Dépouillements

Phase stability and transformations in NiTi from density functional theory calculations / Karthik Guda Vishnu in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 745–752 Titre : Phase stability and transformations in NiTi from density functional theory calculations Type de document : texte imprimé Auteurs : Karthik Guda Vishnu, Auteur ; Alejandro Strachan, Auteur Année de publication : 2011 Article en page(s) : pp. 745–752 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : NiTi  Martensitic  phase  transformation  Density  functional  theory  (DFT)  Shape  memory  alloys  (SMA) Résumé : We used density functional theory to characterize various crystalline phases of NiTi alloys: (i) high-temperature austenite phase B2; (ii) orthorhombic B19; (iii) the monoclinic martensite phase B19′; and (iv) a body-centered orthorhombic phase (BCO), theoretically predicted to be the ground state. We also investigated possible transition pathways between the various phases and the energetics involved. We found B19 to be metastable with a 1 meV energy barrier separating it from B19′. Interestingly, we predicted a new phase of NiTi, denoted B19′′, that is involved in the transition between B19′ and BCO. B19′′ is monoclinic and can exhibit shape memory; furthermore, its presence reduces the internal stress required to stabilize the experimentally observed B19′ structure, and it consequently plays a key role in NiTi’s properties. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006156 [article] Phase stability and transformations in NiTi from density functional theory calculations [texte imprimé] / Karthik Guda Vishnu, Auteur ; Alejandro Strachan, Auteur . - 2011 . - pp. 745–752. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 745–752 Mots-clés : NiTi  Martensitic  phase  transformation  Density  functional  theory  (DFT)  Shape  memory  alloys  (SMA) Résumé : We used density functional theory to characterize various crystalline phases of NiTi alloys: (i) high-temperature austenite phase B2; (ii) orthorhombic B19; (iii) the monoclinic martensite phase B19′; and (iv) a body-centered orthorhombic phase (BCO), theoretically predicted to be the ground state. We also investigated possible transition pathways between the various phases and the energetics involved. We found B19 to be metastable with a 1 meV energy barrier separating it from B19′. Interestingly, we predicted a new phase of NiTi, denoted B19′′, that is involved in the transition between B19′ and BCO. B19′′ is monoclinic and can exhibit shape memory; furthermore, its presence reduces the internal stress required to stabilize the experimentally observed B19′ structure, and it consequently plays a key role in NiTi’s properties. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006156

Kinetics of austenitization under uniaxial compressive stress in Fe–2.96 at.% Ni alloy / Y. C. Liu in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 753–763 Titre : Kinetics of austenitization under uniaxial compressive stress in Fe–2.96 at.% Ni alloy Type de document : texte imprimé Auteurs : Y. C. Liu, Auteur ; F. Sommer, Auteur ; E. J. Mittemeijer, Auteur Année de publication : 2011 Article en page(s) : pp. 753–763 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ferrite–austenite  transformation  Substitutional  Fe-based  alloys  Applied  compressive  stress  Annealing  Dilatometer Résumé : Differential dilatometry has been employed to study the kinetics of the massive ferrite (α) → austenite (γ) transformation upon isochronal heating (i.e. austenitization) of the substitutional Fe–2.96 at.% Ni alloy subjected to a range of applied constant uniaxial compressive stresses. A phase-transformation model, involving site saturation, interface-controlled (continuous) growth and incorporating an impingement correction for an intermediate of the cases of ideally periodically and of ideally randomly dispersed growing particles, has been employed to extract the interface-migration velocity of the α/γ interface and the transformation-induced deformation energy taken up by the specimen. The value obtained for the energy corresponding with the elastic and plastic deformation associated with the accommodation of the α/γ volume misfit depends on the austenite fraction and increases distinctly with an increase in the applied uniaxial compressive stress, which is compensated by, in particular, an increase in the chemical driving force corresponding to an increase in the onset temperature. The opposite effects of an applied uniaxial compressive stress on the α → γ transformation and on the γ → α transformation can be discussed as the outcome of constrained plastic deformation due to transformation-induced strain. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006545 [article] Kinetics of austenitization under uniaxial compressive stress in Fe–2.96 at.% Ni alloy [texte imprimé] / Y. C. Liu, Auteur ; F. Sommer, Auteur ; E. J. Mittemeijer, Auteur . - 2011 . - pp. 753–763. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 753–763 Mots-clés : Ferrite–austenite  transformation  Substitutional  Fe-based  alloys  Applied  compressive  stress  Annealing  Dilatometer Résumé : Differential dilatometry has been employed to study the kinetics of the massive ferrite (α) → austenite (γ) transformation upon isochronal heating (i.e. austenitization) of the substitutional Fe–2.96 at.% Ni alloy subjected to a range of applied constant uniaxial compressive stresses. A phase-transformation model, involving site saturation, interface-controlled (continuous) growth and incorporating an impingement correction for an intermediate of the cases of ideally periodically and of ideally randomly dispersed growing particles, has been employed to extract the interface-migration velocity of the α/γ interface and the transformation-induced deformation energy taken up by the specimen. The value obtained for the energy corresponding with the elastic and plastic deformation associated with the accommodation of the α/γ volume misfit depends on the austenite fraction and increases distinctly with an increase in the applied uniaxial compressive stress, which is compensated by, in particular, an increase in the chemical driving force corresponding to an increase in the onset temperature. The opposite effects of an applied uniaxial compressive stress on the α → γ transformation and on the γ → α transformation can be discussed as the outcome of constrained plastic deformation due to transformation-induced strain. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006545

Synthesis and characterization of novel CoFe2O4–BaTiO3 multiferroic core–shell-type nanostructures / V. Corral-Flores in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 764–769 Titre : Synthesis and characterization of novel CoFe2O4–BaTiO3 multiferroic core–shell-type nanostructures Type de document : texte imprimé Auteurs : V. Corral-Flores, Auteur ; D. Bueno-Baqués, Auteur ; R. F. Ziolo, Auteur Année de publication : 2011 Article en page(s) : pp. 764–769 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocomposite  Multiferroic  Precipitation  Sol–gel Résumé : Novel multiferroic nanostructures of cobalt ferrite–barium titanate were synthesized by a two-step wet chemical procedure, combining co-precipitation and sol–gel techniques. The fraction of cobalt ferrite in the nanostructures was varied from 20 to 60 wt.%. X-ray diffraction confirmed the presence of both the spinel and the perovskite phases, with average crystallite sizes in the range of 15–28 nm. Both the degree of tetragonality of barium titanate and the lattice parameter of cobalt ferrite significantly increased with the content of ferrite in the nanostructures, revealing a crystallographic distortion related to the shell thickness. Transmission electron microscopy data showed two-phase composite nanostructures consisting of a cobalt ferrite core surrounded by a barium titanate shell-like coating. Magnetization data showed expected ferromagnetic behavior. The multiferroic nanostructures are proposed as building blocks for higher-order multiferroic inorganic and hybrid inorganic–organic nanocomposites. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006600 [article] Synthesis and characterization of novel CoFe2O4–BaTiO3 multiferroic core–shell-type nanostructures [texte imprimé] / V. Corral-Flores, Auteur ; D. Bueno-Baqués, Auteur ; R. F. Ziolo, Auteur . - 2011 . - pp. 764–769. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 764–769 Mots-clés : Nanocomposite  Multiferroic  Precipitation  Sol–gel Résumé : Novel multiferroic nanostructures of cobalt ferrite–barium titanate were synthesized by a two-step wet chemical procedure, combining co-precipitation and sol–gel techniques. The fraction of cobalt ferrite in the nanostructures was varied from 20 to 60 wt.%. X-ray diffraction confirmed the presence of both the spinel and the perovskite phases, with average crystallite sizes in the range of 15–28 nm. Both the degree of tetragonality of barium titanate and the lattice parameter of cobalt ferrite significantly increased with the content of ferrite in the nanostructures, revealing a crystallographic distortion related to the shell thickness. Transmission electron microscopy data showed two-phase composite nanostructures consisting of a cobalt ferrite core surrounded by a barium titanate shell-like coating. Magnetization data showed expected ferromagnetic behavior. The multiferroic nanostructures are proposed as building blocks for higher-order multiferroic inorganic and hybrid inorganic–organic nanocomposites. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006600

2-Point correlation function of nanostructured materials via the grey-tone correlation function of electron tomograms / Cedric J. Gommes in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 770–780 Titre : 2-Point correlation function of nanostructured materials via the grey-tone correlation function of electron tomograms : A three-dimensional structural analysis of ordered mesoporous silica Type de document : texte imprimé Auteurs : Cedric J. Gommes, Auteur ; Heiner Friedrich, Auteur ; Petra E. de Jongh, Auteur Année de publication : 2011 Article en page(s) : pp. 770–780 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : 2-Point  correlation  Nanostructure  Porous  material  Image  analysis  Transmission  electron  microscopy Résumé : Electron tomography is a unique technique for imaging the microstructure of materials with a nanometer resolution. The signal-to-noise ratio of electron tomograms is, however, often too low for a reliable segmentation-based image analysis. We derive a general relation between the grey-tone correlation function of the tomograms and the 2-point correlation function of the morphology, which enables us to analyse quantitatively the grey-tone correlation function with a morphological model of the material. The methodology is applied to SBA-15 ordered mesoporous silica. The three-dimensional grey-tone correlation function obtained from electron tomography is analysed in terms of a hexagonal array of Gaussian independent pores. The model enables us to relate the morphology obtained from the 2-point correlation function to macroscopic characterization data of the material, notably small-angle X-ray scattering and nitrogen adsorption. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006612 [article] 2-Point correlation function of nanostructured materials via the grey-tone correlation function of electron tomograms : A three-dimensional structural analysis of ordered mesoporous silica [texte imprimé] / Cedric J. Gommes, Auteur ; Heiner Friedrich, Auteur ; Petra E. de Jongh, Auteur . - 2011 . - pp. 770–780. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 770–780 Mots-clés : 2-Point  correlation  Nanostructure  Porous  material  Image  analysis  Transmission  electron  microscopy Résumé : Electron tomography is a unique technique for imaging the microstructure of materials with a nanometer resolution. The signal-to-noise ratio of electron tomograms is, however, often too low for a reliable segmentation-based image analysis. We derive a general relation between the grey-tone correlation function of the tomograms and the 2-point correlation function of the morphology, which enables us to analyse quantitatively the grey-tone correlation function with a morphological model of the material. The methodology is applied to SBA-15 ordered mesoporous silica. The three-dimensional grey-tone correlation function obtained from electron tomography is analysed in terms of a hexagonal array of Gaussian independent pores. The model enables us to relate the morphology obtained from the 2-point correlation function to macroscopic characterization data of the material, notably small-angle X-ray scattering and nitrogen adsorption. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006612

