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Acta materialia |
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Ajouter le résultat dans votre panierMicrostructure and microtexture evolution during strain path changes of an initially stable Cu single crystal / H. Paul in Acta materialia, Vol. 58 N° 8 (Mai 2010)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2799–2813
Titre : Microstructure and microtexture evolution during strain path changes of an initially stable Cu single crystal Type de document : texte imprimé Auteurs : H. Paul, Auteur ; C. Maurice, Auteur ; J.H. Driver, Auteur Année de publication : 2011 Article en page(s) : pp. 2799–2813 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Shear bands Changing strain path Orientation mapping Texture Copper Résumé : The microstructure and microtexture evolution in a deformed Goss oriented crystal were characterized after a sample rotation and consequent change in strain path, over a range of scales by optical microscopy, high resolution scanning electron microscopy equipped with field emission gun and electron packscattered diffraction facilities and transmission electron microscopy orientation mapping. High purity copper single crystals with initial Goss{1 1 0}〈0 0 1〉 orientation were channel-die compressed 59% to develop a homogeneous structure composed of two sets of symmetrical primary microbands. New samples with ND rotated orientations of Goss{1 1 0}〈0 0 1〉, brass{1 1 0}〈1 1 2〉, M{1 1 0}〈1 1 1〉 and H{1 1 0}〈0 0 1〉, were then cut out and further compressed in channel-die by a few per cent. The change in flow stress could be correlated with the change in dislocation substructure and microtexture, particularly along shear bands initiated by the strain path change. In the H{1 1 0}〈0 1 1〉 and M{1 1 0}〈1 1 1〉 orientations, the flow stress increased by Taylor factor hardening then decreased by intense macroscopic shear band (MSB) formation. In the softer brass orientation and in the absence of Taylor factor hardening, more diffuse MSB formation occurred. The local rotations in the band were used to deduce the possible local slip systems initiated during the strain path change. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000030 [article] Microstructure and microtexture evolution during strain path changes of an initially stable Cu single crystal [texte imprimé] / H. Paul, Auteur ; C. Maurice, Auteur ; J.H. Driver, Auteur . - 2011 . - pp. 2799–2813.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2799–2813
Mots-clés : Shear bands Changing strain path Orientation mapping Texture Copper Résumé : The microstructure and microtexture evolution in a deformed Goss oriented crystal were characterized after a sample rotation and consequent change in strain path, over a range of scales by optical microscopy, high resolution scanning electron microscopy equipped with field emission gun and electron packscattered diffraction facilities and transmission electron microscopy orientation mapping. High purity copper single crystals with initial Goss{1 1 0}〈0 0 1〉 orientation were channel-die compressed 59% to develop a homogeneous structure composed of two sets of symmetrical primary microbands. New samples with ND rotated orientations of Goss{1 1 0}〈0 0 1〉, brass{1 1 0}〈1 1 2〉, M{1 1 0}〈1 1 1〉 and H{1 1 0}〈0 0 1〉, were then cut out and further compressed in channel-die by a few per cent. The change in flow stress could be correlated with the change in dislocation substructure and microtexture, particularly along shear bands initiated by the strain path change. In the H{1 1 0}〈0 1 1〉 and M{1 1 0}〈1 1 1〉 orientations, the flow stress increased by Taylor factor hardening then decreased by intense macroscopic shear band (MSB) formation. In the softer brass orientation and in the absence of Taylor factor hardening, more diffuse MSB formation occurred. The local rotations in the band were used to deduce the possible local slip systems initiated during the strain path change. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000030
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2814–2821
Titre : Lattice rotation induced by plasma nitriding in a 316L polycrystalline stainless steel Type de document : texte imprimé Auteurs : J.C. Stinville, Auteur ; P. Villechaise, Auteur ; C. Templier, Auteur Année de publication : 2011 Article en page(s) : pp. 2814–2821 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Lattice rotation Texture Stainless steel Electron backscattered diffraction Nitriding Résumé : The introduction at moderate temperature of nitrogen in the 316L austenitic stainless steel by plasma nitriding modifies the crystallographic texture in the very near surface region. The evolution of texture components has been quantitatively characterized by electron backscattered diffraction. The analysis of these experiments shows that the amplitude of the lattice rotation as well as the direction of rotation are directly related to the initial orientation of each grain. The retexturing behaviour is consistent with the lattice rotation upon tensile elongation of polycrystalline materials predicted by the Taylor model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000054 [article] Lattice rotation induced by plasma nitriding in a 316L polycrystalline stainless steel [texte imprimé] / J.C. Stinville, Auteur ; P. Villechaise, Auteur ; C. Templier, Auteur . - 2011 . - pp. 2814–2821.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2814–2821
Mots-clés : Lattice rotation Texture Stainless steel Electron backscattered diffraction Nitriding Résumé : The introduction at moderate temperature of nitrogen in the 316L austenitic stainless steel by plasma nitriding modifies the crystallographic texture in the very near surface region. The evolution of texture components has been quantitatively characterized by electron backscattered diffraction. The analysis of these experiments shows that the amplitude of the lattice rotation as well as the direction of rotation are directly related to the initial orientation of each grain. The retexturing behaviour is consistent with the lattice rotation upon tensile elongation of polycrystalline materials predicted by the Taylor model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000054
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2822–2835
Titre : The compressive and shear response of titanium matrix composite lattice structures Type de document : texte imprimé Auteurs : P. Moongkhamklang, Auteur ; V.S. Deshpande, Auteur ; H.N.G. Wadley, Auteur Année de publication : 2011 Article en page(s) : pp. 2822–2835 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cellular materials Metal–matrix composites (MMCs) Mechanical properties Résumé : A method has been developed for fabricating millimeter cell size cellular lattice structures with square and diamond collinear truss topologies from 240 μm diameter Ti–6Al–4V-coated SiC monofilaments (titanium matrix composite (TMC) monofilaments). Lattices with relative densities in the range 10–20% were manufactured and tested in both compression and shear. Because of the very high strength of the TMC monofilaments, the compressive strengths of both topology lattices were dominated by elastic buckling of the constituent struts. However, under shear loading, some of the struts are subjected to tensile stresses and failure is then set by tensile fracture of the monofilaments. Analytical expressions are derived for the elastic moduli and strength of both lattice topologies and the predictions are compared with measurements over the range of relative densities investigated in this study. Excellent agreement between the measurements and predictions is observed. The specific shear strength of the TMC lattices is superior to all other cellular materials investigated to date, including carbon fiber-reinforced polymers (CFRP) honeycombs. Their compressive properties are comparable to CFRP honeycombs. The TMC lattices have a brittle response and undergo catastrophic failure at their peak load. They appear most promising as candidates for the cores in sandwich structures intended for elevated temperature and multifunctional applications where their limited ductility is not a significant constraint. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000078 [article] The compressive and shear response of titanium matrix composite lattice structures [texte imprimé] / P. Moongkhamklang, Auteur ; V.S. Deshpande, Auteur ; H.N.G. Wadley, Auteur . - 2011 . - pp. 2822–2835.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2822–2835
Mots-clés : Cellular materials Metal–matrix composites (MMCs) Mechanical properties Résumé : A method has been developed for fabricating millimeter cell size cellular lattice structures with square and diamond collinear truss topologies from 240 μm diameter Ti–6Al–4V-coated SiC monofilaments (titanium matrix composite (TMC) monofilaments). Lattices with relative densities in the range 10–20% were manufactured and tested in both compression and shear. Because of the very high strength of the TMC monofilaments, the compressive strengths of both topology lattices were dominated by elastic buckling of the constituent struts. However, under shear loading, some of the struts are subjected to tensile stresses and failure is then set by tensile fracture of the monofilaments. Analytical expressions are derived for the elastic moduli and strength of both lattice topologies and the predictions are compared with measurements over the range of relative densities investigated in this study. Excellent agreement between the measurements and predictions is observed. The specific shear strength of the TMC lattices is superior to all other cellular materials investigated to date, including carbon fiber-reinforced polymers (CFRP) honeycombs. Their compressive properties are comparable to CFRP honeycombs. The TMC lattices have a brittle response and undergo catastrophic failure at their peak load. They appear most promising as candidates for the cores in sandwich structures intended for elevated temperature and multifunctional applications where their limited ductility is not a significant constraint. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000078
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2836–2842
Titre : Effects of Co addition on microstructure and magnetic properties of ferromagnetic CoFeSiB alloy films Type de document : texte imprimé Auteurs : B. S. Chun, Auteur ; S.D. Kim, Auteur ; Y.S. Kim, Auteur Année de publication : 2011 Article en page(s) : pp. 2836–2842 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Amorphous materials Magnetic thin films Magnetic properties Crystal structure Résumé : A correlation between composition, microstructure, and magnetic properties of sputter-deposited CoFeSiB alloy films has been studied. Various analytical tools and micromagnetic models were employed to understand the details of microstructural evolution and magnetic reversal processes, respectively. The CoFeSiB alloy film shows significantly different microstructure and magnetic properties depend on the Co concentration. When the Co concentration is below 75 at.%, the alloy has an amorphous phase exhibiting magnetic softness with negative remanence. Meanwhile, beyond 75 at.%, the structure consists of nanocrystals precipitated in the amorphous matrix, which becomes magnetically hard with positive remanence as well as antiferromagnetic exchange coupling. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000091 [article] Effects of Co addition on microstructure and magnetic properties of ferromagnetic CoFeSiB alloy films [texte imprimé] / B. S. Chun, Auteur ; S.D. Kim, Auteur ; Y.S. Kim, Auteur . - 2011 . - pp. 2836–2842.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2836–2842
Mots-clés : Amorphous materials Magnetic thin films Magnetic properties Crystal structure Résumé : A correlation between composition, microstructure, and magnetic properties of sputter-deposited CoFeSiB alloy films has been studied. Various analytical tools and micromagnetic models were employed to understand the details of microstructural evolution and magnetic reversal processes, respectively. The CoFeSiB alloy film shows significantly different microstructure and magnetic properties depend on the Co concentration. When the Co concentration is below 75 at.%, the alloy has an amorphous phase exhibiting magnetic softness with negative remanence. Meanwhile, beyond 75 at.%, the structure consists of nanocrystals precipitated in the amorphous matrix, which becomes magnetically hard with positive remanence as well as antiferromagnetic exchange coupling. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000091
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2843–2853
Titre : Effects of grain size and grain boundaries on defect production in nanocrystalline 3C–SiC Type de document : texte imprimé Auteurs : N. Swaminathan, Auteur ; Paul J. Kamenski, Auteur ; Dane Morgan, Auteur Année de publication : 2011 Article en page(s) : pp. 2843–2853 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocrystalline ceramics Displacement cascades Point defects Silicon carbide Résumé : Cascade simulations in single crystal and nanocrystalline SiC have been conducted in order to determine the role of grain boundaries and grain size on defect production during primary radiation damage. Cascades are performed with 4 and 10 keV silicon as the primary knock-on atom (PKA). Total defect production is found to increase with decreasing grain size, and this effect is shown to be due to increased production in grain boundaries and changing grain boundary volume fraction. In order to consider in-grain defect production, a new mapping methodology is developed to properly normalize in-grain defect production rates for nanocrystalline materials. It is shown that the presence of grain boundaries does not affect the total normalized in-grain defect production significantly (the changes are lower than ∼20%) for the PKA energies considered. Defect production in the single grain containing the PKA is also studied and found to increase for smaller grain sizes. In particular, for smaller grain sizes the defect production decreases with increasing distance from the grain boundary while for larger grain sizes the presence of the grain boundaries has negligible effect on defect production. The results suggest that experimentally observed changes in radiation resistance of nanocrystalline materials may be due to long-term damage evolution rather than changes in defect production rates from primary damage. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000236 [article] Effects of grain size and grain boundaries on defect production in nanocrystalline 3C–SiC [texte imprimé] / N. Swaminathan, Auteur ; Paul J. Kamenski, Auteur ; Dane Morgan, Auteur . - 2011 . - pp. 2843–2853.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2843–2853
