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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The wetting characteristics and surface tension of some Ni-based alloys on yttria, hafnia, alumina, and zirconia substrates

The surface tension and wetting characteristics of four commercial Ni-based alloys (UD718, Waspaloy, UD720, and UD520), pure Ni, and three special alloys (Ni-20 percent Cr, Ni-20 percent Cr-1 percent Al, and Ni-20 percent Cr-4 percent Al) on various ceramic substrates (including alumina, zirconia, hafnia, and yttria) were investigated using sessile drop experiments. Most of the systems studied exhibited a nonwetting behavior. Wetting improved with holding time at a given temperature to the point that some systems, such as Ni-20Cr on alumina, Ni-20Cr-4Al on alumina and on yttria, became marginally wetting. Wetting characteristics were apparently related to constitutional undercooling, which in turn could be affected by the metal dissolving some of the substrate during measurements.

Kanetkar, C. S.↗
NASA NTRS1988

Phase relationships in Fe-Ni alloys at high pressures and temperatures

Diffusionless phase transformations in Fe-Ni alloys with up to 35 wt pct Ni were studied using resistance-heated diamond anvil cells and synchrotron radiation. At temperatures up to 600 C and pressures up to 25 GPa, Fe-35 percent Ni showed only the face-centered cubic (fcc) phase while Fe-25 percent Ni and Fe-10 percent Ni showed the body-centered cubic (bcc) and hexagonal close-packed (hcp) phases in addition to the fcc phase. The phase relationships of these solid phases are topologically similar to those of pure iron. The triple point becomes lower in temperature, and the slope (dT/dP) of the fcc/hcp boundary decreased as Ni-content increases in the alloys. From these results it is inferred that Fe-Ni alloys in the earth's inner core might exist as two phases, fcc and hcp. The existence of these two phases could have played an important role in the separation of the inner and outer core.

Huang, Eugene↗
NASA NTRSDate not supplied

X-Ray Diffraction Measurements of Residual Stress in a Cold Sprayed Ni Coating

X-ray diffraction (XRD) was used to investigate the residual stress in a cold sprayed Ni coating which failed to form a bimetallic joint with NASA HR-1. The objective was to apply pure Ni by cold spray as a diffusion barrier between the Ni-based alloy NASA HR-1 and the Cu-based GRCop-42 for a thrust cell assembly. After additive manufacturing of the GRCop-42 cylinder, the commercially pure Ni coating was cold sprayed onto the cylinder. It was intended to have NASA HR-1 applied directly onto the Ni coating by Directed Energy Deposition (DED), however the bond failed during the first layer of DED. Residual stress measurements were collected via the Sin²ψ method in three equally spaced locations on the top surface of the Ni coating in both as-cold sprayed and heat-treated conditions. The results revealed both compressive and tension stresses on the as-cold sprayed sample and compressive stresses in the heat-treated sample. The results were illuminated when plotted at their respective positions and with their respective orientation angles around a circle. This showed rotational symmetry in the residual stress measurements, which correlated to the processing method used during application of the Ni coating.

Laura Wilson↗
NASA NTRS1983

Ni-H2 batteries for communications satellites

Ni-H2 batteries are just now being put into service. All of the remaining INTELSAT V satellites (approximately 10), starting with the next to be launched in early 1983, will use Ni-H2 batteries. In addition, the next generation of INTELSAT VI satellites, and probably INTELSAT VII and VIII, will use Ni-H2 batteries. This means that international telecommunications satellites will use Ni-H2 batteries through the 1990's. It is projected that the lifetime of these batteries will be greater than 10 years at deep depth-of-discharge (DOD), and that the battery subsystem will no longer limit satellite lifetime or communications capability during eclipse periods. This paper discusses the advantages of the Ni-H2 battery, as compared with the Ni-Cd battery, for telecommunications satellites.

Dunlop, J. D.↗
NASA NTRS1989

Diffusion, phase equilibria and partitioning experiments in the Ni-Fe-Ru system

Results are presented on thin-film diffusion experiments designed to investigate phase equilibria in systems containing high concentrations of Pt-group elements, such as Ni-Fe-Ru-rich systems containing Pt, at temperatures of 1273, 1073, and 873 K. The rate of Ru diffusion in Ni was determined as a function of temperature, and, in addition, the degree of Pt and Ir partitioning between phases in a Ni-Fe-Ru-rich system and of V between phases in a Ni-Fe-O-rich system at 873 were determined. It was found that Pt preferentially partitions into the (gamma)Ni-Fe phase, whereas Ir prefers the (epsilon)Ru-Fe phase. V partitions strongly into Fe oxides relative to (gamma)Ni-Fe. These results have direct application to the origin and thermal history of the alloys rich in Pt-group elements in meteorites.

