First-principles assessment of hydrogen absorption into FeAl and Fe3Si / Donald F. Johnson in Acta materialia, Vol. 58 N° 2 (Janvier 2010)  

Public ISBD [article]  inActa materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 638-648 Titre : First-principles assessment of hydrogen absorption into FeAl and Fe3Si : towards prevention of steel embrittlement Type de document : texte imprimé Auteurs : Donald F. Johnson, Auteur ; Emily A. Carter, Auteur Article en page(s) : pp. 638-648 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Density functional Kinetics Hydrogen absorption diffusion Iron alloys Index. décimale : 669 Métallurgie Résumé : We characterize the ability of two potential surface alloys, FeAl and Fe3Si, to prevent H incorporation into steel, with a view toward inhibiting steel embrittlement. Periodic density functional theory calculations within the generalized gradient approximation are used to evaluate H dissolution energetics and the kinetics of H diffusion into and through FeAl and Fe3Si. We predict increased dissolution endothermicities and diffusion barriers in both alloys compared to bulk Fe. Fe3Si is predicted to be the most effective at inhibiting H incorporation, with a 1.91 eV [0.97 eV] surface-to-subsurface diffusion barrier on the (1 1 0) surface [(1 0 0 surface)] and a 0.79 eV endothermicity to bulk dissolution, compared to a 1.02 eV [0.38 eV] barrier and 0.20 eV dissolution energy in pure Fe [37]. We therefore propose that a thin layer of Fe3Si may provide protection against H embrittlement of the underlying steel. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] First-principles assessment of hydrogen absorption into FeAl and Fe3Si : towards prevention of steel embrittlement [texte imprimé] / Donald F. Johnson, Auteur ; Emily A. Carter, Auteur . - pp. 638-648. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 638-648 Mots-clés : Density functional Kinetics Hydrogen absorption diffusion Iron alloys Index. décimale : 669 Métallurgie Résumé : We characterize the ability of two potential surface alloys, FeAl and Fe3Si, to prevent H incorporation into steel, with a view toward inhibiting steel embrittlement. Periodic density functional theory calculations within the generalized gradient approximation are used to evaluate H dissolution energetics and the kinetics of H diffusion into and through FeAl and Fe3Si. We predict increased dissolution endothermicities and diffusion barriers in both alloys compared to bulk Fe. Fe3Si is predicted to be the most effective at inhibiting H incorporation, with a 1.91 eV [0.97 eV] surface-to-subsurface diffusion barrier on the (1 1 0) surface [(1 0 0 surface)] and a 0.79 eV endothermicity to bulk dissolution, compared to a 1.02 eV [0.38 eV] barrier and 0.20 eV dissolution energy in pure Fe [37]. We therefore propose that a thin layer of Fe3Si may provide protection against H embrittlement of the underlying steel. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

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The effect of platinum on Al diffusion kinetics in β-NiAl / Kristen A. Marino in Acta materialia, Vol. 58 N° 7 (Avril 2010)  

Public ISBD [article]  inActa materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2726–2737 Titre : The effect of platinum on Al diffusion kinetics in β-NiAl : Implications for thermal barrier coating lifetime Type de document : texte imprimé Auteurs : Kristen A. Marino, Auteur ; Emily A. Carter, Auteur Année de publication : 2011 Article en page(s) : pp. 2726–2737 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Diffusion Nickel aluminides Platinum Kinetics Density functional theory Résumé : First-principles density functional theory calculations are used to study Al diffusion in β-NiAl. The activation energy and diffusion constant pre-exponential factors are calculated for five previously postulated Al diffusion mechanisms: next-nearest-neighbor Al jumps, the triple defect mechanism and three variants of the six-jump cycle mechanism beginning with an Al vacancy. We predict that the triple defect mechanism has the lowest activation energy and is the mechanism by which Al diffusion occurs in NiAl. In order to elucidate why Pt has a beneficial effect on thermal barrier coating lifetime, the effect of Pt on each of these mechanisms is also examined. In all cases, Pt decreases the diffusion activation energy, which should enhance Al diffusion in the coatings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000011X [article] The effect of platinum on Al diffusion kinetics in β-NiAl : Implications for thermal barrier coating lifetime [texte imprimé] / Kristen A. Marino, Auteur ; Emily A. Carter, Auteur . - 2011 . - pp. 2726–2737. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2726–2737 Mots-clés : Diffusion Nickel aluminides Platinum Kinetics Density functional theory Résumé : First-principles density functional theory calculations are used to study Al diffusion in β-NiAl. The activation energy and diffusion constant pre-exponential factors are calculated for five previously postulated Al diffusion mechanisms: next-nearest-neighbor Al jumps, the triple defect mechanism and three variants of the six-jump cycle mechanism beginning with an Al vacancy. We predict that the triple defect mechanism has the lowest activation energy and is the mechanism by which Al diffusion occurs in NiAl. In order to elucidate why Pt has a beneficial effect on thermal barrier coating lifetime, the effect of Pt on each of these mechanisms is also examined. In all cases, Pt decreases the diffusion activation energy, which should enhance Al diffusion in the coatings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000011X

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