Mots-clés : Nanocrystalline ceramics Displacement cascades Point defects Silicon carbide Résumé : Cascade simulations in single crystal and nanocrystalline SiC have been conducted in order to determine the role of grain boundaries and grain size on defect production during primary radiation damage. Cascades are performed with 4 and 10 keV silicon as the primary knock-on atom (PKA). Total defect production is found to increase with decreasing grain size, and this effect is shown to be due to increased production in grain boundaries and changing grain boundary volume fraction. In order to consider in-grain defect production, a new mapping methodology is developed to properly normalize in-grain defect production rates for nanocrystalline materials. It is shown that the presence of grain boundaries does not affect the total normalized in-grain defect production significantly (the changes are lower than ∼20%) for the PKA energies considered. Defect production in the single grain containing the PKA is also studied and found to increase for smaller grain sizes. In particular, for smaller grain sizes the defect production decreases with increasing distance from the grain boundary while for larger grain sizes the presence of the grain boundaries has negligible effect on defect production. The results suggest that experimentally observed changes in radiation resistance of nanocrystalline materials may be due to long-term damage evolution rather than changes in defect production rates from primary damage. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000236
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2854–2863
Titre : Investigation of the low-cycle fatigue mechanism for micron-scale monocrystalline silicon films Type de document : texte imprimé Auteurs : E. K. Baumert, Auteur ; P.-O. Theillet, Auteur ; O.N. Pierron, Auteur Année de publication : 2011 Article en page(s) : pp. 2854–2863 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fatigue Monocrystalline silicon Thin film Static fatigue Frequency effects Résumé : This study investigated the cyclic and static fatigue properties of 10 μm thick, deep reactive ion etched, monocrystalline silicon films. Stress–life fatigue curves and fatigue degradation rates vs. stress curves were generated at both 4 and 40 kHz, at 30 °C, 50% relative humidity (RH). A significant frequency effect was observed, with shorter fatigue lives and faster damage accumulation rates at 4 kHz. Static fatigue was also observed with shorter static lifetimes at 80 °C, 90% RH than at 30 °C, 50% RH. Fracture surface evaluation did not reveal any major difference between cyclically and statically fatigued devices. These experimental results confirm that the fatigue of micron-scale silicon is not purely mechanical. The study also proposes a fatigue scenario based on time-dependent subcritical crack growth to account for the low-cycle fatigue regime. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000025X [article] Investigation of the low-cycle fatigue mechanism for micron-scale monocrystalline silicon films [texte imprimé] / E. K. Baumert, Auteur ; P.-O. Theillet, Auteur ; O.N. Pierron, Auteur . - 2011 . - pp. 2854–2863.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2854–2863
Mots-clés : Fatigue Monocrystalline silicon Thin film Static fatigue Frequency effects Résumé : This study investigated the cyclic and static fatigue properties of 10 μm thick, deep reactive ion etched, monocrystalline silicon films. Stress–life fatigue curves and fatigue degradation rates vs. stress curves were generated at both 4 and 40 kHz, at 30 °C, 50% relative humidity (RH). A significant frequency effect was observed, with shorter fatigue lives and faster damage accumulation rates at 4 kHz. Static fatigue was also observed with shorter static lifetimes at 80 °C, 90% RH than at 30 °C, 50% RH. Fracture surface evaluation did not reveal any major difference between cyclically and statically fatigued devices. These experimental results confirm that the fatigue of micron-scale silicon is not purely mechanical. The study also proposes a fatigue scenario based on time-dependent subcritical crack growth to account for the low-cycle fatigue regime. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000025X
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2864–2875
Titre : Modeling fluid flow in three-dimensional single crystal dendritic structures Type de document : texte imprimé Auteurs : J. Madison, Auteur ; J. Spowart, Auteur ; D. Rowenhorst, Auteur Année de publication : 2011 Article en page(s) : pp. 2864–2875 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel alloys Dendritic growth Directional solidification Modeling Permeability Résumé : Convection during directional solidification can cause defects such as freckles and misoriented grains. To gain a better understanding of conditions associated with the onset of convective instabilities, flow was investigated using three-dimensional (3D) computational fluid dynamics simulations in an experimentally obtained dendritic network. A serial-sectioned, 3D data set of directionally solidified nickel-base superalloy measuring 2.3 × 2.3 × 1.5 mm was used to determine the permeability for flow parallel and normal to the solidification direction as a function of solid fraction (fS). Anisotropy of permeability varies significantly from 0.4 < fS < 0.6. High flow velocity channels exhibit spacings commensurate with primary dendrite arms at the base of the mushy zone but rapidly increase by a factor of three to four towards dendrite tips. Permeability is strongly dependent on interfacial surface area, which reaches a maximum at fS = 0.65. Results from the 3D simulation are also compared with empirical permeability models, and the microstructural origins of departures from these models are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000285 [article] Modeling fluid flow in three-dimensional single crystal dendritic structures [texte imprimé] / J. Madison, Auteur ; J. Spowart, Auteur ; D. Rowenhorst, Auteur . - 2011 . - pp. 2864–2875.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2864–2875
Mots-clés : Nickel alloys Dendritic growth Directional solidification Modeling Permeability Résumé : Convection during directional solidification can cause defects such as freckles and misoriented grains. To gain a better understanding of conditions associated with the onset of convective instabilities, flow was investigated using three-dimensional (3D) computational fluid dynamics simulations in an experimentally obtained dendritic network. A serial-sectioned, 3D data set of directionally solidified nickel-base superalloy measuring 2.3 × 2.3 × 1.5 mm was used to determine the permeability for flow parallel and normal to the solidification direction as a function of solid fraction (fS). Anisotropy of permeability varies significantly from 0.4 < fS < 0.6. High flow velocity channels exhibit spacings commensurate with primary dendrite arms at the base of the mushy zone but rapidly increase by a factor of three to four towards dendrite tips. Permeability is strongly dependent on interfacial surface area, which reaches a maximum at fS = 0.65. Results from the 3D simulation are also compared with empirical permeability models, and the microstructural origins of departures from these models are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000285
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2876–2886
Titre : Selective dissolution of nanolamellar Ti–41 at.% Al alloy single crystals Type de document : texte imprimé Auteurs : Yuichiro Koizumi, Auteur ; Atsushi Sugihara, Auteur ; Hiroaki Tsuchiya, Auteur Année de publication : 2011 Article en page(s) : pp. 2876–2886 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Titanium aluminides Multilayers Nanostructure Corrosion Electrochemistry Résumé : The selective dissolution behavior of Ti–41 at.% Al single crystals having a α2/γ-lamellar structure with a lamellar thickness in the range 20 nm to 1 μm have been investigated in 0.5 M NaCl aqueous solution focusing on the effect of lamellar thickness on the dissolution of γ-lamellae. In the case where γ-lamellae were thicker than ∼100 nm on average, γ-lamellae were selectively dissolved and, as a result, crevasses whose widths were close to the γ-lamellae thicknesses were formed. However, not all γ-lamellae were dissolved and the distribution of crevasses was much less uniform compared with that of the γ-lamellae. On the other hand, when the average γ-lamellae thickness was <100 nm relatively thick γ-lamellae were preferentially dissolved, but the distribution of the crevasses was relatively uniform compared with that obtained from the coarse lamellar structure. The reasons for this difference are discussed from the viewpoint of the absence of misfit dislocations in nanoscaled lamellae and the difference in ion transport through crevasses of different width formed by dissolution of γ-lamellae. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000303 [article] Selective dissolution of nanolamellar Ti–41 at.% Al alloy single crystals [texte imprimé] / Yuichiro Koizumi, Auteur ; Atsushi Sugihara, Auteur ; Hiroaki Tsuchiya, Auteur . - 2011 . - pp. 2876–2886.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2876–2886
Mots-clés : Titanium aluminides Multilayers Nanostructure Corrosion Electrochemistry Résumé : The selective dissolution behavior of Ti–41 at.% Al single crystals having a α2/γ-lamellar structure with a lamellar thickness in the range 20 nm to 1 μm have been investigated in 0.5 M NaCl aqueous solution focusing on the effect of lamellar thickness on the dissolution of γ-lamellae. In the case where γ-lamellae were thicker than ∼100 nm on average, γ-lamellae were selectively dissolved and, as a result, crevasses whose widths were close to the γ-lamellae thicknesses were formed. However, not all γ-lamellae were dissolved and the distribution of crevasses was much less uniform compared with that of the γ-lamellae. On the other hand, when the average γ-lamellae thickness was <100 nm relatively thick γ-lamellae were preferentially dissolved, but the distribution of the crevasses was relatively uniform compared with that obtained from the coarse lamellar structure. The reasons for this difference are discussed from the viewpoint of the absence of misfit dislocations in nanoscaled lamellae and the difference in ion transport through crevasses of different width formed by dissolution of γ-lamellae. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000303
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2887–2897
Titre : Hafnium binary alloys from experiments and first principles Type de document : texte imprimé Auteurs : Ohad Levy, Auteur ; Gus L.W. Hart, Auteur ; Stefano Curtarolo, Auteur Année de publication : 2011 Article en page(s) : pp. 2887–2897 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hafnium alloys High throughput Ab initio calculations Résumé : Despite the increasing importance of hafnium in numerous technological applications, experimental and computational data on its binary alloys is sparse. In particular, data is scant on those binary systems believed to be phase-separating. We performed a comprehensive study of hafnium binary systems with alkali metals, alkaline earths, transition metals and metals, using high-throughput first-principles calculations. These computations predict novel unsuspected compounds in six binary systems previously believed to be phase-separating. They also predict a few unreported compounds in additional systems and indicate that some reported compounds may actually be unstable at low temperatures. We report the results for the following systems: AgHf, AlHf, AuHf, BaHf★, BeHf, BiHf, CaHf★, CdHf, CoHf, CrHf, CuHf, FeHf, GaHf, HfHg, HfIn, HfIr, HfK★, HfLa★, HfLi★, HfMg, HfMn, HfMo,HfNa★, HfNb★, HfNi, HfOs, HfPb, HfPd, HfPt, HfRe, HfRh, HfRu, HfSc, HfSn, HfSr★, HfTa★, HfTc, HfTi, HfTl, HfV★, HfW, HfY★, HfZn and HfZr (★ = systems in which the ab initio method predicts that no compounds are stable). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000315 [article] Hafnium binary alloys from experiments and first principles [texte imprimé] / Ohad Levy, Auteur ; Gus L.W. Hart, Auteur ; Stefano Curtarolo, Auteur . - 2011 . - pp. 2887–2897.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2887–2897
Mots-clés : Hafnium alloys High throughput Ab initio calculations Résumé : Despite the increasing importance of hafnium in numerous technological applications, experimental and computational data on its binary alloys is sparse. In particular, data is scant on those binary systems believed to be phase-separating. We performed a comprehensive study of hafnium binary systems with alkali metals, alkaline earths, transition metals and metals, using high-throughput first-principles calculations. These computations predict novel unsuspected compounds in six binary systems previously believed to be phase-separating. They also predict a few unreported compounds in additional systems and indicate that some reported compounds may actually be unstable at low temperatures. We report the results for the following systems: AgHf, AlHf, AuHf, BaHf★, BeHf, BiHf, CaHf★, CdHf, CoHf, CrHf, CuHf, FeHf, GaHf, HfHg, HfIn, HfIr, HfK★, HfLa★, HfLi★, HfMg, HfMn, HfMo,HfNa★, HfNb★, HfNi, HfOs, HfPb, HfPd, HfPt, HfRe, HfRh, HfRu, HfSc, HfSn, HfSr★, HfTa★, HfTc, HfTi, HfTl, HfV★, HfW, HfY★, HfZn and HfZr (★ = systems in which the ab initio method predicts that no compounds are stable). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000315
