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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Composite thin-foil bandpass filter for EUV astronomy Titanium-antimony-titanium

Thin metallic foils of antimony and titanium have been investigated in an attempt to develop an EUV filter with a bandpass from 350 to 550 A. A composite filter has been developed composed of antimony sandwiched between two titanium foils. The transmissions of sample composite foils and of pure titanium foils from 130 to 1216 A are presented. The absorption coefficients of anatimony and titanium and the effect of titanium oxide on the transmission are derived. The composite filter has been found to be quite stable and mechanically rugged. Among other uses, the filter shows substantial promise for EUV astronomy.

Jelinsky, P.↗
NASA NTRS1984

Effects of silver and group 2 fluorides addition to plasma sprayed chromium carbide high temperature solid lubricant for foil gas bearing to 650 deg C

A new self-lubricating coating composition of nickel aluminide-bonded chromium carbide formulated with silver and Group II fluorides was developed in a research program on high temperature solid lubricants. One of the proposed applications for this new coating composition is as a wide temperature spectrum solid lubricant for complaint foil gas bearings. Friction and wear properties were obtained using a foil gas bearing start/stop apparatus at temperatures from 25 to 650 C. The journals were Inconel 718. Some were coated with the plasma sprayed experimental coating, others with unmodified nickel aluminide/chromium carbide as a baseline for comparison. The addtitional components were provided to assist in achieving low friction over the temperature range of interest. Uncoated, preoxidized Inconel X-750 foil bearings were operated against these surfaces. The foils were subjected to repeated start/stop cycles under a 14-kPa (2-psi) bearing unit loading. Sliding contact occurred during lift-off and coastdown at surface velocities less than 6 m/s (3000 rpm). Testing continued until 9000 start/stop cycles were accumulated or until a rise in starting torque indicated the journal/bearing had failed. Comparison in coating performance as well as discussions of their properties and methods of application are given.

Wagner, R. C.↗
NASA NTRS1987

Composition optimization of chromium carbide based solid lubricant coatings for foil gas bearings at temperatures to 650 C

A test program to determine the optimum composition of chromium carbide based solid lubricant coatings for compliant gas bearings is described. The friction and wear properties of the coatings are evaluated using a foil gas bearing test apparatus. The various coatings were prepared by powder blending, then plasma sprayed onto Inconel 718 test journals and diamond ground to the desired coating thickness and surface finish. The journals were operated against preoxidized nickel-chromium alloy foils. The test bearings were subjected to repeated start/stop cycles under a 14 kPa (2 psi) bearing unit load. The bearings were tested for 9000 start/stop cycles or until the specimen wear reached a predetermined failure level. In general, the addition of silver and eutectic to the chromium carbide base stock significantly reduced foil wear and increased journal coating wear. The optimum coating composition, PS212 (70 wt% metal bonded Cr3C2, 15 wt% Ag, 15% BaF2/CaF2 eutectic), reduced foil wear by a factor of two and displayed coating wear well within acceptable limits. The load capacity of the bearing using the plasma-sprayed coating prior to and after a run-in period was ascertained and compared to polished Inconel 718 specimens.

Dellacorte, Christopher↗
NASA NTRS1986

Effects of silver and group II fluoride solid lubricant additions to plasma-sprayed chromium carbide coatings for foil gas bearings to 650 C

A new self-lubricating coating composition of nickel aluminide-bonded chromium carbide formulated with silver and Group II fluorides was developed in a research program on high temperature solid lubricants. One of the proposed applications for this new coating composition is as a wide temperature spectrum solid lubricant for complaint foil gas bearings. Friction and wear properties were obtained using a foil gas bearing start-stop apparatus at temperatures from 25 to 650 C. The journals were Inconel 748. Some were coated with the plasma sprayed experimental coating, others with unmodified nickel aluminide/chromium carbide as a baseline for comparison. The additional components were provided to assist in achieving low friction over the temperature range of interest. Uncoated, preoxidized Inconel X-750 foil bearings were operated against these surfaces. The foils were subjected to repeated start/stop cycles under a 14-kPa (2-Psi) bearing unit loading. Sliding contact occurred during lift-off and coastdown at surface velocities less than 6 m/s (3000 rPm). Testing continued until 9000 start/stop cycles were accumulated or until a rise in starting torque indicated the journal/bearing had failed. Comparison in coating performance as well as discussions of their properties and methods of application are given.

