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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Failure Analysis and Recovery of a 50 MM Highly Elastic Intermetallic NiTi Ball Bearing for an ISS Application

The ISS Distillation Assembly centrifuge is the pathfinder application for 50mm bore, deep-groove ball bearings made from the highly elastic intermetallic material 60NiTi. Superior corrosion and shock resistance are required to withstand the acidic wastewater exposure and heavy spacecraft launch related loads that challenge conventional steel bearings. During early ground testing one bearing unexpectedly and catastrophically failed after operating for only 200 hours of run time. A second bearing running on the same shaft was completely unaffected. A thorough investigation into the root cause of the failure determined that an excessively tight press-fit of the bearing outer race coupled with NiTis relatively low elastic modulus were key contributing factors. The proposed failure mode was successfully duplicated by experiment. To further corroborate the root cause theory, a successful bearing life test using improved installation practices (selective fitting) was conducted. The results show that NiTi bearings are suitable for space applications provided that care is taken to accommodate their unique material characteristics.

failure analyses↗
NASA NTRS1968

Crystal structure analysis of intermetallic compounds

Study concerns crystal structures and lattice parameters for a number of new intermetallic compounds. Crystal structure data have been collected on equiatomic compounds, formed between an element of the Sc, Ti, V, or Cr group and an element of the Co or Ni group. The data, obtained by conventional methods, are presented in an easily usable tabular form.

Conner, R. A., Jr.↗
NASA NTRS1971

Unique intermetallic compounds prepared by shock wave synthesis

Technique compresses fine ground metallic powder mixture beyond crystal fusion point. Absence of vapor pressure voids and elimination of incongruous effects permit application of technique to large scale fabrication of intermetallic compounds with specific characteristics, e.g., semiconduction, superconduction, or magnetic properties.

Otto, G.↗
NASA NTRS1972

New twisted intermetallic compound superconductor: A concept

Method for processing Nb3Sn and other intermetallic compound superconductors produces a twisted, stabilized wire or tube which can be used to wind electromagnetics, armatures, rotors, and field windings for motors and generators as well as other magnetic devices.

Coles, W. D.↗
NASA NTRS1982

Intermetallics as alternative materials

Aluminum containing intermetallics have B2 cubic crystal structures, exist over a wide range of composition, have large solubilities for third element alloying additions, are capable of both low and high temperature plastic flow, and have very high melting temperatures (approximately 1900 K) except for FeAl. The slow strain rate elevated temperature properties of Fe, Ni, and Co aluminides are investigated. Because of the reported difficulties with traditional melting/casting methods, sound polycrystalling materials are fabricated by hot extrusion of steel canned blended prealloyed powders. These binary aluminides are used to develop base line elevated temperature mechanical properties as well as an understanding of the factors which affect/control the strength and ductility.

Whittenberger, J. D.↗
NASA NTRS1985

Slow plastic strain rate compressive flow in binary CoAl intermetallics

Constant-velocity elevated temperature compression tests have been conducted on a series of binary CoAl intermetallics produced by hot extrusion of blended prealloyed powders. The as-extruded materials were polycrystalline, and they retained their nominal 10-micron grain size after being tested between 1100 and 1400 K at strain rates ranging from 2 x 10 to the -4th to 2 x 10 to the -7th per sec. Significant plastic flow was obtained in all cases; while cracking was observed, much of this could be due to failure at matrix-oxide interfaces along extrusion stringers rather than to solely intergranular fracture. A maximum in flow strength occurs at an aluminum-to-cobalt ratio of 0.975, and the stress exponent appears to be constant for aluminum-to-cobalt ratios of 0.85 or more. It is likely that very aluminum-deficient materials deform by a different mechanism than do other compositions.

Whittenberger, J. D.↗
NASA NTRS1988

The oxidation of Ni-rich Ni-Al intermetallics

The oxidation of Ni-Al intermetallic alloys in the beta-NiAl phase field and in the two phase beta-NiAl/gamma'-Ni3Al phase field has been studied between 1000 and 1400 C. The stoichiometric beta-NiAl alloy doped with Zr was superior to other alloy compositions under cyclic and isothermal oxidation. The isothermal growth rates did not increase monotonically as the alloy Al content was decreased. The characteristically ridged alpha-Al2O3 scale morphology, consisting of cells of thin, textured oxide with thick growth ridges at cell boundaries, forms on oxidized beta-NiAl alloys. The correlation of scale features with isothermal growth rates indicates a predominant grain boundary diffusion growth mechanism. The 1200 C cyclic oxidation resistance decreases near the lower end of the beta-NiAl phase field.