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2898–2904
Titre : Bordoni relaxation in kink-chains Type de document : texte imprimé Auteurs : Gunther Schoeck, Auteur Année de publication : 2011 Article en page(s) : pp. 2898–2904 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Internal friction Kink-chain Bordoni relaxation Résumé : The Bordoni relaxation in fcc metals is generally assumed to result from thermally activated kink-pair formation in dislocation segments aligned along Peierls valleys in crystallographic close-packed directions. Objections against this interpretation have been raised by pointing out, that, at the small stresses applied in the experiments, the Paré condition is not satisfied and that the Peierls stress derived from the experiments by far exceeds the experimental values for the flow stress extrapolated to 0 K. It is shown that, when the bow-out configuration of a dislocation segment is treated as a kink-chain, and when the splitting of dislocation into partials is accounted for, both objections cannot be maintained. Under the assumption that the kink mobility is high and using analytical expressions for the kink-chain configuration and the kink-chain enthalpy under stress an expression for the bow-out rate of dislocation segments is obtained. Trivial numerical integration, under the action of a periodic applied stress, leads to a phase-lag between strain and stress and hence to energy dissipation. The dependence of this energy loss on segment lengths, temperature and internal stress is derived explicitly. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000327 [article] Bordoni relaxation in kink-chains [texte imprimé] / Gunther Schoeck, Auteur . - 2011 . - pp. 2898–2904.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2898–2904
Mots-clés : Internal friction Kink-chain Bordoni relaxation Résumé : The Bordoni relaxation in fcc metals is generally assumed to result from thermally activated kink-pair formation in dislocation segments aligned along Peierls valleys in crystallographic close-packed directions. Objections against this interpretation have been raised by pointing out, that, at the small stresses applied in the experiments, the Paré condition is not satisfied and that the Peierls stress derived from the experiments by far exceeds the experimental values for the flow stress extrapolated to 0 K. It is shown that, when the bow-out configuration of a dislocation segment is treated as a kink-chain, and when the splitting of dislocation into partials is accounted for, both objections cannot be maintained. Under the assumption that the kink mobility is high and using analytical expressions for the kink-chain configuration and the kink-chain enthalpy under stress an expression for the bow-out rate of dislocation segments is obtained. Trivial numerical integration, under the action of a periodic applied stress, leads to a phase-lag between strain and stress and hence to energy dissipation. The dependence of this energy loss on segment lengths, temperature and internal stress is derived explicitly. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000327
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2905–2911
Titre : Modeling of diffusional phase transformation in multi-component systems with stoichiometric phases Type de document : texte imprimé Auteurs : J. Svoboda, Auteur ; F.D. Fischer, Auteur ; R. Abart, Auteur Année de publication : 2011 Article en page(s) : pp. 2905–2911 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Interdiffusion Intermetallics Phase transformation kinetics Modeling Kirkendall effect Résumé : In many multi-component systems, phases can be considered stoichiometric. If two phases not stably coexisting are brought into contact, multiple new phases may nucleate at the interface and develop into a sequence of layers with different phase compositions, which grow between the original phases. Inert markers at the original contact may show “splitting” of the marker (Kirkendall) plane, called polyfurcation. Nearly exclusively binary systems have been studied theoretically or experimentally. A thermodynamic model for the kinetics of diffusional phase transformation in multi-component systems and motion of the polyfurcated Kirkendall plane is derived by the thermodynamic extremal principle. The degrees of freedom of the system are discussed rigorously. The model is demonstrated on simulations of kinetics in binary three-phase and ternary four-phase systems. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000339 [article] Modeling of diffusional phase transformation in multi-component systems with stoichiometric phases [texte imprimé] / J. Svoboda, Auteur ; F.D. Fischer, Auteur ; R. Abart, Auteur . - 2011 . - pp. 2905–2911.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2905–2911
Mots-clés : Interdiffusion Intermetallics Phase transformation kinetics Modeling Kirkendall effect Résumé : In many multi-component systems, phases can be considered stoichiometric. If two phases not stably coexisting are brought into contact, multiple new phases may nucleate at the interface and develop into a sequence of layers with different phase compositions, which grow between the original phases. Inert markers at the original contact may show “splitting” of the marker (Kirkendall) plane, called polyfurcation. Nearly exclusively binary systems have been studied theoretically or experimentally. A thermodynamic model for the kinetics of diffusional phase transformation in multi-component systems and motion of the polyfurcated Kirkendall plane is derived by the thermodynamic extremal principle. The degrees of freedom of the system are discussed rigorously. The model is demonstrated on simulations of kinetics in binary three-phase and ternary four-phase systems. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000339
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2912–2925
Titre : Wear and friction of TiAlN/VN coatings against Al2O3 in air at room and elevated temperatures Type de document : texte imprimé Auteurs : Z. Zhou, Auteur ; W.M. Rainforth, Auteur ; Q. Luo, Auteur Année de publication : 2011 Article en page(s) : pp. 2912–2925 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nitride Tribology TEM Infrared spectroscopy Raman spectroscopy Résumé : TiAlN/VN multilayer coatings exhibit excellent dry sliding wear resistance and low friction coefficient, reported to be associated with the formation of self-lubricating V2O5. To investigate this hypothesis, dry sliding ball-on-disc wear tests of TiAlN/VN coatings on flat stainless steel substrates were undertaken against Al2O3 at 25 °C, 300 °C and 635 °C in air. The coating exhibited increased wear rate with temperature. The friction coefficient was 0.53 at 25 °C, which increased to 1.03 at 300 °C and decreased to 0.46 at 635 °C. Detailed investigation of the worn surfaces was undertaken using site-specific transmission electron microscopy (TEM) via focused ion beam (FIB) microscopy, along with Fourier transform infrared (FTIR) and Raman spectroscopy. Microstructure and tribo-induced chemical reactions at these temperatures were correlated with the coating’s wear and friction behaviour. The friction behaviour at room temperature is attributed to the presence of a thin hydrated tribofilm and the presence of V2O5 at high temperature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000340 [article] Wear and friction of TiAlN/VN coatings against Al2O3 in air at room and elevated temperatures [texte imprimé] / Z. Zhou, Auteur ; W.M. Rainforth, Auteur ; Q. Luo, Auteur . - 2011 . - pp. 2912–2925.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2912–2925
Mots-clés : Nitride Tribology TEM Infrared spectroscopy Raman spectroscopy Résumé : TiAlN/VN multilayer coatings exhibit excellent dry sliding wear resistance and low friction coefficient, reported to be associated with the formation of self-lubricating V2O5. To investigate this hypothesis, dry sliding ball-on-disc wear tests of TiAlN/VN coatings on flat stainless steel substrates were undertaken against Al2O3 at 25 °C, 300 °C and 635 °C in air. The coating exhibited increased wear rate with temperature. The friction coefficient was 0.53 at 25 °C, which increased to 1.03 at 300 °C and decreased to 0.46 at 635 °C. Detailed investigation of the worn surfaces was undertaken using site-specific transmission electron microscopy (TEM) via focused ion beam (FIB) microscopy, along with Fourier transform infrared (FTIR) and Raman spectroscopy. Microstructure and tribo-induced chemical reactions at these temperatures were correlated with the coating’s wear and friction behaviour. The friction behaviour at room temperature is attributed to the presence of a thin hydrated tribofilm and the presence of V2O5 at high temperature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000340
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2926–2935
Titre : Impact of intrinsic localized modes of atomic motion on materials properties Type de document : texte imprimé Auteurs : M.E. Manley, Auteur Année de publication : 2011 Article en page(s) : pp. 2926–2935 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Intrinsic localized modes Point defects Diffusion Mechanical properties Thermal conductivity Résumé : Recent neutron and X-ray scattering measurements show intrinsic localized modes (ILMs) in metallic uranium and ionic sodium iodide. Here, the role ILMs play in the behavior of these materials is examined. With the thermal activation of ILMs, thermal expansion is enhanced, made more anisotropic, and, at a microscopic level, becomes inhomogeneous. Interstitial diffusion, ionic conductivity, the annealing rate of radiation damage, and void growth are all influenced by ILMs. The lattice thermal conductivity is suppressed at the ILM activation temperature, while no impact is observed in the electrical conductivity. This complement of transport properties suggests that ILMs could improve thermoelectric performance. Ramifications also include thermal ratcheting, a transition from brittle to ductile fracture, and possibly a phase transformation in uranium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000352 [article] Impact of intrinsic localized modes of atomic motion on materials properties [texte imprimé] / M.E. Manley, Auteur . - 2011 . - pp. 2926–2935.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2926–2935
Mots-clés : Intrinsic localized modes Point defects Diffusion Mechanical properties Thermal conductivity Résumé : Recent neutron and X-ray scattering measurements show intrinsic localized modes (ILMs) in metallic uranium and ionic sodium iodide. Here, the role ILMs play in the behavior of these materials is examined. With the thermal activation of ILMs, thermal expansion is enhanced, made more anisotropic, and, at a microscopic level, becomes inhomogeneous. Interstitial diffusion, ionic conductivity, the annealing rate of radiation damage, and void growth are all influenced by ILMs. The lattice thermal conductivity is suppressed at the ILM activation temperature, while no impact is observed in the electrical conductivity. This complement of transport properties suggests that ILMs could improve thermoelectric performance. Ramifications also include thermal ratcheting, a transition from brittle to ductile fracture, and possibly a phase transformation in uranium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000352
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2936–2947
Titre : The 18R and 14H long-period stacking ordered structures in Mg–Y–Zn alloys Type de document : texte imprimé Auteurs : Y.M. Zhu, Auteur ; A.J. Morton, Auteur ; J.F. Nie, Auteur Année de publication : 2011 Article en page(s) : pp. 2936–2947 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium alloys 18R 14H Crystal structure Ordering Résumé : The 18R and 14H long-period stacking ordered structures formed in Mg–Y–Zn alloys are examined systematically using electron diffraction and high-angle annular dark-field scanning transmission electron microscopy. In contrast to that reported in previous studies, the 18R structure is demonstrated to have an ordered base-centred monoclinic lattice, with Y and Zn atoms having an ordered arrangement in the closely packed planes. Furthermore, the composition of 18R is suggested to be Mg10Y1Zn1, instead of the Mg12Y1Zn1 composition that is commonly accepted. The 14H structure is also ordered. It has a hexagonal unit cell; the ordered distribution of Y and Zn atoms in the unit cell is similar to that in the 18R and its composition is Mg12Y1Zn1. The 18R unit cell has three ABCA-type building blocks arranged in the same shear direction, while the 14H unit cell has two ABCA-type building blocks arranged in opposite shear directions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000364 [article] The 18R and 14H long-period stacking ordered structures in Mg–Y–Zn alloys [texte imprimé] / Y.M. Zhu, Auteur ; A.J. Morton, Auteur ; J.F. Nie, Auteur . - 2011 . - pp. 2936–2947.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2936–2947
Mots-clés : Magnesium alloys 18R 14H Crystal structure Ordering Résumé : The 18R and 14H long-period stacking ordered structures formed in Mg–Y–Zn alloys are examined systematically using electron diffraction and high-angle annular dark-field scanning transmission electron microscopy. In contrast to that reported in previous studies, the 18R structure is demonstrated to have an ordered base-centred monoclinic lattice, with Y and Zn atoms having an ordered arrangement in the closely packed planes. Furthermore, the composition of 18R is suggested to be Mg10Y1Zn1, instead of the Mg12Y1Zn1 composition that is commonly accepted. The 14H structure is also ordered. It has a hexagonal unit cell; the ordered distribution of Y and Zn atoms in the unit cell is similar to that in the 18R and its composition is Mg12Y1Zn1. The 18R unit cell has three ABCA-type building blocks arranged in the same shear direction, while the 14H unit cell has two ABCA-type building blocks arranged in opposite shear directions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000364
