Dépouillements

Dynamic processes of domain switching in lead zirconate titanate under cyclic mechanical loading by in situ neutron diffraction / Soodkhet Pojprapai(Imlao) in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1897–1908 Titre : Dynamic processes of domain switching in lead zirconate titanate under cyclic mechanical loading by in situ neutron diffraction Type de document : texte imprimé Auteurs : Soodkhet Pojprapai(Imlao), Auteur ; Zhenhua Luo, Auteur ; Bjørn Clausen, Auteur Année de publication : 2011 Article en page(s) : pp. 1897–1908 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ferroelectric  Ferroelastic  Domain  switching  Neutron  diffraction Résumé : The performance of ferroelectric ceramics is governed by the ability of domains to switch. A decrease in the switching ability can lead to degradation of the materials and failure of ferroelectric devices. In this work the dynamic properties of domain reorientation are studied. In situ time-of-flight neutron diffraction is used to probe the evolution of ferroelastic domain texture under mechanical cyclic loading in bulk lead zirconate titanate ceramics. The high sensitivity of neutron diffraction to lattice strain is exploited to precisely analyze the change of domain texture and strain through a full-pattern Rietveld method. These results are then used to construct a viscoelastic model, which explains the correlation between macroscopic phenomena (i.e. creep and recovered deformation) and microscopic dynamic behavior (i.e. ferroelastic switching, lattice strain). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008052 [article] Dynamic processes of domain switching in lead zirconate titanate under cyclic mechanical loading by in situ neutron diffraction [texte imprimé] / Soodkhet Pojprapai(Imlao), Auteur ; Zhenhua Luo, Auteur ; Bjørn Clausen, Auteur . - 2011 . - pp. 1897–1908. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1897–1908 Mots-clés : Ferroelectric  Ferroelastic  Domain  switching  Neutron  diffraction Résumé : The performance of ferroelectric ceramics is governed by the ability of domains to switch. A decrease in the switching ability can lead to degradation of the materials and failure of ferroelectric devices. In this work the dynamic properties of domain reorientation are studied. In situ time-of-flight neutron diffraction is used to probe the evolution of ferroelastic domain texture under mechanical cyclic loading in bulk lead zirconate titanate ceramics. The high sensitivity of neutron diffraction to lattice strain is exploited to precisely analyze the change of domain texture and strain through a full-pattern Rietveld method. These results are then used to construct a viscoelastic model, which explains the correlation between macroscopic phenomena (i.e. creep and recovered deformation) and microscopic dynamic behavior (i.e. ferroelastic switching, lattice strain). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008052

Diffusion creep and superplasticity in aluminium alloys / K. Sotoudeh in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1909–1920 Titre : Diffusion creep and superplasticity in aluminium alloys Type de document : texte imprimé Auteurs : K. Sotoudeh, Auteur ; P.S. Bate, Auteur Année de publication : 2011 Article en page(s) : pp. 1909–1920 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Superplasticity  Aluminium  Diffusion  creep Résumé : The plastic deformation of two classes of fine-grained aluminium alloys at elevated temperatures and slow strain rates have been investigated. One class of material, Al–Cu–Zr, was processed to develop banded microstructures; the other class, based on Al–(Mg)–Mn, had near-equiaxed microstructures. In both classes, superplastic behaviour was found in the variants with the higher solute content. The evolution of the banded microstructures and the results from surface grid measurement in the Al–(Mg)–Mn alloys give results which indicate that the superplasticity is primarily a result of diffusion creep, and the effect of solute is proposed to be via an enhancement of solvent self-diffusion. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008131 [article] Diffusion creep and superplasticity in aluminium alloys [texte imprimé] / K. Sotoudeh, Auteur ; P.S. Bate, Auteur . - 2011 . - pp. 1909–1920. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1909–1920 Mots-clés : Superplasticity  Aluminium  Diffusion  creep Résumé : The plastic deformation of two classes of fine-grained aluminium alloys at elevated temperatures and slow strain rates have been investigated. One class of material, Al–Cu–Zr, was processed to develop banded microstructures; the other class, based on Al–(Mg)–Mn, had near-equiaxed microstructures. In both classes, superplastic behaviour was found in the variants with the higher solute content. The evolution of the banded microstructures and the results from surface grid measurement in the Al–(Mg)–Mn alloys give results which indicate that the superplasticity is primarily a result of diffusion creep, and the effect of solute is proposed to be via an enhancement of solvent self-diffusion. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008131

Anisotropic viscosities and shrinkage rates in sintering of particles arranged in a simple orthorhombic structure / F. Wakai in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1921–1929 Titre : Anisotropic viscosities and shrinkage rates in sintering of particles arranged in a simple orthorhombic structure Type de document : texte imprimé Auteurs : F. Wakai, Auteur ; T. Akatsu, Auteur Année de publication : 2011 Article en page(s) : pp. 1921–1929 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Sintering  Simulation  Micromechanical  modeling Résumé : Macroscopic shrinkage in sintering is described as a linear function of the sintering stress tensor and the viscosity tensor, which is determined by taking into account the grain boundary diffusion mechanism and the anisotropy in the microstructure. For a simple orthorhombic structure in equilibrium, the anisotropic shrinkage rate is dominated by the deviatoric component of the viscosity tensor, which is approximately proportional to the logarithm of the aspect ratio of a volume element, and acts so as to deform the elongated structure to be more isotropic. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008143 [article] Anisotropic viscosities and shrinkage rates in sintering of particles arranged in a simple orthorhombic structure [texte imprimé] / F. Wakai, Auteur ; T. Akatsu, Auteur . - 2011 . - pp. 1921–1929. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1921–1929 Mots-clés : Sintering  Simulation  Micromechanical  modeling Résumé : Macroscopic shrinkage in sintering is described as a linear function of the sintering stress tensor and the viscosity tensor, which is determined by taking into account the grain boundary diffusion mechanism and the anisotropy in the microstructure. For a simple orthorhombic structure in equilibrium, the anisotropic shrinkage rate is dominated by the deviatoric component of the viscosity tensor, which is approximately proportional to the logarithm of the aspect ratio of a volume element, and acts so as to deform the elongated structure to be more isotropic. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008143

Reversed anisotropy of grain boundary properties and its effect on grain boundary engineering / Pavel Lejček in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1930–1937 Titre : Reversed anisotropy of grain boundary properties and its effect on grain boundary engineering Type de document : texte imprimé Auteurs : Pavel Lejček, Auteur ; Aleš Jäger, Auteur ; Viera Gärtnerová, Auteur Année de publication : 2011 Article en page(s) : pp. 1930–1937 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  boundary  structure  Grain  boundary  diffusion  Grain  boundary  migration  Grain  boundary  segregation  Thermodynamics Résumé : Data on anisotropy of grain boundary properties are frequently published. In some cases, when they show the reverse course of structural dependence than is expected, they can seem confusing. Examples of this “reversed anisotropy” found for grain boundary segregation, diffusion and migration are presented. We demonstrate that the reversed anisotropy of grain boundary properties is caused by the compensation effect. This can have serious consequences for grain boundary engineering. It is also suggested that grain boundaries can be classified specifically and generally solely on the basis of well-defined thermodynamic parameters. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008155 [article] Reversed anisotropy of grain boundary properties and its effect on grain boundary engineering [texte imprimé] / Pavel Lejček, Auteur ; Aleš Jäger, Auteur ; Viera Gärtnerová, Auteur . - 2011 . - pp. 1930–1937. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1930–1937 Mots-clés : Grain  boundary  structure  Grain  boundary  diffusion  Grain  boundary  migration  Grain  boundary  segregation  Thermodynamics Résumé : Data on anisotropy of grain boundary properties are frequently published. In some cases, when they show the reverse course of structural dependence than is expected, they can seem confusing. Examples of this “reversed anisotropy” found for grain boundary segregation, diffusion and migration are presented. We demonstrate that the reversed anisotropy of grain boundary properties is caused by the compensation effect. This can have serious consequences for grain boundary engineering. It is also suggested that grain boundaries can be classified specifically and generally solely on the basis of well-defined thermodynamic parameters. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008155

Orientation dependence of plastic deformation in nickel-based single crystal superalloys / A. Vattré in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1938–1951 Titre : Orientation dependence of plastic deformation in nickel-based single crystal superalloys : Discrete–continuous model simulations Type de document : texte imprimé Auteurs : A. Vattré, Auteur ; B. Devincre, Auteur ; A. Roos, Auteur Année de publication : 2011 Article en page(s) : pp. 1938–1951 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel  alloys  High-temperature  deformation  Plastic  deformation  Dislocation  dynamics  Work-hardening  modelling Résumé : The anisotropic mechanical response of single-crystal nickel-based superalloys is simulated. At 1123 K, two uniaxial tensile loading cases are simulated: one along [0 0 1] and another along [1 1 1]. Resulting stress–strain curves, stress distributions, interfacial dislocation structures are analysed. In accordance with experiments, the simulations show an anisotropic yield strength. The applied strain is accommodated by dislocations propagating through matrix channels on octahedral slip systems. The net result appears as slip bands along the cubic directions, even though no cubic slip systems are activated. In the [0 0 1] case, the plastic flow is distributed more or less evenly among the three matrix channels, whereas in the [1 1 1] case it is mainly concentrated in one single channel. Typical zig–zag configurations are observed. The elementary mechanisms controlling their formation are explained. Cross-slip does not play any role there. The hardening anisotropy between both loading cases is related to strong differences between the interfacial dislocation microstructures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008167 [article] Orientation dependence of plastic deformation in nickel-based single crystal superalloys : Discrete–continuous model simulations [texte imprimé] / A. Vattré, Auteur ; B. Devincre, Auteur ; A. Roos, Auteur . - 2011 . - pp. 1938–1951. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1938–1951 Mots-clés : Nickel  alloys  High-temperature  deformation  Plastic  deformation  Dislocation  dynamics  Work-hardening  modelling Résumé : The anisotropic mechanical response of single-crystal nickel-based superalloys is simulated. At 1123 K, two uniaxial tensile loading cases are simulated: one along [0 0 1] and another along [1 1 1]. Resulting stress–strain curves, stress distributions, interfacial dislocation structures are analysed. In accordance with experiments, the simulations show an anisotropic yield strength. The applied strain is accommodated by dislocations propagating through matrix channels on octahedral slip systems. The net result appears as slip bands along the cubic directions, even though no cubic slip systems are activated. In the [0 0 1] case, the plastic flow is distributed more or less evenly among the three matrix channels, whereas in the [1 1 1] case it is mainly concentrated in one single channel. Typical zig–zag configurations are observed. The elementary mechanisms controlling their formation are explained. Cross-slip does not play any role there. The hardening anisotropy between both loading cases is related to strong differences between the interfacial dislocation microstructures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008167

