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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Oxidation and Emittance Studies of Coated Mo-Re

A commercially available Fe-Cr-Si coating (R512E) and a silicide coating were evaluated regarding their ability to protect Mo-Re from oxidation. The R512E coating provided very good oxidation protection at 1260 C in atmospheric air. Oxidation tests were also performed at Mach 4 in the HYMETS facility at NASA Langley Research Center where again the R512E provided good oxidation protection but for much shorter times. Emittance measurements as a function of wavelength were also obtained for the R512E coating on Mo-Re after exposure to the Mach 4 environment at 1150 C and 1230 C.

Glass, David E.↗
NASA NTRS1971

Alloyed coatings for dispersion strengthened alloys

Processing techniques were developed for applying several diffusion barriers to TD-Ni and TD-NiCr. Barrier coated specimens of both substrates were clad with Ni-Cr-Al and Fe-Cr-Al alloys and diffusion annealed in argon. Measurement of the aluminum distribution after annealing showed that, of the readily applicable diffusion barriers, a slurry applied tungsten barrier most effectively inhibited the diffusion of aluminum from the Ni-Cr-Al clad into the TD-alloy substrates. No barrier effectively limited interdiffusion of the Fe-Cr-Al clad with the substrates. A duplex process was then developed for applying Ni-Cr-Al coating compositions to the tungsten barrier coated substrates. A Ni-(16 to 32)Cr-3Si modifier was applied by slurry spraying and firing in vacuum, and was then aluminized by a fusion slurry process. Cyclic oxidation tests at 2300 F resulted in early coating failure due to inadequate edge coverage and areas of coating porosity. EMP analysis showed that oxidation had consumed 70 to 80 percent of the aluminum in the coating in less than 50 hours.

Wermuth, F. R.↗
NASA NTRS1975

Optimization of an oxide dispersion strengthened Ni-Cr-Al alloy for gas turbine engine vanes

The investigation was carried out to determine the optimum alloy within the Ni-16Cr-Al-Y2O3 system for use as a vane material in advanced aircraft gas turbine engines. Six alloys containing nominally 4%, 5% and 6% Al with Y2O3 levels of 0.8% and 1.2% were prepared by mechanical attrition. Six small-scale, rectangular extrusions were produced from each powder lot for property evaluation. The approximate temperatures for incipient melting were found to be 1658 K (2525 F), 1644 K (2500 F) and 1630 K (2475 F) for the 4%, 5% and 6% aluminum levels, respectively. With the exception of longitudinal crystallographic texture, the eight extrusions selected for extensive evaluation either exceeded or were close to mechanical property goals. Major differences between the alloys became apparent during dynamic oxidation testing, and in particular during the 1366 K (2000 F)/500 hour Mach 1 tests carried out by NASA-Lewis. An aluminum level of 4.75% was subsequently judged to be optimum based on considerations of dynamic oxidation resistance, susceptibility to thermal fatigue cracking and melting point.

Klarstrom, D. L.↗
NASA NTRS1988

Effect of 0.1 at. pct Zirconium on the cyclic oxidation resistance of beta-NiAl

The effect of 0.1 at. pct Zr on the cyclic oxidation of hipped beta-NiAl was studied. Oxidation testing was performed in static air at 1100-1200 C, using 1-hr exposure cycles for test times up to 3000 hr. The weight change versus time data were modeled with the COSP computer program to analyze and predict cyclic-oxidation behavior. Zr additions significantly change the nature of the scale-spalling process during cooling, so that the oxide spalls near the oxide-air interface at a relatively low depth within the scale. Without Zr, the predominantly alpha-Al2O3 scale tends to spall randomly to bare metal at relatively high effective-scale-loss rates, particularly at 1150 C and 1200 C. This leads to higher rates of Al consumption for the Zr-free aluminide and much earlier depletion of Al, leading to eventual breakaway (i.e., failure).

Barrett, Charles A.↗
DOE OSTI2022

Influence of copper and aluminum substitution on high-temperature oxidation of the FeCoCrNiMn “Cantor” alloy

In this study, the oxidation behavior of FeCoCrNiMn (HEA + Mn) is compared to three modified HEAs manufactured by substituting Mn with Al, Cu, or Al + Cu. Oxidation tests were conducted between 600°C and 800°C for up to 500 h in synthetic air. Substitution of Mn leads to a significant improvement in the oxidation resistance for the three modified HEAs. For FeCoCrNiCu (HEA + Cu), a local attack of a Cu-rich phase was observed, leading to the formation of CuO blisters on the surface. The FeCoCrNiAl (HEA + Al) alloy was characterized by the formation of a thin Al 2 O 3 surface layer for all temperatures. However, for the HEA + Al alloy the formation of AlN was observed after 300 h at 800°C, leading to a partial breakdown of the protective scale. FeCoCrNiCuAl (HEA + Cu + Al) by far showed the best oxidation resistance, characterized by the formation of a highly protective Al 2 O 3 scale that effectively inhibited nitrogen penetration into the metal subsurface and local attack of the Cu-rich phase.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Comparison of unirradiated and irradiated AGR-2 TRISO fuel particle oxidation response

