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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The effect of variations of cobalt content on the cyclic oxidation resistance of selected Ni-base superalloys

Cobalt levels were systematically varied in the Ni-base turbine alloys U-700 (cast), U-700m (PM/HIP), Waspaloy, Mar-M-247, In-738, Nimonic-115, U-720, and SX-R-150. the cobalt levels ranged from 0 wt pct to the nominal commercial content in each alloy. the alloys were tested in cyclic oxidation in static air at 1000, 1100 and 1150 C for 500, 200, and 100 hr, respectively. An oxidation attack parameter, Ka, derived from the specific weight change versus time data was used to evaluate the oxidation behavior of the alloys along with X-ray diffraction analysis of the surface oxides. The alloys tend to form either Cr2O3/chromite spinel or Al2O3/aluminate spinel depending on the Cr/Al ratio in the alloys. Alloys with a ratio of 3.5 or higher tend to favor the Cr oxides while those under 3.0 form mostly Al oxides. In general the Al2O3/aluminate spinel forming alloys have the better oxidation resistance. Increased cobalt content lowers the scaling resistance of the higher Cr allys while a 5.0 wt pct Co content is optimum for the Al controlling alloys. The refractory metals, particularly Ta, appear beneficial to both types of oxides, perhaps due to the formation of the omnipresent trirutile Ni(Ta, Cb, Mo, W)2O6. Both scales break down as increasing amounts of NiO are formed.

Barrett, Charles A.↗
NASA NTRS1987

Sodium sulfate-induced corrosion of pure nickel and superalloy Udimet 700 in a high velocity burner rig at 900 C

Sodium sulfate-induced corrosion of pure nickel and a commercial nickel-base superalloy, Udimet 700 (U-700), were studied at 900 C in a Mach 0.3 burner rig with different Na levels in the combustor. The corrosion rate of Ni was independent of the Na level in the combustor and considerably lower than that measured in laboratory salt spray tests. The lower rates are associated with the deposition of only a small amount of Na2SO4 on the surface of the NiO scale. Corrosion of U-700 was observed to occur in two stages. During the first stage, the corrosion proceeds by reaction of Cr2O3 scale with the Na2SO4 and evaporation of the Na2CrO4 reaction product from the surface of the corroding sample. Cr depletion in the alloy occurs and small sulfide particles are formed in the Cr depletion zone. Extensive sulfidation occurs during the second state of corrosion, and a thick scale forms. The relationship between the corrosion rate of U-700 and the Na level in the combustor gives a good correlation in the range of 0.3 to 1.5 ppm by weight Na. Very low levels of Na in the combustor cause accelerated oxidation of U-700 without producing the typical hot corrosion morphology.

Misra, A. K.↗
NASA NTRS1988

The effect of 0.1 atomic percent zirconium on the cyclic oxidation behavior of beta-NiAl for 300 hours at 1200 C

The long time effect of 0.1 at percent Zr (0.2 wt percent Zr) on the cyclic oxidation behavior of hipped beta-NiAl was studied. Oxidation testing was performed in static air at 1200 C for up to 3000 one-hour exposure cycles. Specific weight change versus time data was modeled with the COSP computer program to analyze cyclic oxidation behavior. The Zr-free stoichiometric alloy oxidized and spalled randomly to bare metal between cycles at a rate high enough to deplete Al to a low enough level that oxidation breakaway took place as nonprotective NiO replaced the alpha-Al2O3/NiAl2O4 scale as the controlling oxide. The Zr minimized this severe type of spalling maintaining the protective alpha-Al2O3 scale even out to 3000 hours for the stoichiometric alloy with no significant Al depletion. A third beta-NiAl alloy containing 0.1 at percent Zr but with 10 percent less Al than the stoichiometric alloy was also tested and showed some depletion of Al, but the protective Al2O3/NiAl2O4 was still maintained to close to 2700 hours.

Barrett, C. A.↗
NASA NTRS1989

Characterization of ceramics and intermetallics fabricated by self-propagating high-temperature synthesis

Three efforts aimed at investigating the process of self-propagating high temperature synthesis (SHS) for the fabrication of structural ceramics and intermetallics are summarized. Of special interest was the influence of processing variables such as exothermic dopants, gravity, and green state morphology in materials produced by SHS. In the first effort directed toward the fabrication of SiC, exothermic dopants of yttrium and zirconium were added to SiO2 or SiO2 + NiO plus carbon powder mix and processed by SHS. This approach was unsuccessful since it did not produce the desired product of crystalline SiC. In the second effort, the influence of gravity was investigated by examining Ni-Al microstructures which were produced by SHS combustion waves traveling with and opposite the gravity direction. Although final composition and total porosities of the combusted Ni-Al compounds were found to be gravity independent, larger pores were created in those specimens which were combusted opposite to the gravity force direction. Finally, it was found that green microstructure has a significant effect on the appearance of the combusted piece. Severe pressing laminations were observed to arrest the combustion front for TiC samples.