Doychak, Joseph↗
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 NTRS1988

Interdiffusional effects between TiBe12 and NiAl intermetallics

The TiBe12/NiAl composites fabricated by a powder metallurgy technique were examined for the extent of interdiffusion between its components, using scanning Auger microscopy. The results revealed an evidence of a reaction between the two component intermetallics after annealing at 1300 K for 100 h, with a 95-micron reaction zone extending from the TiBe12/NiAl interface. The concentration profile across the reaction zone showed that the Ni, Al, and Be concentrations were in a 1:1:2 ratio, while Ti was present in only very small amounts.

Carbone, A. J.↗
NASA NTRS1989

Oxidation of high-temperature intermetallics; Proceedings of the Workshop, Cleveland, OH, Sept. 22, 23, 1988

The present conference on the high-temperature oxidation behavior of aerospace structures-applicable intermetallic compounds discusses the influence of reactive-element additions on the oxidation of Ni3Al base alloys, the effect of Ni3Al oxidation below 850 C on fracture behavior, the oxidation of FeAl + Hf, Zr, and B, the synergistic effect of Al and Si on the oxidation resistance of Fe alloys, and pack cementation coatings of Cr-Al on Fe, Ni, and Co alloys. Also discussed are the formation of alumina on Nb- and Ti-base alloys, the oxidation behavior of titanium aluminide alloys, silicide coatings for refractory metals, the oxidation of chromium disilicide, and the oxidation behavior of nickel beryllides.

Grobstein, Toni↗
NASA NTRS1989

The oxidation of Ni-rich Ni-Al intermetallics

The oxidation of Ni-Al intermetallic alloys in the beta-NiAl phase field and in the two phase beta-NiAl/gamma'-Ni3Al phase field has been studied between 1000 and 1400 C. The stoichiometric beta-NiAl alloy doped with Zr was superior to other alloy compositions under cyclic and isothermal oxidation. The isothermal growth rates did not increase monotonically as the alloy Al content was decreased. The characteristically ridged alpha-Al203 scale morphology, consisting of cells of thin, textured oxide with thick growth ridges at cell boundaries, forms on oxidized beta-NiAl alloys. The correlation of scale features with isothermal growth rates indicates a predominant grain boundary diffusion growth mechanism. The 1200 C cyclic oxidation resistance decreases near the lower end of the beta-NiAl phase field.

Doychak, J.↗
NASA NTRS1989

The effects of surface films on mechanical behavior of B2 ordered intermetallic alloys

Surface films deposited on body-centered cubic metals can greatly reduce the yield and flow stresses and increase the ductility at low homologous temperatures. This softening process is associated with the ability of the film-substrate interface to generate large populations of mobile edge dislocations. This phenomenon is extended to B2 ordered intermetallic alloys, which display many deformation characteristics of bcc metals. Single crystal NiAl coated with thermally formed oxide films and polycrystalline FeAl with electrochemically formed Fe-Al-O films display film softening at and below room temperature. The extent of film softening is shown to depend on many factors, including crystal orientation, deformation temperature, operative slip systems, film thickness, film adherence, and film and substrate properties.

Noebe, R. D.↗
NASA NTRS1989

Elastic crack bridging in ceramic and intermetallic matrix composites

A micromechanics analytical model based on the consistent shear lag theory is developed for predicting the failure modes in a fiber reinforced unidirectional ceramic and intermetallic matrix composite. The model accounts for the relatively large matrix stiffness. The fiber and matrix stresses are established as functions of the applied stress, crack geometry, and most importantly, the microstructural properties of the constituents. From the predicted stress, the mode of failure is established based on the point stress criterion.

Dharani, L. R.↗
NASA NTRS1991

Fatigue life prediction of an intermetallic matrix composite at elevated temperatures

A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the Universal Slopes method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio, number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.

Bartolotta, Paul A.↗
NASA NTRS1984

Method for imparting strength to intermetallic phases

A method for achieving both improved high strength and improved ductility ·in intermediate phases is provided. The method, briefly stated, comprises the steps of providing a melt whose composition substantially corresponds to that of a preselected intermetallic phase having a crystal structure of the L1 2 type, such as nickel. aluminide, modified with from about 0.01 to 2.5 atomic percent boron, and rapidly solidifying the melt at a cooling rate of at least about 10 3 ° C./second to form a solid body, the principal phase of which is of the L1 2 type crystal structure in either its ordered or disordered state.

Shyh-Chin Huang↗
NASA NTRS1990

Intermetallic and ceramic matrix composites for 815 to 1370 C (1500 to 2500 F) gas turbine engine applications

Revolutionary improvements in gas turbine engine specific fuel consumption and specific thrust are expected to be gained through incorporation of CMCs and of MMCs (whose intermetallic matrices are reinforced by highly refractory ceramic fibers). A status development evaluation is presented for NASA's Advanced High Temperature Engine Materials Technology Program, with a view to projections of early-21st century transport aircraft performance levels obtainable through the use of MMCs and CMCs in ultrahigh bypass turbofan engines.

Stephens, Joseph R.↗