Dépouillements

Deformation of solids with nanoscale pores by the action of capillary forces / J. Weissmüller in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 1–13 Titre : Deformation of solids with nanoscale pores by the action of capillary forces Type de document : texte imprimé Auteurs : J. Weissmüller, Auteur ; H.-L. Duan, Auteur ; D. Farkas, Auteur Année de publication : 2010 Article en page(s) : pp. 1–13 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Porous  material  Capillary  phenomena  Interfaces  Elastic  behaviour  Nanostructure Résumé : We analyze the various strain measures by which nanoporous materials react to changes in their surface stress and surface stretch at the solid–pore interface. Results of continuum mechanics are given for model geometries, arrays of spheres and fibres as well as solids with spherical and cylindrical voids. The findings are supported by atomistic simulation. The results for the mean stress agree with predictions of the generalized capillary equation of Weissmüller and Cahn, and they are incompatible with the notion of Laplace pressure. By contrast, no general relation between the mean stress and the macroscopic dimensional change could be identified. Even though certain microstructures with quite different geometry exhibit strikingly similar behaviour, others differ significantly. The macroscopic dimensional change can be largely enhanced compared with the local strain of the nanoscale building blocks. This fact can be exploited to amplify the stroke of nanoporous metal actuators. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005096 [article] Deformation of solids with nanoscale pores by the action of capillary forces [texte imprimé] / J. Weissmüller, Auteur ; H.-L. Duan, Auteur ; D. Farkas, Auteur . - 2010 . - pp. 1–13. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 1–13 Mots-clés : Porous  material  Capillary  phenomena  Interfaces  Elastic  behaviour  Nanostructure Résumé : We analyze the various strain measures by which nanoporous materials react to changes in their surface stress and surface stretch at the solid–pore interface. Results of continuum mechanics are given for model geometries, arrays of spheres and fibres as well as solids with spherical and cylindrical voids. The findings are supported by atomistic simulation. The results for the mean stress agree with predictions of the generalized capillary equation of Weissmüller and Cahn, and they are incompatible with the notion of Laplace pressure. By contrast, no general relation between the mean stress and the macroscopic dimensional change could be identified. Even though certain microstructures with quite different geometry exhibit strikingly similar behaviour, others differ significantly. The macroscopic dimensional change can be largely enhanced compared with the local strain of the nanoscale building blocks. This fact can be exploited to amplify the stroke of nanoporous metal actuators. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005096

Misorientation texture development during grain growth / J. Gruber in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 14–19 Titre : Misorientation texture development during grain growth : Part II: Theory Type de document : texte imprimé Auteurs : J. Gruber, Auteur ; A.D. Rollett, Auteur ; G.S. Rohrer, Auteur Année de publication : 2010 Article en page(s) : pp. 14–19 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Texture  Grain  growth  Anisotropy  Grain  boundaries  Simulation Résumé : A critical event model for the evolution of number- and area-weighted misorientation distribution functions (MDFs) during grain growth is proposed. Predictions from the model are compared to number- and area-weighted MDFs measured in Monte Carlo simulations with anisotropic interfacial properties and several initial orientation distributions, as well as a dense polycrystalline magnesia sample. The steady-state equation of our model appears to be a good fit to all data. The relation between the grain boundary energy and the normalized average boundary area is discussed in the context of triple junction dynamics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900545X [article] Misorientation texture development during grain growth : Part II: Theory [texte imprimé] / J. Gruber, Auteur ; A.D. Rollett, Auteur ; G.S. Rohrer, Auteur . - 2010 . - pp. 14–19. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 14–19 Mots-clés : Texture  Grain  growth  Anisotropy  Grain  boundaries  Simulation Résumé : A critical event model for the evolution of number- and area-weighted misorientation distribution functions (MDFs) during grain growth is proposed. Predictions from the model are compared to number- and area-weighted MDFs measured in Monte Carlo simulations with anisotropic interfacial properties and several initial orientation distributions, as well as a dense polycrystalline magnesia sample. The steady-state equation of our model appears to be a good fit to all data. The relation between the grain boundary energy and the normalized average boundary area is discussed in the context of triple junction dynamics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900545X

Coarsening mechanisms in a dendritic Al–10% Cu alloy / S. Terzi in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 20–30 Titre : Coarsening mechanisms in a dendritic Al–10% Cu alloy Type de document : texte imprimé Auteurs : S. Terzi, Auteur ; L. Salvo, Auteur ; M. Suery, Auteur Année de publication : 2010 Article en page(s) : pp. 20–30 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Coarsening  Aluminium  alloys  X-ray  microtomography  Solidification  microstructure  Semi-solid  processing Résumé : Coarsening of a dendritic Al–10 wt.% Cu alloy at 570 °C was investigated by fast in situ X-ray tomography. The variation of the specific solid–liquid interface area as a function of time was found to follow a power-law relation with an exponent close to −1/4. Three coarsening mechanisms operate in the alloy: (i) melting of small dendrite arms to the benefit of the adjacent arms (small arm melting), similar to Ostwald ripening; (ii) gradual movement of the base of the interdendritic grooves towards the tips (interdendritic groove advancement); (iii) coalescence of dendrites near the tips leading to the entrapment of liquid tubes or droplets (coalescence and groove advancement). The coarsening models proposed in the literature do not adequately resemble or predict the behaviour observed in the experiments. New models were developed for the first two coarsening mechanisms and predict the coarsening rate with very good agreement. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005655 [article] Coarsening mechanisms in a dendritic Al–10% Cu alloy [texte imprimé] / S. Terzi, Auteur ; L. Salvo, Auteur ; M. Suery, Auteur . - 2010 . - pp. 20–30. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 20–30 Mots-clés : Coarsening  Aluminium  alloys  X-ray  microtomography  Solidification  microstructure  Semi-solid  processing Résumé : Coarsening of a dendritic Al–10 wt.% Cu alloy at 570 °C was investigated by fast in situ X-ray tomography. The variation of the specific solid–liquid interface area as a function of time was found to follow a power-law relation with an exponent close to −1/4. Three coarsening mechanisms operate in the alloy: (i) melting of small dendrite arms to the benefit of the adjacent arms (small arm melting), similar to Ostwald ripening; (ii) gradual movement of the base of the interdendritic grooves towards the tips (interdendritic groove advancement); (iii) coalescence of dendrites near the tips leading to the entrapment of liquid tubes or droplets (coalescence and groove advancement). The coarsening models proposed in the literature do not adequately resemble or predict the behaviour observed in the experiments. New models were developed for the first two coarsening mechanisms and predict the coarsening rate with very good agreement. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005655

Anomalous temperature-dependent Young’s modulus of a cast LAST (Pb–Sb–Ag–Te) thermoelectric material / F. Ren in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 31–38 Titre : Anomalous temperature-dependent Young’s modulus of a cast LAST (Pb–Sb–Ag–Te) thermoelectric material Type de document : texte imprimé Auteurs : F. Ren, Auteur ; E. D. Case, Auteur ; E.J. Timm, Auteur Année de publication : 2010 Article en page(s) : pp. 31–38 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Casting  Semiconductor  Elastic  behaviour  Order–disorder  phenomena Résumé : Thermomechanical characterization is important to material evaluation and device design in the development of thermoelectric technology. In this study, we utilize the resonant ultrasound spectroscopy (RUS) technique to examine the elastic behavior of a cast LAST (Pb–Sb–Ag–Te) material with a composition of Ag0.86Pb19Sb1.0Te20 between room temperature and 823 K. The temperature-dependent Young’s modulus exhibits a monotonically decreasing trend with increasing temperature. However, an abnormal slope change in the Young’s modulus–temperature curve around 500 K is observed. In addition, hysteresis between heating and cooling data in the temperature range of 450–550 K is observed, which appears to be dependent on the heating/cooling rate during the RUS experiments such that the hysteresis disappears when the heating/cooling rate was decreased from 5 to 2 K min–1. In this study we propose an order–disorder transition model for the anomalous temperature-dependent Young’s modulus behavior observed in this study. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005667 [article] Anomalous temperature-dependent Young’s modulus of a cast LAST (Pb–Sb–Ag–Te) thermoelectric material [texte imprimé] / F. Ren, Auteur ; E. D. Case, Auteur ; E.J. Timm, Auteur . - 2010 . - pp. 31–38. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 31–38 Mots-clés : Casting  Semiconductor  Elastic  behaviour  Order–disorder  phenomena Résumé : Thermomechanical characterization is important to material evaluation and device design in the development of thermoelectric technology. In this study, we utilize the resonant ultrasound spectroscopy (RUS) technique to examine the elastic behavior of a cast LAST (Pb–Sb–Ag–Te) material with a composition of Ag0.86Pb19Sb1.0Te20 between room temperature and 823 K. The temperature-dependent Young’s modulus exhibits a monotonically decreasing trend with increasing temperature. However, an abnormal slope change in the Young’s modulus–temperature curve around 500 K is observed. In addition, hysteresis between heating and cooling data in the temperature range of 450–550 K is observed, which appears to be dependent on the heating/cooling rate during the RUS experiments such that the hysteresis disappears when the heating/cooling rate was decreased from 5 to 2 K min–1. In this study we propose an order–disorder transition model for the anomalous temperature-dependent Young’s modulus behavior observed in this study. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005667

Effect of space charge on the polarization hysteresis characteristics of monolithic and compositionally graded ferroelectrics / M.B. Okatan in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 39–48 Titre : Effect of space charge on the polarization hysteresis characteristics of monolithic and compositionally graded ferroelectrics Type de document : texte imprimé Auteurs : M.B. Okatan, Auteur ; J.V. Mantese, Auteur ; S. P. Alpay, Auteur Année de publication : 2010 Article en page(s) : pp. 39–48 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dielectrics  Multilayers  Perovskites  Ferroelectricity  Interface  defects Résumé : A non-linear thermodynamic analysis of ferroelectric systems with localized space charges for monolithic and compositionally graded materials is described wherein the electrostatic interlayer interactions are specifically accounted for. The electrostatic coupling is established through the built-in polarization due to the space charges and the intrinsic polarization variations between the ferroelectric layers. The findings show that the polarization hysteresis response of monolithic stress-free barium strontium titanate (BST) ferroelectrics with asymmetrically distributed space charges result in a displacement of the hysteresis loop along the applied electric field axis. In compositionally graded BST multilayers, the hysteresis response is characterized by off-sets along both the polarization and the electric field axes, yet with magnitudes of displacement that are markedly larger than those for monolithic ferroelectrics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005679 [article] Effect of space charge on the polarization hysteresis characteristics of monolithic and compositionally graded ferroelectrics [texte imprimé] / M.B. Okatan, Auteur ; J.V. Mantese, Auteur ; S. P. Alpay, Auteur . - 2010 . - pp. 39–48. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 39–48 Mots-clés : Dielectrics  Multilayers  Perovskites  Ferroelectricity  Interface  defects Résumé : A non-linear thermodynamic analysis of ferroelectric systems with localized space charges for monolithic and compositionally graded materials is described wherein the electrostatic interlayer interactions are specifically accounted for. The electrostatic coupling is established through the built-in polarization due to the space charges and the intrinsic polarization variations between the ferroelectric layers. The findings show that the polarization hysteresis response of monolithic stress-free barium strontium titanate (BST) ferroelectrics with asymmetrically distributed space charges result in a displacement of the hysteresis loop along the applied electric field axis. In compositionally graded BST multilayers, the hysteresis response is characterized by off-sets along both the polarization and the electric field axes, yet with magnitudes of displacement that are markedly larger than those for monolithic ferroelectrics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005679