Effect of microalloying on precipitate evolution in ferritic welds and implications for toughness / Badri K. Narayanan in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 781–791 Titre : Effect of microalloying on precipitate evolution in ferritic welds and implications for toughness Type de document : texte imprimé Auteurs : Badri K. Narayanan, Auteur ; L. Kovarik, Auteur ; Peter M. Sarosi, Auteur Année de publication : 2011 Article en page(s) : pp. 781–791 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Welding  Precipitation  STEM  Toughness  Ferritic  steels Résumé : Ferritic weld metal deposited with a self-shielded arc-welding process has intentional additions of aluminum, magnesium, titanium and zirconium. This results in a complex precipitation process that has been characterized with a combination of electron microscopy techniques. This work indicates that the formation of a spinel oxide is critical for the nucleation of nitrides of zirconium and titanium and prevents the agglomeration of aluminum rich oxides and the formation of large aluminum nitrides. High-resolution transmission electron microscopy has been used to characterize the core/shell structure of the precipitates with microalloying additions. Thermodynamic modeling of the precipitate formation during solidification is consistent with the microstructural observations. The evolution of precipitate formation is critical to limit large inclusions and improve weld metal toughness. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006624 [article] Effect of microalloying on precipitate evolution in ferritic welds and implications for toughness [texte imprimé] / Badri K. Narayanan, Auteur ; L. Kovarik, Auteur ; Peter M. Sarosi, Auteur . - 2011 . - pp. 781–791. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 781–791 Mots-clés : Welding  Precipitation  STEM  Toughness  Ferritic  steels Résumé : Ferritic weld metal deposited with a self-shielded arc-welding process has intentional additions of aluminum, magnesium, titanium and zirconium. This results in a complex precipitation process that has been characterized with a combination of electron microscopy techniques. This work indicates that the formation of a spinel oxide is critical for the nucleation of nitrides of zirconium and titanium and prevents the agglomeration of aluminum rich oxides and the formation of large aluminum nitrides. High-resolution transmission electron microscopy has been used to characterize the core/shell structure of the precipitates with microalloying additions. Thermodynamic modeling of the precipitate formation during solidification is consistent with the microstructural observations. The evolution of precipitate formation is critical to limit large inclusions and improve weld metal toughness. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006624

Surface modification of cellulose by PCL grafts / Olivier Paquet in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 792–801 Titre : Surface modification of cellulose by PCL grafts Type de document : texte imprimé Auteurs : Olivier Paquet, Auteur ; Mohammed Krouit, Auteur ; Julien Bras, Auteur Année de publication : 2011 Article en page(s) : pp. 792–801 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cellulose  fibres  Surface  grafting  Polycaprolactone  XPS  analysis  Biodegradability Résumé : Two cellulosic substrates (microcrystalline cellulose, MCC, and bleached kraft softwood pulps, BSK) were grafted by polycaprolactone (PCL) chains with different molecular weights, following a three-step procedure using non-swelling conditions in order to limit the reaction to their surface. First, one of the two OH PCL ends was blocked by phenyl isocyanate and the reaction product (adduct 1) was subsequently reacted with 2,4-toluene diisocyanate (adduct 2) to provide it with an NCO function, capable of reacting with cellulose. The ensuing PCL-grafted cellulosic materials were characterized by weight gain, elemental analysis, contact angle measurements, attenuated total reflexion–Fourier transform infrared (ATR–FTIR), X-ray photoelectron spectroscopy (XPS) and biodegradation tests. The modification was proven to occur by the presence of nitrogen atoms in the elemental analysis tests and XPS spectra of modified and soxhlet-extracted cellulose. The contact angle measurements have also shown that the surface became as hydrophobic as PCL itself. The polar component of the surface energy of cellulosic substrates before treatment was found to be about 32 and 10 mJ m−2, for MCC and BSK, respectively. This value vanished to practically zero after grafting with different PCLs. The strategy proposed in the present work is original since, to the best of our knowledge, this paper reports for the first time the chemical “grafting onto” of the cellulose surface by PCL macromolecular structures, with the aim of obtaining fibre–matrix co-continuous fully sustainable and biodegradable composite materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006636 [article] Surface modification of cellulose by PCL grafts [texte imprimé] / Olivier Paquet, Auteur ; Mohammed Krouit, Auteur ; Julien Bras, Auteur . - 2011 . - pp. 792–801. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 792–801 Mots-clés : Cellulose  fibres  Surface  grafting  Polycaprolactone  XPS  analysis  Biodegradability Résumé : Two cellulosic substrates (microcrystalline cellulose, MCC, and bleached kraft softwood pulps, BSK) were grafted by polycaprolactone (PCL) chains with different molecular weights, following a three-step procedure using non-swelling conditions in order to limit the reaction to their surface. First, one of the two OH PCL ends was blocked by phenyl isocyanate and the reaction product (adduct 1) was subsequently reacted with 2,4-toluene diisocyanate (adduct 2) to provide it with an NCO function, capable of reacting with cellulose. The ensuing PCL-grafted cellulosic materials were characterized by weight gain, elemental analysis, contact angle measurements, attenuated total reflexion–Fourier transform infrared (ATR–FTIR), X-ray photoelectron spectroscopy (XPS) and biodegradation tests. The modification was proven to occur by the presence of nitrogen atoms in the elemental analysis tests and XPS spectra of modified and soxhlet-extracted cellulose. The contact angle measurements have also shown that the surface became as hydrophobic as PCL itself. The polar component of the surface energy of cellulosic substrates before treatment was found to be about 32 and 10 mJ m−2, for MCC and BSK, respectively. This value vanished to practically zero after grafting with different PCLs. The strategy proposed in the present work is original since, to the best of our knowledge, this paper reports for the first time the chemical “grafting onto” of the cellulose surface by PCL macromolecular structures, with the aim of obtaining fibre–matrix co-continuous fully sustainable and biodegradable composite materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006636

Effect of particle size in aggregated and agglomerated ceramic powders / A. Balakrishnan in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 802–812 Titre : Effect of particle size in aggregated and agglomerated ceramic powders Type de document : texte imprimé Auteurs : A. Balakrishnan, Auteur ; P. Pizette, Auteur ; C. L. Martin, Auteur Année de publication : 2011 Article en page(s) : pp. 802–812 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ceramics  Powder  consolidation  Molecular  dynamics  simulations  Aggregates  Agglomerates Résumé : This work describes the compaction of agglomerated and aggregated ceramic powders with special emphasis on the role of primary particle size. Discrete element simulations are used to model weakly bonded agglomerates as well as strongly bonded aggregates. Crushing tests are carried out to obtain the characteristic strength of single agglomerate and aggregate. Microstructure evolution and stress–strain curves indicate that aggregates undergo a brittle to plastic-like transition as particle size decreases below 50 nm. It is shown that agglomerates made of nanoparticles exhibit much greater strength than those made of micron-sized particles, with an approximately inverse linear relationship with primary particle size. Simulation of the uniaxial compaction of a representative volume element of powder demonstrates that adhesive effects are responsible for the difficulty to compact nanopowders and for the heterogeneity of microstructure prior to sintering. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006648 [article] Effect of particle size in aggregated and agglomerated ceramic powders [texte imprimé] / A. Balakrishnan, Auteur ; P. Pizette, Auteur ; C. L. Martin, Auteur . - 2011 . - pp. 802–812. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 802–812 Mots-clés : Ceramics  Powder  consolidation  Molecular  dynamics  simulations  Aggregates  Agglomerates Résumé : This work describes the compaction of agglomerated and aggregated ceramic powders with special emphasis on the role of primary particle size. Discrete element simulations are used to model weakly bonded agglomerates as well as strongly bonded aggregates. Crushing tests are carried out to obtain the characteristic strength of single agglomerate and aggregate. Microstructure evolution and stress–strain curves indicate that aggregates undergo a brittle to plastic-like transition as particle size decreases below 50 nm. It is shown that agglomerates made of nanoparticles exhibit much greater strength than those made of micron-sized particles, with an approximately inverse linear relationship with primary particle size. Simulation of the uniaxial compaction of a representative volume element of powder demonstrates that adhesive effects are responsible for the difficulty to compact nanopowders and for the heterogeneity of microstructure prior to sintering. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006648

The effects of grain grooves on grain boundary migration in nanofilms / Amy Novick-Cohen in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 813–822 Titre : The effects of grain grooves on grain boundary migration in nanofilms Type de document : texte imprimé Auteurs : Amy Novick-Cohen, Auteur ; Olga Zelekman-Smirin, Auteur ; Arkady Vilenkin, Auteur Année de publication : 2011 Article en page(s) : pp. 813–822 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  boundaries  Grain  growth  Surface  diffusion  Theory Résumé : Using numerical computations and asymptotic analysis, we study the effects of grain grooves on grain boundary migration in nanofilms, focusing for simplicity on axisymmetric bicrystals containing an embedded cylindrical grain located at the origin. We find there is a critical initial grain radius, R∗, such that if RR∗, groove growth during grain shrinkage leads to film break-up. The central cross-section of the grain boundary profile is seen to be parabolic, and an ordinary differential equation which depends on the tilt angle and the groove depth is seen to govern the location of the groove root. Near the annihilation–pinch-off transition, temporary stagnation occurs; thereafter, the shrinking grain accelerates rapidly, then disappears. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900665X [article] The effects of grain grooves on grain boundary migration in nanofilms [texte imprimé] / Amy Novick-Cohen, Auteur ; Olga Zelekman-Smirin, Auteur ; Arkady Vilenkin, Auteur . - 2011 . - pp. 813–822. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 813–822 Mots-clés : Grain  boundaries  Grain  growth  Surface  diffusion  Theory Résumé : Using numerical computations and asymptotic analysis, we study the effects of grain grooves on grain boundary migration in nanofilms, focusing for simplicity on axisymmetric bicrystals containing an embedded cylindrical grain located at the origin. We find there is a critical initial grain radius, R∗, such that if RR∗, groove growth during grain shrinkage leads to film break-up. The central cross-section of the grain boundary profile is seen to be parabolic, and an ordinary differential equation which depends on the tilt angle and the groove depth is seen to govern the location of the groove root. Near the annihilation–pinch-off transition, temporary stagnation occurs; thereafter, the shrinking grain accelerates rapidly, then disappears. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900665X

Misfit strain–film thickness phase diagrams and related electromechanical properties of epitaxial ultra-thin lead zirconate titanate films / Q. Y. Qiu in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 823–835 Titre : Misfit strain–film thickness phase diagrams and related electromechanical properties of epitaxial ultra-thin lead zirconate titanate films Type de document : texte imprimé Auteurs : Q. Y. Qiu, Auteur ; R. Mahjoub, Auteur ; S. P. Alpay, Auteur Année de publication : 2011 Article en page(s) : pp. 823–835 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ferroelectricity  Thin  films  Phase  transformations  Electroceramics  Dielectrics Résumé : The phase stability of ultra-thin (0 0 1) oriented ferroelectric PbZr1–xTixO3 (PZT) epitaxial thin films as a function of the film composition, film thickness, and the misfit strain is analyzed using a non-linear Landau–Ginzburg–Devonshire thermodynamic model taking into account the electrical and mechanical boundary conditions. The theoretical formalism incorporates the role of the depolarization field as well as the possibility of the relaxation of in-plane strains via the formation of microstructural features such as misfit dislocations at the growth temperature and ferroelastic polydomain patterns below the paraelectric–ferroelectric phase transformation temperature. Film thickness–misfit strain phase diagrams are developed for PZT films with four different compositions (x = 1, 0.9, 0.8 and 0.7) as a function of the film thickness. The results show that the so-called rotational r-phase appears in a very narrow range of misfit strain and thickness of the film. Furthermore, the in-plane and out-of-plane dielectric permittivities ε11 and ε33, as well as the out-of-plane piezoelectric coefficients d33 for the PZT thin films, are computed as a function of misfit strain, taking into account substrate-induced clamping. The model reveals that previously predicted ultrahigh piezoelectric coefficients due to misfit-strain-induced phase transitions are practically achievable only in an extremely narrow range of film thickness, composition and misfit strain parameter space. We also show that the dielectric and piezoelectric properties of epitaxial ferroelectric films can be tailored through strain engineering and microstructural optimization. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006661 [article] Misfit strain–film thickness phase diagrams and related electromechanical properties of epitaxial ultra-thin lead zirconate titanate films [texte imprimé] / Q. Y. Qiu, Auteur ; R. Mahjoub, Auteur ; S. P. Alpay, Auteur . - 2011 . - pp. 823–835. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 823–835 Mots-clés : Ferroelectricity  Thin  films  Phase  transformations  Electroceramics  Dielectrics Résumé : The phase stability of ultra-thin (0 0 1) oriented ferroelectric PbZr1–xTixO3 (PZT) epitaxial thin films as a function of the film composition, film thickness, and the misfit strain is analyzed using a non-linear Landau–Ginzburg–Devonshire thermodynamic model taking into account the electrical and mechanical boundary conditions. The theoretical formalism incorporates the role of the depolarization field as well as the possibility of the relaxation of in-plane strains via the formation of microstructural features such as misfit dislocations at the growth temperature and ferroelastic polydomain patterns below the paraelectric–ferroelectric phase transformation temperature. Film thickness–misfit strain phase diagrams are developed for PZT films with four different compositions (x = 1, 0.9, 0.8 and 0.7) as a function of the film thickness. The results show that the so-called rotational r-phase appears in a very narrow range of misfit strain and thickness of the film. Furthermore, the in-plane and out-of-plane dielectric permittivities ε11 and ε33, as well as the out-of-plane piezoelectric coefficients d33 for the PZT thin films, are computed as a function of misfit strain, taking into account substrate-induced clamping. The model reveals that previously predicted ultrahigh piezoelectric coefficients due to misfit-strain-induced phase transitions are practically achievable only in an extremely narrow range of film thickness, composition and misfit strain parameter space. We also show that the dielectric and piezoelectric properties of epitaxial ferroelectric films can be tailored through strain engineering and microstructural optimization. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006661

