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Acta materialia |
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Ajouter le résultat dans votre panierAg/Au-decorated Fe3O4/SiO2 composite nanospheres for catalytic applications / Ling Li in Acta materialia, Vol. 58 N° 11 (Juin 2010)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3825–3831
Titre : Ag/Au-decorated Fe3O4/SiO2 composite nanospheres for catalytic applications Type de document : texte imprimé Auteurs : Ling Li, Auteur ; Eugene S.G. Choo, Auteur ; Xiaosheng Tang, Auteur Année de publication : 2011 Article en page(s) : pp. 3825–3831 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Silica Superparamagnetic Composite Nanoparticle Catalytic Résumé : Noble metal particles in nanoscale (Au, Ag, Pt, etc.) have attracted intensive research interest due to their promising catalysis properties. However, the practical applications of these nanoparticle catalysts are always jeopardized by two problems. One is the difficulty in recovering the used nanoparticles and the other arises from the low catalytic efficiency due to the aggregation of the nanoparticles. In this work, Ag/Au nanoparticles were distributed onto spherical superparamagnetic carriers (SSCNs), which were fabricated through a facile oil-in-DEG emulsion route. The Ag/Au nanoparticles were attached onto the SSCNs by two steps. The Au seeds were attached onto the silica surface through electrostatic attraction first, and the Ag nanoparticles were grown on the basis of the Au seeds. The obtained Ag/Au–SSCN composite nanospheres demonstrated promising catalytic properties, which could also be recycled very easily by using a magnet. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002107 [article] Ag/Au-decorated Fe3O4/SiO2 composite nanospheres for catalytic applications [texte imprimé] / Ling Li, Auteur ; Eugene S.G. Choo, Auteur ; Xiaosheng Tang, Auteur . - 2011 . - pp. 3825–3831.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3825–3831
Mots-clés : Silica Superparamagnetic Composite Nanoparticle Catalytic Résumé : Noble metal particles in nanoscale (Au, Ag, Pt, etc.) have attracted intensive research interest due to their promising catalysis properties. However, the practical applications of these nanoparticle catalysts are always jeopardized by two problems. One is the difficulty in recovering the used nanoparticles and the other arises from the low catalytic efficiency due to the aggregation of the nanoparticles. In this work, Ag/Au nanoparticles were distributed onto spherical superparamagnetic carriers (SSCNs), which were fabricated through a facile oil-in-DEG emulsion route. The Ag/Au nanoparticles were attached onto the SSCNs by two steps. The Au seeds were attached onto the silica surface through electrostatic attraction first, and the Ag nanoparticles were grown on the basis of the Au seeds. The obtained Ag/Au–SSCN composite nanospheres demonstrated promising catalytic properties, which could also be recycled very easily by using a magnet. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002107
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3832–3841
Titre : Precipitation in Fe–15Cr–1Nb alloys after oxygenation Type de document : texte imprimé Auteurs : A. Malfliet, Auteur ; F. Verhaeghe, Auteur ; F. Chassagne, Auteur Année de publication : 2011 Article en page(s) : pp. 3832–3841 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Stainless steels Ferritic steels Non-binary oxides Wavelength dispersive X-ray spectroscopy Résumé : The effect of O on the phase relations at 950 °C in Fe–15Cr–1Nb alloys is experimentally investigated. Fe–15Cr–1Nb alloys are oxygenated by subjecting high-purity Fe–15Cr–1Nb to an O atmosphere at 600 °C. Both the high-purity and the oxygenated Fe–15Cr–1Nb alloys are heat treated for up to 500 h at 950 °C, quenched and investigated by scanning electron microscopy, transmission electron microscopy and electron probe microanalysis. The results show that Fe2Nb is in equilibrium with α (Fe, Cr) with 0.29 at.% Nb in solid solution in the pure Fe–15Cr–1Nb alloy. The presence of a small amount of O induces the precipitation of a Fe6Nb6Ox phase with a cubic crystal structure and lattice parameter 1.13 nm, thereby decreasing the Nb in solid solution in α (Fe, Cr) with increasing O content. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002089 [article] Precipitation in Fe–15Cr–1Nb alloys after oxygenation [texte imprimé] / A. Malfliet, Auteur ; F. Verhaeghe, Auteur ; F. Chassagne, Auteur . - 2011 . - pp. 3832–3841.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3832–3841
Mots-clés : Stainless steels Ferritic steels Non-binary oxides Wavelength dispersive X-ray spectroscopy Résumé : The effect of O on the phase relations at 950 °C in Fe–15Cr–1Nb alloys is experimentally investigated. Fe–15Cr–1Nb alloys are oxygenated by subjecting high-purity Fe–15Cr–1Nb to an O atmosphere at 600 °C. Both the high-purity and the oxygenated Fe–15Cr–1Nb alloys are heat treated for up to 500 h at 950 °C, quenched and investigated by scanning electron microscopy, transmission electron microscopy and electron probe microanalysis. The results show that Fe2Nb is in equilibrium with α (Fe, Cr) with 0.29 at.% Nb in solid solution in the pure Fe–15Cr–1Nb alloy. The presence of a small amount of O induces the precipitation of a Fe6Nb6Ox phase with a cubic crystal structure and lattice parameter 1.13 nm, thereby decreasing the Nb in solid solution in α (Fe, Cr) with increasing O content. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002089
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3842–3850
Titre : Thermodynamics of precipitation and textural development in batch-annealed interstitial-free high-strength steels Type de document : texte imprimé Auteurs : Pampa Ghosh, Auteur ; Chiradeep Ghosh, Auteur ; R.K. Ray, Auteur Année de publication : 2011 Article en page(s) : pp. 3842–3850 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Interstitial-free (IF) steels Precipitation Texture Thermodynamics Kinetics Résumé : A systematic and detailed characterization of precipitates, as a function of steel composition, has been carried out in five batch-annealed interstitial-free high-strength steels. The precipitation behavior has been discussed from the point of view of thermodynamics as well as on the basis of the kinetics. An attempt has been made to explain the discrepancies between the thermodynamic prediction and the actual observations. Finally, the correlation between precipitation and textural evolution and deep drawability has been critically investigated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002065 [article] Thermodynamics of precipitation and textural development in batch-annealed interstitial-free high-strength steels [texte imprimé] / Pampa Ghosh, Auteur ; Chiradeep Ghosh, Auteur ; R.K. Ray, Auteur . - 2011 . - pp. 3842–3850.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3842–3850
Mots-clés : Interstitial-free (IF) steels Precipitation Texture Thermodynamics Kinetics Résumé : A systematic and detailed characterization of precipitates, as a function of steel composition, has been carried out in five batch-annealed interstitial-free high-strength steels. The precipitation behavior has been discussed from the point of view of thermodynamics as well as on the basis of the kinetics. An attempt has been made to explain the discrepancies between the thermodynamic prediction and the actual observations. Finally, the correlation between precipitation and textural evolution and deep drawability has been critically investigated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002065
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3851–3859
Titre : Enhanced densification of Ti–6Al–4V powders by transformation-mismatch plasticity Type de document : texte imprimé Auteurs : Bing Ye, Auteur ; Marc R. Matsen, Auteur ; David C. Dunand, Auteur Année de publication : 2011 Article en page(s) : pp. 3851–3859 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Powder consolidation Hot pressing Titanium Phase transformations Superplasticity Résumé : The densification kinetics of Ti–6Al–4V powders with spherical or angular shapes are compared in uniaxial die pressing experiments between isothermal conditions (at 1020 °C, in the β-field, where deformation occurs by creep) and thermal cycling (between 860 and 1020 °C, within the range of the α–β phase transformation of the alloy, where transformation-mismatch plasticity is activated). Densification kinetics are only moderately affected by powder shape, but are markedly faster under thermal cycling than under isothermal conditions, as expected from the higher deformation rate achieved under transformation-mismatch plasticity conditions as compared to creep conditions. The densification curves for both creep and mismatch plasticity deformation mechanisms are successfully modeled for various applied stresses and for partial cycling, when transformation is incomplete. Tensile properties of specimens fully densified under thermal cycling conditions are similar to literature values from Ti–6Al–4V densified by isothermal hot isostatic pressing. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002053 [article] Enhanced densification of Ti–6Al–4V powders by transformation-mismatch plasticity [texte imprimé] / Bing Ye, Auteur ; Marc R. Matsen, Auteur ; David C. Dunand, Auteur . - 2011 . - pp. 3851–3859.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3851–3859