The silicon carbide (SiC) coating in a tristructural isotropic (TRISO) particle acts as a barrier to fission product release during reactor operation and accident scenarios. Oxidation and subsequent failure of the SiC layer during a rare air ingress event is a proposed mechanism for fission product release in a high-temperature gas-cooled reactor (HTGR). Although previous oxidation studies have analyzed unirradiated TRISO particle response, this study compared the oxidation behavior of irradiated and unirradiated TRISO particles from the second Advanced Gas Reactor Fuel Development and Qualification Program irradiation experiment (AGR-2). Particles with exposed SiC were subjected to six varying oxidizing tests in the Furnace for Irradiated TRISO Testing (FITT), examined for failure fraction with the Irradiated Microsphere Gamma Analyzer (IMGA) and characterized with focused ion beam and scanning/transmission electron microscopy techniques to analyze the oxide layer. Uncorrelated unirradiated particle failures throughout the series of exposures suggests that external factors inherent to the experiment increased particle failure sensitivity. However, irradiated particle observations indicated an increased failure response at 400 h 1400 °C in both 2% and 21% O 2 atmospheres above failure associated with external factors. Oxide thickness measurements after 400 h at 1400 °C revealed a greater oxidation rate than predicted by parabolic growth, which was attributed to the increased complexity of the oxide structure at longer exposure times. Altering the atmosphere from 21% to 2% O 2 reduced the average oxide thickness by approximately 12%–14% in both irradiated and unirradiated particles at 400 h 1400 °C. Altogether, the minor variations observed between irradiated and unirradiated particles in this study led to the conclusion that unirradiated TRISO particles can be used to approximate irradiated TRISO oxidation kinetics.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

The Oxidation of the HiSiMo Cast Irons Alloyed with Cr/Al at 800 °C

To improve the oxidation resistance of cast iron containing Si and Mo (HiSiMo), 1wt.% Cr and 3wt.% Al were added into the base alloy to improve high temperature oxidation resistance for exhaust manifold applications. Oxidation tests were performed in both dry and wet air (air + 10% H 2 O) at 800 °C for 1, 10, 24, and 50 h. The mass change and oxide thickness were measured to evaluate the oxidation resistance. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS) and transmission electron microscopy (TEM) were employed to characterize the oxidized samples. Here, the results showed that the additions of Al or Cr selectively oxidized to form a more oxidation resistant surface oxide layer, which reduced the mass gain during these experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2021

FCET Solid Oxide Fuel Cell Testing and Development: CRADA 526 [Abstract only]

The purpose of the proposed project is for PNNL to test the performance of prototype solid oxide fuel cells (SOFCs) created by FCET. Such testing will provide FCET with independent performance data that can be communicated to potential clients and/or investors. Additionally, PNNL will collaborate with FCET on design changes to improve fuel cell performance. Intellectual property developed in this way will benefit FCET with improved products to market, and PNNL through royalty revenue. The key technology held by FCET is a process to deposit extremely thin layers of oxide materials, from 10-50 nm in thickness. The range of possible materials that can be deposited with their method is broad, but this project will focus on the yttria-stabilized zirconia (YSZ) electrolytes for SOFCs. Thin, gas tight YSZ membranes have been a long-sought target in SOFC research. The thinner the YSZ, the lower the cell resistance, and the higher performance of the cell (or the lower the operating temperature). 10-50 nm would be a major step change in YSZ thickness from the state of the art. PNNL can team with FCET on future R&D projects and push this technology forward to improve energy efficiency and reduce carbon emissions.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS1966

Development of Protective Coatings for Chromium-Base Alloys

Chromium alloy sheet was clad with 5 to 10-mil-thick oxidation-resistant nickel-base alloy foils. Specimens also contained 1/2 to 1-mil-thick intermediate layers of platinum, tungsten, and/or W-25Re. Cladding was done by the isostatic hot gas-pressure bonding,.process. The clad chromium-alloy specimens were cyclic oxidation tested at 2100 F and 2300 F for up to 200 hours to determine the effectiveness of these metal claddings in protecting the chromium alloy Cr-5W from oxidation and contamination. Cladding systems consisting of 5-mil-thick Ni-20Cr-20W modified with 3 to 5 weight percent aluminum and containing a 1 /2-mil tungsten diffusion barrier demonstrated potential for long-time service at temperatures as high as 2300 F.

