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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Cyclic oxidation evaluation - Approaching application conditions.

Review of 1000 to 1200 C cyclic oxidation testing conducted on potential aircraft gas turbine Ni-, Co-, and Fe-base alloys. Furnace and burner rig testing are discussed, and the results are compared for selected alloys. The alloys fall into two groups, depending on their Cr and Al contents. One group forms mainly Cr2O3/chromite spinel scale(s), while the other forms alpha Al2O3/aluminate spinel scale(s). Spalling on thermal cycling leading to increased metal consumption is associated with the appearance of a chromite spinel. In the case of high-velocity burner rig tests this chromite forming tendency is reinforced by Cr2O3 vaporization depleting Cr in the alloy. In both types of tests, specific weight change is used as an indirect indicator of metal attack, since direct metal loss measurements require destructive analysis. An alternative nondestructive metal loss estimating parameter, based on a tentative mass balance gravimetric approach, shows some potential.

Barrett, C. A.↗
NASA NTRS1974

Addition of silicon improves oxidation resistance of nickel based superalloys

Specific weight changes of nickel-base superalloy B-1900 and B-1900 + 1% Si specimens were tested at 1273 K. B-1900 was losing weight at an increasing rate due to spalling of oxide scale while B-1900 + 1% Si was still gaining weight at low, nearly constant rate. Similar comparison in weight change was observed for specimens tested at 1373 K.

Lowell, C. E.↗
NASA NTRS1974

The effect of yttrium and thorium on the oxidation behavior of Ni-Cr-Al alloys

The effect of quaternary additions of 0.5% Y, 0.5 and 1.0% Th to a base alloy of Ni-10CR-5Al on the oxidation behavior and mechanism was studied during oxidation in air over the range of 1000 to 1200 C. The presence of yttrium decreased the oxidation kinetics slightly, whereas, the addition of thorium caused a slight increase. Oxide scale adherence was markedly improved by the addition of the quaternary elements. Although a number of oxides formed on yttrium containing alloys, quantitative X-ray diffraction clearly showed that the rate-controlling step was the diffusion of aluminum through short circuit paths in a thin layer of alumina that formed parabolically with time. Although the scale adherence of the yttrium containing alloy was considerably better than the base alloys, spalling did occur that was attributed to the formation of the voluminous YAG particles which grew in a mushroom-like manner, lifting the protective scale off the subrate locally. The YAG particles formed primarily at grain boundaries in the substrate in which the yttrium originally existed as YNi9.

Kumar, A.↗
NASA NTRS1974

Design and fabrication of prototype system for early warning of impending bearing failure

A test program was conducted with the objective of developing a method and equipment for on-line monitoring of installed ball bearings to detect deterioration or impending failure of the bearings. The program was directed at the spin-axis bearings of a control moment gyro. The bearings were tested at speeds of 6000 and 8000 rpm, thrust loads from 50 to 1000 pounds, with a wide range of lubrication conditions, with and without a simulated fatigue spall implanted in the inner race ball track. It was concluded that a bearing monitor system based on detection and analysis of modulations of a fault indicating bearing resonance frequency can provide a low threshold of sensitivity.

Meacher, J.↗
NASA NTRS1974

Scanning electron microscopy of lunar regolith from the Sea of Fertility

Scanning electron microscopy was used in studying the morphology and cathodoluminescence of lunar regolith particles. Surface and structure of two groups of particles are differentiated: (1) Crystalline with well defined facets and spalling surfaces, which are grains of minerals and rock fragments: and (2) amorphous, fused, and partially or entirely glazed particles. Local melting of particles and the round openings on their surfaces are attributed to secondary influence on the regolith of factors of lunar weathering and above all micrometeoric impacts.

Antoshin, M. K.↗
NASA NTRS1975

Manufacture and static firing of X259-E6 rocket motor serial number XJ04/0001

A single motor was cast and static fired to demonstrate the performance of high energy crosslinked double base (XLDB) propellant in standard X259 rocket motor hardware. Prior to motor fabrication, the motor was analyzed to predict the results of static firing the X259 motor loaded with XLDB propellant. As a result of the analyses, a forward dome shrinkage liner was added to the design. With this design change it was determined that adequate margins of safety existed. The motor, designated the X259-E6 model with serial number XJ04/0001, was fabricated using a slurry-casting technique and was assembled with a standard X259-B4 nozzle which had the nozzle throat machined to a smaller inside diameter than the B4 model and the exit cone cut short for Bacchus Works altitude expansion. The motor was static fired on 20 February 1974 with the nozzle failing during motor operation. Nozzle failure was attributed to spalling of the throat material leading to complete nozzle break-up. However, the propellant functioned as predicted in the motor chamber, ignition was normal, and char and erosion of the internal insulator were as expected.

