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  • 1
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    Oxidation behavior of a thermal barrier coating (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Thermal barrier coatings, consisting of a plasma sprayed calcium silicate ceramic layer and a CoCrAlY or NiCrAlY bond coat, were applied on B-1900 coupons and cycled hourly in air in a rapid-response furnace to maximum temperatures of 1030, 1100, or 1160 C. Eight specimens were tested for each of the six conditions of bond-coat composition and temperature. Specimens were removed from test at the onset of failure, which was taken to be the formation of a fine surface crack visible at 10X magnification. Specimens were weighed periodically, and plots of weight gain vs time indicate that weight is gained at a parabolic rate after an initial period where weight was gained at a much greater rate. The high initial oxidation rate is thought to arise from the initially high surface area in the porous bond coat. Specimen life (time to first crack) was found to be a strong function of temperature. However, while test lives varied greatly with time, the weight gain at the time of specimen failure was quite insensitive to temperature. This indicates that there is a critical weight gain at which the coating fails when subjected to this test.
    Keywords: METALLIC MATERIALS
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    NASA TECHNICAL REPORTS
  • 2
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    Thermal barrier coatings for heat engine components (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: A comprehensive NASA-Lewis program of coating development for aircraft gas turbine blades and vanes is presented. Improved ceramic layer compositions are investigated, along the MCrAlY bond films and the methods of uniform deposition of the coatings; the thermomechanical and fuel impurity tolerance limits of the coatings are being studied. Materials include the ZrO2-Y2O3/NiCrAlY system; the effects of the bond coat and zirconia composition on coating life and Mach 1 burner rig test results are discussed. It is concluded that Diesel engines can also utilize thermal barrier coatings; they have been used successfully on piston crowns and exhaust valves of shipboard engines to combat lower grade fuel combustion corrosion.
    Keywords: METALLIC MATERIALS
    Type: SAMPE Quarterly; 12; Oct. 198
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    NASA TECHNICAL REPORTS
  • 3
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    Performance of thermal barrier coatings in high heat flux environments (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Thermal barrier coatings were exposed to the high temperature and high heat flux produced by a 30 kW plasma torch. Analysis of the specimen heating rates indicates that the temperature drop across the thickness of the 0.038 cm ceramic layer was about 1100 C after 0.5 sec in the flame. An as-sprayed ZrO2-8 percent Y203 specimens survived 3000 of the 0.5 sec cycles with failing. Surface spalling was observed when 2.5 sec cycles were employed but this was attributed to uneven heating caused by surface roughness. This surface spalling was prevented by smoothing the surface with silicon carbide paper or by laser glazing. A coated specimen with no surface modification but which was heat treated in argon also did not surface spall. Heat treatment in air led to spalling in as early as 2 cycle from heating stresses. Failures at edges were investigated and shown to be a minor source of concern. Ceramic coatings formed from ZrO2-12 percent Y2O3 or ZrO2-20 percent Y2O3 were shown to be unsuited for use under the high heat flux conditions of this study.
    Keywords: METALLIC MATERIALS
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    NASA TECHNICAL REPORTS
  • 4
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    Failure analysis of plasma-sprayed thermal barrier coatings (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Thermally induced failure processes of plasma-sprayed thermal barrier coatings are examined. Cracking processes give rise to noise which was monitored by acoustic emission (AE) techniques. The sequential failure of coatings was examined from samples which were thermally cycled. Coatings of yttria-stabilized zirconia with and without a NiCrAlZr bond coat were plasma-sprayed onto U700 alloy rod. In some cases the substrate was intentionally overheated during deposition of the thermal protection system to check how this process variable influenced the AE response of the specimen. In this way a qualitative appraisal of how process variables affect coating integrity could be discerned in terms of cracking behavior. Results from up to seven consecutive thermal cycles are reported here. Coating failure was observed in all cases. Failure of the thermal protection system is progressive, since cracking and crack growth were observed prior to ultimate failure. Thus castastrophic failure occurs at some stage when there is a transformation from the microcrack to a macrocrack network.
    Keywords: METALLIC MATERIALS
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  • 5
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    Corrosion resistant thermal barrier coating (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A thermal barrier coating system for protecting metal surfaces at high temperature in normally corrosive environments is described. The thermal barrier coating system includes a metal alloy bond coating, the alloy containing nickel, cobalt, iron, or a combination of these metals. The system further includes a corrosion resistant thermal barrier oxide coating containing at least one alkaline earth silicate. The preferred oxides are calcium silicate, barium silicate, magnesium silicate, or combinations of these silicates.
