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Compressive creep testing of thermal barrier coated nickel-based superalloys / Ventzislav G. Karaivanov in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 133 N° 9 (Septembre 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 9 (Septembre 2011) . - 09 p. Titre : Compressive creep testing of thermal barrier coated nickel-based superalloys Type de document : texte imprimé Auteurs : Ventzislav G. Karaivanov, Auteur ; William S. Slaughter, Auteur ; Sean Siw, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Aerodynamics  Compressive  strength  Compressive  testing  Creep  Failure  analysis  Gas  turbines  Nanoindentation  Nickel  alloys  Scanning  electron  microscopy  Superalloys  Surface  roughness  Thermal  barrier  coatings Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Turbine airfoils have complex geometries and, during service operation, are subjected to complex loadings. In most publications, results are typically reported for either uniaxial, isothermal tensile creep or for thermal cyclic tests. The former generally provides data for creep of the superalloy and the overall performance, and the later provide data for thermal barrier coating (TBC) spallation as a function of thermally grown oxide thickness, surface roughness, temperature, and thermal mismatch between the layers. Both tests provide valuable data but little is known about the effect of compressive creep strain on the performance of the superalloy/protective system at elevated temperatures. In conjunction with computational model development, laboratory-scale experimental validation was undertaken to verify the viability of the underlying damage mechanics concepts for the evolution of TBC damage. Nickel-based single crystal René N5 coupons that were coated with a ~150–200 µm MCrAlY bond coat and a ~200–240 µm 7-YSZ APS top coat were used in this effort. The coupons were exposed to 900°C, 1000°C, and 1100°C, for periods of 100 h, 300 h, 1000 h, and 3000 h in slotted silicon carbide fixtures. The difference in the coefficients of thermal expansion of the René N5 substrate and the test fixture introduces thermally induced compressive stress in the coupon samples. Exposed samples were cross sectioned and evaluated using scanning electron microscopy. Performance data were collected based on image analysis. Energy-dispersive X-ray was employed to study the elemental distribution in the TBC system after exposure. To better understand the loading and failure mechanisms of the coating system under loading conditions, nanoindentation was used to study the mechanical properties (Young's modulus and hardness) of the components in the TBC system and their evolution with temperature and time. The effect of uniaxial in-plane compressive creep strain on the rate of growth of the thermally grown oxide layer, the time to coating failure in TBC systems, and the evolution in the mechanical properties are presented. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...] [article] Compressive creep testing of thermal barrier coated nickel-based superalloys [texte imprimé] / Ventzislav G. Karaivanov, Auteur ; William S. Slaughter, Auteur ; Sean Siw, Auteur . - 2012 . - 09 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 9 (Septembre 2011) . - 09 p. Mots-clés : Aerodynamics  Compressive  strength  Compressive  testing  Creep  Failure  analysis  Gas  turbines  Nanoindentation  Nickel  alloys  Scanning  electron  microscopy  Superalloys  Surface  roughness  Thermal  barrier  coatings Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Turbine airfoils have complex geometries and, during service operation, are subjected to complex loadings. In most publications, results are typically reported for either uniaxial, isothermal tensile creep or for thermal cyclic tests. The former generally provides data for creep of the superalloy and the overall performance, and the later provide data for thermal barrier coating (TBC) spallation as a function of thermally grown oxide thickness, surface roughness, temperature, and thermal mismatch between the layers. Both tests provide valuable data but little is known about the effect of compressive creep strain on the performance of the superalloy/protective system at elevated temperatures. In conjunction with computational model development, laboratory-scale experimental validation was undertaken to verify the viability of the underlying damage mechanics concepts for the evolution of TBC damage. Nickel-based single crystal René N5 coupons that were coated with a ~150–200 µm MCrAlY bond coat and a ~200–240 µm 7-YSZ APS top coat were used in this effort. The coupons were exposed to 900°C, 1000°C, and 1100°C, for periods of 100 h, 300 h, 1000 h, and 3000 h in slotted silicon carbide fixtures. The difference in the coefficients of thermal expansion of the René N5 substrate and the test fixture introduces thermally induced compressive stress in the coupon samples. Exposed samples were cross sectioned and evaluated using scanning electron microscopy. Performance data were collected based on image analysis. Energy-dispersive X-ray was employed to study the elemental distribution in the TBC system after exposure. To better understand the loading and failure mechanisms of the coating system under loading conditions, nanoindentation was used to study the mechanical properties (Young's modulus and hardness) of the components in the TBC system and their evolution with temperature and time. The effect of uniaxial in-plane compressive creep strain on the rate of growth of the thermally grown oxide layer, the time to coating failure in TBC systems, and the evolution in the mechanical properties are presented. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...]