Blum, Joel D.↗
NASA NTRS2003

Observations of Glide and Decomposition of a<101> Dislocations at High Temperatures in Ni-Al Single Crystals Deformed along the Hard Orientation

Ni-44at.% Al and Ni-50at.% single crystals were tested in compression in the hard (001) orientations. The dislocation processes and deformation behavior were studied as a function of temperature, strain and strain rate. A slip transition in NiAl occurs from alpha(111) slip to non-alphaaaaaaaaaaa9111) slip at intermediate temperatures. In Ni-50at.% Al single crystal, only alpha(010) dislocations are observed above the slip transition temperature. In contrast, alpha(101)(101) glide has been observed to control deformation beyond the slip transition temperature in Ni-44at.%Al. alpha(101) dislocations are observed primarily along both (111) directions in the glide plane. High-resolution transmission electron microscopy observations show that the core of the alpha(101) dislocations along these directions is decomposed into two alpha(010) dislocations, separated by a distance of approximately 2nm. The temperature window of stability for these alpha(101) dislocations depends upon the strain rate. At a strain rate of 1.4 x 10(exp -4)/s, lpha(101) dislocations are observed between 800 and 1000K. Complete decomposition of a alpha(101) dislocations into alpha(010) dislocations occurs beyond 1000K, leading to alpha(010) climb as the deformation mode at higher temperature. At lower strain rates, decomposition of a alpha(101) dislocations has been observed to occur along the edge orientation at temperatures below 1000K. Embedded-atom method calculations and experimental results indicate that alpha(101) dislocation have a large Peieris stress at low temperature. Based on the present microstructural observations and a survey of the literature with respect to vacancy content and diffusion in NiAl, a model is proposed for alpha(101)(101) glide in Ni-44at.%Al, and for the observed yield strength versus temperature behavior of Ni-Al alloys at intermediate and high temperatures.

Srinivasan, R.↗
NASA NTRS1972

Diffusion of chromium and aluminum in Ni-20Cr and TDNiCr /Ni-20Cr-2ThO2/.

Diffusion coefficients have been measured for Cr51 in fine- and coarse-grained TDNiCr (Ni-20Cr-2ThO2) and in fine-grained Ni-20Cr in the temperature range from 1038 to 1200 C. Selective diffusivities have also been determined for specimens of these alloys which were aluminized to give an initial surface concentration of 5.8 wt % Al. Finally, diffusion coefficients for interdiffusion of aluminum in TDNiCr and Ni-20Cr have been obtained from electron probe microanalysis of the aluminized specimens. For a given grain size and temperature there is no difference in diffusivities for chromium diffusion in TDNiCr or Ni-20Cr. Diffusion coefficients increase with decreasing grain size for both alloys. Comparison of aluminum diffusion data obtained from electron microprobe profiles with radiotracer chromium diffusivities suggests that aluminum diffuses approximately three times faster than chromium in TDNiCr and Ni-20Cr.

Seltzer, M. S.↗
NASA NTRS1974

Metal-olivine associations and Ni-Co contents in two Apollo 12 mare basalts

Olivine crystals in mare basalts 12004,8 and 12022,12 are normally zoned with Cr-poor rims. The Ni content of rare 2- to 10-micron metal inclusions in olivine decreases markedly as Fe/Mg in their immediate olivine hosts increases. Each metal grain appears to have been enclosed by late olivine almost immediately after it crystallized. The fractionation trend for the olivine and metal contrasts with the subsolidus equilibration trend for pallasites. For the basalts, not even local equilibrium of Fe, Ni and Co at metal/olivine interfaces can be detected by microprobe. Ni and Co concentrations range from about 300 ppm in olivine cores to about 70 ppm in rims. The limits of detection, at 95% confidence, are 36 ppm (Ni) and 25 ppm (Co). The distribution of Ni and Co in olivine, like that of Mg and Cr, records the depletion of these elements in the melt.