English, J. J.↗
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

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 NTRS1974

Coatings for directional eutectics

Coating compositions were evaluated for oxidation protection of directionally solidified composite alloy NiTaC-13. These coatings included three NiCrAlY compositions (30-5-1, 25-10-1 and 20-15-1), two FeCrAlY compositions (30-5-1 and 25-10-1), a CoCrAlY composition (25-10-1), and one duplex coating, Ni-35Cr + Al. Duplicate pin samples of each composition were evaluated using two cyclic furnace oxidation tests of 100 hours at 871 C and 500 hours at 1093 C. The two best coatings were Ni-20Cr-15Al-lY and Ni-35Cr + Al. The two preferred coatings were deposited on pins and were evaluated in detail in .05 Mach cyclic burner rig oxidation to 1093 C. The NiCrAlY coating was protective after 830 hours of cycling, while the duplex coating withstood 630 hours. Test bars were coated and cycled for up to 500 hours. Tensile tests indicated no effect of coatings on strength. In 871 C air stress rupture, a degradation was observed for coated relative to bare material. The cycled NiCrAlY coating offered excellent protection with properties superior to the bare cycled NiTaC-13 in 1093 C air stress rupture.

Jackson, M. R.↗
NASA NTRS1971

Thermomechanical and Thermochemical Behavior of a Hafnium-20 Percent Tantalum Alloy

An investigation was conducted to determine the thermomechanical and thermochemical behavior of a high temperature, oxidation resistant, hafnium-20 percent tantalum alloy. The elastic and shear moduli of this alloy were determined in air up to 1000 C and in vacuum up to 2000 C using a mechanical resonance technique. The internal friction of the alloy was measured up to temperatures greater than 1400 C. Room temperature stress-strain behavior of the oxidized and unoxidized alloy was established. The effect of annealing on the elastic and shear moduli of the extruded rod material was investigated. The martensitic-type phase transformation occurring in the alloy was studied using hot stage metallography and electron microscopy. Static oxidation tests were conducted on the alloy at temperatures from 1000 C to 1700 C with weight gain measurements made as a function of time and temperatures. Surface morphology studies were conducted on the oxide coatings formed at the different temperatures using scanning electron microscopy and X-ray diffraction techniques.

Howell, J. P.↗
NASA NTRS1987

High temperature isothermal and cyclic oxidation behavior of a single crystal Ni base superalloy

High-temperature oxidation behavior of a Ni-base superalloy, PWA1480, developed for use as single-crystal blades and vanes in advanced gas turbines, has been assessed. Isothermal and cyclic oxidation tests up to 200 hours were conducted at 1323, 1410, and 1473 K. The alloy was evaluated as to sample weight change, type of scale formed, type and amount of spall, and microstructural changes. The oxidation attack was more severe in cyclic as compared with isothermal oxidation. Also, enormous growth of the gamma-prime precipitate was observed at 1423 K during cyclic oxidation.

Hebsur, M. G.↗
DOE OSTI2024

High-Performance Iridium–Molybdenum Oxide Electrocatalysts for Water Oxidation in Acid: Bayesian Optimization Discovery and Experimental Testing

Ir oxides are costly and scarce catalysts for oxygen evolution reaction (OER) in acid. There has been extensive interest in developing alternatives that are either Ir-free or require smaller amounts of Ir to drive the reactions at acceptable rates. One design strategy is to identify Ir-based mixed oxides that achieve similar performance while requiring smaller amounts of Ir. The obstacle to this strategy has been a very large phase space of the Ir-based mixed metal oxides, in terms of the metals combined with Ir and the different crystallographic structures of the mixed oxides, which prevents a thorough exploration of possible materials. In this work, we developed a workflow that uses machine-learning-aided Bayesian optimization in combination with density functional theory to make the exploration of this phase space plausible. This screening identified Mo as a promising dopant for forming acid-tolerant Ir-based oxides for the OER. We synthesized and characterized the Ir–Mo mixed oxides in the form of thin-film electrocatalysts with a known surface area. We show that these mixed oxides exhibited overpotentials ~30 mV lower than a pure Ir control while maintaining 24% lower Ir dissolution rates than the Ir control. Furthermore, these findings suggest that Mo is a promising dopant and highlight the promise of machine learning to guide the experimental exploration and optimization of catalytic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2006

Cyclic Oxidation Behavior of Cold Sprayed CuCrAl-Coated and Uncoated GRCop-84 Substrates for Space Launch Vehicles

A newly developed Cu-23 (wt %) Cr-5%Al (CuCrAl) alloy shown to resist hydridation and oxidation in an as-cast form is currently being considered as a protective coating for GRCop-84, which is an advanced copper alloy containing 8 (at.%) Cr and 4 (at.%) Nb. The coating was deposited on GRCop-84 substrates by the cold spray deposition technique. Cyclic oxidation tests conducted in air on both coated and uncoated substrates between 773 and 1073 K revealed that the coating remained intact and protected the substrate up to 1073 K. No significant weight loss of the coated specimens were observed at 773 and 873 K even after a cumulative cyclic time of 500 h. About a 10 percent weight loss observed at 973 and 1073 K was attributed to the excessive oxidation of the uncoated sides. In contrast, the uncoated substrate lost as much as 80 percent of its original weight under similar test conditions. It is concluded that the cold sprayed CuCrAl coating is suitable for protecting GRCop-84 substrates.

Raj, S. V.↗