Mots-clés : Powder consolidation Hot pressing Titanium Phase transformations Superplasticity Résumé : The densification kinetics of Ti–6Al–4V powders with spherical or angular shapes are compared in uniaxial die pressing experiments between isothermal conditions (at 1020 °C, in the β-field, where deformation occurs by creep) and thermal cycling (between 860 and 1020 °C, within the range of the α–β phase transformation of the alloy, where transformation-mismatch plasticity is activated). Densification kinetics are only moderately affected by powder shape, but are markedly faster under thermal cycling than under isothermal conditions, as expected from the higher deformation rate achieved under transformation-mismatch plasticity conditions as compared to creep conditions. The densification curves for both creep and mismatch plasticity deformation mechanisms are successfully modeled for various applied stresses and for partial cycling, when transformation is incomplete. Tensile properties of specimens fully densified under thermal cycling conditions are similar to literature values from Ti–6Al–4V densified by isothermal hot isostatic pressing. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002053
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3860–3866
Titre : Densification and grain growth during early-stage sintering of Ce0.9Gd0.1O1.95−δ in a reducing atmosphere Type de document : texte imprimé Auteurs : Zeming He, Auteur ; Hao Yuan, Auteur ; Julie Anne Glasscock, Auteur Année de publication : 2011 Article en page(s) : pp. 3860–3866 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Densification Grain growth Sintering Ce0.9Gd0.1O1.95−δ (CGO10) Reducing atmosphere Résumé : The present work investigates the processes of densification and grain growth of Ce0.9Gd0.1O1.95−δ (CGO10) during sintering under reduced oxygen partial pressure. Sintering variables were experimentally characterized and analyzed using defect chemistry and sintering constitutive laws. Based on the results achieved, the grain size–relative density relationship, the densification rate and the grain-growth rate were determined. The activation energies for densification and grain growth were evaluated, and the dominant densification mechanism was indicated. For comparison, the densification behavior of CGO10 sintered in air was also studied. Accelerated densification was observed in early-stage sintering of CGO10 in a reducing atmosphere. This might be attributed to the oxygen vacancies generated by the reduction of Ce4+ to Ce3+ in the reducing atmosphere, which facilitate the diffusion of ions through the lattice. The densification activation energy of CGO10 in the reducing atmosphere was evaluated to be 290 ± 20 kJ mol−1 in the relative density range of 0.64–0.82, which was much smaller than that of CGO10 sintered in air (770 ± 40 kJ mol−1). The grain-growth activation energy of CGO10 sintered in the reducing atmosphere was evaluated to be 280 ± 20 kJ mol−1 in the grain size range of 0.34–0.70 μm. The present work describes a systematic investigation of sintering behavior of CGO10 under reduced oxygen partial pressure, which contributes to the first known determination of the fundamental parameters associated with densification and grain growth during early-stage sintering of CGO10 in a reducing atmosphere. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002041 [article] Densification and grain growth during early-stage sintering of Ce0.9Gd0.1O1.95−δ in a reducing atmosphere [texte imprimé] / Zeming He, Auteur ; Hao Yuan, Auteur ; Julie Anne Glasscock, Auteur . - 2011 . - pp. 3860–3866.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3860–3866
Mots-clés : Densification Grain growth Sintering Ce0.9Gd0.1O1.95−δ (CGO10) Reducing atmosphere Résumé : The present work investigates the processes of densification and grain growth of Ce0.9Gd0.1O1.95−δ (CGO10) during sintering under reduced oxygen partial pressure. Sintering variables were experimentally characterized and analyzed using defect chemistry and sintering constitutive laws. Based on the results achieved, the grain size–relative density relationship, the densification rate and the grain-growth rate were determined. The activation energies for densification and grain growth were evaluated, and the dominant densification mechanism was indicated. For comparison, the densification behavior of CGO10 sintered in air was also studied. Accelerated densification was observed in early-stage sintering of CGO10 in a reducing atmosphere. This might be attributed to the oxygen vacancies generated by the reduction of Ce4+ to Ce3+ in the reducing atmosphere, which facilitate the diffusion of ions through the lattice. The densification activation energy of CGO10 in the reducing atmosphere was evaluated to be 290 ± 20 kJ mol−1 in the relative density range of 0.64–0.82, which was much smaller than that of CGO10 sintered in air (770 ± 40 kJ mol−1). The grain-growth activation energy of CGO10 sintered in the reducing atmosphere was evaluated to be 280 ± 20 kJ mol−1 in the grain size range of 0.34–0.70 μm. The present work describes a systematic investigation of sintering behavior of CGO10 under reduced oxygen partial pressure, which contributes to the first known determination of the fundamental parameters associated with densification and grain growth during early-stage sintering of CGO10 in a reducing atmosphere. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002041
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3867–3876
Titre : α- to γ-Al2O3 martensitic transformation induced by pulsed laser irradiation Type de document : texte imprimé Auteurs : P.F. Yan, Auteur ; M.L. Sui, Auteur Année de publication : 2011 Article en page(s) : pp. 3867–3876 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Martensitic phase transformation Ceramics High-resolution electron microscopy Twinning Alumina Résumé : A martensitic transformation from the α to the γ phase of aluminum oxide was observed by transmission electron microscopy (TEM) upon rapid heating induced by pulsed laser irradiation. Two variants possessing a twin relationship were found in the product. High-resolution TEM reveals that the transformation is achieved via the glide of quarter partial dislocations on every other basal plane of α-Al2O3. The high thermal stress caused by pulsed laser irradiation is believed to be the main driving force of the phase transformation. This martensitic transformation is associated with a positive volume change and substantial shear strain. The overall shear strain could be minimized by the self-accommodating variants. These characteristics suggest potential application of the martensitic transformation for transformation toughening in ceramic materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000203X [article] α- to γ-Al2O3 martensitic transformation induced by pulsed laser irradiation [texte imprimé] / P.F. Yan, Auteur ; M.L. Sui, Auteur . - 2011 . - pp. 3867–3876.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3867–3876
Mots-clés : Martensitic phase transformation Ceramics High-resolution electron microscopy Twinning Alumina Résumé : A martensitic transformation from the α to the γ phase of aluminum oxide was observed by transmission electron microscopy (TEM) upon rapid heating induced by pulsed laser irradiation. Two variants possessing a twin relationship were found in the product. High-resolution TEM reveals that the transformation is achieved via the glide of quarter partial dislocations on every other basal plane of α-Al2O3. The high thermal stress caused by pulsed laser irradiation is believed to be the main driving force of the phase transformation. This martensitic transformation is associated with a positive volume change and substantial shear strain. The overall shear strain could be minimized by the self-accommodating variants. These characteristics suggest potential application of the martensitic transformation for transformation toughening in ceramic materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000203X
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3877–3887
Titre : On plasticity and fracture of nanostructured Cu/X (X = Au, Cr) multilayers : The effects of length scale and interface/boundary Type de document : texte imprimé Auteurs : Y. P. Li, Auteur ; G.P. Zhang, Auteur Année de publication : 2011 Article en page(s) : pp. 3877–3887 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Multilayers Plastic deformation Fracture Length scale Interface Résumé : Plastic deformation and fracture behavior of two different types of Cu/X (X = Au, Cr) multilayers subjected to tensile stress were investigated via three-point bending experiments. It was found that the plastic deformation ability and fracture mode depended on layer thickness and interface/boundary. The Cu/Au multilayer showed significant features of plastic flow before fracture, and such plasticity was gradually suppressed by premature unstable shearing across the layer interface with decreasing layer thickness. In comparison, Cu/Cr multilayers were prone to a quasi-brittle normal fracture with decreasing layer thickness. Both experimental observations and theoretical analyses revealed differences in plasticity and fracture mode between the two types of metallic multilayers and the relevant physical mechanism transition due to length scale constraint and interface/boundary blocking of dislocation motion. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002004 [article] On plasticity and fracture of nanostructured Cu/X (X = Au, Cr) multilayers : The effects of length scale and interface/boundary [texte imprimé] / Y. P. Li, Auteur ; G.P. Zhang, Auteur . - 2011 . - pp. 3877–3887.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3877–3887
