally causes a reduction of the high-temperature (1930 C) tensile strength; maximum creep strength is, however, indicated for alloys with a slight (about 0.05 to 0.1 at. %) excess of hafnium. Particle strengthening is reduced by WC in solid solution with HfC for allow compositions with an excess of carbon. The low-temperature ductility of worked W-4Re-Hf-C alloys appears to be far more dependent on the amount of excess C or Hf present than on the HfC particle content in the range studies.

Witzke, W. R.↗
NASA NTRS1974

Metallographic study of metallic fragment of lunar surface material

A high precision investigation of a metallic fragment from the lunar material returned by the Soviet Luna 16 automatic station revealed three characteristic temperature intervals with different kinetics of solid solution decomposition. The following were found in the structure of the iron-nickel-cobalt alloy: (1) delta-phase and alpha-ferrite of diffusional, displacement origin in the grain boundary and acicular forms; and (2) martensite of isothermal and athermal nature, acicular, lamellar, massive, and dendritic. The diversity of the shapes of structural constituents is associated with the effect on their formation of elastic distortions and various mechanisms of deformation relaxation processes.

Mints, R. I.↗
NASA NTRS1975

Directionally solidified pseudo-binary eutectics of Ni-Cr-(Hf, Zr)

A pseudo-binary eutectic, in which the intermetallic Ni7Hf2 reinforces the Ni-Cr solid solution phase, was previously predicted in the Ni-Cr-Hf system by a computer analysis. The experimental determination of pseudo binary eutectic compositions and the directional solidification of the Ni-Cr-Hf, Zr, and Ni-Cr-Zr eutectic alloys are discussed. To determine unknown eutectics, chemical analyses were made of material bled from near eutectic ingots during incipient melting. Nominal compositions in weight percent of Ni-18.6Cr-24.0HF, Ni19.6Cr-12.8Zr-2.8Hf, and Ni-19.2Cr-14.8Zr formed aligned pseudo-binary eutectic structures. The melting points were about 1270 C. The reinforcing intermetallic phases were identified as noncubic (Ni,Cr)7Hf2 and (Ni,Cr)7(Hf,Zr)2, and face centered cubic (Ni,Cr)5Zr. The volume fraction of the reinforcing phases were about 0.5.

Kim, Y. G.↗
NASA NTRS1975

Hydrogen interactions with metals

Review of the literature on the nature and extent of hydrogen interactions with metals and the role of hydrogen in metal failure. The classification of hydrogen-containing systems is discussed, including such categories as covalent hydrides, volatile hydrides, polymeric hydrides, and transition metal hydride complexes. The use of electronegativity as a correlating parameter in determining hydride type is evaluated. A detailed study is made of the thermodynamics of metal-hydrogen systems, touching upon such aspects as hydrogen solubility, the positions occupied by hydrogen atoms within the solvent metal lattice, the derivation of thermodynamic functions of solid solutions from solubility data, and the construction of statistical models for hydrogen-metal solutions. A number of theories of hydrogen-metal bonding are reviewed, including the rigid-band model, the screened-proton model, and an approach employing the augmented plane wave method to solve the one-electron energy band problem. Finally, the mechanism of hydrogen embrittlement is investigated on the basis of literature data concerning stress effects and the kinetics of hydrogen transport to critical sites.

Mclellan, R. B.↗
NASA NTRS1975

Chemistry of vaporization of refractory materials

A discussion is given of the principles of physical chemistry important in vaporization studies, notably the concepts of equilibrium, phase behavior, thermodynamics, solid solution, and kinetics. The important factors influencing equilibrium vaporization phenomena are discussed and illustrated. A proper course of a vaporization study consisting of 9 stages is proposed. The important experimental techniques of Knudsen effusion, Langmuir vaporization and mass spectrometry are discussed. The principles, the factors, the course of a study and the experimental techniques and procedures are illustrated by recent work on the Ti-O system.