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2948–2956
Titre : Estimation of interfacial fracture toughness based on progressive edge delamination of a thin transparent coating on a polymer substrate Type de document : texte imprimé Auteurs : S. Tarasovs, Auteur ; J. Andersons, Auteur ; Y. Leterrier, Auteur Année de publication : 2011 Article en page(s) : pp. 2948–2956 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Coatings Adhesion Tension test Toughness Finite element analysis Résumé : Evaluation of interfacial toughness of sub-micron-thickness layers deposited on a ductile substrate is a challenging task which has motivated different experimental approaches. Fragmentation testing was used in the present study as a means of interface characterization of a silicon–nitride-coated polyimide substrate. During the test, after an initial rapid segmentation–cracking phase, the coating fragments developed edge delaminations which propagated in a stable manner with further increase in the applied strain. The debonding process was modelled by the finite element method incorporating a cohesive zone at the front of the interfacial crack. The edge cracks were found to be dominated by mode II loading. By fitting the predicted delamination evolution to the experimental data for coating fragments of differing geometry, the mode II critical energy release rate was estimated at 30 J m−2. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000376 [article] Estimation of interfacial fracture toughness based on progressive edge delamination of a thin transparent coating on a polymer substrate [texte imprimé] / S. Tarasovs, Auteur ; J. Andersons, Auteur ; Y. Leterrier, Auteur . - 2011 . - pp. 2948–2956.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2948–2956
Mots-clés : Coatings Adhesion Tension test Toughness Finite element analysis Résumé : Evaluation of interfacial toughness of sub-micron-thickness layers deposited on a ductile substrate is a challenging task which has motivated different experimental approaches. Fragmentation testing was used in the present study as a means of interface characterization of a silicon–nitride-coated polyimide substrate. During the test, after an initial rapid segmentation–cracking phase, the coating fragments developed edge delaminations which propagated in a stable manner with further increase in the applied strain. The debonding process was modelled by the finite element method incorporating a cohesive zone at the front of the interfacial crack. The edge cracks were found to be dominated by mode II loading. By fitting the predicted delamination evolution to the experimental data for coating fragments of differing geometry, the mode II critical energy release rate was estimated at 30 J m−2. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000376
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2957–2967
Titre : Influence of closure on the 3D propagation of fatigue cracks in a nodular cast iron investigated by X-ray tomography and 3D volume correlation Type de document : texte imprimé Auteurs : Nathalie Limodin, Auteur ; Julien Réthoré, Auteur ; Jean-Yves Buffière, Auteur Année de publication : 2011 Article en page(s) : pp. 2957–2967 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Synchrotron X-ray microtomography 3D digital image correlation Crack propagation Stress intensity factors Nodular graphite cast iron Résumé : Synchrotron X-ray tomography was performed during in situ fatigue crack propagation in two small-size specimens made of nodular graphite cast iron. While direct image analysis allows us to retrieve the successive positions of the crack front, and to detect local crack retardation, volume correlation allows for the measurement of displacement fields in the bulk of the specimen. The stress intensity factors (SIFs), which are extracted from the measured displacement fields and the corresponding local crack growth rate all along the front, are in good agreement with published results. In particular, it is possible to link the non-propagation of a crack with crack closure in the crack opening displacement maps or with a local value of the measured SIF range. It is shown that a non-uniform closure process along the crack front induces an asymmetric arrest/growth of the crack. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000388 [article] Influence of closure on the 3D propagation of fatigue cracks in a nodular cast iron investigated by X-ray tomography and 3D volume correlation [texte imprimé] / Nathalie Limodin, Auteur ; Julien Réthoré, Auteur ; Jean-Yves Buffière, Auteur . - 2011 . - pp. 2957–2967.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2957–2967
Mots-clés : Synchrotron X-ray microtomography 3D digital image correlation Crack propagation Stress intensity factors Nodular graphite cast iron Résumé : Synchrotron X-ray tomography was performed during in situ fatigue crack propagation in two small-size specimens made of nodular graphite cast iron. While direct image analysis allows us to retrieve the successive positions of the crack front, and to detect local crack retardation, volume correlation allows for the measurement of displacement fields in the bulk of the specimen. The stress intensity factors (SIFs), which are extracted from the measured displacement fields and the corresponding local crack growth rate all along the front, are in good agreement with published results. In particular, it is possible to link the non-propagation of a crack with crack closure in the crack opening displacement maps or with a local value of the measured SIF range. It is shown that a non-uniform closure process along the crack front induces an asymmetric arrest/growth of the crack. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000388
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2968–2977
Titre : Stability, structure and electronic properties of γ-Fe23C6 from first-principles theory Type de document : texte imprimé Auteurs : C.M. Fang, Auteur ; M.A. van Huis, Auteur ; M.H.F. Sluiter, Auteur Année de publication : 2011 Article en page(s) : pp. 2968–2977 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Iron carbides First-principles’ calculations Crystal structure Stability and formation Résumé : First-principles’ calculations of GGA and GGA + U type have been performed for γ-Fe23C6, a complex iron carbide with 116 atom in the unit cell. GGA results were found to be in better agreement with experimental data than GGA + U results. Various occupancies for Wyckoff positions and corresponding magnetic orderings have been explored. Our calculations reveal that the crystal structure is composed of a framework of strongly linked Fe atoms, and additional stabilizing Fe and C atoms positioned in cavities. The local electronic and magnetic properties vary strongly among the non-equivalent Fe sites in γ-Fe23C6. The lattice parameters of γ-Fe23C6 match those of austenite well. Surprisingly, pure γ-Fe23C6 is found to be more stable than commonly occurring θ-Fe3C cementite. Moreover, the calculations show low vacancy energy (about 0.37 eV) for Fe at 4a sites in γ-Fe23C6. Conditions of formation and factors hampering the formation of γ-Fe23C6 in steel manufacturing processes are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000039X [article] Stability, structure and electronic properties of γ-Fe23C6 from first-principles theory [texte imprimé] / C.M. Fang, Auteur ; M.A. van Huis, Auteur ; M.H.F. Sluiter, Auteur . - 2011 . - pp. 2968–2977.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2968–2977
Mots-clés : Iron carbides First-principles’ calculations Crystal structure Stability and formation Résumé : First-principles’ calculations of GGA and GGA + U type have been performed for γ-Fe23C6, a complex iron carbide with 116 atom in the unit cell. GGA results were found to be in better agreement with experimental data than GGA + U results. Various occupancies for Wyckoff positions and corresponding magnetic orderings have been explored. Our calculations reveal that the crystal structure is composed of a framework of strongly linked Fe atoms, and additional stabilizing Fe and C atoms positioned in cavities. The local electronic and magnetic properties vary strongly among the non-equivalent Fe sites in γ-Fe23C6. The lattice parameters of γ-Fe23C6 match those of austenite well. Surprisingly, pure γ-Fe23C6 is found to be more stable than commonly occurring θ-Fe3C cementite. Moreover, the calculations show low vacancy energy (about 0.37 eV) for Fe at 4a sites in γ-Fe23C6. Conditions of formation and factors hampering the formation of γ-Fe23C6 in steel manufacturing processes are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000039X
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2978–2987
Titre : Dislocation core structure and dynamics in two atomic models of α-zirconium Type de document : texte imprimé Auteurs : H.A. Khater, Auteur ; D. J. Bacon, Auteur Année de publication : 2011 Article en page(s) : pp. 2978–2987 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation dynamics Dislocation structure Stacking faults Molecular dynamics simulations Zirconium Résumé : Properties of basal and first order prism plane dislocations with Burgers vector 1/3 〈View the MathML source〉 in α-Zr have been investigated by computer simulation. Results for a recent interatomic potential (MA07) are assessed and compared with an older one (AWB95). The elastic constants have been calculated with the inner relaxations allowed for and the energy and vector of metastable stacking faults have been determined and compared with published ab initio estimates. The core of the screw dislocation spreads principally in the prism plane in the MA07 model, in contrast to basal plane dissociation in the AWB95 model, and the prism-to-basal ratio of the Peierls stress for the screw is 0.28 with the MA07 model, compared with 3.31 with the AWB95 model. Simulation of the dynamics of dislocation motion under applied stress reveal how the drag coefficient varies with slip system and temperature. The results for the MA07 model are consistent with the known slip geometry of Zr, suggesting that it offers significant advantages for large-scale atomic simulation of dislocation behaviour. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000042X [article] Dislocation core structure and dynamics in two atomic models of α-zirconium [texte imprimé] / H.A. Khater, Auteur ; D. J. Bacon, Auteur . - 2011 . - pp. 2978–2987.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2978–2987
Mots-clés : Dislocation dynamics Dislocation structure Stacking faults Molecular dynamics simulations Zirconium Résumé : Properties of basal and first order prism plane dislocations with Burgers vector 1/3 〈View the MathML source〉 in α-Zr have been investigated by computer simulation. Results for a recent interatomic potential (MA07) are assessed and compared with an older one (AWB95). The elastic constants have been calculated with the inner relaxations allowed for and the energy and vector of metastable stacking faults have been determined and compared with published ab initio estimates. The core of the screw dislocation spreads principally in the prism plane in the MA07 model, in contrast to basal plane dissociation in the AWB95 model, and the prism-to-basal ratio of the Peierls stress for the screw is 0.28 with the MA07 model, compared with 3.31 with the AWB95 model. Simulation of the dynamics of dislocation motion under applied stress reveal how the drag coefficient varies with slip system and temperature. The results for the MA07 model are consistent with the known slip geometry of Zr, suggesting that it offers significant advantages for large-scale atomic simulation of dislocation behaviour. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000042X
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2988–2998
Titre : Mechanical behavior and microstructural evolution of a Mg AZ31 sheet at dynamic strain rates Type de document : texte imprimé Auteurs : I. Ulacia, Auteur ; N.V. Dudamell, Auteur ; F. Gálvez, Auteur Année de publication : 2011 Article en page(s) : pp. 2988–2998 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : AZ31 High strain rate Twinning Slip Anisotropy Résumé : The mechanical behavior of an AZ31 Mg sheet has been investigated at high strain rate (103 s−1) and compared with that observed at low rates (10−3 s−1). Dynamic tests were carried out using a Hopkinson bar at temperatures between 25 and 400 °C. Tensile tests were carried out along the rolling and transverse directions and compression tests along the rolling and the normal directions in both strain rate ranges. The tension–compression yield asymmetry as well as the yield and flow stress in-plane and out-of-plane anisotropies were investigated. The microstructure of the initial and tested samples was examined by electron backscatter diffraction. The dynamic mechanical behavior is characterized by the following observations. At high temperatures the yield asymmetry and the yield anisotropies remain present and twinning is highly active. The rate of decrease in the critical resolved shear stress of non-basal systems with temperature is smaller than at quasi-static rates. Rotational recrystallization mechanisms are activated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000431 [article] Mechanical behavior and microstructural evolution of a Mg AZ31 sheet at dynamic strain rates [texte imprimé] / I. Ulacia, Auteur ; N.V. Dudamell, Auteur ; F. Gálvez, Auteur . - 2011 . - pp. 2988–2998.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2988–2998