Mots-clés : Multilayers Plastic deformation Fracture Length scale Interface Résumé : Plastic deformation and fracture behavior of two different types of Cu/X (X = Au, Cr) multilayers subjected to tensile stress were investigated via three-point bending experiments. It was found that the plastic deformation ability and fracture mode depended on layer thickness and interface/boundary. The Cu/Au multilayer showed significant features of plastic flow before fracture, and such plasticity was gradually suppressed by premature unstable shearing across the layer interface with decreasing layer thickness. In comparison, Cu/Cr multilayers were prone to a quasi-brittle normal fracture with decreasing layer thickness. Both experimental observations and theoretical analyses revealed differences in plasticity and fracture mode between the two types of metallic multilayers and the relevant physical mechanism transition due to length scale constraint and interface/boundary blocking of dislocation motion. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002004
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3888–3894
Titre : Grain and phase boundary segregation in WC–Co with small V, Cr or Mn additions Type de document : texte imprimé Auteurs : Jonathan Weidow, Auteur ; Hans-Olof Andrén, Auteur Année de publication : 2011 Article en page(s) : pp. 3888–3894 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain boundary segregation Phase boundary segregation Atom probe tomography Transmission electron microscopy Energy-dispersive X-ray analysis Résumé : The effect of small additions of V, Cr or Mn on the microchemistry of interfaces in WC–Co was studied using energy-dispersive X-ray spectroscopy in a transmission electron microscope and using atom probe tomography. For WC/binder phase boundaries, segregation of V, Cr and Mn was observed, with V being the element with the largest tendency for segregation. Segregation to WC/WC grain boundaries was observed in all the materials, corresponding to half a monolayer of close packed Co. In the materials containing V or Cr, 1/3 of the Co atoms were replaced by V or Cr. In the material containing Mn, 7% of the Co atoms were replaced by Mn. Co segregation was also observed to a WC/(V, W)Cx phase boundary in the material containing V. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000193X [article] Grain and phase boundary segregation in WC–Co with small V, Cr or Mn additions [texte imprimé] / Jonathan Weidow, Auteur ; Hans-Olof Andrén, Auteur . - 2011 . - pp. 3888–3894.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3888–3894
Mots-clés : Grain boundary segregation Phase boundary segregation Atom probe tomography Transmission electron microscopy Energy-dispersive X-ray analysis Résumé : The effect of small additions of V, Cr or Mn on the microchemistry of interfaces in WC–Co was studied using energy-dispersive X-ray spectroscopy in a transmission electron microscope and using atom probe tomography. For WC/binder phase boundaries, segregation of V, Cr and Mn was observed, with V being the element with the largest tendency for segregation. Segregation to WC/WC grain boundaries was observed in all the materials, corresponding to half a monolayer of close packed Co. In the materials containing V or Cr, 1/3 of the Co atoms were replaced by V or Cr. In the material containing Mn, 7% of the Co atoms were replaced by Mn. Co segregation was also observed to a WC/(V, W)Cx phase boundary in the material containing V. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000193X
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3895–3907
Titre : Fracture of high volume fraction ceramic particle reinforced aluminium under multiaxial stress Type de document : texte imprimé Auteurs : Aude Hauert, Auteur ; Andreas Rossoll, Auteur ; Andreas Mortensen, Auteur Année de publication : 2011 Article en page(s) : pp. 3895–3907 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metal matrix composites (MMC) Particulate reinforced composites Fracture Mean field analysis Stress triaxiality Résumé : Circumferentially notched cylindrical bars of high volume fraction Al2O3 particle reinforced aluminium are tested in tension to probe the role of tensile stress triaxiality on damage and failure of such materials. The transverse strain is monitored with a specially designed video extensometer. A significant dependence of the peak average stress and failure strain on notch radius is observed. Finite-element simulations of the tests are conducted on the basis of a micromechanical model derived from earlier studies of damage and failure of these composites under uniaxial tensile deformation (Journal of the Mechanics and Physics of Solids 2009;57:1781). The simulations show that stress and strain distributions within the notched composite samples deviate significantly from predictions of Bridgman’s simplified analysis. Comparison with data shows that, whereas calculations capture satisfactorily the evolution of the average composite flow stress as a function of notch radius at small strains, the notched samples damage faster and fail at strains lower than predicted. Two phenomena may explain the discrepancy, namely (i) damage coalescence beyond a threshold level, and (ii) the incapacity of the matrix to sustain large hydrostatic stresses, which results from the presence of internal surfaces (cracked particles and possibly matrix voiding). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001928 [article] Fracture of high volume fraction ceramic particle reinforced aluminium under multiaxial stress [texte imprimé] / Aude Hauert, Auteur ; Andreas Rossoll, Auteur ; Andreas Mortensen, Auteur . - 2011 . - pp. 3895–3907.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3895–3907
Mots-clés : Metal matrix composites (MMC) Particulate reinforced composites Fracture Mean field analysis Stress triaxiality Résumé : Circumferentially notched cylindrical bars of high volume fraction Al2O3 particle reinforced aluminium are tested in tension to probe the role of tensile stress triaxiality on damage and failure of such materials. The transverse strain is monitored with a specially designed video extensometer. A significant dependence of the peak average stress and failure strain on notch radius is observed. Finite-element simulations of the tests are conducted on the basis of a micromechanical model derived from earlier studies of damage and failure of these composites under uniaxial tensile deformation (Journal of the Mechanics and Physics of Solids 2009;57:1781). The simulations show that stress and strain distributions within the notched composite samples deviate significantly from predictions of Bridgman’s simplified analysis. Comparison with data shows that, whereas calculations capture satisfactorily the evolution of the average composite flow stress as a function of notch radius at small strains, the notched samples damage faster and fail at strains lower than predicted. Two phenomena may explain the discrepancy, namely (i) damage coalescence beyond a threshold level, and (ii) the incapacity of the matrix to sustain large hydrostatic stresses, which results from the presence of internal surfaces (cracked particles and possibly matrix voiding). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001928
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3908–3918
Titre : The role of microtexture on the faceted fracture morphology in Ti–6Al–4V subjected to high-cycle fatigue Type de document : texte imprimé Auteurs : Ioannis Bantounas, Auteur ; David Dye, Auteur ; Trevor C Lindley, Auteur Année de publication : 2011 Article en page(s) : pp. 3908–3918 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Titanium alloys Fatigue Texture Electron backscattered diffraction (EBSD) Transmission electron microscopy (TEM) Résumé : Microtextured regions (or macrozones) are commonly reported in titanium alloys and are believed to be related to fatigue life. Here, fractographic investigations are conducted on bimodal Ti–6Al–4V plate, including transmission electron microscopy to determine the mechanism of fatigue facet formation and electron backscattered diffraction to examine the underlying macrozone structures. It is found that macrozones oriented with their c-axis close to the loading direction are responsible for facet formation, and that the facets are associated with basal slip. Microtextured regions with c-axis orientations near-perpendicular to the loading direction are believed to act as barriers to faceted crack growth, based on the change in crack morphology as the crack crosses a macrozone boundary. The variant selection occurring during the transformation of the retained beta appears to favour a common orientation with the surrounding primary alpha grains, contributing to the size of the macrozones and therefore to the extent of the observed faceted regions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001916 [article] The role of microtexture on the faceted fracture morphology in Ti–6Al–4V subjected to high-cycle fatigue [texte imprimé] / Ioannis Bantounas, Auteur ; David Dye, Auteur ; Trevor C Lindley, Auteur . - 2011 . - pp. 3908–3918.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3908–3918
