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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Room temperature tensile ductility in powder processed B2 FeAl alloys

It has been shown that it is possible to obtain significant room temperature tensile ductility in FeAl alloys using iron-rich deviations from stoichiometry. A comparison of the room temperature tensile and compressive behaviors of Fe-50 at. pct Al and Fe-40 at. pct Al shows that FeAl is brittle at higher Al contents because it fractures along grain boundaries before general yielding. Lower aluminum contents reduce the yield stress substantially and hence some ductility is observed before fracture. Addition of boron results in measurable improvements in ductility of Fe-40 at. pct Al and is accompanied by an increase in transgranular tearing on the fracture surface, suggesting a grain boundary strengthening mechanism. Increasing the cooling rate following annealing at 1273 K results in a large increase in the yield strength and a corresponding decrease in ductility.

Crimp, M. A.↗
NASA NTRS1989

Fatigue crack propagation in aluminum-lithium alloys

The principal mechanisms which govern the fatigue crack propagation resistance of aluminum-lithium alloys are investigated, with emphasis on their behavior in controlled gaseous and aqueous environments. Extensive data describe the growth kinetics of fatigue cracks in ingot metallurgy Al-Li alloys 2090, 2091, 8090, and 8091 and in powder metallurgy alloys exposed to moist air. Results are compared with data for traditional aluminum alloys 2024, 2124, 2618, 7075, and 7150. Crack growth is found to be dominated by shielding from tortuous crack paths and resultant asperity wedging. Beneficial shielding is minimized for small cracks, for high stress ratios, and for certain loading spectra. While water vapor and aqueous chloride environments enhance crack propagation, Al-Li-Cu alloys behave similarly to 2000-series aluminum alloys. Cracking in water vapor is controlled by hydrogen embrittlement, with surface films having little influence on cyclic plasticity.

Rao, K. T. V.↗
NASA NTRS1982

The relative stress-corrosion-cracking susceptibility of candidate aluminum-lithium alloys for aerospace applications

Stress corrosion tests of Al-Li-Cu powder metallurgy alloys are described. Alloys investigated were Al-2.6% Li-1.4% and Al-2.6% Li-1.4% Cu-1.6% Mg. The base properties of the alloys were characterized. Process, heat treatment, and size/orientational effects on the tensile and fracture behavior were investigated. Metallurgical and electrochemical conditions are identified which provide reproducible and controlled parameters for stress corrosion evaluation. Preliminary stress corrosion test results are reported. Both Al-Li-Cu alloys appear more susceptible to stress corrosion crack initiation than 7075-T6 aluminum, with the magnesium bearing alloy being the most susceptible. Tests to determine the threshold stress intensity for the base and magnesium bearing alloys are underway. Twelve each, bolt loaded DCB type specimens are under test (120 days) and limited crack growth in these precracked specimens has been observed. General corrosion in the aqueous sodium chloride environment is thought to be obscuring results through crack tip blunting.

Pizzo, P. P.↗
NASA NTRSDate not supplied

Investigation into Interfacial Mixing Behavior of Blown Powder Deposited Inconel 625-Copper Alloy Bimetallic for Improvement of Bimetallic Joint Strength

Use of laser blown powder, directed energy deposition (DED) provides a method for fabrication of bimetallic functional materials for high heat flux applications. However, this relatively new process currently has a low technology readiness level (TRL). Key to increasing the TRL is a better understanding of the factors that control mixing of the bi-metallic materials at the interface. The resulting interfaces in specimens obtained from three vendors were characterized using optical and electron microscopy with electron dispersion spectroscopy in addition to mechanical testing. Based on the range of process parameters and resulting interfaces, a model is being developed to predict interfacial mixing for development of specifications for improved and repeatable microstructures.

Additive Manufacturing↗
NASA NTRS1995

Method and apparatus for production of powders

Apparatus and method are disclosed for producing oxides of metals and of metal alloys. The metal or alloy is placed in an oxygen atmosphere in a combustion chamber and ignited. Products of the combustion include one or more oxides of the metal or alloy in powdered form. In one embodiment of the invention a feeder is provided whereby material to be oxidized by combustion can be advanced into a combustion chamber continuously. A product remover receives the powder product of the combustion.

Stolzfus, Joel M.↗
NASA NTRS1997

Method for Production of Powders

Apparatus and method are disclosed for producing oxides of metals and of metal alloys. The metal or alloy is placed in an oxygen atmosphere in a combustion chamber and ignited. Products of the combustion include one or more oxides of the metal or alloy in powdered form. In one embodiment of the invention a feeder is provided whereby material to be oxidized by combustion can be achieved into a combustion chamber continuously. A product remover receives the powder product of the combustion.

Stoltzfus, Joel M.↗
NASA NTRS1998

Method and Apparatus for Production of Powders

Apparatus and method are disclosed for producing oxides of metals and of metal alloys. The metal or alloy is placed in an oxygen atmosphere in a combustion chamber and ignited. Products of the combustion include one or more oxides of the metal or alloy in powdered form. In one embodiment of the invention a feeder is provided whereby material to be oxidized by combustion can be advanced into a combustion chamber continuously. A product remover receives the powder product of the combustion.