Expansion of interatomic distances in platinum catalyst nanoparticles / K. Du in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 836–845 Titre : Expansion of interatomic distances in platinum catalyst nanoparticles Type de document : texte imprimé Auteurs : K. Du, Auteur ; F. Ernst, Auteur ; M. C. Pelsozy, Auteur Année de publication : 2011 Article en page(s) : pp. 836–845 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoparticles  Catalysts  Atomistic  structure  Quantitative  high-resolution  transmission  electron  microscopy  Spherical-aberration-adjusted  transmission  electron  microscopy Résumé : We study the atomistic structure of Pt catalyst nanoparticles using HRTEM (high-resolution transmission electron microscopy). The particles exhibit a faceted, cubo-octahedral shape, extended planar defects, and mono-atomic surface steps. HRTEM imaging with negative spherical aberration yielded atomic-resolution images with a minimum of artifacts. Combining digital image processing, quantitative image analysis, and HRTEM image simulations to determine local variations of the spacing between neighboring Pt atom columns, we have found an expansion of the lattice parameter in the particle core and even larger, locally varying expansion of Pt–Pt next-neighbor distances at the particle surface. The latter likely originates from an amorphous oxide on the nanoparticle surface and/or dissolution of oxygen on subsurface sites. These structural features may significantly impact the catalytic activity of Pt nanoparticles. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006673 [article] Expansion of interatomic distances in platinum catalyst nanoparticles [texte imprimé] / K. Du, Auteur ; F. Ernst, Auteur ; M. C. Pelsozy, Auteur . - 2011 . - pp. 836–845. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 836–845 Mots-clés : Nanoparticles  Catalysts  Atomistic  structure  Quantitative  high-resolution  transmission  electron  microscopy  Spherical-aberration-adjusted  transmission  electron  microscopy Résumé : We study the atomistic structure of Pt catalyst nanoparticles using HRTEM (high-resolution transmission electron microscopy). The particles exhibit a faceted, cubo-octahedral shape, extended planar defects, and mono-atomic surface steps. HRTEM imaging with negative spherical aberration yielded atomic-resolution images with a minimum of artifacts. Combining digital image processing, quantitative image analysis, and HRTEM image simulations to determine local variations of the spacing between neighboring Pt atom columns, we have found an expansion of the lattice parameter in the particle core and even larger, locally varying expansion of Pt–Pt next-neighbor distances at the particle surface. The latter likely originates from an amorphous oxide on the nanoparticle surface and/or dissolution of oxygen on subsurface sites. These structural features may significantly impact the catalytic activity of Pt nanoparticles. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006673

Plastic deformation of single crystals of Ti5Si3 with the hexagonal D88 structure / Kyosuke Kishida in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 846–857 Titre : Plastic deformation of single crystals of Ti5Si3 with the hexagonal D88 structure Type de document : texte imprimé Auteurs : Kyosuke Kishida, Auteur ; Masakazu Fujiwara, Auteur ; Hiroki Adachi, Auteur Année de publication : 2011 Article en page(s) : pp. 846–857 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Transition-metal  silicides  Deformation  behavior  Dislocation  structures  Twinning  Mechanical  properties Résumé : The deformation behavior of Ti5Si3 single crystals with the hexagonal D88 structure has been investigated in compression as a function of crystal orientation in a temperature range from 1200 to 1500 °C. Three different types of deformation modes – {View the MathML source}[0 0 0 1] prismatic slip, {View the MathML source}1/3〈View the MathML source〉 pyramidal slip and {View the MathML source}〈View the MathML source〉 twinning – were identified for the first time as being operative in Ti5Si3 at temperatures above 1300 °C, depending on the loading axis orientation. The critical resolved shear stresses (CRSSs) decrease steeply with increasing temperature for all deformation modes. The values of the CRSSs for {View the MathML source}[0 0 0 1] prismatic slip are considerably lower than those for {View the MathML source}1/3〈View the MathML source〉 pyramidal slip, but are comparable to those for {View the MathML source}〈View the MathML source〉 twinning. The favored deformation modes are discussed on the basis of anisotropic elasticity theory of dislocations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006685 [article] Plastic deformation of single crystals of Ti5Si3 with the hexagonal D88 structure [texte imprimé] / Kyosuke Kishida, Auteur ; Masakazu Fujiwara, Auteur ; Hiroki Adachi, Auteur . - 2011 . - pp. 846–857. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 846–857 Mots-clés : Transition-metal  silicides  Deformation  behavior  Dislocation  structures  Twinning  Mechanical  properties Résumé : The deformation behavior of Ti5Si3 single crystals with the hexagonal D88 structure has been investigated in compression as a function of crystal orientation in a temperature range from 1200 to 1500 °C. Three different types of deformation modes – {View the MathML source}[0 0 0 1] prismatic slip, {View the MathML source}1/3〈View the MathML source〉 pyramidal slip and {View the MathML source}〈View the MathML source〉 twinning – were identified for the first time as being operative in Ti5Si3 at temperatures above 1300 °C, depending on the loading axis orientation. The critical resolved shear stresses (CRSSs) decrease steeply with increasing temperature for all deformation modes. The values of the CRSSs for {View the MathML source}[0 0 0 1] prismatic slip are considerably lower than those for {View the MathML source}1/3〈View the MathML source〉 pyramidal slip, but are comparable to those for {View the MathML source}〈View the MathML source〉 twinning. The favored deformation modes are discussed on the basis of anisotropic elasticity theory of dislocations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006685

Shape memory behaviour in auxetic foams / M. Bianchi in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 858–865 Titre : Shape memory behaviour in auxetic foams : Mechanical properties Type de document : texte imprimé Auteurs : M. Bianchi, Auteur ; F. Scarpa, Auteur ; C. W. Smith, Auteur Année de publication : 2011 Article en page(s) : pp. 858–865 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Foam  Poisson’s  ratio  Auxetic  Mechanical  properties  Shape  memory  polymers Résumé : Shape memory is the property of a material to remember its original shape despite subsequent plastic deformation. The exposure to specific temperature profiles induces a shape memory effect on auxetic (negative Poisson’s ratio) foam specimens, returning them to their initial dimensions. This behaviour is a one-way effect, and it is a property of the polyurethane (PU) constituent of the foam. The foam specimens were transformed from conventional Poisson’s ratio to auxetic, returned to conventional and once again to auxetic under multiple mechanical and thermal loading. At each stage the foams were mechanically characterized under cyclic tensile and compressive loading. The manufacturing route adopted for the auxetic PU specimens involved a multiaxial compression of the native foam, heating of the compressed specimens above the Tg of the foam polymer, and cooling under running water. Twenty specimens, divided equally between two varieties of PU-based foam, were fabricated. Two different compression ratios were used during auxetic conversion for both kinds of foam, and the same final temperature of 135 °C was adopted. Tensile and compressive cyclic tests were performed in order to measure the tangent modulus (i.e. stiffness), Poisson’s ratios and energy dissipated per unit volume. Remarkable differences before and after the memory effect took place were found, showing mechanical behaviour unique to each of these phases. The shape memory effect plays an important role in the mechanical behaviour of the auxetic foams. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006697 [article] Shape memory behaviour in auxetic foams : Mechanical properties [texte imprimé] / M. Bianchi, Auteur ; F. Scarpa, Auteur ; C. W. Smith, Auteur . - 2011 . - pp. 858–865. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 858–865 Mots-clés : Foam  Poisson’s  ratio  Auxetic  Mechanical  properties  Shape  memory  polymers Résumé : Shape memory is the property of a material to remember its original shape despite subsequent plastic deformation. The exposure to specific temperature profiles induces a shape memory effect on auxetic (negative Poisson’s ratio) foam specimens, returning them to their initial dimensions. This behaviour is a one-way effect, and it is a property of the polyurethane (PU) constituent of the foam. The foam specimens were transformed from conventional Poisson’s ratio to auxetic, returned to conventional and once again to auxetic under multiple mechanical and thermal loading. At each stage the foams were mechanically characterized under cyclic tensile and compressive loading. The manufacturing route adopted for the auxetic PU specimens involved a multiaxial compression of the native foam, heating of the compressed specimens above the Tg of the foam polymer, and cooling under running water. Twenty specimens, divided equally between two varieties of PU-based foam, were fabricated. Two different compression ratios were used during auxetic conversion for both kinds of foam, and the same final temperature of 135 °C was adopted. Tensile and compressive cyclic tests were performed in order to measure the tangent modulus (i.e. stiffness), Poisson’s ratios and energy dissipated per unit volume. Remarkable differences before and after the memory effect took place were found, showing mechanical behaviour unique to each of these phases. The shape memory effect plays an important role in the mechanical behaviour of the auxetic foams. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006697

Self-assembled 3-D flower-shaped SnO2 nanostructures with improved electrochemical performance for lithium storage / Rong Yang in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 866–874 Titre : Self-assembled 3-D flower-shaped SnO2 nanostructures with improved electrochemical performance for lithium storage Type de document : texte imprimé Auteurs : Rong Yang, Auteur ; Yingan Gu, Auteur ; Yaoqi Li, Auteur Année de publication : 2011 Article en page(s) : pp. 866–874 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : SnO2  Crystal  growth  Nanostructure  Electrochemistry Résumé : Flower-shaped SnO2 nanoplates were successfully synthesized via a simple hydrothermal treatment of a mixture of tin(II) dichloride dihydrate (SnCl2·2H2O) and sodium citrate (Na3C6H5O7·2H2O) in alkali solution. The obtained SnO2 nanoplates were less than 5 nm thick and self-assembled into flower-shaped nanostructures. The introduction of citrate was essential for the preparation of the SnO2 nanoplates. The nanoscale shape and self-assembled architecture of SnO2 nanoparticles were mainly controlled by the alkalinity of the solution. When the self-assembled SnO2 nanostructures were used as anode materials in Li-ion batteries, they exhibit a reversible capacity of 670 mA h g−1 after 30 cycles and an average capacity fading of 0.95% per cycle after the second cycle. The good electrochemical performance of the SnO2 sample prepared via the hydrothermal synthesis indicates the possibility of fabricating specific self-assembled three-dimensional nanostructures for Li-ion batteries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006806 [article] Self-assembled 3-D flower-shaped SnO2 nanostructures with improved electrochemical performance for lithium storage [texte imprimé] / Rong Yang, Auteur ; Yingan Gu, Auteur ; Yaoqi Li, Auteur . - 2011 . - pp. 866–874. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 866–874 Mots-clés : SnO2  Crystal  growth  Nanostructure  Electrochemistry Résumé : Flower-shaped SnO2 nanoplates were successfully synthesized via a simple hydrothermal treatment of a mixture of tin(II) dichloride dihydrate (SnCl2·2H2O) and sodium citrate (Na3C6H5O7·2H2O) in alkali solution. The obtained SnO2 nanoplates were less than 5 nm thick and self-assembled into flower-shaped nanostructures. The introduction of citrate was essential for the preparation of the SnO2 nanoplates. The nanoscale shape and self-assembled architecture of SnO2 nanoparticles were mainly controlled by the alkalinity of the solution. When the self-assembled SnO2 nanostructures were used as anode materials in Li-ion batteries, they exhibit a reversible capacity of 670 mA h g−1 after 30 cycles and an average capacity fading of 0.95% per cycle after the second cycle. The good electrochemical performance of the SnO2 sample prepared via the hydrothermal synthesis indicates the possibility of fabricating specific self-assembled three-dimensional nanostructures for Li-ion batteries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006806