Recovery as a measure of oriented crystalline structure in poly(l-lactide) used as shape memory polymer / Y.S. Wong in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 49–58 Titre : Recovery as a measure of oriented crystalline structure in poly(l-lactide) used as shape memory polymer Type de document : texte imprimé Auteurs : Y.S. Wong, Auteur ; S.S. Venkatraman, Auteur Année de publication : 2010 Article en page(s) : pp. 49–58 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Poly(l-lactide)  Recovery Résumé : Semicrystalline poly(l-lactide), or PLLA, has been reported as possessing shape-memory effect [1], [2], [3], [4] and [5]; however, the mechanism responsible for the shape recovery has not been well addressed. Therefore, in this paper, we attempted to investigate the structural evolution in PLLA during the shape memory process by means of differential scanning calorimetry, dynamic mechanical analysis (DMA), optical birefringence and wide-angle X-ray diffraction measurements. The shape recovery behaviour and recovery stress as a function of stretch ratio and deformation temperature were quantified. Based on the present results, shape recovery decreases with increasing stretch ratio and deformation temperature. It is suggested that the shape recovery is associated with the disorientation of oriented amorphous chains formed during stretching and the drop in recovery is attributed to the strain-induced crystallization and the formation of highly oriented microfibrillar structure, hindering the mobility in the amorphous phase and thus impeding recovery. In particular, the validity of the stress-optical law is considered. It is shown that the stress-optical properties show divergence from the Gaussian theory for stretch ratio greater than ∼1.5. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005680 [article] Recovery as a measure of oriented crystalline structure in poly(l-lactide) used as shape memory polymer [texte imprimé] / Y.S. Wong, Auteur ; S.S. Venkatraman, Auteur . - 2010 . - pp. 49–58. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 49–58 Mots-clés : Poly(l-lactide)  Recovery Résumé : Semicrystalline poly(l-lactide), or PLLA, has been reported as possessing shape-memory effect [1], [2], [3], [4] and [5]; however, the mechanism responsible for the shape recovery has not been well addressed. Therefore, in this paper, we attempted to investigate the structural evolution in PLLA during the shape memory process by means of differential scanning calorimetry, dynamic mechanical analysis (DMA), optical birefringence and wide-angle X-ray diffraction measurements. The shape recovery behaviour and recovery stress as a function of stretch ratio and deformation temperature were quantified. Based on the present results, shape recovery decreases with increasing stretch ratio and deformation temperature. It is suggested that the shape recovery is associated with the disorientation of oriented amorphous chains formed during stretching and the drop in recovery is attributed to the strain-induced crystallization and the formation of highly oriented microfibrillar structure, hindering the mobility in the amorphous phase and thus impeding recovery. In particular, the validity of the stress-optical law is considered. It is shown that the stress-optical properties show divergence from the Gaussian theory for stretch ratio greater than ∼1.5. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005680

Onset of plasticity in InxGa1−xAs multilayers / S. Korte in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 59–66 Titre : Onset of plasticity in InxGa1−xAs multilayers Type de document : texte imprimé Auteurs : S. Korte, Auteur ; W.J. Clegg, Auteur Année de publication : 2010 Article en page(s) : pp. 59–66 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoindentation  Transmission  electron  microscopy  Semiconductors  Multilayers Résumé : Coherently strained InxGa1−xAs multilayers with zero net strain have been investigated in order to determine the influence of coherency strains on the yield stress. The deformation behaviour has been studied using both ex- and in situ nanoindentation and transmission electron microscopy. Nanoindentation showed that the pressure required for the onset of yield decreased with increasing coherency strain, consistent with previous work, while the hardness remained constant. Transmission electron microscopy revealed that deformation was more prevalent in one layer. Using these observations, a straightforward analysis has been developed in which the yield pressure of the multilayer is related to the onset of flow in the weaker layer determined by both its intrinsic yield pressure and coherency strains. This gives good agreement with the experimental observations and is consistent with the observations of the effects of internal stresses in films elsewhere in the literature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005692 [article] Onset of plasticity in InxGa1−xAs multilayers [texte imprimé] / S. Korte, Auteur ; W.J. Clegg, Auteur . - 2010 . - pp. 59–66. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 59–66 Mots-clés : Nanoindentation  Transmission  electron  microscopy  Semiconductors  Multilayers Résumé : Coherently strained InxGa1−xAs multilayers with zero net strain have been investigated in order to determine the influence of coherency strains on the yield stress. The deformation behaviour has been studied using both ex- and in situ nanoindentation and transmission electron microscopy. Nanoindentation showed that the pressure required for the onset of yield decreased with increasing coherency strain, consistent with previous work, while the hardness remained constant. Transmission electron microscopy revealed that deformation was more prevalent in one layer. Using these observations, a straightforward analysis has been developed in which the yield pressure of the multilayer is related to the onset of flow in the weaker layer determined by both its intrinsic yield pressure and coherency strains. This gives good agreement with the experimental observations and is consistent with the observations of the effects of internal stresses in films elsewhere in the literature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005692

Collective dynamics in nanostructured polycrystalline ferroelectric thin films using local time-resolved measurements and switching spectroscopy / Samantha Wicks in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 67–75 Titre : Collective dynamics in nanostructured polycrystalline ferroelectric thin films using local time-resolved measurements and switching spectroscopy Type de document : texte imprimé Auteurs : Samantha Wicks, Auteur ; Katyayani Seal, Auteur ; Stephen Jesse, Auteur Année de publication : 2010 Article en page(s) : pp. 67–75 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ferroelectricity  Nanostructure  Piezoelectricity Résumé : Grain-to-grain long-range interactions and the ensuing collective dynamics in the domain behavior of nanostructured polycrystalline Pb(Zr,Ti)O3 ferroelectric thin films have been investigated. To identify the key factors and interactions controlling local polarization dynamics we utilize a synergistic approach based on focused ion beam (FIB) milled damage-free nanostructures to isolate single grains and grain clusters, time-resolved piezoresponse force microscopy and switching spectroscopy PFM (SSPFM) (PFM) to address polarization dynamics within individual grains, and finite-element simulations to quantify the local ferroelectric interactions and hence assess the weight of several possible switching mechanisms. The experiments find that of the three possible switching mechanisms, namely direct electromechanical coupling, local built-in electric field and strain, and grain boundary electrostatic charges, the last one is the dominant mechanism. Although finite-element simulations find that direct electromechanical coupling and local built-in field-induced switching are possible, calculations confirm that for the utilized material properties, the aforementioned mechanisms are energetically unfavored. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005709 [article] Collective dynamics in nanostructured polycrystalline ferroelectric thin films using local time-resolved measurements and switching spectroscopy [texte imprimé] / Samantha Wicks, Auteur ; Katyayani Seal, Auteur ; Stephen Jesse, Auteur . - 2010 . - pp. 67–75. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 67–75 Mots-clés : Ferroelectricity  Nanostructure  Piezoelectricity Résumé : Grain-to-grain long-range interactions and the ensuing collective dynamics in the domain behavior of nanostructured polycrystalline Pb(Zr,Ti)O3 ferroelectric thin films have been investigated. To identify the key factors and interactions controlling local polarization dynamics we utilize a synergistic approach based on focused ion beam (FIB) milled damage-free nanostructures to isolate single grains and grain clusters, time-resolved piezoresponse force microscopy and switching spectroscopy PFM (SSPFM) (PFM) to address polarization dynamics within individual grains, and finite-element simulations to quantify the local ferroelectric interactions and hence assess the weight of several possible switching mechanisms. The experiments find that of the three possible switching mechanisms, namely direct electromechanical coupling, local built-in electric field and strain, and grain boundary electrostatic charges, the last one is the dominant mechanism. Although finite-element simulations find that direct electromechanical coupling and local built-in field-induced switching are possible, calculations confirm that for the utilized material properties, the aforementioned mechanisms are energetically unfavored. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005709

Anisotropic elastic constants and thermal expansivities in monocrystal CrB2, TiB2, and ZrB2 / Norihiko L. Okamoto in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 76–84 Titre : Anisotropic elastic constants and thermal expansivities in monocrystal CrB2, TiB2, and ZrB2 Type de document : texte imprimé Auteurs : Norihiko L. Okamoto, Auteur ; Misato Kusakari, Auteur ; Katsushi Tanaka, Auteur Année de publication : 2010 Article en page(s) : pp. 76–84 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Borides  Transition  metals  Monocrystals  Anisotropy  High  temperatures Résumé : The elastic constants and thermal expansivities in monocrystals of three transition-metal diborides with the AlB2 structure, CrB2, TiB2, and ZrB2, have been investigated in the temperature ranges from 300 to 1373 K and from 300 to 1073 K. The anisotropic parameters deduced from the measured elastic constants and thermal expansivities indicate that of the three diborides, the anisotropy is the most and least significant in CrB2 and ZrB2, respectively. The factors determining the significance in anisotropy in atomic bonding in AlB2-type diborides are analyzed by an approach similar to the valence-force-field method and are discussed in terms of the deformation of the electronic charge around the metal atoms occurring to fit themselves in the (0 0 0 1) basal plane. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005710 [article] Anisotropic elastic constants and thermal expansivities in monocrystal CrB2, TiB2, and ZrB2 [texte imprimé] / Norihiko L. Okamoto, Auteur ; Misato Kusakari, Auteur ; Katsushi Tanaka, Auteur . - 2010 . - pp. 76–84. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 76–84 Mots-clés : Borides  Transition  metals  Monocrystals  Anisotropy  High  temperatures Résumé : The elastic constants and thermal expansivities in monocrystals of three transition-metal diborides with the AlB2 structure, CrB2, TiB2, and ZrB2, have been investigated in the temperature ranges from 300 to 1373 K and from 300 to 1073 K. The anisotropic parameters deduced from the measured elastic constants and thermal expansivities indicate that of the three diborides, the anisotropy is the most and least significant in CrB2 and ZrB2, respectively. The factors determining the significance in anisotropy in atomic bonding in AlB2-type diborides are analyzed by an approach similar to the valence-force-field method and are discussed in terms of the deformation of the electronic charge around the metal atoms occurring to fit themselves in the (0 0 0 1) basal plane. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005710