Storltzfus, Joel M.↗
NASA NTRS1978

Evaluation of Cyclic Behavior of Aircraft Turbine Disk Alloys

An evaluation of the cyclic behavior of three aircraft engine turbine disk materials was conducted to compare their relative crack initiation and crack propagation resistance. The disk alloys investigated were Inconel 718, hot isostatically pressed and forged powder metallurgy Rene '95, and as-hot-isostatically pressed Rene '95. The objective was to compare the hot isostatically pressed powder metallurgy alloy forms with conventionally processed superalloys as represented by Inconel 718. Cyclic behavior was evaluated at 650 C both under continuously cycling and a fifteen minute tensile hold time cycle to simulate engine conditions. Analysis of the test data were made to evaluate the strain range partitioning and energy exhaustion concepts for predicting hold time effects on low cycle fatigue.

Shahani, V.↗
NASA NTRS1983

Stress-corrosion behavior of aluminum-lithium alloys in aqueous environments

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Pizzo, P. P.↗
NASA NTRS1984

Stress-corrosion behavior of aluminum-lithium alloys in aqueous salt environments

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg; two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Pizzo, P. P.↗
NASA NTRS1982

Dual-Alloy Disks are Formed by Powder Metallurgy

High-performance disks have widely varying properties from hub to rim. Dual property disk is fabricated using two nickel-base alloys, AF-115 for rim and Rene 95 for hub. Dual-alloy fabrication may find applications in automobiles, earth-moving equipment, and energy conversion systems as well as aircraft powerplants. There is potential for such applications as shafts, gears, and blades.

Harf, F. H.↗
NASA NTRS1982

Oxide dispersion hardened mechanically alloyed materials for high temperatures

The procedure of mechanical alloying makes it possible to obtain, with the aid of powder-metallurgy techniques, alloys that consist of a metallic matrix in which very fine oxide particles are dispersed. Mechanically alloyed compound powders can be used for making either forged or hot-rolled semifinished products. For these products, dispersion strengthening and precipitation hardening has been combined. At high temperatures, the strength characteristics of the alloy are determined by both dispersion hardening and by precipitation hardening processes. The effect produced by each process is independent of that due to the other. Attention is given to the principle of mechanical alloying developed by Benjamin (1970, 1976), the strength characteristics of mechanically alloyed materials, the corrosion resistance of mechanically alloyed material at high temperatures, and the preparation and characteristics of the alloy MA 6000 E.

Benjamin, J. S.↗
NASA NTRS1985

Properties and microstructures for dual alloy combinations of three superalloys with alloy 901

Dual alloy combinations have potential for use in aircraft engine components such as turbine disks where a wide range of stress and temperature regimes exists during operation. Such alloy combinations may directly result in the conservation of elements which are costly or not available domestically. Preferably, a uniform heat treatment yielding good properties for both alloys should be used. Dual alloy combinations of iron rich Alloy 901 with nickel base superalloys Rene 95, Astroloy, or MERL 76 were not isostatically pressed from prealloyed powders. Individual alloys, alloy mixtures, and layered alloy combinations were given the heat treatments specified for their use in turbine disks or appropriate for Alloy 901. Selected specimens were overaged for 1500 hr at 650 C. Metallographic examinations revealed the absence of phases not originally present in either alloy of a combination. Mechanical tests showed adequate properties in combinations of Rene 95 or Astroloy with Alloy 901 when given the Alloy 901 heat treatment. Combinations with MERL 76 had better properties when given the MERL 76 heat treatment. The results indicate that these combinations are promising candidates for use in turbine disks.

Harf, F. H.↗
NASA NTRS2002

Initial Assessment of the Effects of Nonmetallic Inclusions on Fatigue Life of Powder-Metallurgy-Processed Udimet(TM) 720

The fatigue lives of modern powder metallurgy (PM) disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary due to the different steps of materials/component processing and machining. One of these variables, the presence of nonmetallic inclusions, has been shown to significantly degrade low-cycle fatigue (LCF) life. Nonmetallic inclusions are inherent defects in powder alloys that are a by-product of powder-processing techniques. Contamination of the powder can occur in the melt, during powder atomization, or during any of the various handling processes through consolidation. In modern nickel disk powder processing facilities, the levels of inclusion contamination have been reduced to less than 1 part per million by weight. Despite the efforts of manufacturers to ensure the cleanliness of their powder production processes, the presence of inclusions remains a source of great concern for the designer. the objective of this study was to investigate the effects on fatigue life of these inclusions. Since natural inclusions occur so infrequently, elevated levels of inclusions were carefully introduced in a nickel-based disk superalloy, Udimet 720 (registered trademark of Special Metals Corporation), produced using PM processing. Multiple strain-controlled fatigue tests were then performed on this material at 650 C. Analyses were performed to compare the LCF lives and failure initiation sites as functions of inclusion content and fatigue conditions. A large majority of the failures in specimens with introduced inclusions occurred at cracks initiating from inclusions at the specimen surface. The inclusions could reduce fatigue life by up to 100 times. These effects were found to be dependent on strain range and strain ratio. Tests at lower strain ranges and higher strain ratios produced larger effects of inclusions on life.

Gabb, T. P.↗
NASA NTRS1980

Development of a high strength hot isostatically pressed /HIP/ disk alloy, MERL 76

A nickel-based powder metal disk alloy developed for use in advanced commercial gas turbines is described. Consideration is given to final alloy chemistry modifications made to achieve a desirable balance between tensile strength and stress rupture life and ductility. The effects of post-consolidation heat treatment are discussed, the preliminary mechanical properties obtained from full-scale turbine disks are presented.

Evans, D. J.↗