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Ab initio calculations of the uranium–hydrogen system / Christopher D. Taylor in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1045-1055 Titre : Ab initio calculations of the uranium–hydrogen system : thermodynamics, hydrogen saturation of α-U and phase-transformation to UH3 Type de document : texte imprimé Auteurs : Christopher D. Taylor, Auteur ; Turab Lookman, Auteur ; R. Scott Lillard Article en page(s) : pp. 1045-1055 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hydrides  Thermodynamics  Density  functional  theory  Uranium  Phase  transformation Index. décimale : 669 Métallurgie Résumé : Total energy calculations based on density functional theory (DFT) have been performed for various uranium–hydrogen configurations relevant to the uranium hydriding reaction. Herein, we investigate the transformation of the supersaturated α-U lattice to the α-UH3 lattice, where α-UH3 is believed to be a precursor to the formation of β-UH3, the stable phase of UH3. The total energy DFT calculations for α- and β-UH3 were validated by comparing the predicted and measured decomposition temperatures of the hydride at standard pressure. Calculated energies also confirm the metastability of α-UH3 vs. β-UH3. Computational group theory and DFT calculations elucidate this transition, and indicate that the transformation itself is kinetically facile. On the basis of this work, it is proposed that the formation of the volume-expanded, H-saturated α-U phase is the primary kinetic barrier to hydride formation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Ab initio calculations of the uranium–hydrogen system : thermodynamics, hydrogen saturation of α-U and phase-transformation to UH3 [texte imprimé] / Christopher D. Taylor, Auteur ; Turab Lookman, Auteur ; R. Scott Lillard . - pp. 1045-1055. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1045-1055 Mots-clés : Hydrides  Thermodynamics  Density  functional  theory  Uranium  Phase  transformation Index. décimale : 669 Métallurgie Résumé : Total energy calculations based on density functional theory (DFT) have been performed for various uranium–hydrogen configurations relevant to the uranium hydriding reaction. Herein, we investigate the transformation of the supersaturated α-U lattice to the α-UH3 lattice, where α-UH3 is believed to be a precursor to the formation of β-UH3, the stable phase of UH3. The total energy DFT calculations for α- and β-UH3 were validated by comparing the predicted and measured decomposition temperatures of the hydride at standard pressure. Calculated energies also confirm the metastability of α-UH3 vs. β-UH3. Computational group theory and DFT calculations elucidate this transition, and indicate that the transformation itself is kinetically facile. On the basis of this work, it is proposed that the formation of the volume-expanded, H-saturated α-U phase is the primary kinetic barrier to hydride formation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Ab initio calculations of the uranium–hydrogen system / Christopher D. Taylor in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1045–1055 Titre : Ab initio calculations of the uranium–hydrogen system : Thermodynamics, hydrogen saturation of α-U and phase-transformation to UH3 Type de document : texte imprimé Auteurs : Christopher D. Taylor, Auteur ; Turab Lookman, Auteur ; R. Scott Lillard, Auteur Année de publication : 2011 Article en page(s) : pp. 1045–1055 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hydrides  Thermodynamics  Density  functional  theory  Uranium  Phase  transformation Résumé : Total energy calculations based on density functional theory (DFT) have been performed for various uranium–hydrogen configurations relevant to the uranium hydriding reaction. Herein, we investigate the transformation of the supersaturated α-U lattice to the α-UH3 lattice, where α-UH3 is believed to be a precursor to the formation of β-UH3, the stable phase of UH3. The total energy DFT calculations for α- and β-UH3 were validated by comparing the predicted and measured decomposition temperatures of the hydride at standard pressure. Calculated energies also confirm the metastability of α-UH3 vs. β-UH3. Computational group theory and DFT calculations elucidate this transition, and indicate that the transformation itself is kinetically facile. On the basis of this work, it is proposed that the formation of the volume-expanded, H-saturated α-U phase is the primary kinetic barrier to hydride formation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007101 [article] Ab initio calculations of the uranium–hydrogen system : Thermodynamics, hydrogen saturation of α-U and phase-transformation to UH3 [texte imprimé] / Christopher D. Taylor, Auteur ; Turab Lookman, Auteur ; R. Scott Lillard, Auteur . - 2011 . - pp. 1045–1055. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1045–1055 Mots-clés : Hydrides  Thermodynamics  Density  functional  theory  Uranium  Phase  transformation Résumé : Total energy calculations based on density functional theory (DFT) have been performed for various uranium–hydrogen configurations relevant to the uranium hydriding reaction. Herein, we investigate the transformation of the supersaturated α-U lattice to the α-UH3 lattice, where α-UH3 is believed to be a precursor to the formation of β-UH3, the stable phase of UH3. The total energy DFT calculations for α- and β-UH3 were validated by comparing the predicted and measured decomposition temperatures of the hydride at standard pressure. Calculated energies also confirm the metastability of α-UH3 vs. β-UH3. Computational group theory and DFT calculations elucidate this transition, and indicate that the transformation itself is kinetically facile. On the basis of this work, it is proposed that the formation of the volume-expanded, H-saturated α-U phase is the primary kinetic barrier to hydride formation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007101

Thermodynamic theory of dislocation-mediated plasticity / J.S. Langer in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3718–3732 Titre : Thermodynamic theory of dislocation-mediated plasticity Type de document : texte imprimé Auteurs : J.S. Langer, Auteur ; Eran Bouchbinder, Auteur ; Turab Lookman, Auteur Année de publication : 2011 Article en page(s) : pp. 3718–3732 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  theory  Hardening  Thermodynamics Résumé : We reformulate the theory of polycrystalline plasticity, in externally driven, nonequilibrium situations, by writing equations of motion for the flow of energy and entropy associated with dislocations. Within this general framework, and using a minimal model of thermally assisted depinning with essentially only one adjustable parameter, we find that our theory fits the strain-hardening data for Cu over a wide range of temperatures and six decades of strain rate. We predict the transition between stage II and stage III hardening, including the observation that this transition occurs at smaller strains for higher temperatures. We also explain why strain-rate hardening is very weak up to large rates; and, with just one additional number, we accurately predict the crossover to power-law rate hardening in the strong-shock regime. Our analysis differs in several important respects from conventional dislocation-mediated continuum theories. We provide some historical background and discuss our rationale for these differences. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001540 [article] Thermodynamic theory of dislocation-mediated plasticity [texte imprimé] / J.S. Langer, Auteur ; Eran Bouchbinder, Auteur ; Turab Lookman, Auteur . - 2011 . - pp. 3718–3732. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3718–3732 Mots-clés : Dislocation  theory  Hardening  Thermodynamics Résumé : We reformulate the theory of polycrystalline plasticity, in externally driven, nonequilibrium situations, by writing equations of motion for the flow of energy and entropy associated with dislocations. Within this general framework, and using a minimal model of thermally assisted depinning with essentially only one adjustable parameter, we find that our theory fits the strain-hardening data for Cu over a wide range of temperatures and six decades of strain rate. We predict the transition between stage II and stage III hardening, including the observation that this transition occurs at smaller strains for higher temperatures. We also explain why strain-rate hardening is very weak up to large rates; and, with just one additional number, we accurately predict the crossover to power-law rate hardening in the strong-shock regime. Our analysis differs in several important respects from conventional dislocation-mediated continuum theories. We provide some historical background and discuss our rationale for these differences. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001540