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  • 1
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    Investigation of Thermal High Cycle and Low Cycle Fatigue Mechanisms of Thick Thermal Barrier Coatings (1998)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Ceramic thermal barrier coatings have attracted increased attention for diesel engine applications. The advantages of using the ceramic coatings include a potential increase in efficiency and power density and a decrease in maintenance cost. Zirconia-based ceramics are the most important coating materials for such applications because of their low thermal conductivity, relatively high thermal expansivity and excellent mechanical properties. However, durability of thick thermal barrier coatings (TBCS) under severe temperature cycling encountered in engine conditions, remains a major question. The thermal transients associated with the start/stop and no-load/full-load engine cycle, and with the in-cylinder combustion process, generate thermal low cycle fatigue (LCF) and thermal high cycle fatigue (HCF) in the coating system. Therefore, the failure mechanisms of thick TBCs are expected to be quite different from those of thin TBCs under these temperature transients. The coating failure is related not only to thermal expansion mismatch and oxidation of the bond coats and substrates, but also to the steep thermal stress gradients induced in the coating systems. Although it has been reported that stresses generated by thermal transients can initiate surface and interface cracks in a coating system, the mechanisms of the crack propagation and of coating failure under the complex LCF and HCF conditions are still not understood. In this paper, the thermal fatigue behavior of an yttria partially stabilized zirconia coating system under simulated LCF and HCF engine conditions is investigated. The effects of LCF and HCF on surface crack initiation and propagation are also discussed.
    Keywords: Nonmetallic Materials
    Type: Thermal Barrier Coating Workshop, 1997; 139-150; NASA/CP-1998-207429
    Format: text
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  • 2
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    Thermal barrier coatings for aircraft engines: History and directions (1995)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Thin thermal barrier coatings for protecting aircraft turbine section airfoils are examined in this paper. The discussion focuses on those advances that led first to their use for component life extension, and more recently as an integral part of airfoil design. Development has been driven by laboratory rig and furnace testing corroborated by engine testing and engine field experience. The technology has also been supported by performance modeling to demonstrate benefits and life modeling for mission analysis. Factors which have led to the selection of the current state-of-the-art plasma sprayed and physical vapor deposited zirconia-yttria/MCrAlX TBC's are emphasized, as are observations fundamentally related to the their behavior. Current directions in research into thermal barrier coatings and recent progress at NASA are also noted.
    Keywords: Nonmetallic Materials
    Type: Thermal Barrier Coating Workshop; 17-34; NASA-CP-3312
    Format: text
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  • 3
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    Deformation and Tensile Cyclic Fatigue of Plasma-Sprayed ZrO2-8wt% Y2O3 Thermal Barrier Coatings (2001)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Deformation (constitutive relations) of free-standing, thick thermal barrier coatings of sprayed ZrO2-8Wt% Y2O3 was determined at ambient temperature in both pure tension and pure compression using cylindrical bar test specimens. The material exhibited both significant nonlinearity and hysteresis in its load-strain curves, The load-strain relations in four-point uniaxial flexure were determined from tension and compression sides and were compared with individual pure tension and compression constitutive data. Effect of sintering on deformation behavior was significant, resulting in a dramatic change in constitutive relation. Cyclic fatigue testing of the coating material in tension-tension at room temperature showed an insignificant susceptibility to fatigue, similar to the slow crack growth behavior of the material in flexure in 800 C air.