    Keywords: METALLIC MATERIALS
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  • 6
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    Design and evaluation of thin metal surface insulation for hypersonic flight (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An all-metal insulation was studied as a thermal protection system for hypersonic vehicles. Key program goals included fabricating the insulation in thin packages which are optimized for high temperature insulation of an actively cooled aluminum structure, and the use of state-of-the-art alloys. The insulation was fabricated from 300 series stainless steel in thicknesses of 0.8 to 12 mm. The outer, 0.127 mm thick, skin was textured to accommodate thermal expansion and oxidized to increase emittance. The thin insulating package was achieved using an insulation concept consisting of foil radiation shields spaced within the package, and conical foil supports to carry loads from the skin and maintain package dimensions. Samples of the metal-insulation were tested to evaluate thermal insulation capability, rain and sand erosion resistance, high temperature oxidation resistance, applied load capability, and high temperature emittance.
    Keywords: METALLIC MATERIALS
    Type: NASA-CR-144914
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Gaseous sodium sulfate formation in flames and flowing gas environments (1977)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Formation of Na2SO4(g) in flames and hot flowing gas systems was studied by high pressure, free-jet expansion, modulated molecular beam mass spectrometric sampling. Fuel-lean CH4-O2 flames doped with SO2, H2O and NaCl yielded the gaseous Na2SO4 molecule in residence times of less than one millisecond. Intermediate species NaSO2(g) and NaSO3(g) were also observed and measured. Composition profiles were obtained for all reaction products. Nonflame flowing gas experiments showed that Na2SO4 and NaSO3 gaseous molecules were formed at 1140 C in mixtures of O2, H2O(g), SO2 and NaCl(g). Experimental results are compared with calculated equilibrium thermodynamic predictions.
    Keywords: METALLIC MATERIALS
    Type: NASA-TM-X-73600 , E-9029 , Symp. on Corrosion Probl. Involving Volatile Corrosion Products; May 08, 1977 - May 13, 1977; Philadelphia
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  • 8
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    Volatile products in the corrosion of Cr, Mo, Ti and four superalloys exposed to O2 containing H2O and gaseous NaCl (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Keywords: METALLIC MATERIALS
    Type: Symposium on Corrosion Problems Involving Volatile Corrosion Products; May 12, 1977; Philadelphia, PA
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    NASA TECHNICAL REPORTS
  • 9
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    Volatile products in the corrosion of Cr, Mo, Ti and four superalloys exposed to O2 containing H2O and gaseous NaCl (1977)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Cooled target collection techniques were used to study the formation of volatile products when samples of Cr, Ti, IN-738, 713C, NASA-TRW VIA and B-1900 were exposed, at elevated temperatures, to oxidizing environments containing H2O(g) and NaCl(g). Samples were heated to 1050 C in one atmosphere of slowly flowing oxygen, saturated with water at 21 C, and containing about 50 ppm NaCl(g). Volatile products were detected for all materials except B-1900 and Ti. High pressure mass spectrometric sampling was used to directly identify volatile products emanating from samples of Cr and IN-738 subject to the above environments.
    Keywords: METALLIC MATERIALS
    Type: NASA-TM-X-73599 , E-9074 , Symp. on Corrosion Probl. Involving Volatile Corrosion Products; May 08, 1977 - May 13, 1977; Philadelphia
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    NASA TECHNICAL REPORTS
  • 10
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    Failure mechanisms of thermal barrier coatings exposed to elevated temperatures (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The failure of a ZrO2-8%Y2O3/Ni-14% Al-0.1% Zr coating system on Rene 41 in Mach 0.3 burner rig tests was characterized. High flame and metal temperatures were employed in order to accelerate coating failure. Failure by delamination was shown to precede surface cracking or spalling. This type of failure could be duplicated by cooling down the specimen after a single long duration isothermal high temperature cycle in a burner rig or a furnace, but only if the atmosphere was oxidizing. Stresses due to thermal expansion mismatch on cooling coupled with the effects of plastic deformation of the bond coat and oxidation of the irregular bond coat are the probable life limiting factors. Heat up stresses alone could not fail the coating in the burner rig tests. Spalling eventually occurs on heat up but only after the coating has already failed through delamination.
    Keywords: METALLIC MATERIALS
    Type: NASA-TM-82905 , E-1289 , NAS 1.15:82905
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