Elemental partitioning of platinum group metal containing Ni-base superalloys using electron microprobe analysis and atom probe tomography / J.S. Van Sluytman in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1952–1962 Titre : Elemental partitioning of platinum group metal containing Ni-base superalloys using electron microprobe analysis and atom probe tomography Type de document : texte imprimé Auteurs : J.S. Van Sluytman, Auteur ; A. La Fontaine, Auteur ; J. M. Cairney, Auteur Année de publication : 2011 Article en page(s) : pp. 1952–1962 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Platinum  group  metals  Elemental  partitioning  Electron  microprobe  analysis  Atom  probe  tomography  Nickel-base  superalloys Résumé : The partitioning of platinum group metal (PGM) additions in polycrystalline Ni-base superalloys has been investigated. Alloys with a baseline composition of 15Al–5Cr–1Re–2Ta–0.1Hf (at.%) with systematic variations in Pt, Ir, Ru and W were cast and heat-treated to produce bimodal two-phase γ–γ′ microstructures. Electron microprobe analysis was used to measure the composition of coarse γ′ particles. Selected alloys were studied using atom probe tomography. Pt and Ru weakly partition to the γ′ and γ phases, respectively, whereas Ir partitions equally between both phases. Pt and Ru do not change partitioning behavior appreciably with additional W and Re. Interestingly, Ir lowers γ′ volume fraction and reduces partitioning of W, Re, Ru, Al and Pt. Tungsten partitioning coefficients exhibit an unusually strong temperature dependence, with increased partitioning of W to the matrix at lower temperatures. The thermodynamics of these PGM-containing systems are analyzed and the implications for partitioning are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008179 [article] Elemental partitioning of platinum group metal containing Ni-base superalloys using electron microprobe analysis and atom probe tomography [texte imprimé] / J.S. Van Sluytman, Auteur ; A. La Fontaine, Auteur ; J. M. Cairney, Auteur . - 2011 . - pp. 1952–1962. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1952–1962 Mots-clés : Platinum  group  metals  Elemental  partitioning  Electron  microprobe  analysis  Atom  probe  tomography  Nickel-base  superalloys Résumé : The partitioning of platinum group metal (PGM) additions in polycrystalline Ni-base superalloys has been investigated. Alloys with a baseline composition of 15Al–5Cr–1Re–2Ta–0.1Hf (at.%) with systematic variations in Pt, Ir, Ru and W were cast and heat-treated to produce bimodal two-phase γ–γ′ microstructures. Electron microprobe analysis was used to measure the composition of coarse γ′ particles. Selected alloys were studied using atom probe tomography. Pt and Ru weakly partition to the γ′ and γ phases, respectively, whereas Ir partitions equally between both phases. Pt and Ru do not change partitioning behavior appreciably with additional W and Re. Interestingly, Ir lowers γ′ volume fraction and reduces partitioning of W, Re, Ru, Al and Pt. Tungsten partitioning coefficients exhibit an unusually strong temperature dependence, with increased partitioning of W to the matrix at lower temperatures. The thermodynamics of these PGM-containing systems are analyzed and the implications for partitioning are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008179

Tensile and compressive mechanical behavior of twinned silicon carbide nanowires / Z.G. Wang in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1963–1971 Titre : Tensile and compressive mechanical behavior of twinned silicon carbide nanowires Type de document : texte imprimé Auteurs : Z.G. Wang, Auteur ; J.B. Li, Auteur ; F. Gao, Auteur Année de publication : 2011 Article en page(s) : pp. 1963–1971 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Twinning  Nanotructures  Fracture  Buckling  Molecular  dynamics Résumé : Molecular dynamics simulations with the Tersoff potential were used to study the response of twinned SiC nanowires under tensile and compressive strain. The critical strain of the twinned nanowires can be enhanced by twin stacking faults, and their critical strains are larger than those of perfect nanowires with the same diameters. Under axial tensile strain, the bonds of the nanowires are stretched just before failure. The failure behavior is found to depend on the twin segment thickness and the diameter of the nanowires. An atomic chain is observed for thin nanowires with small twin segment thickness under tension strain. Under axial compressive strain, the collapse of twinned SiC nanowires exhibits two different failure modes, depending on the length and diameter of the nanowires, i.e., shell buckling for short nanowires and columnar buckling for longer nanowires. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008180 [article] Tensile and compressive mechanical behavior of twinned silicon carbide nanowires [texte imprimé] / Z.G. Wang, Auteur ; J.B. Li, Auteur ; F. Gao, Auteur . - 2011 . - pp. 1963–1971. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1963–1971 Mots-clés : Twinning  Nanotructures  Fracture  Buckling  Molecular  dynamics Résumé : Molecular dynamics simulations with the Tersoff potential were used to study the response of twinned SiC nanowires under tensile and compressive strain. The critical strain of the twinned nanowires can be enhanced by twin stacking faults, and their critical strains are larger than those of perfect nanowires with the same diameters. Under axial tensile strain, the bonds of the nanowires are stretched just before failure. The failure behavior is found to depend on the twin segment thickness and the diameter of the nanowires. An atomic chain is observed for thin nanowires with small twin segment thickness under tension strain. Under axial compressive strain, the collapse of twinned SiC nanowires exhibits two different failure modes, depending on the length and diameter of the nanowires, i.e., shell buckling for short nanowires and columnar buckling for longer nanowires. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008180

An intrinsic effect of hydrogen on cyclic slip deformation around a {1 1 0} fatigue crack in Fe–3.2 wt.% Si alloy / Y. Takahashi in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1972–1981 Titre : An intrinsic effect of hydrogen on cyclic slip deformation around a {1 1 0} fatigue crack in Fe–3.2 wt.% Si alloy Type de document : texte imprimé Auteurs : Y. Takahashi, Auteur ; M. Tanaka, Auteur ; K. Higashida, Auteur Année de publication : 2011 Article en page(s) : pp. 1972–1981 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hydrogen  embrittlement  Fatigue  TEM  Iron  alloys  Crack  tip Résumé : The effect of gaseous hydrogen on cyclic slip behavior around a fatigue crack tip introduced along the {1 1 0} plane in a Fe–3.2 wt.% Si alloy is precisely investigated by cross-sectional transmission electron microscopy and fractography. The results clearly suggest that the fatigue crack growth rate is promoted by hydrogen, whereas the number of dislocations emitted per load cycle is reduced. In addition, dislocation distribution is localized around the crack, causing quasi-brittle crack morphology. A sustained load test confirms that no subcritical crack growth caused by cleavage or micro-void coalescence exists along the {1 1 0} plane, which indicates that the observed increase in the fatigue crack growth rate is correlated solely to the intrinsic effect of hydrogen on the cyclic slip-off process around the crack tip. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008192 [article] An intrinsic effect of hydrogen on cyclic slip deformation around a {1 1 0} fatigue crack in Fe–3.2 wt.% Si alloy [texte imprimé] / Y. Takahashi, Auteur ; M. Tanaka, Auteur ; K. Higashida, Auteur . - 2011 . - pp. 1972–1981. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1972–1981 Mots-clés : Hydrogen  embrittlement  Fatigue  TEM  Iron  alloys  Crack  tip Résumé : The effect of gaseous hydrogen on cyclic slip behavior around a fatigue crack tip introduced along the {1 1 0} plane in a Fe–3.2 wt.% Si alloy is precisely investigated by cross-sectional transmission electron microscopy and fractography. The results clearly suggest that the fatigue crack growth rate is promoted by hydrogen, whereas the number of dislocations emitted per load cycle is reduced. In addition, dislocation distribution is localized around the crack, causing quasi-brittle crack morphology. A sustained load test confirms that no subcritical crack growth caused by cleavage or micro-void coalescence exists along the {1 1 0} plane, which indicates that the observed increase in the fatigue crack growth rate is correlated solely to the intrinsic effect of hydrogen on the cyclic slip-off process around the crack tip. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008192

Calculation of impurity diffusivities in α-Fe using first-principles methods / Shenyan Huang in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1982–1993 Titre : Calculation of impurity diffusivities in α-Fe using first-principles methods Type de document : texte imprimé Auteurs : Shenyan Huang, Auteur ; Daniel L. Worthington, Auteur ; Mark Asta, Auteur Année de publication : 2011 Article en page(s) : pp. 1982–1993 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bulk  diffusion  Ab  initio  electron  theory  Kinetics  Iron  alloys Résumé : Self- and impurity diffusivities in body-centered-cubic (bcc) iron have been calculated within the formalisms of harmonic transition-state theory and the Le Claire nine-frequency model for vacancy-mediated diffusion. The approach combines first-principles calculations of vacancy formation, migration, and solute-binding enthalpies and entropies in the ferromagnetic phase, with an empirical relationship for the effect of magnetic disorder on diffusion activation energies. Calculated Fe self-diffusion and Mo and W impurity-diffusion coefficients are shown to agree within a factor of five with the most recent experimental measurements in both the ferromagnetic and paramagnetic phases. Calculated diffusion coefficients for Mo and W impurities are comparable to or larger than that for Fe self-diffusion at all temperatures below the α–γ phase transition. Calculated activation energies for Ta and Hf impurities suggest that these solutes should also display impurity-diffusion coefficients larger than that for self-diffusion in body-centered cubic Fe. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008209 [article] Calculation of impurity diffusivities in α-Fe using first-principles methods [texte imprimé] / Shenyan Huang, Auteur ; Daniel L. Worthington, Auteur ; Mark Asta, Auteur . - 2011 . - pp. 1982–1993. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1982–1993 Mots-clés : Bulk  diffusion  Ab  initio  electron  theory  Kinetics  Iron  alloys Résumé : Self- and impurity diffusivities in body-centered-cubic (bcc) iron have been calculated within the formalisms of harmonic transition-state theory and the Le Claire nine-frequency model for vacancy-mediated diffusion. The approach combines first-principles calculations of vacancy formation, migration, and solute-binding enthalpies and entropies in the ferromagnetic phase, with an empirical relationship for the effect of magnetic disorder on diffusion activation energies. Calculated Fe self-diffusion and Mo and W impurity-diffusion coefficients are shown to agree within a factor of five with the most recent experimental measurements in both the ferromagnetic and paramagnetic phases. Calculated diffusion coefficients for Mo and W impurities are comparable to or larger than that for Fe self-diffusion at all temperatures below the α–γ phase transition. Calculated activation energies for Ta and Hf impurities suggest that these solutes should also display impurity-diffusion coefficients larger than that for self-diffusion in body-centered cubic Fe. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008209

On the stress-free lattice expansion of porous cordierite / Giovanni Bruno in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1994–2003 Titre : On the stress-free lattice expansion of porous cordierite Type de document : texte imprimé Auteurs : Giovanni Bruno, Auteur ; Alexander M. Efremov, Auteur ; Bjørn Clausen, Auteur Année de publication : 2011 Article en page(s) : pp. 1994–2003 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Micro-strains  Neutron  diffraction  Thermal  expansion  Integrity  factor  Micro-cracking Résumé : An extensive investigation of the lattice expansion (up to 1200 °C) of porous synthetic cordierite (obtained by firing a mixture of talc, clay, alumina and silica) was carried out using time-of-flight neutron diffraction at LANSCE, Los Alamos, NM, USA and FNLP, Dubna, Russia. An extruded rod and several powders, with different particle size (dispersity), were studied, with the aim of monitoring the variation of the (lattice) micro-strain as a function of temperature and its influence on the microscopic and macroscopic thermal expansion. Results show a different expansion of the a- and b-axes of the orthorhombic cell (in the rod above 800 °C). While the finest powder seems to contract more along the c-axis, thus hinting at the presence of smaller stress, the integral peak width increases as a function of temperature in the intermediate range (300–700 °C). This could be explained by the integrity factor modeling in terms of micro-cracking. In polycrystalline cordierite, the model implies tension along the a- and b-axes (positive thermal expansion) accompanied by compression along the c-axis (negative thermal expansion) and a stress release upon cooling, via a thermal micro-cracking mechanism. The calculations of the cordierite macroscopic thermal expansion having as input crystal axial expansions assumed to be stress-free allowed us to conclude that even a fine powder (5 μm particle size) cannot be considered completely stress-free. This conclusion is supported by microstructural observations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008210 [article] On the stress-free lattice expansion of porous cordierite [texte imprimé] / Giovanni Bruno, Auteur ; Alexander M. Efremov, Auteur ; Bjørn Clausen, Auteur . - 2011 . - pp. 1994–2003. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 1994–2003 Mots-clés : Micro-strains  Neutron  diffraction  Thermal  expansion  Integrity  factor  Micro-cracking Résumé : An extensive investigation of the lattice expansion (up to 1200 °C) of porous synthetic cordierite (obtained by firing a mixture of talc, clay, alumina and silica) was carried out using time-of-flight neutron diffraction at LANSCE, Los Alamos, NM, USA and FNLP, Dubna, Russia. An extruded rod and several powders, with different particle size (dispersity), were studied, with the aim of monitoring the variation of the (lattice) micro-strain as a function of temperature and its influence on the microscopic and macroscopic thermal expansion. Results show a different expansion of the a- and b-axes of the orthorhombic cell (in the rod above 800 °C). While the finest powder seems to contract more along the c-axis, thus hinting at the presence of smaller stress, the integral peak width increases as a function of temperature in the intermediate range (300–700 °C). This could be explained by the integrity factor modeling in terms of micro-cracking. In polycrystalline cordierite, the model implies tension along the a- and b-axes (positive thermal expansion) accompanied by compression along the c-axis (negative thermal expansion) and a stress release upon cooling, via a thermal micro-cracking mechanism. The calculations of the cordierite macroscopic thermal expansion having as input crystal axial expansions assumed to be stress-free allowed us to conclude that even a fine powder (5 μm particle size) cannot be considered completely stress-free. This conclusion is supported by microstructural observations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008210

