Dépouillements

Plastic deformation of wadsleyite / Arnaud Metsue in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1467–1478 Titre : Plastic deformation of wadsleyite : IV Dislocation core modelling based on the Peierls–Nabarro–Galerkin model Type de document : texte imprimé Auteurs : Arnaud Metsue, Auteur ; Philippe Carrez, Auteur ; Christophe Denoual, Auteur Année de publication : 2011 Article en page(s) : pp. 1467–1478 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Wadsleyite  Dislocations  Modelling  Peierls–Nabarro  Element-free  Galerkin Résumé : In this paper, we determine dislocation core structures and Peierls stresses of wadsleyite, a high-pressure mineral present in the Earth mantle. We use a Peierls–Nabarro model combined with a finite-element method in which we introduce two-dimensional generalized stacking fault energies. Several potential slip planes of wadsleyite are considered. The results show that dislocations in this mineral can exhibit complex dislocation cores with linear or non-collinear dissociation and even three-dimensional dislocation cores. The calculation of the Peierls stresses gives information on the potential activity of slip systems governing the plasticity of wadsleyite. Our study confirms experimental observations that ½〈1 1 1〉{1 0 1} is the easiest slip system in this structure at high-pressure and that [1 0 0](0 1 0) is the second easiest. Both these easily slip systems have dislocations that dissociate into collinear partial dislocations. In contrast [0 1 0] dislocations with very large Burgers vector (11.2 Å) are stabilized by complex dissociations involving four partial dislocations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007502 [article] Plastic deformation of wadsleyite : IV Dislocation core modelling based on the Peierls–Nabarro–Galerkin model [texte imprimé] / Arnaud Metsue, Auteur ; Philippe Carrez, Auteur ; Christophe Denoual, Auteur . - 2011 . - pp. 1467–1478. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1467–1478 Mots-clés : Wadsleyite  Dislocations  Modelling  Peierls–Nabarro  Element-free  Galerkin Résumé : In this paper, we determine dislocation core structures and Peierls stresses of wadsleyite, a high-pressure mineral present in the Earth mantle. We use a Peierls–Nabarro model combined with a finite-element method in which we introduce two-dimensional generalized stacking fault energies. Several potential slip planes of wadsleyite are considered. The results show that dislocations in this mineral can exhibit complex dislocation cores with linear or non-collinear dissociation and even three-dimensional dislocation cores. The calculation of the Peierls stresses gives information on the potential activity of slip systems governing the plasticity of wadsleyite. Our study confirms experimental observations that ½〈1 1 1〉{1 0 1} is the easiest slip system in this structure at high-pressure and that [1 0 0](0 1 0) is the second easiest. Both these easily slip systems have dislocations that dissociate into collinear partial dislocations. In contrast [0 1 0] dislocations with very large Burgers vector (11.2 Å) are stabilized by complex dissociations involving four partial dislocations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007502

Strain hardening and heterogeneous deformation during twinning in Hadfield steel / C. Efstathiou in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1479–1488 Titre : Strain hardening and heterogeneous deformation during twinning in Hadfield steel Type de document : texte imprimé Auteurs : C. Efstathiou, Auteur ; H. Sehitoglu, Auteur Année de publication : 2011 Article en page(s) : pp. 1479–1488 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Manganese  steel  Secondary  twinning  Digital  image  correlation  (DIC)  Low  stacking  fault  energy  Fcc  alloy Résumé : We identify the role of deformation twinning and twin–twin intersections on the strain hardening behavior of Hadfield steel single crystals using strain field measurements. In situ and ex situ strain field measurements resolved at micrometer length scales are obtained using digital image correlation. Ex situ measurements reveal that macroscopic twin-bands, which are composed of a mixture of fine twin-lamella and matrix material, generate approximately 30% axial strain. This measurement is comparable to strain predictions based on twinning crystallography. In situ measurements reveal that primary and secondary twins may nucleate simultaneously, but the primary twin-system remains predominantly active with increased deformation. The intersection of primary and secondary twin-systems was directly linked to an increase in the strain hardening response. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007575 [article] Strain hardening and heterogeneous deformation during twinning in Hadfield steel [texte imprimé] / C. Efstathiou, Auteur ; H. Sehitoglu, Auteur . - 2011 . - pp. 1479–1488. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1479–1488 Mots-clés : Manganese  steel  Secondary  twinning  Digital  image  correlation  (DIC)  Low  stacking  fault  energy  Fcc  alloy Résumé : We identify the role of deformation twinning and twin–twin intersections on the strain hardening behavior of Hadfield steel single crystals using strain field measurements. In situ and ex situ strain field measurements resolved at micrometer length scales are obtained using digital image correlation. Ex situ measurements reveal that macroscopic twin-bands, which are composed of a mixture of fine twin-lamella and matrix material, generate approximately 30% axial strain. This measurement is comparable to strain predictions based on twinning crystallography. In situ measurements reveal that primary and secondary twins may nucleate simultaneously, but the primary twin-system remains predominantly active with increased deformation. The intersection of primary and secondary twin-systems was directly linked to an increase in the strain hardening response. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007575