Mots-clés : Titanium alloys Fatigue Texture Electron backscattered diffraction (EBSD) Transmission electron microscopy (TEM) Résumé : Microtextured regions (or macrozones) are commonly reported in titanium alloys and are believed to be related to fatigue life. Here, fractographic investigations are conducted on bimodal Ti–6Al–4V plate, including transmission electron microscopy to determine the mechanism of fatigue facet formation and electron backscattered diffraction to examine the underlying macrozone structures. It is found that macrozones oriented with their c-axis close to the loading direction are responsible for facet formation, and that the facets are associated with basal slip. Microtextured regions with c-axis orientations near-perpendicular to the loading direction are believed to act as barriers to faceted crack growth, based on the change in crack morphology as the crack crosses a macrozone boundary. The variant selection occurring during the transformation of the retained beta appears to favour a common orientation with the surrounding primary alpha grains, contributing to the size of the macrozones and therefore to the extent of the observed faceted regions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001916
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3919–3926
Titre : Primary crystallization in Al-rich metallic glasses at unusually low temperatures Type de document : texte imprimé Auteurs : J. Bokeloh, Auteur ; N. Boucharat, Auteur ; H. Rösner, Auteur Année de publication : 2011 Article en page(s) : pp. 3919–3926 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocrystallization Metallic glasses Modulated differential scanning calorimetry Phase separation Résumé : The initial stage of the primary crystallization reaction and the glass transition of the marginal metallic glass Al89Y6Fe5 were investigated by conventional differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC), microcalorimetry, X-ray diffraction (XRD) and transmission electron microscopy. A sharp onset of the primary crystallization was found by microcalorimetry and XRD studies at temperatures which were 120 °C below the primary crystallization peak observed in conventional DSC. A systematic MDSC study of annealed samples revealed a wide spectrum of glass transition onsets, which show a strong dependence on the annealing conditions. In addition, the glass transition onsets can be linked to the initial stage of the primary crystallization. The spectrum of glass transition onsets observed is discussed with respect to the occurrence of phase separation preceding the nucleation and growth of dendritic aluminium nanocrystals. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001904 [article] Primary crystallization in Al-rich metallic glasses at unusually low temperatures [texte imprimé] / J. Bokeloh, Auteur ; N. Boucharat, Auteur ; H. Rösner, Auteur . - 2011 . - pp. 3919–3926.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3919–3926
Mots-clés : Nanocrystallization Metallic glasses Modulated differential scanning calorimetry Phase separation Résumé : The initial stage of the primary crystallization reaction and the glass transition of the marginal metallic glass Al89Y6Fe5 were investigated by conventional differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC), microcalorimetry, X-ray diffraction (XRD) and transmission electron microscopy. A sharp onset of the primary crystallization was found by microcalorimetry and XRD studies at temperatures which were 120 °C below the primary crystallization peak observed in conventional DSC. A systematic MDSC study of annealed samples revealed a wide spectrum of glass transition onsets, which show a strong dependence on the annealing conditions. In addition, the glass transition onsets can be linked to the initial stage of the primary crystallization. The spectrum of glass transition onsets observed is discussed with respect to the occurrence of phase separation preceding the nucleation and growth of dendritic aluminium nanocrystals. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001904
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3927–3938
Titre : Ab initio study on plane defects in zirconium–hydrogen solid solution and zirconium hydride Type de document : texte imprimé Auteurs : Yutaka Udagawa, Auteur ; Masatake Yamaguchi, Auteur ; Hiroaki Abe, Auteur Année de publication : 2011 Article en page(s) : pp. 3927–3938 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cladding Zircaloy Zirconium Hydride Ab initio Résumé : Hydrogen embrittlement of zirconium alloys is one of the main causes of the mechanical degradation of the fuel cladding in light water reactors, and has therefore been extensively studied. Although various conjectures have been proposed as the origin of such embrittlement, it is not known which one plays the most important role: the brittle nature of the hydride, micro-crack nucleation by interaction of hydride precipitates with dislocations or void nucleation at the interface between hydride precipitates and zirconium matrix. The purpose of the present study was to elucidate the origin of the embrittlement by investigating the fracture properties of the hydride. We have evaluated the surface energy γS and unstable stacking energy γUS of Zr–H systems by using ab initio calculations. The ductile/brittle behavior of the hydride is discussed based on the difference between γS and γUS among the hydride, pure zirconium and hydrogen solid solution. For the solid solution at a H/Zr ratio less than 0.5 we obtained a monotonous decrease by 15–34% and 50–100% in γS and γUS, respectively, from those in pure zirconium, indicating a reduction in both brittleness and ductility. Thus, hydrogen-induced embrittlement of the hcp Zr matrix was not confirmed. On the other hand, for the hydride we obtained a 25% smaller γS and a 200–300% larger γUS than those in pure zirconium. This indicates that zirconium hydride has an extremely brittle nature due to the synergistic effect of a small γS, implying easy generation of a fracture surface, and large γUS, implying a difficulty in dislocation motion, compared with pure zirconium. Furthermore, Rice’s ductile/brittle parameter D was 1.4 in the δ-hydride, indicating that it undergoes brittle fracture more easily than iridium, known as an extremely brittle material. These results seem sufficient to attribute hydrogen embrittlement of zirconium alloys substantially to the brittle nature of the hydride. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001898 [article] Ab initio study on plane defects in zirconium–hydrogen solid solution and zirconium hydride [texte imprimé] / Yutaka Udagawa, Auteur ; Masatake Yamaguchi, Auteur ; Hiroaki Abe, Auteur . - 2011 . - pp. 3927–3938.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3927–3938
Mots-clés : Cladding Zircaloy Zirconium Hydride Ab initio Résumé : Hydrogen embrittlement of zirconium alloys is one of the main causes of the mechanical degradation of the fuel cladding in light water reactors, and has therefore been extensively studied. Although various conjectures have been proposed as the origin of such embrittlement, it is not known which one plays the most important role: the brittle nature of the hydride, micro-crack nucleation by interaction of hydride precipitates with dislocations or void nucleation at the interface between hydride precipitates and zirconium matrix. The purpose of the present study was to elucidate the origin of the embrittlement by investigating the fracture properties of the hydride. We have evaluated the surface energy γS and unstable stacking energy γUS of Zr–H systems by using ab initio calculations. The ductile/brittle behavior of the hydride is discussed based on the difference between γS and γUS among the hydride, pure zirconium and hydrogen solid solution. For the solid solution at a H/Zr ratio less than 0.5 we obtained a monotonous decrease by 15–34% and 50–100% in γS and γUS, respectively, from those in pure zirconium, indicating a reduction in both brittleness and ductility. Thus, hydrogen-induced embrittlement of the hcp Zr matrix was not confirmed. On the other hand, for the hydride we obtained a 25% smaller γS and a 200–300% larger γUS than those in pure zirconium. This indicates that zirconium hydride has an extremely brittle nature due to the synergistic effect of a small γS, implying easy generation of a fracture surface, and large γUS, implying a difficulty in dislocation motion, compared with pure zirconium. Furthermore, Rice’s ductile/brittle parameter D was 1.4 in the δ-hydride, indicating that it undergoes brittle fracture more easily than iridium, known as an extremely brittle material. These results seem sufficient to attribute hydrogen embrittlement of zirconium alloys substantially to the brittle nature of the hydride. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001898
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3939–3951