Transformation potential predictions for the stress-induced austenite to martensite transformation in steel / A. Creuziger in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 85–91 Titre : Transformation potential predictions for the stress-induced austenite to martensite transformation in steel Type de document : texte imprimé Auteurs : A. Creuziger, Auteur ; T. Foecke, Auteur Année de publication : 2010 Article en page(s) : pp. 85–91 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : TRIP  steel  Texture  Austenitic  steels  Martensitic  phase  transformation Résumé : The stress-induced transformation behavior of retained austenite is considered in this work. With the development of transformation-induced plasticity (TRIP) steels this deformation mode is of growing importance. Twinned martensite structures were calculated using the crystallographic theory of martensite. An available work criterion was used to predict the transformation potentials for 16 different in-plane stress states for sheet sample geometry. By rotating the twinned martensite structures over all crystallographic orientations using Euler angles, the magnitude of the transformation potential was plotted as an orientation distribution plot for comparison with typical texture components. From these data, the Brass and Copper orientation components that are typical in retained austenite such as in TRIP steels were found to have low transformation potential values. Grains aligned with these orientations would require higher stresses to transform than other orientations, and may therefore never transform. This correlates to experimental observations that heavily deformed TRIP steel contains residual retained austenite. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005825 [article] Transformation potential predictions for the stress-induced austenite to martensite transformation in steel [texte imprimé] / A. Creuziger, Auteur ; T. Foecke, Auteur . - 2010 . - pp. 85–91. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 85–91 Mots-clés : TRIP  steel  Texture  Austenitic  steels  Martensitic  phase  transformation Résumé : The stress-induced transformation behavior of retained austenite is considered in this work. With the development of transformation-induced plasticity (TRIP) steels this deformation mode is of growing importance. Twinned martensite structures were calculated using the crystallographic theory of martensite. An available work criterion was used to predict the transformation potentials for 16 different in-plane stress states for sheet sample geometry. By rotating the twinned martensite structures over all crystallographic orientations using Euler angles, the magnitude of the transformation potential was plotted as an orientation distribution plot for comparison with typical texture components. From these data, the Brass and Copper orientation components that are typical in retained austenite such as in TRIP steels were found to have low transformation potential values. Grains aligned with these orientations would require higher stresses to transform than other orientations, and may therefore never transform. This correlates to experimental observations that heavily deformed TRIP steel contains residual retained austenite. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005825

Analytical modeling of stress-induced martensitic transformation in the crack tip region of nickel–titanium alloys / Carmine Maletta in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 92–101 Titre : Analytical modeling of stress-induced martensitic transformation in the crack tip region of nickel–titanium alloys Type de document : texte imprimé Auteurs : Carmine Maletta, Auteur ; Franco Furgiuele, Auteur Année de publication : 2010 Article en page(s) : pp. 92–101 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Shape  memory  alloys  (SMAs)  Fracture  Martensitic  phase  transformation  Analytical  methods Résumé : A novel analytical method, which predicts the extent of the stress-induced martensitic transformation (SIM) in the crack tip vicinity of nickel–titanium (NiTi)-based shape memory alloys, as well as describing the stress distribution in both transformed and untransformed regions, is presented. The method has been validated by comparisons with results from finite-element simulations with good agreement. Furthermore, the method has been used to analyze the effects of various thermomechanical parameters on the extent of the transformation region near the crack tip. Finally, the effects of several thermomechanical loading conditions, in terms of both applied stress and temperature, on the crack tip transformation behavior have been analyzed. The results highlight a marked effect of temperature on the extent of the transformation region and, consequently, on the crack tip stress distribution. As a consequence, temperature plays a role in the fracture process of NiTi alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005837 [article] Analytical modeling of stress-induced martensitic transformation in the crack tip region of nickel–titanium alloys [texte imprimé] / Carmine Maletta, Auteur ; Franco Furgiuele, Auteur . - 2010 . - pp. 92–101. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 92–101 Mots-clés : Shape  memory  alloys  (SMAs)  Fracture  Martensitic  phase  transformation  Analytical  methods Résumé : A novel analytical method, which predicts the extent of the stress-induced martensitic transformation (SIM) in the crack tip vicinity of nickel–titanium (NiTi)-based shape memory alloys, as well as describing the stress distribution in both transformed and untransformed regions, is presented. The method has been validated by comparisons with results from finite-element simulations with good agreement. Furthermore, the method has been used to analyze the effects of various thermomechanical parameters on the extent of the transformation region near the crack tip. Finally, the effects of several thermomechanical loading conditions, in terms of both applied stress and temperature, on the crack tip transformation behavior have been analyzed. The results highlight a marked effect of temperature on the extent of the transformation region and, consequently, on the crack tip stress distribution. As a consequence, temperature plays a role in the fracture process of NiTi alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005837

Homology metrics for microstructure response fields in polycrystals / Thomas Wanner in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 102–110 Titre : Homology metrics for microstructure response fields in polycrystals Type de document : texte imprimé Auteurs : Thomas Wanner, Auteur ; Edwin R. Fuller Jr., Auteur ; David M. Saylor, Auteur Année de publication : 2010 Article en page(s) : pp. 102–110 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Homology  metrics  Microstructures  Polycrystals  Finite  element  simulations  Thermal  expansion  anisotropy Résumé : Quantitative homology metrics are proposed for characterizing the thermal–elastic response of polycrystalline materials. Simulations for a calcite-based polycrystal, marble, are used as an illustrative example. The homology metrics are based on topological measurements, such as the number of components and the number of handles of the thermal–elastic response fields for a complex microstructure. These homology metrics are applied to characterize not only the elastic energy density and maximum principal stress response fields in a polycrystal but also the correlated grain-boundary misorientation distributions that influenced the formation of these response fields. It is demonstrated that the topological analysis can quantitatively distinguish between different types of grain-boundary misorientations, as well as between differences in the resulting response fields. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005849 [article] Homology metrics for microstructure response fields in polycrystals [texte imprimé] / Thomas Wanner, Auteur ; Edwin R. Fuller Jr., Auteur ; David M. Saylor, Auteur . - 2010 . - pp. 102–110. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 102–110 Mots-clés : Homology  metrics  Microstructures  Polycrystals  Finite  element  simulations  Thermal  expansion  anisotropy Résumé : Quantitative homology metrics are proposed for characterizing the thermal–elastic response of polycrystalline materials. Simulations for a calcite-based polycrystal, marble, are used as an illustrative example. The homology metrics are based on topological measurements, such as the number of components and the number of handles of the thermal–elastic response fields for a complex microstructure. These homology metrics are applied to characterize not only the elastic energy density and maximum principal stress response fields in a polycrystal but also the correlated grain-boundary misorientation distributions that influenced the formation of these response fields. It is demonstrated that the topological analysis can quantitatively distinguish between different types of grain-boundary misorientations, as well as between differences in the resulting response fields. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005849

Recovery kinetics in the presence of precipitates / R. Roumina in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 111–121 Titre : Recovery kinetics in the presence of precipitates : The softening response of an Al–Mg–Sc alloy Type de document : texte imprimé Auteurs : R. Roumina, Auteur ; C.W. Sinclair, Auteur Année de publication : 2010 Article en page(s) : pp. 111–121 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Recovery  Al–Sc  alloy  Precipitation  Yield  strength Résumé : Recovery of an Al–Mg–Sc alloy in the presence of Al3Sc precipitates has been studied. The results demonstrate that recovery can be separated into two stages. The initial stage is precipitate-independent and consistent with the recovery kinetics of binary Al–Mg alloys. The second is strongly influenced by the presence of precipitates. Precipitates slow recovery, allowing recovered microstructures to be maintained over long annealing times to high homologous temperatures without recrystallization. A physically based model that accounts for the precipitate dependence of recovery is presented and compared to experimental results. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005850 [article] Recovery kinetics in the presence of precipitates : The softening response of an Al–Mg–Sc alloy [texte imprimé] / R. Roumina, Auteur ; C.W. Sinclair, Auteur . - 2010 . - pp. 111–121. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 111–121 Mots-clés : Recovery  Al–Sc  alloy  Precipitation  Yield  strength Résumé : Recovery of an Al–Mg–Sc alloy in the presence of Al3Sc precipitates has been studied. The results demonstrate that recovery can be separated into two stages. The initial stage is precipitate-independent and consistent with the recovery kinetics of binary Al–Mg alloys. The second is strongly influenced by the presence of precipitates. Precipitates slow recovery, allowing recovered microstructures to be maintained over long annealing times to high homologous temperatures without recrystallization. A physically based model that accounts for the precipitate dependence of recovery is presented and compared to experimental results. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005850

Simulation of cooling of liquid Al–33 wt.% Cu droplet impinging on a metallic substrate and its experimental validation / A. Kumar in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 122–133 Titre : Simulation of cooling of liquid Al–33 wt.% Cu droplet impinging on a metallic substrate and its experimental validation Type de document : texte imprimé Auteurs : A. Kumar, Auteur ; S. Ghosh, Auteur ; B. K. Dhindaw, Auteur Année de publication : 2010 Article en page(s) : pp. 122–133 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Eutectic  Alloy  droplet  Substrate  Solidification  Modeling Résumé : In the present work a model for heat transfer during collision of a falling liquid Al–33 wt.% Cu droplet on a 304 stainless steel substrate has been developed on a FLUENT 6.3.16 platform. The model simultaneously takes into account the fluid flow and heat transfer in the liquid droplet and the surrounding gas, and the heat transfer in the substrate. The liquid–gas interface was tracked using the volume of fluid method and the contact resistance between Al–33 wt.% Cu and the substrate was taken into account. The comprehensive model correctly predicted the total spread in the droplet. As per the predicted transient thermal field, the solidification front speed oscillated along the radius of the spread droplet. Based on the estimated front speeds at these locations and Jackson–Hunt plot for Al–33 wt.% Cu, the variation of interlamellar spacing along the radial direction was found. It matched well with the variation of the experimentally measured interlamellar spacing at different locations along the radius. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005862 [article] Simulation of cooling of liquid Al–33 wt.% Cu droplet impinging on a metallic substrate and its experimental validation [texte imprimé] / A. Kumar, Auteur ; S. Ghosh, Auteur ; B. K. Dhindaw, Auteur . - 2010 . - pp. 122–133. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 122–133 Mots-clés : Eutectic  Alloy  droplet  Substrate  Solidification  Modeling Résumé : In the present work a model for heat transfer during collision of a falling liquid Al–33 wt.% Cu droplet on a 304 stainless steel substrate has been developed on a FLUENT 6.3.16 platform. The model simultaneously takes into account the fluid flow and heat transfer in the liquid droplet and the surrounding gas, and the heat transfer in the substrate. The liquid–gas interface was tracked using the volume of fluid method and the contact resistance between Al–33 wt.% Cu and the substrate was taken into account. The comprehensive model correctly predicted the total spread in the droplet. As per the predicted transient thermal field, the solidification front speed oscillated along the radius of the spread droplet. Based on the estimated front speeds at these locations and Jackson–Hunt plot for Al–33 wt.% Cu, the variation of interlamellar spacing along the radial direction was found. It matched well with the variation of the experimentally measured interlamellar spacing at different locations along the radius. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005862

