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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Application of surface analysis to solve problems of wear

Results are presented for the use of surface analytical tools including field ion microscopy, Auger emission spectroscopy analysis (AES), cylindrical mirror Auger analysis and X-ray photoelectron spectroscopy (XPS). Data from the field ion microscope reveal adhesive transfer (wear) at the atomic level with the formation of surface compounds not found in the bulk, and AES reveals that this transfer will occur even in the presence of surface oxides. Both AES and XPS reveal that in abrasive wear with silicon carbide and diamond contacting the transition metals, the surface and the abrasive undergo a chemical or structural change which effects wear. With silicon carbide, silicon volatilizes leaving behind a pseudo-graphitic surface and the surface of diamond is observed to graphitize.

Buckley, D. H.↗
NASA NTRS1982

Microstructural effects on the room and elevated temperature low cycle fatigue behavior of Waspaloy

Longitudinal specimens of Waspaloy containing either coarse grains with small gamma or fine grains with large gamma were tested in air at a frequency of 0.33 Hz or 0.50 Hz. The coarse grained structures exhibited planar slip on (III) planes and precipitate shearing at all temperatures. Cracks initiated by a Stage 1 mechanism and propagated by a striation forming mechanism. At 700 C and 800 C, cleavage and intergranular cracking were observed. Testing at 500 C, 700 C, and 800 C caused precipitation of grain boundary carbides. At 700 C, carbides precipitated on slip bands. The fine grained structures exhibited planar slip on (111) planes. Dislocations looped the large gamma precipitates. This structure led to stress saturation and propagation was observed. Increasing temperatures resulted in increased specimen oxidation for both heat treatments. Slip band and grain boundary oxidation were observed. At 800 C, oxidized grain boundaries were cracked by intersecting slip bands which resulted in intergranular failure. The fine specimens had crack initiation later in the fatigue life, but with more rapid propagation crack propagation.

Lerch, B. A.↗
NASA NTRS1982

Refractory coatings and method of producing the same

The adhesion, friction, and wear properties of sputtered refractory coatings on substrates of materials that form stable nitrides is improved by placing each substrate directly below a titanium carbide target of a commercial radiofrequency diode apparatus in a vacuum chamber. Nitrogen is bled into the system through a nozzle resulting in a small partial pressure of about 0.5% to 2.5% during the first two minutes of deposition. The flow of nitrogen is then stopped, and the sputtering ambient is reduced to pure argon through a nozzle without interrupting the sputtering process. When nitrogen is deliberately introduced during the crucial interface formation, some of the titanium at the interface reacts to form titanium nitride while the metal of the substrate also forms the nitride. These two nitrides atomically mixed together in the interfacial region act to more strongly bond the growing titanium carbide coating as it forms on the substrate.

Brainard, W. A.↗
NASA NTRS1981

Non-noble catalysts and catalyst supports for phosphoric acid fuel cells

Tungsten carbide, which is active for hydrogen oxidation, is CO tolerant and has a hexagonal structure is discussed. Titanium carbide is inactive and has a cubic structure. Four different samples of the cubic alloys W sub x-1Ti sub XC sub 1-y were found to be active and CO tolerant. When the activities of these cubic alloys are weighted by the reciprocal of the square to those of highly forms of WC. They offer important insight into the nature of the active sites on W-C anode catalysts for use in phosphoric acid fuel cells.

Mcalister, A. J.↗
NASA NTRS1982

Occurrence of spherical ceramic debris in indentation and sliding contact

Indenting experiments were conducted with the silicon carbide (0001) surface in contact with a spherical diamond indenter in air. Sliding friction experiments were also conducted with silicon carbide in contact with iron and iron-based binary alloys at room temperature and 800 C. Fracture pits with a spherical particle and spherical wear debris were observed as a result of indenting and sliding. Spherical debris may be produced by a mechanism that involves a spherical-shaped fracture along the circular or spherical stress trajectories under the inelastic deformation zone.

Miyoshi, K.↗
NASA NTRS1984

SixNyCz Fibers for Safer Composites

Silicon nitride/silicon carbide fibers prepared by pyrolysis of polycarbosilazanes proposed substitute for carbon fibers. Silicon nitride/silicon carbide fibers tested pyrolyzed from polycarbosilazanes prepared from tris(N-methylamino) methylsilane. Polycarbosilazane resin drawn into fiber from melt, treated and pyrolyzed. Pyrolyzed fibers are shiny black. Tests show new fibers have physical properties comparable to graphite but with lower conductivity.