Titre : Investigation on sintering mechanism of nanoscale tungsten powder based on atomistic simulation Type de document : texte imprimé Auteurs : Amitava Moitra, Auteur ; Sungho Kim, Auteur ; Seong-Gon Kim, Auteur Année de publication : 2011 Article en page(s) : pp. 3939–3951 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Atomistic simulation Nanoscale Tungsten Grain boundary misalignment Neck growth Résumé : Atomistic simulations focusing on sintering of crystalline tungsten powders at the submicroscopic level are performed to shed light on the processing on the nanoscale powders. The neck growth and shrinkage were calculated during these sintering simulations, making it possible to extend these results to the evolution of global physical properties that occurs during sintering. The densification and grain growth during sintering were calculated with variations in temperature, pressure, particle configuration and crystalline misalignment between particles. These findings lay the foundation for a virtual approach to setting the processing cycles and materials design applicable to nanoscale powders. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001886 [article] Investigation on sintering mechanism of nanoscale tungsten powder based on atomistic simulation [texte imprimé] / Amitava Moitra, Auteur ; Sungho Kim, Auteur ; Seong-Gon Kim, Auteur . - 2011 . - pp. 3939–3951.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3939–3951
Mots-clés : Atomistic simulation Nanoscale Tungsten Grain boundary misalignment Neck growth Résumé : Atomistic simulations focusing on sintering of crystalline tungsten powders at the submicroscopic level are performed to shed light on the processing on the nanoscale powders. The neck growth and shrinkage were calculated during these sintering simulations, making it possible to extend these results to the evolution of global physical properties that occurs during sintering. The densification and grain growth during sintering were calculated with variations in temperature, pressure, particle configuration and crystalline misalignment between particles. These findings lay the foundation for a virtual approach to setting the processing cycles and materials design applicable to nanoscale powders. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001886
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3952–3962
Titre : Effects of surface roughness and training on the twinning stress of Ni–Mn–Ga single crystals Type de document : texte imprimé Auteurs : M. Chmielus, Auteur ; K. Rolfs, Auteur ; R. Wimpory, Auteur Année de publication : 2011 Article en page(s) : pp. 3952–3962 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnetic shape memory alloys Mechanical properties Mechanical training Neutron scattering Surface treatments Résumé : Spark eroding, which is commonly employed to cut samples out of magnetic shape-memory alloy single crystals, produces a rough surface layer. Directly after cutting, the single crystals exhibit a high twinning stress. After removal of a surface layer by electropolishing, the twinning stress reduces significantly and stress–strain curves become serrated. The reduction of twinning stress has previously been attributed to the removal of the defective surface layer. In this work, it is shown that different surface treatments in combination with repeated mechanical deformation experiments significantly reduce the twinning stress, regardless of whether or not electropolishing is used. The reduction of the twinning stress is due to softening that takes place as a mechanical training effect, which occurs with mechanical testing. In addition, the stress–strain curves of samples subjected to different surface treatments differed in so far as the curves of electropolished samples showed serrated flow, while the curves of unpolished samples and those of mechanically polished samples were smooth. Furthermore, the unpolished samples displayed significant hardening at higher strain. Following subsequent mechanical polishing, this hardening reduced to nearly zero, and the average twinning stress decreased another 30–50% to 1.6 MPa and below. For these samples, the twinning stress stayed at a very low level until twinning was complete. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000176X [article] Effects of surface roughness and training on the twinning stress of Ni–Mn–Ga single crystals [texte imprimé] / M. Chmielus, Auteur ; K. Rolfs, Auteur ; R. Wimpory, Auteur . - 2011 . - pp. 3952–3962.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3952–3962
Mots-clés : Magnetic shape memory alloys Mechanical properties Mechanical training Neutron scattering Surface treatments Résumé : Spark eroding, which is commonly employed to cut samples out of magnetic shape-memory alloy single crystals, produces a rough surface layer. Directly after cutting, the single crystals exhibit a high twinning stress. After removal of a surface layer by electropolishing, the twinning stress reduces significantly and stress–strain curves become serrated. The reduction of twinning stress has previously been attributed to the removal of the defective surface layer. In this work, it is shown that different surface treatments in combination with repeated mechanical deformation experiments significantly reduce the twinning stress, regardless of whether or not electropolishing is used. The reduction of the twinning stress is due to softening that takes place as a mechanical training effect, which occurs with mechanical testing. In addition, the stress–strain curves of samples subjected to different surface treatments differed in so far as the curves of electropolished samples showed serrated flow, while the curves of unpolished samples and those of mechanically polished samples were smooth. Furthermore, the unpolished samples displayed significant hardening at higher strain. Following subsequent mechanical polishing, this hardening reduced to nearly zero, and the average twinning stress decreased another 30–50% to 1.6 MPa and below. For these samples, the twinning stress stayed at a very low level until twinning was complete. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000176X
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3963–3969
Titre : Icosahedral clustering with medium-range order and local elastic properties of amorphous metals Type de document : texte imprimé Auteurs : M. Wakeda, Auteur ; Y. Shibutani, Auteur Année de publication : 2011 Article en page(s) : pp. 3963–3969 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metallic glasses Medium-range order Elastic behavior Molecular dynamics simulations Résumé : The paper focuses on the relationship between icosahedral clustering with medium-range order in amorphous metals and local elastic properties. Using a Cu–Zr binary amorphous model constructed by rapid quenching in the framework of molecular dynamics simulations, Voronoi polyhedra analysis shows that the icosahedra are not randomly distributed in space, but form characteristic interpenetrating icosahedral clustering with medium-range order. It is shown that the center atoms of icosahedra within the highly developed interpenetrating icosahedral clusters have higher local elastic moduli than those of independently existing icosahedra and other polyhedra with lower coordination numbers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001746 [article] Icosahedral clustering with medium-range order and local elastic properties of amorphous metals [texte imprimé] / M. Wakeda, Auteur ; Y. Shibutani, Auteur . - 2011 . - pp. 3963–3969.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3963–3969
Mots-clés : Metallic glasses Medium-range order Elastic behavior Molecular dynamics simulations Résumé : The paper focuses on the relationship between icosahedral clustering with medium-range order in amorphous metals and local elastic properties. Using a Cu–Zr binary amorphous model constructed by rapid quenching in the framework of molecular dynamics simulations, Voronoi polyhedra analysis shows that the icosahedra are not randomly distributed in space, but form characteristic interpenetrating icosahedral clustering with medium-range order. It is shown that the center atoms of icosahedra within the highly developed interpenetrating icosahedral clusters have higher local elastic moduli than those of independently existing icosahedra and other polyhedra with lower coordination numbers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001746
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3970–3983
Titre : Variant selection during secondary twinning in Mg–3%Al Type de document : texte imprimé Auteurs : É. Martin, Auteur ; L. Capolungo, Auteur ; L. Jiang, Auteur Année de publication : 2011 Article en page(s) : pp. 3970–3983 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Twinning Double twinning Magnesium EBSD Variant selection Résumé : Secondary twin formation during the tensile deformation of Mg–3.4%Al–0.33%Mn was studied by means of the electron backscatter diffraction technique. This was employed to identify the particular variants that formed in each grain. For this purpose, the variants were characterized with respect to the orientation of the parent grain rather than that of its host primary twin. This approach led to a regrouping of the 36 possible variants into four sets, namely SA, SB, SC and SD, consisting of variants that are geometrically equivalent. A statistical analysis revealed that the observed secondary twins were almost entirely of SA and SD type (misorientations of 37.5° and 69.9°, respectively). The former variant is shown to require the least accommodation strain within the parent grain and to have the greatest potential for growth. Formation of the SD variant, in contrast, can be attributed to its being favored by the highest resolved shear stresses, i.e., it obeys Schmid’s law. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001722 [article] Variant selection during secondary twinning in Mg–3%Al [texte imprimé] / É. Martin, Auteur ; L. Capolungo, Auteur ; L. Jiang, Auteur . - 2011 . - pp. 3970–3983.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3970–3983