Transmission electron microscopy analysis of a coated conductor produced by chemical deposition methods / V. Cloet in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1489–1494 Titre : Transmission electron microscopy analysis of a coated conductor produced by chemical deposition methods Type de document : texte imprimé Auteurs : V. Cloet, Auteur ; T. Thersleff, Auteur ; O. Stadel, Auteur Année de publication : 2011 Article en page(s) : pp. 1489–1494 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Sol–gel  Thin  films  STEM  Interface  structures  Ceramic  superconductors Résumé : A water-based precursor solution was used to deposit a thin La2Zr2O7 layer (70 nm) on a NiW substrate. The characterization of the La2Zr2O7 (LZO) consisted of X-ray diffraction, pole figures, reflection high-energy electron diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy (TEM) of the cross-section. The results reveal that high-quality LZO layers can be produced using completely water-based solutions, rendering a high degree of texture (full width at half maximum = 6.5°). In order to test the quality of this coating as a buffer layer, a 350 nm thick layer of YBCO was deposited by metal organic chemical vapor deposition. The superconducting properties were measured inductively (Cryoscan, THEVA). A thorough TEM study of all the interfaces present was carried out. Several secondary phases were found at these interfaces. Since the buffer layer was thin, oxidation of the substrate could not be prevented. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007587 [article] Transmission electron microscopy analysis of a coated conductor produced by chemical deposition methods [texte imprimé] / V. Cloet, Auteur ; T. Thersleff, Auteur ; O. Stadel, Auteur . - 2011 . - pp. 1489–1494. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1489–1494 Mots-clés : Sol–gel  Thin  films  STEM  Interface  structures  Ceramic  superconductors Résumé : A water-based precursor solution was used to deposit a thin La2Zr2O7 layer (70 nm) on a NiW substrate. The characterization of the La2Zr2O7 (LZO) consisted of X-ray diffraction, pole figures, reflection high-energy electron diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy (TEM) of the cross-section. The results reveal that high-quality LZO layers can be produced using completely water-based solutions, rendering a high degree of texture (full width at half maximum = 6.5°). In order to test the quality of this coating as a buffer layer, a 350 nm thick layer of YBCO was deposited by metal organic chemical vapor deposition. The superconducting properties were measured inductively (Cryoscan, THEVA). A thorough TEM study of all the interfaces present was carried out. Several secondary phases were found at these interfaces. Since the buffer layer was thin, oxidation of the substrate could not be prevented. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007587

Development of novel grain morphology during hot extrusion of magnesium AZ21 alloy / M. A. Azeem in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1495–1502 Titre : Development of novel grain morphology during hot extrusion of magnesium AZ21 alloy Type de document : texte imprimé Auteurs : M. A. Azeem, Auteur ; A. Tewari, Auteur ; S. Mishra, Auteur Année de publication : 2011 Article en page(s) : pp. 1495–1502 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium  alloy  Extrusion  Dynamic  recrystallization  Annealing  Electron  backscattering  diffraction  (EBSD) Résumé : Microstructure and microtexture evolution during static annealing of a hot-extruded AZ21 magnesium alloy was studied. Apart from fine recrystallized equiaxed grains and large elongated deformed grains, a new third kind of abnormal grains that are stacked one after the other in a row parallel to the extrusion direction were observed. The crystallographic misorientation inside these grains was similar to that of the fine recrystallized grains. The large elongated grains exhibited significant in-grain misorientation. A self-consistent mechanistic model was developed to describe the formation of these grain morphologies during dynamic recrystallization (DRX). The texture of pre-extruded material, although lost in DRX, leaves a unique signature which manifests itself in the form of these grain morphologies. The origin of abnormal stacked grains was associated with slow nucleation in pre-extruded grains of a certain orientation. Further annealing resulted in large secondary recrystallized grains with occasional extension twins. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007599 [article] Development of novel grain morphology during hot extrusion of magnesium AZ21 alloy [texte imprimé] / M. A. Azeem, Auteur ; A. Tewari, Auteur ; S. Mishra, Auteur . - 2011 . - pp. 1495–1502. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1495–1502 Mots-clés : Magnesium  alloy  Extrusion  Dynamic  recrystallization  Annealing  Electron  backscattering  diffraction  (EBSD) Résumé : Microstructure and microtexture evolution during static annealing of a hot-extruded AZ21 magnesium alloy was studied. Apart from fine recrystallized equiaxed grains and large elongated deformed grains, a new third kind of abnormal grains that are stacked one after the other in a row parallel to the extrusion direction were observed. The crystallographic misorientation inside these grains was similar to that of the fine recrystallized grains. The large elongated grains exhibited significant in-grain misorientation. A self-consistent mechanistic model was developed to describe the formation of these grain morphologies during dynamic recrystallization (DRX). The texture of pre-extruded material, although lost in DRX, leaves a unique signature which manifests itself in the form of these grain morphologies. The origin of abnormal stacked grains was associated with slow nucleation in pre-extruded grains of a certain orientation. Further annealing resulted in large secondary recrystallized grains with occasional extension twins. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007599