Influence of minor aluminum concentration changes in zirconium-based bulk metallic glasses on the elastic, anelastic, and plastic properties / A. Caron in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2004–2013 Titre : Influence of minor aluminum concentration changes in zirconium-based bulk metallic glasses on the elastic, anelastic, and plastic properties Type de document : texte imprimé Auteurs : A. Caron, Auteur ; R. Wunderlich, Auteur ; D.V. Louzguine-Luzgin, Auteur Année de publication : 2011 Article en page(s) : pp. 2004–2013 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bulk  metallic  glasses  Ultrasound  Elasticity  Ductility Résumé : The Poisson’s ratio of Zr-based bulk metallic glasses in the system Zr63−xCu24AlxNi10Co3 was found to exhibit a non-monotonous behavior as a function of x when measured with ultrasound by the pulse–echo technique. In addition, from wave propagation velocity measurements at different frequencies, i.e. f = 2.25 MHz and f = 10 MHz, a composition-dependent anelastic behavior as a function of x is found, exhibiting a similar non-monotonous behavior. In this work we further investigated the plastic deformation and the creep properties of this glass system in compression tests and by nanoindentation. The plastic strain and the measured creep deformation show correlations with the Poisson’s ratio. We then discuss the anelastic behavior observed while measuring the sound-wave propagation velocity in the frame of the thermoelastic damping and the bond reorientation as proposed by Egami. Finally we discuss these effects with regard to X-ray diffraction analysis. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008222 [article] Influence of minor aluminum concentration changes in zirconium-based bulk metallic glasses on the elastic, anelastic, and plastic properties [texte imprimé] / A. Caron, Auteur ; R. Wunderlich, Auteur ; D.V. Louzguine-Luzgin, Auteur . - 2011 . - pp. 2004–2013. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2004–2013 Mots-clés : Bulk  metallic  glasses  Ultrasound  Elasticity  Ductility Résumé : The Poisson’s ratio of Zr-based bulk metallic glasses in the system Zr63−xCu24AlxNi10Co3 was found to exhibit a non-monotonous behavior as a function of x when measured with ultrasound by the pulse–echo technique. In addition, from wave propagation velocity measurements at different frequencies, i.e. f = 2.25 MHz and f = 10 MHz, a composition-dependent anelastic behavior as a function of x is found, exhibiting a similar non-monotonous behavior. In this work we further investigated the plastic deformation and the creep properties of this glass system in compression tests and by nanoindentation. The plastic strain and the measured creep deformation show correlations with the Poisson’s ratio. We then discuss the anelastic behavior observed while measuring the sound-wave propagation velocity in the frame of the thermoelastic damping and the bond reorientation as proposed by Egami. Finally we discuss these effects with regard to X-ray diffraction analysis. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008222

Influence of high-temperature solution treatments on mechanical properties of an Al–Si–Cu aluminum alloy / Hiroyuki Toda in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2014–2025 Titre : Influence of high-temperature solution treatments on mechanical properties of an Al–Si–Cu aluminum alloy Type de document : texte imprimé Auteurs : Hiroyuki Toda, Auteur ; Takanori Nishimura, Auteur ; Kentaro Uesugi, Auteur Année de publication : 2011 Article en page(s) : pp. 2014–2025 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cast  aluminum  alloys  High-temperature  solution  heat  treatment  X-ray  tomography  K-edge  subtraction  imaging  Chemical  concentration  mapping Résumé : It has been demonstrated that the strength of an Al–Si–Cu alloy is maximized by high-temperature solution treatment at 807 K, which is approximately 16 K higher than the ternary eutectic temperature. The dual-energy K-edge subtraction imaging technique has been employed to obtain the spatial distribution of copper and its change during its solution treatment in three dimensions quantitatively, providing interpretations of the improved mechanical properties in terms of age-hardenability and its spatial variation. It has been also confirmed that the occurrence of incipient local melting and the accompanying growth of micro pores adjacent to the melt regions lead to fractures caused by these defects. However, it can be inferred that the positive effects can outweigh the negative effects even above the eutectic temperature, thereby realizing the maximum strength at such relative high temperature levels. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008234 [article] Influence of high-temperature solution treatments on mechanical properties of an Al–Si–Cu aluminum alloy [texte imprimé] / Hiroyuki Toda, Auteur ; Takanori Nishimura, Auteur ; Kentaro Uesugi, Auteur . - 2011 . - pp. 2014–2025. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2014–2025 Mots-clés : Cast  aluminum  alloys  High-temperature  solution  heat  treatment  X-ray  tomography  K-edge  subtraction  imaging  Chemical  concentration  mapping Résumé : It has been demonstrated that the strength of an Al–Si–Cu alloy is maximized by high-temperature solution treatment at 807 K, which is approximately 16 K higher than the ternary eutectic temperature. The dual-energy K-edge subtraction imaging technique has been employed to obtain the spatial distribution of copper and its change during its solution treatment in three dimensions quantitatively, providing interpretations of the improved mechanical properties in terms of age-hardenability and its spatial variation. It has been also confirmed that the occurrence of incipient local melting and the accompanying growth of micro pores adjacent to the melt regions lead to fractures caused by these defects. However, it can be inferred that the positive effects can outweigh the negative effects even above the eutectic temperature, thereby realizing the maximum strength at such relative high temperature levels. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008234

Experimental evidence and thermodynamics analysis of high magnetic field effects on the austenite to ferrite transformation temperature in Fe–C–Mn alloys / T. Garcin in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2026–2032 Titre : Experimental evidence and thermodynamics analysis of high magnetic field effects on the austenite to ferrite transformation temperature in Fe–C–Mn alloys Type de document : texte imprimé Auteurs : T. Garcin, Auteur ; S. Rivoirard, Auteur ; C. Elgoyhen, Auteur Année de publication : 2011 Article en page(s) : pp. 2026–2032 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thermomagnetic  processing  Dilatometry  Steels  Phase  transformations  Thermodynamics Résumé : The non-isothermal decomposition of austenite into ferrite and pearlite in Fe–xC–1.5 wt.% Mn steels with x = 0.1, 0.2 and 0.3 wt.% C is investigated by in situ dilatometry and microstructure characterization in magnetic fields up to 16 T. The global shift towards higher temperatures of the respective austenite, ferrite + austenite and ferrite + pearlite stability regions is experimentally quantified. A systematic increase in the ferrite area fraction and proportional reduction of the Vickers hardness values with the magnetic field intensity are also reported. Moreover, the steels’ magnetizations, measured up to 3.5 T and 1100 K, are used to calculate the magnetic contribution to the free energy of the transformation and to account thermodynamically for the field dependence of the transformation temperature. The impact of magnetic field is found to be greater with increasing carbon content in the steels. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008246 [article] Experimental evidence and thermodynamics analysis of high magnetic field effects on the austenite to ferrite transformation temperature in Fe–C–Mn alloys [texte imprimé] / T. Garcin, Auteur ; S. Rivoirard, Auteur ; C. Elgoyhen, Auteur . - 2011 . - pp. 2026–2032. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2026–2032 Mots-clés : Thermomagnetic  processing  Dilatometry  Steels  Phase  transformations  Thermodynamics Résumé : The non-isothermal decomposition of austenite into ferrite and pearlite in Fe–xC–1.5 wt.% Mn steels with x = 0.1, 0.2 and 0.3 wt.% C is investigated by in situ dilatometry and microstructure characterization in magnetic fields up to 16 T. The global shift towards higher temperatures of the respective austenite, ferrite + austenite and ferrite + pearlite stability regions is experimentally quantified. A systematic increase in the ferrite area fraction and proportional reduction of the Vickers hardness values with the magnetic field intensity are also reported. Moreover, the steels’ magnetizations, measured up to 3.5 T and 1100 K, are used to calculate the magnetic contribution to the free energy of the transformation and to account thermodynamically for the field dependence of the transformation temperature. The impact of magnetic field is found to be greater with increasing carbon content in the steels. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008246

Indentation behavior of metal–ceramic multilayers at the nanoscale / G. Tang in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2033–2044 Titre : Indentation behavior of metal–ceramic multilayers at the nanoscale : Numerical analysis and experimental verification Type de document : texte imprimé Auteurs : G. Tang, Auteur ; Y.-L. Shen, Auteur ; D.R.P. Singh, Auteur Année de publication : 2011 Article en page(s) : pp. 2033–2044 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoindentation  Multilayers  Nanocomposites  Finite  element  analysis  Plastic  deformation Résumé : The behavior of aluminum/silicon carbide nanolayered composite in response to nanoindentation loading is studied. The effects of heterogeneity on the deformation fields, as well as the hardness and elastic modulus obtained from indentation, are investigated using finite element analysis. Attention is also devoted to correlating the numerical results with experimental deformation and damage features. The model uses an explicit layered structure within the axisymmetric framework. It is found that the nanolayered composite results in unique deformation patterns. Significant tensile stresses can be generated locally along certain directions, which offers a mechanistic rationale for the internal cracking observed experimentally. The unloading process also leads to an expansion of the tension-stressed area, as well as continued plastic flow in parts of the aluminum layers. Comparisons of hardness and indentation-derived modulus between modeling and experiments also point to the importance of incorporating the detailed geometric features when performing indentation analyses. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008258 [article] Indentation behavior of metal–ceramic multilayers at the nanoscale : Numerical analysis and experimental verification [texte imprimé] / G. Tang, Auteur ; Y.-L. Shen, Auteur ; D.R.P. Singh, Auteur . - 2011 . - pp. 2033–2044. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2033–2044 Mots-clés : Nanoindentation  Multilayers  Nanocomposites  Finite  element  analysis  Plastic  deformation Résumé : The behavior of aluminum/silicon carbide nanolayered composite in response to nanoindentation loading is studied. The effects of heterogeneity on the deformation fields, as well as the hardness and elastic modulus obtained from indentation, are investigated using finite element analysis. Attention is also devoted to correlating the numerical results with experimental deformation and damage features. The model uses an explicit layered structure within the axisymmetric framework. It is found that the nanolayered composite results in unique deformation patterns. Significant tensile stresses can be generated locally along certain directions, which offers a mechanistic rationale for the internal cracking observed experimentally. The unloading process also leads to an expansion of the tension-stressed area, as well as continued plastic flow in parts of the aluminum layers. Comparisons of hardness and indentation-derived modulus between modeling and experiments also point to the importance of incorporating the detailed geometric features when performing indentation analyses. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008258