Mots-clés : Twinning Double twinning Magnesium EBSD Variant selection Résumé : Secondary twin formation during the tensile deformation of Mg–3.4%Al–0.33%Mn was studied by means of the electron backscatter diffraction technique. This was employed to identify the particular variants that formed in each grain. For this purpose, the variants were characterized with respect to the orientation of the parent grain rather than that of its host primary twin. This approach led to a regrouping of the 36 possible variants into four sets, namely SA, SB, SC and SD, consisting of variants that are geometrically equivalent. A statistical analysis revealed that the observed secondary twins were almost entirely of SA and SD type (misorientations of 37.5° and 69.9°, respectively). The former variant is shown to require the least accommodation strain within the parent grain and to have the greatest potential for growth. Formation of the SD variant, in contrast, can be attributed to its being favored by the highest resolved shear stresses, i.e., it obeys Schmid’s law. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001722
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3984–3994
Titre : Grain refinement of LY2 aluminum alloy induced by ultra-high plastic strain during multiple laser shock processing impacts Type de document : texte imprimé Auteurs : J.Z. Lu, Auteur ; K.Y. Luo, Auteur ; Y.K. Zhang, Auteur Année de publication : 2011 Article en page(s) : pp. 3984–3994 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Laser shock processing LY2 aluminum alloy Residual stress Plastic deformation Micro-structure Résumé : The plastic deformation behavior and the effects of the impact time on the LY2 aluminum (Al) alloy during multiple laser shock processing (LSP) impacts were investigated. The residual stress in the near-surface region was determined by X-ray diffraction. In addition, the micro-structural features of the hardening layer were characterized by scanning electron microscopy, optical microscopy and transmission electron microscopy. It was found that the micro-structure was obviously refined due to the ultra-high plastic strain induced by multiple LSP impacts. The minimum grain size in the top surface after multiple LSP impacts was about 100–200 nm. The grain refinement process after multiple LSP impacts can be described as follows: (i) the formation and development of dislocation lines in original grains; (ii) dislocation tangles (DTs) and the formation of dense dislocation walls (DDWs); (iii) transformation of DTs and DDWs into subgrain boundaries; and (iv) evolution of the continuous dynamic recrystallization in subgrain boundaries to refined grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001710 [article] Grain refinement of LY2 aluminum alloy induced by ultra-high plastic strain during multiple laser shock processing impacts [texte imprimé] / J.Z. Lu, Auteur ; K.Y. Luo, Auteur ; Y.K. Zhang, Auteur . - 2011 . - pp. 3984–3994.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3984–3994
Mots-clés : Laser shock processing LY2 aluminum alloy Residual stress Plastic deformation Micro-structure Résumé : The plastic deformation behavior and the effects of the impact time on the LY2 aluminum (Al) alloy during multiple laser shock processing (LSP) impacts were investigated. The residual stress in the near-surface region was determined by X-ray diffraction. In addition, the micro-structural features of the hardening layer were characterized by scanning electron microscopy, optical microscopy and transmission electron microscopy. It was found that the micro-structure was obviously refined due to the ultra-high plastic strain induced by multiple LSP impacts. The minimum grain size in the top surface after multiple LSP impacts was about 100–200 nm. The grain refinement process after multiple LSP impacts can be described as follows: (i) the formation and development of dislocation lines in original grains; (ii) dislocation tangles (DTs) and the formation of dense dislocation walls (DDWs); (iii) transformation of DTs and DDWs into subgrain boundaries; and (iv) evolution of the continuous dynamic recrystallization in subgrain boundaries to refined grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001710
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3995–4002
Titre : High thermoelectric performance of Yb0.26Co4Sb12/yGaSb nanocomposites originating from scattering electrons of low energy Type de document : texte imprimé Auteurs : Zhen Xiong, Auteur ; Xihong Chen, Auteur ; Xiangyang Huang, Auteur Année de publication : 2011 Article en page(s) : pp. 3995–4002 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thermoelectric Nanoinclusions Seebeck coefficient Scattering Résumé : n-type filled skutterudite Yb0.26Co4Sb12 composites in which p-type GaSb nanostructured inclusions (5–20 nm) were dispersed were fabricated by an in situ method involving the introduction of metastable void-filling impurity Ga and enrichment of Sb in the synthesis procedure. With the homogeneously dispersed GaSb nanoinclusions, which probably result from the scattering of low-energy electrons by the GaSb-related boundary energy barriers, the power factor is enhanced due to the significant enhancement of the Seebeck coefficient. The total thermal conductivity was decreased with the depression of electronic thermal conductivity. As a result, the dimensionless thermoelectric figure of merit ZT value was improved over a wide working temperature range of 300–850 K, and the expected optimal thermal-electric conversion efficiency ηopt 15.0% was obtained for the Yb0.26Co4Sb12/0.2GaSb nanocomposite. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001709 [article] High thermoelectric performance of Yb0.26Co4Sb12/yGaSb nanocomposites originating from scattering electrons of low energy [texte imprimé] / Zhen Xiong, Auteur ; Xihong Chen, Auteur ; Xiangyang Huang, Auteur . - 2011 . - pp. 3995–4002.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3995–4002
Mots-clés : Thermoelectric Nanoinclusions Seebeck coefficient Scattering Résumé : n-type filled skutterudite Yb0.26Co4Sb12 composites in which p-type GaSb nanostructured inclusions (5–20 nm) were dispersed were fabricated by an in situ method involving the introduction of metastable void-filling impurity Ga and enrichment of Sb in the synthesis procedure. With the homogeneously dispersed GaSb nanoinclusions, which probably result from the scattering of low-energy electrons by the GaSb-related boundary energy barriers, the power factor is enhanced due to the significant enhancement of the Seebeck coefficient. The total thermal conductivity was decreased with the depression of electronic thermal conductivity. As a result, the dimensionless thermoelectric figure of merit ZT value was improved over a wide working temperature range of 300–850 K, and the expected optimal thermal-electric conversion efficiency ηopt 15.0% was obtained for the Yb0.26Co4Sb12/0.2GaSb nanocomposite. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001709
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4003–4011
Titre : An investigation of the effect of structural order on magnetostriction and magnetic behavior of Fe–Ga alloy thin films Type de document : texte imprimé Auteurs : A. Javed, Auteur ; T. Szumiata, Auteur ; N.A. Morley, Auteur Année de publication : 2011 Article en page(s) : pp. 4003–4011 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fe–Ga alloy Thin films Growth parameters CEMS Magnetostriction Résumé : This paper reports results from a comprehensive study of Fe–Ga films fabricated over a wide range of growth conditions. Polycrystalline Fe100−xGax films (14 ⩽ x ⩽ 32) were deposited (using three different combinations of growth parameters) on Si(1 0 0) using a co-sputtering and evaporation technique. The growth parameters (sputter power, Ga evaporation rate and chamber pressure) were used primarily to control the Fe:Ga ratio in the films. X-ray diffraction showed that all films had 〈1 1 0〉 crystallographic texture normal to the film plane. The lattice parameter increased with % Ga up to x = 22 and was independent of growth parameters. Conversion electron Mössbauer spectroscopy studies showed a predominance of the disordered A2 phase in all films. It appears that the use of vacuum deposition with appropriate parameters can effectively suppress the D03 ordered phase. Systematic studies of the effective magnetostriction constant as a function of composition support this conclusion. It was found that films of high effective saturation magnetostriction constant and low stress could be fabricated using low Ar pressure, irrespective of sputter power or evaporation rate, giving properties useful for application in microelectromechanical systems. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001680 [article] An investigation of the effect of structural order on magnetostriction and magnetic behavior of Fe–Ga alloy thin films [texte imprimé] / A. Javed, Auteur ; T. Szumiata, Auteur ; N.A. Morley, Auteur . - 2011 . - pp. 4003–4011.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4003–4011