Wagner, R. C.↗
NASA NTRS1988

Tribological composition optimization of chromium-carbide-based solid lubricant coatings for foil gas bearings at temperatures to 650 C

The determination of the tribilogically optimum composition of chromium-carbide-based solid lubricant coatings using a foil gas bearing test apparatus is described. The coatings contain a wear resistant chromium carbide `base stock' with the lubricant additives silver and BaF2-CaF2 eutectic. The coating composition is optimized for air-lubricated foil gas bearings at temperatures ranging from 25 to 650 C. The various compositions were prepared by powder blending, then plasma sprayed onto Inconel 718 test journals and diamond ground to the desired coating thickness and surface finish. The journals were operated against preoxidized Ni-Cr alloy foils, and the test bearings were subjected to repeated start-stop cycles under a bearing unit of 14 kPa. Sliding contact between the coated journal and the smooth foil occurs during bearing start-up before lift-off or hydrodynamic lubrication by the air film and during bearing coast-down. The bearings were tested for 9000 start-stop cycles or until specimen reached a predetermined failure level.

Dellacorte, Christopher↗
NASA NTRS1990

Charge exchange of low-energy ions in thin carbon foils

In order to calibrate a time-of-flight mass spectrometer which is to be flown in the solar wind, the charge exchange properties of low-energy ions in thin carbon foils have been investigated. Incident ions of He, C, N, O, Ne, and Ar with energies in the range 0.5-2 keV/nucleon have been used to measure charge-state distribution, residual energy, and angular distribution after transmission through thin (1-6 microgram/sq cm) carbon foils. Within such foils, an equilibrium between ionization and recombination of the projectile is rapidly established, and, consequently, the charge state of the emerging particle depends essentially on its residual velocity. A comparison of the charge exchange properties of Ne-22 with Ne-20 demonstrates that indeed the velocity (and not the energy) of the emerging particle determines its final charge. A comparison of properties of different elements provides an indication of an electron shell effect. Predictions for the energy loss of ions within the carbon foils made with the TRIM code are in good agreement with the experimental results presented in this paper.

Buergi, Alfred↗
NASA NTRS1993

Foil bearing performance in liquid nitrogen and liquid oxygen

Space transfer vehicles and other power and propulsion systems require long-life turbopumps. Rolling-element bearings used in current turbopumps do not have sufficient life for these applications. Process fluid foil bearings have established long life, with exceptional reliability, over a wide range of temperatures and fluids in many high-speed turbomachinery applications. However, actual data on bearing performance in cryogenic fluids has been minimal. The National Aeronautics and Space Administration (NASA) and AlliedSignal Aerospace Systems and Equipment (ASE) have attempted to characterize the leaf-type compliant foil bearing in oxygen and nitrogen. The work performed under a joint internal research and development program between Marshall Space Flight Center (MSFC) and ASE demonstrated that the foil bearing has load capacities of at least 266 psi in liquid oxygen and 352 psi in liquid nitrogen. In addition, the bearing demonstrated a direct damping coefficient of 40 to 50 lb-sec/in. with a damping ratio of .7 to 1.4 in. liquid nitrogen using a bearing sized for upper-stage turbopumps. With the results from this testing and the years of successful use in air cycle machines and other applications, leaf-type compliant foil bearings are ready for testing in liquid oxygen turbopumps.

Genge, Gary G.↗
NASA NTRS1993

Cryogenic foil bearing turbopumps

Cryogenic foil bearing turbopumps offer high reliability and low cost. The fundamental cryogenic foil bearing technology has been validated in both liquid hydrogen and liquid oxygen. High load capacity, excellent rotor dynamics, and negligible bearing wear after over 100 starts and stops, and over many hours of testing, were observed in both fluids. An experimental liquid hydrogen foil bearing turbopump was also successfully demonstrated. The results indicate excellent stability, high reliability, wide throttle-ability, low bearing cooling flow, and two-phase bearing operability. A liquid oxygen foil bearing turbopump has been built and is being tested at NASA MSFC.

Gu, Alston L.↗
NASA NTRS1995

Foil Patches Seal Small Vacuum Leaks

Report discloses technique to patch holes in nickel-alloy rocket-engine nozzle parts prior to vacuum brazing. Technique involves lightly spot-welding nickel foil 0.002 in. thick over hole patched, then spot-welding corrosion-resistant steel foil of same thickness over nickel foil. Once patches subject to pressure and temperature of vacuum brazing, nickel foil diffuses to bond with nickel-alloy nozzle, making vacuum-tight seal.