Effect of Re in γ phase, γ′ phase and γ/γ′ interface of Ni-based single-crystal superalloys / Tao Zhu in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2045–2055 Titre : Effect of Re in γ phase, γ′ phase and γ/γ′ interface of Ni-based single-crystal superalloys Type de document : texte imprimé Auteurs : Tao Zhu, Auteur ; Chong-yu Wang, Auteur ; Yong Gan, Auteur Année de publication : 2011 Article en page(s) : pp. 2045–2055 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Molecular  dynamics  simulations  First-principle  electron  theory  Dislocation  structure  Electronic  structure  Nickel  alloys Résumé : Molecular dynamics (MD) within the framework of the embedded atom method and the first-principles discrete variational method (DVM) are both used to study the effect of Re in the γ phase, the γ′ phase and the γ/γ′ interface of Ni-based single-crystal superalloys. From the MD relaxation it is found that the γ/γ′ interface only has two atomic configurations, i.e. a coherent region and a misfit dislocation region, and the “cage-like” misfit dislocation networks, consist of View the MathML source{0 0 1} edge dislocations winding over the precipitate phase. The MD results also show that the substitution atom Re stabilizes both the γ phase and the γ′ phase, and influences the degree of mismatch between γ and γ′. From the simulation results we find that Re atoms have a tendency to cluster in both the γ phase and the γ′ phase. Based on the MD simulation we have chosen six clusters of the γ/γ′ interface for the DVM study, in which the interatomic energy, the charge distribution, the partial density of states and the electron density difference are all calculated. It is found that a Re atom occupying either a Ni site in the γ phase or an Al site in the γ′ phase can strongly enhance the bonding strength between Re and its nearest neighboring atoms, suggesting that the substitution atom Re will influence dislocation motion along the γ/γ′ interface. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900826X [article] Effect of Re in γ phase, γ′ phase and γ/γ′ interface of Ni-based single-crystal superalloys [texte imprimé] / Tao Zhu, Auteur ; Chong-yu Wang, Auteur ; Yong Gan, Auteur . - 2011 . - pp. 2045–2055. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2045–2055 Mots-clés : Molecular  dynamics  simulations  First-principle  electron  theory  Dislocation  structure  Electronic  structure  Nickel  alloys Résumé : Molecular dynamics (MD) within the framework of the embedded atom method and the first-principles discrete variational method (DVM) are both used to study the effect of Re in the γ phase, the γ′ phase and the γ/γ′ interface of Ni-based single-crystal superalloys. From the MD relaxation it is found that the γ/γ′ interface only has two atomic configurations, i.e. a coherent region and a misfit dislocation region, and the “cage-like” misfit dislocation networks, consist of View the MathML source{0 0 1} edge dislocations winding over the precipitate phase. The MD results also show that the substitution atom Re stabilizes both the γ phase and the γ′ phase, and influences the degree of mismatch between γ and γ′. From the simulation results we find that Re atoms have a tendency to cluster in both the γ phase and the γ′ phase. Based on the MD simulation we have chosen six clusters of the γ/γ′ interface for the DVM study, in which the interatomic energy, the charge distribution, the partial density of states and the electron density difference are all calculated. It is found that a Re atom occupying either a Ni site in the γ phase or an Al site in the γ′ phase can strongly enhance the bonding strength between Re and its nearest neighboring atoms, suggesting that the substitution atom Re will influence dislocation motion along the γ/γ′ interface. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900826X

Mechanical and metallurgical effects of in process cooling during friction stir welding of AA7075-T6 butt joints / L. Fratini in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2056–2067 Titre : Mechanical and metallurgical effects of in process cooling during friction stir welding of AA7075-T6 butt joints Type de document : texte imprimé Auteurs : L. Fratini, Auteur ; G. Buffa, Auteur ; R. Shivpuri, Auteur Année de publication : 2011 Article en page(s) : pp. 2056–2067 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Friction  stir  welding  Finite  element  modeling  In  process  cooling  treatments Résumé : This paper presents the results of a combined experimental and numerical investigation focused on the effects of an in process water cooling treatment aimed at improving the final quality of friction stir welded butt joints in terms of mechanical resistance and metallurgy of the processed material. Micro and macro observations, together with the evolution of an already developed finite element tool, have been used to analyze specimens obtained under different process conditions. Water cooling was found to enhance joint strength, reducing the material softening usually observed in the thermo-mechanically affected zone area, with no detrimental effect on nugget integrity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008271 [article] Mechanical and metallurgical effects of in process cooling during friction stir welding of AA7075-T6 butt joints [texte imprimé] / L. Fratini, Auteur ; G. Buffa, Auteur ; R. Shivpuri, Auteur . - 2011 . - pp. 2056–2067. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2056–2067 Mots-clés : Friction  stir  welding  Finite  element  modeling  In  process  cooling  treatments Résumé : This paper presents the results of a combined experimental and numerical investigation focused on the effects of an in process water cooling treatment aimed at improving the final quality of friction stir welded butt joints in terms of mechanical resistance and metallurgy of the processed material. Micro and macro observations, together with the evolution of an already developed finite element tool, have been used to analyze specimens obtained under different process conditions. Water cooling was found to enhance joint strength, reducing the material softening usually observed in the thermo-mechanically affected zone area, with no detrimental effect on nugget integrity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008271

Role of substrate commensurability on non-reactive wetting kinetics of liquid metals / M. Benhassine in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2068–2078 Titre : Role of substrate commensurability on non-reactive wetting kinetics of liquid metals Type de document : texte imprimé Auteurs : M. Benhassine, Auteur ; E. Saiz, Auteur ; A.P. Tomsia, Auteur Année de publication : 2011 Article en page(s) : pp. 2068–2078 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : High-temperature  spreading  Diffusion  Wetting  Liquid  metals  Molecular  dynamics Résumé : The dynamics of spreading of liquid metal atoms via molecular dynamics is considered vs. the commensurability of the solid surface with respect to the size of the liquid atoms. The solid surfaces are modeled as rigid (1 0 0) oriented Ni and, for two series of simulations, the lattice spacing of the substrate is varied from the regular equilibrium spacing to a commensurate situation with Au or Ag drops spreading spontaneously on top. The diffusion is calculated in the layered region of the liquid in contact with the two different solid surfaces and then compared. Then, the dynamic evolution of the contact angle is fitted to Molecular Kinetic Theory and compared with the two substrate geometries. It is observed that the friction parameter scales as the inverse of the diffusion in the interfacial region. The change in ordering induced by the commensurate substrate is characterized by examining the density profiles across the solid/liquid interface and fitting the curve by an exponential decay with a characteristic correlation distance 1/κ. It is shown that the commensurability/non-commensurability of the solid surface with respect to the liquid atoms changes the ordering, which plays a significant role in the dynamics, a feature not properly taken into account in the present formulation of Molecular Kinetic Theory. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008283 [article] Role of substrate commensurability on non-reactive wetting kinetics of liquid metals [texte imprimé] / M. Benhassine, Auteur ; E. Saiz, Auteur ; A.P. Tomsia, Auteur . - 2011 . - pp. 2068–2078. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2068–2078 Mots-clés : High-temperature  spreading  Diffusion  Wetting  Liquid  metals  Molecular  dynamics Résumé : The dynamics of spreading of liquid metal atoms via molecular dynamics is considered vs. the commensurability of the solid surface with respect to the size of the liquid atoms. The solid surfaces are modeled as rigid (1 0 0) oriented Ni and, for two series of simulations, the lattice spacing of the substrate is varied from the regular equilibrium spacing to a commensurate situation with Au or Ag drops spreading spontaneously on top. The diffusion is calculated in the layered region of the liquid in contact with the two different solid surfaces and then compared. Then, the dynamic evolution of the contact angle is fitted to Molecular Kinetic Theory and compared with the two substrate geometries. It is observed that the friction parameter scales as the inverse of the diffusion in the interfacial region. The change in ordering induced by the commensurate substrate is characterized by examining the density profiles across the solid/liquid interface and fitting the curve by an exponential decay with a characteristic correlation distance 1/κ. It is shown that the commensurability/non-commensurability of the solid surface with respect to the liquid atoms changes the ordering, which plays a significant role in the dynamics, a feature not properly taken into account in the present formulation of Molecular Kinetic Theory. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008283

Creep damage characterization using non-linear ultrasonic techniques / Jitendra S. Valluri in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2079–2090 Titre : Creep damage characterization using non-linear ultrasonic techniques Type de document : texte imprimé Auteurs : Jitendra S. Valluri, Auteur ; Krishnan Balasubramaniam, Auteur ; Raghu V. Prakash, Auteur Année de publication : 2011 Article en page(s) : pp. 2079–2090 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Non-linear  ultrasonic  Second  order  harmonics  Third  order  harmonics  Creep  damage  Copper Résumé : This paper describes the use of non-linear ultrasonic techniques for the characterization of material degradation in 99.98% pure copper due to high-temperature creep. Flat dog-bone-shaped specimens were subjected to constant load creep testing at different stress and temperature levels. Creep damage progression was monitored by conducting continuous and interrupted mode creep tests. In the case of continuous loading non-linear ultrasonic (NLU) measurements were conducted after fracture at different locations along the gage length of the sample. For interrupted tests the NLU measurements were conducted on different creep life fractions, through periodic interruption of the creep test. In all cases a through transmission NLU measurement technique was employed. Three different non-linear measurements, namely static displacement, second harmonic and third harmonic, were taken and their responses compared. The NLU measurements were found to be significantly sensitive to the extent of creep damage (∼200–2500% of base level), while the linear ultrasonic measurements, representing the change in longitudinal velocities, were only in the range 10–30% for a comparable creep damage level. NLU measurements carried out on fractured samples suggest that the NLU response was locally high at locations where the creep damage was concentrated, compared with other locations, even within the gage length of the specimen. This was confirmed using micrograph observations. Of the three non-linear measurements, the third harmonic data was most sensitive to creep damage. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008295 [article] Creep damage characterization using non-linear ultrasonic techniques [texte imprimé] / Jitendra S. Valluri, Auteur ; Krishnan Balasubramaniam, Auteur ; Raghu V. Prakash, Auteur . - 2011 . - pp. 2079–2090. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2079–2090 Mots-clés : Non-linear  ultrasonic  Second  order  harmonics  Third  order  harmonics  Creep  damage  Copper Résumé : This paper describes the use of non-linear ultrasonic techniques for the characterization of material degradation in 99.98% pure copper due to high-temperature creep. Flat dog-bone-shaped specimens were subjected to constant load creep testing at different stress and temperature levels. Creep damage progression was monitored by conducting continuous and interrupted mode creep tests. In the case of continuous loading non-linear ultrasonic (NLU) measurements were conducted after fracture at different locations along the gage length of the sample. For interrupted tests the NLU measurements were conducted on different creep life fractions, through periodic interruption of the creep test. In all cases a through transmission NLU measurement technique was employed. Three different non-linear measurements, namely static displacement, second harmonic and third harmonic, were taken and their responses compared. The NLU measurements were found to be significantly sensitive to the extent of creep damage (∼200–2500% of base level), while the linear ultrasonic measurements, representing the change in longitudinal velocities, were only in the range 10–30% for a comparable creep damage level. NLU measurements carried out on fractured samples suggest that the NLU response was locally high at locations where the creep damage was concentrated, compared with other locations, even within the gage length of the specimen. This was confirmed using micrograph observations. Of the three non-linear measurements, the third harmonic data was most sensitive to creep damage. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008295

