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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Enhanced oxidative vaporization of Cr2O3 and chromium by oxygen atoms

Rates of oxidative vaporization of Cr2O3 have been found to be markedly enhanced in the presence of oxygen atoms. Investigations were conducted over the temperature range 200-1250 C. For Cr2O3 the enhancement was about 10 to the 9th power at 550 C in oxygen containing 2.5% atoms. Rapid oxidative vaporization of bare chromium was observed below 800 C, the rate being about one-half that of Cr2O3. Results are interpreted in terms of thermochemical analysis.

Fryburg, G. C.↗
NASA NTRS1976

Hot hardness of nickel-rich nickel-chromium-aluminum alloys

Rockwell A hardness of cast nickel-chromium-aluminum (NiCrAl) alloys was examined from ambient to 1150 K and compared to cast NiAl and IN-100. Alloy constitution was either gamma, gamma prime + gamma or gamma + beta + alpha + gamma prime. Below 1000 K beta containing NiCrAl alloys have hardnesses comparable to IN-100; above 1000 K they soften faster than IN-100. At 1150 K the hardness of beta-containing NiCrAl alloys decreases with increasing beta-content. The beta-containing NiCrAl alloys were harder than beta-NiAl. The ultimate tensile strengths of the NiCrAl alloys were estimated. The effects of NiCrAl coatings on strength and fatigue life of cooled turbine components were deduced.

Levine, S. R.↗
NASA NTRS1976

Effect of a chromium-containing fuel additive on hot corrosion

Four superalloys were tested at 900 C in high velocity combustion gases containing synthetic sea salt and, in some cases, a chromium containing fuel additive. While the additive reduced hot corrosion of the alloys over the 100 hour test period, the attack was not eliminated nor was the mode of attack changed. Reduction of the number of thermal cycles had as large a beneficial effect as the Cr additive. Intermittent washing during testing had either small beneficial or adverse effects depending on the alloy.

Lowell, C. E.↗
NASA NTRS1977

Influence of temperature and the role of chromium on the kinetics of sulfidation of 310 stainless steel

The sulfidation of 310 stainless steel was studied over the temperature range from 910 K to 1285 K. By adjusting the ratio of hydrogen sulfide, variations in sulfur potential were obtained. The effect of temperature on sulfidation was determined at three different sulfur potentials: 39/sqNm, 0.014/sqNm, and 0.00015/sqNm. All sulfide scales contained one or two surface layers in addition to a subscale. The second outer layer (OL-II), furthest from the alloy, contained primarily Fe-Ni-S. The first outer layer (OL-I), nearest the subscale, contained FE-Cr-S. The subscale consisted of sulfide inclusions in the metal matrix. At a given temperature and sulfur potential, the weight gain data obeyed the parabolic rate law after an initial transient period. The parabolic rate constants obtained at the sulfur potential of 39/sqNm did not show a break when the logarithm of the rate constant was plotted as a function of the inverse of absolute temperature. Sulfidation carried out at sulfur potentials below 0.02/sqNm, however, did show a break at 1145 K, which is termed as the transition temperature. This break was found to be associated with the changes which had occurred in the Fe:Cr ratio of OL-I. Below the transition temperature the activation energy was found to be approximately 125 kj/mole. Above the transition temperature the rate of sulfidation decreased with temperature but dependent on the Fe:Cr ratio in the iron-chromium-sulfide layers of the OL-I. A reaction mechanism consistent with the experimental results has been proposed.

Rao, D. B.↗
NASA NTRS1976

Partitioning of chromium between silicate crystals and melts

Experiments were performed determining the distribution of chromium between olivine, pyroxenes, and melt at oxygen fugacity values near those of lunar rocks for a wide range of bulk compositions. The range of values of D-Cr (wt% of Cr2O3 in crystals/Cr2O3 in melt) is 0.6-1.3 for olivine and 1.6-3.5 for pyroxene; this ratio shows no obvious dependence on any experimental parameter.

Huebner, J. S.↗
NASA NTRS1978

Feasibility study of tungsten as a diffusion barrier between nickel-chromium-aluminum and Gamma/Gamma prime - Delta eutectic alloys

Coating systems proposed for potential use on eutectic alloy components in high-temperature gas turbine engines were studied with emphasis on deterioration of such systems by diffusion. A 1-mil thick W sheet was placed between eutectic alloys and a NiCrAl layer. Layered test specimens were aged at 1100 C for as long as long as 500 hours. Without the W barrier, the delta phase of the eutectic deteriorated by diffusion of Nb into the NiCrAl. Insertion of the W barrier stopped the diffusion of Nb from delta. Chromium diffusion from the NiCrAl into the gamma/gamma prime phase of the eutectic was greatly reduced by the barrier. However, the barrier thickness decreased with time; and W diffused into both the NiCrAl and the eutectic. When the delta platelets were alined parallel to the NiCrAl layer, rather than perpendicular, diffusion into the eutectic was reduced.

Young, S. G.↗
NASA NTRS1979

Effects of yttrium, aluminum, and chromium concentrations in bond coatings on the performance of zirconia-yttria thermal barriers

A cyclic furnace study was conducted between 990 - 280 C and 1095 - 280 C to evaluate the effects of yttrium, chromium, and aluminum concentrations in nickel base alloy bond coatings and also the effect of the bond coating thickness on the performance of yttria-stabilized zirconia thermal barrier coatings. The presence and the concentration of yttrium is very critical. Without yttrium, rapid oxidation of Ni-Al, Ni-Cr, and Ni-Cr-Al bond coatings causes zirconia thermal barrier coatings to fail very rapidly. Concentrations of chrominum and aluminum in Ni-Cr-Al-Y bond coating have a very significant effect on the thermal barrier coating life. This effect, however, is not as great as that due to yttrium. Furthermore, the thickness and the thickness uniformity also have a very significant effect on the life of the thermal barrier system.