Mots-clés : Fe–Ga alloy Thin films Growth parameters CEMS Magnetostriction Résumé : This paper reports results from a comprehensive study of Fe–Ga films fabricated over a wide range of growth conditions. Polycrystalline Fe100−xGax films (14 ⩽ x ⩽ 32) were deposited (using three different combinations of growth parameters) on Si(1 0 0) using a co-sputtering and evaporation technique. The growth parameters (sputter power, Ga evaporation rate and chamber pressure) were used primarily to control the Fe:Ga ratio in the films. X-ray diffraction showed that all films had 〈1 1 0〉 crystallographic texture normal to the film plane. The lattice parameter increased with % Ga up to x = 22 and was independent of growth parameters. Conversion electron Mössbauer spectroscopy studies showed a predominance of the disordered A2 phase in all films. It appears that the use of vacuum deposition with appropriate parameters can effectively suppress the D03 ordered phase. Systematic studies of the effective magnetostriction constant as a function of composition support this conclusion. It was found that films of high effective saturation magnetostriction constant and low stress could be fabricated using low Ar pressure, irrespective of sputter power or evaporation rate, giving properties useful for application in microelectromechanical systems. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001680
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4012–4018
Titre : First-principles calculations of the elastic, phonon and thermodynamic properties of Al12Mg17 Type de document : texte imprimé Auteurs : H. Zhang, Auteur ; S.L. Shang, Auteur ; Y. Wang, Auteur Année de publication : 2011 Article en page(s) : pp. 4012–4018 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : First-principles electron theory Intermetallic compounds Elastic behavior Thermodynamics Résumé : The elastic, phonon and thermodynamic properties of Al12Mg17 have been investigated by first-principles calculations. The obtained structural parameters, phonon dispersion curves and the predicted thermodynamic properties for all the phases studied herein agree well with available experimental data. The temperature-dependent single-crystal elastic constants are also predicted along with the polycrystalline aggregate properties, including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio. The brittleness of Al12Mg17 that we predict is consistent with experiments, in contrast to the previous calculation showing ductile behavior. Detailed analysis of density of states further explains the present theoretical findings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001655 [article] First-principles calculations of the elastic, phonon and thermodynamic properties of Al12Mg17 [texte imprimé] / H. Zhang, Auteur ; S.L. Shang, Auteur ; Y. Wang, Auteur . - 2011 . - pp. 4012–4018.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4012–4018
Mots-clés : First-principles electron theory Intermetallic compounds Elastic behavior Thermodynamics Résumé : The elastic, phonon and thermodynamic properties of Al12Mg17 have been investigated by first-principles calculations. The obtained structural parameters, phonon dispersion curves and the predicted thermodynamic properties for all the phases studied herein agree well with available experimental data. The temperature-dependent single-crystal elastic constants are also predicted along with the polycrystalline aggregate properties, including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio. The brittleness of Al12Mg17 that we predict is consistent with experiments, in contrast to the previous calculation showing ductile behavior. Detailed analysis of density of states further explains the present theoretical findings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001655
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4019–4028
Titre : Coarsening of a multimodal nickel-base superalloy Type de document : texte imprimé Auteurs : James Coakley, Auteur ; Hector Basoalto, Auteur ; David Dye, Auteur Année de publication : 2011 Article en page(s) : pp. 4019–4028 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel alloys Coarsening Diffusion Modelling Résumé : The coarsening of γ′-Ni3Al precipitates in the nickel superalloy Ni115 has been examined and compared to the results of a numerical model based on LSW coarsening theory. Ni115 has a γ′ fraction of around 60%, and at the coarsening temperatures of interest the γ′ distribution is bimodal, with two populations ∼5 nm and ∼90 nm in radius. It is found that during the initial transient (around 2000 h at 800 °C), the fine γ′ dissolve, leading to a rapid increase in the mean radius followed by a plateau. At long times, the expected steady-state unimodal t1/3 coarsening is observed. The model reproduces these features in form and approximately in magnitude, a first for LSW model-experiment comparisons in nickel superalloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000162X [article] Coarsening of a multimodal nickel-base superalloy [texte imprimé] / James Coakley, Auteur ; Hector Basoalto, Auteur ; David Dye, Auteur . - 2011 . - pp. 4019–4028.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4019–4028
Mots-clés : Nickel alloys Coarsening Diffusion Modelling Résumé : The coarsening of γ′-Ni3Al precipitates in the nickel superalloy Ni115 has been examined and compared to the results of a numerical model based on LSW coarsening theory. Ni115 has a γ′ fraction of around 60%, and at the coarsening temperatures of interest the γ′ distribution is bimodal, with two populations ∼5 nm and ∼90 nm in radius. It is found that during the initial transient (around 2000 h at 800 °C), the fine γ′ dissolve, leading to a rapid increase in the mean radius followed by a plateau. At long times, the expected steady-state unimodal t1/3 coarsening is observed. The model reproduces these features in form and approximately in magnitude, a first for LSW model-experiment comparisons in nickel superalloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000162X
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4029–4038
Titre : Microporosity effects on cyclic plasticity and fatigue of LENS™-processed steel Type de document : texte imprimé Auteurs : Y. Xue, Auteur ; A. Pascu, Auteur ; M.F. Horstemeyer, Auteur Année de publication : 2011 Article en page(s) : pp. 4029–4038 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fatigue micromechanism LENS™)-processed steel Multistage fatigue modeling Résumé : Special microstructures of the newly developed Laser Engineered Net Shaping (LENS™)-processed steel induce a new variability in fatigue damage formation and evolution mechanisms. The microporosity and mechanism of fatigue damage formation and growth were invested using X-ray computed tomography and scanning electron microscopy. Systematic observations were made of the variations in the fracture surfaces according to three fatigue damage evolution stages: fatigue crack formation (incubation), microstructurally/physically small cracks, and long cracks. The fatigue crack was formed almost exclusively at the relatively large pores located at or near the specimen surface, with rare cases at incompletely melted power particles on the surface. Distributed cracks from large interior pores coalesced with each other in the microstructurally small crack regime to form the major critical crack that eventually fractured the specimen. This coalescence accelerated the fatigue crack growth, which in turn decreased the fatigue life but not significantly. In the long-crack regime, the fracture surface was rougher, but the overall surface tended to be perpendicular to the loading direction, indicating a Mode I type fracture. Cyclic strain-softening, with reduced strain-hardening, was also observed. The multistage fatigue model of McDowell et al. was used to capture the microstructure effects in the three fatigue damage evolution regimes, and the upper and lower bounds for the strain–life are predicted. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000159X [article] Microporosity effects on cyclic plasticity and fatigue of LENS™-processed steel [texte imprimé] / Y. Xue, Auteur ; A. Pascu, Auteur ; M.F. Horstemeyer, Auteur . - 2011 . - pp. 4029–4038.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4029–4038
Mots-clés : Fatigue micromechanism LENS™)-processed steel Multistage fatigue modeling Résumé : Special microstructures of the newly developed Laser Engineered Net Shaping (LENS™)-processed steel induce a new variability in fatigue damage formation and evolution mechanisms. The microporosity and mechanism of fatigue damage formation and growth were invested using X-ray computed tomography and scanning electron microscopy. Systematic observations were made of the variations in the fracture surfaces according to three fatigue damage evolution stages: fatigue crack formation (incubation), microstructurally/physically small cracks, and long cracks. The fatigue crack was formed almost exclusively at the relatively large pores located at or near the specimen surface, with rare cases at incompletely melted power particles on the surface. Distributed cracks from large interior pores coalesced with each other in the microstructurally small crack regime to form the major critical crack that eventually fractured the specimen. This coalescence accelerated the fatigue crack growth, which in turn decreased the fatigue life but not significantly. In the long-crack regime, the fracture surface was rougher, but the overall surface tended to be perpendicular to the loading direction, indicating a Mode I type fracture. Cyclic strain-softening, with reduced strain-hardening, was also observed. The multistage fatigue model of McDowell et al. was used to capture the microstructure effects in the three fatigue damage evolution regimes, and the upper and lower bounds for the strain–life are predicted. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000159X
