Dépouillements

Effect of total dopant concentration and dopant ratio on conductivity of (DyO1.5)x–(WO3)y–(BiO1.5)1−x−y / Doh Won Jung in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 355-363 Titre : Effect of total dopant concentration and dopant ratio on conductivity of (DyO1.5)x–(WO3)y–(BiO1.5)1−x−y Type de document : texte imprimé Auteurs : Doh Won Jung, Auteur ; Keith L. Duncan, Auteur ; Eric D. Wachsman, Auteur Article en page(s) : pp. 355-363 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Solid  electrolytes  Bismuth  oxide  Lattice  parameter  Conductivity  Total  dopant  concentration Index. décimale : 669 Métallurgie Résumé : Dysprosium- and tungsten-stabilized bismuth oxide (DWSB) electrolytes were developed to achieve higher conductivity. With double doping, stabilization of the cubic phase was achieved with as little as 12 mol.% total dopant concentration, resulting in higher conductivity. The conductivity of DWSB electrolytes increased linearly as the total dopant concentrations decreased with fixed dopant ratio. Overall, DWSB has a closer inherent structure to pure δ-Bi2O3 than any singly doped compositions. Both lattice parameter and conductivity linearly extrapolate with total dopant concentration to that of pure δ-Bi2O3, resulting in the ability to stabilize δ-phase at lower dopant concentration, and thus achieving higher conductivity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Effect of total dopant concentration and dopant ratio on conductivity of (DyO1.5)x–(WO3)y–(BiO1.5)1−x−y [texte imprimé] / Doh Won Jung, Auteur ; Keith L. Duncan, Auteur ; Eric D. Wachsman, Auteur . - pp. 355-363. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 355-363 Mots-clés : Solid  electrolytes  Bismuth  oxide  Lattice  parameter  Conductivity  Total  dopant  concentration Index. décimale : 669 Métallurgie Résumé : Dysprosium- and tungsten-stabilized bismuth oxide (DWSB) electrolytes were developed to achieve higher conductivity. With double doping, stabilization of the cubic phase was achieved with as little as 12 mol.% total dopant concentration, resulting in higher conductivity. The conductivity of DWSB electrolytes increased linearly as the total dopant concentrations decreased with fixed dopant ratio. Overall, DWSB has a closer inherent structure to pure δ-Bi2O3 than any singly doped compositions. Both lattice parameter and conductivity linearly extrapolate with total dopant concentration to that of pure δ-Bi2O3, resulting in the ability to stabilize δ-phase at lower dopant concentration, and thus achieving higher conductivity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

A more accurate two-dimensional grain growth algorithm / Emanuel A. Lazar in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 364-372 Titre : A more accurate two-dimensional grain growth algorithm Type de document : texte imprimé Auteurs : Emanuel A. Lazar, Auteur ; Robert D. MacPherson, Auteur ; David J. Srolovitz, Auteur Article en page(s) : pp. 364-372 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  growth  Simulation  von  Neumann–Mullins  theory Index. décimale : 669 Métallurgie Résumé : We describe a method for evolving two-dimensional polycrystalline microstructures via mean curvature flow that satisfies the von Neumann–Mullins relation with an absolute error O(Δt2). This is a significant improvement over a different method currently used that has an absolute error O(Δt). We describe the implementation of this method and show that while both approaches lead to indistinguishable evolution when the spatial discretization is very fine, the differences can be substantial when the discretization is left unrefined. We demonstrate that this new front-tracking approach can be pushed to the limit in which the only mesh nodes are those coincident with triple junctions. This reduces the method to a vertex model that is consistent with the exact kinetic law for grain growth. We briefly discuss an extension of the method to higher spatial dimensions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] A more accurate two-dimensional grain growth algorithm [texte imprimé] / Emanuel A. Lazar, Auteur ; Robert D. MacPherson, Auteur ; David J. Srolovitz, Auteur . - pp. 364-372. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 364-372 Mots-clés : Grain  growth  Simulation  von  Neumann–Mullins  theory Index. décimale : 669 Métallurgie Résumé : We describe a method for evolving two-dimensional polycrystalline microstructures via mean curvature flow that satisfies the von Neumann–Mullins relation with an absolute error O(Δt2). This is a significant improvement over a different method currently used that has an absolute error O(Δt). We describe the implementation of this method and show that while both approaches lead to indistinguishable evolution when the spatial discretization is very fine, the differences can be substantial when the discretization is left unrefined. We demonstrate that this new front-tracking approach can be pushed to the limit in which the only mesh nodes are those coincident with triple junctions. This reduces the method to a vertex model that is consistent with the exact kinetic law for grain growth. We briefly discuss an extension of the method to higher spatial dimensions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Structural and optical properties of encapsulated ZnO in porous host matrix / Noppadon Sathitsuksanoh in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 373-378 Titre : Structural and optical properties of encapsulated ZnO in porous host matrix Type de document : texte imprimé Auteurs : Noppadon Sathitsuksanoh, Auteur ; Dake Wang, Auteur ; HongYun Yang, Auteur Article en page(s) : pp. 373-378 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : ZnO  Nanoparticles  Impregnation  Raman  Photoluminescence Index. décimale : 669 Métallurgie Résumé : ZnO nanoparticles were encapsulated in the porous activated carbon matrix by incipient-wetness impregnation. The use of the small host matrix allowed the size confinement of ZnO by utilizing the porous nature of the host matrix. Partial fixation of ZnO in the porous matrix determines the size and the dispersion of the particles. Experiments at different calcination temperatures were carried out to investigate structural and optical properties of ZnO nanoparticles in the porous activated carbon matrix using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and photoluminescence. The optimal calcination temperature was found to be not, vert, similar450 °C in order to confine ZnO nanoparticles in the porous ACP matrix. Near-band-edge UV emission and green emission were both associated with the deep-level defect state. A decrease in full width at half maximum of E2 mode in Raman spectrum confirmed an increase in crystallite size due to higher calcination temperature, causing an increase in phonon lifetime. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Structural and optical properties of encapsulated ZnO in porous host matrix [texte imprimé] / Noppadon Sathitsuksanoh, Auteur ; Dake Wang, Auteur ; HongYun Yang, Auteur . - pp. 373-378. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 373-378 Mots-clés : ZnO  Nanoparticles  Impregnation  Raman  Photoluminescence Index. décimale : 669 Métallurgie Résumé : ZnO nanoparticles were encapsulated in the porous activated carbon matrix by incipient-wetness impregnation. The use of the small host matrix allowed the size confinement of ZnO by utilizing the porous nature of the host matrix. Partial fixation of ZnO in the porous matrix determines the size and the dispersion of the particles. Experiments at different calcination temperatures were carried out to investigate structural and optical properties of ZnO nanoparticles in the porous activated carbon matrix using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and photoluminescence. The optimal calcination temperature was found to be not, vert, similar450 °C in order to confine ZnO nanoparticles in the porous ACP matrix. Near-band-edge UV emission and green emission were both associated with the deep-level defect state. A decrease in full width at half maximum of E2 mode in Raman spectrum confirmed an increase in crystallite size due to higher calcination temperature, causing an increase in phonon lifetime. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Point defects in multicomponent ordered alloys / Rémy Besson in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 379-385 Titre : Point defects in multicomponent ordered alloys : methodological issues and working equations Type de document : texte imprimé Auteurs : Rémy Besson, Auteur Article en page(s) : pp. 379-385 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Complex  alloys  Thermodynamics  Point  defects Index. décimale : 669 Métallurgie Résumé : The aim of this work is to give the independent-point-defect thermodynamics of ordered compounds a sufficiently general flavour, adapted to and working for multicomponent alloys. Generalizing previous approaches, we first show that an appropriate description for a crystal with point defects allows treatment of the practically important pressure and defect volume parameters in the grand canonical framework, the equivalence of which is explicited with the closer to experiments isothermal–isobaric conditions. Since industrial applications often involve multialloyed compounds, we then derive an operational tool for atomic-scale investigations of long-range order alloys with complex crystallographies and multiple additions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Point defects in multicomponent ordered alloys : methodological issues and working equations [texte imprimé] / Rémy Besson, Auteur . - pp. 379-385. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 379-385 Mots-clés : Complex  alloys  Thermodynamics  Point  defects Index. décimale : 669 Métallurgie Résumé : The aim of this work is to give the independent-point-defect thermodynamics of ordered compounds a sufficiently general flavour, adapted to and working for multicomponent alloys. Generalizing previous approaches, we first show that an appropriate description for a crystal with point defects allows treatment of the practically important pressure and defect volume parameters in the grand canonical framework, the equivalence of which is explicited with the closer to experiments isothermal–isobaric conditions. Since industrial applications often involve multialloyed compounds, we then derive an operational tool for atomic-scale investigations of long-range order alloys with complex crystallographies and multiple additions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Grain boundary self-diffusion in polycrystalline nickel of different purity levels / Sergiy V. Divinski in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 386-395 Titre : Grain boundary self-diffusion in polycrystalline nickel of different purity levels Type de document : texte imprimé Auteurs : Sergiy V. Divinski, Auteur ; Gerrit Reglitz, Auteur ; Gerhard Wilde, Auteur Article en page(s) : pp. 386-395 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel  Grain  boundary  diffusion  Grain  boundary  segregation  Grain  boundary  width Index. décimale : 669 Métallurgie Résumé : Grain boundary self-diffusion in Ni materials of two different purity levels (99.6 and 99.999 wt.%) was measured over wide temperature intervals using the radiotracer technique and applying the 63Ni radioisotope. The diffusion experiments were performed in both Harrison’s type B and type C kinetic regimes. The diffusional grain boundary width, δ, was found to be equal to 0.54 ± 0.1 nm, that is reasonably close to the accepted value of View the MathML source in face-centred cubic metals. The purer the material, the higher the grain boundary diffusivity and the lower the corresponding activation enthalpy of self-diffusion along general high-angle grain boundaries. Using the semi-empirical approach of Borisov et al., the average energy of high-angle grain boundaries was estimated to be about 0.79 and 0.98 J m−2 in the low- and high-purity Ni materials at room temperature, respectively. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Grain boundary self-diffusion in polycrystalline nickel of different purity levels [texte imprimé] / Sergiy V. Divinski, Auteur ; Gerrit Reglitz, Auteur ; Gerhard Wilde, Auteur . - pp. 386-395. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 386-395 Mots-clés : Nickel  Grain  boundary  diffusion  Grain  boundary  segregation  Grain  boundary  width Index. décimale : 669 Métallurgie Résumé : Grain boundary self-diffusion in Ni materials of two different purity levels (99.6 and 99.999 wt.%) was measured over wide temperature intervals using the radiotracer technique and applying the 63Ni radioisotope. The diffusion experiments were performed in both Harrison’s type B and type C kinetic regimes. The diffusional grain boundary width, δ, was found to be equal to 0.54 ± 0.1 nm, that is reasonably close to the accepted value of View the MathML source in face-centred cubic metals. The purer the material, the higher the grain boundary diffusivity and the lower the corresponding activation enthalpy of self-diffusion along general high-angle grain boundaries. Using the semi-empirical approach of Borisov et al., the average energy of high-angle grain boundaries was estimated to be about 0.79 and 0.98 J m−2 in the low- and high-purity Ni materials at room temperature, respectively. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Thermodynamic and experimental study on phase stability in nanocrystalline alloys / Wenwu Xu in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 396-407 Titre : Thermodynamic and experimental study on phase stability in nanocrystalline alloys Type de document : texte imprimé Auteurs : Wenwu Xu, Auteur ; Xiaoyan Song, Auteur ; Nianduan Lu, Auteur Article en page(s) : pp. 396-407 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocrystalline  materials  Thermodynamics  Phase  transformations  Grain  boundary  energy  Grain  boundary  structure Index. décimale : 669 Métallurgie Résumé : Nanocrystalline alloys exhibit apparently different phase transformation characteristics in comparison to the conventional polycrystalline alloys. The special phase stability and phase transformation behavior, as well as the essential mechanisms of the nanocrystalline alloys, were described quantitatively in a nanothermodynamic point of view. By introducing the relationship between the excess volume at the grain boundary and the nanograin size, the Gibbs free energy was determined distinctly as a function of temperature and the nanograin size. Accordingly, the grain-size-dependence of the phase stability and phase transformation characteristics of the nanocrystalline alloy were calculated systematically, and the correlations between the phase constitution, the phase transformation temperature and the critical nanograin size were predicted. A series of experiments was performed to investigate the phase transformations at room temperature and high temperatures using the nanocrystalline Sm2Co17 alloy as an example. The phase constitution and phase transformation sequence found in nanocrystalline Sm2Co17 alloys with various grain-size levels agree well with the calculations by the nanothermodynamic model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Thermodynamic and experimental study on phase stability in nanocrystalline alloys [texte imprimé] / Wenwu Xu, Auteur ; Xiaoyan Song, Auteur ; Nianduan Lu, Auteur . - pp. 396-407. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 396-407 Mots-clés : Nanocrystalline  materials  Thermodynamics  Phase  transformations  Grain  boundary  energy  Grain  boundary  structure Index. décimale : 669 Métallurgie Résumé : Nanocrystalline alloys exhibit apparently different phase transformation characteristics in comparison to the conventional polycrystalline alloys. The special phase stability and phase transformation behavior, as well as the essential mechanisms of the nanocrystalline alloys, were described quantitatively in a nanothermodynamic point of view. By introducing the relationship between the excess volume at the grain boundary and the nanograin size, the Gibbs free energy was determined distinctly as a function of temperature and the nanograin size. Accordingly, the grain-size-dependence of the phase stability and phase transformation characteristics of the nanocrystalline alloy were calculated systematically, and the correlations between the phase constitution, the phase transformation temperature and the critical nanograin size were predicted. A series of experiments was performed to investigate the phase transformations at room temperature and high temperatures using the nanocrystalline Sm2Co17 alloy as an example. The phase constitution and phase transformation sequence found in nanocrystalline Sm2Co17 alloys with various grain-size levels agree well with the calculations by the nanothermodynamic model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Temperature and structural dependence of electrochemical activity and fuel cell performance / Jun Jie Niu in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 408-414 Titre : Temperature and structural dependence of electrochemical activity and fuel cell performance Type de document : texte imprimé Auteurs : Jun Jie Niu, Auteur ; Jian Nong Wang, Auteur Article en page(s) : pp. 408-414 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Temperature  and  structure  Electrochemical  activity  Fuel  cell  performance Index. décimale : 669 Métallurgie Résumé : The dependence on temperature and structure of the electrochemical activity of a catalyst supported on hollow carbon nanocages (HCNCs) with large scales (>5 g h–1) by a simple N2-bubbling floating method is discussed. The effect of gas flow on an HCNC-supported catalyst was systematically studied in our previous work. Here we specify the electrocatalytic activity of the samples with different temperatures and graphite structures under 900 and 1000°C by cyclic voltammograms. The peak current density of H2-adsorption/desorption is four times higher than that of the commercial Pt/C (Vulcan XC-72). Besides the comparison with commercial carbon, the fuel cell performance was measured. The single fuel cell test for Pt/HCNCs showed a high turn-on voltage of 0.9 V and a relatively high power density of 0.13 W cm–2 under a low temperature of 60 °C and a low gas pressure of 1 atm. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Temperature and structural dependence of electrochemical activity and fuel cell performance [texte imprimé] / Jun Jie Niu, Auteur ; Jian Nong Wang, Auteur . - pp. 408-414. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 408-414 Mots-clés : Temperature  and  structure  Electrochemical  activity  Fuel  cell  performance Index. décimale : 669 Métallurgie Résumé : The dependence on temperature and structure of the electrochemical activity of a catalyst supported on hollow carbon nanocages (HCNCs) with large scales (>5 g h–1) by a simple N2-bubbling floating method is discussed. The effect of gas flow on an HCNC-supported catalyst was systematically studied in our previous work. Here we specify the electrocatalytic activity of the samples with different temperatures and graphite structures under 900 and 1000°C by cyclic voltammograms. The peak current density of H2-adsorption/desorption is four times higher than that of the commercial Pt/C (Vulcan XC-72). Besides the comparison with commercial carbon, the fuel cell performance was measured. The single fuel cell test for Pt/HCNCs showed a high turn-on voltage of 0.9 V and a relatively high power density of 0.13 W cm–2 under a low temperature of 60 °C and a low gas pressure of 1 atm. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Mechanical characterization of hotplate synthesized vanadium oxide nanobelts / Yanwu Zhu in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 415-420 Titre : Mechanical characterization of hotplate synthesized vanadium oxide nanobelts Type de document : texte imprimé Auteurs : Yanwu Zhu, Auteur ; Yousheng Zhang, Auteur ; Ling Dai, Auteur Article en page(s) : pp. 415-420 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Vanadium  oxide  Nanobelts  Young’s  modulus  Structure  characterization Index. décimale : 669 Métallurgie Résumé : Vanadium oxide nanobelts have been synthesized on Si or SiN substrates by simply heating vanadium foils on a hotplate. As-grown nanobelts were characterized as V2O5·nH2O (0.3 < n < 1.7) layer structures containing water molecular intercalation. Using an electromechanical resonance method, the Young’s modulus of the nanobelts was measured in situ in a scanning electron microscope. It was found that the Young’s modulus of as-grown nanobelts varied between 5.6 and 98 GPa, with a typical Q-factor of 120. Such scattered values were attributed to the different contents of water molecules in the nanobelts. After annealing at 450 °C in vacuum, the nanobelts were converted to α-V2O5 phase and a polycrystalline structure was observed. The Young’s modulus of the annealed nanobelts showed more consistent values at an average of 28.9 GPa, lower than the calculated modulus of bulk α-V2O5 at 68 GPa. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Mechanical characterization of hotplate synthesized vanadium oxide nanobelts [texte imprimé] / Yanwu Zhu, Auteur ; Yousheng Zhang, Auteur ; Ling Dai, Auteur . - pp. 415-420. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 415-420 Mots-clés : Vanadium  oxide  Nanobelts  Young’s  modulus  Structure  characterization Index. décimale : 669 Métallurgie Résumé : Vanadium oxide nanobelts have been synthesized on Si or SiN substrates by simply heating vanadium foils on a hotplate. As-grown nanobelts were characterized as V2O5·nH2O (0.3 < n < 1.7) layer structures containing water molecular intercalation. Using an electromechanical resonance method, the Young’s modulus of the nanobelts was measured in situ in a scanning electron microscope. It was found that the Young’s modulus of as-grown nanobelts varied between 5.6 and 98 GPa, with a typical Q-factor of 120. Such scattered values were attributed to the different contents of water molecules in the nanobelts. After annealing at 450 °C in vacuum, the nanobelts were converted to α-V2O5 phase and a polycrystalline structure was observed. The Young’s modulus of the annealed nanobelts showed more consistent values at an average of 28.9 GPa, lower than the calculated modulus of bulk α-V2O5 at 68 GPa. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Effects of boron on the microstructure and thermal stability of directionally solidified NiAl–Mo eutectic / A. Gali in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 421-428 Titre : Effects of boron on the microstructure and thermal stability of directionally solidified NiAl–Mo eutectic Type de document : texte imprimé Auteurs : A. Gali, Auteur ; H. Bei, Auteur ; E.P. George, Auteur Article en page(s) : pp. 421-428 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Interfaces  Segregation  Directional  solidification  Coarsening  Composites Index. décimale : 669 Métallurgie Résumé : Microalloying with 0.01 at.% B decreases the range of growth speeds over which a well-aligned fibrous eutectic microstructure can be obtained in directionally solidified NiAl–Mo. Compared to the undoped alloy, the size/spacing of the Mo fibers is larger, and the fiber density smaller, in the B-doped alloy. Annealing at 1400 °C coarsens the fibers by a mechanism involving fault migration and annihilation driven by diffusion along the fiber–matrix interface. The coarsening kinetics, given by the decrease in Mo fiber density with time, is exponential, and microalloying with B decreases the coarsening rate. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Effects of boron on the microstructure and thermal stability of directionally solidified NiAl–Mo eutectic [texte imprimé] / A. Gali, Auteur ; H. Bei, Auteur ; E.P. George, Auteur . - pp. 421-428. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 421-428 Mots-clés : Interfaces  Segregation  Directional  solidification  Coarsening  Composites Index. décimale : 669 Métallurgie Résumé : Microalloying with 0.01 at.% B decreases the range of growth speeds over which a well-aligned fibrous eutectic microstructure can be obtained in directionally solidified NiAl–Mo. Compared to the undoped alloy, the size/spacing of the Mo fibers is larger, and the fiber density smaller, in the B-doped alloy. Annealing at 1400 °C coarsens the fibers by a mechanism involving fault migration and annihilation driven by diffusion along the fiber–matrix interface. The coarsening kinetics, given by the decrease in Mo fiber density with time, is exponential, and microalloying with B decreases the coarsening rate. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Structural rejuvenation in a bulk metallic glass induced by severe plastic deformation / W. Dmowski in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 429-438 Titre : Structural rejuvenation in a bulk metallic glass induced by severe plastic deformation Type de document : texte imprimé Auteurs : W. Dmowski, Auteur ; Y. Yokoyama, Auteur ; A. Chuang, Auteur Article en page(s) : pp. 429-438 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : X-ray  diffraction  Bulk  amorphous  materials  Plastic  deformation  Pair  distribution  function Index. décimale : 669 Métallurgie Résumé : Using high-energy X-ray diffraction we examined the atomic structure in bulk metallic glass samples which underwent severe plastic deformation by the high-pressure torsion (HPT) technique. We obtained the atomic pair distribution function (PDF) and determined the changes in the PDFs due to deformation. The observed changes in the PDF clearly show structural disordering, which suggests structural rejuvenation by heavy deformation. However, the changes cannot be explained simply in terms of creating excess free volume, and they indicate that much more extensive atomic rearrangements take place as a consequence of deformation. Also, we suggest that the observed structural change may well be an outcome of local heating due to deformation and may not directly provide the knowledge of the atomistic mechanism of strain localization. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Structural rejuvenation in a bulk metallic glass induced by severe plastic deformation [texte imprimé] / W. Dmowski, Auteur ; Y. Yokoyama, Auteur ; A. Chuang, Auteur . - pp. 429-438. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 429-438 Mots-clés : X-ray  diffraction  Bulk  amorphous  materials  Plastic  deformation  Pair  distribution  function Index. décimale : 669 Métallurgie Résumé : Using high-energy X-ray diffraction we examined the atomic structure in bulk metallic glass samples which underwent severe plastic deformation by the high-pressure torsion (HPT) technique. We obtained the atomic pair distribution function (PDF) and determined the changes in the PDFs due to deformation. The observed changes in the PDF clearly show structural disordering, which suggests structural rejuvenation by heavy deformation. However, the changes cannot be explained simply in terms of creating excess free volume, and they indicate that much more extensive atomic rearrangements take place as a consequence of deformation. Also, we suggest that the observed structural change may well be an outcome of local heating due to deformation and may not directly provide the knowledge of the atomistic mechanism of strain localization. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Stronger silicon for microsystems / B. L. Boyce in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 439-448 Titre : Stronger silicon for microsystems Type de document : texte imprimé Auteurs : B. L. Boyce, Auteur ; M.J. Shaw, Auteur ; P. Lu, Auteur Article en page(s) : pp. 439-448 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Lithography  Chemical  vapor  deposition  Fracture  Tension  test  Ultrafine-grained  microstructure Index. décimale : 669 Métallurgie Résumé : Few studies have deliberately varied the microstructure of microfabricated polycrystalline silicon (polySi) to examine their effects on resulting mechanical performance and reliability. In the present study, the tensile strength distributions of four microfabricated polySi variants were examined, corresponding to two different grain sizes (285 nm vs. 125 nm) in both the undoped and heavily P-doped conditions. Microtensile tests revealed that the coarse-grained materials exhibited significantly lower characteristic strengths (1.48–1.76 GPa) compared to the fine-grained material (2.80–2.83 GPa). The difference in strength was attributed largely to preferential etching of grain boundary grooves that were considerably more pronounced in the coarse-grained material. The presence of phosphorous doping had a less pronounced effect on strength values, lowering the characteristic strength of coarse-grained material by merely 16% and having little or no effect on the fine-grained material. DEWEY : 669 ISSN : 359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Stronger silicon for microsystems [texte imprimé] / B. L. Boyce, Auteur ; M.J. Shaw, Auteur ; P. Lu, Auteur . - pp. 439-448. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 439-448 Mots-clés : Lithography  Chemical  vapor  deposition  Fracture  Tension  test  Ultrafine-grained  microstructure Index. décimale : 669 Métallurgie Résumé : Few studies have deliberately varied the microstructure of microfabricated polycrystalline silicon (polySi) to examine their effects on resulting mechanical performance and reliability. In the present study, the tensile strength distributions of four microfabricated polySi variants were examined, corresponding to two different grain sizes (285 nm vs. 125 nm) in both the undoped and heavily P-doped conditions. Microtensile tests revealed that the coarse-grained materials exhibited significantly lower characteristic strengths (1.48–1.76 GPa) compared to the fine-grained material (2.80–2.83 GPa). The difference in strength was attributed largely to preferential etching of grain boundary grooves that were considerably more pronounced in the coarse-grained material. The presence of phosphorous doping had a less pronounced effect on strength values, lowering the characteristic strength of coarse-grained material by merely 16% and having little or no effect on the fine-grained material. DEWEY : 669 ISSN : 359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Liquid structure as a guide for phase stability in the solid state / Emre S. Tasci in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 449-456 Titre : Liquid structure as a guide for phase stability in the solid state : discovery of a stable compound in the Au–Si alloy system Type de document : texte imprimé Auteurs : Emre S. Tasci, Auteur ; Marcel H.F. Sluiter, Auteur ; Alain Pasturel, Auteur Article en page(s) : pp. 449-456 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Crystal  structure  Modelling  Amorphous  materials  Metallic  glasses  Datamining Index. décimale : 669 Métallurgie Résumé : A new crystalline ground state was discovered in the Au–Si system through first-principles electronic structure calculations. The new structure was found using the experimentally and theoretically determined local atomic structure in the liquid as a guide for the solid state. Local atomic structure in the liquid was matched with that for all known crystal structures as compiled in the Pauling File structural database. The best matching crystalline structures were then explicitly calculated using first-principles methods. Most candidate crystal structures were found to be close, but above the enthalpy of a composition weighted average of the face-centered cubic Au and diamond structure Si terminal phases, but one crystal structure was more stable than the terminal phases by about 10 meV atom–1 at T = 0 K. As first-principles simulations of local structure are feasible for most liquid alloys, the present methodology is applicable to other alloys lying near a eutectic composition. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Liquid structure as a guide for phase stability in the solid state : discovery of a stable compound in the Au–Si alloy system [texte imprimé] / Emre S. Tasci, Auteur ; Marcel H.F. Sluiter, Auteur ; Alain Pasturel, Auteur . - pp. 449-456. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 449-456 Mots-clés : Crystal  structure  Modelling  Amorphous  materials  Metallic  glasses  Datamining Index. décimale : 669 Métallurgie Résumé : A new crystalline ground state was discovered in the Au–Si system through first-principles electronic structure calculations. The new structure was found using the experimentally and theoretically determined local atomic structure in the liquid as a guide for the solid state. Local atomic structure in the liquid was matched with that for all known crystal structures as compiled in the Pauling File structural database. The best matching crystalline structures were then explicitly calculated using first-principles methods. Most candidate crystal structures were found to be close, but above the enthalpy of a composition weighted average of the face-centered cubic Au and diamond structure Si terminal phases, but one crystal structure was more stable than the terminal phases by about 10 meV atom–1 at T = 0 K. As first-principles simulations of local structure are feasible for most liquid alloys, the present methodology is applicable to other alloys lying near a eutectic composition. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Pulsed laser deposition-induced reduction of SrTiO3 crystals / Matthew L. Scullin in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 457-463 Titre : Pulsed laser deposition-induced reduction of SrTiO3 crystals Type de document : texte imprimé Auteurs : Matthew L. Scullin, Auteur ; Jayakanth Ravichandran, Auteur ; Choongho Yu, Auteur Article en page(s) : pp. 457-463 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Perovskites  Thin-films  Laser  deposition  Electrical  resistivity  Secondary  ion  mass  spectroscopy Index. décimale : 669 Métallurgie Résumé : We report a generic method for fast and efficient reduction of strontium titanate (SrTiO3, STO) single crystals by pulsed laser deposition (PLD) of thin-films. The reduction was largely independent of the thin-film material deposited on the crystals. It is shown that thermodynamic conditions (450°C, 10−7 torr, 10–60 min), which normally reduce STO (0 0 1) substrates to roughly 5 nm into a crystal substrate, can reduce the same crystals throughout their 500 μm thickness when coupled with the PLD. In situ characterization of the STO substrate resistance during thin-film growth is presented. This process opens up the possibility of employing STO substrates as a back-gate in functional oxide devices. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Pulsed laser deposition-induced reduction of SrTiO3 crystals [texte imprimé] / Matthew L. Scullin, Auteur ; Jayakanth Ravichandran, Auteur ; Choongho Yu, Auteur . - pp. 457-463. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 457-463 Mots-clés : Perovskites  Thin-films  Laser  deposition  Electrical  resistivity  Secondary  ion  mass  spectroscopy Index. décimale : 669 Métallurgie Résumé : We report a generic method for fast and efficient reduction of strontium titanate (SrTiO3, STO) single crystals by pulsed laser deposition (PLD) of thin-films. The reduction was largely independent of the thin-film material deposited on the crystals. It is shown that thermodynamic conditions (450°C, 10−7 torr, 10–60 min), which normally reduce STO (0 0 1) substrates to roughly 5 nm into a crystal substrate, can reduce the same crystals throughout their 500 μm thickness when coupled with the PLD. In situ characterization of the STO substrate resistance during thin-film growth is presented. This process opens up the possibility of employing STO substrates as a back-gate in functional oxide devices. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Characterization of planar features in Mg–Y–Zn alloys / Y.M. Zhu in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 464-475 Titre : Characterization of planar features in Mg–Y–Zn alloys Type de document : texte imprimé Auteurs : Y.M. Zhu, Auteur ; A.J. Morton, Auteur ; M. Weyland, Auteur Article en page(s) : pp. 464-475 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium  alloys  Precipitates  Stacking  faults  Dislocations  HAADF-STEM Index. décimale : 669 Métallurgie Résumé : The planar features in a Mg–8Y–2Zn–0.6Zr (wt.%) alloy solution-treated at 500°C for 1 h have been examined using conventional transmission electron microscopy and atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. Three types of planar features are detected in the microstructure. The first type, which was previously reported to be an intrinsic stacking fault I1 bounded by a Frank partial dislocation, is shown to be the 14H precipitate phase that is associated with Shockley partial dislocations. The second type is also a precipitate phase that has a single unit cell height and is associated with Shockley partial dislocations. The third type of planar feature comprises small ribbon-like stacking faults. These stacking faults are determined as intrinsic I2 type bounded by two Shockley partial dislocations, which is further confirmed by computer simulation. The stacking fault energy associated with the faults is much smaller than that of pure magnesium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Characterization of planar features in Mg–Y–Zn alloys [texte imprimé] / Y.M. Zhu, Auteur ; A.J. Morton, Auteur ; M. Weyland, Auteur . - pp. 464-475. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 464-475 Mots-clés : Magnesium  alloys  Precipitates  Stacking  faults  Dislocations  HAADF-STEM Index. décimale : 669 Métallurgie Résumé : The planar features in a Mg–8Y–2Zn–0.6Zr (wt.%) alloy solution-treated at 500°C for 1 h have been examined using conventional transmission electron microscopy and atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. Three types of planar features are detected in the microstructure. The first type, which was previously reported to be an intrinsic stacking fault I1 bounded by a Frank partial dislocation, is shown to be the 14H precipitate phase that is associated with Shockley partial dislocations. The second type is also a precipitate phase that has a single unit cell height and is associated with Shockley partial dislocations. The third type of planar feature comprises small ribbon-like stacking faults. These stacking faults are determined as intrinsic I2 type bounded by two Shockley partial dislocations, which is further confirmed by computer simulation. The stacking fault energy associated with the faults is much smaller than that of pure magnesium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Relationships between rolled grain shape, deformation bands, microstructures and recrystallization textures in Al–5%Mg / C. S. T. Chang in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 476-489 Titre : Relationships between rolled grain shape, deformation bands, microstructures and recrystallization textures in Al–5%Mg Type de document : texte imprimé Auteurs : C. S. T. Chang, Auteur ; B. J. Duggan, Auteur Article en page(s) : pp. 476-489 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Rolling  Recrystallization  texture  Shear  bands  Electron  backscattering  patterns  (EBSP)  Aluminium  alloys Index. décimale : 669 Métallurgie Résumé : In this study, the textures and microstructures of Al–5%Mg after cold rolling 95% and recrystallization at 300 and 450°C have been investigated. The cold rolling textures were typical but the recrystallization textures at 300°C comprised Cube and S and at 450 °C, Cube, ND Rotated Cube plus a weak Q component. The deformed grains were wavy in the longitudinal section as a result of composite-like behaviour, and the narrowed regions had scattered orientations which weakened the final annealing texture. Another feature was grains dividing into their respective crystallographic complements. S grains frequently behaved in this way and nucleation of S-oriented recrystallized material at low temperature was common. Cube-oriented volumes were often found between complementary S volumes, and this favoured micro-growth selection and a detailed discussion of the Cube origins are given. Remarkably, recrystallization texture is largely determined by the behaviour of S- and Cube-oriented material. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Relationships between rolled grain shape, deformation bands, microstructures and recrystallization textures in Al–5%Mg [texte imprimé] / C. S. T. Chang, Auteur ; B. J. Duggan, Auteur . - pp. 476-489. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 476-489 Mots-clés : Rolling  Recrystallization  texture  Shear  bands  Electron  backscattering  patterns  (EBSP)  Aluminium  alloys Index. décimale : 669 Métallurgie Résumé : In this study, the textures and microstructures of Al–5%Mg after cold rolling 95% and recrystallization at 300 and 450°C have been investigated. The cold rolling textures were typical but the recrystallization textures at 300°C comprised Cube and S and at 450 °C, Cube, ND Rotated Cube plus a weak Q component. The deformed grains were wavy in the longitudinal section as a result of composite-like behaviour, and the narrowed regions had scattered orientations which weakened the final annealing texture. Another feature was grains dividing into their respective crystallographic complements. S grains frequently behaved in this way and nucleation of S-oriented recrystallized material at low temperature was common. Cube-oriented volumes were often found between complementary S volumes, and this favoured micro-growth selection and a detailed discussion of the Cube origins are given. Remarkably, recrystallization texture is largely determined by the behaviour of S- and Cube-oriented material. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Direct observation of the NiTi martensitic phase transformation in nanoscale volumes / Jia Ye in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 490-498 Titre : Direct observation of the NiTi martensitic phase transformation in nanoscale volumes Type de document : texte imprimé Auteurs : Jia Ye, Auteur ; Raja K. Mishra, Auteur ; Alan R. Pelton, Auteur Article en page(s) : pp. 490-498 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Transmission  electron  microscopy  Compression  Phase  transformation  Shape  memory  alloys  Ni–Ti Index. décimale : 669 Métallurgie Résumé : We report on quantitative in situ transmission electron microscopy nanocompression tests used to study the deformation behavior of NiTi pillars on the nanometer scale. By recording the diffraction patterns in real time we have obtained direct evidence that the stress-induced B2 to B19′ (austenite to martensite) transformation exists in NiTi even when the sample size is below 200 nm. Correlation of the appearance of the B19′ phase in the diffraction pattern with our quantitative data showed that the transformation starts at approximately 1 GPa. We found that the transformation occurred through a multi-step process, and that the reverse transformation did not occur due to extensive deformation of the B19′ phase. Our results have direct implications for the application of the shape memory effect in nanoscale NiTi devices. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Direct observation of the NiTi martensitic phase transformation in nanoscale volumes [texte imprimé] / Jia Ye, Auteur ; Raja K. Mishra, Auteur ; Alan R. Pelton, Auteur . - pp. 490-498. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 490-498 Mots-clés : Transmission  electron  microscopy  Compression  Phase  transformation  Shape  memory  alloys  Ni–Ti Index. décimale : 669 Métallurgie Résumé : We report on quantitative in situ transmission electron microscopy nanocompression tests used to study the deformation behavior of NiTi pillars on the nanometer scale. By recording the diffraction patterns in real time we have obtained direct evidence that the stress-induced B2 to B19′ (austenite to martensite) transformation exists in NiTi even when the sample size is below 200 nm. Correlation of the appearance of the B19′ phase in the diffraction pattern with our quantitative data showed that the transformation starts at approximately 1 GPa. We found that the transformation occurred through a multi-step process, and that the reverse transformation did not occur due to extensive deformation of the B19′ phase. Our results have direct implications for the application of the shape memory effect in nanoscale NiTi devices. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Orientation stress field analysis in polycrystalline bcc steel using neutron diffraction / R. Dakhlaoui in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 499-509 Titre : Orientation stress field analysis in polycrystalline bcc steel using neutron diffraction Type de document : texte imprimé Auteurs : R. Dakhlaoui, Auteur ; V. Klosek, Auteur ; M.H. Mathon, Auteur Article en page(s) : pp. 499-509 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Orientation  stresses  Neutron  diffraction  Deformation  heterogeneities  Bainitic  steel Index. décimale : 669 Métallurgie Résumé : We propose a methodology associating texture determinations and strains measurements by neutron diffraction in order to analyse the stress fields within families of crystallites with the same crystallographic orientation in polycrystalline materials. This stress analysis method allows an intermediate approach between a local and a global scale characterization within the bulk of massive samples, and appears promising for coupling with modelling methods due to the statistically representative informations it provides. We report here its application to characterize in situ the mechanical behaviour under uniaxial tension of a low alloyed 16MND5 bainitic steel used for nuclear reactor pressure vessels. It appears that the selected investigated phases exhibit very different mechanical responses. A large plastic deformation heterogeneity is observed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Orientation stress field analysis in polycrystalline bcc steel using neutron diffraction [texte imprimé] / R. Dakhlaoui, Auteur ; V. Klosek, Auteur ; M.H. Mathon, Auteur . - pp. 499-509. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 499-509 Mots-clés : Orientation  stresses  Neutron  diffraction  Deformation  heterogeneities  Bainitic  steel Index. décimale : 669 Métallurgie Résumé : We propose a methodology associating texture determinations and strains measurements by neutron diffraction in order to analyse the stress fields within families of crystallites with the same crystallographic orientation in polycrystalline materials. This stress analysis method allows an intermediate approach between a local and a global scale characterization within the bulk of massive samples, and appears promising for coupling with modelling methods due to the statistically representative informations it provides. We report here its application to characterize in situ the mechanical behaviour under uniaxial tension of a low alloyed 16MND5 bainitic steel used for nuclear reactor pressure vessels. It appears that the selected investigated phases exhibit very different mechanical responses. A large plastic deformation heterogeneity is observed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Lattice dynamical finite-element method / Xiaohui Liu in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 510-523 Titre : Lattice dynamical finite-element method Type de document : texte imprimé Auteurs : Xiaohui Liu, Auteur ; Jianfeng Gu, Auteur ; Yao Shen, Directeur de thèse Article en page(s) : pp. 510-523 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Lattice  instability  Multiscale  modeling  Modulated  structure  Dislocation  nucleation  Phase  transformation Index. décimale : 669 Métallurgie Résumé : A lattice dynamical finite-element method (LDFEM) is proposed for multiscale analysis of stressed complex crystals. Interatomic potential is embedded into the constitutive relation within the hyperelasticity framework, and two energy-based lattice instability criteria, the Λ criterion and the soft phonon criterion, are incorporated into LDFEM for capturing stress-driven instabilities in a perfect crystal. The simulations of uniaxial loadings and a two-dimensional nanoindentation of B2-NiAl are performed using both LDFEM and molecular dynamics (MD). The good agreement of the simulated mechanical responses between the two methods validates the proposed method. Combination of the two criteria can provide a powerful tool for predicting lattice instabilities in complex crystals under load at zero or low temperatures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Lattice dynamical finite-element method [texte imprimé] / Xiaohui Liu, Auteur ; Jianfeng Gu, Auteur ; Yao Shen, Directeur de thèse . - pp. 510-523. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 510-523 Mots-clés : Lattice  instability  Multiscale  modeling  Modulated  structure  Dislocation  nucleation  Phase  transformation Index. décimale : 669 Métallurgie Résumé : A lattice dynamical finite-element method (LDFEM) is proposed for multiscale analysis of stressed complex crystals. Interatomic potential is embedded into the constitutive relation within the hyperelasticity framework, and two energy-based lattice instability criteria, the Λ criterion and the soft phonon criterion, are incorporated into LDFEM for capturing stress-driven instabilities in a perfect crystal. The simulations of uniaxial loadings and a two-dimensional nanoindentation of B2-NiAl are performed using both LDFEM and molecular dynamics (MD). The good agreement of the simulated mechanical responses between the two methods validates the proposed method. Combination of the two criteria can provide a powerful tool for predicting lattice instabilities in complex crystals under load at zero or low temperatures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Kinetic stages in the crystallization of deeply undercooled body-centered-cubic and face-centered-cubic metals / Y. Ashkenazy in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 524-530 Titre : Kinetic stages in the crystallization of deeply undercooled body-centered-cubic and face-centered-cubic metals Type de document : texte imprimé Auteurs : Y. Ashkenazy, Auteur ; R. S. Averback, Auteur Article en page(s) : pp. 524-530 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Crystallization  Interface  dynamics  Kinetics  Molecular  dynamics  Metals Index. décimale : 669 Métallurgie Résumé : Crystallization velocities in several face-centered-cubic (fcc) and body-centered-cubic (bcc) metals are calculated using molecular dynamics computer simulations for the (1 0 0) and densely packed (1 1 1) or (1 1 0) planar interfaces. We show that the crystallization kinetics can be divided into high- and low-temperature regimes, separated at a crossover temperature, Tc, which is associated with kinetic arrest. In the high-temperature regime, the velocity in both fcc and bcc metals initially increases with the degree of undercooling before reaching a maximum somewhat above the glass temperature. The kinetics is characterized by a thermally activated process. In the low-temperature regime, stresses develop in the interface and reduce the apparent activation energies for interface mobility. For the fcc metals (Cu, Ni, Ag and Pt) the activation energies fall essentially to zero, indicating an athermal process. For bcc metals (Fe, Mo, V, Ta) the activation energies remain finite, varying from ≈0.013 eV (Ta) to ≈0.2 eV (Mo). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Kinetic stages in the crystallization of deeply undercooled body-centered-cubic and face-centered-cubic metals [texte imprimé] / Y. Ashkenazy, Auteur ; R. S. Averback, Auteur . - pp. 524-530. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 524-530 Mots-clés : Crystallization  Interface  dynamics  Kinetics  Molecular  dynamics  Metals Index. décimale : 669 Métallurgie Résumé : Crystallization velocities in several face-centered-cubic (fcc) and body-centered-cubic (bcc) metals are calculated using molecular dynamics computer simulations for the (1 0 0) and densely packed (1 1 1) or (1 1 0) planar interfaces. We show that the crystallization kinetics can be divided into high- and low-temperature regimes, separated at a crossover temperature, Tc, which is associated with kinetic arrest. In the high-temperature regime, the velocity in both fcc and bcc metals initially increases with the degree of undercooling before reaching a maximum somewhat above the glass temperature. The kinetics is characterized by a thermally activated process. In the low-temperature regime, stresses develop in the interface and reduce the apparent activation energies for interface mobility. For the fcc metals (Cu, Ni, Ag and Pt) the activation energies fall essentially to zero, indicating an athermal process. For bcc metals (Fe, Mo, V, Ta) the activation energies remain finite, varying from ≈0.013 eV (Ta) to ≈0.2 eV (Mo). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

First-principles study of solute–vacancy binding in magnesium / Dongwon Shin in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 531-540 Titre : First-principles study of solute–vacancy binding in magnesium Type de document : texte imprimé Auteurs : Dongwon Shin, Auteur ; Christopher Wolverton, Auteur Article en page(s) : pp. 531-540 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Solute–vacancy  binding  Magnesium  alloys  First-principles  calculations Index. décimale : 669 Métallurgie Résumé : Solute–vacancy binding is a key quantity in understanding diffusion kinetics, and may also have a considerable impact on the hardening response in Mg alloys. However, the binding energetics between solute impurities and vacancies in Mg are notoriously difficult to measure accurately and are largely unknown. Here, we present a large database of solute–vacancy binding energies in Mg from first-principles calculations based on density functional theory. Our vacancy formation energy and dilute mixing energy, which are byproducts of the solute–vacancy binding calculations, show good agreement with experiments, where available. We have investigated the simple physical effects controlling solute–vacancy binding in Mg and find that there is a modest correlation between binding energy and solute size, with larger solute atoms more favorably binding with neighboring vacancies to relax the strain induced by the solutes. Most early 3d transition metal solutes do not favorably bind with vacancies, indicating that a simple bond-counting argument is not sufficient to explain the trends in binding, in contrast to the case of binding in Al. We also predict positive vacancy binding energies for some commonly used microalloying elements in Mg which are known to improve age hardenability, i.e. Na, In, Zn, Ag and Ca. Even larger vacancy binding energies are found for some other solutes (e.g. Cu, Sn, Pb, Bi and Pt), which await experimental validation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] First-principles study of solute–vacancy binding in magnesium [texte imprimé] / Dongwon Shin, Auteur ; Christopher Wolverton, Auteur . - pp. 531-540. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 531-540 Mots-clés : Solute–vacancy  binding  Magnesium  alloys  First-principles  calculations Index. décimale : 669 Métallurgie Résumé : Solute–vacancy binding is a key quantity in understanding diffusion kinetics, and may also have a considerable impact on the hardening response in Mg alloys. However, the binding energetics between solute impurities and vacancies in Mg are notoriously difficult to measure accurately and are largely unknown. Here, we present a large database of solute–vacancy binding energies in Mg from first-principles calculations based on density functional theory. Our vacancy formation energy and dilute mixing energy, which are byproducts of the solute–vacancy binding calculations, show good agreement with experiments, where available. We have investigated the simple physical effects controlling solute–vacancy binding in Mg and find that there is a modest correlation between binding energy and solute size, with larger solute atoms more favorably binding with neighboring vacancies to relax the strain induced by the solutes. Most early 3d transition metal solutes do not favorably bind with vacancies, indicating that a simple bond-counting argument is not sufficient to explain the trends in binding, in contrast to the case of binding in Al. We also predict positive vacancy binding energies for some commonly used microalloying elements in Mg which are known to improve age hardenability, i.e. Na, In, Zn, Ag and Ca. Even larger vacancy binding energies are found for some other solutes (e.g. Cu, Sn, Pb, Bi and Pt), which await experimental validation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Effects of Ti, Zr, and Hf on the phase stability of Mo_ss + Mo3Si + Mo5SiB2 alloys at 1600 °C / Ying Yang in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 541-548 Titre : Effects of Ti, Zr, and Hf on the phase stability of Mo_ss + Mo3Si + Mo5SiB2 alloys at 1600 °C Type de document : texte imprimé Auteurs : Ying Yang, Auteur ; H. Bei, Auteur ; Shuanglin Chen, Auteur Article en page(s) : pp. 541-548 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Refractory  metals  Silicides  Multicomponent  phase  equilibrium  CALPHAD  Thermodynamics Index. décimale : 669 Métallurgie Résumé : Understanding the stability of the three-phase Mo_ss + Mo3Si + Mo5SiB2 region is important for alloy design of Mo–Si–B-based refractory metal intermetallic composites. In this work, thermodynamic modeling is coupled with guided experiments to study phase stability in this three-phase region of the Mo–Si–B–X (X = Ti, Zr, Hf) system. Both the calculated and experimental results show that additions of Zr and Hf limit significantly the stability of the three-phase region because of the formation of the ternary phases MoSiZr and MoSiHf, while Ti addition leads to a much larger region of stability for the three-phase equilibrium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Effects of Ti, Zr, and Hf on the phase stability of Mo_ss + Mo3Si + Mo5SiB2 alloys at 1600 °C [texte imprimé] / Ying Yang, Auteur ; H. Bei, Auteur ; Shuanglin Chen, Auteur . - pp. 541-548. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 541-548 Mots-clés : Refractory  metals  Silicides  Multicomponent  phase  equilibrium  CALPHAD  Thermodynamics Index. décimale : 669 Métallurgie Résumé : Understanding the stability of the three-phase Mo_ss + Mo3Si + Mo5SiB2 region is important for alloy design of Mo–Si–B-based refractory metal intermetallic composites. In this work, thermodynamic modeling is coupled with guided experiments to study phase stability in this three-phase region of the Mo–Si–B–X (X = Ti, Zr, Hf) system. Both the calculated and experimental results show that additions of Zr and Hf limit significantly the stability of the three-phase region because of the formation of the ternary phases MoSiZr and MoSiHf, while Ti addition leads to a much larger region of stability for the three-phase equilibrium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Orientation dependence of shock-induced twinning and substructures in a copper bicrystal / Fang Cao in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 549-559 Titre : Orientation dependence of shock-induced twinning and substructures in a copper bicrystal Type de document : texte imprimé Auteurs : Fang Cao, Auteur ; Irene J. Beyerlein, Auteur ; Francis L. Addessio, Auteur Article en page(s) : pp. 549-559 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Copper  Shock  recovery  Deformation  structure  Twinning  Dislocation  structure Index. décimale : 669 Métallurgie Résumé : Shock recovery experiments have been conducted to assess the role of shock stress and orientation dependence on substructure evolution and deformation twinning of a [1 0 0]/View the MathML source copper bicrystal. Transmission electron microscopy of the post-shock specimens revealed that well-defined dislocation cell structures developed in both grains and the average cell size decreased with increasing shock pressure from 5 to 10 GPa. Twinning occurred in the [1 0 0] grain, but not the View the MathML source grain, at the 10 GPa shock pressure. The stress and orientation dependence of incipient twinning can be predicted by the stress and orientation conditions required to dissociate slip dislocations into glissile twinning dislocations. The dynamic widths between the two partials are calculated considering the three-dimensional deviatoric stress state induced by the shock as calculated using plane-strain plate impact simulations and the relativistic and drag effects on dislocations moving at high speeds. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Orientation dependence of shock-induced twinning and substructures in a copper bicrystal [texte imprimé] / Fang Cao, Auteur ; Irene J. Beyerlein, Auteur ; Francis L. Addessio, Auteur . - pp. 549-559. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 549-559 Mots-clés : Copper  Shock  recovery  Deformation  structure  Twinning  Dislocation  structure Index. décimale : 669 Métallurgie Résumé : Shock recovery experiments have been conducted to assess the role of shock stress and orientation dependence on substructure evolution and deformation twinning of a [1 0 0]/View the MathML source copper bicrystal. Transmission electron microscopy of the post-shock specimens revealed that well-defined dislocation cell structures developed in both grains and the average cell size decreased with increasing shock pressure from 5 to 10 GPa. Twinning occurred in the [1 0 0] grain, but not the View the MathML source grain, at the 10 GPa shock pressure. The stress and orientation dependence of incipient twinning can be predicted by the stress and orientation conditions required to dissociate slip dislocations into glissile twinning dislocations. The dynamic widths between the two partials are calculated considering the three-dimensional deviatoric stress state induced by the shock as calculated using plane-strain plate impact simulations and the relativistic and drag effects on dislocations moving at high speeds. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Single-step, rapid low-temperature synthesis of Si quantum dots embedded in an amorphous SiC matrix in high-density reactive plasmas / Qijin Cheng in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 560-569 Titre : Single-step, rapid low-temperature synthesis of Si quantum dots embedded in an amorphous SiC matrix in high-density reactive plasmas Type de document : texte imprimé Auteurs : Qijin Cheng, Auteur ; Shuyan Xu, Auteur ; Kostya (Ken) Ostrikov, Auteur Article en page(s) : pp. 560-569 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Chemical  vapor  deposition  Quantum  dots  Inductively  coupled  plasmas  Solar  cells Index. décimale : 669 Métallurgie Résumé : A simple, effective and innovative approach based on low-pressure, thermally nonequilibrium, high-density inductively coupled plasmas is proposed to rapidly synthesize Si quantum dots (QDs) embedded in an amorphous SiC (a-SiC) matrix at a low substrate temperature and without any commonly used hydrogen dilution. The experimental results clearly demonstrate that uniform crystalline Si QDs with a size of 3–4 nm embedded in the silicon-rich (carbon content up to 10.7at.%) a-SiC matrix can be formed from the reactive mixture of silane and methane gases, with high growth rates of not, vert, similar1.27–2.34 nm s−1 and at a low substrate temperature of 200°C. The achievement of the high-rate growth of Si QDs embedded in the a-SiC without any commonly used hydrogen dilution is discussed based on the unique properties of the inductively coupled plasma-based process. This work is particularly important for the development of the all-Si tandem cell-based third generation photovoltaic solar cells. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Single-step, rapid low-temperature synthesis of Si quantum dots embedded in an amorphous SiC matrix in high-density reactive plasmas [texte imprimé] / Qijin Cheng, Auteur ; Shuyan Xu, Auteur ; Kostya (Ken) Ostrikov, Auteur . - pp. 560-569. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 560-569 Mots-clés : Chemical  vapor  deposition  Quantum  dots  Inductively  coupled  plasmas  Solar  cells Index. décimale : 669 Métallurgie Résumé : A simple, effective and innovative approach based on low-pressure, thermally nonequilibrium, high-density inductively coupled plasmas is proposed to rapidly synthesize Si quantum dots (QDs) embedded in an amorphous SiC (a-SiC) matrix at a low substrate temperature and without any commonly used hydrogen dilution. The experimental results clearly demonstrate that uniform crystalline Si QDs with a size of 3–4 nm embedded in the silicon-rich (carbon content up to 10.7at.%) a-SiC matrix can be formed from the reactive mixture of silane and methane gases, with high growth rates of not, vert, similar1.27–2.34 nm s−1 and at a low substrate temperature of 200°C. The achievement of the high-rate growth of Si QDs embedded in the a-SiC without any commonly used hydrogen dilution is discussed based on the unique properties of the inductively coupled plasma-based process. This work is particularly important for the development of the all-Si tandem cell-based third generation photovoltaic solar cells. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Thermal conductivity of semiconductor (bismuth–telluride)–semimetal (antimony) superlattice nanostructures / D. Pinisetty in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 570-576 Titre : Thermal conductivity of semiconductor (bismuth–telluride)–semimetal (antimony) superlattice nanostructures Type de document : texte imprimé Auteurs : D. Pinisetty, Auteur ; R.V. Devireddy, Auteur Article en page(s) : pp. 570-576 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thermoelectric  figure  of  merit  Boltzmann  transport  equation  Nanotubes  Nanowires  Matthiessen  model Index. décimale : 669 Métallurgie Résumé : In the present study, the thermal conductivity of superlattice bismuth–telluride (semiconductor)–antimony (semimetal) (Bi2Te3–Sb) nanostructures (nanowires and nanotubes) has been modeled using an incoherent particle model, approximating all the scattering to be diffuse and gray, and applying a Matthiessen-type simplification. The effect of varying the ratio of the superlattice nanowire segment lengths (L) of Sb and Bi2Te3 has also been studied assuming: (i) LSb = LBi2Te3; (ii) LSb = 0.25 × LBi2Te3; (iii) LSb = 0.5 × LBi2Te3; (iv) LSb = 2.0 × LBi2Te3; and (v) LSb = 4.0 × LBi2Te3. It is shown that thermal conductivity of the superlattice nanowires reduces either with a reduction of segment lengths (LSb and LBi2Te3) or with a reduction of nanowire diameter. Specifically, the thermal conductivity is lower than 2 W m−1 K−1 (the bulk value for Bi2Te3), even when the nanowire diameters (10 nm) are 10 times larger than the mean free path (1 nm) of Bi2Te3, provided the individual segment lengths (LSb and LBi2Te3) are lower than the mean free path limit. The thermal conductivity of either superlattice nanowires or superlattice nanotubes was also observed to decrease, as the segment length of semimetal (Sb) is lowered relative to the segment length of semiconductor (Bi2Te3). In the case of superlattice nanotubes, a reduction in wall thickness caused a corresponding reduction in thermal conductivity as well. For example, with a fixed outer diameter value of 5 nm, the thermal conductivity of the nanotubes can be lowered by not, vert, similar33% by decreasing the tube wall thickness from 0.75 to 0.1 nm. Our predictions also suggest that for a given value of the segment lengths of LSb and LBi2Te3, nanotubes exhibit a lower thermal conductivity than nanowires. This therefore suggests that nanotubes of superlattice structures of Sb and Bi2Te3 should exhibit a higher thermoelectric figure of merit (ZT) than nanowires under corresponding conditions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Thermal conductivity of semiconductor (bismuth–telluride)–semimetal (antimony) superlattice nanostructures [texte imprimé] / D. Pinisetty, Auteur ; R.V. Devireddy, Auteur . - pp. 570-576. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 570-576 Mots-clés : Thermoelectric  figure  of  merit  Boltzmann  transport  equation  Nanotubes  Nanowires  Matthiessen  model Index. décimale : 669 Métallurgie Résumé : In the present study, the thermal conductivity of superlattice bismuth–telluride (semiconductor)–antimony (semimetal) (Bi2Te3–Sb) nanostructures (nanowires and nanotubes) has been modeled using an incoherent particle model, approximating all the scattering to be diffuse and gray, and applying a Matthiessen-type simplification. The effect of varying the ratio of the superlattice nanowire segment lengths (L) of Sb and Bi2Te3 has also been studied assuming: (i) LSb = LBi2Te3; (ii) LSb = 0.25 × LBi2Te3; (iii) LSb = 0.5 × LBi2Te3; (iv) LSb = 2.0 × LBi2Te3; and (v) LSb = 4.0 × LBi2Te3. It is shown that thermal conductivity of the superlattice nanowires reduces either with a reduction of segment lengths (LSb and LBi2Te3) or with a reduction of nanowire diameter. Specifically, the thermal conductivity is lower than 2 W m−1 K−1 (the bulk value for Bi2Te3), even when the nanowire diameters (10 nm) are 10 times larger than the mean free path (1 nm) of Bi2Te3, provided the individual segment lengths (LSb and LBi2Te3) are lower than the mean free path limit. The thermal conductivity of either superlattice nanowires or superlattice nanotubes was also observed to decrease, as the segment length of semimetal (Sb) is lowered relative to the segment length of semiconductor (Bi2Te3). In the case of superlattice nanotubes, a reduction in wall thickness caused a corresponding reduction in thermal conductivity as well. For example, with a fixed outer diameter value of 5 nm, the thermal conductivity of the nanotubes can be lowered by not, vert, similar33% by decreasing the tube wall thickness from 0.75 to 0.1 nm. Our predictions also suggest that for a given value of the segment lengths of LSb and LBi2Te3, nanotubes exhibit a lower thermal conductivity than nanowires. This therefore suggests that nanotubes of superlattice structures of Sb and Bi2Te3 should exhibit a higher thermoelectric figure of merit (ZT) than nanowires under corresponding conditions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Sr- and Ti-site substitution, lattice dynamics, and octahedral tilt transition relationship in SrTiO3: Mn ceramics / Alexander Tkach in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 577-582 Titre : Sr- and Ti-site substitution, lattice dynamics, and octahedral tilt transition relationship in SrTiO3: Mn ceramics Type de document : texte imprimé Auteurs : Alexander Tkach, Auteur ; Paula M. Vilarinho, Auteur ; Dmitry Nuzhnyy, Auteur Article en page(s) : pp. 577-582 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : SrTiO3  Dopants  Structural  phase  transition  Phonon  dynamics  Infrared  and  terahertz  spectroscopy Index. décimale : 669 Métallurgie Résumé : SrTiO3:Mn ceramics, prepared according to the chemical formulae Sr1–xMnxTiO3 and SrTi1–yMnyO3, are studied by Fourier transform infrared and time-domain terahertz spectroscopy in the temperature range of 10–300 K to support the incorporation of Mn ions into the perovskite lattice of SrTiO3, and to ascertain their different lattice site locations. The polar soft mode of the incipient ferroelectric SrTiO3 is found to be hardened in the whole temperature range by the substitution of Mn ions on Ti sites, and only in the low-temperature range by the Sr site substitution. Activation of the mode, associated with the R point condensation of the Brillouin zone due to the doubling of the unit cell by antiphase rotations of the O-octahedra below the structural transition temperature Ta, shows that the substitution of Mn ions on the Sr sites increases Ta, whereas the Ti-site substitution suppresses Ta with respect to the undoped SrTiO3. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Sr- and Ti-site substitution, lattice dynamics, and octahedral tilt transition relationship in SrTiO3: Mn ceramics [texte imprimé] / Alexander Tkach, Auteur ; Paula M. Vilarinho, Auteur ; Dmitry Nuzhnyy, Auteur . - pp. 577-582. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 577-582 Mots-clés : SrTiO3  Dopants  Structural  phase  transition  Phonon  dynamics  Infrared  and  terahertz  spectroscopy Index. décimale : 669 Métallurgie Résumé : SrTiO3:Mn ceramics, prepared according to the chemical formulae Sr1–xMnxTiO3 and SrTi1–yMnyO3, are studied by Fourier transform infrared and time-domain terahertz spectroscopy in the temperature range of 10–300 K to support the incorporation of Mn ions into the perovskite lattice of SrTiO3, and to ascertain their different lattice site locations. The polar soft mode of the incipient ferroelectric SrTiO3 is found to be hardened in the whole temperature range by the substitution of Mn ions on Ti sites, and only in the low-temperature range by the Sr site substitution. Activation of the mode, associated with the R point condensation of the Brillouin zone due to the doubling of the unit cell by antiphase rotations of the O-octahedra below the structural transition temperature Ta, shows that the substitution of Mn ions on the Sr sites increases Ta, whereas the Ti-site substitution suppresses Ta with respect to the undoped SrTiO3. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

A model for oxidation-assisted low cycle fatigue of superalloys / M.Y. He in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 583-591 Titre : A model for oxidation-assisted low cycle fatigue of superalloys Type de document : texte imprimé Auteurs : M.Y. He, Auteur ; A.G. Evans, Auteur Article en page(s) : pp. 583-591 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Low  cycle  fatigue  Superalloys  Thermally  grown  oxide  Finite  element  Creep Index. décimale : 669 Métallurgie Résumé : Cracks in superalloys subject to an isothermal, sustained hold, compressive strain cycle experience cycle-by-cycle extension. The phenomenon has been attributed to the strains induced by the formation a thermally grown oxide (TGO) on the crack faces with the strain accommodated by alloy creep. Basic features have been elucidated through finite element calculations. The present objective is to develop a straightforward model that explicitly relates the fatigue to the TGO strains and the alloy creep rates. For this purpose, insights are first developed through finite element simulations. The results are rationalized through simple mechanics assessments, leading to analytic expressions for the crack growth rate. Insights are gained using a plasticity model that demonstrates how the TGO growth strains are accommodated and the stress distributed at various stages during the strain cycle. Creep calculations highlight the time-dependent phenomena occurring during the hold interlude. Finally, an expression for the crack growth rate is presented in terms of the TGO growth strain rate, its thickness, the alloy creep strength and the hold time. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] A model for oxidation-assisted low cycle fatigue of superalloys [texte imprimé] / M.Y. He, Auteur ; A.G. Evans, Auteur . - pp. 583-591. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 583-591 Mots-clés : Low  cycle  fatigue  Superalloys  Thermally  grown  oxide  Finite  element  Creep Index. décimale : 669 Métallurgie Résumé : Cracks in superalloys subject to an isothermal, sustained hold, compressive strain cycle experience cycle-by-cycle extension. The phenomenon has been attributed to the strains induced by the formation a thermally grown oxide (TGO) on the crack faces with the strain accommodated by alloy creep. Basic features have been elucidated through finite element calculations. The present objective is to develop a straightforward model that explicitly relates the fatigue to the TGO strains and the alloy creep rates. For this purpose, insights are first developed through finite element simulations. The results are rationalized through simple mechanics assessments, leading to analytic expressions for the crack growth rate. Insights are gained using a plasticity model that demonstrates how the TGO growth strains are accommodated and the stress distributed at various stages during the strain cycle. Creep calculations highlight the time-dependent phenomena occurring during the hold interlude. Finally, an expression for the crack growth rate is presented in terms of the TGO growth strain rate, its thickness, the alloy creep strength and the hold time. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Mechanical anisotropy and deep drawing behaviour of AZ31 and ZE10 magnesium alloy sheets / Sangbong Yi in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 592-605 Titre : Mechanical anisotropy and deep drawing behaviour of AZ31 and ZE10 magnesium alloy sheets Type de document : texte imprimé Auteurs : Sangbong Yi, Auteur ; Jan Bohlen, Auteur ; Frank Heinemann, Auteur Article en page(s) : pp. 592-605 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium  alloys  Mechanical  properties  Texture  Deep  drawing  Dynamic  recrystallization Index. décimale : 669 Métallurgie Résumé : The influence of the initial microstructure on the deep drawability and the associated microstructural evolution in two different magnesium alloy sheets, AZ31 and ZE10, has been examined. Tensile testing at room temperature shows that the AZ31 sheet has high plastic strain ratios, r = 2–3, which are caused by strong basal-type texture. The ZE10 sheet shows lower r values, r not, vert, similar 1, as a result of its weak texture. Deep drawing experiments carried out over the temperature range 100–300 °C revealed that the ZE10 sheet can be successfully deep-drawn at lower temperatures than the AZ31 sheet. The ZE10 cups show earing despite the weak texture and low normal anisotropy, while earing of the AZ31 cups is negligible. In the ZE10 cups, deformation is accommodated mainly by left angle bracketaright-pointing angle bracket slips and by compression as well as secondary twinning. The occurrence of dynamic recrystallization is observed in successfully deep-drawn AZ31 cups. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Mechanical anisotropy and deep drawing behaviour of AZ31 and ZE10 magnesium alloy sheets [texte imprimé] / Sangbong Yi, Auteur ; Jan Bohlen, Auteur ; Frank Heinemann, Auteur . - pp. 592-605. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 592-605 Mots-clés : Magnesium  alloys  Mechanical  properties  Texture  Deep  drawing  Dynamic  recrystallization Index. décimale : 669 Métallurgie Résumé : The influence of the initial microstructure on the deep drawability and the associated microstructural evolution in two different magnesium alloy sheets, AZ31 and ZE10, has been examined. Tensile testing at room temperature shows that the AZ31 sheet has high plastic strain ratios, r = 2–3, which are caused by strong basal-type texture. The ZE10 sheet shows lower r values, r not, vert, similar 1, as a result of its weak texture. Deep drawing experiments carried out over the temperature range 100–300 °C revealed that the ZE10 sheet can be successfully deep-drawn at lower temperatures than the AZ31 sheet. The ZE10 cups show earing despite the weak texture and low normal anisotropy, while earing of the AZ31 cups is negligible. In the ZE10 cups, deformation is accommodated mainly by left angle bracketaright-pointing angle bracket slips and by compression as well as secondary twinning. The occurrence of dynamic recrystallization is observed in successfully deep-drawn AZ31 cups. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Wettability of pure Ti by molten pure Mg droplets / Katsuyoshi Kondoh in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 606-614 Titre : Wettability of pure Ti by molten pure Mg droplets Type de document : texte imprimé Auteurs : Katsuyoshi Kondoh, Auteur ; Masashi Kawakami, Auteur ; Hisashi Imai, Auteur Article en page(s) : pp. 606-614 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Pure  magnesium  Titanium  Contact  angle  Young’s  equation  Evaporation Index. décimale : 669 Métallurgie Résumé : The wetting behavior of molten pure Mg droplets on pure Ti substrate, a crucial phenomenon in the design of Mg matrix composites reinforced with Ti particles, was investigated by the sessile drop method. The contact angle was measured in high-purity argon (99.999%) at 1073 K. In particular, the effects of two important parameters on the contact angle were evaluated: Mg evaporation during the wetting test; and surface oxide film of the substrate. The calculation method to estimate the modified contact angle involved taking the morphological changes of the droplet outline due to the evaporation into consideration. By changing the thickness of the surface oxide films on the Ti substrate, it was possible to examine the wettability and the chemical reactions at the interface between the solidified Mg drop and the substrate were investigated by scanning electron microscopy–energy dispersive X-ray spectrometry analysis. At the initial wetting stage, a large contact angle with 95–110° was obtained, which depended on the reduction of TiO2 surface films by Mg droplets. When the molten Mg contacts an area of pure Ti after reduction, the contact angle suddenly decreased. The equilibrium value at the stable state strongly depended on the surface roughness of the Ti plate. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Wettability of pure Ti by molten pure Mg droplets [texte imprimé] / Katsuyoshi Kondoh, Auteur ; Masashi Kawakami, Auteur ; Hisashi Imai, Auteur . - pp. 606-614. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 606-614 Mots-clés : Pure  magnesium  Titanium  Contact  angle  Young’s  equation  Evaporation Index. décimale : 669 Métallurgie Résumé : The wetting behavior of molten pure Mg droplets on pure Ti substrate, a crucial phenomenon in the design of Mg matrix composites reinforced with Ti particles, was investigated by the sessile drop method. The contact angle was measured in high-purity argon (99.999%) at 1073 K. In particular, the effects of two important parameters on the contact angle were evaluated: Mg evaporation during the wetting test; and surface oxide film of the substrate. The calculation method to estimate the modified contact angle involved taking the morphological changes of the droplet outline due to the evaporation into consideration. By changing the thickness of the surface oxide films on the Ti substrate, it was possible to examine the wettability and the chemical reactions at the interface between the solidified Mg drop and the substrate were investigated by scanning electron microscopy–energy dispersive X-ray spectrometry analysis. At the initial wetting stage, a large contact angle with 95–110° was obtained, which depended on the reduction of TiO2 surface films by Mg droplets. When the molten Mg contacts an area of pure Ti after reduction, the contact angle suddenly decreased. The equilibrium value at the stable state strongly depended on the surface roughness of the Ti plate. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

The geometry, topology and structure of amorphous solids / Cheuk-Yu Lee in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 615-625 Titre : The geometry, topology and structure of amorphous solids Type de document : texte imprimé Auteurs : Cheuk-Yu Lee, Auteur ; Zbigniew H. Stachurski, Auteur ; T. Richard Welberry, Auteur Article en page(s) : pp. 615-625 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cluster  topology  Multiatomic  glass  Debye  scattering  Amorphousness Index. décimale : 669 Métallurgie Résumé : Clusters of atoms can be divided into three categories depending on their topology. One of the categories provides the basis for development of a model of a perfectly random structure (ideal amorphous solid) using the non-equilateral triangle topology in the coordination shell. Metallic glasses solidify as amorphous solids with random arrangement of atoms. A model of Zr-based metallic glass has been constructed and described in terms of cluster topology, and compared with a recently published dynamic molecular model of the same alloy. It is shown that the pair distribution function for the ideal amorphous model relates to the pair correlation function obtained from the dynamic model. Debye X-ray scattering computations reveal the presence of vacancies and other flaws relative to the ideal amorphous solid. A shift in the peak position can be predicted using the Erhenfest formula. Two atomic displacement mechanisms involving a five-atom sub-cluster are identified as the fundamental means of compositional redistribution between clusters in the alloy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] The geometry, topology and structure of amorphous solids [texte imprimé] / Cheuk-Yu Lee, Auteur ; Zbigniew H. Stachurski, Auteur ; T. Richard Welberry, Auteur . - pp. 615-625. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 615-625 Mots-clés : Cluster  topology  Multiatomic  glass  Debye  scattering  Amorphousness Index. décimale : 669 Métallurgie Résumé : Clusters of atoms can be divided into three categories depending on their topology. One of the categories provides the basis for development of a model of a perfectly random structure (ideal amorphous solid) using the non-equilateral triangle topology in the coordination shell. Metallic glasses solidify as amorphous solids with random arrangement of atoms. A model of Zr-based metallic glass has been constructed and described in terms of cluster topology, and compared with a recently published dynamic molecular model of the same alloy. It is shown that the pair distribution function for the ideal amorphous model relates to the pair correlation function obtained from the dynamic model. Debye X-ray scattering computations reveal the presence of vacancies and other flaws relative to the ideal amorphous solid. A shift in the peak position can be predicted using the Erhenfest formula. Two atomic displacement mechanisms involving a five-atom sub-cluster are identified as the fundamental means of compositional redistribution between clusters in the alloy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Micromechanics of high-temperature damage in dual-phase stainless steel / B. Chéhab in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 626-637 Titre : Micromechanics of high-temperature damage in dual-phase stainless steel Type de document : texte imprimé Auteurs : B. Chéhab, Auteur ; Y. Bréchet, Auteur ; M. Véron, Auteur Article en page(s) : pp. 626-637 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hot  working  Stainless  steels  Ductility  High-temperature  deformation  Micromechanical  modelling Index. décimale : 669 Métallurgie Résumé : High-temperature ductility of dual-phase stainless steels is investigated using a micromechanics approach of damage and fracture. Two different microstructures are studied with either a lamellar or a globular morphology of the ferrite phase, the latter being twice as ductile as the former at 1150 °C. The high-temperature damage evolution is characterized at different loading rates using notched round cylindrical bars producing different stress triaxialities, supplemented by fractographic analysis. The experimental observations have generated an advanced elasto-viscoplastic micromechanical damage model for both microstructures. With a detailed account of the process of nucleation, growth and coalescence of voids, the model properly captures the effect of stress triaxiality, strain rate, and morphology of the ferritic phase on the high-temperature ductility. The key factor controlling the loss of ductility in the lamellar microstructure is the constraint induced by the harder austenite layer on the softer ferrite zones. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Micromechanics of high-temperature damage in dual-phase stainless steel [texte imprimé] / B. Chéhab, Auteur ; Y. Bréchet, Auteur ; M. Véron, Auteur . - pp. 626-637. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 626-637 Mots-clés : Hot  working  Stainless  steels  Ductility  High-temperature  deformation  Micromechanical  modelling Index. décimale : 669 Métallurgie Résumé : High-temperature ductility of dual-phase stainless steels is investigated using a micromechanics approach of damage and fracture. Two different microstructures are studied with either a lamellar or a globular morphology of the ferrite phase, the latter being twice as ductile as the former at 1150 °C. The high-temperature damage evolution is characterized at different loading rates using notched round cylindrical bars producing different stress triaxialities, supplemented by fractographic analysis. The experimental observations have generated an advanced elasto-viscoplastic micromechanical damage model for both microstructures. With a detailed account of the process of nucleation, growth and coalescence of voids, the model properly captures the effect of stress triaxiality, strain rate, and morphology of the ferritic phase on the high-temperature ductility. The key factor controlling the loss of ductility in the lamellar microstructure is the constraint induced by the harder austenite layer on the softer ferrite zones. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

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

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