Spiegel, Kirk W.↗
NASA NTRS1996

Large deflection analysis of a tension-foil bearing

The rolling element bearings (REB's) which support many turbomachinery rotors offer high load capacity, low power requirements, and durability. Two disadvantages of REB's are as follows: rolling or sliding contact within the bearing has life-limiting consequences; and REB's provide essentially no damping. The REB's in the Space Shuttle Main Engine (SSME) turbopumps must sustain high static and dynamic loads, at high speeds, with a cryogenic fluid as lubricant and coolant. The pump end ball bearings limit the life of the SSME high pressure oxygen turbopump (HPOTP). Compliant foil bearing (CFB) manufacturers have proposed replacing turbopump REB's with CFB's. CFB's work well in aircraft air cycle machines, auxiliary power units, and refrigeration compressors. In a CFB, the rotor only contacts the foil support structure during start up and shut down. CFB damping is higher than REB damping. However, the load capacity of the CFB is low, compared to a REB. Furthermore, little stiffness and damping data exist for the CFB. A rotordynamic analysis for turbomachinery critical speeds and stability requires the input of bearing stiffness and damping coefficients. The two basic types of CFB are the tension-dominated bearing and the bending-dominated bearing. Many investigators have analyzed and measured characteristics of tension-dominated foil bearings, which are applied principally in magnetic tape recording. The bending-dominated CFB is used more in rotating machinery. Recently, a new tension-foil bearing configuration has been proposed for turbomachinery applications.

Elrod, David A.↗
NASA NTRS1998

Evaluation of Advanced Solid Lubricant Coatings for Foil Air Bearings Operating at 25 and 500 C

The tribological properties of one chrome oxide and one chrome carbide based solid lubricant coating were evaluated in a partial-arc foil bearing at 25 and 500 C. Start/stop bearing operation up to 20,000 cycles were run under 10 kPa (1.5 psi) static deadweight load. Bearing friction (torque) was measured during the test. Specimen wear and SEM/EDS surface analyses were conducted after testing to understand and elucidate the tribological characteristics observed. The chrome oxide coating which contains both (Ag) and (BaF2/CaF2) for low and high temperature lubrication, exhibited low friction in sliding against Al2O3 coated foils at 25 and 500 C. The chrome carbide coating, which lacked a low temperature lubricant but contained BaF2/CaF2 as a high temperature lubricant, exhibited high friction at 25 C and low friction at 500 C against both bare and Al2O3 coated superalloy foil surfaces. Post test surface analyses suggest that improved tribological performance is exhibited when a lubricant film from the coating transfers to the foil surface.

DellaCorte, Christopher↗
NASA NTRS2000

Scattering/Transmission of Energetic H+,He+, and O+ Through a Thin Composite Si/Lexan/C Foil

The need for a thin foil to serve both as an extreme ultraviolet (EUV) radiation attenuator and as a secondary electron generator for time-of-flight (TOF) instruments and energetic neutral atom (ENA) imagers has led us to test the scattering and transmission characteristics of a layered foil of nominal aerial thicknesses of 5 micrograms (raised dot) per square centimeter Si, 4 micrograms (raised dot) per square centimeter Lexan (C16H14O3), and 1 microgram (raised dot) per square centimeter C. We report the scattering/transmission results of subjecting this foil to H(+), He(+), and O(+) beams of energies less than or equal to 120 keV. The scattering of these particles, defined by the half-angular-width at half-maximum (HWHM), decreases with increasing energy and found to be 10 degrees for 10 keV H(+), 22 keV for He(+), and 100 keV for O(+). The 50% transmission threshold for these particles was found to be 3.9 keV for H(+), 8.6 keV for He(+), and 49.5 keV for O(+). Computer simulations of H(+)-foil interactions using SRIM96 agree well with the H(+) data, while yielding less scattering and higher transmission than indicated by the O(+) data.