Stecura, S.↗
NASA NTRS1979

Development of RF sputtered chromium oxide coating for wear application

The radio frequency sputtering technique was used to deposite a hard refractory, chromium oxide coating on an Inconel X-750 foil 0.1 mm thick. Optimized sputtering parameters for a smooth and adherent coating were found to be as follows: target-to-substrate spacing, 41.3 mm; argon pressure, 5-10 mTorr; total power to the sputtering module, 400 W (voltage at the target, 1600 V), and a water-cooled substrate. The coating on the annealed foil was more adherent than that on the heat-treated foil. Substrate biasing during the sputter deposition of Cr2O3 adversely affected adherence by removing naturally occurring interfacial oxide layers. The deposited coatings were amorphous and oxygen deficient. Since amorphous materials are extremely hard, the structure was considered to be desirable.

Bhushan, B.↗
NASA NTRS1981

Environmental durability of electroplated black chromium

A study was undertaken to determine the durability of nickel-black chromium plated aluminum in an outdoor rural industrial, and seacoast environment. Test panels were exposed to these environments for 60, 36, and 13 months, respectively. The results of this study showed that no significant optical degradation occurred from exposure to either of these environments, although a considerable amount of corrosion occurred on the panels exposed to the seacoast environment. The rural and industrial atmosphere produced only a slight amount of corrosion on test panels.

Lowery, J. R.↗
NASA NTRS1982

Chromium ion plating studies for enhancement of bearing lifetime

Six 440-C hardened stainless steel roller bearing test rods were ion plated with various chromium films of thicknesses from .2 microns to 7 microns. The thinner (approximately .2 microns) coating sample had 3 times the fatigue life of the unplated (standard) specimens. Contrastingly, the samples having thicker coatings (several microns) had short fatigue lives (about 3% of the unplated standard).

Davis, J. H.↗
NASA NTRS1981

The chemical behavior of acidified chromium (3) solutions

A unique energy-storage system has been developed at NASA's Lewis Research Center called REDOX. This NASA-REDOX system is an electrochemical storage device that utilized the oxidation and reduction of two fully soluble redox couples for charging and discharging. The redox couples now being investigated are acidified chloride solutions of chromium (Cr(+2)/Cr(+3)) and iron (Fe(+2)/Fe(+3)).

Terman, D. K.↗
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 NTRS1985

Effects of chromium and aluminum on mechanical and oxidation properties of iron-nickel-base superalloys based on CG-27

The effects of chromium and aluminum on the mechanical and oxidation properties of a series of gamma-prime-strengthened alloys based on CG-27 were studied. Gamma-prime dispersion and solid-solution strengthening were the principal modes of alloy strengthening. The oxidation attack parameter K sub a decreased with increasing Cr and Al contents for each alloy group based on Al content. As a group, alloys with 3 wt % Al had the lowest attack parameters. Therefore, 3 wt % is the optimum level of Al for parabolic oxidation behavior. Spalling, due to diffusion-induced grain growth, was controlled by the overall Cr and Al levels. The alloy with 4 wt % Cr and 3 wt % Al had stress-rupture properties superior to those of the base alloy, CG-27, and maintained parabolic oxidation behavior while the Cr content was reduced by two-thirds of its value in cast CG-27.

Schuon, S. R.↗
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

Laser action in chromium-doped forsterite

This paper reports on pulsed laser operation obtained in chromium-activated forsterite Cr(3+):Mg2SiO4 at room temperature. The spectrum of the free-running laser peaks at 1235 nm and a bandwidth of about 22 nm. The spectral range of the laser emission is expected to extend from 850 to 1300, provided the parasitic impurity absorption may be minimized by improved crystal growth techique.

Petricevic, V.↗
NASA NTRS1988

Laser action in chromium-activated forsterite for near infrared excitation

This paper reports on laser action in chromium-doped forsterite (Cr:Mg2SiO4) for 1064-nm excitation of the crystal's double-hump absorption band spanning the 850-1200-nm wavelength range. The cavity arrangement used for obtaining laser action in Cr:Mg2SiO2 was similar to that described by Petricevic et al. (1988). The fundamental and second harmonic emissions from a Q-switched Nd:YAG laser operating at a 10-Hz repetition rate were used for excitation of the NIR and visible bands, respectively. Pulsed laser action was readily observed for both the 1064-nm and 532-nm pumping at or above the respective thresholds. The laser parameters of the 532-nm and 1064-nm excitations were similar, indicating that the IR band is responsible for laser action for both excitations.

Petricevic, V.↗
NASA NTRS1988

Nickel and chromium isotopes in Allende inclusions

High-precision nickel and chromium isotopic measurements were carried out on nine Allende inclusions. It is found that Ni-62, Ni-64, excesses are present in at least three of the samples. The results suggest that the most likely mechanism for the anomalies is a neutron-rich statistical equilibrium process. An indication of elevated Ni-60 is found in almost every inclusion measured. This effect is thought to be related to the decay of now extinct Fe-60. An upper limit of 1.6 X 10 to the -6th is calculated for the Fe-60/Fe-56 ratio at the time these Allende inclusions crystallized.

Birck, J. L.↗