Core–shell nanoscale precipitates in Al–0.06 at.% Sc microalloyed with Tb, Ho, Tm or Lu / Matthew E. Krug in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 134–145 Titre : Core–shell nanoscale precipitates in Al–0.06 at.% Sc microalloyed with Tb, Ho, Tm or Lu Type de document : texte imprimé Auteurs : Matthew E. Krug, Auteur ; Alexandra Werber, Auteur ; David C. Dunand, Auteur Année de publication : 2010 Article en page(s) : pp. 134–145 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Rare  earth  Precipitation  Microhardness  Atom-probe  field-ion  microscopy  (AP-FIM)  Aluminum  alloys Résumé : The age-hardening response at 300 °C of Al–0.06Sc–0.02RE (at.%, with RE = Tb, Ho, Tm or Lu) is found to be similar to that of binary Al–0.08Sc (at.%), except that a shorter incubation period for hardening is observed, which is associated with nanoscale RE-rich Al3(RE1−xScx) precipitates. In addition, Al–0.06Sc–0.02Tb (at.%) has a much lower peak microhardness than that of Al–0.08Sc (at.%) due to the small solubility of Tb in α-Al(Sc). Peak-age hardening occurs after 24 h, and is associated with a high number density of nanoscale Sc-rich Al3(Sc1−xREx) precipitates. Analysis by three-dimensional local-electrode atom-probe tomography shows that x increases with increasing atomic number, and that the REs partition to the core of the precipitates. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005874 [article] Core–shell nanoscale precipitates in Al–0.06 at.% Sc microalloyed with Tb, Ho, Tm or Lu [texte imprimé] / Matthew E. Krug, Auteur ; Alexandra Werber, Auteur ; David C. Dunand, Auteur . - 2010 . - pp. 134–145. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 134–145 Mots-clés : Rare  earth  Precipitation  Microhardness  Atom-probe  field-ion  microscopy  (AP-FIM)  Aluminum  alloys Résumé : The age-hardening response at 300 °C of Al–0.06Sc–0.02RE (at.%, with RE = Tb, Ho, Tm or Lu) is found to be similar to that of binary Al–0.08Sc (at.%), except that a shorter incubation period for hardening is observed, which is associated with nanoscale RE-rich Al3(RE1−xScx) precipitates. In addition, Al–0.06Sc–0.02Tb (at.%) has a much lower peak microhardness than that of Al–0.08Sc (at.%) due to the small solubility of Tb in α-Al(Sc). Peak-age hardening occurs after 24 h, and is associated with a high number density of nanoscale Sc-rich Al3(Sc1−xREx) precipitates. Analysis by three-dimensional local-electrode atom-probe tomography shows that x increases with increasing atomic number, and that the REs partition to the core of the precipitates. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005874

The c-axis texturing of seeded Si3N4 with β-Si3N4 whiskers by slip casting in a rotating magnetic field / X.W. Zhu in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 146–161 Titre : The c-axis texturing of seeded Si3N4 with β-Si3N4 whiskers by slip casting in a rotating magnetic field Type de document : texte imprimé Auteurs : X.W. Zhu, Auteur ; Y. Sakka, Auteur ; T.S. Suzuki, Auteur Année de publication : 2010 Article en page(s) : pp. 146–161 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Silicon  nitride  Slip  casting  Rotating  magnetic  field  Texture  Thermal  conductivity Résumé : The c-axis texture development in seeded Si3N4 with β-Si3N4 whiskers by slip casting in a rotating magnetic field was investigated by powder X-ray diffraction, scanning electron microscopy and thermal anisotropy evaluation, including the effects of magnetic flux density, suspension rheological properties and rotational speed. By increasing the magnetic flux density from 1 to 12 T, the c-axis orientation of β-Si3N4 whiskers is achieved in the well-dispersed 30 vol.% suspension but hindered in the flocculated 40 vol.% suspension. The degree of orientation tends to decrease with increasing rotational speed from 5 to 30 rpm. The green body shows no density gradient but nonuniform orientation of β-Si3N4 whiskers regardless of the rotational speed, resulting in the similar nonuniform texture in the sintered body. The nonuniform texture is featured in three major layers: lower surface, inner region and upper surface, corresponding to the lower, higher and lower c-axis orientation, respectively. The resultant c-axis textured Si3N4 exhibits thermal anisotropy as high as 55%, slightly lower than the intrinsic thermal anisotropy (62%) of β-Si3N4. A theoretical analysis is performed to help understand the key factors affecting the orientation of β-Si3N4 whiskers by slip casting in the rotating magnetic field. The formation mechanisms of the nonuniform texture were discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005886 [article] The c-axis texturing of seeded Si3N4 with β-Si3N4 whiskers by slip casting in a rotating magnetic field [texte imprimé] / X.W. Zhu, Auteur ; Y. Sakka, Auteur ; T.S. Suzuki, Auteur . - 2010 . - pp. 146–161. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 146–161 Mots-clés : Silicon  nitride  Slip  casting  Rotating  magnetic  field  Texture  Thermal  conductivity Résumé : The c-axis texture development in seeded Si3N4 with β-Si3N4 whiskers by slip casting in a rotating magnetic field was investigated by powder X-ray diffraction, scanning electron microscopy and thermal anisotropy evaluation, including the effects of magnetic flux density, suspension rheological properties and rotational speed. By increasing the magnetic flux density from 1 to 12 T, the c-axis orientation of β-Si3N4 whiskers is achieved in the well-dispersed 30 vol.% suspension but hindered in the flocculated 40 vol.% suspension. The degree of orientation tends to decrease with increasing rotational speed from 5 to 30 rpm. The green body shows no density gradient but nonuniform orientation of β-Si3N4 whiskers regardless of the rotational speed, resulting in the similar nonuniform texture in the sintered body. The nonuniform texture is featured in three major layers: lower surface, inner region and upper surface, corresponding to the lower, higher and lower c-axis orientation, respectively. The resultant c-axis textured Si3N4 exhibits thermal anisotropy as high as 55%, slightly lower than the intrinsic thermal anisotropy (62%) of β-Si3N4. A theoretical analysis is performed to help understand the key factors affecting the orientation of β-Si3N4 whiskers by slip casting in the rotating magnetic field. The formation mechanisms of the nonuniform texture were discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005886

Strain mapping along Al–Pb interfaces / Harald Rösner in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 162–172 Titre : Strain mapping along Al–Pb interfaces Type de document : texte imprimé Auteurs : Harald Rösner, Auteur ; Christoph T. Koch, Auteur ; Gerhard Wilde, Auteur Année de publication : 2010 Article en page(s) : pp. 162–172 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Misfit  dislocation  Strain  mapping  Size-dependent  melting  Focus  series  reconstruction Résumé : Local strains at particle–matrix hetero-interfaces in an Al–Pb composite produced by high-energy ball-milling were measured by means of geometric phase analysis (GPA) on the basis of high-resolution transmission electron microscope (HRTEM) images. A through-focus series of 10 experimental micrographs was used to retrieve the complex exit-face wave function and subsequently to calculate the components of the strain tensor using Pb as the reference lattice. The strain analysis revealed considerable strain for the interface regions with compressive strain for the Pb side and tensile strain for the Al side. The strained zones extend up to 2–3 lattice spacings on either side of the interface. The interface regions are not sheared or significantly rotated, which shows that the whole state of the interface is elastically strained but not plastically deformed. A new possible interpretation of the melting behaviour of the Pb particles in terms of the strains is discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005898 [article] Strain mapping along Al–Pb interfaces [texte imprimé] / Harald Rösner, Auteur ; Christoph T. Koch, Auteur ; Gerhard Wilde, Auteur . - 2010 . - pp. 162–172. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 162–172 Mots-clés : Misfit  dislocation  Strain  mapping  Size-dependent  melting  Focus  series  reconstruction Résumé : Local strains at particle–matrix hetero-interfaces in an Al–Pb composite produced by high-energy ball-milling were measured by means of geometric phase analysis (GPA) on the basis of high-resolution transmission electron microscope (HRTEM) images. A through-focus series of 10 experimental micrographs was used to retrieve the complex exit-face wave function and subsequently to calculate the components of the strain tensor using Pb as the reference lattice. The strain analysis revealed considerable strain for the interface regions with compressive strain for the Pb side and tensile strain for the Al side. The strained zones extend up to 2–3 lattice spacings on either side of the interface. The interface regions are not sheared or significantly rotated, which shows that the whole state of the interface is elastically strained but not plastically deformed. A new possible interpretation of the melting behaviour of the Pb particles in terms of the strains is discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005898