A ternary phase-field model incorporating commercial CALPHAD software and its application to precipitation in superalloys / Y. H. Wen in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 875–885 Titre : A ternary phase-field model incorporating commercial CALPHAD software and its application to precipitation in superalloys Type de document : texte imprimé Auteurs : Y. H. Wen, Auteur ; J. V. Lill, Auteur ; S. L. Chen, Auteur Année de publication : 2011 Article en page(s) : pp. 875–885 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ni–Al–Cr  alloys  Ternary  phase-field  models  Precipitation  Commercial  CALPHAD  software  Uphill  diffusion Résumé : A ternary phase-field model was developed that is linked directly to commercial CALPHAD software to provide quantitative thermodynamic driving forces. A recently available diffusion mobility database for ordered phases is also implemented to give a better description of the diffusion behavior in alloys. Because the targeted application of this model is the study of precipitation in Ni-based superalloys, a Ni–Al–Cr model alloy was constructed. A detailed description of this model is given in the paper. We have considered the misfit effects of the partitioning of the two solute elements. Transformation rules of the dual representation of the γ+γ′ microstructure by CALPHAD and by the phase field are established and the link with commercial CALPHAD software is described. Proof-of-concept tests were performed to evaluate the model and the results demonstrate that the model can qualitatively reproduce observed γ′ precipitation behavior. Uphill diffusion of Al is observed in a few diffusion couples, showing the significant influence of Cr on the chemical potential of Al. Possible applications of this model are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006818 [article] A ternary phase-field model incorporating commercial CALPHAD software and its application to precipitation in superalloys [texte imprimé] / Y. H. Wen, Auteur ; J. V. Lill, Auteur ; S. L. Chen, Auteur . - 2011 . - pp. 875–885. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 875–885 Mots-clés : Ni–Al–Cr  alloys  Ternary  phase-field  models  Precipitation  Commercial  CALPHAD  software  Uphill  diffusion Résumé : A ternary phase-field model was developed that is linked directly to commercial CALPHAD software to provide quantitative thermodynamic driving forces. A recently available diffusion mobility database for ordered phases is also implemented to give a better description of the diffusion behavior in alloys. Because the targeted application of this model is the study of precipitation in Ni-based superalloys, a Ni–Al–Cr model alloy was constructed. A detailed description of this model is given in the paper. We have considered the misfit effects of the partitioning of the two solute elements. Transformation rules of the dual representation of the γ+γ′ microstructure by CALPHAD and by the phase field are established and the link with commercial CALPHAD software is described. Proof-of-concept tests were performed to evaluate the model and the results demonstrate that the model can qualitatively reproduce observed γ′ precipitation behavior. Uphill diffusion of Al is observed in a few diffusion couples, showing the significant influence of Cr on the chemical potential of Al. Possible applications of this model are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006818

Reversible–irreversible plasticity transition in twinned copper nanopillars / J. A. Brown in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 886–894 Titre : Reversible–irreversible plasticity transition in twinned copper nanopillars Type de document : texte imprimé Auteurs : J. A. Brown, Auteur ; N. M. Ghoniem, Auteur Année de publication : 2011 Article en page(s) : pp. 886–894 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Copper  MD  simulations  Twin  boundary  Nanopillars  Plasticity Résumé : Through computer simulations, we show that plasticity in twinned copper nanopillars can be either reversible or irreversible depending on the applied stress state. Copper nanopillars, containing twinned crystals, are subjected to both compression and tension, and the ratio of the resolved shear (σR) to the normal stress (σN), R, is adjusted through variation of the orientation of the twin boundary plane with respect to the loading axis. It is found that the yield locus on the σR–σN plane for twinned nanopillars is asymmetric with respect to the sign of R. For a 9 nm diameter copper nanopillar under compression, plastic deformation can be totally reversed when σR is in the range View the MathML source, with a corresponding increase in the compressive normal stress, up to ≈2.5 GPa. It is shown that these conditions are achieved for axial strains <3.3%, and that the transition to plastic irreversibility takes place at larger strains or normal stresses. The mechanism responsible for the plastic reversible–irreversible transition is shown to be a competition between the nucleation of Shockley partial dislocations at the nanopillar surface for irreversible plasticity vs. twinning dislocations for reversible plasticity. Furthermore, the speed of Shockley partials at twin boundaries is subsonic when there is either tension or compression acting on the twin boundary, and slightly supersonic when only shear is applied. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900682X [article] Reversible–irreversible plasticity transition in twinned copper nanopillars [texte imprimé] / J. A. Brown, Auteur ; N. M. Ghoniem, Auteur . - 2011 . - pp. 886–894. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 886–894 Mots-clés : Copper  MD  simulations  Twin  boundary  Nanopillars  Plasticity Résumé : Through computer simulations, we show that plasticity in twinned copper nanopillars can be either reversible or irreversible depending on the applied stress state. Copper nanopillars, containing twinned crystals, are subjected to both compression and tension, and the ratio of the resolved shear (σR) to the normal stress (σN), R, is adjusted through variation of the orientation of the twin boundary plane with respect to the loading axis. It is found that the yield locus on the σR–σN plane for twinned nanopillars is asymmetric with respect to the sign of R. For a 9 nm diameter copper nanopillar under compression, plastic deformation can be totally reversed when σR is in the range View the MathML source, with a corresponding increase in the compressive normal stress, up to ≈2.5 GPa. It is shown that these conditions are achieved for axial strains <3.3%, and that the transition to plastic irreversibility takes place at larger strains or normal stresses. The mechanism responsible for the plastic reversible–irreversible transition is shown to be a competition between the nucleation of Shockley partial dislocations at the nanopillar surface for irreversible plasticity vs. twinning dislocations for reversible plasticity. Furthermore, the speed of Shockley partials at twin boundaries is subsonic when there is either tension or compression acting on the twin boundary, and slightly supersonic when only shear is applied. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900682X

Deformation-induced martensitic transformation behavior in cold-rolled and cold-drawn type 316 stainless steels / Nobuo Nakada in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 895–903 Titre : Deformation-induced martensitic transformation behavior in cold-rolled and cold-drawn type 316 stainless steels Type de document : texte imprimé Auteurs : Nobuo Nakada, Auteur ; Hidetoshi Ito, Auteur ; Yoshikazu Matsuoka, Auteur Année de publication : 2011 Article en page(s) : pp. 895–903 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Austenitic  stainless  steel  Deformation-induced  martensite  Deformation  twin  Variant  restriction Résumé : We investigate deformation-induced martensitic transformation behavior in cold-rolled and cold-drawn specimens of type 316 stainless steel. Deformation-induced martensite preferentially nucleates at the twin boundary between the austenite matrix and a deformation twin. In the cold-rolled specimen, martensite formed at the twin boundary has a Kurdjumov–Sachs (K–S) relationship with both the austenite matrix and the deformation twin (“double K–S relationship”). In the cold-drawn specimen, two kinds of deformation twins with different twin planes are typically formed, and therefore deformation-induced martensites are formed where the deformation twin boundaries intersect: martensite thus has an imperfect “triple K–S relationship” with the austenite matrix and the two deformation twins. The complicated crystallographic orientation relationship between austenite and martensite grains strongly restricts the formation of some variants of deformation-induced martensites. Because of the difference in number of nucleation sites in the cold-drawn and cold-rolled specimens, martensitic transformation is more enhanced in the former than in the latter. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006831 [article] Deformation-induced martensitic transformation behavior in cold-rolled and cold-drawn type 316 stainless steels [texte imprimé] / Nobuo Nakada, Auteur ; Hidetoshi Ito, Auteur ; Yoshikazu Matsuoka, Auteur . - 2011 . - pp. 895–903. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 895–903 Mots-clés : Austenitic  stainless  steel  Deformation-induced  martensite  Deformation  twin  Variant  restriction Résumé : We investigate deformation-induced martensitic transformation behavior in cold-rolled and cold-drawn specimens of type 316 stainless steel. Deformation-induced martensite preferentially nucleates at the twin boundary between the austenite matrix and a deformation twin. In the cold-rolled specimen, martensite formed at the twin boundary has a Kurdjumov–Sachs (K–S) relationship with both the austenite matrix and the deformation twin (“double K–S relationship”). In the cold-drawn specimen, two kinds of deformation twins with different twin planes are typically formed, and therefore deformation-induced martensites are formed where the deformation twin boundaries intersect: martensite thus has an imperfect “triple K–S relationship” with the austenite matrix and the two deformation twins. The complicated crystallographic orientation relationship between austenite and martensite grains strongly restricts the formation of some variants of deformation-induced martensites. Because of the difference in number of nucleation sites in the cold-drawn and cold-rolled specimens, martensitic transformation is more enhanced in the former than in the latter. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006831

Stable flowing of localized shear bands in soft bulk metallic glasses / Q. S. Zhang in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 904–909 Titre : Stable flowing of localized shear bands in soft bulk metallic glasses Type de document : texte imprimé Auteurs : Q. S. Zhang, Auteur ; W. Zhang, Auteur ; G. Q. Xie, Auteur Année de publication : 2011 Article en page(s) : pp. 904–909 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metallic  glasses  Hardness  test  Compression  test  Plastic  deformation Résumé : This paper reports a novel class of Zr–Cu–Fe–Al bulk metallic glasses (BMGs) with high Zr content and unusual deformation behavior. Higher content of Zr results in lower hardness, but favors the generation of highly localized shear bands, even if nanocrystalline phases precipitate in the glassy matrix. Moreover, flow of the dominant shear band proceeds slowly under compressive stress without rapid shear rupture and facture. The unusual deformation behavior suggests that designing BMG with a high content of solvent element and low hardness might be a promising new way of developing ductile BMG. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006843 [article] Stable flowing of localized shear bands in soft bulk metallic glasses [texte imprimé] / Q. S. Zhang, Auteur ; W. Zhang, Auteur ; G. Q. Xie, Auteur . - 2011 . - pp. 904–909. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 904–909 Mots-clés : Metallic  glasses  Hardness  test  Compression  test  Plastic  deformation Résumé : This paper reports a novel class of Zr–Cu–Fe–Al bulk metallic glasses (BMGs) with high Zr content and unusual deformation behavior. Higher content of Zr results in lower hardness, but favors the generation of highly localized shear bands, even if nanocrystalline phases precipitate in the glassy matrix. Moreover, flow of the dominant shear band proceeds slowly under compressive stress without rapid shear rupture and facture. The unusual deformation behavior suggests that designing BMG with a high content of solvent element and low hardness might be a promising new way of developing ductile BMG. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006843

