Constrained sintering of an air-plasma-sprayed thermal barrier coating / A.C.F. Cocks in Acta materialia, Vol. 58 N° 12 (Juillet 2010)  

Public ISBD [article]  inActa materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4233–4244 Titre : Constrained sintering of an air-plasma-sprayed thermal barrier coating Type de document : texte imprimé Auteurs : A.C.F. Cocks, Auteur ; N.A. Fleck, Auteur Année de publication : 2011 Article en page(s) : pp. 4233–4244 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Sintering Coatings Variational methods Micromechanical modelling Creep Résumé : A micromechanical model is presented for the constrained sintering of an air-plasma-sprayed, thermal barrier coating upon a thick superalloy substrate. The coating comprises random splats with intervening penny-shaped cracks. The crack faces make contact at asperities, which progressively sinter in-service by interfacial diffusion, accommodated by bulk creep. Diffusion is driven by the reduction in interfacial energy at the developing contacts and by the local asperity contact stress. At elevated operating temperature, both sintering and creep strains accumulate within the plane of the coating. The sensitivities of sintering rate and microstructure evolution rate to the kinetic parameters and thermodynamic driving forces are explored. It is demonstrated that the sintering response is governed by three independent timescales, as dictated by the material and geometric properties of the coating. Finally, the role of substrate constraint is assessed by comparing the rate of constrained sintering with that for free sintering. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002314 [article] Constrained sintering of an air-plasma-sprayed thermal barrier coating [texte imprimé] / A.C.F. Cocks, Auteur ; N.A. Fleck, Auteur . - 2011 . - pp. 4233–4244. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4233–4244 Mots-clés : Sintering Coatings Variational methods Micromechanical modelling Creep Résumé : A micromechanical model is presented for the constrained sintering of an air-plasma-sprayed, thermal barrier coating upon a thick superalloy substrate. The coating comprises random splats with intervening penny-shaped cracks. The crack faces make contact at asperities, which progressively sinter in-service by interfacial diffusion, accommodated by bulk creep. Diffusion is driven by the reduction in interfacial energy at the developing contacts and by the local asperity contact stress. At elevated operating temperature, both sintering and creep strains accumulate within the plane of the coating. The sensitivities of sintering rate and microstructure evolution rate to the kinetic parameters and thermodynamic driving forces are explored. It is demonstrated that the sintering response is governed by three independent timescales, as dictated by the material and geometric properties of the coating. Finally, the role of substrate constraint is assessed by comparing the rate of constrained sintering with that for free sintering. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002314

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The fracture toughness of a cordierite square lattice / I. Quintana-Alonso in Acta materialia, Vol. 58 N° 1 (Janvier 2010)  

Public ISBD [article]  inActa materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 201–207 Titre : The fracture toughness of a cordierite square lattice Type de document : texte imprimé Auteurs : I. Quintana-Alonso, Auteur ; S.P. Mai, Auteur ; N.A. Fleck, Auteur Année de publication : 2010 Article en page(s) : pp. 201–207 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Finite element analysis Fracture toughness Lattice materials Ceramics Toughness test Résumé : A single-edge-notch bend test was developed for the measurement of fracture toughness of a ±45° square lattice made from an elastic-brittle solid. The finite element method was used to obtain the K-calibration for an orthotropic elastic solid, with elastic constants equal to that of the ±45° square lattice. Finite element simulations were also used to predict the fracture strength of the cracked lattice, with failure dictated by the tensile strength of the cell-wall material. The conditions for K-dominance and for failure by a net-section strength criterion of the specimen were thereby determined. A set of fracture tests on single-edge-notch bend specimens made from the ceramic cordierite validate the predictions. The measured fracture toughness of the cordierite lattices scales linearly with the stockiness of the lattice. DEWEY : 1359-6454 ISSN : 669 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900593X [article] The fracture toughness of a cordierite square lattice [texte imprimé] / I. Quintana-Alonso, Auteur ; S.P. Mai, Auteur ; N.A. Fleck, Auteur . - 2010 . - pp. 201–207. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 201–207 Mots-clés : Finite element analysis Fracture toughness Lattice materials Ceramics Toughness test Résumé : A single-edge-notch bend test was developed for the measurement of fracture toughness of a ±45° square lattice made from an elastic-brittle solid. The finite element method was used to obtain the K-calibration for an orthotropic elastic solid, with elastic constants equal to that of the ±45° square lattice. Finite element simulations were also used to predict the fracture strength of the cracked lattice, with failure dictated by the tensile strength of the cell-wall material. The conditions for K-dominance and for failure by a net-section strength criterion of the specimen were thereby determined. A set of fracture tests on single-edge-notch bend specimens made from the ceramic cordierite validate the predictions. The measured fracture toughness of the cordierite lattices scales linearly with the stockiness of the lattice. DEWEY : 1359-6454 ISSN : 669 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900593X

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