Transmission electron microscopy study of stacking faults and their interaction with pyramidal dislocations in deformed Mg / B. Li in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 173–179 Titre : Transmission electron microscopy study of stacking faults and their interaction with pyramidal dislocations in deformed Mg Type de document : texte imprimé Auteurs : B. Li, Auteur ; P.F. Yan, Auteur ; M.L. Sui, Auteur Année de publication : 2010 Article en page(s) : pp. 173–179 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocations  Stacking  fault  Magnesium  TEM Résumé : We present transmission electron microscopy (TEM) observations of stacking faults (SFs) and their interactions with pyramidal dislocations, in plastically deformed polycrystalline pure magnesium. We have observed well-defined fringes as well as streaking in diffraction patterns, typical of SFs. The basal SFs are decorated by a large number of dark speckles, which are created by the interaction with pyramidal dislocations that have both 〈c〉 and 〈a〉 components as revealed by our contrast analysis. The SFs do not appear to result from the splitting of unit dislocations, as the SFs are relatively wide and no dislocation nodes were observed. By tilting the specimen systematically inside TEM, the SFs and the associated dislocations in Mg are found to exhibit a rich variety of features in terms of their morphology and diffraction contrast. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005904 [article] Transmission electron microscopy study of stacking faults and their interaction with pyramidal dislocations in deformed Mg [texte imprimé] / B. Li, Auteur ; P.F. Yan, Auteur ; M.L. Sui, Auteur . - 2010 . - pp. 173–179. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 173–179 Mots-clés : Dislocations  Stacking  fault  Magnesium  TEM Résumé : We present transmission electron microscopy (TEM) observations of stacking faults (SFs) and their interactions with pyramidal dislocations, in plastically deformed polycrystalline pure magnesium. We have observed well-defined fringes as well as streaking in diffraction patterns, typical of SFs. The basal SFs are decorated by a large number of dark speckles, which are created by the interaction with pyramidal dislocations that have both 〈c〉 and 〈a〉 components as revealed by our contrast analysis. The SFs do not appear to result from the splitting of unit dislocations, as the SFs are relatively wide and no dislocation nodes were observed. By tilting the specimen systematically inside TEM, the SFs and the associated dislocations in Mg are found to exhibit a rich variety of features in terms of their morphology and diffraction contrast. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005904

Study of the Ni-rich multi-phase equilibria in Ni–Al–Pt alloys using the cluster/site approximation for the face-centered cubic phases / Zhu, J. in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 180–188 Titre : Study of the Ni-rich multi-phase equilibria in Ni–Al–Pt alloys using the cluster/site approximation for the face-centered cubic phases Type de document : texte imprimé Auteurs : Zhu, J., Auteur ; C. Zhang, Auteur ; D. Ballard, Auteur Année de publication : 2010 Article en page(s) : pp. 180–188 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel  alloys  Cluster/site  approximation  Thermodynamics  CALPHAD Résumé : The modified cluster/site approximation was used to describe the thermodynamics of the various face-centered cubic phases in Ni–Al–Pt, the Bragg–Williams approximation for the B2 phase, and a modified regular solution formalism for the liquid phase. Coupled computational thermodynamics with key phase equilibrium measurements in the solid state, a thermodynamic description of this ternary for Ni contents higher than 50% was obtained based on these data and those given in the literature as well as the descriptions of its constituent binaries. Not only did the model-calculated solid-state phase equilibria agree with the measured data, the model-calculated liquidus projection is also able to account for the phases formed during solidification. In addition, the calculated chemical potentials or activities of Ni and Al are also in accord with the measured data as a function of temperature using mass spectrometry. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005916 [article] Study of the Ni-rich multi-phase equilibria in Ni–Al–Pt alloys using the cluster/site approximation for the face-centered cubic phases [texte imprimé] / Zhu, J., Auteur ; C. Zhang, Auteur ; D. Ballard, Auteur . - 2010 . - pp. 180–188. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 180–188 Mots-clés : Nickel  alloys  Cluster/site  approximation  Thermodynamics  CALPHAD Résumé : The modified cluster/site approximation was used to describe the thermodynamics of the various face-centered cubic phases in Ni–Al–Pt, the Bragg–Williams approximation for the B2 phase, and a modified regular solution formalism for the liquid phase. Coupled computational thermodynamics with key phase equilibrium measurements in the solid state, a thermodynamic description of this ternary for Ni contents higher than 50% was obtained based on these data and those given in the literature as well as the descriptions of its constituent binaries. Not only did the model-calculated solid-state phase equilibria agree with the measured data, the model-calculated liquidus projection is also able to account for the phases formed during solidification. In addition, the calculated chemical potentials or activities of Ni and Al are also in accord with the measured data as a function of temperature using mass spectrometry. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005916

Effects of size on the mechanical response of metallic glasses investigated through in situ TEM bending and compression experiments / C.Q. Chen in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 189–200 Titre : Effects of size on the mechanical response of metallic glasses investigated through in situ TEM bending and compression experiments Type de document : texte imprimé Auteurs : C.Q. Chen, Auteur ; Y.T. Pei, Auteur ; J.T.M. De Hosson, Auteur Année de publication : 2010 Article en page(s) : pp. 189–200 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Transmission  electron  microscopy  (TEM)  Amorphous  metals  Mechanical  properties Résumé : Quantitative bending and compression tests on micropillars made of two different amorphous alloys, with tip diameters ranging from 93 to 645 nm, are performed in situ in a transmission electron microscope (TEM). Under microcompression each pillar shows an intermittent plastic flow accommodated by inhomogeneous shear banding. However, the individual shear banding events are strongly size-dependent, i.e. in larger pillars the deformation is controlled by nucleation of shear bands, but in smaller pillars it becomes propagation-controlled. On the other hand, the yield stress is essentially size-independent. Microbending tests show further advantages by amplifying size effects and minimizing artifacts. An interesting finding is that by microbending, a switch from highly inhomogeneous to fully homogeneous deformation is observed at an experimentally accessible size regime near 200 nm, whereas it is not accessible under microcompression, even at a sub-100 nm scale. These size effects are well interpreted by a micromechanical model, leading to a deformation map in the stress-size space. A physical picture of nanoscale shear localization process is also provided. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005928 [article] Effects of size on the mechanical response of metallic glasses investigated through in situ TEM bending and compression experiments [texte imprimé] / C.Q. Chen, Auteur ; Y.T. Pei, Auteur ; J.T.M. De Hosson, Auteur . - 2010 . - pp. 189–200. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 189–200 Mots-clés : Transmission  electron  microscopy  (TEM)  Amorphous  metals  Mechanical  properties Résumé : Quantitative bending and compression tests on micropillars made of two different amorphous alloys, with tip diameters ranging from 93 to 645 nm, are performed in situ in a transmission electron microscope (TEM). Under microcompression each pillar shows an intermittent plastic flow accommodated by inhomogeneous shear banding. However, the individual shear banding events are strongly size-dependent, i.e. in larger pillars the deformation is controlled by nucleation of shear bands, but in smaller pillars it becomes propagation-controlled. On the other hand, the yield stress is essentially size-independent. Microbending tests show further advantages by amplifying size effects and minimizing artifacts. An interesting finding is that by microbending, a switch from highly inhomogeneous to fully homogeneous deformation is observed at an experimentally accessible size regime near 200 nm, whereas it is not accessible under microcompression, even at a sub-100 nm scale. These size effects are well interpreted by a micromechanical model, leading to a deformation map in the stress-size space. A physical picture of nanoscale shear localization process is also provided. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005928

The fracture toughness of a cordierite square lattice / I. Quintana-Alonso in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 201–207 Titre : The fracture toughness of a cordierite square lattice Type de document : texte imprimé Auteurs : I. Quintana-Alonso, Auteur ; S.P. Mai, Auteur ; N.A. Fleck, Auteur Année de publication : 2010 Article en page(s) : pp. 201–207 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Finite  element  analysis  Fracture  toughness  Lattice  materials  Ceramics  Toughness  test Résumé : A single-edge-notch bend test was developed for the measurement of fracture toughness of a ±45° square lattice made from an elastic-brittle solid. The finite element method was used to obtain the K-calibration for an orthotropic elastic solid, with elastic constants equal to that of the ±45° square lattice. Finite element simulations were also used to predict the fracture strength of the cracked lattice, with failure dictated by the tensile strength of the cell-wall material. The conditions for K-dominance and for failure by a net-section strength criterion of the specimen were thereby determined. A set of fracture tests on single-edge-notch bend specimens made from the ceramic cordierite validate the predictions. The measured fracture toughness of the cordierite lattices scales linearly with the stockiness of the lattice. DEWEY : 1359-6454 ISSN : 669 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900593X [article] The fracture toughness of a cordierite square lattice [texte imprimé] / I. Quintana-Alonso, Auteur ; S.P. Mai, Auteur ; N.A. Fleck, Auteur . - 2010 . - pp. 201–207. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 201–207 Mots-clés : Finite  element  analysis  Fracture  toughness  Lattice  materials  Ceramics  Toughness  test Résumé : A single-edge-notch bend test was developed for the measurement of fracture toughness of a ±45° square lattice made from an elastic-brittle solid. The finite element method was used to obtain the K-calibration for an orthotropic elastic solid, with elastic constants equal to that of the ±45° square lattice. Finite element simulations were also used to predict the fracture strength of the cracked lattice, with failure dictated by the tensile strength of the cell-wall material. The conditions for K-dominance and for failure by a net-section strength criterion of the specimen were thereby determined. A set of fracture tests on single-edge-notch bend specimens made from the ceramic cordierite validate the predictions. The measured fracture toughness of the cordierite lattices scales linearly with the stockiness of the lattice. DEWEY : 1359-6454 ISSN : 669 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900593X

Structures of dissociated 〈1 View the MathML source 0 0〉 dislocations and {1 View the MathML source 0 0} stacking faults of alumina (α-Al2O3) / E. Tochigi in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 208–215 Titre : Structures of dissociated 〈1 View the MathML source 0 0〉 dislocations and {1 View the MathML source 0 0} stacking faults of alumina (α-Al2O3) Type de document : texte imprimé Auteurs : E. Tochigi, Auteur ; N. Shibata, Auteur ; A. Nakamura, Auteur Année de publication : 2010 Article en page(s) : pp. 208–215 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Alumina  (α-Al2O3)  Grain  boundary  Dislocation  Stacking  fault  Transmission  electron  microscopy  (TEM) Résumé : An alumina (α-Al2O3) bicrystal with a {1 View the MathML source 0 0}/〈1 1 View the MathML source 0〉 2° low-angle grain boundary was fabricated by diffusion bonding, and the grain boundary was observed by high-resolution transmission electron microscopy (HRTEM). It was found that 1/3〈1 View the MathML source 0 0〉 partial-dislocation triplets were periodically arrayed along the boundary. The atomic structure within the {1 View the MathML source 0 0} stacking faults in between the partial-dislocation triplets was determined by HRTEM combined with first-principles calculations. We discuss the stacking fault structures and their excess energies in detail. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005941 [article] Structures of dissociated 〈1 View the MathML source 0 0〉 dislocations and {1 View the MathML source 0 0} stacking faults of alumina (α-Al2O3) [texte imprimé] / E. Tochigi, Auteur ; N. Shibata, Auteur ; A. Nakamura, Auteur . - 2010 . - pp. 208–215. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 208–215 Mots-clés : Alumina  (α-Al2O3)  Grain  boundary  Dislocation  Stacking  fault  Transmission  electron  microscopy  (TEM) Résumé : An alumina (α-Al2O3) bicrystal with a {1 View the MathML source 0 0}/〈1 1 View the MathML source 0〉 2° low-angle grain boundary was fabricated by diffusion bonding, and the grain boundary was observed by high-resolution transmission electron microscopy (HRTEM). It was found that 1/3〈1 View the MathML source 0 0〉 partial-dislocation triplets were periodically arrayed along the boundary. The atomic structure within the {1 View the MathML source 0 0} stacking faults in between the partial-dislocation triplets was determined by HRTEM combined with first-principles calculations. We discuss the stacking fault structures and their excess energies in detail. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005941