Mots-clés : AZ31 High strain rate Twinning Slip Anisotropy Résumé : The mechanical behavior of an AZ31 Mg sheet has been investigated at high strain rate (103 s−1) and compared with that observed at low rates (10−3 s−1). Dynamic tests were carried out using a Hopkinson bar at temperatures between 25 and 400 °C. Tensile tests were carried out along the rolling and transverse directions and compression tests along the rolling and the normal directions in both strain rate ranges. The tension–compression yield asymmetry as well as the yield and flow stress in-plane and out-of-plane anisotropies were investigated. The microstructure of the initial and tested samples was examined by electron backscatter diffraction. The dynamic mechanical behavior is characterized by the following observations. At high temperatures the yield asymmetry and the yield anisotropies remain present and twinning is highly active. The rate of decrease in the critical resolved shear stress of non-basal systems with temperature is smaller than at quasi-static rates. Rotational recrystallization mechanisms are activated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000431
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2999–3005
Titre : Atomic-scale imaging and the effect of yttrium on the fracture toughness of silicon carbide ceramics Type de document : texte imprimé Auteurs : A.M. Kueck, Auteur ; Q.M. Ramasse, Auteur ; L.C. De Jonghe, Auteur Année de publication : 2011 Article en page(s) : pp. 2999–3005 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ceramics Silicon carbide Yttrium dopants Fracture toughness Résumé : In SiC sintered with Al, B and C additions (ABC–SiC), the presence of Y in the Al–Si–O–C grain-boundary phase leads to less frequent crack deflection and lower toughness. When Y is absent from the grain-boundary phase and remains in the triple pockets, crack deflection is restored, and higher toughness results from grain-bridging mechanisms. The observations are consistent with elastic modulus changes in the intergranular phase, which depend on their yttria and silica content, and indicate that these can play an important role in determining crack deflection. While high-toughness ceramics such as ABC–SiC and Si3N4 rely on sintering additives forming crack-deflecting intergranular films, the present case is a striking example where the presence of a segregant in the grain boundary promotes transgranular fracture by raising the modulus of the nanoscale intergranular grain-boundary film. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000455 [article] Atomic-scale imaging and the effect of yttrium on the fracture toughness of silicon carbide ceramics [texte imprimé] / A.M. Kueck, Auteur ; Q.M. Ramasse, Auteur ; L.C. De Jonghe, Auteur . - 2011 . - pp. 2999–3005.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 2999–3005
Mots-clés : Ceramics Silicon carbide Yttrium dopants Fracture toughness Résumé : In SiC sintered with Al, B and C additions (ABC–SiC), the presence of Y in the Al–Si–O–C grain-boundary phase leads to less frequent crack deflection and lower toughness. When Y is absent from the grain-boundary phase and remains in the triple pockets, crack deflection is restored, and higher toughness results from grain-bridging mechanisms. The observations are consistent with elastic modulus changes in the intergranular phase, which depend on their yttria and silica content, and indicate that these can play an important role in determining crack deflection. While high-toughness ceramics such as ABC–SiC and Si3N4 rely on sintering additives forming crack-deflecting intergranular films, the present case is a striking example where the presence of a segregant in the grain boundary promotes transgranular fracture by raising the modulus of the nanoscale intergranular grain-boundary film. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000455
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3006–3013
Titre : Size effects in aluminium alloy castings Type de document : texte imprimé Auteurs : Q.G. Wang, Auteur ; M. Praud, Auteur ; A. Needleman, Auteur Année de publication : 2011 Article en page(s) : pp. 3006–3013 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Al castings Hall–Petch Dendrite arm spacing Discrete dislocations Résumé : A finding by Benzerga et al. (Acta Mater 2001; 49:3071) that the yield strength of Al–7Si–0.3Mg castings is smaller for castings with a fine secondary dendrite arm spacing (SDAS) than for those with a coarse SDAS is revisited. Previous experimental data for Al–Si–Mg castings are reviewed, and new experiments carried out, both on the original castings used in Benzerga et al. and on Al–Si binary alloy castings whose microstructures more closely conform to the theoretical model of Benzerga et al. The experimental results show that the inverse size effect reported by Benzerga et al. was a consequence of different heat-treatments applied to the original castings, rather than to any intrinsic size effect. The present results confirm that there is a negligibly small size effect in both heat-treatable (Al–Si–Mg) and non-heat-treatable (Al–Si) castings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000467 [article] Size effects in aluminium alloy castings [texte imprimé] / Q.G. Wang, Auteur ; M. Praud, Auteur ; A. Needleman, Auteur . - 2011 . - pp. 3006–3013.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3006–3013
Mots-clés : Al castings Hall–Petch Dendrite arm spacing Discrete dislocations Résumé : A finding by Benzerga et al. (Acta Mater 2001; 49:3071) that the yield strength of Al–7Si–0.3Mg castings is smaller for castings with a fine secondary dendrite arm spacing (SDAS) than for those with a coarse SDAS is revisited. Previous experimental data for Al–Si–Mg castings are reviewed, and new experiments carried out, both on the original castings used in Benzerga et al. and on Al–Si binary alloy castings whose microstructures more closely conform to the theoretical model of Benzerga et al. The experimental results show that the inverse size effect reported by Benzerga et al. was a consequence of different heat-treatments applied to the original castings, rather than to any intrinsic size effect. The present results confirm that there is a negligibly small size effect in both heat-treatable (Al–Si–Mg) and non-heat-treatable (Al–Si) castings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000467
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3014–3021
Titre : Microstructural characterization of alumina–zirconia layered ceramics using positron annihilation spectroscopy Type de document : texte imprimé Auteurs : P. Parente, Auteur ; Y. Ortega, Auteur ; B. Savoini, Auteur Année de publication : 2011 Article en page(s) : pp. 3014–3021 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Residual stresses Ceramics Multilayers Positron annihilation Nanoindentation Résumé : Positron annihilation spectroscopy (PAS), indentation, nanoindentation experiments and scanning electron microscopy (SEM) observations were performed on Al2O3–ZrO2 laminates samples to assess the effect of residual stresses on their mechanical and microstructural properties. Layered samples were implemented by slip-casting, constituted by two thin Al2O3 external layers and an intermediate thick one, consisting of a mixture of Al2O3 and monoclinic ZrO2 in the range 0–30 vol.%. In these systems residual tensile stresses fields were generated inside the external layers during cooling from the sintering temperature, by the expansion of the adjacent ZrO2-containing layer. SEM observations showed the microstructural effects due to the level of tension related to the zirconia content. A correlation between the PAS parameters and the microstructural changes caused by the presence of residual stresses was found. Nanoindentation measurements were used to trace the sign and magnitude of the residual stress gradient across the interface between the layers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000479 [article] Microstructural characterization of alumina–zirconia layered ceramics using positron annihilation spectroscopy [texte imprimé] / P. Parente, Auteur ; Y. Ortega, Auteur ; B. Savoini, Auteur . - 2011 . - pp. 3014–3021.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3014–3021
Mots-clés : Residual stresses Ceramics Multilayers Positron annihilation Nanoindentation Résumé : Positron annihilation spectroscopy (PAS), indentation, nanoindentation experiments and scanning electron microscopy (SEM) observations were performed on Al2O3–ZrO2 laminates samples to assess the effect of residual stresses on their mechanical and microstructural properties. Layered samples were implemented by slip-casting, constituted by two thin Al2O3 external layers and an intermediate thick one, consisting of a mixture of Al2O3 and monoclinic ZrO2 in the range 0–30 vol.%. In these systems residual tensile stresses fields were generated inside the external layers during cooling from the sintering temperature, by the expansion of the adjacent ZrO2-containing layer. SEM observations showed the microstructural effects due to the level of tension related to the zirconia content. A correlation between the PAS parameters and the microstructural changes caused by the presence of residual stresses was found. Nanoindentation measurements were used to trace the sign and magnitude of the residual stress gradient across the interface between the layers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000479
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3022–3034
Titre : Microband evolution during large plastic strains of stable {1 1 0}〈1 1 2〉 Al and Al–Mn crystals Type de document : texte imprimé Auteurs : A. Albou, Auteur ; J.H. Driver, Auteur ; C. Maurice, Auteur Année de publication : 2011 Article en page(s) : pp. 3022–3034 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Microstructure Microbands Disorientation EBSD Aluminium Résumé : The deformation microstructures of Al and Al–Mn {1 1 0}〈1 1 2〉 single crystals have been characterized after room temperature channel-die compression up to true strains of 2.1. The evolution of local misorientations and microband structures were quantified by high-resolution electron backscatter diffraction in a field emission gun scanning electron microscope and their alignments compared with the traces of active slip planes and macroscopic shear stress planes. During plane-strain compression these “Brass” oriented crystals remain stable in terms of the final, average, orientation, with a small orientation spread. However, the microband alignment varies with strain and also with solute content. There is a general tendency for the microbands to be both crystallographic and non-crystallographic at low strains, then crystallographic, and finally mixed again at high strains (with some lamellar banding). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000480 [article] Microband evolution during large plastic strains of stable {1 1 0}〈1 1 2〉 Al and Al–Mn crystals [texte imprimé] / A. Albou, Auteur ; J.H. Driver, Auteur ; C. Maurice, Auteur . - 2011 . - pp. 3022–3034.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3022–3034
Mots-clés : Microstructure Microbands Disorientation EBSD Aluminium Résumé : The deformation microstructures of Al and Al–Mn {1 1 0}〈1 1 2〉 single crystals have been characterized after room temperature channel-die compression up to true strains of 2.1. The evolution of local misorientations and microband structures were quantified by high-resolution electron backscatter diffraction in a field emission gun scanning electron microscope and their alignments compared with the traces of active slip planes and macroscopic shear stress planes. During plane-strain compression these “Brass” oriented crystals remain stable in terms of the final, average, orientation, with a small orientation spread. However, the microband alignment varies with strain and also with solute content. There is a general tendency for the microbands to be both crystallographic and non-crystallographic at low strains, then crystallographic, and finally mixed again at high strains (with some lamellar banding). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000480
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3035–3041
Titre : Color-tunable luminescence of Eu3+ in LaF3 embedded nanocomposite for light emitting diode Type de document : texte imprimé Auteurs : Daqin Chen, Auteur ; Yunlong Yu, Auteur ; Ping Huang, Auteur Année de publication : 2011 Article en page(s) : pp. 3035–3041 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Crystallization Nanocomposite Microstructure Optical properties High-resolution electron microscopy Résumé : Eu3+-doped transparent nanocomposite of SiO2–Al2O3–NaF–LaF3 was fabricated by melt-quenching and subsequent heating. X-ray diffraction and transmission electron microscopy analyses evidenced that hexagonal LaF3 nanocrystals were homogeneously precipitated among the aluminosilicate glass matrix. The distribution of Eu3+ ions in the nanocomposite was investigated by energy dispersive X-ray spectroscopy, photoluminescence and time-resolved luminescence spectra. The nanocomposite exhibited intense blue and green emissions originating from the 5D1,2,3 levels of Eu3+ incorporated in the low-phonon-energy LaF3 nanocrystals, and red emission corresponding to the Eu3+:5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions, under the excitation of single wavelength light at 394 nm. By adjusting the Eu3+ doping content, various luminescent colors, including perfect white light, were easily tuned through cross relaxation processes between Eu3+ ions. The results suggest that the Eu3+-doped transparent nanocomposite could be potentially applicable as a white-light-emitting material under UV chip excitation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000492 [article] Color-tunable luminescence of Eu3+ in LaF3 embedded nanocomposite for light emitting diode [texte imprimé] / Daqin Chen, Auteur ; Yunlong Yu, Auteur ; Ping Huang, Auteur . - 2011 . - pp. 3035–3041.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3035–3041