Development and characterization of cube-textured Ni–Cu–Co substrates for YBCO-coated conductors / A. Vannozzi in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 910–918 Titre : Development and characterization of cube-textured Ni–Cu–Co substrates for YBCO-coated conductors Type de document : texte imprimé Auteurs : A. Vannozzi, Auteur ; Gy Thalmaier, Auteur ; A. Angrisani Armenio, Auteur Année de publication : 2011 Article en page(s) : pp. 910–918 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel–copper  alloys  Thermomechanical  processing  Recrystallization  texture  Electron  backscattering  diffraction  Ceramic  superconductors Résumé : Ni–Cu–Co alloys were studied for the development of textured substrates for YBCO-coated conductor application. Three compositions were obtained by adding a fixed amount of 3 at.% Co to the binary NixCu100−x, where x = 40, 50 and 60. Cube texture was induced by conventional cold rolling followed by high-temperature annealing. The structural, microstructural, morphological, electrical, magnetic, mechanical and oxidation properties were evaluated and compared with those exhibited by the binary Ni–Cu alloy, as well as by Ni–W and pure Ni. A low Ni content is detrimental for the development of the cube texture with respect to higher concentrations. Nevertheless, the use of high annealing temperatures enabled an area fraction of cube orientation as high as 95% to be obtained for x = 40, and >97.5% in the case of Ni-richer alloys. Compared with Ni and Ni–W, Ni–Cu–Co alloys oxidize more easily and exhibit higher electrical resistance. In addition, the presence of copper enables the Curie temperature to be reduced to 60 K for x = 40 and to 155 K for x = 50. Furthermore, the introduction of cobalt reduces the oxidation rate at temperatures normally used for the deposition of ceramic buffer layers, thus allowing the successful development of a CeO2/YSZ/CeO2 architecture on ternary Ni–Cu–Co alloy. YBCO/buffer multilayer architecture deposited by pulsed laser deposition on a selected alloy tape exhibits a critical current density exceeding 1 MA cm−2 at 77 K in self-field, indicating that this alloy substrate is suitable for YBCO-coated conductor application. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006855 [article] Development and characterization of cube-textured Ni–Cu–Co substrates for YBCO-coated conductors [texte imprimé] / A. Vannozzi, Auteur ; Gy Thalmaier, Auteur ; A. Angrisani Armenio, Auteur . - 2011 . - pp. 910–918. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 910–918 Mots-clés : Nickel–copper  alloys  Thermomechanical  processing  Recrystallization  texture  Electron  backscattering  diffraction  Ceramic  superconductors Résumé : Ni–Cu–Co alloys were studied for the development of textured substrates for YBCO-coated conductor application. Three compositions were obtained by adding a fixed amount of 3 at.% Co to the binary NixCu100−x, where x = 40, 50 and 60. Cube texture was induced by conventional cold rolling followed by high-temperature annealing. The structural, microstructural, morphological, electrical, magnetic, mechanical and oxidation properties were evaluated and compared with those exhibited by the binary Ni–Cu alloy, as well as by Ni–W and pure Ni. A low Ni content is detrimental for the development of the cube texture with respect to higher concentrations. Nevertheless, the use of high annealing temperatures enabled an area fraction of cube orientation as high as 95% to be obtained for x = 40, and >97.5% in the case of Ni-richer alloys. Compared with Ni and Ni–W, Ni–Cu–Co alloys oxidize more easily and exhibit higher electrical resistance. In addition, the presence of copper enables the Curie temperature to be reduced to 60 K for x = 40 and to 155 K for x = 50. Furthermore, the introduction of cobalt reduces the oxidation rate at temperatures normally used for the deposition of ceramic buffer layers, thus allowing the successful development of a CeO2/YSZ/CeO2 architecture on ternary Ni–Cu–Co alloy. YBCO/buffer multilayer architecture deposited by pulsed laser deposition on a selected alloy tape exhibits a critical current density exceeding 1 MA cm−2 at 77 K in self-field, indicating that this alloy substrate is suitable for YBCO-coated conductor application. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006855

Microstructural evolution in a two-phase alloy processed by high-pressure torsion / Megumi Kawasaki in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 919–930 Titre : Microstructural evolution in a two-phase alloy processed by high-pressure torsion Type de document : texte imprimé Auteurs : Megumi Kawasaki, Auteur ; Byungmin Ahn, Auteur ; Terence G. Langdon, Auteur Année de publication : 2011 Article en page(s) : pp. 919–930 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hardness  High-pressure  torsion  Homogeneity  Severe  plastic  deformation  Zinc–aluminum  alloys Résumé : Experiments were conducted to evaluate the microstructural evolution occurring in the Zn–22% Al eutectoid alloy when processed by high-pressure torsion (HPT) over a range of experimental conditions. Processing by HPT reduces the grain size and at the edges of the disks it produces agglomerates of Zn-rich and Al-rich grains lying in bands delineating the torsional straining. Unlike most metals processed by HPT, the measured hardness values are lower than in the initial annealed condition. This is due to a significant reduction during processing in the distribution of Zn precipitates which are visible within the Al-rich grains in the annealed condition. It is shown that all of the hardness measurements are mutually consistent when plotted against the calculated equivalent strain. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006867 [article] Microstructural evolution in a two-phase alloy processed by high-pressure torsion [texte imprimé] / Megumi Kawasaki, Auteur ; Byungmin Ahn, Auteur ; Terence G. Langdon, Auteur . - 2011 . - pp. 919–930. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 919–930 Mots-clés : Hardness  High-pressure  torsion  Homogeneity  Severe  plastic  deformation  Zinc–aluminum  alloys Résumé : Experiments were conducted to evaluate the microstructural evolution occurring in the Zn–22% Al eutectoid alloy when processed by high-pressure torsion (HPT) over a range of experimental conditions. Processing by HPT reduces the grain size and at the edges of the disks it produces agglomerates of Zn-rich and Al-rich grains lying in bands delineating the torsional straining. Unlike most metals processed by HPT, the measured hardness values are lower than in the initial annealed condition. This is due to a significant reduction during processing in the distribution of Zn precipitates which are visible within the Al-rich grains in the annealed condition. It is shown that all of the hardness measurements are mutually consistent when plotted against the calculated equivalent strain. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006867

Atom probe tomography analysis of the distribution of rhenium in nickel alloys / A. Mottura in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 931–942 Titre : Atom probe tomography analysis of the distribution of rhenium in nickel alloys Type de document : texte imprimé Auteurs : A. Mottura, Auteur ; N. Warnken, Auteur ; M. K. Miller, Auteur Année de publication : 2011 Article en page(s) : pp. 931–942 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel  alloys  Atom  probe  tomography  Rhenium-effect Résumé : Atom probe tomography (APT) is used to characterise the distributions of rhenium in a binary Ni–Re alloy and the nickel-based single-crystal CMSX-4 superalloy. A purpose-built algorithm is developed to quantify the size distribution of solute clusters, and applied to the APT datasets to critique the hypothesis that rhenium is prone to the formation of clusters in these systems. No evidence is found to indicate that rhenium forms solute clusters above the level expected from random fluctuations. In CMSX-4, enrichment of Re is detected in the matrix phase close to the matrix/precipitate (γ/γ′) phase boundaries. Phase field modelling indicates that this is due to the migration of the γ/γ′ interface during cooling from the temperature of operation. Thus, neither clustering of rhenium nor interface enrichments can be the cause of the enhancement in high temperature mechanical properties conferred by rhenium alloying. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006879 [article] Atom probe tomography analysis of the distribution of rhenium in nickel alloys [texte imprimé] / A. Mottura, Auteur ; N. Warnken, Auteur ; M. K. Miller, Auteur . - 2011 . - pp. 931–942. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 931–942 Mots-clés : Nickel  alloys  Atom  probe  tomography  Rhenium-effect Résumé : Atom probe tomography (APT) is used to characterise the distributions of rhenium in a binary Ni–Re alloy and the nickel-based single-crystal CMSX-4 superalloy. A purpose-built algorithm is developed to quantify the size distribution of solute clusters, and applied to the APT datasets to critique the hypothesis that rhenium is prone to the formation of clusters in these systems. No evidence is found to indicate that rhenium forms solute clusters above the level expected from random fluctuations. In CMSX-4, enrichment of Re is detected in the matrix phase close to the matrix/precipitate (γ/γ′) phase boundaries. Phase field modelling indicates that this is due to the migration of the γ/γ′ interface during cooling from the temperature of operation. Thus, neither clustering of rhenium nor interface enrichments can be the cause of the enhancement in high temperature mechanical properties conferred by rhenium alloying. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006879

Through-thickness determination of phase composition and residual stresses in thermal barrier coatings using high-energy X-rays / C.M. Weyant in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 943–951 Titre : Through-thickness determination of phase composition and residual stresses in thermal barrier coatings using high-energy X-rays Type de document : texte imprimé Auteurs : C.M. Weyant, Auteur ; J. Almer, Auteur ; K. T. Faber, Auteur Année de publication : 2011 Article en page(s) : pp. 943–951 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Plasma  spraying  X-ray  diffraction  Crystalline  oxides  Coatings  Residual  stresses Résumé : High-energy X-rays were used to determine the local phase composition and residual stresses through the thickness of as-sprayed and heat-treated plasma-sprayed thermal barrier coatings consisting of a NiCoCrAlY bond coat and an yttria-stabilized zirconia (YSZ) topcoat produced with through-thickness segmentation cracks. The as-sprayed residual stresses reflected the combined influence of quenching stresses from the plasma spray process, thermal expansion mismatch between the topcoat, bond coat and substrate, and stress relief from the segmentation cracks. Heat treatments led to the formation of a thermally grown oxide (TGO) which was in compression in the plane, as well as relief of quenching stresses and development of a stress gradient in the YSZ topcoat. The high-energy X-ray technique used in this study revealed the effects that TGO and segmentation cracks have on the in-plane stress state of the entire coating. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006892 [article] Through-thickness determination of phase composition and residual stresses in thermal barrier coatings using high-energy X-rays [texte imprimé] / C.M. Weyant, Auteur ; J. Almer, Auteur ; K. T. Faber, Auteur . - 2011 . - pp. 943–951. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 943–951 Mots-clés : Plasma  spraying  X-ray  diffraction  Crystalline  oxides  Coatings  Residual  stresses Résumé : High-energy X-rays were used to determine the local phase composition and residual stresses through the thickness of as-sprayed and heat-treated plasma-sprayed thermal barrier coatings consisting of a NiCoCrAlY bond coat and an yttria-stabilized zirconia (YSZ) topcoat produced with through-thickness segmentation cracks. The as-sprayed residual stresses reflected the combined influence of quenching stresses from the plasma spray process, thermal expansion mismatch between the topcoat, bond coat and substrate, and stress relief from the segmentation cracks. Heat treatments led to the formation of a thermally grown oxide (TGO) which was in compression in the plane, as well as relief of quenching stresses and development of a stress gradient in the YSZ topcoat. The high-energy X-ray technique used in this study revealed the effects that TGO and segmentation cracks have on the in-plane stress state of the entire coating. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006892