Adrian, M. L.↗
NASA NTRS2000

Scattering/Transmission of Energetic H(sup +), He(sup +), and O(sup +) Through a Thin Composite Si/Lexan/C Foil

The need for a thin foil to serve both as an extreme ultraviolet (EUV) radiation attenuator and as a secondary electron generator for time-of-flight (TOF) instruments and energetic neutral atom (ENA) imagers has led us to test the scattering and transmission characteristics of a layered foil of nominal aerial thicknesses of 5 microns/sq cm Si, 4 microns/sq.cm Lexan ((C16)H(14)O3), and 1 micron/sq.cm C. We report the scattering and transmission results of subjecting this foil to H(sup +), He(sup +), and O(sup +) beams of energy less than 120 keV. The scattering of these particles, defined by the half-angular-width at half-maximum (HWHM), decreases with increasing energy and is found to be 10 deg for 10 keV H(sup +), 22 keV for He(sup +), and 100 keV for O(sup +). The 50% transmission threshold for these particles was found to be 3.9 keV for H(sup +), 8.6 keV for He(sup +), and 49.5 keV for O(sup +). Additionally, ion transmission shows evidence of resonance scattering from a rectangular potential independent of incident ion mass. Particularly evident is a local transmission minimum at 70 keV possessing a Gaussian-width of 20 keV. For incident energies below 50 keV, computer simulations of H+-foil interactions using SRIM96 agree well with the H(sup +) data, while yielding less scattering and higher transmission than indicated by the O(sup +) data.

Adrian, M. L.↗
NASA NTRS2002

The Role of Radial Clearance on the Performance of Foil Air Bearings

Load capacity tests were conducted to determine how radial clearance variations affect the load capacity coefficient of foil air bearings. Two Generation III foil air bearings with the same design but possessing different initial radial clearances were tested at room temperature against an as-ground PS304 coated journal operating at 30,000 rpm. Increases in radial clearance were accomplished by reducing the journal's outside diameter via an in-place grinding system. From each load capacity test the bearing load capacity coefficient was calculated from the rule-of-thumb (ROT) model developed for foil air bearings. The test results indicate that, in terms of the load capacity coefficient, radial clearance has a direct impact on the performance of the foil air bearing. Each test bearing exhibited an optimum radial clearance that resulted in a maximum load capacity coefficient. Relative to this optimum value are two separate operating regimes that are governed by different modes of failure. Bearings operating with radial clearances less than the optimum exhibit load capacity coefficients that are a strong function of radial clearance and are prone to a thermal runaway failure mechanism and bearing seizure. Conversely, a bearing operating with a radial clearance twice the optimum suffered only a 20 percent decline in its maximum load capacity coefficient and did not experience any thermal management problems. However, it is unknown to what degree these changes in radial clearance had on other performance parameters, such as the stiffness and damping properties of the bearings.

Radil, Kevin↗
NASA NTRS2003

Compliant Foil Seal Investigations

NASA Glenn Research Center has been working with Mohawk Innovative Technology, Inc. (MiTi) to develop a Compliant Foil Seal for use in gas turbine engines. MiTi was awarded phase I and phase II SBIR contracts to analyze, develop, and test foil seals. As part of the Phase II contract, MiTi delivered an 8.5 inch diameter foil seal to NASA GRC for testing. Today I will be presenting some results of testing the 8.5 inch foil seal at NASA.

Proctor, Margaret↗
NASA NTRS2004

Consideration of Alternate Working Fluid Properties in Gas Lubricated Foil Journal Bearings

The Oil-Free Turbomachinery Program at the NASA Glenn Research center is committed to, revolutionary improvements in performance, efficiency and reliability of turbomachinery propulsion systems. One of the key breakthroughs by which this goal is being achieved is the maturation of air lubricated foil bearing technology. Through experimental testing, foil bearings have demonstrated a variety of exceptional qualities that show them to have an important role in the future of rotordynamic lubrication. Most of the work done with foil bearings thus far has considered ambient air at atmospheric pressure as the working fluid or lubricating fluid in the bearing. However, special applications of oil-free technology require the use of air at non- standard ambient conditions or completely different working fluids altogether. The NASA Jupiter Icy Moon Orbiter program presents power generation needs far beyond that of any previous space exploration effort. The proposed spacecraft will require significant power generation to provide the propulsion necessary to reach the moons of Jupiter and navigate between them. Once there, extensive scientific research will be conducted that will also present significant power requirements. Such extreme needs require exploring a new method for power generation in space. A proposed solution involves a Brayton cycle nuclear fission reactor. The nature of this application requires reliable performance of all reactor components for many years of operation under demanding conditions. This includes the bearings which will be operating with an alternative working fluid that is a combination of Helium and Xenon gases commonly known as HeXe. This fluid has transport and thermal properties that vary significantly from that of air and the effect of these property differences on bearing performance must be considered. One of the most promising applications of oil-free technology is in aircraft turbine engines. Eliminating the oil supply systems from aircraft engines will lead to significant weight and maintenance reduction. In such applications, the lubricating fluid will be high altitude air. This air will be at much lower pressure than that at sea level. Again this property change will result in a change in bearing performance, and analysis is required to quantify this effect. The study of these alternate working fluid properties will be conducted in two ways: analytically and experimentally. Analytical research will include the use of a mathematical code that can predict film thickness profiles for various ambient conditions. Estimations of load capacity can be made based upon the film thickness trends. These values will then be compared to those obtained from classical rigid bearing analysis. Experimental Research will include testing a foil bearing at a variety of ambient air pressures. The analytical and experimental data will be compared to draw conclusions on bearing performance under alternate working fluid properties.