Ledbetter, F. E., III↗
NASA NTRS1982

The effects of Ni, Mo, Ti and Si on the mechanical properties of Cr free Mn steel (Fe-25Mn-5Al-2C)

The FeMnAlC alloys may hold potential as Cr-free replacements for high strategic material iron base superalloys, but little is known about their intermediate temperature (650 C to 870 C) mechanical properties. The effects of alloying elements on the mechanical properties of model FeMnAlC alloys were studied. Results showed that modified FeMnAlC alloys had promising short term, intermediate temperature properties but had relatively poor stress rupture lives at 172 MPa and 788 C. Room temperature and 788 C tensile strength of FeMnAlC alloys were better than common cast stainless steels. Changes in room temperature tensile and 788 C tensile strength and ductility, and 788 C stress rupture life were correlated with changes in Ni, Mo, Ti, and Si levels due to alloying effects on interstitial carbon levels and carbide morphology. Fe-25Mn-5Al-2C had a very poor stress rupture life at 172 MPa and 788 C. Addition of carbide-forming elements improved the stress rupture life.

Schuon, S. R.↗
NASA NTRS1982

Part 1: Silicon ingot casting. Heat Exchanger Method (HEM)

Directional solidification by the Heat Exchanger Method (HEM) is a viable approach for directional solidification of silicon ingots used for terrestrial solar cell applications. Some of the significant advances made during this phase of the program were: ingot size, 34 cm x 34 cm x 17 cm - 45 kg, usable material yield - 90%, solar cell efficiency averaged over the whole ingot - 85% of control CZ (35 kg ingot), very uniform resistivity over the boule, and cycle time for 36 kg ingots - 56 hours. Some of the problems encountered were growth rate decrease with increased ingot height, silicon carbide precipitates, and high dislocation density in HEM material. The silicon carbide is attributed to backstreaming of oil vapors from the vacuum pump; the high dislocation density is associated with the thermal history of the boule.

Source record↗
NASA NTRS1984

Calculation of vaporization rates assuming various rate determining steps: Application to the resistojet

The various steps that could control the vaporization rate of a material are discussed. These steps include the actual vaporization, flow rate of matrix gas, chemical reaction, gas diffusion, and solid state diffusion. The applicable equations have been collected from diverse appropriate sources, and their use is explained. Rate equations are derived for conditions where more than one step is rate controlling. Calculations are made for two model materials: rhenium which vaporizes congruently, and tantalum carbide which vaporizes incongruently. The case of vaporization under thermal gradient conditions is also treated. The existence of a thermal gradient in the resistojet means that the vaporization rate of a material may be only one thousandth of that predicted under isothermal conditions. Calculations show that rhenium might have a 100,000 hr lifetime at temperature in a 2500 C resistojet. Tantalum carbide would have a life of only 660 sec under similar conditions.

May, C. E.↗
NASA NTRS1985

Improving Emittance of High-Temperature Insulating Tile

Simple addition to ceramic insulating tiles provides backup properties that minimize transfer of heat through tiles when their surfaces become damaged. Addition of 3 percent by weight of 320- or 600-grit silicon carbide powder to ceramic during production results in impregnated tile material that resists overheating. Silicon carbide increases emittance and decreases transmittance of ceramic.

Gzowski, E. R.↗
NASA NTRS1986

Drilling Holes in Graphite/Epoxy Composites

Slurry of silicon carbide powder in water fed onto bit while drilling. Slurry contains about 60 percent silicon carbide by weight. Slurry recirculated by low-power pump. With slurry, dull tools cut as fast as, or faster than, sharp ones. Holes drilled rapidly and efficiently regardless of ply orientation; whether unidirectional, quasi-isotropic symmetrical, or cross-ply.

Daniels, J. G.↗
NASA NTRS1984

Silicon nitride sintered body

The sintering of silicon carbide and it production are described. The method of production is by calcination in which molding is followed by sintering without compression. The invention improves the composition of the silicon carbide ceramic. Six examples of the invention are illustrated and discussed.

