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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Morphology of gold and copper ion-plated coatings

Copper and gold films (0.2 to 2 microns thick) were ion plated onto polished 304-stainless-steel, glass, mica surfaces. These coatings were examined by SEM for defects in their morphological growth. Three types of defects were distinguished: nodular growth, abnormal or runaway growth, and spits. The cause for each type of defect was investigated. Nodular growth is due to inherent substrate microdefects, abnormal or runaway growth is due to external surface inclusions, and spits are due to nonuniform evaporation (ejection of droplets). All these defects induce stresses and produce porosity in the coatings and thus weaken their mechanical properties. During surface rubbing, large nodules are pulled out, leaving vacancies in the coatings.

Spalvins, T.↗
NASA NTRS1977

Effects of silicon on the oxidation, hot-corrosion, and mechanical behavior of two cast nickel-base superalloys

Cast specimens of nickel-base superalloys 713C and Mar-M200 with nominal additions of 0, 0.5, and 1 wt% Si were evaluated for oxidation and corrosion resistance, tensile and stress-rupture properties, microstructure, and phase relations. Results are compared with those of an earlier study of the effects of Si in B-1900. Si had similar effects on all three superalloys. It improves oxidation resistance but the improvement in 713C and Mar-M200 was considerably less than in B-1900. Hot-corrosion resistance is also improved somewhat. Si is, however, detrimental to mechanical properties, in particular, rupture strength and tensile ductility. Si has two obvious microstructural effects. It increases the amount of gamma-prime precipitated in eutectic nodules and promotes a Mo(Ni,Si)2 Laves phase in the alloys containing Mo. These microstructural effects do not appear responsible for the degradation of mechanical properties, however.

Miner, R. V., Jr.↗
NASA NTRS1977

Regimes for the ocean, outer space, and weather

The allocation of resources among users of the oceans, outer space and the weather is discussed. Attention is given to the international management of maritime navigation, the control of fisheries, offshore oil and gas exploitation, mineral exploitation in the deep seabed (especially the mining of manganese nodules), and the regulation of oceanographic studies. The management of outer space is considered, with special reference to remote sensing by satellites, television broadcasting, the technical requirements of maritime satellites, and problems associated with satellite frequency and orbit allocation. Rainmaking and typhoon modification, as well as the distribution of weather modification capabilities in the world, are also mentioned. The United Nations, international agencies and tribunals, and multi- or bilateral agreements are some of the implements suggested for use in the regulation of the oceans, outer space and the weather.

Brown, S.↗
NASA NTRS1978

Analysis of ablation debris from natural and artificial iron meteorites

Iron and nickel-iron samples subjected to treatment by an arc-heated plasma of ionized air were used to model meteor ablation. The artificial ablation debris and fusion crusts were compared to the fusion crusts of three natural iron meteorities and to magnetic spherules from deep-sea manganese nodules. An outer discontinuous crust of magnetite and wuestite, followed by an unoxidized metallic zone, was observed in the artificially produced samples. Fractionation of less volatile elements was also noted.

Blanchard, M. B.↗
NASA NTRS1978

Tysnes Island - An unusual clast composed of solidified, immiscible, Fe-FeS and silicate melts

An inclusion found in the Tysnes Island gas-rich H4 chondrite is described. The clast consists of two distinct portions, separated by a smooth boundary; the portions are a tear-drop shaped Fe-FeS eutecticlike intergrowth (0.5 cm greatest dimension) and a silicate consisting primarily of olivine in glass. Nickel enrichment is found in the metal at the metal-sulfide boundaries and in nodules within the metal. It is thought that the portions separated from one another as immiscible liquids and that the modal composition of each portion agrees with the compositions predicted for a total melt of an H-group chondrite. The inclusion is discussed in terms of the process of metal-silicate fractionation suggested by Fodor and Keil (1976).