Oxidation and crystallization mechanisms in plasma-sprayed Cu-based bulk metallic glass coatings / Junghwan Kim in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 952–962 Titre : Oxidation and crystallization mechanisms in plasma-sprayed Cu-based bulk metallic glass coatings Type de document : texte imprimé Auteurs : Junghwan Kim, Auteur ; Kicheol Kang, Auteur ; Sanghoon Yoon, Auteur Année de publication : 2011 Article en page(s) : pp. 952–962 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bulk  metallic  glass  Atmospheric  plasma  spraying  Oxidation  Crystallization Résumé : Cu-based bulk metallic glass (BMG) coatings were built-up by the atmospheric plasma spraying (APS) process at different hydrogen flow rates. As the hydrogen flow rate increased, thermal energy in the plasma jet increased the melting state of the Cu-based BMG particles. Although it was expected that the difference in melting states would quantitatively affect the amorphous fractions in the coatings, both the amorphous fraction and the oxide content of the layers were independent of hydrogen flow rate. However, different melting states resulting from different hydrogen gas flow rates, and the subsequent oxidation which inevitably occurred during spraying, generated different crystallization processes in the coating. In this paper, crystallization mechanisms in plasma-sprayed BMG were studied using their microstructures. Specific analyses of the particles deposited at high travel speed and quenched in cold water also served for further understanding of the melting state and change in composition of the particles undergo during deposition. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006909 [article] Oxidation and crystallization mechanisms in plasma-sprayed Cu-based bulk metallic glass coatings [texte imprimé] / Junghwan Kim, Auteur ; Kicheol Kang, Auteur ; Sanghoon Yoon, Auteur . - 2011 . - pp. 952–962. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 952–962 Mots-clés : Bulk  metallic  glass  Atmospheric  plasma  spraying  Oxidation  Crystallization Résumé : Cu-based bulk metallic glass (BMG) coatings were built-up by the atmospheric plasma spraying (APS) process at different hydrogen flow rates. As the hydrogen flow rate increased, thermal energy in the plasma jet increased the melting state of the Cu-based BMG particles. Although it was expected that the difference in melting states would quantitatively affect the amorphous fractions in the coatings, both the amorphous fraction and the oxide content of the layers were independent of hydrogen flow rate. However, different melting states resulting from different hydrogen gas flow rates, and the subsequent oxidation which inevitably occurred during spraying, generated different crystallization processes in the coating. In this paper, crystallization mechanisms in plasma-sprayed BMG were studied using their microstructures. Specific analyses of the particles deposited at high travel speed and quenched in cold water also served for further understanding of the melting state and change in composition of the particles undergo during deposition. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006909

Role of lattice strain on thermal stability of a nanocrystalline FeMo alloy / A. Molinari in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 963–966 Titre : Role of lattice strain on thermal stability of a nanocrystalline FeMo alloy Type de document : texte imprimé Auteurs : A. Molinari, Auteur ; S. Libardi, Auteur ; M. Leoni, Auteur Année de publication : 2011 Article en page(s) : pp. 963–966 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Mechanical  milling  X-ray  diffraction  Nanocrystalline  materials  Iron  alloy  Grain  growth Résumé : The thermal stability of a nanocrystalline Fe–1.5 wt.% Mo powder milled with nano-SiO2 was investigated in situ by synchrotron radiation X-ray diffraction. Crystallite size is stabilized by the grain-boundary strain, therefore grain growth starts only after a certain amount of this strain has been released. The phenomenon was rationalized by a micromechanics approach, which considers the equilibrium between forces acting on the grain boundary surface. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006910 [article] Role of lattice strain on thermal stability of a nanocrystalline FeMo alloy [texte imprimé] / A. Molinari, Auteur ; S. Libardi, Auteur ; M. Leoni, Auteur . - 2011 . - pp. 963–966. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 963–966 Mots-clés : Mechanical  milling  X-ray  diffraction  Nanocrystalline  materials  Iron  alloy  Grain  growth Résumé : The thermal stability of a nanocrystalline Fe–1.5 wt.% Mo powder milled with nano-SiO2 was investigated in situ by synchrotron radiation X-ray diffraction. Crystallite size is stabilized by the grain-boundary strain, therefore grain growth starts only after a certain amount of this strain has been released. The phenomenon was rationalized by a micromechanics approach, which considers the equilibrium between forces acting on the grain boundary surface. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006910

Mechanical behaviour and in situ observation of shear bands in ultrafine grained Pd and Pd–Ag alloys / A. Caron in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 967–978 Titre : Mechanical behaviour and in situ observation of shear bands in ultrafine grained Pd and Pd–Ag alloys Type de document : texte imprimé Auteurs : A. Caron, Auteur Année de publication : 2011 Article en page(s) : pp. 967–978 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : In  situ  tensile  test  Grey  scale  correlation  analysis  Ultrafine  grained  materials  High-pressure  torsion Résumé : An in situ tensile test with grey scale correlation has been performed to study the deformation process in ultrafine grained (UFG) Pd and Pd–x at.% Ag (x = 5 or 20) alloys produced by high-pressure torsion. Shear band nucleation and propagation was found to be an important deformation mechanism after strain localization during the tensile test. The underlying microscopic mechanism is related to cooperative grain boundary sliding. Moreover, the additional influence of stacking fault energy was found to change the nature of the deformation mechanism from localized strain in Pd to more homogeneous deformation in Pd–20% Ag. In situ analysis and the findings are new and give innovative insight into the basics of deformation in UFG face-centred cubic metals. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006922 [article] Mechanical behaviour and in situ observation of shear bands in ultrafine grained Pd and Pd–Ag alloys [texte imprimé] / A. Caron, Auteur . - 2011 . - pp. 967–978. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 967–978 Mots-clés : In  situ  tensile  test  Grey  scale  correlation  analysis  Ultrafine  grained  materials  High-pressure  torsion Résumé : An in situ tensile test with grey scale correlation has been performed to study the deformation process in ultrafine grained (UFG) Pd and Pd–x at.% Ag (x = 5 or 20) alloys produced by high-pressure torsion. Shear band nucleation and propagation was found to be an important deformation mechanism after strain localization during the tensile test. The underlying microscopic mechanism is related to cooperative grain boundary sliding. Moreover, the additional influence of stacking fault energy was found to change the nature of the deformation mechanism from localized strain in Pd to more homogeneous deformation in Pd–20% Ag. In situ analysis and the findings are new and give innovative insight into the basics of deformation in UFG face-centred cubic metals. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006922

Effect of addition of N on L10 transformation and atomic diffusion in FePt films / V. Phatak in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 979–988 Titre : Effect of addition of N on L10 transformation and atomic diffusion in FePt films Type de document : texte imprimé Auteurs : V. Phatak, Auteur ; A. Gupta, Auteur ; V. R. Reddy, Auteur Année de publication : 2011 Article en page(s) : pp. 979–988 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : L10  transformation  Self-diffusion  Nuclear  resonance  reflectivity  Secondary  ion  mass  spectrometry Résumé : The effect of nitrogen incorporation on the kinetics of L10 transformation in FePt alloy films was studied. Films with a maximum possible amount of nitrogen were prepared by sputtering a FePt compound target with pure nitrogen. As-prepared films consisting of nano-grains of Pt and Fe0.7N0.3 transformed to face-centered cubic FePt phase with a certain amount of nitrogen incorporated in the grains after annealing at 573 K. It was found that the presence of N results in faster kinetics of L10 transformation compared with pure FePt alloy films, as well as a substantial reduction in grain size. Detailed structural and diffusion measurements were carried out to elucidate the mechanism of enhanced transformation kinetics as well as grain size reduction. The activation energy for volume diffusion of Fe in FePtN films was found to be 0.27 ± 0.14 eV, while that in FePt was 0.50 ± 0.17 eV. Faster atomic diffusion in nitrogen-containing films was the cause of an enhanced rate of L10 transformation. Further studies reveal that, in partially transformed FePtN alloy films, N is incorporated mainly in the grain boundary region, which hinders grain growth and results in a smaller grain size. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006934 [article] Effect of addition of N on L10 transformation and atomic diffusion in FePt films [texte imprimé] / V. Phatak, Auteur ; A. Gupta, Auteur ; V. R. Reddy, Auteur . - 2011 . - pp. 979–988. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 979–988 Mots-clés : L10  transformation  Self-diffusion  Nuclear  resonance  reflectivity  Secondary  ion  mass  spectrometry Résumé : The effect of nitrogen incorporation on the kinetics of L10 transformation in FePt alloy films was studied. Films with a maximum possible amount of nitrogen were prepared by sputtering a FePt compound target with pure nitrogen. As-prepared films consisting of nano-grains of Pt and Fe0.7N0.3 transformed to face-centered cubic FePt phase with a certain amount of nitrogen incorporated in the grains after annealing at 573 K. It was found that the presence of N results in faster kinetics of L10 transformation compared with pure FePt alloy films, as well as a substantial reduction in grain size. Detailed structural and diffusion measurements were carried out to elucidate the mechanism of enhanced transformation kinetics as well as grain size reduction. The activation energy for volume diffusion of Fe in FePtN films was found to be 0.27 ± 0.14 eV, while that in FePt was 0.50 ± 0.17 eV. Faster atomic diffusion in nitrogen-containing films was the cause of an enhanced rate of L10 transformation. Further studies reveal that, in partially transformed FePtN alloy films, N is incorporated mainly in the grain boundary region, which hinders grain growth and results in a smaller grain size. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006934

Effect of friction stir processing on fatigue behavior of an investment cast Al–7Si–0.6 Mg alloy / S. Jana in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 989–1003 Titre : Effect of friction stir processing on fatigue behavior of an investment cast Al–7Si–0.6 Mg alloy Type de document : texte imprimé Auteurs : S. Jana, Auteur ; R. S. Mishra, Auteur ; J. B. Baumann, Auteur Année de publication : 2011 Article en page(s) : pp. 989–1003 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminum  alloys  Friction  stir  processing  Fatigue  Microstructure Résumé : Cast aluminum alloys in general show poor fatigue performance due to the presence of defects. Friction stir processing (FSP) can be used as a tool to enhance the mechanical properties of cast alloys by eliminating such defects. In the present study FSP led to a five times improvement in fatigue life of an investment cast Al–7Si–0.6 Mg hypoeutectic alloy. The reason for such an enhancement was linked to the closure of casting porosities, which acted as crack nucleation sites in the as cast condition. Porosities acted as notches in the as cast alloy and led to an order of magnitude higher crack growth rate. As FSP eliminated the porosities and refined the Si particles the crack growth rate dropped, due to elimination of the notch effect, together with increased crack path tortuosity. Finally, short crack behavior was noted in both the cast and FSP specimens. The critical crack length, where a transition from a short crack to a long crack behavior took place is related to the respective microstructural characteristic dimensions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006946 [article] Effect of friction stir processing on fatigue behavior of an investment cast Al–7Si–0.6 Mg alloy [texte imprimé] / S. Jana, Auteur ; R. S. Mishra, Auteur ; J. B. Baumann, Auteur . - 2011 . - pp. 989–1003. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 989–1003 Mots-clés : Aluminum  alloys  Friction  stir  processing  Fatigue  Microstructure Résumé : Cast aluminum alloys in general show poor fatigue performance due to the presence of defects. Friction stir processing (FSP) can be used as a tool to enhance the mechanical properties of cast alloys by eliminating such defects. In the present study FSP led to a five times improvement in fatigue life of an investment cast Al–7Si–0.6 Mg hypoeutectic alloy. The reason for such an enhancement was linked to the closure of casting porosities, which acted as crack nucleation sites in the as cast condition. Porosities acted as notches in the as cast alloy and led to an order of magnitude higher crack growth rate. As FSP eliminated the porosities and refined the Si particles the crack growth rate dropped, due to elimination of the notch effect, together with increased crack path tortuosity. Finally, short crack behavior was noted in both the cast and FSP specimens. The critical crack length, where a transition from a short crack to a long crack behavior took place is related to the respective microstructural characteristic dimensions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006946