On the mechanism of Ag exudation during internal oxidation / Gunther Schimmel in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2091–2102 Titre : On the mechanism of Ag exudation during internal oxidation Type de document : texte imprimé Auteurs : Gunther Schimmel, Auteur ; Julia Sorina-Müller, Auteur ; Bernd Kempf, Auteur Année de publication : 2011 Article en page(s) : pp. 2091–2102 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Oxidation  Internal  stresses  Finite  element  modeling  Phase  nucleation  and  growth  Nodule  formation Résumé : Internal oxidation experiments under different oxidation conditions focusing on the characteristics of noble metal exudation are presented together with finite element method (FEM) simulation calculations of the build-up of internal stresses. In a high-temperature bending test with a fully oxidized Ag–SnO2–In2O3 sample stress states that were comparable with those occurring during internal oxidation were generated, but exudation of Ag was not observed. From further targeted internal oxidation experiments in combination with FEM simulation calculations of internal stress distributions it can be concluded that internal stresses play a minor role in the occurrence of noble metal exudation. It is suggested that exudation occurs due to a gradient in the chemical potential of the noble metal. The potential gradient is a consequence of the concentration gradient of inward diffusing oxygen. The influence of the oxygen-induced driving force on the development of microstructure considering internal and external noble metal layers is discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008301 [article] On the mechanism of Ag exudation during internal oxidation [texte imprimé] / Gunther Schimmel, Auteur ; Julia Sorina-Müller, Auteur ; Bernd Kempf, Auteur . - 2011 . - pp. 2091–2102. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2091–2102 Mots-clés : Oxidation  Internal  stresses  Finite  element  modeling  Phase  nucleation  and  growth  Nodule  formation Résumé : Internal oxidation experiments under different oxidation conditions focusing on the characteristics of noble metal exudation are presented together with finite element method (FEM) simulation calculations of the build-up of internal stresses. In a high-temperature bending test with a fully oxidized Ag–SnO2–In2O3 sample stress states that were comparable with those occurring during internal oxidation were generated, but exudation of Ag was not observed. From further targeted internal oxidation experiments in combination with FEM simulation calculations of internal stress distributions it can be concluded that internal stresses play a minor role in the occurrence of noble metal exudation. It is suggested that exudation occurs due to a gradient in the chemical potential of the noble metal. The potential gradient is a consequence of the concentration gradient of inward diffusing oxygen. The influence of the oxygen-induced driving force on the development of microstructure considering internal and external noble metal layers is discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008301

Electric-field-induced phase-change behavior in (Bi0.5Na0.5)TiO3–BaTiO3–(K0.5Na0.5)NbO3 / John E. Daniels in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2103–2111 Titre : Electric-field-induced phase-change behavior in (Bi0.5Na0.5)TiO3–BaTiO3–(K0.5Na0.5)NbO3 : A combinatorial investigation Type de document : texte imprimé Auteurs : John E. Daniels, Auteur ; Wook Jo, Auteur ; Jürgen Rödel, Auteur Année de publication : 2011 Article en page(s) : pp. 2103–2111 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Electroceramics  Piezoelectricity  Phase  transformation  X-ray  diffraction  (XRD)  X-ray  fluorescence Résumé : The electric-field-induced strain behavior in (1 − x − y)(Bi0.5Na0.5)TiO3–xBaTiO3–y(K0.5Na0.5)NbO3 electroceramics has been studied using a combinatorial technique. A stoichiometrically graded sample was produced to contain compositions across the ternary phase diagram between the two end-member components of 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 and 0.86(Bi0.5Na0.5)TiO3–0.14(K0.5Na0.5)NbO3. Both composition and structural information were measured simultaneously during the application of electric fields using secondary X-ray fluorescence and high-energy X-ray microdiffraction, respectively. An initial electric-field-induced distortion from the pseudo-cubic structure is seen across all compositions, while those with a greater concentration of BaTiO3 also undergo an electric-field-induced phase transformation. The microstructural contribution to the macroscopic strain within the 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 end member is quantified at a field strength of 5.5 kV mm−1; 0.08% and 0.11% of the measured macroscopic strain of 0.4% is contributed by the induced ferroelastic domain texture and the volumetric strain associated with the electric-field-induced phase transformation, respectively. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008313 [article] Electric-field-induced phase-change behavior in (Bi0.5Na0.5)TiO3–BaTiO3–(K0.5Na0.5)NbO3 : A combinatorial investigation [texte imprimé] / John E. Daniels, Auteur ; Wook Jo, Auteur ; Jürgen Rödel, Auteur . - 2011 . - pp. 2103–2111. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2103–2111 Mots-clés : Electroceramics  Piezoelectricity  Phase  transformation  X-ray  diffraction  (XRD)  X-ray  fluorescence Résumé : The electric-field-induced strain behavior in (1 − x − y)(Bi0.5Na0.5)TiO3–xBaTiO3–y(K0.5Na0.5)NbO3 electroceramics has been studied using a combinatorial technique. A stoichiometrically graded sample was produced to contain compositions across the ternary phase diagram between the two end-member components of 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 and 0.86(Bi0.5Na0.5)TiO3–0.14(K0.5Na0.5)NbO3. Both composition and structural information were measured simultaneously during the application of electric fields using secondary X-ray fluorescence and high-energy X-ray microdiffraction, respectively. An initial electric-field-induced distortion from the pseudo-cubic structure is seen across all compositions, while those with a greater concentration of BaTiO3 also undergo an electric-field-induced phase transformation. The microstructural contribution to the macroscopic strain within the 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 end member is quantified at a field strength of 5.5 kV mm−1; 0.08% and 0.11% of the measured macroscopic strain of 0.4% is contributed by the induced ferroelastic domain texture and the volumetric strain associated with the electric-field-induced phase transformation, respectively. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008313

Plastic deformation mechanism of ultra-fine-grained AA6063 processed by equal-channel angular pressing / Tao Qian in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2112–2123 Titre : Plastic deformation mechanism of ultra-fine-grained AA6063 processed by equal-channel angular pressing Type de document : texte imprimé Auteurs : Tao Qian, Auteur ; Michael Marx, Auteur ; Kerstin Schüler, Auteur Année de publication : 2011 Article en page(s) : pp. 2112–2123 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : UFG  material  ECAP  Backscatter  contrast  Electron  backscatter  diffraction  Scanning  TEM Résumé : Equal-channel angular pressing (ECAP) is an established method to produce ultra-fine-grained (UFG) materials with extraordinary mechanical properties. However, different methods to characterize the complex microstructure give contradictory results. Therefore an ECAP-processed UFG aluminum alloy AA6063 was characterized by various electron-microscopy-based methods such as backscattered electron contrast, electron backscatter diffraction, transmission electron microscopy and low-voltage scanning transmission electron microscopy. Only a skilful combination of all methods reveals the complete information about the microstructure which is needed to understand the results of the mechanical testing by nanoindentation, tensile tests and strain-rate jump test. The main difference is the amount of low-angle grain boundaries and high-angle grain boundaries which determine hardness, tensile and yield strength and strain-rate sensitivity of ECAP materials produced by different numbers of passes and routes. This is explained by the interaction of dislocations with the different grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008325 [article] Plastic deformation mechanism of ultra-fine-grained AA6063 processed by equal-channel angular pressing [texte imprimé] / Tao Qian, Auteur ; Michael Marx, Auteur ; Kerstin Schüler, Auteur . - 2011 . - pp. 2112–2123. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2112–2123 Mots-clés : UFG  material  ECAP  Backscatter  contrast  Electron  backscatter  diffraction  Scanning  TEM Résumé : Equal-channel angular pressing (ECAP) is an established method to produce ultra-fine-grained (UFG) materials with extraordinary mechanical properties. However, different methods to characterize the complex microstructure give contradictory results. Therefore an ECAP-processed UFG aluminum alloy AA6063 was characterized by various electron-microscopy-based methods such as backscattered electron contrast, electron backscatter diffraction, transmission electron microscopy and low-voltage scanning transmission electron microscopy. Only a skilful combination of all methods reveals the complete information about the microstructure which is needed to understand the results of the mechanical testing by nanoindentation, tensile tests and strain-rate jump test. The main difference is the amount of low-angle grain boundaries and high-angle grain boundaries which determine hardness, tensile and yield strength and strain-rate sensitivity of ECAP materials produced by different numbers of passes and routes. This is explained by the interaction of dislocations with the different grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008325

Tensile creep of Mo–Si–B alloys / P. Jain in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2124–2142 Titre : Tensile creep of Mo–Si–B alloys Type de document : texte imprimé Auteurs : P. Jain, Auteur ; K.S. Kumar, Auteur Année de publication : 2011 Article en page(s) : pp. 2124–2142 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Refractory  metals  High  temperature  deformation  Dislocations  Segregation  Precipitation Résumé : Multiphase Mo–Si–B alloys containing a Mo solid solution matrix and brittle Mo3Si and Mo5SiB2 (T2) intermetallic phases are candidates for ultra-high-temperature applications. The elevated temperature uniaxial tensile response at a nominal strain rate of 10−4 s–1 and the tensile creep response at constant load between 1000 °C and 1300 °C of a (i) single phase solid solution (Mo–3.0Si–1.3B in at.%), (ii) two-phase alloy containing ∼35 vol.% T2 phase (Mo–6Si–8B in at.%) and (iii) three-phase alloy with ∼50 vol.% T2 + Mo3Si phases (Mo–8.6Si–8.7B in at.%) were evaluated. The results confirm that Si in solid solution significantly enhances both the yield strength and the creep resistance of these materials. A Larson–Miller plot of the creep data showed improved creep resistance of the two- and three-phase alloys in comparison with Ni-based superalloys. The extent of Si dissolved in the solid solution phase varied in these three alloys and Si appeared to segregate to dislocations and grain boundaries. A stress exponent of ∼5 for the solid solution alloy and ∼7 at 1200 °C for the two multiphase alloys suggested dislocation climb to be the controlling mechanism. Grain boundary precipitation of the T2 phase during creep deformation was observed and the precipitation kinetics appear to be affected by the test temperature and applied stress. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008337 [article] Tensile creep of Mo–Si–B alloys [texte imprimé] / P. Jain, Auteur ; K.S. Kumar, Auteur . - 2011 . - pp. 2124–2142. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2124–2142 Mots-clés : Refractory  metals  High  temperature  deformation  Dislocations  Segregation  Precipitation Résumé : Multiphase Mo–Si–B alloys containing a Mo solid solution matrix and brittle Mo3Si and Mo5SiB2 (T2) intermetallic phases are candidates for ultra-high-temperature applications. The elevated temperature uniaxial tensile response at a nominal strain rate of 10−4 s–1 and the tensile creep response at constant load between 1000 °C and 1300 °C of a (i) single phase solid solution (Mo–3.0Si–1.3B in at.%), (ii) two-phase alloy containing ∼35 vol.% T2 phase (Mo–6Si–8B in at.%) and (iii) three-phase alloy with ∼50 vol.% T2 + Mo3Si phases (Mo–8.6Si–8.7B in at.%) were evaluated. The results confirm that Si in solid solution significantly enhances both the yield strength and the creep resistance of these materials. A Larson–Miller plot of the creep data showed improved creep resistance of the two- and three-phase alloys in comparison with Ni-based superalloys. The extent of Si dissolved in the solid solution phase varied in these three alloys and Si appeared to segregate to dislocations and grain boundaries. A stress exponent of ∼5 for the solid solution alloy and ∼7 at 1200 °C for the two multiphase alloys suggested dislocation climb to be the controlling mechanism. Grain boundary precipitation of the T2 phase during creep deformation was observed and the precipitation kinetics appear to be affected by the test temperature and applied stress. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008337