Wilkening, L. L.↗
NASA NTRS1979

Characterization of defect growth structure in ion plated films by scanning electron microscopy

Copper and gold films (0.2 to 2 microns) were ion plated onto polished 304-stainless-steel surfaces. These coatings were examined by scanning electron microscopy for coating growth defects. Three types of defects were distinguished: nodular growth, abnormal or runaway growth, and spits. The cause and origin for each type of defect was traced. Nodular growth is primarily due to inherent substrate microdefects, abnormal or runaway growth is due to external surface inclusions, and spits are due to nonuniform evaporation. All these defects have adverse effects on the coatings. They induce stresses and produce porosity in the coatings and thus weaken their mechanical properties. Friction and wear characteristics are affected by coating defects, since the large nodules are pulled out and additional wear debris is generated.

Spalvins, T.↗
NASA NTRS1981

Partitioning REE between minerals and coexisting melts during partial melting of a garnet lherzolite

Partition coefficients for Ce, Sm, and Tm between garnet, clinopyroxene, orthopyroxene, olivine, and melt are determined at 35 kbar for 2.3, 8, 20, and 37.7% melting of a garnet lherzolite nodule with chondritic REE abundances. Partition coefficients are found to increase as the degree of partial melting increases. From 2.3 to 8% melting, this increase is for the most part a consequence of non-Henry's law behavior of REE in minerals.

Harrison, W. J.↗
NASA NTRS1983

Evaluation of low-cost aluminum composites for aircraft engine structural applications

Panels of discontinuous SiC composites, with several aluminum matrices, were fabricated and evaluated. Modulus, yield strength and tensile strength results indicated that the properties of composites containing SiC whisker, nodule or particulate reinforcements were similar. The modulus of the composites was controlled by the volume percentage of the SiC reinforcement content, while the strength and ductility were controlled by both the reinforcement content and the matrix alloy. The feasibility of fabricating structural shapes by both wire performs and direct casting was demonstrated for Al2O3/Al composites. The feasibility of fabricating high performance composites into structural shapes by low pressure hot molding was demonstrated for B4C-coated B/Al composites.

Mcdanels, D. L.↗
NASA NTRS1984

Analysis of stress-strain, fracture and ductility behavior of aluminum matrix composites containing discontinuous silicon carbide reinforcement

Mechanical properties and stress-strain behavior for several types of commercially fabricated aluminum matrix composites, containing up to 40 vol % discontinuous SiC whisker, nodule, or particulate reinforcement were evaluated. It was found that the elastic modulus of the composites was isotropic, to be independent of type of reinforcement, and to be controlled solely by the volume percentage of SiC reinforcement present. The yield/tensile strengths and ductility were controlled primarily by the matrix alloy and temper condition. Ductility decreased with increasing reinforcement content, however, the fracture strains observed were higher than those reported in the literature for this type of composite. This increase in fracture strain is attributed to cleaner matrix powder and increased mechanical working during fabrication. Conventional aluminum and titanium structural alloys were compared and have shown that the properties of these low cost, lightweight composites have good potential for application to aerospace structures.

Mcdanels, D. L.↗
NASA NTRS1984

'Fluffy' Type A Ca-, Al-rich inclusions in the Allende meteorite

Inclusions called 'fluffy' Type A's or FTA's in the Allende meteorite are examined as possible candidates for relict vapor-solid condensate grains, remaining from the original solar nebula. Type A inclusions are characterized by abundant melilite and absence of primary anorthite and titaniferous pyroxene. Fluffy Type A's were probably loosely bound clumps of crystals drifting in the solar nebula, analogous to dustballs or snowflakes. Polished thin sections of all samples were studied optically and with a JEOL JSM-35 scanning electron microscope. It is reasonably clear that neither whole FTA's nor constituent nodules of the coarser grained ones were ever molten. Despite solid-state recrystallization which has affected these inclusions to varying degrees, the coarser grained material remaining in many of them is probably a relic of vapor-solid condensation in the solar nebula.