Suzuki, K.↗
NASA NTRS1985

The effect of tantalum on the structure/properties of two polycrystalline nickel-base superalloys: B-1900 + Hf MAR-M247

The microstructure, phase compositions, and phase fractions were studied in conventionally cast B-1900 + Hf and both conventionally cast and directionally solidified MAR-M247 as a function of tantalum concentration. The hot tensile and creep rupture properties of the solutionized and aged MAR-M247-type alloys were also determined as a function of tantalum level. The effects of tantalum on the microstructure and phase compositions of B-1900 + Hf and MAR-M247 (conventionally cast and directionally solidified) were found to be very similar. The addition of tantalum to the as cast and heat treated alloys was shown to cause the partial replacement of the Hf in the MC carbides by Ta, although the degree of replacement was decreased by the solutionizing and aging heat treatment. The gamma prime and minor phase fractions (primarily MC type carbides) both increased approximately linearly with tantalum concentration. The gamma prime phase compositions were relatively insensitive to tantalum variations with the exception of the tantalum and/or hafnium levels. Bulk tantalum additions increased the tantalum, chromium, and cobalt levels of the gamma phase in both alloy series. The increase in the concentrations of the latter two elements in the gamma phase was a result of the decrease in the gamma phase fraction with increasing bulk tantalum concentration and constant gamma/gamma prime partitioning ratio. Tantalum additions increased the yield stress and ultimate tensile strength of the directionally solidified MAR-M247 type alloys and had no significant effect on ductility.

Janowski, G. M.↗
NASA NTRS1984

Breakway friction and dynamic friction/wear measurements of various ceramic materials from 25 C (75 F) to 650 C (1200 F)

This report describes the results of a program designed to evaluate the breakaway friction and dynamic friction/wear characteristics of materials having potential for use as load bearing components in a high-performance high-temperature heavy duty diesel engine. Ten candidate materials were selected, six of which were evaluated under all possible material combinations as both stationary as well as moving breakaway specimens. The remaining materials were evaluated either in the static mode against themselves and all other materials, or against themselves only. Experiments were performed at five temperatures up to 650 C (1200 F) and unit pressures of 700 kPa (100 lb/sq in.), 3500 kPa (500 lb/sq in.), and 7000 kPa (1000 lb/sq in.). Experimental results indicate that under dynamic conditions, four of the ten materials exhibited good to excellent friction/wear characteristics in various material combinations. These materials were: titanium carbide, silicon nitride, silicon carbide (reaction sintered), and Refel (SiC).

Boes, D. J.↗
NASA NTRS1985

Increased voltage photovoltaic cell

A photovoltaic cell, such as a solar cell, is provided which has a higher output voltage than prior cells. The improved cell includes a substrate of doped silicon, a first layer of silicon disposed on the substrate and having opposite doping, and a second layer of silicon carbide disposed on the first layer. The silicon carbide preferably has the same type of doping as the first layer.

Ross, B.↗
NASA NTRS1985

Laboratory infrared spectra of predicted condensates in carbon-rich stars

Laboratory spectra and mass absorption coefficients of MgS, CaS, FeS, SiS2, FeS2, Fe3C, and a commercial iron carbide are presented over the wavelength range 125-15 microns. These spectra confirm that MgS is the most likely source of the unidentified 30-micron emission in carbon-rich sources and that FeS, Fe3C, and 'iron carbide' cannot be responsible for this feature although they could contribute to the continuum in this region. CaS and FeS2 may contribute to the 30-micron feature; however, both higher resolution and higher precision astronomical observations are needed before their presence can be established. SiS2 has a peak near 22 microns and therefore cannot be a significant component of the dust in such regions.

Nuth, J. A.↗
NASA NTRS1984

Effects of cobalt on the hot workability of nickel-base superalloys

The effect of cobalt on the workability of nickel-base superalloys is examined with reference to experimental results for four heats of alloys based on the Nimonic 115 composition with varying amounts of nickel substituted for the nominal 14 percent cobalt. It is shown that Co lowers the gamma-prime solvus, which in turn lowers the Cr23C6 carbide solvus. It is further shown that these solvus temperatures bracket the hot working range for the alloys. However, thermomechanical processing modifications reflecting the effect of Co on the gamma-prime and carbide solvi are shown to restore the workability and the properties of alloys with little or no cobalt.

Jarrett, R. N.↗
NASA NTRS1985

Superalloy microstructural variations induced by gravity level during directional solidification

The Ni-base superalloy MAR-M246 (Hf) was directionally solidified during low gravity maneuvers aboard a NASA KC-135 aircraft. Gravity force variations during this process yielded a concomitant variation in microstructure and microsegregation. Secondary dendrite arm spacings are noted to be larger in the low-g portion; this, in turn, decreases the extent of interdendritic segregation. The amount of Hf in both the carbides and interdendritic eutectic increases as the gravity force diminishes. Fewer carbides are present in the low-g regions.

Johnston, M. H.↗