Spinodal single-domain → polydomain transition and P–E hysteresis in thin ferroelectric films / A. Artemev in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1004–1015 Titre : Spinodal single-domain → polydomain transition and P–E hysteresis in thin ferroelectric films Type de document : texte imprimé Auteurs : A. Artemev, Auteur ; A. Roytburd, Auteur Année de publication : 2011 Article en page(s) : pp. 1004–1015 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ferroelectricity  Thin  films  Spinodal  decomposition  Phase  field  models Résumé : This study investigates the spinodal mechanism of domain formation and switching through the loss of stability of a single-domain (SD) state with respect to a polydomain (PD) state in thin ferroelectric films with dead layers. The macroscopic thermodynamic model of a homogenized domain structure (DS) is used to analyze the depolarizing field effect on the transitions between SD and PD states and the shape of the P(E) hysteresis loop. Phase field modeling is used to study the inhomogeneities and film thickness effects on DS and P(E) hysteresis. Such modeling of relatively thick films produces P(E) hysteresis loops of a shape similar to that predicted by the macroscopic model. The results of the analysis demonstrate that the SD → PD transition can proceed by the spinodal mechanism in thin films, while the nucleation and growth mechanism should operate in thick films. It is shown that columnar and stripe DS can be produced in thin films. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006958 [article] Spinodal single-domain → polydomain transition and P–E hysteresis in thin ferroelectric films [texte imprimé] / A. Artemev, Auteur ; A. Roytburd, Auteur . - 2011 . - pp. 1004–1015. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1004–1015 Mots-clés : Ferroelectricity  Thin  films  Spinodal  decomposition  Phase  field  models Résumé : This study investigates the spinodal mechanism of domain formation and switching through the loss of stability of a single-domain (SD) state with respect to a polydomain (PD) state in thin ferroelectric films with dead layers. The macroscopic thermodynamic model of a homogenized domain structure (DS) is used to analyze the depolarizing field effect on the transitions between SD and PD states and the shape of the P(E) hysteresis loop. Phase field modeling is used to study the inhomogeneities and film thickness effects on DS and P(E) hysteresis. Such modeling of relatively thick films produces P(E) hysteresis loops of a shape similar to that predicted by the macroscopic model. The results of the analysis demonstrate that the SD → PD transition can proceed by the spinodal mechanism in thin films, while the nucleation and growth mechanism should operate in thick films. It is shown that columnar and stripe DS can be produced in thin films. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006958

Au–Fe alloy solidification and solid-state transformations / D. Favez in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1016–1025 Titre : Au–Fe alloy solidification and solid-state transformations Type de document : texte imprimé Auteurs : D. Favez, Auteur ; J.-D. Wagnière, Auteur ; M. Rappaz, Auteur Année de publication : 2011 Article en page(s) : pp. 1016–1025 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Au–Fe  Differential  thermal  analysis  (DTA)  Peritectic  solidification  Discontinuous  precipitation  Coherency  relationship Résumé : In order to better understand the microstructure that forms during laser welding of an 18 carat gold and an austenitic stainless steel, solidification of the Au–Fe binary analog has been studied using thermal analysis and interrupted Bridgman experiments. For a hypoperitectic composition, the formation of the primary phase, its coarsening and the peculiar macrosegregation associated with the large density difference between the elements have been studied. Just after the peritectic phase forms around the primary dendrites, continuous and discontinuous precipitation has been shown to occur as a result of the immiscibility of the two face-centered cubic phases below the peritectic temperature. Finally, the solid-state transformations associated with the eutectoid have been characterized. DEWEY : 1359-6454 ISSN : 669 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900696X [article] Au–Fe alloy solidification and solid-state transformations [texte imprimé] / D. Favez, Auteur ; J.-D. Wagnière, Auteur ; M. Rappaz, Auteur . - 2011 . - pp. 1016–1025. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1016–1025 Mots-clés : Au–Fe  Differential  thermal  analysis  (DTA)  Peritectic  solidification  Discontinuous  precipitation  Coherency  relationship Résumé : In order to better understand the microstructure that forms during laser welding of an 18 carat gold and an austenitic stainless steel, solidification of the Au–Fe binary analog has been studied using thermal analysis and interrupted Bridgman experiments. For a hypoperitectic composition, the formation of the primary phase, its coarsening and the peculiar macrosegregation associated with the large density difference between the elements have been studied. Just after the peritectic phase forms around the primary dendrites, continuous and discontinuous precipitation has been shown to occur as a result of the immiscibility of the two face-centered cubic phases below the peritectic temperature. Finally, the solid-state transformations associated with the eutectoid have been characterized. DEWEY : 1359-6454 ISSN : 669 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900696X

Pressure effects on metallic glasses / J. Caris in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1026–1036 Titre : Pressure effects on metallic glasses Type de document : texte imprimé Auteurs : J. Caris, Auteur ; J. J. Lewandowski, Auteur Année de publication : 2011 Article en page(s) : pp. 1026–1036 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metallic  glass  Shear  bands  Tension  test  Acoustic  methods  Pressure  effects Résumé : The effects of normal stress/superimposed pressure on the flow/fracture of two different zirconium-based glasses and a hafnium-based bulk metallic glass (BMG) tested at Case Western Reserve University is presented. These results are compared with the pressure sensitivity of the bulk modulus and shear modulus of amorphous metals in the manner previously conducted by Spitzig and Richmond for crystalline metals. Although few experimental results of this nature exist, the data obtained to date reveal minimal normal stress/pressure sensitivity for the BMG examined in this study, consistent with the small pressure dependence of the shear modulus. Comparison with various yield/fracture criteria is also provided. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006971 [article] Pressure effects on metallic glasses [texte imprimé] / J. Caris, Auteur ; J. J. Lewandowski, Auteur . - 2011 . - pp. 1026–1036. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1026–1036 Mots-clés : Metallic  glass  Shear  bands  Tension  test  Acoustic  methods  Pressure  effects Résumé : The effects of normal stress/superimposed pressure on the flow/fracture of two different zirconium-based glasses and a hafnium-based bulk metallic glass (BMG) tested at Case Western Reserve University is presented. These results are compared with the pressure sensitivity of the bulk modulus and shear modulus of amorphous metals in the manner previously conducted by Spitzig and Richmond for crystalline metals. Although few experimental results of this nature exist, the data obtained to date reveal minimal normal stress/pressure sensitivity for the BMG examined in this study, consistent with the small pressure dependence of the shear modulus. Comparison with various yield/fracture criteria is also provided. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006971

Self-similar grain size distribution in three dimensions: A stochastic treatment / C. S. Pande in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1037–1044 Titre : Self-similar grain size distribution in three dimensions: A stochastic treatment Type de document : texte imprimé Auteurs : C. S. Pande, Auteur ; G. B. McFadden, Auteur Année de publication : 2011 Article en page(s) : pp. 1037–1044 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  growth  Modelling  Theory Résumé : In this paper, a stochastic formulation of three-dimensional grain growth is presented. This formulation employs the recent extension of the von Neumann law to three dimensions, and leads to a Fokker–Planck equation for the size distribution. The self-similar solutions of the Fokker–Planck equation presented here are based on the assumption of quasi-stationary distributions reached in the long time limit. The resulting grain size distributions, obtained both numerically and analytically, are shown to be in good agreement with each other and also with those obtained from computer simulations, indicating the validity of the stochastic approach. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007095 [article] Self-similar grain size distribution in three dimensions: A stochastic treatment [texte imprimé] / C. S. Pande, Auteur ; G. B. McFadden, Auteur . - 2011 . - pp. 1037–1044. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1037–1044 Mots-clés : Grain  growth  Modelling  Theory Résumé : In this paper, a stochastic formulation of three-dimensional grain growth is presented. This formulation employs the recent extension of the von Neumann law to three dimensions, and leads to a Fokker–Planck equation for the size distribution. The self-similar solutions of the Fokker–Planck equation presented here are based on the assumption of quasi-stationary distributions reached in the long time limit. The resulting grain size distributions, obtained both numerically and analytically, are shown to be in good agreement with each other and also with those obtained from computer simulations, indicating the validity of the stochastic approach. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007095

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

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

Decay-dissipative Belousov–Zhabotinsky nanobands and nanoparticles in NiAl / J. A. Sekhar in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1056–1073 Titre : Decay-dissipative Belousov–Zhabotinsky nanobands and nanoparticles in NiAl Type de document : texte imprimé Auteurs : J. A. Sekhar, Auteur ; H. P. Li, Auteur ; G. K. Dey, Auteur Année de publication : 2011 Article en page(s) : pp. 1056–1073 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Micropyretic  synthesis  Self-propagating  high-temperature  synthesis  (SHS)  Nano  structure  High-temperature  Belousov–Zhabotinsky  reactions Résumé : A relationship is inferred between dissipative reactions, nanocrystal formation and nanobands in micropyretically synthesized equimolar Ni–Al alloys. Various microkinetic mechanisms may be operative, depending on the chosen processing conditions and alloy chemistry. Time-lapse X-ray reports, microstructural studies, process conditions and combustion calculations are correlated to understand the microkinetics of the synthesis process. Dissipative oscillatory chemical reactions, called Belousov–Zhabotinsky (BZ) reactions, are proposed as one synthesis mechanism, which leads to the formation of the observed nanoscale features such as nanoparticles and nanobands. Nanoband features in a solid-state combustion processes are discussed for the first time. The dissipative oscillations that are a consequence of the nonlinear reaction rate equations create and simultaneously disperse nanoparticles and nanobands depending on the initial temperature, composition and other process conditions chosen. The spatiotemporal structure from a moving geometrical configuration such as a micropyretic solid-state combustion front can contain a decaying dissipative reaction product, e.g. a spin combustion microstructure. Nanoband-forming waves and nanocrystals possibly interact, leading to unique variations in the structure. Such nanostructural possibilities could be advantageously controlled by manipulating the initial conditions. The implications of the BZ finding could be significant, as it offers a method of forming bulk near-net-shaped objects containing nanostructured enhancements. For the NiAl material in particular, this could be a significant technical advantage from a manufacturing viewpoint. Some possible methods to influence the process and the resultant structure on the nanoscale are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007113 [article] Decay-dissipative Belousov–Zhabotinsky nanobands and nanoparticles in NiAl [texte imprimé] / J. A. Sekhar, Auteur ; H. P. Li, Auteur ; G. K. Dey, Auteur . - 2011 . - pp. 1056–1073. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1056–1073 Mots-clés : Micropyretic  synthesis  Self-propagating  high-temperature  synthesis  (SHS)  Nano  structure  High-temperature  Belousov–Zhabotinsky  reactions Résumé : A relationship is inferred between dissipative reactions, nanocrystal formation and nanobands in micropyretically synthesized equimolar Ni–Al alloys. Various microkinetic mechanisms may be operative, depending on the chosen processing conditions and alloy chemistry. Time-lapse X-ray reports, microstructural studies, process conditions and combustion calculations are correlated to understand the microkinetics of the synthesis process. Dissipative oscillatory chemical reactions, called Belousov–Zhabotinsky (BZ) reactions, are proposed as one synthesis mechanism, which leads to the formation of the observed nanoscale features such as nanoparticles and nanobands. Nanoband features in a solid-state combustion processes are discussed for the first time. The dissipative oscillations that are a consequence of the nonlinear reaction rate equations create and simultaneously disperse nanoparticles and nanobands depending on the initial temperature, composition and other process conditions chosen. The spatiotemporal structure from a moving geometrical configuration such as a micropyretic solid-state combustion front can contain a decaying dissipative reaction product, e.g. a spin combustion microstructure. Nanoband-forming waves and nanocrystals possibly interact, leading to unique variations in the structure. Such nanostructural possibilities could be advantageously controlled by manipulating the initial conditions. The implications of the BZ finding could be significant, as it offers a method of forming bulk near-net-shaped objects containing nanostructured enhancements. For the NiAl material in particular, this could be a significant technical advantage from a manufacturing viewpoint. Some possible methods to influence the process and the resultant structure on the nanoscale are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007113