Investigation of deformation twinning in a fine-grained and coarse-grained ZM20 Mg alloy / O. Muránsky in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1503–1517 Titre : Investigation of deformation twinning in a fine-grained and coarse-grained ZM20 Mg alloy : Combined in situ neutron diffraction and acoustic emission Type de document : texte imprimé Auteurs : O. Muránsky, Auteur ; M.R. Barnett, Auteur ; D. G. Carr, Auteur Année de publication : 2011 Article en page(s) : pp. 1503–1517 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium  Deformation  twinning  Twin  nucleation  Neutron  diffraction  Acoustic  emission Résumé : Neutron diffraction and acoustic emission were used in a single in situ experiment in order to study the deformation twinning of two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these two techniques facilitates the distinction between twin nucleation and twin growth. It is shown that yielding and immediate post-yielding plasticity in compression along the extrusion direction is governed primarily by twin nucleation, whereas plasticity at higher strains is presumably governed by twin growth and dislocation slip. It is further shown that, in the fine-grained alloy, collaborative twin nucleation in many grains dominates yielding, whereas twin nucleation in the coarse-grained alloy is progressive and occurs over a larger strain range. In addition, it is shown that, despite twin nucleation stresses increasing with decreasing grain size, roughly the same overall volume fraction of twins is formed in both fine and coarse parent grains. This confirms the difficulty of the alternative deformation modes and suggests a negligible suppressive effect of grain size on twinning in the case of the strongly textured fine-grained alloy. The current results also show that twins in the coarse-grained alloy are born less relaxed with respect to surrounding polycrystalline aggregate than those in the fine-grained alloy. This is believed to lead to lower reversal stresses acting on twin grains in the coarse-grained alloy upon unloading and thus to less untwinning and thus to a smaller pseudoelastic-like hysteresis. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007605 [article] Investigation of deformation twinning in a fine-grained and coarse-grained ZM20 Mg alloy : Combined in situ neutron diffraction and acoustic emission [texte imprimé] / O. Muránsky, Auteur ; M.R. Barnett, Auteur ; D. G. Carr, Auteur . - 2011 . - pp. 1503–1517. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1503–1517 Mots-clés : Magnesium  Deformation  twinning  Twin  nucleation  Neutron  diffraction  Acoustic  emission Résumé : Neutron diffraction and acoustic emission were used in a single in situ experiment in order to study the deformation twinning of two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these two techniques facilitates the distinction between twin nucleation and twin growth. It is shown that yielding and immediate post-yielding plasticity in compression along the extrusion direction is governed primarily by twin nucleation, whereas plasticity at higher strains is presumably governed by twin growth and dislocation slip. It is further shown that, in the fine-grained alloy, collaborative twin nucleation in many grains dominates yielding, whereas twin nucleation in the coarse-grained alloy is progressive and occurs over a larger strain range. In addition, it is shown that, despite twin nucleation stresses increasing with decreasing grain size, roughly the same overall volume fraction of twins is formed in both fine and coarse parent grains. This confirms the difficulty of the alternative deformation modes and suggests a negligible suppressive effect of grain size on twinning in the case of the strongly textured fine-grained alloy. The current results also show that twins in the coarse-grained alloy are born less relaxed with respect to surrounding polycrystalline aggregate than those in the fine-grained alloy. This is believed to lead to lower reversal stresses acting on twin grains in the coarse-grained alloy upon unloading and thus to less untwinning and thus to a smaller pseudoelastic-like hysteresis. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007605

