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A chromia forming thermal barrier coating system / M. P. Taylor in Materials and corrosion, Vol. 62 N° 7 (Juillet 2011) 

Public ISBD [article]  in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 668–673 Titre : A chromia forming thermal barrier coating system Type de document : texte imprimé Auteurs : M. P. Taylor, Auteur ; H. E. Evans, Auteur ; S. Gray, Auteur Année de publication : 2011 Article en page(s) : pp. 668–673 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Thermal  barrier  coatings  Chromia-forming  bond  coat  Oxidation  Hot  corrosion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Conventional thermal barrier coating (TBC) systems consist of an insulating ceramic topcoat, a bond coat for oxidation protection and the underlying superalloy designed to combat the oxidising conditions in aero- and land-based gas turbines. Under high-temperature oxidation, the use of an alumina forming bond coat is warranted, thus all current TBC systems are optimised for the early formation of a dense, protective thermally grown oxide (TGO) of alumina. This also offers protection against Type I hot corrosion but a chromia layer gives better protection against Type II corrosion and intermediate temperatures, the conditions found in land-based gas turbines. In this paper the authors present the first known results for a chromia forming TBC system. Tests have been performed under oxidising conditions, up to 1000 h, at temperatures between 750 °C and 900 °C, and under Type I (900 °C) and Type II (700 °C) hot corrosion conditions up to 500 h. Under all these conditions no cracking, spallation or degradation was observed. Examination showed the formation of an adherent, dense chromia TGO at the bond coat / topcoat interface. These initial results are very encouraging and the TGO thicknesses agree well with comparable results reported in the literature. DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005881/abstract [article] A chromia forming thermal barrier coating system [texte imprimé] / M. P. Taylor, Auteur ; H. E. Evans, Auteur ; S. Gray, Auteur . - 2011 . - pp. 668–673. Génie Mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 668–673 Mots-clés : Thermal  barrier  coatings  Chromia-forming  bond  coat  Oxidation  Hot  corrosion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Conventional thermal barrier coating (TBC) systems consist of an insulating ceramic topcoat, a bond coat for oxidation protection and the underlying superalloy designed to combat the oxidising conditions in aero- and land-based gas turbines. Under high-temperature oxidation, the use of an alumina forming bond coat is warranted, thus all current TBC systems are optimised for the early formation of a dense, protective thermally grown oxide (TGO) of alumina. This also offers protection against Type I hot corrosion but a chromia layer gives better protection against Type II corrosion and intermediate temperatures, the conditions found in land-based gas turbines. In this paper the authors present the first known results for a chromia forming TBC system. Tests have been performed under oxidising conditions, up to 1000 h, at temperatures between 750 °C and 900 °C, and under Type I (900 °C) and Type II (700 °C) hot corrosion conditions up to 500 h. Under all these conditions no cracking, spallation or degradation was observed. Examination showed the formation of an adherent, dense chromia TGO at the bond coat / topcoat interface. These initial results are very encouraging and the TGO thicknesses agree well with comparable results reported in the literature. DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005881/abstract

Effects of breakaway oxidation on local stresses in thermal barrier coatings / E. P. Busso in Acta materialia, Vol. 58 N° 4 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 4 (Fevrier 2010) . - pp. 1242–1251 Titre : Effects of breakaway oxidation on local stresses in thermal barrier coatings Type de document : texte imprimé Auteurs : E. P. Busso, Auteur ; H. E. Evans, Auteur ; Z.Q. Qian, Auteur Année de publication : 2011 Article en page(s) : pp. 1242–1251 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thermal  barrier  coatings  Finite-element  modelling  Breakaway  oxidation  Stress  development Résumé : It is known that fast-growing non-alumina scales in thermal barrier coating (TBC) systems tend to form at features where aluminium depletion is enhanced due to a high surface-area to volume ratio, a phenomenon known as breakaway oxidation. In this work, the influence of breakaway oxidation around protuberances in an MCrAlY bond coat in a TBC system during isothermal oxidation and after cooling is quantified numerically. A finite element approach is used which incorporates elastic, plastic and creep deformation of the bond coat and thermally grown oxide (TGO) and, importantly, the volumetric strains associated with oxide formation during the isothermal exposure. It is shown how volumetric strains which develop during breakaway oxidation can result in the formation of significant (>0.5 GPa) out-of-plane tensile stresses within the yttria-stabilized zirconia top coat at the oxidation temperature. These stresses are located along the flanks of the bond coat protuberances in locations where sub-critical cracks have previously been reported. The magnitude of the stresses increases with bond coat surface roughness, after the initiation of breakaway oxidation and after cooling. Results are also presented for the normal tractions across both TGO interfaces, and the influence of breakaway oxidation on these is discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007228 [article] Effects of breakaway oxidation on local stresses in thermal barrier coatings [texte imprimé] / E. P. Busso, Auteur ; H. E. Evans, Auteur ; Z.Q. Qian, Auteur . - 2011 . - pp. 1242–1251. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 4 (Fevrier 2010) . - pp. 1242–1251 Mots-clés : Thermal  barrier  coatings  Finite-element  modelling  Breakaway  oxidation  Stress  development Résumé : It is known that fast-growing non-alumina scales in thermal barrier coating (TBC) systems tend to form at features where aluminium depletion is enhanced due to a high surface-area to volume ratio, a phenomenon known as breakaway oxidation. In this work, the influence of breakaway oxidation around protuberances in an MCrAlY bond coat in a TBC system during isothermal oxidation and after cooling is quantified numerically. A finite element approach is used which incorporates elastic, plastic and creep deformation of the bond coat and thermally grown oxide (TGO) and, importantly, the volumetric strains associated with oxide formation during the isothermal exposure. It is shown how volumetric strains which develop during breakaway oxidation can result in the formation of significant (>0.5 GPa) out-of-plane tensile stresses within the yttria-stabilized zirconia top coat at the oxidation temperature. These stresses are located along the flanks of the bond coat protuberances in locations where sub-critical cracks have previously been reported. The magnitude of the stresses increases with bond coat surface roughness, after the initiation of breakaway oxidation and after cooling. Results are also presented for the normal tractions across both TGO interfaces, and the influence of breakaway oxidation on these is discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007228