Mots-clés : Crystallization Nanocomposite Microstructure Optical properties High-resolution electron microscopy Résumé : Eu3+-doped transparent nanocomposite of SiO2–Al2O3–NaF–LaF3 was fabricated by melt-quenching and subsequent heating. X-ray diffraction and transmission electron microscopy analyses evidenced that hexagonal LaF3 nanocrystals were homogeneously precipitated among the aluminosilicate glass matrix. The distribution of Eu3+ ions in the nanocomposite was investigated by energy dispersive X-ray spectroscopy, photoluminescence and time-resolved luminescence spectra. The nanocomposite exhibited intense blue and green emissions originating from the 5D1,2,3 levels of Eu3+ incorporated in the low-phonon-energy LaF3 nanocrystals, and red emission corresponding to the Eu3+:5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions, under the excitation of single wavelength light at 394 nm. By adjusting the Eu3+ doping content, various luminescent colors, including perfect white light, were easily tuned through cross relaxation processes between Eu3+ ions. The results suggest that the Eu3+-doped transparent nanocomposite could be potentially applicable as a white-light-emitting material under UV chip excitation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000492
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3042–3049
Titre : Hydrogen behavior in nanocrystalline titanium thin films Type de document : texte imprimé Auteurs : E. Tal-Gutelmacher, Auteur ; R. Gemma, Auteur ; A. Pundt, Auteur Année de publication : 2011 Article en page(s) : pp. 3042–3049 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Titanium Thin films Sputtering Hydrogen Stress Résumé : Nanocrystalline titanium films of different thicknesses, sputtered on sapphire substrates, were charged electrochemically with hydrogen. Hydrogen absorption and the thermodynamics of the nanocrystalline Ti–H thin film system were studied using electromotive force (EMF) measurements. The phase boundaries obtained from the EMF–pressure–concentration curves were confirmed by X-ray diffraction, complemented by in situ stress measurements during hydrogen charging. The change in the stress increase with hydrogen concentration was found to be in good agreement with the obtained phase boundaries. In comparison to bulk Ti–H system, considerable changes, such as shifted phase boundaries, and narrowed and sloped miscibility gaps, were observed in Ti–H thin films. These changes vary among the films of different crystalline orientation and are attributed to both microstructural effects and stress contributions. The influence of the initial crystallographic growth orientation of Ti films on the measured thermodynamic isotherms, phase transitions and stress development is discussed in detail. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000509 [article] Hydrogen behavior in nanocrystalline titanium thin films [texte imprimé] / E. Tal-Gutelmacher, Auteur ; R. Gemma, Auteur ; A. Pundt, Auteur . - 2011 . - pp. 3042–3049.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3042–3049
Mots-clés : Titanium Thin films Sputtering Hydrogen Stress Résumé : Nanocrystalline titanium films of different thicknesses, sputtered on sapphire substrates, were charged electrochemically with hydrogen. Hydrogen absorption and the thermodynamics of the nanocrystalline Ti–H thin film system were studied using electromotive force (EMF) measurements. The phase boundaries obtained from the EMF–pressure–concentration curves were confirmed by X-ray diffraction, complemented by in situ stress measurements during hydrogen charging. The change in the stress increase with hydrogen concentration was found to be in good agreement with the obtained phase boundaries. In comparison to bulk Ti–H system, considerable changes, such as shifted phase boundaries, and narrowed and sloped miscibility gaps, were observed in Ti–H thin films. These changes vary among the films of different crystalline orientation and are attributed to both microstructural effects and stress contributions. The influence of the initial crystallographic growth orientation of Ti films on the measured thermodynamic isotherms, phase transitions and stress development is discussed in detail. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000509
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3050–3058
Titre : Critical properties of symmetric nanoscale metal–ferroelectric–metal capacitors Type de document : texte imprimé Auteurs : Yue Zheng, Auteur ; M.Q. Cai, Auteur ; C.H. Woo, Auteur Année de publication : 2011 Article en page(s) : pp. 3050–3058 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ferroelectric Curie temperature Critical thickness Stability analysis Résumé : The size, surface and interface effects on the magnitude and stability of spontaneous polarization in a symmetric nanoscale ferroelectric capacitor were studied by analyzing its evolutionary trajectory based on a thermodynamic model. Analytic expressions of the Curie temperature, spontaneous polarization, critical thickness and the Curie–Weiss relation were derived, taking into account the effects of the depolarization field, built-in electric field, interfaces and surfaces. Our results show that the critical properties are not only functions of the ambient temperature, misfit strain and electromechanical boundary conditions, but also depend on the characteristics of electrodes, surfaces and interfaces, through the incomplete charge compensation, near-surface variation of polarization and work function steps of ferroelectric–electrode interfaces, which are adjustable. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000534 [article] Critical properties of symmetric nanoscale metal–ferroelectric–metal capacitors [texte imprimé] / Yue Zheng, Auteur ; M.Q. Cai, Auteur ; C.H. Woo, Auteur . - 2011 . - pp. 3050–3058.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3050–3058
Mots-clés : Ferroelectric Curie temperature Critical thickness Stability analysis Résumé : The size, surface and interface effects on the magnitude and stability of spontaneous polarization in a symmetric nanoscale ferroelectric capacitor were studied by analyzing its evolutionary trajectory based on a thermodynamic model. Analytic expressions of the Curie temperature, spontaneous polarization, critical thickness and the Curie–Weiss relation were derived, taking into account the effects of the depolarization field, built-in electric field, interfaces and surfaces. Our results show that the critical properties are not only functions of the ambient temperature, misfit strain and electromechanical boundary conditions, but also depend on the characteristics of electrodes, surfaces and interfaces, through the incomplete charge compensation, near-surface variation of polarization and work function steps of ferroelectric–electrode interfaces, which are adjustable. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000534
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3059–3067
Titre : Melting of Ni nanowires with and without oxide capping Type de document : texte imprimé Auteurs : Z.F. Zhou, Auteur ; Y.C. Zhou, Auteur ; Y. Pan, Auteur Année de publication : 2011 Article en page(s) : pp. 3059–3067 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel Nanocrystalline materials Melting point Surface Grain boundaries Résumé : The effects of wire diameter and grain size on the melting point of Ni nanowires with and without oxide capping were systematically examined. It was found that, for uncapped Ni nanowires, the melting point drops monotonically with grain size and also with the nanowire diameter; for oxide-capped Ni nanowires, the melting point rises when the nanowire diameter is decreased. Findings indicate that: (i) the reduced cohesive energy of under-coordinated atoms at the surface skin or grain boundaries and the fraction of such under-coordinated atoms dominate the undercooling of pure Ni nanowires; (ii) bond nature alteration by oxidation strengthens the surface bonds and hence results in the observed overheating; (iii) the bonds in the core interior retain their bulk nature, making contribution to neither the observed undercooling nor overheating. All these findings are very consistent with the bond–order–length–strength theoretical predictions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000546 [article] Melting of Ni nanowires with and without oxide capping [texte imprimé] / Z.F. Zhou, Auteur ; Y.C. Zhou, Auteur ; Y. Pan, Auteur . - 2011 . - pp. 3059–3067.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3059–3067
Mots-clés : Nickel Nanocrystalline materials Melting point Surface Grain boundaries Résumé : The effects of wire diameter and grain size on the melting point of Ni nanowires with and without oxide capping were systematically examined. It was found that, for uncapped Ni nanowires, the melting point drops monotonically with grain size and also with the nanowire diameter; for oxide-capped Ni nanowires, the melting point rises when the nanowire diameter is decreased. Findings indicate that: (i) the reduced cohesive energy of under-coordinated atoms at the surface skin or grain boundaries and the fraction of such under-coordinated atoms dominate the undercooling of pure Ni nanowires; (ii) bond nature alteration by oxidation strengthens the surface bonds and hence results in the observed overheating; (iii) the bonds in the core interior retain their bulk nature, making contribution to neither the observed undercooling nor overheating. All these findings are very consistent with the bond–order–length–strength theoretical predictions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000546
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3068–3072
Titre : Broadband anti-reflection and enhanced field emission from catalyst-free grown small-sized ITO nanowires at a low temperature Type de document : texte imprimé Auteurs : Neng Wan, Auteur ; Jun Xu, Auteur ; Guran Chen, Auteur Année de publication : 2011 Article en page(s) : pp. 3068–3072 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : ITO Nanostructure e-Beam evaporation Field emission Anti-reflection Résumé : Small-sized indium tin oxide (ITO) nanowires were fabricated using the electron beam evaporation (EBE) technique at low temperature (∼150 °C) without adding any catalyst. The ITO nanowires have a typical diameter of around 10 nm and a length of more than 100 nm, with body-centered cubic crystal structures that grow along the 〈1 0 0〉 directions, as revealed by transmission electron microscopy. The growth mechanism of the branched ITO nanowires was found to be a vapor–solid process. The nanowire films show a broadband anti-reflection property due to the graded refraction index from the film surface to the substrate. Enhanced field emission properties with a low turn-on electric field and a high field enhancement factor were also observed in the ITO nanowires. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000558 [article] Broadband anti-reflection and enhanced field emission from catalyst-free grown small-sized ITO nanowires at a low temperature [texte imprimé] / Neng Wan, Auteur ; Jun Xu, Auteur ; Guran Chen, Auteur . - 2011 . - pp. 3068–3072.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3068–3072
Mots-clés : ITO Nanostructure e-Beam evaporation Field emission Anti-reflection Résumé : Small-sized indium tin oxide (ITO) nanowires were fabricated using the electron beam evaporation (EBE) technique at low temperature (∼150 °C) without adding any catalyst. The ITO nanowires have a typical diameter of around 10 nm and a length of more than 100 nm, with body-centered cubic crystal structures that grow along the 〈1 0 0〉 directions, as revealed by transmission electron microscopy. The growth mechanism of the branched ITO nanowires was found to be a vapor–solid process. The nanowire films show a broadband anti-reflection property due to the graded refraction index from the film surface to the substrate. Enhanced field emission properties with a low turn-on electric field and a high field enhancement factor were also observed in the ITO nanowires. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000558
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3073–3078
Titre : Control of austenite to martensite transformation through equal channel angular pressing aided by thermodynamic calculations Type de document : texte imprimé Auteurs : F. Hajiakbari, Auteur ; M. Nili-Ahmadabadi, Auteur ; B. Poorganji, Auteur Année de publication : 2011 Article en page(s) : pp. 3073–3078 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Martensitic phase transformation Driving force Equal channel angular pressing Résumé : The martensite start temperature and driving force were calculated for the austenite to martensite transformation of a dual-phase bainitic ferrite–austenite steel at room temperature. The mechanical energy was estimated during the first and the second pass of equal channel angular pressing (ECAP). The applied mechanical energy during the first pass is not enough to induce the austenite to martensite transformation. However, the mechanical energy during the second pass can provide the required energy for the martensite formation. Microstructural observations by transmission electron microscopy and scanning electron microscopy of as-received and ECAPed samples confirm the formation of martensite during the second pass. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000741 [article] Control of austenite to martensite transformation through equal channel angular pressing aided by thermodynamic calculations [texte imprimé] / F. Hajiakbari, Auteur ; M. Nili-Ahmadabadi, Auteur ; B. Poorganji, Auteur . - 2011 . - pp. 3073–3078.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3073–3078
Mots-clés : Martensitic phase transformation Driving force Equal channel angular pressing Résumé : The martensite start temperature and driving force were calculated for the austenite to martensite transformation of a dual-phase bainitic ferrite–austenite steel at room temperature. The mechanical energy was estimated during the first and the second pass of equal channel angular pressing (ECAP). The applied mechanical energy during the first pass is not enough to induce the austenite to martensite transformation. However, the mechanical energy during the second pass can provide the required energy for the martensite formation. Microstructural observations by transmission electron microscopy and scanning electron microscopy of as-received and ECAPed samples confirm the formation of martensite during the second pass. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000741