In situ characterization of fatigue damage evolution in a cast Al alloy via nonlinear ultrasonic measurements / Anish Kumar in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2143–2154 Titre : In situ characterization of fatigue damage evolution in a cast Al alloy via nonlinear ultrasonic measurements Type de document : texte imprimé Auteurs : Anish Kumar, Auteur ; Christopher J. Torbet, Auteur ; Tresa M. Pollock, Auteur Année de publication : 2011 Article en page(s) : pp. 2143–2154 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nonlinear  ultrasonics  Fatigue  crack  initiation  Fatigue  crack  growth  Casting  pores  Cast  Al  alloy Résumé : A new methodology is described for in situ characterization of fatigue damage accumulation using nonlinear ultrasonic measurements via analysis of the feedback signal of a closed-loop ultrasonic fatigue system. In the very high-cycle fatigue regime, ultrasonic nonlinearity increases with initiation and growth of a dominant, life-limiting fatigue crack. Based on the increase in the ultrasonic nonlinearity with fatigue cycling, crack initiation, small fatigue crack growth and fast crack growth regimes have been distinguished during cycling in specimens with different pore sizes tested at various stress amplitudes. The fraction of fatigue life spent in initiation of a life-limiting fatigue crack decreases with increasing stress amplitude. For a constant stress amplitude, the initiation life also decreases with increasing pore size. The present study also demonstrates the applicability of the methodology for fatigue crack growth studies from natural defects located internally or at the surface in smooth specimens. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008349 [article] In situ characterization of fatigue damage evolution in a cast Al alloy via nonlinear ultrasonic measurements [texte imprimé] / Anish Kumar, Auteur ; Christopher J. Torbet, Auteur ; Tresa M. Pollock, Auteur . - 2011 . - pp. 2143–2154. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2143–2154 Mots-clés : Nonlinear  ultrasonics  Fatigue  crack  initiation  Fatigue  crack  growth  Casting  pores  Cast  Al  alloy Résumé : A new methodology is described for in situ characterization of fatigue damage accumulation using nonlinear ultrasonic measurements via analysis of the feedback signal of a closed-loop ultrasonic fatigue system. In the very high-cycle fatigue regime, ultrasonic nonlinearity increases with initiation and growth of a dominant, life-limiting fatigue crack. Based on the increase in the ultrasonic nonlinearity with fatigue cycling, crack initiation, small fatigue crack growth and fast crack growth regimes have been distinguished during cycling in specimens with different pore sizes tested at various stress amplitudes. The fraction of fatigue life spent in initiation of a life-limiting fatigue crack decreases with increasing stress amplitude. For a constant stress amplitude, the initiation life also decreases with increasing pore size. The present study also demonstrates the applicability of the methodology for fatigue crack growth studies from natural defects located internally or at the surface in smooth specimens. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008349

A quantitative multi-phase field model of polycrystalline alloy solidification / Nana Ofori-Opoku in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2155–2164 Titre : A quantitative multi-phase field model of polycrystalline alloy solidification Type de document : texte imprimé Auteurs : Nana Ofori-Opoku, Auteur ; Nikolas Provatas, Auteur Année de publication : 2011 Article en page(s) : pp. 2155–2164 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Solidification  Dendritic  growth  Phase  field  modeling Résumé : A multi-phase field model for quantitative simulations of polycrystalline solidification of binary alloys is introduced. During the free-growth stage of solidification, the model exploits the thin-interface analysis developed by Karma [3] in order to realistically capture bulk phase diffusion and the sharp interface corrections predicted by traditional models of solidification. During grain boundary coalescence, the model is constructed to reproduce the properties of repulsive grain boundaries described by Rappaz et al. [29]. The model provides a very simple mechanism for decoupling of solute and concentration fields at steady state, an important feature for calculating grain boundary energies. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008350 [article] A quantitative multi-phase field model of polycrystalline alloy solidification [texte imprimé] / Nana Ofori-Opoku, Auteur ; Nikolas Provatas, Auteur . - 2011 . - pp. 2155–2164. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2155–2164 Mots-clés : Solidification  Dendritic  growth  Phase  field  modeling Résumé : A multi-phase field model for quantitative simulations of polycrystalline solidification of binary alloys is introduced. During the free-growth stage of solidification, the model exploits the thin-interface analysis developed by Karma [3] in order to realistically capture bulk phase diffusion and the sharp interface corrections predicted by traditional models of solidification. During grain boundary coalescence, the model is constructed to reproduce the properties of repulsive grain boundaries described by Rappaz et al. [29]. The model provides a very simple mechanism for decoupling of solute and concentration fields at steady state, an important feature for calculating grain boundary energies. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008350

Surface and defect microstructure of GaN and AlN layers grown on hydrogen-etched 6H–SiC(0001) substrates / Z.J. Reitmeier in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2165–2175 Titre : Surface and defect microstructure of GaN and AlN layers grown on hydrogen-etched 6H–SiC(0001) substrates Type de document : texte imprimé Auteurs : Z.J. Reitmeier, Auteur ; S. Einfeldt, Auteur ; R.F. Davis, Auteur Année de publication : 2011 Article en page(s) : pp. 2165–2175 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Group  III-nitrides  Dislocations  Heteroepitaxy  AFM  MOCVD Résumé : Hydrogen-etching of 6H–SiC(0001) substrates removed mechanical polishing damage and produced an array of parallel, unit cell high steps. The initial stage of AlN deposition on these etched substrates occurred via island nucleation, both on step edges and on terraces. Coalesced AlN films did not show scratch-induced undulations observed on the surfaces of AlN films deposited on as-received substrates. The films also had a lower density of growth pits. The majority of threading dislocations (TDs) observed in these films were of a type. Jagged networks of misfit dislocations were seen on the terraces in the 15 nm thick AlN/hydrogen-etched SiC composite. GaN islands nucleated primarily at undulations in AlN layers and at hillocks on the AlN surface of as-received and hydrogen-etched substrates, respectively. Complete coalescence of these islands occurred at thicknesses close to 20 nm, and subsequent growth occurred via the step-flow mechanism. Strain measurements showed more strain relaxation in GaN films grown on the hydrogen-etched substrate. On- and off-axis X-ray rocking curves revealed statistically similar full width at half maximum values for both on- and off-axis reflections, indicating similar densities of TDs in the two types of films. The majority of TDs in GaN epi-layers resulted from defective regions observed contiguous to the GaN/AlN interfaces. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008362 [article] Surface and defect microstructure of GaN and AlN layers grown on hydrogen-etched 6H–SiC(0001) substrates [texte imprimé] / Z.J. Reitmeier, Auteur ; S. Einfeldt, Auteur ; R.F. Davis, Auteur . - 2011 . - pp. 2165–2175. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2165–2175 Mots-clés : Group  III-nitrides  Dislocations  Heteroepitaxy  AFM  MOCVD Résumé : Hydrogen-etching of 6H–SiC(0001) substrates removed mechanical polishing damage and produced an array of parallel, unit cell high steps. The initial stage of AlN deposition on these etched substrates occurred via island nucleation, both on step edges and on terraces. Coalesced AlN films did not show scratch-induced undulations observed on the surfaces of AlN films deposited on as-received substrates. The films also had a lower density of growth pits. The majority of threading dislocations (TDs) observed in these films were of a type. Jagged networks of misfit dislocations were seen on the terraces in the 15 nm thick AlN/hydrogen-etched SiC composite. GaN islands nucleated primarily at undulations in AlN layers and at hillocks on the AlN surface of as-received and hydrogen-etched substrates, respectively. Complete coalescence of these islands occurred at thicknesses close to 20 nm, and subsequent growth occurred via the step-flow mechanism. Strain measurements showed more strain relaxation in GaN films grown on the hydrogen-etched substrate. On- and off-axis X-ray rocking curves revealed statistically similar full width at half maximum values for both on- and off-axis reflections, indicating similar densities of TDs in the two types of films. The majority of TDs in GaN epi-layers resulted from defective regions observed contiguous to the GaN/AlN interfaces. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008362

Plastic deformation of nanocrystalline aluminum at high temperatures and strain rate / A.P. Gerlich in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2176–2185 Titre : Plastic deformation of nanocrystalline aluminum at high temperatures and strain rate Type de document : texte imprimé Auteurs : A.P. Gerlich, Auteur ; L. Yue, Auteur ; P.F. Mendez, Auteur Année de publication : 2011 Article en page(s) : pp. 2176–2185 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocrystalline  materials  Plastic  deformation  High  temperature  Molecular  dynamics Résumé : The deformation of nanocrystalline aluminum was studied using molecular dynamics simulation at homologous temperatures up to 0.97. The microstructures and stress–strain response were examined in a polycrystalline and bicrystal configuration. The activation energies for dislocation-based deformation as well as grain boundary sliding and migration were quantified by fitting simulation data to temperature using an Arrhenius relation. The activation energy for the flow stress response suggests that deformation is largely accommodated by sliding and migration of grain boundaries. This is in agreement with simulated microstructures, indicating a negligible degree of dislocation interaction within each grain, and microstructural observations from high strain rate processes are also consistent with this result. A steady-state grain size is maintained in the recrystallized structure following yielding due to boundary migration and grain rotation mechanisms, rather than by diffusion-based dislocation climb. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008374 [article] Plastic deformation of nanocrystalline aluminum at high temperatures and strain rate [texte imprimé] / A.P. Gerlich, Auteur ; L. Yue, Auteur ; P.F. Mendez, Auteur . - 2011 . - pp. 2176–2185. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2176–2185 Mots-clés : Nanocrystalline  materials  Plastic  deformation  High  temperature  Molecular  dynamics Résumé : The deformation of nanocrystalline aluminum was studied using molecular dynamics simulation at homologous temperatures up to 0.97. The microstructures and stress–strain response were examined in a polycrystalline and bicrystal configuration. The activation energies for dislocation-based deformation as well as grain boundary sliding and migration were quantified by fitting simulation data to temperature using an Arrhenius relation. The activation energy for the flow stress response suggests that deformation is largely accommodated by sliding and migration of grain boundaries. This is in agreement with simulated microstructures, indicating a negligible degree of dislocation interaction within each grain, and microstructural observations from high strain rate processes are also consistent with this result. A steady-state grain size is maintained in the recrystallized structure following yielding due to boundary migration and grain rotation mechanisms, rather than by diffusion-based dislocation climb. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008374

Phase stability for the Cu–Zr system / S.H. Zhou in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2186–2196 Titre : Phase stability for the Cu–Zr system : First-principles, experiments and solution-based modeling Type de document : texte imprimé Auteurs : S.H. Zhou, Auteur ; R.E. Napolitano, Auteur Année de publication : 2011 Article en page(s) : pp. 2186–2196 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Copper  alloys  Intermetallic  compounds  Thermodynamics  Phase  transformations Résumé : First-principles calculations and experimental methods were employed to investigate the relative stability of intermetallic phases in the Cu–Zr system. Computed enthalpies of formation indicate that Cu51Zr14-β and CuZr2-C11b are stable phases, while Cu5Zr-C15b, Cu10Zr7-ϕ and CuZr-B2 are metastable at 0 K. Heat treatment and microanalysis revealed two important findings which clarify the phase equilibria. First, the stability range for the Cu5Zr-C15b phase was found to have a lower bound associated with an eutectoid invariant between 802 and 955 K, below which it decomposes to face-centered cubic Cu plus Cu51Zr14-β. Second, the Cu5Zr8 phase, previously reported as stable, was not observed in a Cu–56.4 at.% Zr alloy after holding at 955 and 1036 K for >100 h. This phase, therefore, was not considered to be stable. Based on computational and experimental results, Gibbs free energies were modeled, including the Cu2Zr-σ, Cu24Zr13-μ and metastable CuZr-(B19′ and B33) phases. The associated phase diagrams are presented. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008386 [article] Phase stability for the Cu–Zr system : First-principles, experiments and solution-based modeling [texte imprimé] / S.H. Zhou, Auteur ; R.E. Napolitano, Auteur . - 2011 . - pp. 2186–2196. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2186–2196 Mots-clés : Copper  alloys  Intermetallic  compounds  Thermodynamics  Phase  transformations Résumé : First-principles calculations and experimental methods were employed to investigate the relative stability of intermetallic phases in the Cu–Zr system. Computed enthalpies of formation indicate that Cu51Zr14-β and CuZr2-C11b are stable phases, while Cu5Zr-C15b, Cu10Zr7-ϕ and CuZr-B2 are metastable at 0 K. Heat treatment and microanalysis revealed two important findings which clarify the phase equilibria. First, the stability range for the Cu5Zr-C15b phase was found to have a lower bound associated with an eutectoid invariant between 802 and 955 K, below which it decomposes to face-centered cubic Cu plus Cu51Zr14-β. Second, the Cu5Zr8 phase, previously reported as stable, was not observed in a Cu–56.4 at.% Zr alloy after holding at 955 and 1036 K for >100 h. This phase, therefore, was not considered to be stable. Based on computational and experimental results, Gibbs free energies were modeled, including the Cu2Zr-σ, Cu24Zr13-μ and metastable CuZr-(B19′ and B33) phases. The associated phase diagrams are presented. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008386