Smith, Matthew J.↗
NASA NTRS1999

Deformation Behaviors of HIPped Foil Compared with Those of Sheet Titanium Alloys

Micromechanics-based modeling of composite material behaviors requires an accurate assessment of the constituent properties and behaviors. For the specific case of continuous-fiber-reinforced metal matrix composites (MMC's) manufactured from a foil/fiber/foil process, much emphasis has been placed on characterizing foil-based matrix materials that have been fabricated in the same way as the composite. Such materials are believed to yield mechanical properties and behaviors that are representative of the matrix constituent within the composite (in situ matrix). Therefore, these materials are desired for micromechanics modeling input. Unfortunately, such foils are extremely expensive to fabricate and procure because of the labor-intensive rolling process needed to produce them. As a potential solution to this problem that would maintain appropriately representative in situ properties, the matrix constituent could be characterized with sheet-based materials, which are considerably less expensive to manufacture than foils, are more readily procured, and result in fewer plies to obtain a desired panel thickness. The critical question is, however, does the consolidated sheet material exhibit the same properties and behaviors as do the consolidated foils? Researchers at NASA Lewis Research Center's Life Prediction Branch completed a detailed experimental investigation to answer this question for three titanium alloys commonly used in metal matrix composite form.

Castelli, Michael G.↗
NASA NTRS2004

Thin-Film Solar Cells on Metal Foil Substrates for Space Power

Photovoltaic arrays have played a key role in power generation in space. The current technology will continue to evolve but is limited in the important mass specific power metric (MSP or power/weight ratio) because it is based on bulk crystal technology. The objective of this research is to continue development of an innovative photovoltaic technology for satellite power sources that could provide up to an order of magnitude saving in both weight and cost, and is inherently radiation-tolerant through use of thin film technology and thin foil substrates such as 5-mil thick stainless steel foil or 1-mil thick Ti. Current single crystal technology for space power can cost more than $300 per watt at the array level and weigh more than 1 kg/sq m equivalent to specific power of approx. 65 W/kg. Thin film material such as CuIn(1-x),Ga(x)S2, (CIGS2), CuIn(1-x), G(x)Se(2-y),S(y), (CIGSS) or amorphous hydrogenated silicon (a-Si:H) may be able to reduce both the cost and mass per unit area by an order of magnitude. Manufacturing costs for solar arrays are an important consideration for total spacecraft budget. For a medium sized 5kW satellite, for example, the array manufacturing cost alone may exceed $2 million. Moving to thin film technology could reduce this expense to less than $500 K. Previous work at FSEC demonstrated the potential of achieving higher efficiencies from CIGSS thin film solar cells on 5-mil thick stainless steel foil as well as initial stages of facility augmentation for depositing thin film solar cells on larger (6"x 4") substrates. This paper presents further progress in processing on metal foil substrates. Also, previous work at DayStar demonstrated the feasibility of flexible-thin-film copper-indium-gallium-diselenide (CIGS) solar cells with a power-to-weight ratio in excess of 1000 W/kg. We will comment on progress on the critical issue of scale-up of the solar cell absorber deposition process. Several important technical issues need to be resolved to realize the benefits of lightweight technologies for solar arrays, such as: monolithic interconnects, lightweight array structures, and new ultra-light support and deployment mechanisms. Once the technology has gained spaceflight certification it should find rapid acceptance in specific satellite markets.

Raffaelle, Ryne P.↗