Robertson, D. R.↗
NASA NTRS1975

Thermal expansion in the nickel-chromium-aluminum and cobalt-chromium-aluminum systems to 1200 degrees C

Thermal expansion data were obtained on 12 Ni-Cr-Al and 9 Co-Cr-Al alloys by high temperature X-ray diffraction. The data were computer fit to an empirical thermal expansion equation developed in the study. It is shown that the fit is excellent to good, and that the expansion constants depend on phase but not on composition. Phases for the Ni-Cr-Al system and Co-Cr-Al system are given. Results indicate that only alpha Cr has an expansion constant low enough to minimize oxide spalling or coating cracking induced by thermal expansion mismatch.

Lowell, C. E.↗
NASA NTRS1974

The effect of yttrium and thorium on the oxidation behavior of Ni-Cr-Al alloys

The investigation reported included a determination of the optimum composition of a Ni-Cr-Al ternary alloy with respect to oxidation resistance and minimum film-spalling tendencies. Yttrium and thorium in small amounts were added to the ternary alloy and an investigation of the oxidation mechanism and the oxide scale adherence was conducted. It was found that the oxidation mechanism of Ni-Cr-Al ternary alloys depends upon the composition of the alloy as well as the time, oxygen pressure, and temperature of oxidation.

Kumar, A.↗
NASA NTRS1974

Fatigue life of high-speed ball bearings with silicon nitride balls

Evaluation of hot-pressed silicon nitride as a rolling-element bearing material. Two grades of hot-pressed silicon nitride balls were tested under rolling contact conditions in a five-ball fatigue tester. A digital computer program was used to predict the dynamic performance characteristics and fatigue life of high-speed ball bearings with silicon nitride balls relative to that with bearings containing steel balls. The results obtained include the finding that fatigue spalls on silicon nitride balls are similar in appearance to those obtained with typical bearing steels.

Parker, R. J.↗
NASA NTRS1974

A proposed origin of the Olympus Mons escarpment

Olympus Mons (Nix Olympica) on Mars is delimited by a unique steep, nearly circular scarp. A pyroclastic model is proposed for the construct's origin. It is postulated that the Olympus Mons plateau is constructed predominantly of numerous ash-flow tuffs which were erupted from central sources over an extended period of time. Lava flows may be intercalated with the tuffs. A schematic radial profile incorporating the inferred compaction zones for an ash sheet is proposed. Following emplacement, eolian (and possibly fluvial) erosion and abrasion during dust storms would act on the ash sheets. Interior portions of the sheets would spall and slump following eolian erosion, generating steep, relatively smooth boundary scarps. The scarp would be circular due to symmetrical distribution of compaction zones. The model implies further that the Olympus Mons plateau rests on a more resistant rock substrate.

King, J. S.↗
NASA NTRS1975

Comparison of isothermal and cyclic oxidation behavior of twenty-five commercial sheet alloys at 1150 C

Twenty-five commercial nickel-, iron-, and cobalt-base sheet alloys incorporating chromium or chromium and aluminum additions for oxidation resistance were tested at 1150 C in air for 100 hr in both isothermal and 1-hr cyclic furnace exposures. The alloys were evaluated by sample specific weight change, by type of scale formed, by amount and type of spall, and by sample thickness change and microstructure.-

Barrett, C. A.↗
NASA NTRS1975

Characterization of BCL strain gages for use to 1366 K (2000 F)

Strain gage behavior under static and transient heating conditions at various strain rates and high temperatures (1366 K(2000 F) was studied. Optimum time-temperature parameters were developed for preconditioning (prestabilizing) the gages. A limited study was carried out to determine the extent of spalling of platinum cladding during fabrication of platinum-clad wire strain gages. Further verification was also carried out on the convergence and repeatability of the apparent strain characteristics of the gage under heating and cooling cycles. The significance of these characteristics from the standpoint of enhancing measurement accuracy is also discussed. It was concluded that the gage should perform satisfactorily to temperatures approaching 1366 K (2000 F).

Lemcoe, M. M.↗
NASA NTRS1975

A study of the use of vibration and stress wave sensing for the detection of bearing failure

Results from an experimental study of vibrations and stress waves emitted from ball bearings are presented. Fatique tests were run with both high quality bearings and man faulted bearings, all of one size. Tests were instrumented with different sensors to detect the noises from 10 Hz to 1 MHz. Frequency spectrum plots are presented. The modulation characteristics of the ultrasonic noises were analyzed, and acoustic emission type measurements were conducted. Results are presented which show that there are usable acoustic signal levels even beyond 500 KHz. These signal levels are modulated by a low frequency carrier which is a function of the stress loading and acoustic transmissibility. The results were correlated to fault size in the bearings. The correlation shows that the sensor used for signals from 100 KHz to 1 MHz gave the best sensitivity and detected the generation of very small spalls or pits.