Atomistic simulations of surface segregation of defects in solid oxide electrolytes / Hark B. Lee in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2197–2206 Titre : Atomistic simulations of surface segregation of defects in solid oxide electrolytes Type de document : texte imprimé Auteurs : Hark B. Lee, Auteur ; Friedrich B. Prinz, Auteur ; Wei Cai, Auteur Année de publication : 2011 Article en page(s) : pp. 2197–2206 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Segregation  Monte  Carlo  Molecular  dynamics  Yttria-stabilized  zirconia  Gadolinia-doped  ceria Résumé : We performed atomistic simulations of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) to study the segregation of point defects near (1 0 0) surfaces. A hybrid Monte Carlo–molecular dynamics algorithm was developed to sample the equilibrium distributions of dopant cations and oxygen vacancies. The simulations predict an increase of dopant concentration near the surface, which is consistent with experimental observations. Oxygen vacancies are also found to segregate in the first anion layer beneath the surface and to be depleted in the subsequent anion layers. While the ionic size mismatch between dopant and host cations has been considered as a driving force for dopant segregation to the surface, our simulations show that the correlation between individual point defects plays a dominant role in determining their equilibrium distributions. This correlation effect leads to more pronounced dopant segregation in GDC than in YSZ, even though the size mismatch between dopant and host cations is much greater in YSZ than in GDC. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008398 [article] Atomistic simulations of surface segregation of defects in solid oxide electrolytes [texte imprimé] / Hark B. Lee, Auteur ; Friedrich B. Prinz, Auteur ; Wei Cai, Auteur . - 2011 . - pp. 2197–2206. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2197–2206 Mots-clés : Segregation  Monte  Carlo  Molecular  dynamics  Yttria-stabilized  zirconia  Gadolinia-doped  ceria Résumé : We performed atomistic simulations of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) to study the segregation of point defects near (1 0 0) surfaces. A hybrid Monte Carlo–molecular dynamics algorithm was developed to sample the equilibrium distributions of dopant cations and oxygen vacancies. The simulations predict an increase of dopant concentration near the surface, which is consistent with experimental observations. Oxygen vacancies are also found to segregate in the first anion layer beneath the surface and to be depleted in the subsequent anion layers. While the ionic size mismatch between dopant and host cations has been considered as a driving force for dopant segregation to the surface, our simulations show that the correlation between individual point defects plays a dominant role in determining their equilibrium distributions. This correlation effect leads to more pronounced dopant segregation in GDC than in YSZ, even though the size mismatch between dopant and host cations is much greater in YSZ than in GDC. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008398

An optimization-based computational model for domain evolution in polycrystalline ferroelastics / F.X. Li in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2207–2215 Titre : An optimization-based computational model for domain evolution in polycrystalline ferroelastics Type de document : texte imprimé Auteurs : F.X. Li, Auteur ; A.K. Soh, Auteur Année de publication : 2011 Article en page(s) : pp. 2207–2215 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ferroelastics  Polycrystalline  Domain  switching  Optimization  Plasticity Résumé : An optimization-based computational model is proposed to study domain evolution in polycrystalline ferroelastics composed of numerous randomly oriented grains, each of which consists of multiple types of domains. Under any prescribed loading, the volume fraction of each domain in a grain is obtained by minimizing the free energy of the said grain using an optimization method. The mechanical constraint from the neighboring grains is considered using Eshelby inclusion approach. This model has the similar superiority as the phase field model, which does not require imposition of any priori domain-switching criterion. The computational efficiency of this model is fairly high and it is feasible to study three-dimensional cases using numerous grains. Furthermore, this model can reproduce Taylor’s rule of plasticity very well. Simulation results for tetragonal, rhombohedral and morphotropic PZT ceramics are employed to validate the superiority and efficiency of this model. The domain texture evolution process can also be calculated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008404 [article] An optimization-based computational model for domain evolution in polycrystalline ferroelastics [texte imprimé] / F.X. Li, Auteur ; A.K. Soh, Auteur . - 2011 . - pp. 2207–2215. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2207–2215 Mots-clés : Ferroelastics  Polycrystalline  Domain  switching  Optimization  Plasticity Résumé : An optimization-based computational model is proposed to study domain evolution in polycrystalline ferroelastics composed of numerous randomly oriented grains, each of which consists of multiple types of domains. Under any prescribed loading, the volume fraction of each domain in a grain is obtained by minimizing the free energy of the said grain using an optimization method. The mechanical constraint from the neighboring grains is considered using Eshelby inclusion approach. This model has the similar superiority as the phase field model, which does not require imposition of any priori domain-switching criterion. The computational efficiency of this model is fairly high and it is feasible to study three-dimensional cases using numerous grains. Furthermore, this model can reproduce Taylor’s rule of plasticity very well. Simulation results for tetragonal, rhombohedral and morphotropic PZT ceramics are employed to validate the superiority and efficiency of this model. The domain texture evolution process can also be calculated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008404

Superelastic cycling and room temperature recovery of Ti74Nb26 shape memory alloy / Ma, J. in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2216–2224 Titre : Superelastic cycling and room temperature recovery of Ti74Nb26 shape memory alloy Type de document : texte imprimé Auteurs : Ma, J., Auteur ; I. Karaman, Auteur ; H.J. Maier, Auteur Année de publication : 2011 Article en page(s) : pp. 2216–2224 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Superelasticity  Shape  memory  alloys  Martensitic  phase  transformation  Cyclic  behavior  Titanium  alloys Résumé : The superelastic cyclic response of Ti74Nb26 shape memory alloy (SMA), and the nature of cyclic evolution of its superelastic properties and their unexpected static recovery process after cycling, were investigated at room temperature. The critical stress for stress-induced martensitic transformation (σSIM) and stress hysteresis (Δσ) continuously decrease with increasing number of superelastic cycles. However, cumulative irrecoverable strain during cycling in samples of particular processing conditions increases only up to a certain number of cycles before decreasing with further cycling. Stress-free aging at room temperature after cycling was shown to increase σSIM and Δσ. The unexpected room temperature recovery is attributed to the recovery of retained martensite and point defects. Similar experiments conducted on conventional Ni-rich Ni–Ti SMAs also show static recovery at room temperature, indicating that the recovery process is not unique to Ti–Nb SMAs. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008519 [article] Superelastic cycling and room temperature recovery of Ti74Nb26 shape memory alloy [texte imprimé] / Ma, J., Auteur ; I. Karaman, Auteur ; H.J. Maier, Auteur . - 2011 . - pp. 2216–2224. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2216–2224 Mots-clés : Superelasticity  Shape  memory  alloys  Martensitic  phase  transformation  Cyclic  behavior  Titanium  alloys Résumé : The superelastic cyclic response of Ti74Nb26 shape memory alloy (SMA), and the nature of cyclic evolution of its superelastic properties and their unexpected static recovery process after cycling, were investigated at room temperature. The critical stress for stress-induced martensitic transformation (σSIM) and stress hysteresis (Δσ) continuously decrease with increasing number of superelastic cycles. However, cumulative irrecoverable strain during cycling in samples of particular processing conditions increases only up to a certain number of cycles before decreasing with further cycling. Stress-free aging at room temperature after cycling was shown to increase σSIM and Δσ. The unexpected room temperature recovery is attributed to the recovery of retained martensite and point defects. Similar experiments conducted on conventional Ni-rich Ni–Ti SMAs also show static recovery at room temperature, indicating that the recovery process is not unique to Ti–Nb SMAs. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008519

Atomistic Monte Carlo simulations on the influence of sulphur during high-temperature decarburization of molten iron–carbon alloys / R. Khanna in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2225–2236 Titre : Atomistic Monte Carlo simulations on the influence of sulphur during high-temperature decarburization of molten iron–carbon alloys Type de document : texte imprimé Auteurs : R. Khanna, Auteur ; V. Sahajwalla, Auteur ; N. Simento, Auteur Année de publication : 2011 Article en page(s) : pp. 2225–2236 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Surface  segregation  Iron  alloys  Modelling  Simulation Résumé : We report a Monte Carlo simulation study of the molten Fe–C–S system with the aim of developing a theoretical understanding of the influence of sulphur during decarburization reactions in Fe–C alloys. Focussing specifically on the role played by free surfaces, computer simulations were based on the hexagonal atomistic model of Fe–C–S system using isotropic atomic interaction parameters; free surfaces were characterized by a missing layer of atoms. Three geometrical configurations, namely a liquid bath, a prismatic block and a spherical droplet, were investigated. Simulations were carried out as a function of melt carbon and sulphur concentration, temperatures and surface/volume ratios of the simulation cell. Sulphur atoms were found to preferentially concentrate in the top few layers, with the second layer showing the highest amounts of sulphur; very little sulphur was observed in the bulk liquid. This trend was observed in all three simulation configurations over a wide carbon/sulphur concentration range and temperatures. Significant levels of iron were observed in the top surface layer. The influence of free surfaces on atomic concentration profiles was found to be a strong function of the surface/volume ratio. The surface segregation of S was more pronounced for small exposed surfaces and was much smaller for liquids with large exposed surfaces. The presence of surface-active sulphur resulted in a major re-distribution of carbon. Carbon tended to concentrate deeper in the bulk, with the surface region being severely depleted of carbon. In addition to several new findings and a better understanding of liquid surfaces, these simulations have helped overcome major limitations of Sain and Belton’s model. Key experimental results on decarburization have been explained within the framework of our simulations. These simulation results have significant implications for surface decarburization reactions and carbon-boil phenomena in smelting technologies. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008520 [article] Atomistic Monte Carlo simulations on the influence of sulphur during high-temperature decarburization of molten iron–carbon alloys [texte imprimé] / R. Khanna, Auteur ; V. Sahajwalla, Auteur ; N. Simento, Auteur . - 2011 . - pp. 2225–2236. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2225–2236 Mots-clés : Surface  segregation  Iron  alloys  Modelling  Simulation Résumé : We report a Monte Carlo simulation study of the molten Fe–C–S system with the aim of developing a theoretical understanding of the influence of sulphur during decarburization reactions in Fe–C alloys. Focussing specifically on the role played by free surfaces, computer simulations were based on the hexagonal atomistic model of Fe–C–S system using isotropic atomic interaction parameters; free surfaces were characterized by a missing layer of atoms. Three geometrical configurations, namely a liquid bath, a prismatic block and a spherical droplet, were investigated. Simulations were carried out as a function of melt carbon and sulphur concentration, temperatures and surface/volume ratios of the simulation cell. Sulphur atoms were found to preferentially concentrate in the top few layers, with the second layer showing the highest amounts of sulphur; very little sulphur was observed in the bulk liquid. This trend was observed in all three simulation configurations over a wide carbon/sulphur concentration range and temperatures. Significant levels of iron were observed in the top surface layer. The influence of free surfaces on atomic concentration profiles was found to be a strong function of the surface/volume ratio. The surface segregation of S was more pronounced for small exposed surfaces and was much smaller for liquids with large exposed surfaces. The presence of surface-active sulphur resulted in a major re-distribution of carbon. Carbon tended to concentrate deeper in the bulk, with the surface region being severely depleted of carbon. In addition to several new findings and a better understanding of liquid surfaces, these simulations have helped overcome major limitations of Sain and Belton’s model. Key experimental results on decarburization have been explained within the framework of our simulations. These simulation results have significant implications for surface decarburization reactions and carbon-boil phenomena in smelting technologies. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008520