Strontium niobate high-k dielectrics / A. Hardy in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 216–225 Titre : Strontium niobate high-k dielectrics : Film deposition and material properties Type de document : texte imprimé Auteurs : A. Hardy, Auteur ; S. Van Elshocht, Auteur ; C. Adelmann, Auteur Année de publication : 2010 Article en page(s) : pp. 216–225 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Deposition  Sol–gel  Oxides  Thin  films  Dielectric  constant Résumé : Strontium niobate ultrathin films were processed by water-based chemical solution deposition, an approach that offers environmental benefits. SrNb2O6 and Sr2Nb2O7 show high-k values, which is important for applications such as alternative gate dielectrics. The study of ultrathin films (thickness <30 nm) is crucial, as this is the thickness range for the application envisaged, and as film properties depend strongly on the film thickness. SrNb2O6 had a lower crystallization temperature, less interfacial silicate, lower carbonate content, and higher roughness compared to Sr2Nb2O7. The k values of amorphous films were limited for both compositions (k = 12–14). Crystallization and complete removal of organics or carbonates were accomplished by high-temperature annealing, but increased the roughness and leakage current. For Sr2Nb2O7, interfacial silicates were formed as well. Intermediate calcination steps improved the surface smoothness and increased the k value of SrNb2O6 up to 30. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005953 [article] Strontium niobate high-k dielectrics : Film deposition and material properties [texte imprimé] / A. Hardy, Auteur ; S. Van Elshocht, Auteur ; C. Adelmann, Auteur . - 2010 . - pp. 216–225. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 216–225 Mots-clés : Deposition  Sol–gel  Oxides  Thin  films  Dielectric  constant Résumé : Strontium niobate ultrathin films were processed by water-based chemical solution deposition, an approach that offers environmental benefits. SrNb2O6 and Sr2Nb2O7 show high-k values, which is important for applications such as alternative gate dielectrics. The study of ultrathin films (thickness <30 nm) is crucial, as this is the thickness range for the application envisaged, and as film properties depend strongly on the film thickness. SrNb2O6 had a lower crystallization temperature, less interfacial silicate, lower carbonate content, and higher roughness compared to Sr2Nb2O7. The k values of amorphous films were limited for both compositions (k = 12–14). Crystallization and complete removal of organics or carbonates were accomplished by high-temperature annealing, but increased the roughness and leakage current. For Sr2Nb2O7, interfacial silicates were formed as well. Intermediate calcination steps improved the surface smoothness and increased the k value of SrNb2O6 up to 30. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005953

Dislocation cross-slip in heteroepitaxial multilayer films / S.S. Quek in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 226–234 Titre : Dislocation cross-slip in heteroepitaxial multilayer films Type de document : texte imprimé Auteurs : S.S. Quek, Auteur ; Y.W. Zhang, Auteur Année de publication : 2010 Article en page(s) : pp. 226–234 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  dynamics  Thin  film  Heteroepitaxy  Multilayers  Cross-slip Résumé : We simulated dislocation dynamics in heteroepitaxial multilayer thin film systems, considering the case where threading dislocations emerging from the substrate replicate themselves into the thin film during the film growth process. In the regime where the thin film layer thickness is tens of nanometers, the strain hardening mechanism involves the glide of single threading dislocation segments in the thin film instead of by dislocation pile-ups. We studied the dislocations’ evolution behavior and their interactions since these then became significant to the strain hardening of the multilayer structure. Cross-slip of threading dislocation segments in multilayer structure was found to be more prevalent compared to a single-layered thin film. This can result in a more complex pattern of interfacial dislocations and may have a significant contribution to the interactions between threading and interfacial dislocations. The simulation was carried out using the level set method incorporating thin film growth. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005965 [article] Dislocation cross-slip in heteroepitaxial multilayer films [texte imprimé] / S.S. Quek, Auteur ; Y.W. Zhang, Auteur . - 2010 . - pp. 226–234. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 226–234 Mots-clés : Dislocation  dynamics  Thin  film  Heteroepitaxy  Multilayers  Cross-slip Résumé : We simulated dislocation dynamics in heteroepitaxial multilayer thin film systems, considering the case where threading dislocations emerging from the substrate replicate themselves into the thin film during the film growth process. In the regime where the thin film layer thickness is tens of nanometers, the strain hardening mechanism involves the glide of single threading dislocation segments in the thin film instead of by dislocation pile-ups. We studied the dislocations’ evolution behavior and their interactions since these then became significant to the strain hardening of the multilayer structure. Cross-slip of threading dislocation segments in multilayer structure was found to be more prevalent compared to a single-layered thin film. This can result in a more complex pattern of interfacial dislocations and may have a significant contribution to the interactions between threading and interfacial dislocations. The simulation was carried out using the level set method incorporating thin film growth. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005965

Application of ultrasonic methods to determine elastic anisotropy of polycrystalline copper processed by equal-channel angular pressing / Hanuš Seiner in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 235–247 Titre : Application of ultrasonic methods to determine elastic anisotropy of polycrystalline copper processed by equal-channel angular pressing Type de document : texte imprimé Auteurs : Hanuš Seiner, Auteur ; Lucie Bodnárová, Auteur ; Petr Sedlák, Auteur Année de publication : 2010 Article en page(s) : pp. 235–247 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Equal-channel  angular  pressing  Acoustic  methods  Copper Résumé : Anisotropy of elastic properties of ultrafine-grained polycrystalline copper after one, two and four passes of equal-channel angular pressing (ECAP) is investigated by means of ultrasonic methods. For each material, Young’s and shear moduli in the principal processing directions are evaluated and the symmetry and orientation of the anisotropy are identified. The relation between the determined symmetry and the processing mechanisms is discussed. It is shown that the material after one and two passes of ECAP exhibits a measurable anisotropy, while the material after the fourth pass behaves isotropically. Within the discussion, it is shown that the origin of the observed anisotropy may be attributed to the spatial arrangement of grain boundaries rather than to the crystallographic texture. In the light of this conclusion, the obtained results correspond well with optical and transmission electron microscopy observations of the microstructures of ECAPed materials documented in the literature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005977 [article] Application of ultrasonic methods to determine elastic anisotropy of polycrystalline copper processed by equal-channel angular pressing [texte imprimé] / Hanuš Seiner, Auteur ; Lucie Bodnárová, Auteur ; Petr Sedlák, Auteur . - 2010 . - pp. 235–247. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 235–247 Mots-clés : Equal-channel  angular  pressing  Acoustic  methods  Copper Résumé : Anisotropy of elastic properties of ultrafine-grained polycrystalline copper after one, two and four passes of equal-channel angular pressing (ECAP) is investigated by means of ultrasonic methods. For each material, Young’s and shear moduli in the principal processing directions are evaluated and the symmetry and orientation of the anisotropy are identified. The relation between the determined symmetry and the processing mechanisms is discussed. It is shown that the material after one and two passes of ECAP exhibits a measurable anisotropy, while the material after the fourth pass behaves isotropically. Within the discussion, it is shown that the origin of the observed anisotropy may be attributed to the spatial arrangement of grain boundaries rather than to the crystallographic texture. In the light of this conclusion, the obtained results correspond well with optical and transmission electron microscopy observations of the microstructures of ECAPed materials documented in the literature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005977

Influence of alloy composition and heat treatment on precipitate composition in Al–Zn–Mg–Cu alloys / T. Marlaud in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 248–260 Titre : Influence of alloy composition and heat treatment on precipitate composition in Al–Zn–Mg–Cu alloys Type de document : texte imprimé Auteurs : T. Marlaud, Auteur ; Deschamps, A., Auteur ; F. Bley, Auteur Année de publication : 2010 Article en page(s) : pp. 248–260 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminium  alloys  Small  angle  X-ray  scattering  Three-dimensional  atom  probe  Phase  transformation  kinetics Résumé : The composition of precipitates in three alloys of the Al–Zn–Mg–Cu system has been investigated for different heat treatments, including peak-aged and over-aged states as well as near-equilibrium conditions, by combining atom probe tomography and systematic anomalous small-angle X-ray scattering experiments. We show that the concentration of Cu in the precipitates changes during heat treatments and is alloy dependent. At low ageing temperature (120 °C) the Cu content in the precipitates is close to the alloy content. The precipitate Cu content is shown to increase with increasing temperature and Cu alloy content. We show that in near-equilibrium conditions the precipitate compositions are 33 at.% in Mg, about 15 at.% in Al, about 13 at.% in Cu and balance Zn. Our results strongly suggest that the gradual incorporation of Cu in the precipitates during the heat treatment is essentially related to the slower diffusivity of this element in aluminium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005989 [article] Influence of alloy composition and heat treatment on precipitate composition in Al–Zn–Mg–Cu alloys [texte imprimé] / T. Marlaud, Auteur ; Deschamps, A., Auteur ; F. Bley, Auteur . - 2010 . - pp. 248–260. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 248–260 Mots-clés : Aluminium  alloys  Small  angle  X-ray  scattering  Three-dimensional  atom  probe  Phase  transformation  kinetics Résumé : The composition of precipitates in three alloys of the Al–Zn–Mg–Cu system has been investigated for different heat treatments, including peak-aged and over-aged states as well as near-equilibrium conditions, by combining atom probe tomography and systematic anomalous small-angle X-ray scattering experiments. We show that the concentration of Cu in the precipitates changes during heat treatments and is alloy dependent. At low ageing temperature (120 °C) the Cu content in the precipitates is close to the alloy content. The precipitate Cu content is shown to increase with increasing temperature and Cu alloy content. We show that in near-equilibrium conditions the precipitate compositions are 33 at.% in Mg, about 15 at.% in Al, about 13 at.% in Cu and balance Zn. Our results strongly suggest that the gradual incorporation of Cu in the precipitates during the heat treatment is essentially related to the slower diffusivity of this element in aluminium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005989