    Keywords: Nonmetallic Materials
    Type: Ceramic Engineering and Science Proceedings; Volume 22; 427-434
    Format: text
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  • 4
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    Investigation of Thermal High Cycle and Low Cycle Fatigue Mechanisms of Thick Thermal Barrier Coatings (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Thick thermal barrier coating systems in a diesel engine experience severe thermal low cycle fatigue (LCF) and high cycle fatigue (HCF) during engine operation. In this paper, the mechanisms of fatigue crack initiation and propagation in a ZrO2-8wt% Y2O3 thermal barrier coating, under simulated engine thermal LCF and HCF conditions, are investigated using a high power CO2 laser. Experiments showed that the combined LCF-HCF tests induced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. Lateral crack branching and the ceramic/bond coat interface delaminations were also facilitated by HCF thermal loads, even in the absence of severe interfacial oxidation. Fatigue damage at crack wake surfaces, due to such phenomena as asperity/debris contact induced cracking and splat pull-out bending during cycling, was observed especially for the combined LCF-HCF tests. It is found that the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. The failure associated with HCF process, however, is mainly associated with a surface wedging mechanism. The interaction between the LCF, HCF and ceramic coating creep, and the relative importance of LCF and HCF in crack propagation are also discussed based on the experimental evidence.
    Keywords: Nonmetallic Materials
    Type: Materials Science and Engineering (ISSN 0921-5093); Volume A245; 212-223
    Format: text
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  • 5
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    Determination of Creep Behavior of Thermal Barrier Coatings Under Laser Imposed High Thermal and Stress Gradient Conditions (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: A laser sintering/creep technique has been established to determine the creep behavior of thermal barrier coatings under steady-state high heat flux conditions. For a plasma sprayed zirconia-8 wt. % yttria coating, a significant primary creep strain and a low apparent creep activation energy were observed. Possible creep mechanisms involved include stress induced mechanical sliding and temperature and stress enhanced cation diffusion through the splat and grain boundaries. The elastic modulus evolution, stress response, and total accumulated creep strain variation across the ceramic coating are simulated using a finite difference approach. The modeled creep response is consistent with experimental observations.
    Keywords: Nonmetallic Materials
    Type: Journal of Materials Research; Volume 14; No. 1; 146-161
    Format: text
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  • 6
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    Reduction of Calcofluor in Solithane Conformal Coatings of Printed Wiring Boards (1997)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An investigation on the outgassing of a pigment employed as a fluorescent medium in conformal coatings has been performed. The conformal coatings in question are used to protect printed wiring boards from environmental hazards such as dust and moisture. The pigment is included in the coating at low concentration to allow visual inspection of the conformal coating for flaw detection. Calcofluor, the fluorescent pigment has been found to be a significant outgasser under vacuum conditions and a potential source of contamination to flight hardware. A minimum acceptable concentration of Calcofluor for flaw detection is desirable. Tests have been carried out using a series of Solithane(TM) conformal coating samples, with progressively lower Calcofluor concentrations, to determine the minimum required concentration of Calcofluor. It was found that the concentration of Calcofluor could be reduced from 0.115% to 0.0135% without significant loss in the ability to detect flaws, while at the same time significant reductions in Calcofluor outgassing and possible contamination of systems could be realized.
    Keywords: Nonmetallic Materials
    Type: Nineteenth Space Simulation Conference Cost Effective Testing for the 21st Century; 59-65; NASA-CP-3341
    Format: application/pdf
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  • 7
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    Advanced Environmental Barrier Coatings Development for Si-Based Ceramics (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-27
    Description: Advanced environmental barrier coating concepts based on multi-component HfO2 (ZrO2) and modified mullite systems are developed for monolithic Si3N4 and SiC/SiC ceramic matrix composite (CMC) applications. Comprehensive testing approaches were established using the water vapor cyclic furnace, high pressure burner rig and laser heat flux steam rig to evaluate the coating water vapor stability, cyclic durability, radiation and erosion resistance under simulated engine environments. Test results demonstrated the feasibility and durability of the environmental barrier coating systems for 2700 to 3000 F monolithic Si3N4 and SiC/SiC CMC component applications. The high-temperature-capable environmental barrier coating systems are being further developed and optimized in collaboration with engine companies for advanced turbine engine applications.