Macpherson, G. J.↗
NASA NTRS1984

Directional solidification of flake and nodular cast iron during KC-135 low-g maneuvers

Alloys solidified in a low-gravity environment can, due to the elimination of sedimentation and convection, form unique and often desirable microstructures. One method of studying the effects of low-gravity (low-g) on alloy solidification was the use of the NASA KC-135 aircraft flying repetitive low-g maneuvers. Each maneuver gives from 20 to 30 seconds of low-g which is between about 0.1 and 0.001 gravity. A directional solidification furnace was used to study the behavior of off eutectic composition case irons in a low-g environment. The solidification interface of hypereutectic flake and spheroidal graphite case irons was slowly advanced through a rod sample, 5 mm in diameter. Controlled solidification was continued through a number of aircraft parabolas. The known solidification rate of the sample was then correlated with accelerometer data to determine the gravity level during solidification for any location of the sample. The thermal gradient and solidification rate were controlled independently. Samples run on the KC-135 aircraft exhibited bands of coarser graphite or of larger nodules usually corresponding to the regions solidified under low-g. Samples containing high phosphorous (used in order to determine the eutectic cell) exhibited larger eutectic cells in the low-g zone, followed by a band of coarser graphite.

Curreri, P. A.↗
NASA NTRS1985

Processes and imagery of first-year fast sea ice during the melt season

In June and July 1982, a field program was conducted in the Canadian Arctic on Prince Patrick Island to study sea ice during the melt season with in situ measurements and microwave instrumentation operated near the surface and from aircraft. The objective of the program was to measure physical characteristics together with microwave backscatter and emission coefficients of sea ice during this major period of transition. The present paper is concerned with a study of both surface measurements and imagery of first-year fast ice during the melt season. The melting process observed in first-year fast ice was found to begin with the gradual reduction of the snow cover. For a two- to three-day period in this melt stage, a layer of superimposed ice nodules formed at the snow/ice interface as meltwater froze around ice and snow grains.

Holt, B.↗
NASA NTRS1985

Analysis of stress-strain, fracture, and ductility behavior of aluminum maxtrix composites containing discontinuous silicon carbide reinforcement

Mechanical properties and stress-strain behavior were evaluated for several types of commercially fabricated aluminum matrix composites, containing up to 40 vol pct discontinuous SiC whisker, nodule, or particulate reinforcement. The elastic modulus of the composites was found to be isotropic, to be independent of type of reinforcement, and to be controlled solely by the volume percentage of SiC reinforcement present. The yield/tensile strengths and ductility were controlled primarily by the matrix alloy and temper condition. Type and orientation of reinforcement had some effect on the strengths of composites, but only for those in which the whisker reinforcement was highly oriented. Ductility decreased with increasing reinforcement content; however, the fracture strains observed were higher than those reported in the literature for this type of composite. This increase in fracture strain was probably attributable to cleaner matrix powder, better mixing, and increased mechanical working during fabrication. Comparison of properties with conventional aluminum and titanium structural alloys showed that the properties of the low-cost, lightweight composites demonstrated very good potential for application to aerospace structures.

Mcdanels, D. L.↗
NASA NTRS1985

Impact melt products of chondritic material

Experimental data concerning impact melting processes in chondritic material are reviewed. It is shown that a large variety of objects in chondritic meteorites could have formed as a result of impact melting, including: shock veins; metal-troilite mixtures; metal and sulfide nodules; melt pockets and vugs. The type of object produced in an impact melt is related to the interaction of the shock waves with the particular target rock. It is suggested that various iron meteorites (including groups IAB, IIICD, and IIE, as well as several ungrouped irons) were formed from individual melt pools in chondritic regoliths. The small-scale structure of impact-melted metallic Fe,Ni and troilite in Weston (H chondrite regolith breccia) is illustrated in a photograph.