Agglomeration and bending of equiaxed crystals during solidification of hypoeutectic Al and Mg alloys / S. Otarawanna in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 261–271 Titre : Agglomeration and bending of equiaxed crystals during solidification of hypoeutectic Al and Mg alloys Type de document : texte imprimé Auteurs : S. Otarawanna, Auteur ; C.M. Gourlay, Auteur ; H.I. Laukli, Auteur Année de publication : 2010 Article en page(s) : pp. 261–271 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Solidification  microstructure  Electron  backscattering  diffraction  (EBSD)  Aluminum  alloys  Grain  boundary  energy  Misorientation Résumé : Agglomeration and bending of equiaxed crystals were studied by microstructural characterization of specimens produced by near-static cooling, high-pressure die casting and Thixomolding®, where the solidifying crystals experience different levels of mechanical stresses. EBSD was used to acquire statistical grain misorientation data which is linked to crystal agglomeration and bending behavior during solidification. An aluminum alloy and two magnesium alloys were used to compare grain misorientations for different crystal structures. The length fraction of low-energy grain boundaries in HPDC and Thixomolded samples was substantially higher than in “statically cooled” samples. This is attributed to the high shear stresses and pressure applied on the solidifying alloy, which promote crystal collisions and agglomeration. In-grain misorientations were found to be significant only in branched dendritic crystals which were subjected to significant shear stresses. This is related to the increased bending moment acting on long, protruding dendrite arms compared to more compact crystal morphologies. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005990 [article] Agglomeration and bending of equiaxed crystals during solidification of hypoeutectic Al and Mg alloys [texte imprimé] / S. Otarawanna, Auteur ; C.M. Gourlay, Auteur ; H.I. Laukli, Auteur . - 2010 . - pp. 261–271. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 261–271 Mots-clés : Solidification  microstructure  Electron  backscattering  diffraction  (EBSD)  Aluminum  alloys  Grain  boundary  energy  Misorientation Résumé : Agglomeration and bending of equiaxed crystals were studied by microstructural characterization of specimens produced by near-static cooling, high-pressure die casting and Thixomolding®, where the solidifying crystals experience different levels of mechanical stresses. EBSD was used to acquire statistical grain misorientation data which is linked to crystal agglomeration and bending behavior during solidification. An aluminum alloy and two magnesium alloys were used to compare grain misorientations for different crystal structures. The length fraction of low-energy grain boundaries in HPDC and Thixomolded samples was substantially higher than in “statically cooled” samples. This is attributed to the high shear stresses and pressure applied on the solidifying alloy, which promote crystal collisions and agglomeration. In-grain misorientations were found to be significant only in branched dendritic crystals which were subjected to significant shear stresses. This is related to the increased bending moment acting on long, protruding dendrite arms compared to more compact crystal morphologies. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005990

Phase-field theory of grain growth in the presence of mobile second-phase particles / Srikanth Vedantam in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 272–281 Titre : Phase-field theory of grain growth in the presence of mobile second-phase particles Type de document : texte imprimé Auteurs : Srikanth Vedantam, Auteur ; Ashis Mallick, Auteur Année de publication : 2010 Article en page(s) : pp. 272–281 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Phase  field  modeling  Crystal  growth  Grain  size Résumé : We have developed a phase-field model for grain growth in the presence of mobile second-phase particles. In this model, each grain and particle is represented by a unique order parameter. The grain boundaries sweep the mobile particles during grain growth. The particle velocity is taken to be proportional to the driving force arising from the curvature of the phase boundary in the neighborhood of the particle. The proportionality factor is the constitutive parameter representing the mobility of the particle. We first study the model in a one-dimensional axisymmetric setting and compare the results with theoretical calculations. We then study the interaction of a bicrystal grain boundary with a dilute distribution of particles. Finally we show the effect of particles on polycrystalline grain growth. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006004 [article] Phase-field theory of grain growth in the presence of mobile second-phase particles [texte imprimé] / Srikanth Vedantam, Auteur ; Ashis Mallick, Auteur . - 2010 . - pp. 272–281. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 272–281 Mots-clés : Phase  field  modeling  Crystal  growth  Grain  size Résumé : We have developed a phase-field model for grain growth in the presence of mobile second-phase particles. In this model, each grain and particle is represented by a unique order parameter. The grain boundaries sweep the mobile particles during grain growth. The particle velocity is taken to be proportional to the driving force arising from the curvature of the phase boundary in the neighborhood of the particle. The proportionality factor is the constitutive parameter representing the mobility of the particle. We first study the model in a one-dimensional axisymmetric setting and compare the results with theoretical calculations. We then study the interaction of a bicrystal grain boundary with a dilute distribution of particles. Finally we show the effect of particles on polycrystalline grain growth. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006004

Design of a highly ordered and uniform porous structure with multisized pores in film and particle forms using a template-driven self-assembly technique / Asep Bayu Dani Nandiyanto in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 282–289 Titre : Design of a highly ordered and uniform porous structure with multisized pores in film and particle forms using a template-driven self-assembly technique Type de document : texte imprimé Auteurs : Asep Bayu Dani Nandiyanto, Auteur ; Nobuhiro Hagura, Auteur ; Ferry Iskandar, Auteur Année de publication : 2010 Article en page(s) : pp. 282–289 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Porous  structure  film  Porous  particle  Ultralow  refractive  index  Spray-drying  method  Dip-coating  method Résumé : A highly ordered arrangement of pores with multiple sizes in film and particle forms was successfully prepared using the dip-coating and spray-drying methods, respectively. The template-driven self-assembly technique was effective when a combination of 5 nm silica (as a model of an inorganic nanoparticle) and two different sizes of monodispersed polystyrene (PS) spheres (as models of the template) were self-assembled to produce a composite silica/PS template. Heat treatment was then used to remove the PS, which produced the porous particle. A material with spherical pores in an “art-design” organization was produced. The size of the pores (large pore: 100–1000 nm; small pore: 30–200 nm) could be controlled simply by adjusting the PS size. Sufficient numbers of large/small pores made it possible to produce a material of ultralow density with an ultralow refractive index, because the multiple pores allocated free space, all of which was confirmed by calculation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006016 [article] Design of a highly ordered and uniform porous structure with multisized pores in film and particle forms using a template-driven self-assembly technique [texte imprimé] / Asep Bayu Dani Nandiyanto, Auteur ; Nobuhiro Hagura, Auteur ; Ferry Iskandar, Auteur . - 2010 . - pp. 282–289. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 282–289 Mots-clés : Porous  structure  film  Porous  particle  Ultralow  refractive  index  Spray-drying  method  Dip-coating  method Résumé : A highly ordered arrangement of pores with multiple sizes in film and particle forms was successfully prepared using the dip-coating and spray-drying methods, respectively. The template-driven self-assembly technique was effective when a combination of 5 nm silica (as a model of an inorganic nanoparticle) and two different sizes of monodispersed polystyrene (PS) spheres (as models of the template) were self-assembled to produce a composite silica/PS template. Heat treatment was then used to remove the PS, which produced the porous particle. A material with spherical pores in an “art-design” organization was produced. The size of the pores (large pore: 100–1000 nm; small pore: 30–200 nm) could be controlled simply by adjusting the PS size. Sufficient numbers of large/small pores made it possible to produce a material of ultralow density with an ultralow refractive index, because the multiple pores allocated free space, all of which was confirmed by calculation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006016

Abnormal grain growth in undoped strontium and barium titanate / M. Bäurer in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 290–300 Titre : Abnormal grain growth in undoped strontium and barium titanate Type de document : texte imprimé Auteurs : M. Bäurer, Auteur ; S.-J. Shih, Auteur ; C. Bishop, Auteur Année de publication : 2010 Article en page(s) : pp. 290–300 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Abnormal  grain  growth  Grain  boundaries  Grain  boundary  migration  Perovskites  Analytical  electron  microscopy Résumé : Abnormal grain growth is a commonly observed phenomenon in perovskite materials. In order to study this phenomenon, grain growth experiments were conducted over a temperature range from 1425 to 1600 °C for the model system SrTiO3 to analyse the nucleation of abnormal grains and to identify the growth mechanism involved for normal and abnormal grains. Grain boundaries of normal and abnormal grains were investigated in quenched samples by high-resolution transmission electron microscopy and by energy-dispersive spectroscopy in a scanning transmission electron microscope. No amorphous film was observed at the grain boundaries for either normal or abnormal grains. Non-stoichiometry at the grain boundaries was identified as a possible reason for the differences in growth speed. The results are compared to the nucleation and growth of abnormal grains in BaTiO3. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006028 [article] Abnormal grain growth in undoped strontium and barium titanate [texte imprimé] / M. Bäurer, Auteur ; S.-J. Shih, Auteur ; C. Bishop, Auteur . - 2010 . - pp. 290–300. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 290–300 Mots-clés : Abnormal  grain  growth  Grain  boundaries  Grain  boundary  migration  Perovskites  Analytical  electron  microscopy Résumé : Abnormal grain growth is a commonly observed phenomenon in perovskite materials. In order to study this phenomenon, grain growth experiments were conducted over a temperature range from 1425 to 1600 °C for the model system SrTiO3 to analyse the nucleation of abnormal grains and to identify the growth mechanism involved for normal and abnormal grains. Grain boundaries of normal and abnormal grains were investigated in quenched samples by high-resolution transmission electron microscopy and by energy-dispersive spectroscopy in a scanning transmission electron microscope. No amorphous film was observed at the grain boundaries for either normal or abnormal grains. Non-stoichiometry at the grain boundaries was identified as a possible reason for the differences in growth speed. The results are compared to the nucleation and growth of abnormal grains in BaTiO3. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006028