Gilles, P. W.↗
NASA NTRS1976

The 55 K specific heat anomaly in palladium hydride

A specific heat anomaly in PdH and PdD has been observed by Aston et al. (1957) close to 55 K. Its position was found to be independent of hydrogen concentration and its magnitude to be linear in hydrogen concentration. Ferguson's (1965) and Brodowsky's (1972) explanations of the anomaly are shown to be unsatisfactory. This is true also for the detailed mechanical statistical model proposed by Staford and McLellan (1974) for interstitial solid solutions of hydrogen in transition metals. It is shown that Gopal's (1966) simple Schottky model of specific heat anomaly, which considers a system of several levels with Boltzmann statistics, provides much better agreement with experiment than the more elaborate models, both in magnitude and in predicting a linear dependence on hydrogen concentration.

Jacobi, N.↗
NASA NTRS1976

Directionally solidified iron-base eutectic alloys

Pseudobinary eutectic alloys with nominal compositions of Fe-25Ta-22Ni-10Cr and Fe-15.5Nb-14.5Ni-6.0Cr were directionally solidified at 0.5 centimeter per hour. Their microstructure consisted of the fcc, iron solid-solution, matrix phase reinforced by about 41-volume-percent, hcp, faceted Fe2Ta fibers and 41-volume-percent, hcp, Fe2Nb lamellae for the tantalum- and niobium-containing alloys, respectively. The microstructural stability under thermal cycling and the temperature dependence of tensile properties were investigated. These alloys showed low elevated-temperature strength and were not considered suitable for application in aircraft-gas-turbine blades although they may have applicability as vane materials.

Tewari, S. N.↗
NASA NTRS1976

A simple approach to metal hydride alloy optimization

Certain metals and related alloys can combine with hydrogen in a reversible fashion, so that on being heated, they release a portion of the gas. Such materials may find application in the large scale storage of hydrogen. Metal and alloys which show high dissociation pressure at low temperatures, and low endothermic heat of dissociation, and are therefore desirable for hydrogen storage, give values of the Hildebrand-Scott solubility parameter that lie between 100-118 Hildebrands, (Ref. 1), close to that of dissociated hydrogen. All of the less practical storage systems give much lower values of the solubility parameter. By using the Hildebrand solubility parameter as a criterion, and applying the mixing rule to combinations of known alloys and solid solutions, correlations are made to optimize alloy compositions and maximize hydrogen storage capacity.

Lawson, D. D.↗
NASA NTRS1976

Metal melting, joining, and alloying under weightlessness

During the Skylab mission experiments were conducted concerning the influence of weightlessness on molten metals and the solidification process. It was found that the absence of gravity-induced thermal convection and sedimentation modified the properties of the bulk melt. A metals melting experiment was conducted to study the behavior of metal melted by an electron beam and to evaluate the feasibility of joining metals in space. An exothermic brazing experiment investigated the spreading, mixing, and capillary flow of molten braze material. The containerless melting and solidification of small samples of several metals was studied in another experiment. A description is also given of a study of the directional solidification of solid solution alloys.

Snyder, R. S.↗
NASA NTRS1977

Microstructure and composition of InSb-GaSb ingots directionally solidified aboard Skylab

InSb-GaSb solid solution ingots prepared by directional solidification aboard Skylab and on earth consist of twins with (111) twin planes parallel to the direction of solidification and growth directions that lie along 211, 110, or 321 crystallographic directions. Significant fractions of several ingots prepared aboard Skylab were solidified from melts that were not in contact with container walls, resulting in convection driven by surface tension gradients in the melt and corresponding radially-symmetric composition variations in the ingot. In these regions, adjacent twins exhibit marked differences in indium content, indicating a substantial dependence of composition on crystallographic orientation.

Lefever, R. A.↗
NASA NTRS1977

Pressure sintering of Si3N4-Al2O3 /Sialon/

Essentially pore-free Sialon bodies were obtained by pressure sintering for three blends (mol ratios of 4:1, 2:3, and 3:2) of Si3N4 and Al2O3 powders under the conditions of 27.6 MN/sq m and a temperature of 1700 C for 2 h. These dense bodies consist mainly of a Sialon solid solution with a minor amount of a particular second phase. The higher the Al2O3 content (20 to 60 mol% range) in Sialon, the higher the densification rate. Fully dense bodies can be obtained at temperatures as low as 1500 C at 27.6 MN/sq m for 2 h with no second phase detectable by X-ray diffraction. A 100% dense body can be obtained by heating at 1700 C at 27.6 MN/sq m without a holding time.

Yeh, H. C.↗