Rubin, A. E.↗
NASA NTRS1985

A refractory inclusion in the Kaba CV3 chondrite - Some implications for the origin of spinel-rich objects in chondrites

The first detailed petrographic and mineralogical study of a Ca, Al-rich inclusion (CAI) from the Kaba CV3 chondrite is reported. This 'fine-grained' CAI contains abundant small, rounded, rimmed, spinel-rich objects which have important features in common with the spinel-rich objects in other carbonaceous and ordinary chondrites. These nodules are interpreted as fractionated distillation residues of primitive dust. However, the available data do not unambiguously rule out a condensation origin for at least some of these objects. Finally, the preservation of distinct diopside-hedenbergite rims on the spinel-rich bodies and the small grain size of many minerals in the CAI matrix material both suggest that the CAI accreted cool and had a relatively cool thermal history in the Kaba parent body.

Fegley, B., Jr.↗
NASA NTRS1986

Properties of the Guin ungrouped iron meteorite - The origin of Guin and of group-IIE irons

The composition and structure of the Guin ungrouped iron meteorite inclusions have been investigated experimentally. The structural characteristics of polished and etched slabs of the meteorite were studied microscopically in reflected light. Modal abundances of troilite nodules and silicate inclusions were determined by weighing paper traces. The bulk composition of the silicate inclusions was calculated by combining modal phase abundances and mineral compositions. It is found that the largest silicate inclusion (2 x 4 cm) consists mostly of a shock-melted plagioclase-rich matrix surrounding large, partly melted augite grains. The oxygen isotopic composition of the inclusion is near that of LL chondrites. The inclusion is found to be similar in composition to selected melt pocket glasses in ordinary chondrites produced in situ by preferential melting of plagioclase rock due to shock compression. It is suggested that the Guin assemblage was formed by impact melting on a chondritic parent body. Silicate inclusions in IIE irons share many of the compositional and petrological characteristics of the Guin inclusions, indicating that IIE irons also formed by impact-melting of chondritic materials. Black and white photomicrographs of the silicate inclusions are provided.

Rubin, A. E.↗
NASA NTRS1985

Geochemical and petrological sampling and studies at the first moon base

Strategic sampling appropriate to the first-order lunar base can advance a variety of first-order lunar geochemical and petrological problems. Field observation and collection of samples would be done on the lunar surface, but detailed analysis would be done mainly in terrestrial laboratories. Among the most important areas of investigation for which field observations can be made and samples can be collected at the initial base are regolith studies, studies of mare and highlands stratigraphy, and a search for rare materials such as mantle nodules. Since the range of exploration may be limited to a radius of about 20 km from the first lunar base, locating the base near a mare-highlands boundary would enable the greatest latitude in addressing these problems.

Haskin, L. A.↗
NASA NTRS1986

Shuttle Imaging Radar - Physical controls on signal penetration and subsurface scattering in the Eastern Sahara

Interpretation of Shuttle Imaging Radar-A (SIR-A) images by McCauley et al. (1982) dramatically changed previous concepts of the role that fluvial processes have played over the past 10,000 to 30 million years in shaping this now extremely flat, featureless, and hyperarid landscape. In the present paper, the near-surface stratigraphy, the electrical properties of materials, and the types of radar interfaces found to be responsible for different classes of SIR-A tonal response are summarized. The dominant factors related to efficient microwave signal penetration into the sediment blanket include (1) favorable distribution of particle sizes, (2) extremely low moisture content and (3) reduced geometric scattering at the SIR-A frequency (1.3 GHz). The depth of signal penetration that results in a recorded backscatter, here called 'radar imaging depth', was documented in the field to be a maximum of 1.5 m, or 0.25 of the calculated 'skin depth', for the sediment blanket. Radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials. Diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops. Calcium carbonate nodules and rhizoliths concentrated in sandy alluvium of Pleistocene age south of Safsaf oasis in south Egypt provide effective contrast in premittivity and thus act as volume scatterers that enhance SIR-A portrayal of younger inset stream channels.

Schaber, G. G.↗