Hewins, R. H.↗
NASA NTRS1978

A feasibility study of a diffusion barrier between Ni-Cr-Al coatings and nickel-based eutectic alloys

Coating systems have been proposed for potential use on eutectic alloy components in high-temperature gas turbine engines. In a study to prevent the deterioration of such systems by diffusion, a tungsten sheet 25 microns thick was placed between eutectic alloys and an Ni-Cr-Al layer. Layered test specimens were aged at 1100 C for as long as 500 h. Without the tungsten barrier the delta phase of the eutectic deteriorated by diffusion of niobium into the Ni-Cr-Al. Insertion of the tungsten barrier stopped the diffusion of niobium from the delta phase. Chromium diffusion from the Ni-Cr-Al into the gamma/gamma-prime phase of the eutectic was greatly reduced by the barrier. However, the barrier thickness decreased with time, and tungsten diffused into both the Ni-Cr-Al and the eutectic. When the delta platelets were aligned parallel rather than perpendicular to the Ni-Cr-Al layer, diffusion into the eutectic was reduced.

Young, S. G.↗
NASA NTRS1979

Deep-level transient spectroscopy studies of Ni- and Zn-diffused vapor-phase-epitaxy n-GaAs

The paper presents deep-level transient spectroscopy studies of Ni- and Zn-diffused vapor-phase epitaxy n-GaAs. Nickel diffused into VPE n-GaAs reduces the hole diffusion length L sub p from 4.3 to 1.1 microns. Deep-level transient spectroscopy was used to identify energy levels in Ni-diffused GaAs; the as-grown VPE GaAs contains traces of these levels and an electron trap. Ni diffusion reduces the concentration of this level by an amount that matches the increase in concentration of each of the two Ni-related levels. A technique for measuring minority-carrier capture cross sections was developed, which indicates that L sub p in Ni-diffused VPE n-GaAs is controlled by the E sub c - 0.39 eV defect level.

Partin, D. L.↗
NASA NTRS1983

Ni isotopic compositions in Allende and other meteorites

A new technique for high-precision isotopic analyses of Ni is applied to terrestrial samples, Allende inclusions, and materials from other meteorites. It is noted that most of the Allende inclusions analyzed here were previously reported to contain isotopically anomalous Ti. In contrast, the Ni isotopic abundances are found to be indistinguishable from normal within presently obtainable precision, with only one possible exception. The latter inclusion has been shown by others to contain a significantly fractionated magnesium isotopic pattern of 9 parts per thousand/amu. A normal Ni isotopic pattern has also been observed for the chromite/carbon fraction of an Allende acid residue, which is known to have heavy noble gases of highly anomalous isotopic composition. All other meteoritic samples analyzed reveal normal isotopic compositions of Ni; no evidence for effects from now extinct Fe-60 could be detected. Despite ubiquitous isotopic anomalies in Ti from normal Allende inclusions there is no signature of isotopic variations in Ni from the same samples.

Shimamura, T.↗
NASA NTRS1985

ac susceptibility of thermally annealed and neutron irradiated Cu-Ni alloys

Thermal annealing and high-flux neutron irradiation are used to vary the degree of short-range atomic order in Cu-Ni alloys of composition 40, 50, and 60 at. pct Ni. The magnetic state is measured by ac magnetic susceptibility measurements. It is shown that annealing at 350 C causes significant changes in the susceptibility of all the samples. In the 50 and 60 at. pct Ni samples, the transition is broadened and extended to higher temperatures, while the 40 at. pct Ni sample changes from a paramagnetic system to a weakly ferromagnetic system. The neutron irradiation, in contrast to the thermal treatment, causes the development of smaller size cluster formations. The irradiated 60 at. pct Ni sample exhibits no change in the shape of its susceptibility curve from that of the quenched sample, whereas, the 40 pct alloy is changed, by irradiation, from a paramagnetic system to a spin-glass system.

Catchings, R. M., III↗
NASA NTRS1985

Detection of Ni 2 lambda 7378 in six Seyfert galaxies

A line due to Ni 2 7378 in the Seyfert galaxies NGC 1068, 2110, 3227, 4151, 5506, and Arp 102 B was detected. The average Ni abundance is about 2 times solar, which is 5 times less than in the filaments of the Crab Nebula. This argues for nucleosynthetic processing in the latter. The Ni 2 line is spatially revolved in NGC 1068, and shows at least a factor of 4 enhancement in the Ni abundance away from the nucleus. The off-nuclear abundance of Ni in NGC 1068 approaches that of the Crab, which strongly suggests that type supernovae enriched the off-nuclear gas clouds.