Hurst, Janet B.↗
NASA NTRS1989

The effect of 0.1 atomic percent zirconium on the cyclic oxidation behavior of beta-NiAl for 3000 hours at 1200 C

The long time effect of 0.1 at percent Zr (0.2 wt percent Zr) on the cyclic oxidation behavior of hipped beta-NiAl was studied. Oxidation testing was performed in static air at 1200 C for up to 3000 one-hour exposure cycles. Specific weight change versus time data was modeled with the COSP computer program to analyze cyclic oxidation behavior. The Zr-free stoichiometric alloy oxidized and spalled randomly to bare metal between cycles at a rate high enough to deplete Al to a low enough level that oxidation breakaway took place as nonprotective NiO replaced the alpha-Al203/NiAl204 scale as the controlling oxide. The Zr minimized this severe type of spalling maintaining the protective alpha-Al203 scale even out to 3000 hours for the stoichiometric alloy with no significant Al depletion. A third beta-NiAl alloy containing 0.1 at percent Zr but with 10 percent less Al than the stoichiometric alloy was also tested and showed some depletion of Al, but the protective Al203/NiAl204 was still maintained to close to 2700 hours.

Barrett, C. A.↗
NASA NTRS1992

Milling and mechanical alloying of inorganic nonmetallics

The versatility of high energy grinding for instigating mechanochemical reactions in inorganic systems has been studied. High-energy grinding can be used to produce amorphous carbon from synthetic graphite and some forms of natural graphite. Elemental sulfur can be amorphized by prolonged energy grinding. The presence of iron resulting from wear of the grinding media strongly affects phase transformations of alphaFe2O3 and mechanochemical reactions of this phase with ZnO and NiO. Data obtained confirm that low-temperature mechanochemical method is a robust process route for production of a wide range of materials.

Kosmac, T.↗
NASA NTRS1956

Friction, Wear, and Surface Damage of Metals as Affected by Solid Surface Films

As predicted by friction theory, experiments showed that friction and surface damage of metals can be reduced by solid surface films. The ability of materials to form surface films that prevent welding was a very important factor in wear of dry and boundary lubricated surfaces. Films of graphitic carbon on cast irons, nio on nickel alloys, and feo and fe sub 3 o sub 4 on ferrous materials were found to be beneficial. Abrasive films such as fe sub 2 o sub 3 or moo sub 3 were definitely detrimental. It appears that the importance of oxide films to friction and wear processes has not been fully appreciated.

Bisson, Edmond E↗
NASA NTRS1993

Siderophile elements in the upper mantle of the Earth: New clues from metal-silicate partition coefficients

New, precise data on the solubilities of Ni, Co, and Mo in silicate melts at 1400 C and fO2 from IW to IW-2 are presented. The results suggest NiO, CoO as stable species in the melt. No evidence for metallic Ni or Co was found. Equilibrium was ensured by reversals with initially high Ni and Co in the glass. Mo appears to change oxidation state at IW-1, from MoO3 to MoO2. Metal-silicate partition coefficients calculated from these data and recent data on Pd indicate similar partition coefficients for Pd and Mo at the conditions of core formation. This unexpected result constrains models of core formation in the Earth.

Holzheid, A.↗
NASA NTRS1994

The Effect of Polymer Char on Nitridation Kinetics of Silicon

Effects of polymer char on nitridation kinetics of attrition milled silicon powder have been investigated from 1200 to 1350 C. Results indicate that at and above 1250 C, the silicon compacts containing 3.5 wt percent polymer char were fully converted to Si3N4 after 24 hr exposure in nitrogen. In contrast, the silicon compacts without polymer char could not be fully converted to Si3N4 at 1350 C under similar exposure conditions. At 1250 and 1350 C, the silicon compacts with polymer char showed faster nitridation kinetics than those without the polymer char. As the polymer char content is increased, the amount of SiC in the nitrided material is also increased. By adding small amounts (approx. 2.5 wt percent) of NiO, the silicon compacts containing polymer char can be completely nitrided at 1200 C. The probable mechanism for the accelerated nitridation of silicon containing polymer char is discussed.