Modeling size effects on fracture toughness by dislocation dynamics / X.H. Zeng in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 301–310 Titre : Modeling size effects on fracture toughness by dislocation dynamics Type de document : texte imprimé Auteurs : X.H. Zeng, Auteur ; A. Hartmaier, Auteur Année de publication : 2010 Article en page(s) : pp. 301–310 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fracture  Plastic  deformation  Grain  boundary  embrittlement  Micromechanical  modelling  Refractory  metals Résumé : The effects of grain size and of crack-tip blunting radius on the fracture toughness of tungsten polycrystals are studied by using a combined dislocation dynamics/cohesive zone model (CZM). Two-dimensional dislocation dynamics are employed to analyze crack-tip plasticity and crack propagation is characterized by a CZM. The geometry of the crack and the corresponding boundary conditions are described by means of a boundary element method with dislocation dipoles as fundamental solution. Grain boundaries are introduced as obstacles for dislocation motion. Numerical experiments reveal that the fracture toughness decreases with grain size, because grain boundaries confine the plastic zone. This effect is particularly pronounced at small loading rates, where the unconfined plastic zone is large. Our results also show that fracture toughness scales with the tip radius as the stress concentration at the crack tip is reduced and the plastic zone is enlarged. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006041 [article] Modeling size effects on fracture toughness by dislocation dynamics [texte imprimé] / X.H. Zeng, Auteur ; A. Hartmaier, Auteur . - 2010 . - pp. 301–310. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 301–310 Mots-clés : Fracture  Plastic  deformation  Grain  boundary  embrittlement  Micromechanical  modelling  Refractory  metals Résumé : The effects of grain size and of crack-tip blunting radius on the fracture toughness of tungsten polycrystals are studied by using a combined dislocation dynamics/cohesive zone model (CZM). Two-dimensional dislocation dynamics are employed to analyze crack-tip plasticity and crack propagation is characterized by a CZM. The geometry of the crack and the corresponding boundary conditions are described by means of a boundary element method with dislocation dipoles as fundamental solution. Grain boundaries are introduced as obstacles for dislocation motion. Numerical experiments reveal that the fracture toughness decreases with grain size, because grain boundaries confine the plastic zone. This effect is particularly pronounced at small loading rates, where the unconfined plastic zone is large. Our results also show that fracture toughness scales with the tip radius as the stress concentration at the crack tip is reduced and the plastic zone is enlarged. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006041

Iron–chromium alloy nanoparticles produced by pulsed sonoelectrochemistry / Valentina Zin in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 311–319 Titre : Iron–chromium alloy nanoparticles produced by pulsed sonoelectrochemistry : Synthesis and characterization Type de document : texte imprimé Auteurs : Valentina Zin, Auteur ; Manuele Dabalà, Auteur Année de publication : 2010 Article en page(s) : pp. 311–319 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocrystalline  materials  Nanostructure  Electrochemistry  Iron  alloys  Ultrasound Résumé : This study describes synthesis of Fe–Cr alloy nanoparticles by using a method which couples electrodeposition of metals with the employment of high power ultrasound. The production of alloyed nanoparticles was performed using a 20 kHz titanium alloy horn ultrasound generator, a “sonoelectrode” generating short current pulses (tON) triggered and followed immediately by ultrasonic pulses (tUS). A rest time (tr) restores the initial conditions close to the sonoelectrode. The final product is a suspension of nanoparticles with high purity and high surface/volume ratio, which could be controlled by varying process parameters like time management and current density. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006053 [article] Iron–chromium alloy nanoparticles produced by pulsed sonoelectrochemistry : Synthesis and characterization [texte imprimé] / Valentina Zin, Auteur ; Manuele Dabalà, Auteur . - 2010 . - pp. 311–319. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 311–319 Mots-clés : Nanocrystalline  materials  Nanostructure  Electrochemistry  Iron  alloys  Ultrasound Résumé : This study describes synthesis of Fe–Cr alloy nanoparticles by using a method which couples electrodeposition of metals with the employment of high power ultrasound. The production of alloyed nanoparticles was performed using a 20 kHz titanium alloy horn ultrasound generator, a “sonoelectrode” generating short current pulses (tON) triggered and followed immediately by ultrasonic pulses (tUS). A rest time (tr) restores the initial conditions close to the sonoelectrode. The final product is a suspension of nanoparticles with high purity and high surface/volume ratio, which could be controlled by varying process parameters like time management and current density. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006053

Simulation of stress concentration in Mg alloys using the crystal plasticity finite element method / S.-H. Choi in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 320–329 Titre : Simulation of stress concentration in Mg alloys using the crystal plasticity finite element method Type de document : texte imprimé Auteurs : S.-H. Choi, Auteur ; D.H. Kim, Auteur ; S.-S. Park, Auteur Année de publication : 2010 Article en page(s) : pp. 320–329 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Crystal  plasticity  Finite  element  Stress  concentration  Texture  Twinning Résumé : A crystal plasticity finite element method (CPFEM), considering both crystallographic slip and deformation twinning, was developed to simulate the spatial stress concentration in AZ31 Mg alloys during in-plane compression. A predominant twin reorientation (PTR) model was successfully implemented to capture grain reorientation due to deformation twinning in twin-dominated deformation. By using the direct mapping technique for electron backscatter diffraction (EBSD) data, CPFEM can capture the heterogeneity of stress concentration at the grain boundaries in AZ31 Mg alloys during in-plane compression. The model demonstrated that deformation twinning enhances the local stress concentration at the grain boundaries between untwinned and twinned grains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006065 [article] Simulation of stress concentration in Mg alloys using the crystal plasticity finite element method [texte imprimé] / S.-H. Choi, Auteur ; D.H. Kim, Auteur ; S.-S. Park, Auteur . - 2010 . - pp. 320–329. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 320–329 Mots-clés : Crystal  plasticity  Finite  element  Stress  concentration  Texture  Twinning Résumé : A crystal plasticity finite element method (CPFEM), considering both crystallographic slip and deformation twinning, was developed to simulate the spatial stress concentration in AZ31 Mg alloys during in-plane compression. A predominant twin reorientation (PTR) model was successfully implemented to capture grain reorientation due to deformation twinning in twin-dominated deformation. By using the direct mapping technique for electron backscatter diffraction (EBSD) data, CPFEM can capture the heterogeneity of stress concentration at the grain boundaries in AZ31 Mg alloys during in-plane compression. The model demonstrated that deformation twinning enhances the local stress concentration at the grain boundaries between untwinned and twinned grains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006065

Atomistic simulations of void migration under thermal gradient in UO2 / Tapan G. Desai in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 330–339 Titre : Atomistic simulations of void migration under thermal gradient in UO2 Type de document : texte imprimé Auteurs : Tapan G. Desai, Auteur ; Paul Millett, Auteur ; Michael Tonks, Auteur Année de publication : 2010 Article en page(s) : pp. 330–339 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Molecular  dynamics  simulation  Thermal  gradient  Void  migration  Uranium  dioxide  Nuclear Résumé : It is well known that within a few hours after startup of a nuclear reactor, the temperature gradient within a fuel element causes migration of voids/bubbles radially inwards to form a central hole. To understand the atomic processes that control this migration of voids, we performed molecular dynamics (MD) simulations on single crystal UO2 with voids of diameter 2.2 nm. An external temperature gradient was applied across the simulation cell. At the end of the simulation run, it was observed that the voids had moved towards the hot end of the simulation cell. The void migration velocity obtained from the simulations was compared with the available phenomenological equations for void migration due to different transport mechanisms. Surface diffusion of the slowest moving specie, i.e. uranium, was found to be the dominant mechanism for void migration. The contribution from lattice diffusion and the thermal stress gradient to the void migration was analyzed and found to be negligible. By extrapolation, a crossover from the surface-diffusion-controlled mechanism to the lattice-diffusion-controlled mechanism was found to occur for voids with sizes in the μm range. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006077 [article] Atomistic simulations of void migration under thermal gradient in UO2 [texte imprimé] / Tapan G. Desai, Auteur ; Paul Millett, Auteur ; Michael Tonks, Auteur . - 2010 . - pp. 330–339. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 330–339 Mots-clés : Molecular  dynamics  simulation  Thermal  gradient  Void  migration  Uranium  dioxide  Nuclear Résumé : It is well known that within a few hours after startup of a nuclear reactor, the temperature gradient within a fuel element causes migration of voids/bubbles radially inwards to form a central hole. To understand the atomic processes that control this migration of voids, we performed molecular dynamics (MD) simulations on single crystal UO2 with voids of diameter 2.2 nm. An external temperature gradient was applied across the simulation cell. At the end of the simulation run, it was observed that the voids had moved towards the hot end of the simulation cell. The void migration velocity obtained from the simulations was compared with the available phenomenological equations for void migration due to different transport mechanisms. Surface diffusion of the slowest moving specie, i.e. uranium, was found to be the dominant mechanism for void migration. The contribution from lattice diffusion and the thermal stress gradient to the void migration was analyzed and found to be negligible. By extrapolation, a crossover from the surface-diffusion-controlled mechanism to the lattice-diffusion-controlled mechanism was found to occur for voids with sizes in the μm range. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006077

A three-dimensional sharp interface model for the quantitative simulation of solutal dendritic growth / Shiyan Pan in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 340–352 Titre : A three-dimensional sharp interface model for the quantitative simulation of solutal dendritic growth Type de document : texte imprimé Auteurs : Shiyan Pan, Auteur ; Mingfang Zhu, Auteur Année de publication : 2010 Article en page(s) : pp. 340–352 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Microstructure  modeling  Solutal  dendritic  growth  Weighted  mean  curvature  Three  dimensions Résumé : A three-dimensional (3-D) sharp interface model is developed to simulate the solutal dendritic growth in the low Péclet number regime. The model adopts a previously proposed solutal equilibrium approach to calculate the evolution of the solid/liquid interface. To describe specific crystallographic orientations of 3-D dendritic growth, a weighted mean curvature algorithm incorporated with the anisotropy of surface energy is proposed, allowing the simulation of 3-D dendrites with various orientations in a straightforward manner. The model validation is performed by comparing the simulations with the analytical predictions and experimental data for both single and multi-dendritic growth, which demonstrates the quantitative capabilities of the proposed model. The model efficiently reproduces realistic 3-D multi-equiaxed and columnar dendrites with various orientations and well-developed side branches. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006089 [article] A three-dimensional sharp interface model for the quantitative simulation of solutal dendritic growth [texte imprimé] / Shiyan Pan, Auteur ; Mingfang Zhu, Auteur . - 2010 . - pp. 340–352. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 340–352 Mots-clés : Microstructure  modeling  Solutal  dendritic  growth  Weighted  mean  curvature  Three  dimensions Résumé : A three-dimensional (3-D) sharp interface model is developed to simulate the solutal dendritic growth in the low Péclet number regime. The model adopts a previously proposed solutal equilibrium approach to calculate the evolution of the solid/liquid interface. To describe specific crystallographic orientations of 3-D dendritic growth, a weighted mean curvature algorithm incorporated with the anisotropy of surface energy is proposed, allowing the simulation of 3-D dendrites with various orientations in a straightforward manner. The model validation is performed by comparing the simulations with the analytical predictions and experimental data for both single and multi-dendritic growth, which demonstrates the quantitative capabilities of the proposed model. The model efficiently reproduces realistic 3-D multi-equiaxed and columnar dendrites with various orientations and well-developed side branches. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409006089

Exemplaires

Bibliothèque Ecole Nationale Polytechnique d'Alger

Accueil

Se connecter

Météo

Adresse