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3079–3090
Titre : Effect of deformation and annealing on the formation and reversion of ε-martensite in an Fe–Mn–C alloy Type de document : texte imprimé Auteurs : Yaping Lü, Auteur ; Bevis Hutchinson, Auteur ; Dmitri A. Molodov, Auteur Année de publication : 2011 Article en page(s) : pp. 3079–3090 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fe–Mn alloys Mechanical twinning ε-martensite Phase transformation Texture Résumé : Microstructure and texture evolution during cold rolling and subsequent annealing were studied in an Fe–22 wt.% Mn–0.376 wt.% C alloy. During rolling the deformation mechanisms were found to be dislocation slip, mechanical twinning, deformation-induced ε-martensite transformation and shear banding. At higher strains, the brass-type texture with a spread towards the Goss-type texture dominated. A decrease in the Cu- and S- components was attributed to the preferential transformation to ε-martensite in Cu- and S-oriented grains. The texture of ε-martensite was sharp and could be described as {1 1 2 9}〈3 3 6 2〉. The orientation relationship {1 1 1}γ//{0 0 0 1}ε and 〈110〉γ//〈1 1 –2 0〉ε between ε-martensite and austenite was observed but only certain variants were selected. On subsequent annealing, the ε-martensite transformed reversely to austenite by a diffusionless mechanism. Changes in length along rolling, normal and transverse directions on heating were anisotropic due to a combination of volume expansion and shape memory effects. The S-texture component increased significantly due to transformation from the ε-martensite. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000753 [article] Effect of deformation and annealing on the formation and reversion of ε-martensite in an Fe–Mn–C alloy [texte imprimé] / Yaping Lü, Auteur ; Bevis Hutchinson, Auteur ; Dmitri A. Molodov, Auteur . - 2011 . - pp. 3079–3090.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3079–3090
Mots-clés : Fe–Mn alloys Mechanical twinning ε-martensite Phase transformation Texture Résumé : Microstructure and texture evolution during cold rolling and subsequent annealing were studied in an Fe–22 wt.% Mn–0.376 wt.% C alloy. During rolling the deformation mechanisms were found to be dislocation slip, mechanical twinning, deformation-induced ε-martensite transformation and shear banding. At higher strains, the brass-type texture with a spread towards the Goss-type texture dominated. A decrease in the Cu- and S- components was attributed to the preferential transformation to ε-martensite in Cu- and S-oriented grains. The texture of ε-martensite was sharp and could be described as {1 1 2 9}〈3 3 6 2〉. The orientation relationship {1 1 1}γ//{0 0 0 1}ε and 〈110〉γ//〈1 1 –2 0〉ε between ε-martensite and austenite was observed but only certain variants were selected. On subsequent annealing, the ε-martensite transformed reversely to austenite by a diffusionless mechanism. Changes in length along rolling, normal and transverse directions on heating were anisotropic due to a combination of volume expansion and shape memory effects. The S-texture component increased significantly due to transformation from the ε-martensite. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000753
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3091–3095
Titre : Identifying close-packed planes in complex crystal structures Type de document : texte imprimé Auteurs : P.M. Kelly, Auteur ; H.-P. Ren, Auteur ; D. Qiu, Auteur Année de publication : 2011 Article en page(s) : pp. 3091–3095 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Crystal structure Modelling Close-packed planes Metals Intermetallic compounds Résumé : It is often necessary to identify close-packed or nearly close-packed planes in a crystal. This can be done by inspection in crystal structures where one atom occupies each lattice point – i.e. face-centred cubic and body-centred cubic crystals. However, in more complex crystal structures intuitive inspection becomes rather difficult. The present paper describes a simple method for identifying close-packed or nearly close-packed planes in crystals containing more than one atom per lattice point. The method also distinguishes between “flat” planes, where all the atom centres lie in the plane, and “rumpled” planes, where the atom centres do not lie in the plane. The extent of the departure from true “flatness” can also be estimated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000765 [article] Identifying close-packed planes in complex crystal structures [texte imprimé] / P.M. Kelly, Auteur ; H.-P. Ren, Auteur ; D. Qiu, Auteur . - 2011 . - pp. 3091–3095.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3091–3095
Mots-clés : Crystal structure Modelling Close-packed planes Metals Intermetallic compounds Résumé : It is often necessary to identify close-packed or nearly close-packed planes in a crystal. This can be done by inspection in crystal structures where one atom occupies each lattice point – i.e. face-centred cubic and body-centred cubic crystals. However, in more complex crystal structures intuitive inspection becomes rather difficult. The present paper describes a simple method for identifying close-packed or nearly close-packed planes in crystals containing more than one atom per lattice point. The method also distinguishes between “flat” planes, where all the atom centres lie in the plane, and “rumpled” planes, where the atom centres do not lie in the plane. The extent of the departure from true “flatness” can also be estimated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000765
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3096–3102
Titre : Nanoscale contact plasticity of crystalline metal : Experiment and analytical investigation via atomistic and discrete dislocation models Type de document : texte imprimé Auteurs : T. Tsuru, Auteur ; Y. Shibutani, Auteur ; Y. Kaji, Auteur Année de publication : 2011 Article en page(s) : pp. 3096–3102 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoplasticity Molecular statics Discrete dislocation mechanics Boundary element method Nanoindentation Résumé : Nanoscale incipient plastic deformation in crystalline metals occurs as the result of the collective motion of dislocations. It is known as “nanoplasticity” and is recognized as the elementary process of the macroscopic deformation. Abrupt increases in indent displacements called displacement bursts were observed in recent nanoindentation experiments; that is, the specific behavior for nanoplasticity. In the present study, experimental tests are first conducted to educe the unique nature of the nanoscale deformation. Subsequently, large-scale atomistic simulations are performed to predict the incipient plastic deformation and a new discrete dislocation model combined with the boundary element analysis is constructed to capture the collective motion of the dislocations. Our results suggest that the incipient plastic deformation requires much higher critical shear stress than the theoretical shear strength due to high compressive stress distribution beneath the indenter, and that the displacement burst is induced by surface rearrangement corresponding to hundreds of dislocation dipoles. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000789 [article] Nanoscale contact plasticity of crystalline metal : Experiment and analytical investigation via atomistic and discrete dislocation models [texte imprimé] / T. Tsuru, Auteur ; Y. Shibutani, Auteur ; Y. Kaji, Auteur . - 2011 . - pp. 3096–3102.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3096–3102
Mots-clés : Nanoplasticity Molecular statics Discrete dislocation mechanics Boundary element method Nanoindentation Résumé : Nanoscale incipient plastic deformation in crystalline metals occurs as the result of the collective motion of dislocations. It is known as “nanoplasticity” and is recognized as the elementary process of the macroscopic deformation. Abrupt increases in indent displacements called displacement bursts were observed in recent nanoindentation experiments; that is, the specific behavior for nanoplasticity. In the present study, experimental tests are first conducted to educe the unique nature of the nanoscale deformation. Subsequently, large-scale atomistic simulations are performed to predict the incipient plastic deformation and a new discrete dislocation model combined with the boundary element analysis is constructed to capture the collective motion of the dislocations. Our results suggest that the incipient plastic deformation requires much higher critical shear stress than the theoretical shear strength due to high compressive stress distribution beneath the indenter, and that the displacement burst is induced by surface rearrangement corresponding to hundreds of dislocation dipoles. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000789
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3103–3116
Titre : Nucleation and thickening of shear bands in nano-scale twin/matrix lamellae of a Cu–Al alloy processed by dynamic plastic deformation Type de document : texte imprimé Auteurs : C.S. Hong, Auteur ; N.R. Tao, Auteur ; X. Huang, Auteur Année de publication : 2011 Article en page(s) : pp. 3103–3116 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dynamic plastic deformation Shear bands Nano-scale twins Nano-grained structure Dislocation structure Résumé : Microstructural evolution associated with the shear banding in nano-scale twin/matrix (T/M) lamellae of a Cu–Al alloy processed by means of dynamic plastic deformation was investigated using transmission electron microscopy (TEM) and high-resolution TEM. The development of a shear band was found to be a two-stage process, namely a nucleation stage resulting in a narrow band composed of nano-sized (sub)grains intersecting the T/M lamellae, followed by a thickening stage of the narrow band into adjacent T/M lamellae regions. The nucleation stage occurred within a narrow region of an almost constant thickness (100–200 nm thick, referred to as “core” region) and consisted of three steps: (1) initiation of localized deformation (bending, necking, and detwinning) against the T/M lamellae, (2) evolution of a dislocation structure within the detwinned band, and (3) transformation of the detwinned dislocation structure (DDS) into a nano-sized (sub)grain structure (NGS). On the two sides of a core region, two transition layers (TRLs) exist where the T/M lamellae experienced much less shear strain. The interface boundaries separating the core region and the TRLs are characterized by very large shear strain gradients accommodated by high density of dislocations. Increasing shear strains leads to thickening of shear bands at the expense of the adjoining T/M lamellae, which is composed of thickening of the core region by transforming the TRLs into the core region with DDS and NGS, analogous to steps (2) and (3) of the nucleation process, and outward movement of the TRLs by deforming the adjoining T/M lamellae. Grain sizes in the well-developed shear bands are obviously larger than the lamellar thickness of original T/M lamellae. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000790 [article] Nucleation and thickening of shear bands in nano-scale twin/matrix lamellae of a Cu–Al alloy processed by dynamic plastic deformation [texte imprimé] / C.S. Hong, Auteur ; N.R. Tao, Auteur ; X. Huang, Auteur . - 2011 . - pp. 3103–3116.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3103–3116
Mots-clés : Dynamic plastic deformation Shear bands Nano-scale twins Nano-grained structure Dislocation structure Résumé : Microstructural evolution associated with the shear banding in nano-scale twin/matrix (T/M) lamellae of a Cu–Al alloy processed by means of dynamic plastic deformation was investigated using transmission electron microscopy (TEM) and high-resolution TEM. The development of a shear band was found to be a two-stage process, namely a nucleation stage resulting in a narrow band composed of nano-sized (sub)grains intersecting the T/M lamellae, followed by a thickening stage of the narrow band into adjacent T/M lamellae regions. The nucleation stage occurred within a narrow region of an almost constant thickness (100–200 nm thick, referred to as “core” region) and consisted of three steps: (1) initiation of localized deformation (bending, necking, and detwinning) against the T/M lamellae, (2) evolution of a dislocation structure within the detwinned band, and (3) transformation of the detwinned dislocation structure (DDS) into a nano-sized (sub)grain structure (NGS). On the two sides of a core region, two transition layers (TRLs) exist where the T/M lamellae experienced much less shear strain. The interface boundaries separating the core region and the TRLs are characterized by very large shear strain gradients accommodated by high density of dislocations. Increasing shear strains leads to thickening of shear bands at the expense of the adjoining T/M lamellae, which is composed of thickening of the core region by transforming the TRLs into the core region with DDS and NGS, analogous to steps (2) and (3) of the nucleation process, and outward movement of the TRLs by deforming the adjoining T/M lamellae. Grain sizes in the well-developed shear bands are obviously larger than the lamellar thickness of original T/M lamellae. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000790
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3117–3123