Chan, Rickmond C.↗
NASA NTRS1996

Fabrication of Iron-Containing Carbon Materials From Graphite Fluoride

Carbon materials containing iron alloy, iron metal, iron oxide or iron halide were fabricated. Typical samples of these metals were estimated to contain 1 iron atom per 3.5 to 5 carbon atoms. Those carbon materials containing iron alloy, iron metal, and/or Fe3O4 were magnetic. The kinetics of the fabrication process were studied by exposing graphite fluoride (CF(0.68)) to FeCl3 over a 280 to 420 C temperature range. Between 280 and 295 C, FeCl3 quickly entered the structure of CF(0.68), broke the carbon-fluorine bonds, and within 10 to 30 min, completely converted it to carbon made up of graphite planes between which particles of crystalline FeF3 and noncrystalline FeCl3 were located. Longer reaction times (e.g., 28 hr) or higher reaction temperatures (e.g., 420 C) produced materials containing graphite, a FeCl3-graphite intercalation compound, FeCl2(center dot)4H2O, and FeCl2(center dot)2H2O. These products were further heat treated to produce iron-containing carbon materials. When the heating temperature was kept in the 750 to 850 C range, and the oxygen supply was kept at the optimum level, the iron halides in the carbon structure were converted to iron oxides. Raising the heat to temperatures higher than 900 C reduced such iron oxides to iron metal. The kinetics of these reactions were used to suggest processes for fabricating carbon materials containing iron alloy. Such processes were then tested experimentally. In one of the successful trial runs, commercially purchased CF(0.7) powder was used as the reactant, and NiO was added during the final heating to 1200 C as a source of both nickel and oxygen. The product thus obtained was magnetic and was confirmed to be a nickel-iron alloy in carbon.

Hung, Ching-cheh↗
NASA NTRS2001

Laser Induced Aluminum Surface Breakdown Model

Laser powered propulsion systems involve complex fluid dynamics, thermodynamics and radiative transfer processes. Based on an unstructured grid., pressure-based computational aerothermodynamics, platform, several sub-nio"'dels describing such underlying physics as laser ray tracing and focusing, thermal non-equilibrium, plasma radiation and air spark ignition have been developed. This proposed work shall extend the numerical platform and existing sub-models to include the aluminum wall surface Inverse Bremsstrahlung (113) effect from which surface ablation and free-electron generation can be initiated without relying on the air spark ignition sub-model. The following tasks will be performed to accomplish the research objectives.

Chen, Yen-Sen↗
NASA NTRS2002

Oxidation of a Silica-Containing Material in a Mach 0.3 Burner Rig

A primarily silica-containing material with traces of organic compounds, as well as aluminum and calcium additions, was exposed to a Mach 0.3 burner rig at atmospheric pressure using jet fuel. The sample was exposed for 5 continuous hours at 1370 C. Post exposure x-ray diffraction analyses indicate formation of cristobalite, quartz, NiO and Spinel (Al(Ni)CR2O4). The rig hardware is composed of a nickel-based superalloy with traces of Fe. These elements are indicated in the energy dispersive spectroscopy (EDS) results. This material was studied as a candidate for high temperature applications under an engine technology program.

Nguyen, QuynhGiao N.↗
NASA NTRS2005

Polynomial Expressions for Estimating Elastic Constants From the Resonance of Circular Plates

Two approaches were taken to make convenient spread sheet calculations of elastic constants from resonance data and the tables in ASTM C1259 and E1876: polynomials were fit to the tables; and an automated spread sheet interpolation routine was generated. To compare the approaches, the resonant frequencies of circular plates made of glass, hardened maraging steel, alpha silicon carbide, silicon nitride, tungsten carbide, tape cast NiO-YSZ, and zinc selenide were measured. The elastic constants, as calculated via the polynomials and linear interpolation of the tabular data in ASTM C1259 and E1876, were found comparable for engineering purposes, with the differences typically being less than 0.5 percent. Calculation of additional v values at t/R between 0 and 0.2 would allow better curve fits. This is not necessary for common engineering purposes, however, it might benefit the testing of emerging thin structures such as fuel cell electrolytes, gas conversion membranes, and coatings when Poisson s ratio is less than 0.15 and high precision is needed.