Ensor, L. C.↗
NASA NTRS1976

Endurance and failure characteristics of main-shaft jet engine bearings at 3x10 to the 6th power DN

Groups of thirty 120-mm bore angular contact ball bearings were endurance tested at a speed of 12,000 and 25,000 rpm and a thrust load of 66 721 N. The bearings were manufactured from a single heat of VIM-VAR AISI M-50 steel. At 1.44X1 million and 3.0x1 million DN, 84 483 and 74 800 bearing test hours were accumulated, respectively. Test results were compared with similar bearings made from CVM AISI M-50 steel run under the same conditions. Bearing lives at speeds of 3x1 million DN with the VIM-VAR AISI M-50 steel were nearly equivalent to those obtained at lower speeds. A combined processing and material life factor of 44 was found for VIM-VAR AISI M-50 steel. Continuous running after a spall has occurred at 3.0x1 million DN can result in a destructive fracture of the bearing inner race.

Bamberger, E. N.↗
NASA NTRS1976

Resistance of nickel-chromium-aluminum alloys to cyclic oxidation at 1100 C and 1200 C

Nickel-rich alloys in the Ni-Cr-Al system were evaluated for cyclic oxidation resistance in still air at 1,100 and 1,200 C. A first approximation oxidation attack parameter Ka was derived from specific weight change data involving both a scaling growth constant and a spalling constant. An estimating equation was derived with Ka as a function of the Cr and Al content by multiple linear regression and translated into countour ternary diagrams showing regions of minimum attack. An additional factor inferred from the regression analysis was that alloys melted in zirconia crucibles had significantly greater oxidation resistance than comparable alloys melted otherwise.

Barrett, C. A.↗
NASA NTRS1976

Two-layer thermal barrier coating for turbine airfoils - furnace and burner rig test results

A simple, two-layer plasma-sprayed thermal barrier coating system was developed which has the potential for protecting high temperature air-cooled gas turbine components. Of those coatings initially examined, the most promising system consisted of a Ni-16Cr-6Al-0.6Y (in wt%) thermal barrier coating (about 0.005 to 0.010 cm thick) and a ZrO2-12Y2O3 (in wt%) thermal barrier coating (about 0.025 to 0.064 cm thick). This thermal barrier substantially lowered the metal temperature of an air-cooled airfoil. The coating withstood 3,200 cycles (80 sec at 1,280 C surface temperature) and 275 cycles (1 hr at 1,490 C surface temperature) without cracking or spalling. No separation of the thermal barrier from the bond coating or the bond coating from the substrate was observed.

Stecura, S.↗
NASA NTRS1976

Graphite and ablative material response to CO2 laser, carbon-arc, and xenon-arc radiation

The behavior was investigated of graphite and several charring ablators in a variety of high-radiative heat-flux environments. A commercial-grade graphite and nine state-of-the-art charring ablators were subjected to various radiative environments produced by a CO2 laser and a carbon arc. Graphite was also tested in xenon-arc radiation. Heat-flux levels ranged from 10 to 47 MW/sq m. Tests were conducted in air, nitrogen, helium, and a CO2-N2 mixture which simulated the Venus atmosphere. The experimental results were compared with theoretical results obtained with a one-dimensional charring-ablator analysis and a two-dimensional subliming-ablator analysis. Neither the graphite nor the charring ablators showed significant differences in appearance or microstructure after testing in the different radiative environments. The performance of phenolic nylon and graphite was predicted satisfactorily with existing analyses and published material property data. Good agreement between experimental and analytical results was obtained by using sublimation parameters from a chemical nonequilibrium analysis of graphite sublimation. Some charring ablators performed reasonably well and could withstand radiative fluxes of the level encountered in certain planetary entries. Other materials showed excessive surface recession and/or large amounts of cracking and spalling, and appear to be unsuitable for severe radiative environments.

Brewer, W. D.↗
NASA NTRS1976

Endurance and failure characteristic of main-shaft jet engine bearing at 3 million DN

Groups of thirty 120-mm bore angular-contact ball bearings were endurance tested at a speed of 12,000 and 25,000 rpm (1.44 million and 3.0 million DN, where DN is the product of the bearing bore in mm and the shaft speed in rpm) and a thrust load of 66,721 N. The bearings were manufactured from a single heat of VIM-VAR AISI M-50 steel. At 1.44 million and 3.0 million DN, 84,483 and 74,800 bearing test hours were accumulated, respectively. Test results were compared with similar bearings made from CVM AISI M-50 steel run under the same conditions. Bearing lives at speeds of 3 million DN with the VIM-VAR AISI M-50 steel were nearly equivalent to those obtained at lower speeds. A combined processing and material life factor of 44 was found for VIM-VAR AISI M-50 steel. Continuous running after a spall has occurred at 3.0 million DN can result in a destructive fracture of the bearing inner race.

Bamberger, E. N.↗