Investigation into the effects of Fe additions on the equilibrium phase compositions, phase fractions and phase stabilities in the Ni–Cr–Al system / Kaka Ma in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1518–1529 Titre : Investigation into the effects of Fe additions on the equilibrium phase compositions, phase fractions and phase stabilities in the Ni–Cr–Al system Type de document : texte imprimé Auteurs : Kaka Ma, Auteur ; Feng Tang, Auteur ; Julie M. Schoenung, Auteur Année de publication : 2011 Article en page(s) : pp. 1518–1529 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel  alloy  Iron  Phase  transformations  Thermodynamics  Microstructure Résumé : NiCrAl alloys are commonly used for the bond coat in thermal barrier coatings (TBCs). Previous work has investigated the effects of intentional chemical additions on phase stability, but there is also a need to consider the effects of unintentional additions. For instance, cryomilling of NiCrAlY powder, which has been demonstrated to increase TBC lifetime, results in unintentional Fe additions. In this study, the effects of Fe additions are evaluated both through experimentation and computational simulation. The combined results indicate that the presence of Fe stabilizes the high-temperature γ and β phases, corresponding to a decrease in the transformation temperature. These results are explained on the basis of Gibbs free energy for individual phases. Phase composition is also investigated, indicating that, even without Fe, the phases are more complex than typically assumed and that, at the low concentrations associated with cryomilling, the Fe goes into solution in the Ni-rich phases. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007629 [article] Investigation into the effects of Fe additions on the equilibrium phase compositions, phase fractions and phase stabilities in the Ni–Cr–Al system [texte imprimé] / Kaka Ma, Auteur ; Feng Tang, Auteur ; Julie M. Schoenung, Auteur . - 2011 . - pp. 1518–1529. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1518–1529 Mots-clés : Nickel  alloy  Iron  Phase  transformations  Thermodynamics  Microstructure Résumé : NiCrAl alloys are commonly used for the bond coat in thermal barrier coatings (TBCs). Previous work has investigated the effects of intentional chemical additions on phase stability, but there is also a need to consider the effects of unintentional additions. For instance, cryomilling of NiCrAlY powder, which has been demonstrated to increase TBC lifetime, results in unintentional Fe additions. In this study, the effects of Fe additions are evaluated both through experimentation and computational simulation. The combined results indicate that the presence of Fe stabilizes the high-temperature γ and β phases, corresponding to a decrease in the transformation temperature. These results are explained on the basis of Gibbs free energy for individual phases. Phase composition is also investigated, indicating that, even without Fe, the phases are more complex than typically assumed and that, at the low concentrations associated with cryomilling, the Fe goes into solution in the Ni-rich phases. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007629

Full elastic tensor of a crystal of the superhard compound ReB2 / J.B. Levine in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1530–1535 Titre : Full elastic tensor of a crystal of the superhard compound ReB2 Type de document : texte imprimé Auteurs : J.B. Levine, Auteur ; J. B. Betts, Auteur ; J.D. Garrett, Auteur Année de publication : 2011 Article en page(s) : pp. 1530–1535 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Borides  Elastic  moduli  Hardness  Resonant  ultrasound  spectroscopy  X-ray  diffraction Résumé : The search for superhard materials, driven by their widespread use in industrial applications, highlights one of the most difficult problems in the field of materials science: the accurate characterization of a material’s intrinsic physical properties. This paper reports on the full elastic tensor of two polycrystalline isotropic specimens and one specimen of ReB2 consisting of highly oriented grains. The high-monocrystal bulk modulus value extracted from the grain-oriented specimen, measured by resonant ultrasound spectroscopy, validates the ultra-incompressibility of ReB2. An observed hardness of 40 GPa and a Debye temperature of 731 K were calculated for the ReB2 crystal, confirming its superhard and super-stiff properties. All the measured moduli of the ReB2 grain-oriented crystal exceed the comparable ones for the polycrystal by amounts that cannot be explained by averaging over direction, which may reveal why recent measurements reported on ReB2 containing excess boron yield values that are not as hard or incompressible as the crystal. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007630 [article] Full elastic tensor of a crystal of the superhard compound ReB2 [texte imprimé] / J.B. Levine, Auteur ; J. B. Betts, Auteur ; J.D. Garrett, Auteur . - 2011 . - pp. 1530–1535. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1530–1535 Mots-clés : Borides  Elastic  moduli  Hardness  Resonant  ultrasound  spectroscopy  X-ray  diffraction Résumé : The search for superhard materials, driven by their widespread use in industrial applications, highlights one of the most difficult problems in the field of materials science: the accurate characterization of a material’s intrinsic physical properties. This paper reports on the full elastic tensor of two polycrystalline isotropic specimens and one specimen of ReB2 consisting of highly oriented grains. The high-monocrystal bulk modulus value extracted from the grain-oriented specimen, measured by resonant ultrasound spectroscopy, validates the ultra-incompressibility of ReB2. An observed hardness of 40 GPa and a Debye temperature of 731 K were calculated for the ReB2 crystal, confirming its superhard and super-stiff properties. All the measured moduli of the ReB2 grain-oriented crystal exceed the comparable ones for the polycrystal by amounts that cannot be explained by averaging over direction, which may reveal why recent measurements reported on ReB2 containing excess boron yield values that are not as hard or incompressible as the crystal. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007630