Domain switching and creep behavior of a poled PZT wafer under through-thickness electric fields at high temperatures / Sang-Joo Kim in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2237–2249 Titre : Domain switching and creep behavior of a poled PZT wafer under through-thickness electric fields at high temperatures Type de document : texte imprimé Auteurs : Sang-Joo Kim, Auteur ; Ju Hong Kim, Auteur ; Chang-Hoan Lee, Auteur Année de publication : 2011 Article en page(s) : pp. 2237–2249 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : PZT  wafer  High  temperature  Domain  switching  Creep  Electric  field Résumé : Various constant magnitudes of through-thickness electric field are applied to a poled PZT wafer for about 1800 s at four different high temperatures. The wafer is then removed swiftly from the field and kept at zero electric field for about 1000 s. During the whole period of nonzero and zero electric field loading time, the electric displacement in thickness direction and the in-plane strain of the wafer are measured over time. The measured responses at different electric fields and temperatures are discussed and compared with one another. The dependence of various linear moduli on remanent quantities and temperature is obtained; the creep responses of the wafer at high temperatures are compared and discussed; and finally the domain-switching processes at different electric fields and temperatures are discussed in terms of reference remanent quantities. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008532 [article] Domain switching and creep behavior of a poled PZT wafer under through-thickness electric fields at high temperatures [texte imprimé] / Sang-Joo Kim, Auteur ; Ju Hong Kim, Auteur ; Chang-Hoan Lee, Auteur . - 2011 . - pp. 2237–2249. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2237–2249 Mots-clés : PZT  wafer  High  temperature  Domain  switching  Creep  Electric  field Résumé : Various constant magnitudes of through-thickness electric field are applied to a poled PZT wafer for about 1800 s at four different high temperatures. The wafer is then removed swiftly from the field and kept at zero electric field for about 1000 s. During the whole period of nonzero and zero electric field loading time, the electric displacement in thickness direction and the in-plane strain of the wafer are measured over time. The measured responses at different electric fields and temperatures are discussed and compared with one another. The dependence of various linear moduli on remanent quantities and temperature is obtained; the creep responses of the wafer at high temperatures are compared and discussed; and finally the domain-switching processes at different electric fields and temperatures are discussed in terms of reference remanent quantities. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008532

Elastically driven morphology of coherent trigonal precipitates inside a close-packed hexagonal matrix / Ludovic Thuinet in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2250–2261 Titre : Elastically driven morphology of coherent trigonal precipitates inside a close-packed hexagonal matrix Type de document : texte imprimé Auteurs : Ludovic Thuinet, Auteur ; Alexandre Legris, Auteur Année de publication : 2011 Article en page(s) : pp. 2250–2261 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Precipitation  Micromechanical  modeling  Internal  stresses  Hydrides Résumé : The influence of a crystallographic symmetry break on the morphology of precipitates during the coherent precipitation of a trigonal phase in a close-packed hexagonal matrix is analyzed. It is pointed out that in spite of the isotropy of the stress-free strain of the precipitate in the basal plane, the existence of an extra elastic constant in the precipitate (associated to the loss of symmetry) induces a morphological evolution from a shape having a symmetry of revolution around the threefold axis to a needle-like one oriented along the compact directions in the basal plane. These general considerations are applied to the case of zirconium hydrides, the crystallography of which has recently been identified to be coherent with that of the αZr matrix. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008544 [article] Elastically driven morphology of coherent trigonal precipitates inside a close-packed hexagonal matrix [texte imprimé] / Ludovic Thuinet, Auteur ; Alexandre Legris, Auteur . - 2011 . - pp. 2250–2261. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2250–2261 Mots-clés : Precipitation  Micromechanical  modeling  Internal  stresses  Hydrides Résumé : The influence of a crystallographic symmetry break on the morphology of precipitates during the coherent precipitation of a trigonal phase in a close-packed hexagonal matrix is analyzed. It is pointed out that in spite of the isotropy of the stress-free strain of the precipitate in the basal plane, the existence of an extra elastic constant in the precipitate (associated to the loss of symmetry) induces a morphological evolution from a shape having a symmetry of revolution around the threefold axis to a needle-like one oriented along the compact directions in the basal plane. These general considerations are applied to the case of zirconium hydrides, the crystallography of which has recently been identified to be coherent with that of the αZr matrix. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008544

Detwinning mechanisms for growth twins in face-centered cubic metals / J. Wang in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2262–2270 Titre : Detwinning mechanisms for growth twins in face-centered cubic metals Type de document : texte imprimé Auteurs : J. Wang, Auteur ; N. Li, Auteur ; O. Anderoglu, Auteur Année de publication : 2011 Article en page(s) : pp. 2262–2270 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanotwins  Detwinning  In  situ  TEM  Atomistic  simulations Résumé : Using in situ transmission electron microscopy, we studied the stability of growth twins. We observed the rapid migration of incoherent twin boundaries (ITBs), indicating that nanotwins are unstable. Topological analysis and atomistic simulations are adopted to explore detwinning mechanisms. The results show that: (i) the detwinning process is accomplished via the collective glide of multiple twinning dislocations that form an ITB; (ii) detwinning can easily occur for thin twins, and the driving force is mainly attributed to a variation of the excess energy of a coherent twin boundary; (iii) shear stresses enable ITBs to migrate easily, causing the motion of coherent twin boundaries; and (iv) the migration velocity depends on stacking fault energy. The results imply that detwinning becomes the dominant deformation mechanism for growth twins of the order of a few nanometers thick. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008556 [article] Detwinning mechanisms for growth twins in face-centered cubic metals [texte imprimé] / J. Wang, Auteur ; N. Li, Auteur ; O. Anderoglu, Auteur . - 2011 . - pp. 2262–2270. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2262–2270 Mots-clés : Nanotwins  Detwinning  In  situ  TEM  Atomistic  simulations Résumé : Using in situ transmission electron microscopy, we studied the stability of growth twins. We observed the rapid migration of incoherent twin boundaries (ITBs), indicating that nanotwins are unstable. Topological analysis and atomistic simulations are adopted to explore detwinning mechanisms. The results show that: (i) the detwinning process is accomplished via the collective glide of multiple twinning dislocations that form an ITB; (ii) detwinning can easily occur for thin twins, and the driving force is mainly attributed to a variation of the excess energy of a coherent twin boundary; (iii) shear stresses enable ITBs to migrate easily, causing the motion of coherent twin boundaries; and (iv) the migration velocity depends on stacking fault energy. The results imply that detwinning becomes the dominant deformation mechanism for growth twins of the order of a few nanometers thick. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008556

Microtexture tracking in hot-deformed polycrystalline aluminium / R. Quey in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2271–2281 Titre : Microtexture tracking in hot-deformed polycrystalline aluminium : Comparison with simulations Type de document : texte imprimé Auteurs : R. Quey, Auteur ; D. Piot, Auteur ; J.H. Driver, Auteur Année de publication : 2011 Article en page(s) : pp. 2271–2281 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Microstructure  Plastic  deformation  Modelling  Electron  backscattering  diffraction  (EBSD)  Aluminium  alloys Résumé : The average rotations of 157 individual grains measured in an Al–0.1%Mn polycrystal deformed in hot plane-strain compression to a strain of 1.2 have been compared to the predictions from several crystal plasticity models. The Taylor model successfully predicts the distributions of the rotation angles, but overestimates the rate of evolution of the rotation axes, which explains the overestimation of the final texture. The model also provides a first-order agreement for the rotation axes and the final components of the individual grains. The discrepancies are related to the influence of grain interaction. The main mechanisms of texture development at the level of the individual grains are identified through an analysis of their orientation trajectories. The introduction of local grain interactions, which produce a rotation variability at constant orientation, is shown to weaken texture development. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008568 [article] Microtexture tracking in hot-deformed polycrystalline aluminium : Comparison with simulations [texte imprimé] / R. Quey, Auteur ; D. Piot, Auteur ; J.H. Driver, Auteur . - 2011 . - pp. 2271–2281. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2271–2281 Mots-clés : Microstructure  Plastic  deformation  Modelling  Electron  backscattering  diffraction  (EBSD)  Aluminium  alloys Résumé : The average rotations of 157 individual grains measured in an Al–0.1%Mn polycrystal deformed in hot plane-strain compression to a strain of 1.2 have been compared to the predictions from several crystal plasticity models. The Taylor model successfully predicts the distributions of the rotation angles, but overestimates the rate of evolution of the rotation axes, which explains the overestimation of the final texture. The model also provides a first-order agreement for the rotation axes and the final components of the individual grains. The discrepancies are related to the influence of grain interaction. The main mechanisms of texture development at the level of the individual grains are identified through an analysis of their orientation trajectories. The introduction of local grain interactions, which produce a rotation variability at constant orientation, is shown to weaken texture development. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008568

Ceramic processing strategies for thick films on copper foils / Aiying Wu in Acta materialia, Vol. 58 N° 6 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2282–2290 Titre : Ceramic processing strategies for thick films on copper foils Type de document : texte imprimé Auteurs : Aiying Wu, Auteur ; Paula M. Vilarinho, Auteur ; Angus I. Kingon, Auteur Année de publication : 2011 Article en page(s) : pp. 2282–2290 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Electroceramics  Perovkskites  Copper  Sintering  Ferroelectricity Résumé : Functional oxides on Cu have multiple applications. For thick films the required high sintering temperatures present a challenge for processing on base metal substrates. In this study it is shown that it is possible to adapt well-known ceramic processing strategies to the fabrication of thick lead zirconate titanate (PZT) films on Cu with useful ferroelectric properties. PZT powders with optimized particle sizes are used to fabricate thick films by electrophoretic deposition in combination with a post-deposition isostatic pressing step. This approach to maximize green packing is sufficient to dramatically lower the required sintering temperatures. 25 μm thick PZT films on Cu sintered at 900 °C have a dielectric permittivity of 585, a loss tangent at 10 kHz of 0.03, a remanent polarization of 19 μC cm−2 and a coercive field of 22 kV cm−1. This significant improvement in the dielectric response opens the possibility of using thick PZT films on Cu for a wide range of devices where cost, yield and reliability are concerns. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008581 [article] Ceramic processing strategies for thick films on copper foils [texte imprimé] / Aiying Wu, Auteur ; Paula M. Vilarinho, Auteur ; Angus I. Kingon, Auteur . - 2011 . - pp. 2282–2290. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 6 (Avril 2010) . - pp. 2282–2290 Mots-clés : Electroceramics  Perovkskites  Copper  Sintering  Ferroelectricity Résumé : Functional oxides on Cu have multiple applications. For thick films the required high sintering temperatures present a challenge for processing on base metal substrates. In this study it is shown that it is possible to adapt well-known ceramic processing strategies to the fabrication of thick lead zirconate titanate (PZT) films on Cu with useful ferroelectric properties. PZT powders with optimized particle sizes are used to fabricate thick films by electrophoretic deposition in combination with a post-deposition isostatic pressing step. This approach to maximize green packing is sufficient to dramatically lower the required sintering temperatures. 25 μm thick PZT films on Cu sintered at 900 °C have a dielectric permittivity of 585, a loss tangent at 10 kHz of 0.03, a remanent polarization of 19 μC cm−2 and a coercive field of 22 kV cm−1. This significant improvement in the dielectric response opens the possibility of using thick PZT films on Cu for a wide range of devices where cost, yield and reliability are concerns. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008581

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