Titre : The theoretical shear strength of fcc crystals under superimposed triaxial stress Type de document : texte imprimé Auteurs : M. Černý, Auteur ; J. Pokluda, Auteur Année de publication : 2011 Article en page(s) : pp. 3117–3123 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ideal shear strength Homogeneous deformation Ab initio calculations fcc metals Résumé : The influence of a triaxial stress applied normally to shear planes and shear direction during affine shear deformation of face-centered cubic crystals on the theoretical shear strength is studied for the View the MathML source shear system using first-principles methods. The applied relaxation procedure guarantees that the modeled system is subjected to a superposition of shear, normal and in-plane stresses with individually adjustable in-plane and normal stress values. The theoretical shear strengths of individual elements prove to be qualitatively different functions of the superimposed stresses. In the special case of hydrostatic loading, however, these functions are qualitatively uniform. This behavior is discussed in terms of the electronic structure. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000807 [article] The theoretical shear strength of fcc crystals under superimposed triaxial stress [texte imprimé] / M. Černý, Auteur ; J. Pokluda, Auteur . - 2011 . - pp. 3117–3123.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3117–3123
Mots-clés : Ideal shear strength Homogeneous deformation Ab initio calculations fcc metals Résumé : The influence of a triaxial stress applied normally to shear planes and shear direction during affine shear deformation of face-centered cubic crystals on the theoretical shear strength is studied for the View the MathML source shear system using first-principles methods. The applied relaxation procedure guarantees that the modeled system is subjected to a superposition of shear, normal and in-plane stresses with individually adjustable in-plane and normal stress values. The theoretical shear strengths of individual elements prove to be qualitatively different functions of the superimposed stresses. In the special case of hydrostatic loading, however, these functions are qualitatively uniform. This behavior is discussed in terms of the electronic structure. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000807
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3124–3130
Titre : Electrochemical synthesis of a biomedically important Co–Cr alloy Type de document : texte imprimé Auteurs : D.J.S. Hyslop, Auteur ; A. M. Abdelkader, Auteur Année de publication : 2011 Article en page(s) : pp. 3124–3130 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Electro-deoxidation FFC-Cambridge Process Co–Cr Résumé : Co–30 wt.% Cr alloy was prepared by electro-deoxidation in molten calcium chloride at 1123 K. A preliminary study was conducted into the preparation of the mixture of the Co3O4 and Cr2O3 and the formation of the non-stoichiometric, spinel structured, mixed oxide nominally labeled CoxCryO4. Constant voltage chronoamperometry was used both to prepare the alloy and to investigate its mechanism of formation. Electro-deoxidation proceeds by the simultaneous rapid reduction of CoO to Co and the slower reduction/substitution of CoxCryO4 to CaCr2O4 and Co metal. The final step of the electro-deoxidation is the reduction of CaCr2O4 to Cr metal, which alloys with the Co metal, and release of Ca2+ back into the electrolyte. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000832 [article] Electrochemical synthesis of a biomedically important Co–Cr alloy [texte imprimé] / D.J.S. Hyslop, Auteur ; A. M. Abdelkader, Auteur . - 2011 . - pp. 3124–3130.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3124–3130
Mots-clés : Electro-deoxidation FFC-Cambridge Process Co–Cr Résumé : Co–30 wt.% Cr alloy was prepared by electro-deoxidation in molten calcium chloride at 1123 K. A preliminary study was conducted into the preparation of the mixture of the Co3O4 and Cr2O3 and the formation of the non-stoichiometric, spinel structured, mixed oxide nominally labeled CoxCryO4. Constant voltage chronoamperometry was used both to prepare the alloy and to investigate its mechanism of formation. Electro-deoxidation proceeds by the simultaneous rapid reduction of CoO to Co and the slower reduction/substitution of CoxCryO4 to CaCr2O4 and Co metal. The final step of the electro-deoxidation is the reduction of CaCr2O4 to Cr metal, which alloys with the Co metal, and release of Ca2+ back into the electrolyte. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000832
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3131–3161
Titre : Changes in internal stress distributions during yielding of square prismatic gold nano-specimens Type de document : texte imprimé Auteurs : R. C. Batra, Auteur ; A.A. Pacheco, Auteur Année de publication : 2011 Article en page(s) : pp. 3131–3161 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Molecular statics Stress distributions Yielding Instabilities Résumé : We use molecular statics simulations with the tight-binding potential to analyze stress evolution in nanosize square prismatic gold specimens of different aspect ratios (length/width) deformed in either simple tension/compression or tension/compression. In the former case atoms on end faces are displaced axially but are free to move laterally, and in the latter case atoms on end faces are restrained from moving laterally during their axial displacement. It is found that the stress distribution in the unloaded reference configuration is non-uniform, and it satisfies the local and the global equilibrium equations. Large values of the von Mises stress and the maximum shear stress occur on atoms located at the third layer beneath the traction free surfaces forming different patterns for specimens loaded in tension and compression. The specimen is assumed to yield when its total strain energy drops noticeably. Maximum values of the von Mises stress and the maximum shear stress at yielding are essentially independent of specimen’s length for specimens deformed in tension. For specimens deformed in compression, wave-like patterns of stresses along the axial centroidal axis are observed when the specimen yields. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000844 [article] Changes in internal stress distributions during yielding of square prismatic gold nano-specimens [texte imprimé] / R. C. Batra, Auteur ; A.A. Pacheco, Auteur . - 2011 . - pp. 3131–3161.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3131–3161
Mots-clés : Molecular statics Stress distributions Yielding Instabilities Résumé : We use molecular statics simulations with the tight-binding potential to analyze stress evolution in nanosize square prismatic gold specimens of different aspect ratios (length/width) deformed in either simple tension/compression or tension/compression. In the former case atoms on end faces are displaced axially but are free to move laterally, and in the latter case atoms on end faces are restrained from moving laterally during their axial displacement. It is found that the stress distribution in the unloaded reference configuration is non-uniform, and it satisfies the local and the global equilibrium equations. Large values of the von Mises stress and the maximum shear stress occur on atoms located at the third layer beneath the traction free surfaces forming different patterns for specimens loaded in tension and compression. The specimen is assumed to yield when its total strain energy drops noticeably. Maximum values of the von Mises stress and the maximum shear stress at yielding are essentially independent of specimen’s length for specimens deformed in tension. For specimens deformed in compression, wave-like patterns of stresses along the axial centroidal axis are observed when the specimen yields. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000844
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3162–3172
Titre : Analysis of deformation twins and the partially dehydrogenated microstructure in nanocrystalline magnesium hydride (MgH2) powder Type de document : texte imprimé Auteurs : M. Danaie, Auteur ; S.X. Tao, Auteur ; P. Kalisvaart, Auteur Année de publication : 2011 Article en page(s) : pp. 3162–3172 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hydrogen storage TEM Magnesium hydride Résumé : Cryo-stage transmission electron microscopy (TEM), supported by Density Functional Theory (DFT), is employed to explore the microstructure of magnesium hydride (MgH2) powders. Mechanical milling results in deformation twinning of the hydride. The crystallography of the twins is established. DFT analysis shows that the twin unit cell is just as thermodynamically stable as the undeformed α-MgH2 matrix. It is hypothesized that the twins contribute significantly to the observed milling-induced kinetic enhancement by acting as high diffusivity paths for hydrogen. Energy-filtered TEM analysis on partially desorbed MgH2 demonstrates that nucleation and growth of metallic magnesium occurs non-uniformly. Larger powder particles are a composite of isolated magnesium grains heterogeneously nucleated on the remaining hydride. Smaller particles are either fully transformed to magnesium or remain entirely a hydride. There is little evidence for any “core–shell” structure. It is also shown that in situ hydrogen desorption in the TEM is not representative of the elevated-temperature ex situ sequence. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000856 [article] Analysis of deformation twins and the partially dehydrogenated microstructure in nanocrystalline magnesium hydride (MgH2) powder [texte imprimé] / M. Danaie, Auteur ; S.X. Tao, Auteur ; P. Kalisvaart, Auteur . - 2011 . - pp. 3162–3172.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3162–3172
Mots-clés : Hydrogen storage TEM Magnesium hydride Résumé : Cryo-stage transmission electron microscopy (TEM), supported by Density Functional Theory (DFT), is employed to explore the microstructure of magnesium hydride (MgH2) powders. Mechanical milling results in deformation twinning of the hydride. The crystallography of the twins is established. DFT analysis shows that the twin unit cell is just as thermodynamically stable as the undeformed α-MgH2 matrix. It is hypothesized that the twins contribute significantly to the observed milling-induced kinetic enhancement by acting as high diffusivity paths for hydrogen. Energy-filtered TEM analysis on partially desorbed MgH2 demonstrates that nucleation and growth of metallic magnesium occurs non-uniformly. Larger powder particles are a composite of isolated magnesium grains heterogeneously nucleated on the remaining hydride. Smaller particles are either fully transformed to magnesium or remain entirely a hydride. There is little evidence for any “core–shell” structure. It is also shown that in situ hydrogen desorption in the TEM is not representative of the elevated-temperature ex situ sequence. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000856
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3173–3186
Titre : Correlation between stacking fault energy and deformation microstructure in high-interstitial-alloyed austenitic steels Type de document : texte imprimé Auteurs : Tae-Ho Lee, Auteur ; Eunjoo Shin, Auteur ; Chang-Seok Oh, Auteur Année de publication : 2011 Article en page(s) : pp. 3173–3186 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Stacking fault energy Austenitic steels Martensitic transformation Twinning Neutron diffraction Résumé : The correlation between stacking fault energy (SFE) and deformation microstructure of high-interstitial-alloyed austenitic Fe–18Cr–10Mn–(N or N + C) alloys was investigated. As the content of the interstitial elements increased, the deformation microstructure changed in a sequence strain-induced martensitic transformation, mixture of martensite and twin, and finally deformation twin. The SFE, playing an important role in the transition of deformation microstructure, was evaluated by the Rietveld whole-profile fitting combined with the double-Voigt size–strain analysis for neutron diffraction profiles of tensile-strained bulk samples. At fixed N + C content, the ratio of mean-squared strain to stacking fault probability remained constant regardless of the accumulated strain, whereas the ratio gradually increased with increasing N + C content. Almost linear dependence of measured SFE on N + C content could be established. According to the SFE, deformation bands exhibited distinct substructures, and their particular intersecting behavior resulted in the formation of different types of products (secondary ε martensite, α′ martensite and secondary twin) at the intersecting regions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000868 [article] Correlation between stacking fault energy and deformation microstructure in high-interstitial-alloyed austenitic steels [texte imprimé] / Tae-Ho Lee, Auteur ; Eunjoo Shin, Auteur ; Chang-Seok Oh, Auteur . - 2011 . - pp. 3173–3186.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3173–3186
Mots-clés : Stacking fault energy Austenitic steels Martensitic transformation Twinning Neutron diffraction Résumé : The correlation between stacking fault energy (SFE) and deformation microstructure of high-interstitial-alloyed austenitic Fe–18Cr–10Mn–(N or N + C) alloys was investigated. As the content of the interstitial elements increased, the deformation microstructure changed in a sequence strain-induced martensitic transformation, mixture of martensite and twin, and finally deformation twin. The SFE, playing an important role in the transition of deformation microstructure, was evaluated by the Rietveld whole-profile fitting combined with the double-Voigt size–strain analysis for neutron diffraction profiles of tensile-strained bulk samples. At fixed N + C content, the ratio of mean-squared strain to stacking fault probability remained constant regardless of the accumulated strain, whereas the ratio gradually increased with increasing N + C content. Almost linear dependence of measured SFE on N + C content could be established. According to the SFE, deformation bands exhibited distinct substructures, and their particular intersecting behavior resulted in the formation of different types of products (secondary ε martensite, α′ martensite and secondary twin) at the intersecting regions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000868
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