Salem, Jonathan A.↗
NASA NTRS2003

Experimental and Petrological Constraints on Lunar Differentiation from the Apollo 15 Green Picritic Glasses

Phase equilibrium experiments on the most magnesian Apollo 15C green picritic glass composition indicate a multiple saturation point with olivine and orthopyroxene at 1520 C and 1.3 GPa (about 260 km depth in the moon). This composition has the highest Mg# of any lunar picritic glass and the shallowest multiple saturation point. Experiments on an Apollo 15A composition indicate a multiple saturation point with olivine and orthopyroxene at 1520 C and 2.2 GPa (about 440 km depth in the moon). The importance of the distinctive compositional trends of the Apollo 15 groups A, B, and C picritic glasses merits the reanalysis of NASA slide 15426,72 with modern electron microprobe techniques. We confirm the compositional trends reported by Delano (1979, 1986) in the major element oxides SiO2, TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, and CaO, and we also obtained data for the trace elements P2O5, K2O, Na2O, NiO, S, Cu, Cl, Zn, and F. Petrogenetic modeling demonstrates that the Apollo 15 A-B-C glass trends could not have been formed by fractional crystallization or any continuous assimilation/fractional crystallization (AFC) process. The B and C glass compositional trends could not have been formed by batch or incremental melting of an olivine + orthopyroxene source or any other homogeneous source, though the A glasses may have been formed by congruent melting over a small pressure range at depth. The B compositional trend is well modeled by starting with an intermediate A composition and assimilating a shallower, melted cumulate, and the C compositional trend is well modeled by a second assimilation event. The assimilation process envisioned is one in which heat and mass transfer were separated in space and time. In an initial intrusive event, a picritic magma crystallized and provided heat to melt magma ocean cumulates. In a later replenishment event, the picritic magma incrementally mixed with the melted cumulate (creating the compositional trends in the green glass data set), ascended to the lunar surface, and erupted as a fire fountain. A barometer created from multiple saturation points provides a depth estimate of other glasses in the A-B-C trend and of the depths of assimilation. This barometer demonstrates that the Apollo 15 A-B-C trend originated over a depth range of approx.460 km to approx.260 km within the moon.

Elkins-Tanton, Linda T.↗
NASA NTRS2006

Oxygen Fugacity at High Pressure: Equations of State of Metal-Oxide Pairs

Oxygen fugacity (fO2) varies by orders of magnitude in nature, and can induce profound changes in the chemical state of a substance, and also in the chemical equilibrium of multicomponent systems. One prominent area in high pressure geochemistry, in which fO2 is widely recognized as a principal controlling factor, is that of metal-silicate partitioning of siderophile trace elements (e.g., [1]). Numerous experiments have shown that high pressures and temperatures can significantly affect metal/silicate partitioning of siderophile and moderately siderophile elements. Parameterization of these experimental results over P, T, X, and fO2 can allow the observed siderophile element composition of the mantle to be associated with particular thermodynamic conditions [2]. However, this is best done only if quantitative control exists over each thermodynamic variable relevant to the experiments. The fO2 values for many of these partitioning experiments were determined relative to a particular metal-oxide buffer (e.g., Fe-FeO (IW), Ni-NiO (NNO), Co-CoO, Re-ReO2 (RRO)), but the parameterization of all experimental results is weakened by the fact that the pressure-induced relative changes between these buffer systems are imprecisely known.

Campbell A. J.↗
NASA NTRS2011

Oxide Scales Formed on NiTi and NiPtTi Shape Memory Alloys

Ni-49Ti and Ni-30Pt-50Ti (at.%) shape memory alloys were oxidized isothermally in air over the temperature range of 500 to 900 C. The microstructure, composition, and phase content of the scales were studied by SEM, EDS, XRD, and metallography. Extensive plan view SEM/EDS identified various features of intact or spalled scale surfaces. The outer surface of the scale was a relatively pure TiO2 rutile structure, typified by a distinct highly striated and faceted crystal morphology. Crystal size increased significantly with temperature. Spalled regions exhibited some porosity and less distinct features. More detailed information was obtained by correlation of SEM/EDS studies of 700 C/100 hr cross-sections with XRD analyses of serial or taper-polishing of plan surfaces. Overall, multiple layers exhibited graded mixtures of NiO, TiO2, NiTiO3, Ni(Ti) or Pt(Ni,Ti) metal dispersoids, Ni3Ti or Pt3Ti depletion zones, and substrate, in that order. The NiTi alloy contained a 3 at.% Fe impurity that appeared in embedded localized Fe-Ti-rich oxides, while the NiPtTi alloy contained a 2 v/o dispersion of TiC that appeared in lower layers. The oxidation kinetics of both alloys (in a previous report) indicated parabolic growth and an activation energy (250 kJ/mole) near those reported in other Ti and NiTi studies. This is generally consistent with TiO2 existing as the primary scale constituent, as described here.

Smialek, James L.↗