Halpern, J. P.↗
NASA NTRS1985

Modulus measurements in ordered Co-Al, Fe-Al, and Ni-Al alloys

The composition and/or temperature dependence of the dynamic Young's modulus for the ordered B2 Co-Al, Fe-Al, and Ni-Al aluminides has been investigated using the piezoelectric ultrasonic composite oscillator technique (PUCOT). The modulus has been measured in the composition interval 48.49 to 52.58 at. pct Co, 50.87 to 60.2 at. pct Fe, and 49.22 to 55.95 at. pct Ni for Co-Al, Fe-Al, and Ni-Al, respectively. The measured values for Co-Al are in the temperature interval 300 to 1300 K, while those for the other systems are for ambient temperature only. The data points show that Co-Al is stiffer than Fe-Al, which is stiffer than Ni-Al. The data points for Fe-Al and Ni-Al are slightly higher than those reported in the literature.

Harmouche, M. R.↗
NASA NTRS1986

Detection of forbidden Ni II lambda 7378 in six Seyfert galaxies

A line due to Ni 2 7378 in the Seyfert galaxies NGC 1068, 2110, 3227, 4151, 5506, and Arp 102 B was detected. The average Ni abundance is about 2 times solar, which is 5 times less than in the filaments of the Crab Nebula. This argues for nucleosynthetic processing in the latter. The Ni 2 line is spatially resolved in NGC 1068, and shows at least a factor of 4 enhancement in the Ni abundance away from the nucleus. The off-nuclear abundance of Ni in NGC 1068 approaches that of the Crab, which strongly suggests that type supernovae enriched the off-nuclear gas clouds.

Halpern, J. P.↗
NASA NTRS1986

Experimental investigations of trace element fractionation in iron meteorites. III - Elemental partitioning in the system Fe-Ni-S-P

Measurements of solid metal/liquid metal trace element partition coefficients, which are used to interpret the crystallization history of magmatic iron meteorite groups differ greatly between different research groups, using different experimental techniques. Specifically, partition coefficients measured utilizing 'static' experiments which approach equilibrium cannot be reconciled with the results of 'dynamic' experiments which mimic fractional crystallization. We report new tests of our 'static' experimental technique and demonstrate that our methodology yields reliable equilibrium values for Ni, P and Ge partition coefficients. Partition coefficients in the Fe-Ni-S-P system are well matched by interpolation between the Fe-Ni-S and Fe-Ni-P subsystems. In contrast, the predictions of 'dynamic' experiments do not agree with our measurements and, consequently, the ability of 'dynamic' experiments to reproduce iron meteorite Ge vs. Ni fractionation trends successfully must be regarded as fortuitous.

Malvin, D. J.↗
NASA NTRS1988

Metal with anomalously low Ni and Ge concentrations in the Allan Hills A77081 winonaite

The Ge content of metal in the Allan Hills A77081 winonaite was determined by high-sensitivity electron microprobe analysis. By optimizing analytical conditions for Ge determination, a detection limit of about 75 ppm could be achieved. In A77081 some small kamacite grains contain less Ni and Ge and more Co than coarse-grained metal. These small grains are always associated with sulfide, raising the possibility that anomalous metal is related to eutectic melting. However, when published partition coefficients for Ni and Ge in the Fe-Ni-S system are used to model fractionation of these elements during eutectic melting, one finds that secondary metal should be enriched in Ni and depleted in Ge. Thus, the positive Ni-Ge correlation found in this study is the opposite of the expected trend. No explanation for this discrepancy has yet been found. Nonetheless, the existence of anomalous metal is an indication that A77081, and probably other winonaites as well, have undergone some fractionation. This supports the notion that the high-temperature history of winonaites is related to the formation of IAB iron meteorites, whose silicate inclusions are very similar to winonaites.

Kracher, Alfred↗
NASA NTRS1989

Predicting minimum Al concentrations for protective scale fromation on Ni-base alloys. I - Isothermal oxidation. II - Cyclic oxidation

Criteria proposed to predict the minimum bulk Al concentration for the formation of protective Al2O3 scales on Ni-based alloys during isothermal oxidation (two criteria proposed by Wagner, 1952 and 1959) and cyclic oxidation (the criteria proposed by Wahl, 1983, and Whittle, 1972/Wahl, 1983) were applied to Ni-Al and Ni-Cr-Al(Zr) alloys, respectively. It is shown that the first Wagner (1952) criterion underpredicted, by a factor of 3, the experimentally observed minimum Al concentration for the formation of an external Al2O3 scale on Ni-Al alloys at 1200 C; the second Wagner criterion predicted a transition from internal oxidation to continuous Al2O3 formation in good agreement with experimentally observed concentrations. It was also found that the two criteria for an Al2O3 scale formation during cyclic oxidation of Ni-Cr-Al(Zr) alloys were inadequate to predict the minimum Al concentration necessary for repeated formation of an Al2O3 scale, regardless of the adherence of the scale.

Nesbitt, James A.↗