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  • 1
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    Friction Studies of Various Materials in Liquid Nitrogen (1958)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Type: NACA-TN-4211
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Method of fabricating an abradable gas path seal (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The thermal shock resistance of a ceramic layer is improved. The invention is particularly directed to an improved abradable lining that is deposited on shroud forming a gas path in turbomachinery. Improved thermal shock resistance of a shroud is effected through the deliberate introduction of benign cracks. These are microcracks which will not propagate appreciably upon exposure to the thermal shock environment in which a turbine seal must function. Laser surface fusion treatment is used to introduce these microcracks. The ceramic surface is laser scanned to form a continuous dense layer. As this layer cools and solidifies, shrinkage results in the formation of a very fine crack network. The presence of this deliberately introduced fine crack network precludes the formation of a catastrophic crack during thermal shock exposure.
    Keywords: MECHANICAL ENGINEERING
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  • 3
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    Effects of geometric variables on rub characteristics of Ti-6Al-4V (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Experiments simulating rub interactions between Ti-6Al-4V blade tips and various seal materials were conducted. The number of blade tips and the blade tip geometry were varied to determine their effects on rub forces and on wear phenomena. Contact was found to be quite unsteady for all blade tip geometries except for those incorporating deliberately rounded blade tips. The unsteady contact was characterized by long periods of rubbing contact and increasing blade tip that terminated in sudden rapid metal removal, sometimes accompanied by tearing and disruption of porous seal material under the rub surface. A model describing the blade tip loading is proposed and is based on the propagation of an elastic stress wave through the seal material as the seal material is dynamically compressed by the blade tip leading edge.
    Keywords: METALLIC MATERIALS
    Type: NASA-TP-1835 , AVRADCOM-TR-80-C-19 , E-449
    Format: application/pdf
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  • 4
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    Fully plasma-sprayed compliant backed ceramic turbine seal (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A seal having a high temperature abradable lining material encircling the tips of turbine blades in turbomachinery is discussed. The minimum operating clearances between the blade tips and the lining of a high pressure turbine are maintained. A low temperature easily decomposable material, such as a polymer, in powder form is blended with a high temperature oxidation resistant metal powder. The two materials are simultaneously deposited on a substrate formed by the turbine casing. Alternately, the polymer powder may be added to the metal powder during plasma spraying. A ceramic layer is then deposited directly onto the metal polymer composite. The polymer additive mixed with the metal is then completely volatilized to provide a porous layer between the ceramic layer and the substrate.
    Keywords: NONMETALLIC MATERIALS
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  • 5
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    Friction and wear of selected metals and alloys in sliding contact with AISI 440 C stainless steel in liquid methane and in liquid natural gas (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Aluminum, titanium, beryllium, nickel, iron, copper, and several copper alloys were run in sliding contact with AISI 440C in liquid methane and natural gas. All of the metals run except copper and the copper alloys of tin and tin-lead showed severely galled wear scars. Friction coefficients varied from 0.2 to 1.0, the lowest being for copper, copper-17 wt. % tin, and copper-8 wt. % tin-22 wt. % lead. The wear rate for copper was two orders of magnitude lower than that of the other metals run. An additional order of magnitude of wear reduction was achieved by the addition of tin and/or lead to copper.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TP-1150 , E-9195
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  • 6
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    Preliminary study of cyclic thermal shock resistance of plasma-sprayed zirconium oxide turbine outer air seal shrouds (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Several experimental concepts representing potential high pressure turbine seal material systems were subjected to cyclic thermal shock exposures similar to those that might be encountered under severe engine start-up and shut-down sequences. All of the experimental concepts consisted of plasma-sprayed yttria stabilized ZrO2 on the high temperature side of the blade tip seal shroud. Between the ZrO2 and a cooled, dense metal backing, various intermediate layer concepts intended to mitigate thermal stresses were incorporated. Performance was judged on the basis of the number of thermal shock cycles required to cause loss of seal material through spallation. The most effective approach was to include a low modulus, sintered metal pad between the ZrO2 and the metallic backing. It was also found that reducing the density of the ZrO2 layer significantly improved the performance of specimens with plasma-sprayed metal/ceramic composite intermediate layers.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TM-73852 , E-9404
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  • 7
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    Friction and wear of several compressor gas-path seal movements (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Rub interaction experiments were conducted on a series of sintered and plasma sprayed compressor gas path seal materials in contact with Ti-6Al-4V blade tip and knife edge rotors. The most rub tolerant materials investigated were sintered Nichrome and plasma sprayed nickel 25 percent graphite. The effectiveness of providing a compliant substrate for dense seal material coatings was also demonstrated. In general, it was observed that rotor wear and high frictional energy generation rates accompanied smearing or surface densification of the materials investigated. The onset of smearing was sensitive to rub interaction parameters and seal geometry. Two complementary models were proposed to account for the smearing trends. One is based on thermal effects, the other on particulate escape effects. They were shown to be consistent with the experimental evidence at hand, and together they predict that smearing, with the onset of high energy rub conditions, is favored when incursion rates (radial motion) are low, incursion depths are high, the seal geometry is of a knife-edge character, and the seal particle size is small.
    Keywords: METALLIC MATERIALS
    Type: NASA-TP-1128 , E-9276
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  • 8
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    Performance of 40-millimeter-bore ball bearings with lead- and lead-alloy-plated retainers in liquid hydrogen at 1.2 million DN (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Forty-millimeter-bore ball bearings with lead- and lead-alloy-coated retainers were operated in liquid hydrogen at 30,000 rpm under a thrust load of 1780 N (400 lb.) Four different substrate materials were used for the retainer. Longer bearing run times were achieved with a lead-tin-copper alloy coating plated onto a leaded-bronze material (22.5 hr) and an aluminum-bronze alloy (19.3 hr). One bearing with a pure lead coating achieved the desired objective of 10 hr. This bearing had an aluminum - bronze substrate retainer and ran successfully for 12.4 hr. Additions of antimony to the lead provided an alloy coating with better wear resistance than pure lead; however, this coating was abrasive to the outer-race lands.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TN-D-6981 , E-6916
    Format: application/pdf
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  • 9
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    Role of plastic deformation in wear of copper and copper - 10-percent-aluminum alloy in cryogenic fuels (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: High-purity copper specimens and a copper-aluminum (10%) alloy specimen were subjected to sliding against Type 440 C in cryogenic fuel environments. It was found that virtually all wear occurred by the plastic deformation of a recrystallized layer extending to about 10 micrometers below the wear scar surface of the copper or copper alloy. The wear debris was in the form of a layered structure adhering to the exit region of the wear scar. Measurements on the high purity copper specimens indicated that the wear rate was proportional to the applied load and to the sliding velocity squared. A physical model of the wear process is proposed to account for these observations.
    Keywords: MATERIALS, METALLIC
    Type: NASA-TN-D-7253 , E-7314
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  • 10
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    Friction and wear of titanium alloys and copper alloys sliding against titanium 6-percent-aluminum - 4-percent-vanadium alloy in air at 430 C (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Experiments were conducted to determine the friction and wear characteristics of aluminum bronzes and copper-tin, titanium-tin, and copper-silver alloys sliding against a titanium-6% aluminum-4% vanadium alloy (Ti-6Al-4V). Hemispherically tipped riders of aluminum bronze and the titanium and copper alloys were run against Ti-6Al-4V disks in air at 430 C. The sliding velocity was 13 cm/sec, and the load was 250 g. Results revealed that high tin content titanium and copper alloys underwent significantly less wear and galling than commonly used aluminum bronzes. Also friction force was less erratic than with the aluminum bronzes.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TN-D-8207 , E-8522
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