    Keywords: Nonmetallic Materials
    Type: NASA/TM-2005-213444 , E-14980 , Third Annual Workshop on Environmental Barriwe Coatings and Enhanced Silicon Nitrides for Gas Turbines; 17-18 2004; Nashville, TN; United States
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  • 8
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    Radiation Transport Properties of Potential In Situ-Developed Regolith-Epoxy Materials for Martian Habitats (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: We will evaluate the radiation transport properties of epoxy-martian regolith composites. Such composites, which would use both in situ materials and chemicals fabricated from elements found in the martian atmosphere, are candidates for use in habitats on Mars. The principal objective is to evaluate the transmission properties of these materials with respect to the protons and heavy charged particles in the galactic cosmic rays which bombard the martian surface. The secondary objective is to evaluate fabrication methods which could lead to technologies for in situ fabrication. The composites will be prepared by NASA Langley Research Center using simulated martian regolith. Initial evaluation of the radiation shielding properties will be made using transport models developed at NASA-LaRC and the results of these calculations will be used to select the composites with the most favorable radiation transmission properties. These candidates will then be empirically evaluated at particle accelerators which produce beams of protons and heavy charged particles comparable in energy to the radiation at the surface of Mars.
    Keywords: Nonmetallic Materials
    Type: Microgravity Materials Science Conference 2000; 2; 446; NASA/CP-2000-210827/VOL2
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  • 9
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    Thermal Conductivity of Advanced Ceramic Thermal Barrier Coatings Determined by a Steady-state Laser Heat-flux Approach (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The development of low conductivity and high temperature capable thermal barrier coatings requires advanced testing techniques that can accurately and effectively evaluate coating thermal conductivity under future high-performance and low-emission engine heat-flux conditions. In this paper, a unique steady-state CO2 laser (wavelength 10.6 microns) heat-flux approach is described for determining the thermal conductivity and conductivity deduced cyclic durability of ceramic thermal and environmental barrier coating systems at very high temperatures (up to 1700 C) under large thermal gradients. The thermal conductivity behavior of advanced thermal and environmental barrier coatings for metallic and Si-based ceramic matrix composite (CMC) component applications has also been investigated using the laser conductivity approach. The relationships between the lattice and radiation conductivities as a function of heat flux and thermal gradient at high temperatures have been examined for the ceramic coating systems. The steady-state laser heat-flux conductivity approach has been demonstrated as a viable means for the development and life prediction of advanced thermal barrier coatings for future turbine engine applications.
    Keywords: Nonmetallic Materials
    Type: NASA/TM-2004-213040 , E-14474 , ARL-TR-3262 , 27th International Thermal Conductivity Conference; Oct 26, 2003 - Oct 29, 2003; Knoxville, TN; United States
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  • 10
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    Design and Performance Optimizations of Advanced Erosion-Resistant Low Conductivity Thermal Barrier Coatings for Rotorcraft Engines (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future rotorcraft engine higher fuel efficiency and lower emission goals. For thermal barrier coatings designed for rotorcraft turbine airfoil applications, further improved erosion and impact resistance are crucial for engine performance and durability, because the rotorcraft are often operated in the most severe sand erosive environments. Advanced low thermal conductivity and erosion-resistant thermal barrier coatings are being developed, with the current emphasis being placed on thermal barrier coating toughness improvements using multicomponent alloying and processing optimization approaches. The performance of the advanced thermal barrier coatings has been evaluated in a high temperature erosion burner rig and a laser heat-flux rig to simulate engine erosion and thermal gradient environments. The results have shown that the coating composition and architecture optimizations can effectively improve the erosion and impact resistance of the coating systems, while maintaining low thermal conductivity and cyclic oxidation durability
    Keywords: Nonmetallic Materials
    Type: NASA/TM-2012-217138 , E-17874 , 66th Annual Forum and Technology Display (AHS Forum 66); May 11, 2010 - May 13, 2010; Phoenix, AZ; United States
    Format: application/pdf
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