Effect of high-pressure torsion on hydrogen trapping in Fe–0.01 mass% C and type 310S austenitic stainless steel / Yoji Mine in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 649-657 Titre : Effect of high-pressure torsion on hydrogen trapping in Fe–0.01 mass% C and type 310S austenitic stainless steel Type de document : texte imprimé Auteurs : Yoji Mine, Auteur ; Zenji Horita, Auteur ; Yukitaka Murakami, Auteur Article en page(s) : pp. 649-657 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : High-pressure  torsion  Hydrogen  Grain  boundaries  Dislocations  Iron Index. décimale : 669 Métallurgie Résumé : The effect of high-pressure torsion (HPT) on hydrogen trapping in Fe–0.01 mass% C and type 310S stainless steel was studied by metallographic characterization and hydrogen measurement after hydrogen gas charging. Hardening of both materials after processing by HPT was achieved through grain refinement. Hydrogen trapping in the Fe–0.01 mass% C was significantly increased by HPT processing, because of high binding energies of hydrogen with lattice defects such as dislocations and grain boundaries in body-centred cubic iron. In the type 310S processed by HPT, the hydrogen content that trapped by dislocations was less than that dissolved within the lattice and the contribution of grain boundaries on hydrogen trapping can be neglected. In the stable austenitic stainless steel processed by HPT, decreasing the dislocation density can reduce the trapped hydrogen to the solution-treated level while the hardening by grain refinement is retained. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Effect of high-pressure torsion on hydrogen trapping in Fe–0.01 mass% C and type 310S austenitic stainless steel [texte imprimé] / Yoji Mine, Auteur ; Zenji Horita, Auteur ; Yukitaka Murakami, Auteur . - pp. 649-657. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 649-657 Mots-clés : High-pressure  torsion  Hydrogen  Grain  boundaries  Dislocations  Iron Index. décimale : 669 Métallurgie Résumé : The effect of high-pressure torsion (HPT) on hydrogen trapping in Fe–0.01 mass% C and type 310S stainless steel was studied by metallographic characterization and hydrogen measurement after hydrogen gas charging. Hardening of both materials after processing by HPT was achieved through grain refinement. Hydrogen trapping in the Fe–0.01 mass% C was significantly increased by HPT processing, because of high binding energies of hydrogen with lattice defects such as dislocations and grain boundaries in body-centred cubic iron. In the type 310S processed by HPT, the hydrogen content that trapped by dislocations was less than that dissolved within the lattice and the contribution of grain boundaries on hydrogen trapping can be neglected. In the stable austenitic stainless steel processed by HPT, decreasing the dislocation density can reduce the trapped hydrogen to the solution-treated level while the hardening by grain refinement is retained. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Hydrogenography of MgyNi1−yHx gradient thin films / R. Gremaud in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 658-668 Titre : Hydrogenography of MgyNi1−yHx gradient thin films : interplay between the thermodynamics and kinetics of hydrogenation Type de document : texte imprimé Auteurs : R. Gremaud, Auteur ; C. P. Broedersz, Auteur ; A. Borgschulte, Auteur Article en page(s) : pp. 658-668 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hydrogen  storage  Magnesium  nickel  hydride  Mg2NiH4  MgH2  Hydrogenography Index. décimale : 669 Métallurgie Résumé : We monitor the hydrogenation of PTFE/Pd-capped MgyNi1−yHx gradient thin films using the change in optical transmission as a function of time, temperature and hydrogen pressure, to study the relation between kinetics and thermodynamics of hydrogenation of this multiphase hydride system. The interplay between kinetics and thermodynamics is used to extrapolate the hydrogenation equilibrium pressures via the H-absorption rate. Pressure–optical-transmission–isotherms determined independently at different temperatures provide a cross-check for the equilibrium pressure and the enthalpy of H-absorption. We find that the hydrogenation reaction is destabilized with respect to the Mg2Ni → Mg2NiH4 reaction for Mg fractions close to the Mg2Ni–Mg eutectic point. From a comparison with calculated enthalpies obtained from density functional theory, we conclude that the experimentally observed destabilization originates from the well-mixed microstructure around the eutectic point. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Hydrogenography of MgyNi1−yHx gradient thin films : interplay between the thermodynamics and kinetics of hydrogenation [texte imprimé] / R. Gremaud, Auteur ; C. P. Broedersz, Auteur ; A. Borgschulte, Auteur . - pp. 658-668. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 658-668 Mots-clés : Hydrogen  storage  Magnesium  nickel  hydride  Mg2NiH4  MgH2  Hydrogenography Index. décimale : 669 Métallurgie Résumé : We monitor the hydrogenation of PTFE/Pd-capped MgyNi1−yHx gradient thin films using the change in optical transmission as a function of time, temperature and hydrogen pressure, to study the relation between kinetics and thermodynamics of hydrogenation of this multiphase hydride system. The interplay between kinetics and thermodynamics is used to extrapolate the hydrogenation equilibrium pressures via the H-absorption rate. Pressure–optical-transmission–isotherms determined independently at different temperatures provide a cross-check for the equilibrium pressure and the enthalpy of H-absorption. We find that the hydrogenation reaction is destabilized with respect to the Mg2Ni → Mg2NiH4 reaction for Mg fractions close to the Mg2Ni–Mg eutectic point. From a comparison with calculated enthalpies obtained from density functional theory, we conclude that the experimentally observed destabilization originates from the well-mixed microstructure around the eutectic point. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Conversion of MX nitrides to Z-phase in a martensitic 12% Cr steel / Leonardo Cipolla in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 669-679 Titre : Conversion of MX nitrides to Z-phase in a martensitic 12% Cr steel Type de document : texte imprimé Auteurs : Leonardo Cipolla, Auteur ; Hilmar K. Danielsen, Auteur ; Dario Venditti, Auteur Article en page(s) : pp. 669-679 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : TEM  XRD  Heat  resistant  steels  Nitrides  Phase  transformation  kinetics Index. décimale : 669 Métallurgie Résumé : A 12% Cr model steel was designed with the purpose of studying the nucleation and growth of modified Z-phase, Cr(V,Nb)N. The model alloy develops Z-phase after relatively short ageing times and contains only nitrides of Cr, V and Nb. Interferences from the presence of carbides and the development of Laves phase were avoided by keeping the C, W and Mo contents as low as possible. Transmission electron microscopy and X-ray diffraction analysis of extracted particles were used to follow the evolutions of phase composition, phase morphology and phase fraction, particularly of the precipitation of Z-phase, during ageing at 600, 650 and 700°C for up to 103 h. The development of Z-phase appears to be accomplished by the diffusion of Cr atoms into (V,Nb)N particles and their subsequent conversion into cubic or tetragonal Z-phase. Studies at various temperatures indicate that Z-phase development proceeds fastest at 650°C and that Z-phase forms faster at prior austenite grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Conversion of MX nitrides to Z-phase in a martensitic 12% Cr steel [texte imprimé] / Leonardo Cipolla, Auteur ; Hilmar K. Danielsen, Auteur ; Dario Venditti, Auteur . - pp. 669-679. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 669-679 Mots-clés : TEM  XRD  Heat  resistant  steels  Nitrides  Phase  transformation  kinetics Index. décimale : 669 Métallurgie Résumé : A 12% Cr model steel was designed with the purpose of studying the nucleation and growth of modified Z-phase, Cr(V,Nb)N. The model alloy develops Z-phase after relatively short ageing times and contains only nitrides of Cr, V and Nb. Interferences from the presence of carbides and the development of Laves phase were avoided by keeping the C, W and Mo contents as low as possible. Transmission electron microscopy and X-ray diffraction analysis of extracted particles were used to follow the evolutions of phase composition, phase morphology and phase fraction, particularly of the precipitation of Z-phase, during ageing at 600, 650 and 700°C for up to 103 h. The development of Z-phase appears to be accomplished by the diffusion of Cr atoms into (V,Nb)N particles and their subsequent conversion into cubic or tetragonal Z-phase. Studies at various temperatures indicate that Z-phase development proceeds fastest at 650°C and that Z-phase forms faster at prior austenite grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Crystal structure, morphology and physical properties of LaCo1−xTixO3±δ perovskites prepared by a citric acid assisted soft chemistry synthesis / Rosa Robert in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 680-691 Titre : Crystal structure, morphology and physical properties of LaCo1−xTixO3±δ perovskites prepared by a citric acid assisted soft chemistry synthesis Type de document : texte imprimé Auteurs : Rosa Robert, Auteur ; Dmitry Logvinovich, Auteur ; Myriam H. Aguirre, Auteur Article en page(s) : pp. 680-691 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Physical  properties  Soft  chemistry  synthesis  XANES  Co-oxidation  state  Nanocrystalline  perovskites Index. décimale : 669 Métallurgie Résumé : The influence of the partial substitution of Co by Ti in the LaCoO3 perovskite system is studied by evaluating the electrical conductivity, the Seebeck coefficient and the thermal conductivity of the compounds up to T = 1273 K. The X-ray diffraction patterns of the LaCo1−xTixO3±δ (0.01 less-than-or-equals, slant x less-than-or-equals, slant 0.5) phases show two structural modifications depending on the Ti content. Compounds with x < 0.3 crystallize in the rhombohedrally distorted perovskite structure while samples with x greater-or-equal, slanted 0.3 possess an orthorhombic unit cell. The oxidation state of the Co ions is studied by X-ray absorption near edge structure (XANES) spectroscopy. A negative thermoelectric power is found in the LaCoO3 system for low level Ti substitution (x = 0.01). In contrast, samples with higher Ti content show a large positive Seebeck coefficient, indicating positive majority charge carriers in the system. The electrical resistivity of the studied materials reveals a semiconducting-like behaviour. The lattice thermal conductivity was found to be low and nearly temperature-independent. The samples exhibit very small crystallite sizes in the range of few nanometres. Therefore, the low thermal conductivity can be assigned to an enhanced phonon scattering on grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Crystal structure, morphology and physical properties of LaCo1−xTixO3±δ perovskites prepared by a citric acid assisted soft chemistry synthesis [texte imprimé] / Rosa Robert, Auteur ; Dmitry Logvinovich, Auteur ; Myriam H. Aguirre, Auteur . - pp. 680-691. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 680-691 Mots-clés : Physical  properties  Soft  chemistry  synthesis  XANES  Co-oxidation  state  Nanocrystalline  perovskites Index. décimale : 669 Métallurgie Résumé : The influence of the partial substitution of Co by Ti in the LaCoO3 perovskite system is studied by evaluating the electrical conductivity, the Seebeck coefficient and the thermal conductivity of the compounds up to T = 1273 K. The X-ray diffraction patterns of the LaCo1−xTixO3±δ (0.01 less-than-or-equals, slant x less-than-or-equals, slant 0.5) phases show two structural modifications depending on the Ti content. Compounds with x < 0.3 crystallize in the rhombohedrally distorted perovskite structure while samples with x greater-or-equal, slanted 0.3 possess an orthorhombic unit cell. The oxidation state of the Co ions is studied by X-ray absorption near edge structure (XANES) spectroscopy. A negative thermoelectric power is found in the LaCoO3 system for low level Ti substitution (x = 0.01). In contrast, samples with higher Ti content show a large positive Seebeck coefficient, indicating positive majority charge carriers in the system. The electrical resistivity of the studied materials reveals a semiconducting-like behaviour. The lattice thermal conductivity was found to be low and nearly temperature-independent. The samples exhibit very small crystallite sizes in the range of few nanometres. Therefore, the low thermal conductivity can be assigned to an enhanced phonon scattering on grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Kinetic effects in the mixed β to View the MathML source martensitic transformation in a Cu–Al–Ni shape memory alloy / J. Rodríguez-Aseguinolaza in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 692-701 Titre : Kinetic effects in the mixed β to View the MathML source martensitic transformation in a Cu–Al–Ni shape memory alloy Type de document : texte imprimé Auteurs : J. Rodríguez-Aseguinolaza, Auteur ; I. Ruiz-Larrea, Auteur ; M.L. Nó, Auteur Article en page(s) : pp. 692-701 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Shape  memory  alloys  Adiabatic  calorimetry  Martensitic  transformation  Cu–Al–Ni  Phase  transformation  kinetics Index. décimale : 669 Métallurgie Résumé : A single crystal with a selected composition of a Cu–Al–Ni shape memory alloy, undergoing two martensitic phase transformations when cooling from the common parent phase, View the MathML source, has been studied by adiabatic calorimetry. As the coexistence of two different martensites has a strong influence on the transformation kinetics, both the forward and the reverse phase martensitic transformation have been carefully studied by means of very low thermal rate dynamic thermograms. Temperature memory effects have been observed in the View the MathML source transformation but not in the View the MathML source one. Finally, radiation-cooling procedures were used to study the forward transformation and showed the interaction between the two types of martensite variants on the nucleation processes. This last technique was found useful to evaluate the latent heat released at each individual nucleation event, throughout the transformation progress. The consequent sample self-heating alters this process, which dramatically affects the View the MathML source ratio and the final martensitic state. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Kinetic effects in the mixed β to View the MathML source martensitic transformation in a Cu–Al–Ni shape memory alloy [texte imprimé] / J. Rodríguez-Aseguinolaza, Auteur ; I. Ruiz-Larrea, Auteur ; M.L. Nó, Auteur . - pp. 692-701. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 692-701 Mots-clés : Shape  memory  alloys  Adiabatic  calorimetry  Martensitic  transformation  Cu–Al–Ni  Phase  transformation  kinetics Index. décimale : 669 Métallurgie Résumé : A single crystal with a selected composition of a Cu–Al–Ni shape memory alloy, undergoing two martensitic phase transformations when cooling from the common parent phase, View the MathML source, has been studied by adiabatic calorimetry. As the coexistence of two different martensites has a strong influence on the transformation kinetics, both the forward and the reverse phase martensitic transformation have been carefully studied by means of very low thermal rate dynamic thermograms. Temperature memory effects have been observed in the View the MathML source transformation but not in the View the MathML source one. Finally, radiation-cooling procedures were used to study the forward transformation and showed the interaction between the two types of martensite variants on the nucleation processes. This last technique was found useful to evaluate the latent heat released at each individual nucleation event, throughout the transformation progress. The consequent sample self-heating alters this process, which dramatically affects the View the MathML source ratio and the final martensitic state. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Colossal anelasticity in polycrystals deforming under conditions of diffusional creep / P. Lee in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 702-708 Titre : Colossal anelasticity in polycrystals deforming under conditions of diffusional creep Type de document : texte imprimé Auteurs : P. Lee, Auteur ; R. Raj, Auteur Article en page(s) : pp. 702-708 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Anelasticity  Diffusional  creep  Grain  size  distribution Index. décimale : 669 Métallurgie Résumé : Since diffusional creep viscosity depends strongly on the grain size, a variability in the grain size in a polycrystal can generate significant internal stresses. Upon unloading, the non-uniform internal stresses recover, leading to anelastic strains. The anelastic strains can be very large, approaching 100 times the elastic strains. We solve the case of bimodal viscosity in closed form to highlight the features of this type of anelasticity. The results are compared to the anelastic behavior of two-phase superplastic alloys. In such alloys the spatial variability in the diffusional viscosity can arise from the variability in the activation energy of grain boundary diffusion, which, because of its Arrhenius nature, can produce a much higher degree of variability than the grain size. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Colossal anelasticity in polycrystals deforming under conditions of diffusional creep [texte imprimé] / P. Lee, Auteur ; R. Raj, Auteur . - pp. 702-708. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 702-708 Mots-clés : Anelasticity  Diffusional  creep  Grain  size  distribution Index. décimale : 669 Métallurgie Résumé : Since diffusional creep viscosity depends strongly on the grain size, a variability in the grain size in a polycrystal can generate significant internal stresses. Upon unloading, the non-uniform internal stresses recover, leading to anelastic strains. The anelastic strains can be very large, approaching 100 times the elastic strains. We solve the case of bimodal viscosity in closed form to highlight the features of this type of anelasticity. The results are compared to the anelastic behavior of two-phase superplastic alloys. In such alloys the spatial variability in the diffusional viscosity can arise from the variability in the activation energy of grain boundary diffusion, which, because of its Arrhenius nature, can produce a much higher degree of variability than the grain size. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Structural properties of materials created through freeze casting / Stephen A. Barr in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 709-715 Titre : Structural properties of materials created through freeze casting Type de document : texte imprimé Auteurs : Stephen A. Barr, Auteur ; Erik Luijten, Auteur Article en page(s) : pp. 709-715 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Directional  solidification  Layered  structures  Porous  material  Molecular  dynamics  simulations  Freeze  casting Index. décimale : 669 Métallurgie Résumé : Upon freezing of an aqueous suspension of colloidal particles, ice platelets or dendrites with high aspect ratios are formed that engulf or reject the particles, depending on their size and the velocity of the advancing ice front. As the particles are pushed between the growing crystals, concentrated regions of colloidal particles are formed. Recent experiments have exploited this to create strong, porous materials with a well-controlled microstructure. We investigate this process by means of molecular dynamics simulations, focusing on the effect of the ice front velocity on the structure of the resulting material. We develop a model that accounts for particle engulfment or rejection by the ice front, and study both columnar and lamellar geometries. The degree of order of the resulting solid and the thickness of the walls surrounding the pores are shown to be determined by front velocity and initial particle concentration in the suspension. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Structural properties of materials created through freeze casting [texte imprimé] / Stephen A. Barr, Auteur ; Erik Luijten, Auteur . - pp. 709-715. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 709-715 Mots-clés : Directional  solidification  Layered  structures  Porous  material  Molecular  dynamics  simulations  Freeze  casting Index. décimale : 669 Métallurgie Résumé : Upon freezing of an aqueous suspension of colloidal particles, ice platelets or dendrites with high aspect ratios are formed that engulf or reject the particles, depending on their size and the velocity of the advancing ice front. As the particles are pushed between the growing crystals, concentrated regions of colloidal particles are formed. Recent experiments have exploited this to create strong, porous materials with a well-controlled microstructure. We investigate this process by means of molecular dynamics simulations, focusing on the effect of the ice front velocity on the structure of the resulting material. We develop a model that accounts for particle engulfment or rejection by the ice front, and study both columnar and lamellar geometries. The degree of order of the resulting solid and the thickness of the walls surrounding the pores are shown to be determined by front velocity and initial particle concentration in the suspension. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Optimization of the mechanical properties of virtual porous solids using a hybrid approach / Sofiane Guessasma in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 716-725 Titre : Optimization of the mechanical properties of virtual porous solids using a hybrid approach Type de document : texte imprimé Auteurs : Sofiane Guessasma, Auteur ; David Bassir, Auteur Article en page(s) : pp. 716-725 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Artificial  neural  network  Optimization  Genetic  algorithm  Porous  structures  Young’s  modulus Index. décimale : 669 Métallurgie Résumé : A hybrid strategy based on artificial neural network/genetic algorithms is suggested to optimize the mechanical properties of cellular solids. Three-dimensional void structures are generated using a random sequential addition algorithm in which spherical void particles are positioned in a solid phase matrix with a control of their size distribution and overlapping. This allows us to create an open-cell structure with relative densities in the range 0.1–0.3. Finite element calculation is used to assess the effective Young’s modulus as a function of generation parameters. Relative Young’s moduli in the three main directions of the solid are isotropic with respect to the generation algorithm constraints and adhere qualitatively to the common theory on effective properties of open-cell structures. Moreover, the effective response is found to be correlated to the randomness of the void structure, which exhibits, in some cases, an ordered cell configuration. In order to quantitatively describe these correlations and to check the sensitivity of the mechanical response to the structural features in addition to sampling and discretization levels, the hybrid strategy described above is considered. The main motivation was to decrease the finite element simulation time by predicting, where possible, the correlations instead of calculating them. In addition, the use of the hybrid strategy informs about the optimal mesh with respect to the generation variables. This strategy proved to be an efficient technique in enhancing the predictions and complementary to the finite element methodology. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Optimization of the mechanical properties of virtual porous solids using a hybrid approach [texte imprimé] / Sofiane Guessasma, Auteur ; David Bassir, Auteur . - pp. 716-725. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 716-725 Mots-clés : Artificial  neural  network  Optimization  Genetic  algorithm  Porous  structures  Young’s  modulus Index. décimale : 669 Métallurgie Résumé : A hybrid strategy based on artificial neural network/genetic algorithms is suggested to optimize the mechanical properties of cellular solids. Three-dimensional void structures are generated using a random sequential addition algorithm in which spherical void particles are positioned in a solid phase matrix with a control of their size distribution and overlapping. This allows us to create an open-cell structure with relative densities in the range 0.1–0.3. Finite element calculation is used to assess the effective Young’s modulus as a function of generation parameters. Relative Young’s moduli in the three main directions of the solid are isotropic with respect to the generation algorithm constraints and adhere qualitatively to the common theory on effective properties of open-cell structures. Moreover, the effective response is found to be correlated to the randomness of the void structure, which exhibits, in some cases, an ordered cell configuration. In order to quantitatively describe these correlations and to check the sensitivity of the mechanical response to the structural features in addition to sampling and discretization levels, the hybrid strategy described above is considered. The main motivation was to decrease the finite element simulation time by predicting, where possible, the correlations instead of calculating them. In addition, the use of the hybrid strategy informs about the optimal mesh with respect to the generation variables. This strategy proved to be an efficient technique in enhancing the predictions and complementary to the finite element methodology. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Preparation and formation mechanism of nanocomposites with fluorescent and magnetic properties / H. Yan in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 726-733 Titre : Preparation and formation mechanism of nanocomposites with fluorescent and magnetic properties Type de document : texte imprimé Auteurs : H. Yan, Auteur ; J.C. Zhang, Auteur ; B.W. Yu, Auteur Article en page(s) : pp. 726-733 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocomposites  Magnetic  properties  Optical  properties  Mechanism Index. décimale : 669 Métallurgie Résumé : Fluorescent magnetic nanocomposites were successfully synthesized using the self-prepared Fe3O4 magnetic liquid and CdTe quantum dots (QDs) as precursors. High-resolution transmission electron microscopy, selected area electron diffraction, energy-dispersive spectroscopy and Fourier transform infrared spectroscopy were used to characterize the size, morphology, structure and composition of the nanocomposites. A fluorescent microscope was used to observe their micro-morphology. Magnetic and optical properties were characterized by a vibrating sample magnetometer and fluorescent spectrophotometer, respectively. The characterized results indicated that the Fe3O4 nanoparticles had been successfully combined with CdTe QDs. The products could exist stably in the aqueous phase, and had better biocompatibility. It was found that the nanocomposites, which had higher magnetization intensity and better fluorescent properties synchronously, were fabricated by the formation of chemical bond with amide structure. Thus this type of nanocomposite could be applied in various science and technology fields in the future. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Preparation and formation mechanism of nanocomposites with fluorescent and magnetic properties [texte imprimé] / H. Yan, Auteur ; J.C. Zhang, Auteur ; B.W. Yu, Auteur . - pp. 726-733. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 726-733 Mots-clés : Nanocomposites  Magnetic  properties  Optical  properties  Mechanism Index. décimale : 669 Métallurgie Résumé : Fluorescent magnetic nanocomposites were successfully synthesized using the self-prepared Fe3O4 magnetic liquid and CdTe quantum dots (QDs) as precursors. High-resolution transmission electron microscopy, selected area electron diffraction, energy-dispersive spectroscopy and Fourier transform infrared spectroscopy were used to characterize the size, morphology, structure and composition of the nanocomposites. A fluorescent microscope was used to observe their micro-morphology. Magnetic and optical properties were characterized by a vibrating sample magnetometer and fluorescent spectrophotometer, respectively. The characterized results indicated that the Fe3O4 nanoparticles had been successfully combined with CdTe QDs. The products could exist stably in the aqueous phase, and had better biocompatibility. It was found that the nanocomposites, which had higher magnetization intensity and better fluorescent properties synchronously, were fabricated by the formation of chemical bond with amide structure. Thus this type of nanocomposite could be applied in various science and technology fields in the future. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

Load partitioning between single bulk grains in a two-phase duplex stainless steel during tensile loading / Peter Hedström in Acta materialia, Vol. 58 N° 2 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 734-744 Titre : Load partitioning between single bulk grains in a two-phase duplex stainless steel during tensile loading Type de document : texte imprimé Auteurs : Peter Hedström, Auteur ; Tong-Seok Han, Auteur ; Ulrich Lienert, Auteur Article en page(s) : pp. 734-744 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : X-ray  diffraction  Synchrotron  radiation  Stainless  steels  Finite-element  modeling  (FEM)  Single-grain  strain Index. décimale : 669 Métallurgie Résumé : The lattice strain tensor evolution for single bulk grains of austenite and ferrite in a duplex stainless steel during tensile loading to 0.02 applied strain has been investigated using in situ high-energy X-ray measurements and finite-element modeling. Single-grain X-ray diffraction lattice strain data for the eight austenite and seven ferrite grains measured show a large variation of residual lattice strains, which evolves upon deformation to the point where some grains with comparable crystallographic orientations have lattice strains different by 1.5 × 10−3, corresponding to a stress of not, vert, similar300 MPa. The finite-element simulations of the 15 measured grains in three different spatial arrangements confirmed the complex deformation constraint and importance of local grain environment. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...] [article] Load partitioning between single bulk grains in a two-phase duplex stainless steel during tensile loading [texte imprimé] / Peter Hedström, Auteur ; Tong-Seok Han, Auteur ; Ulrich Lienert, Auteur . - pp. 734-744. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 2 (Janvier 2010) . - pp. 734-744 Mots-clés : X-ray  diffraction  Synchrotron  radiation  Stainless  steels  Finite-element  modeling  (FEM)  Single-grain  strain Index. décimale : 669 Métallurgie Résumé : The lattice strain tensor evolution for single bulk grains of austenite and ferrite in a duplex stainless steel during tensile loading to 0.02 applied strain has been investigated using in situ high-energy X-ray measurements and finite-element modeling. Single-grain X-ray diffraction lattice strain data for the eight austenite and seven ferrite grains measured show a large variation of residual lattice strains, which evolves upon deformation to the point where some grains with comparable crystallographic orientations have lattice strains different by 1.5 × 10−3, corresponding to a stress of not, vert, similar300 MPa. The finite-element simulations of the 15 measured grains in three different spatial arrangements confirmed the complex deformation constraint and importance of local grain environment. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235556%23 [...]

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