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4039–4052
Titre : The evolution of crack-tip stresses during a fatigue overload event Type de document : texte imprimé Auteurs : A. Steuwer, Auteur ; M. Rahman, Auteur ; A. Shterenlikht, Auteur Année de publication : 2011 Article en page(s) : pp. 4039–4052 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Plasticity-induced closure Stress intensity factor Crack-tip stress field Overload Retardation Résumé : The mechanisms responsible for the transient retardation or acceleration of fatigue crack growth subsequent to overloading are a matter of intense debate. Plasticity-induced closure and residual stresses have often been invoked to explain these phenomena, but closure mechanisms are disputed, especially under conditions approximating to generalised plane strain. In this paper we exploit synchrotron radiation to report very high spatial resolution two-dimensional elastic strain and stress maps at maximum and minimum loading measured under plane strain during a normal fatigue cycle, as well as during and after a 100% overload event, in ultra-fine grained AA5091 aluminium alloy. These observations provide direct evidence of the material stress state in the vicinity of the crack-tip in thick samples. Significant compressive residual stresses were found both in front of and behind the crack-tip immediately following the overload event. The effective stress intensity at the crack-tip was determined directly from the local stress field measured deep within the bulk (plane strain) by comparison with linear elastic fracture mechanical theory. This agrees well with that nominally applied at maximum load and 100% overload. After overload, however, the stress fields were not well described by classical K fields due to closure-related residual stresses. Little evidence of overload closure was observed sometime after the overload event, in our case possibly because the overload plastic zone was very small. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001588 [article] The evolution of crack-tip stresses during a fatigue overload event [texte imprimé] / A. Steuwer, Auteur ; M. Rahman, Auteur ; A. Shterenlikht, Auteur . - 2011 . - pp. 4039–4052.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4039–4052
Mots-clés : Plasticity-induced closure Stress intensity factor Crack-tip stress field Overload Retardation Résumé : The mechanisms responsible for the transient retardation or acceleration of fatigue crack growth subsequent to overloading are a matter of intense debate. Plasticity-induced closure and residual stresses have often been invoked to explain these phenomena, but closure mechanisms are disputed, especially under conditions approximating to generalised plane strain. In this paper we exploit synchrotron radiation to report very high spatial resolution two-dimensional elastic strain and stress maps at maximum and minimum loading measured under plane strain during a normal fatigue cycle, as well as during and after a 100% overload event, in ultra-fine grained AA5091 aluminium alloy. These observations provide direct evidence of the material stress state in the vicinity of the crack-tip in thick samples. Significant compressive residual stresses were found both in front of and behind the crack-tip immediately following the overload event. The effective stress intensity at the crack-tip was determined directly from the local stress field measured deep within the bulk (plane strain) by comparison with linear elastic fracture mechanical theory. This agrees well with that nominally applied at maximum load and 100% overload. After overload, however, the stress fields were not well described by classical K fields due to closure-related residual stresses. Little evidence of overload closure was observed sometime after the overload event, in our case possibly because the overload plastic zone was very small. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001588
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4053–4066
Titre : Texture inheritance and variant selection through an hcp–bcc–hcp phase transformation Type de document : texte imprimé Auteurs : M.R. Daymond, Auteur ; R. A. Holt, Auteur ; S. Cai, Auteur Année de publication : 2011 Article en page(s) : pp. 4053–4066 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Zirconium Phase transformations Internal stresses Neutron diffraction Texture Résumé : In situ phase transformation experiments have been carried out using neutron diffraction to monitor the texture evolution during the α → β → α phase transformation in a common zirconium alloy. In contrast to recently reported results by other authors, there is clear evidence of a strong variant selection occurring during the α → β transformation and a weaker variant selection during the β → α transformation. Modeling of the texture change associated with the phase transformation has been successful in describing the variant selection occurring during the α → β transformation, and gives insights into the selection occurring during the β → α transformation. The results are relevant to processing of both zirconium and titanium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001576 [article] Texture inheritance and variant selection through an hcp–bcc–hcp phase transformation [texte imprimé] / M.R. Daymond, Auteur ; R. A. Holt, Auteur ; S. Cai, Auteur . - 2011 . - pp. 4053–4066.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4053–4066
Mots-clés : Zirconium Phase transformations Internal stresses Neutron diffraction Texture Résumé : In situ phase transformation experiments have been carried out using neutron diffraction to monitor the texture evolution during the α → β → α phase transformation in a common zirconium alloy. In contrast to recently reported results by other authors, there is clear evidence of a strong variant selection occurring during the α → β transformation and a weaker variant selection during the β → α transformation. Modeling of the texture change associated with the phase transformation has been successful in describing the variant selection occurring during the α → β transformation, and gives insights into the selection occurring during the β → α transformation. The results are relevant to processing of both zirconium and titanium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001576
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4067–4075
Titre : A new ultrahigh-strength stainless steel strengthened by various coexisting nanoprecipitates Type de document : texte imprimé Auteurs : W. Xu, Auteur ; P.E.J. Rivera-Díaz-del-Castillo, Auteur ; W. Yan, Auteur Année de publication : 2011 Article en page(s) : pp. 4067–4075 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Maraging steels Stainless steels Thermodynamics Precipitation Alloy design Résumé : A general computational alloy design approach based on thermodynamic and physical metallurgical principles and coupled with a genetic optimization scheme is presented. The model is applied to develop a new ultrahigh-strength maraging stainless steel. The alloy composition and heat treatment parameters are integrally optimized so as to achieve microstructures of fully lath martensite matrix strengthened by multiple precipitates of MC carbides, Cu particles and Ni3Ti intermetallics. The combined mechanical properties, corrosion resistance and identification of actual strengthening precipitates in the experimental prototype produced on the basic of the model predictions provide a strong justification for the alloy design approach. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001503 [article] A new ultrahigh-strength stainless steel strengthened by various coexisting nanoprecipitates [texte imprimé] / W. Xu, Auteur ; P.E.J. Rivera-Díaz-del-Castillo, Auteur ; W. Yan, Auteur . - 2011 . - pp. 4067–4075.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 4067–4075
Mots-clés : Maraging steels Stainless steels Thermodynamics Precipitation Alloy design Résumé : A general computational alloy design approach based on thermodynamic and physical metallurgical principles and coupled with a genetic optimization scheme is presented. The model is applied to develop a new ultrahigh-strength maraging stainless steel. The alloy composition and heat treatment parameters are integrally optimized so as to achieve microstructures of fully lath martensite matrix strengthened by multiple precipitates of MC carbides, Cu particles and Ni3Ti intermetallics. The combined mechanical properties, corrosion resistance and identification of actual strengthening precipitates in the experimental prototype produced on the basic of the model predictions provide a strong justification for the alloy design approach. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001503
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