Microstructure-based multiscale modeling of elevated temperature deformation in aluminum alloys / Paul E. Krajewski in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1074–1086 Titre : Microstructure-based multiscale modeling of elevated temperature deformation in aluminum alloys Type de document : texte imprimé Auteurs : Paul E. Krajewski, Auteur ; Louis G. Hector Jr., Auteur ; Ningning Du, Auteur Année de publication : 2011 Article en page(s) : pp. 1074–1086 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminum  alloys  Creep  Superplasticity  Grain  boundaries  Micromechanical  modeling Résumé : A multiscale model for predicting elevated temperature deformation in Al–Mg alloys is presented. Constitutive models are generated from a theoretical methodology and used to investigate the effects of grain size on formability. Flow data are computed with a polycrystalline, microstructure-based model which accounts for grain boundary sliding, stress-induced diffusion, and dislocation creep. Favorable agreement is found between the computed flow data and elevated temperature tensile measurements. A creep constitutive model is then fit to the computed flow data and used in finite-element simulations of two simple gas pressure forming processes, where favorable results are observed. These results are fully consistent with gas pressure forming experiments, and suggest a greater role for constitutive models, derived largely from theoretical methodologies, in the design of Al alloys with enhanced elevated temperature formability. The methodology detailed herein provides a framework for incorporation of results from atomistic-scale models of dislocation creep and diffusion. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007125 [article] Microstructure-based multiscale modeling of elevated temperature deformation in aluminum alloys [texte imprimé] / Paul E. Krajewski, Auteur ; Louis G. Hector Jr., Auteur ; Ningning Du, Auteur . - 2011 . - pp. 1074–1086. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1074–1086 Mots-clés : Aluminum  alloys  Creep  Superplasticity  Grain  boundaries  Micromechanical  modeling Résumé : A multiscale model for predicting elevated temperature deformation in Al–Mg alloys is presented. Constitutive models are generated from a theoretical methodology and used to investigate the effects of grain size on formability. Flow data are computed with a polycrystalline, microstructure-based model which accounts for grain boundary sliding, stress-induced diffusion, and dislocation creep. Favorable agreement is found between the computed flow data and elevated temperature tensile measurements. A creep constitutive model is then fit to the computed flow data and used in finite-element simulations of two simple gas pressure forming processes, where favorable results are observed. These results are fully consistent with gas pressure forming experiments, and suggest a greater role for constitutive models, derived largely from theoretical methodologies, in the design of Al alloys with enhanced elevated temperature formability. The methodology detailed herein provides a framework for incorporation of results from atomistic-scale models of dislocation creep and diffusion. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007125

Simulation of slip band evolution in duplex Ti–6Al–4V / M. Zhang in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1087–1096 Titre : Simulation of slip band evolution in duplex Ti–6Al–4V Type de document : texte imprimé Auteurs : M. Zhang, Auteur ; F. Bridier, Auteur ; P. Villechaise, Auteur Année de publication : 2011 Article en page(s) : pp. 1087–1096 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fatigue  Slip  bands  Ti–6Al–4V  Microstructure Résumé : Formation of slip bands plays an important role in deformation and fatigue processes of duplex Ti–6Al–4V. In this study, shear-enhanced crystal plasticity constitutive relations are proposed to account for the slip softening due to breakdown of the short-range order between titanium and aluminum atoms. A hybrid strategy is developed which allows the softening to occur in slip bands only within the primary α phase, with the degree of localization depending on the specific polycrystalline initial-boundary-value problem and the requirements for compatibility of each grain or phase with its neighbors. The proposed model is calibrated by performing finite-element (FE) simulations on an experimentally studied Ti–6Al–4V alloy. The slip behavior of a Ti–6Al–4V sample subjected to an in situ (scanning electron microscopy (SEM)) tensile test is investigated. A two-dimensional (2-D) FE with 3-D crystal plasticity relations is constructed to represent the microstructure of the Ti–6Al–4V sample. Due to the lack of access to fully 3-D microstructure, a generalized plane-strain condition is used in the FE model which assumes columnar grains that are free of net traction in the direction normal to the surface. The assumption of columnar grains significantly reduces the computational cost. The contours of effective plastic strain are compared with the surface SEM micrographs from experiments at various strain levels. It is shown that the proposed approach for modeling slip bands qualitatively captures experimentally observed slip band behavior. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007198 [article] Simulation of slip band evolution in duplex Ti–6Al–4V [texte imprimé] / M. Zhang, Auteur ; F. Bridier, Auteur ; P. Villechaise, Auteur . - 2011 . - pp. 1087–1096. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1087–1096 Mots-clés : Fatigue  Slip  bands  Ti–6Al–4V  Microstructure Résumé : Formation of slip bands plays an important role in deformation and fatigue processes of duplex Ti–6Al–4V. In this study, shear-enhanced crystal plasticity constitutive relations are proposed to account for the slip softening due to breakdown of the short-range order between titanium and aluminum atoms. A hybrid strategy is developed which allows the softening to occur in slip bands only within the primary α phase, with the degree of localization depending on the specific polycrystalline initial-boundary-value problem and the requirements for compatibility of each grain or phase with its neighbors. The proposed model is calibrated by performing finite-element (FE) simulations on an experimentally studied Ti–6Al–4V alloy. The slip behavior of a Ti–6Al–4V sample subjected to an in situ (scanning electron microscopy (SEM)) tensile test is investigated. A two-dimensional (2-D) FE with 3-D crystal plasticity relations is constructed to represent the microstructure of the Ti–6Al–4V sample. Due to the lack of access to fully 3-D microstructure, a generalized plane-strain condition is used in the FE model which assumes columnar grains that are free of net traction in the direction normal to the surface. The assumption of columnar grains significantly reduces the computational cost. The contours of effective plastic strain are compared with the surface SEM micrographs from experiments at various strain levels. It is shown that the proposed approach for modeling slip bands qualitatively captures experimentally observed slip band behavior. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007198

Nonpolar ZnO film growth and mechanism for anisotropic in-plane strain relaxation / P. Pant in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1097–1103 Titre : Nonpolar ZnO film growth and mechanism for anisotropic in-plane strain relaxation Type de document : texte imprimé Auteurs : P. Pant, Auteur ; J. D. Budai, Auteur ; J. Narayan, Auteur Année de publication : 2011 Article en page(s) : pp. 1097–1103 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Epitaxy  Nonpolar  Anisotropic  strain  X-ray  TEM Résumé : Using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction, we investigated the strain relaxation mechanisms for nonpolar (1 1 −2 0) a-plane ZnO epitaxy on (1 −1 0 2) r-plane sapphire, where the in-plane misfit ranges from −1.5% for the [0 0 0 1]ZnO‖[1 −1 0 −1]sapphire to −18.3% for the [−1 1 0 0]ZnO‖[−1 −1 2 0]sapphire direction. For the large misfit [−1 1 0 0]ZnO direction the misfit strains are fully relaxed at the growth temperature, and only thermal misfit and defect strains, which cannot be relaxed fully by slip dislocations, remain on cooling. For the small misfit direction, lattice misfit is not fully relaxed at the growth temperature. As a result, additive unrelaxed lattice and thermal misfit and defect strains contribute to the measured strain. Our X-ray diffraction measurements of lattice parameters show that the anisotropic in-plane biaxial strain leads to a distortion of the hexagonal symmetry of the ZnO basal plane. Based on the anisotropic strain relaxation observed along the orthogonal in-plane [−1 1 0 0] and [0 0 0 1]ZnO stress directions and our HRTEM investigations of the interface, we show that the plastic relaxation occurring in the small misfit direction [0 0 0 1]ZnO by dislocation nucleation is incomplete. These results are consistent with the domain-matching paradigm of a complete strain relaxation for large misfits and a difficulty in relaxing the film strain for small misfits. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007204 [article] Nonpolar ZnO film growth and mechanism for anisotropic in-plane strain relaxation [texte imprimé] / P. Pant, Auteur ; J. D. Budai, Auteur ; J. Narayan, Auteur . - 2011 . - pp. 1097–1103. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1097–1103 Mots-clés : Epitaxy  Nonpolar  Anisotropic  strain  X-ray  TEM Résumé : Using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction, we investigated the strain relaxation mechanisms for nonpolar (1 1 −2 0) a-plane ZnO epitaxy on (1 −1 0 2) r-plane sapphire, where the in-plane misfit ranges from −1.5% for the [0 0 0 1]ZnO‖[1 −1 0 −1]sapphire to −18.3% for the [−1 1 0 0]ZnO‖[−1 −1 2 0]sapphire direction. For the large misfit [−1 1 0 0]ZnO direction the misfit strains are fully relaxed at the growth temperature, and only thermal misfit and defect strains, which cannot be relaxed fully by slip dislocations, remain on cooling. For the small misfit direction, lattice misfit is not fully relaxed at the growth temperature. As a result, additive unrelaxed lattice and thermal misfit and defect strains contribute to the measured strain. Our X-ray diffraction measurements of lattice parameters show that the anisotropic in-plane biaxial strain leads to a distortion of the hexagonal symmetry of the ZnO basal plane. Based on the anisotropic strain relaxation observed along the orthogonal in-plane [−1 1 0 0] and [0 0 0 1]ZnO stress directions and our HRTEM investigations of the interface, we show that the plastic relaxation occurring in the small misfit direction [0 0 0 1]ZnO by dislocation nucleation is incomplete. These results are consistent with the domain-matching paradigm of a complete strain relaxation for large misfits and a difficulty in relaxing the film strain for small misfits. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007204

Effects of plastic deformation on lamellar structure formation in Ti–39 at.% Al single crystals / Y. Koizumi in Acta materialia, Vol. 58 N° 3 (Fevrier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1104–1115 Titre : Effects of plastic deformation on lamellar structure formation in Ti–39 at.% Al single crystals Type de document : texte imprimé Auteurs : Y. Koizumi, Auteur ; T. Fujita, Auteur ; Y. Minamino, Auteur Année de publication : 2011 Article en page(s) : pp. 1104–1115 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Quenching  Annealing  Intermetallic  compounds  Titanium  aluminides  Layered  structures Résumé : The effects of plastic deformation on lamellar structure formation in solution-treated Ti–39 at.% Al single crystals were investigated, focusing on the role of dislocations of different slip systems. The dislocations were introduced by indentation on the surfaces of solution-treated single crystals with different crystallographic orientations. Traces of basal and prism slips were observed, depending on the position relative to the indentation. During annealing at α2 + γ dual-phase temperatures, lamellar structures were formed faster where basal slip had occurred than where prism slip had occurred. After long annealing, the length scale of lamellar structures formed depends on the slip system operated during prior deformation: in the region where only one of either basal or prism slip had occurred the lamellar structure was coarser than in undeformed crystal, while in the region where both basal and prism slips occurred the lamellar structure was finer than those formed in undeformed crystal. The reasons for the differences in lamellar structures are discussed on the basis of the frequencies of stacking fault formation on (0 0 0 1) planes as precursors to γ-precipitates. The results suggest that the cross-slip of dislocations between basal and prism planes, which gives rise to the formation of multiple stacking faults on many parallel (0 0 0 1) planes, is responsible for the refinement of lamellar structures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007216 [article] Effects of plastic deformation on lamellar structure formation in Ti–39 at.% Al single crystals [texte imprimé] / Y. Koizumi, Auteur ; T. Fujita, Auteur ; Y. Minamino, Auteur . - 2011 . - pp. 1104–1115. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 3 (Fevrier 2010) . - pp. 1104–1115 Mots-clés : Quenching  Annealing  Intermetallic  compounds  Titanium  aluminides  Layered  structures Résumé : The effects of plastic deformation on lamellar structure formation in solution-treated Ti–39 at.% Al single crystals were investigated, focusing on the role of dislocations of different slip systems. The dislocations were introduced by indentation on the surfaces of solution-treated single crystals with different crystallographic orientations. Traces of basal and prism slips were observed, depending on the position relative to the indentation. During annealing at α2 + γ dual-phase temperatures, lamellar structures were formed faster where basal slip had occurred than where prism slip had occurred. After long annealing, the length scale of lamellar structures formed depends on the slip system operated during prior deformation: in the region where only one of either basal or prism slip had occurred the lamellar structure was coarser than in undeformed crystal, while in the region where both basal and prism slips occurred the lamellar structure was finer than those formed in undeformed crystal. The reasons for the differences in lamellar structures are discussed on the basis of the frequencies of stacking fault formation on (0 0 0 1) planes as precursors to γ-precipitates. The results suggest that the cross-slip of dislocations between basal and prism planes, which gives rise to the formation of multiple stacking faults on many parallel (0 0 0 1) planes, is responsible for the refinement of lamellar structures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007216

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