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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Investigation of the reaction of 5Al-2.5Sn titanium with hydrogen at subzero temperature

An investigation of the effect of temperature on the surface hydriding reaction of 5Al-2.5Sn titanium exposed to hydrogen at 250 psig was made. The temperature range studied extended from 160 F to -160 F. Reaction conditions were controlled so as to expose a vacuum-cleaned, oxide-free alloy surface to an ultrapure hydrogen atmosphere. Reaction times up to 1458 hours were studied. The hydriding reaction was extremely sensitive to experimental variables and the reproducibility of reaction behavior was poor. However, it was demonstrated that the reaction proceeded quite rapidly at 160 F; as much as 1 mil surface hydriding being observed after exposure for 162 hours. The amount of hydriding appeared to decrease with decreasing temperature at 75 F, -36 F, and -76 F. No surface hydriding was detected either by vacuum fusion analysis or by metallographic examination after exposure for 1458 hours at -110 F or -160 F. Tensile properties were unaffected by surface hydriding of the severity developed in this program (up to 1 mil thick) as determined by slow strain rate testing of hydrided sheet tensile samples.

Williams, D. N.↗
NASA NTRS1972

Gaseous hydrogen-induced cracking of Ti-5Al-2.5Sn.

Study of the kinetics of hydrogen-induced cracking in the Ti-5Al-2.5Sn titanium alloy, which has a structure of acicular alpha platelets in a beta matrix. The crack-growth rate at low stress-intensity levels was found to be exponentially dependent on stress intensity but essentially independent of temperature. The crack-growth rate at intermediate stress-intensity levels was found to be independent of stress intensity but dependent on temperature in such a way that crack-growth rate was controlled by a thermally activated mechanism having an activation energy of 5500 cal/mole and varied as the square root of the hydrogen pressure. The crack-growth rate at stress-intensity levels very near the fracture toughness is presumed to be independent of environment. The results are interpreted to suggest that crack growth at high stress intensities is controlled by normal, bulk failure mechanisms such as void coalescence and the like. At intermediate stress-intensity levels the transport of hydrogen to some interaction site along the alpha-beta boundary is the rate-controlling mechanism. The crack-growth behavior at low stress intensities suggests that the hydrogen interacts at this site to produce a strain-induced hydride which, in turn, induces crack growth by restricting plastic flow at the crack tip.

Williams, D. P.↗
NASA NTRS1973

Neutron emission following muon capture in Ce-142, Ce-140, Ba-138, and Sn-120.

Branching ratios to excited nuclear states formed after muon capture have been measured with Ge(Li) detectors. The delayed gamma rays were observed in studies of muonic Ce-142, Ce-140, Ba-138, and Sn-120, using separated isotopes. The resulting isotopes formed indicate at least a 60% probability of neutron emission upon muon capture, with the most likely product resulting from single-neutron emission. No evidence for delayed proton emission with a probability higher than 2% was found. Using our more precise energies for the observed nuclear transitions, we present revised energy levels schemes for La-141, La-139, Cs-137, and In-119.

Lucas, G. R., Jr.↗
NASA NTRS1973

Combined effects of weld-induced residual stresses and flaws on the fracture strength of Ti-5Al-2.5Sn

The combined effects of weld-induced residual stresses and flaws on fracture strength were experimentally evaluated by testing Ti-5Al-2.5Sn surface flawed specimens at -320F (-195C) in liquid nitrogen. Flaws were located in weld metal with crack planes either parallel to or perpendicular to gas tungsten arc weld centerlines, and in base metal with the crack plane perpendicular to the rolling direction. Tests were conducted using two different flaw sizes to effect fracture stresses at two different levels including one level either at or near, and one level well below the tensile yield strength. Three different residual stress levels were generated, measured, and tested. Results were evaluated using modified linear elastic fracture mechanics theory.

Hall, L. R.↗
NASA NTRS1975

Superconducting properties of Pb-Sn-In alloys directionally solidified aboard Skylab

Superconducting alloys of Pb-Sn-In were directionally solidified in the absence of gravity-induced convection and segregation by processing in a near weightless condition aboard Skylab. Lead-rich and tin-rich lamellar structures were obtained with both high and low G/R (temperature gradient/solidification rate) samples processed at 0-g and at 1-g in a ground-based laboratory. Thinner, higher density lamellae were found with the 0-g specimens. Magnetization curves at 4.2 K showed hysteresis effects with large areas under the curves indicating magnetic flux pinning by the normal state tin-rich phase.

Anderson, W. T., Jr.↗
NASA NTRS1977

Laser operation by dissociation of metal complexes. II - New transitions in Cd, Fe, Ni, Se, Sn, Te, V, and Zn

The reported investigation is a continuation of a study conducted by Chou and Cool (1976). The experimental results discussed are partly related to laser transitions in Cd(I), Cd(II), and Zn(II). Laser transitions in Fe(I), Ni(I), Sn(I), Te(I), and V(I) are also considered along with the observation of a laser pulse with two peaks in connection with the study of laser transitions in Se(I). Experiments related to prospective visible laser operation in thallium at 6550 and 6714 are also discussed, giving attention to spontaneous emission measurements at 6550 and 5350 A, the effects of additive molecules, and laser cavity experiments at 6550 and 6714 A.

Chou, M. S.↗
NASA NTRS1977

Compositional variations in the undercooled Pb-Sn eutectic solidified at various acceleration levels

Ingots of Pb-61.9 Sn were undercooled and solidified under increasing gravity levels in order to investigate the effects of segregation. The onset of convective flow subsequent to the nucleation of lead is demonstrated. It is shown that when material system in the molten state contains constituents of varying densities, the combination of gravitational forces on the nucleating species and the amount of undercooling of the melt will determine the resultant segregation.

Johnston, M. H.↗
NASA NTRS1977

The influence of composition, annealing treatment, and texture on the fracture toughness of Ti-5Al-2.5Sn plate at cryogenic temperatures

The plane strain fracture toughness K sub Ic and conventional tensile properties of two commercially produced one-inch thick Ti-5Al-2.5Sn plates were determined at cryogenic temperatures. One plate was extra-low interstitial (ELI) grade, the other normal interstitial. Portions of each plate were mill annealed at 1088 K (1500 F) followed by either air cooling or furnace cooling. The tensile properties, flow curves, and K sub Ic of these plates were determined at 295 K (room temperature), 77 K (liquid nitrogen temperature), and 20 K (liquid hydrogen temperature).

Vanstone, R. H.↗
NASA NTRS1978

Optical emission from a fast shock wave - The remnants of Tycho's supernova and SN 1006

The faint optical filaments in Tycho's supernova remnant appear to be emission from a shock front moving at 5600 km/s. The intensity of the hydrogen lines, the absence of forbidden lines of heavy elements in the spectrum, and the width of the filaments are explained by a model in which a collisionless shock wave is moving into partially neutral gas. The presence of the neutral gas can be used to set an upper limit of approximately 5 x 10 to the 47th power ergs to the energy in ionizing radiation emitted by a Type I supernova. The patchy neutral gas is probably part of the warm neutral component of the interstellar medium. The existing information on the remnant of SN 1006 indicates that its emission is similar in nature to that from Tycho's remnant.

Chevalier, R. A.↗