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  • 1
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    Polyphase Magmatism During the Formation of the Northern East Greenland Continental Margin (2021)
    Details
    Publication Date: 2021-09-15
    Description: New marine geophysical data acquired across the partly ice-covered northern East Greenland continental margin highlight a complex interaction between tectonic and magmatic events. Breakup-related lava flows are imaged in reflection seismic data as seaward dipping reflectors, which are found to decrease in size both northward and southward from a central point at 75°N. We provide evidence that the magnetic anomaly pattern in the shelf area is related to volcanic phases and not to the presence of oceanic crust. The remnant magnetization of the individual lava flows is used to deduce a relative timing of the emplacement of the volcanic wedges. We find that the seaward dipping reflectors have been emplaced over a period of 2–4 Ma progressively from north to south and from landward to seaward. The new data indicate a major post-middle Eocene magmatic phase around the landward termination of the West Jan Mayen Fracture Zone. This post-40-Ma volcanism likely was associated with the progressive separation of the Jan Mayen microcontinent from East Greenland. The breakup of the Greenland Sea started at several isolated seafloor spreading cells whose location was controlled by rift structures and led to the present-day segmentation of the margin. The original rift basins were subsequently connected by steady-state seafloor spreading that propagated southward, from the Greenland Fracture Zone to the Jan Mayen Fracture Zone.
    Keywords: 551 ; 559 ; NE Greenland ; seismic reflection ; seaward dipping reflectors ; continent-ocean transition ; rifting ; Greenland Sea
    Language: English
    Type: article
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    CITATION GEO-LEO
  • 2
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    Mechanical property measurements of plasma-sprayed thermal-barrier coatings subjected to oxidation (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Techniques have been developed for measuring the tensile properties of plasma-sprayed coatings which are used in thermal barrier applications. The measurements have included the average Young's modulus, bond strength and elongation at failure. The oxidation behavior of the bond coat plays an important role in the integrity and adhesion of plasma-sprayed thermal barrier coatings. This work studies the nature of the high temperature degradation on the mechanical properties of the coating. Furnace tests have been carried out on U-700 alloy with bond coats of NiCrAlY or NiCrAlZr and an overlay of ZrO2-8 percent Y2O3. Weight gain measurements on the coatings have been examined with relation to the adhesion strength and failure observations. The results from an initial study are reported in this work.
    Keywords: NONMETALLIC MATERIALS
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 5; 479-490
    Format: text
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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 Y2O3 specimens survived 3000 of the 0.5 sec cycles with falling. 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 1 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 ZrO2-2O percent Y2O3 were shown to be unsuited for use under the high heat flux conditions of this study.
    Keywords: NONMETALLIC MATERIALS
    Type: Thin Solid Films (ISSN 0040-6090); 119; 195-202
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Thermal spray processing (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Thermal spray processing has been used for a number of years to cost-effecticely apply TBC's for a wide range of heat engine applications. In particular, bond coats are applied by plasma spray and HVOF techniques and partially-stabilized zirconia top coats are applied by plasma spray methods. Thermal spray involves melting and rapid transport of the molten particles to the substrate, where high-rate solidification and coating build-up occur. It is the very nature of this melt processing that leads to the unique layered microstructure, as well as the apparent imperfections, so readily identified with thermal spray. Modeling the process, process-induced residual stresses, and thermal conductivity will be discussed in light of a new understanding of porosity and its anisotropy. Microcracking can be understood using new approaches, allowing a fuller view of the processing-performance connection. Detailed electron microscopic, novel neutron diffraction and fracture analysis of the deposits can lead to a better understanding of how overall microstructure can be controlled to influence critical properties of the deposited TBC system.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA. Lewis Research Center, Thermal Barrier Coating Workshop; p 23
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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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
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Neutron and X-ray diffraction of plasma-sprayed zirconia-yttria thermal barrier coatings (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: ZrO2-7.8mol. pct. YO1.5, a fused powder, and ZrO2-8.7mol. pct. YO1.5, a prereacted powder, were plasma-sprayed onto steel substrates. Neutron diffraction and X-ray diffraction of the as-received powder, the powder plasma sprayed into water, as-sprayed coatings, and coatings heat-treated for 10 and 100 h were carried out to study phase transformations and ordering of the oxygen ions on the oxygen sublattice. The as-received fused powder has a much lower monoclinic percentage than does the pre-reacted powder, this resulting in a much lower monoclinic percentage in the coating. Heat treatment increases the percentages of the cubic and monoclinic phases, while decreasing the tetragonal content. An ordered tetragonal phase is detected by the presence of extra neutron diffraction peaks. These phase transformations and ordering will result in volume changes. The implications of these transformations on the performance of partially stabilized zirconia thermal barrier coatings is discussed.
    Keywords: NONMETALLIC MATERIALS
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Tensile adhesion test measurements on plasma-sprayed coatings (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Adhesion measurements on plasma-sprayed coatings are briefly studied, including a critical analysis of the experimental scatter for duplicate tests. The application of a simple method which presents adhesion strength data in a fracture mechanics perspective is demonstrated. Available data are analyzed in a way which suggests an approach to finding the overall defect contribution to reducing the apparent strength of coatings.
    Keywords: NONMETALLIC MATERIALS
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Fracture toughness tests on plasma-sprayed coatings (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Fracture toughness measurements have been performed on plasma-sprayed coatings. The intrinsic fracture toughness of plasma-sprayed coatings may be ascertained by means of a double cantilever beam (DCB) test. Emphasis is placed on calibration of the specimen geometry. Representative values for alumina coatings are presented.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Mechanical behavior of thermal barrier coatings for gas turbine blades (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Plasma-sprayed thermal barrier coatings (TBCs) will enable turbine components to operate at higher temperatures and lower cooling gas flow rates; thereby improving their efficiency. Future developments are limited by precise knowledge of the material properties and failure mechanisms of the coating system. Details of this nature are needed for realistic modeling of the coating system which will, in turn, promote advancements in coating technology. Complementary experiments and analytical modeling which were undertaken in order to define and measure the important failure processes for plasma-sprayed coatings are presented. The experimental portion includes two different tests which were developed to measure coating properties. These are termed tensile adhesion and acoustic emission tests. The analytical modeling section details a finite element method which was used to calculate the stress distribution in the coating system. Some preliminary results are presented.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA. Lewis Research Center Turbine Engine Hot Section Technology, 1984; 12 p
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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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
    Format: text
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    NASA TECHNICAL REPORTS
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