Prediction of structural, electronic and elastic properties of Y2Ti2O7 and Y2TiO5 / Yong Jiang in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1536–1543 Titre : Prediction of structural, electronic and elastic properties of Y2Ti2O7 and Y2TiO5 Type de document : texte imprimé Auteurs : Yong Jiang, Auteur ; John R. Smith, Auteur ; G. Robert Odette, Auteur Année de publication : 2011 Article en page(s) : pp. 1536–1543 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Density  functional  Simulation  Elastic  behavior  Y2Ti2O7  Y2TiO5 Résumé : Density functional theory calculations have been performed to study the structural, electronic and elastic properties, and formation energies, of pyrochlore Y2Ti2O7 and orthorhombic Y2TiO5. These oxides are among the hardening features in nano-dispersion-strengthened ferritic alloys that are promising for future advanced fission/fusion energy applications. Calculations employ pseudo-potentials generated within the projector-augmented wave (PAW) method and the generalized gradient approximation (GGA) as well as the local density approximation (LDA) to the exchange–correlation functional. The calculated equilibrium structural parameters agree well with experiment for both oxides. The PAW–GGA yields the better bulk modulus of Y2Ti2O7, and hence is used for all the elastic calculations. A complete set of elastic parameters for both oxides are reported. Analysis of electron localization functions, charge densities, and densities of states suggest that the oxide bonds are highly ionic, but with some covalent character. In both cases the Ti–O bonds exhibit higher covalency than the Y–O bonds. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007642 [article] Prediction of structural, electronic and elastic properties of Y2Ti2O7 and Y2TiO5 [texte imprimé] / Yong Jiang, Auteur ; John R. Smith, Auteur ; G. Robert Odette, Auteur . - 2011 . - pp. 1536–1543. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1536–1543 Mots-clés : Density  functional  Simulation  Elastic  behavior  Y2Ti2O7  Y2TiO5 Résumé : Density functional theory calculations have been performed to study the structural, electronic and elastic properties, and formation energies, of pyrochlore Y2Ti2O7 and orthorhombic Y2TiO5. These oxides are among the hardening features in nano-dispersion-strengthened ferritic alloys that are promising for future advanced fission/fusion energy applications. Calculations employ pseudo-potentials generated within the projector-augmented wave (PAW) method and the generalized gradient approximation (GGA) as well as the local density approximation (LDA) to the exchange–correlation functional. The calculated equilibrium structural parameters agree well with experiment for both oxides. The PAW–GGA yields the better bulk modulus of Y2Ti2O7, and hence is used for all the elastic calculations. A complete set of elastic parameters for both oxides are reported. Analysis of electron localization functions, charge densities, and densities of states suggest that the oxide bonds are highly ionic, but with some covalent character. In both cases the Ti–O bonds exhibit higher covalency than the Y–O bonds. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007642

The effect of lutetium dopant on oxygen permeability of alumina polycrystals under oxygen potential gradients at ultra-high temperatures / Tsuneaki Matsudaira in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1544–1553 Titre : The effect of lutetium dopant on oxygen permeability of alumina polycrystals under oxygen potential gradients at ultra-high temperatures Type de document : texte imprimé Auteurs : Tsuneaki Matsudaira, Auteur ; Masashi Wada, Auteur ; Tomohiro Saitoh, Auteur Année de publication : 2011 Article en page(s) : pp. 1544–1553 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Alumina  Oxygen  permeation  Oxygen  potential  gradient  Diffusion  Grain  boundary Résumé : The oxygen permeability of undoped and lutetia-doped polycrystalline alumina wafers that were exposed to oxygen potential gradients was evaluated at temperatures up to 1973 K. The main diffusion species during oxygen permeation through the alumina grain boundaries were found to depend on oxygen partial O2 pressures (PO2), which created oxygen potential gradients. Under oxygen potential gradients generated by PO2 values below 10−3 Pa, where oxygen permeation occurred by oxygen diffusion from regions of higher to lower PO2, segregated lutetium at the grain boundaries suppressed only the mobility of oxygen in the wafers, without affecting the oxygen permeation mechanism. By contrast, under oxygen potential gradients generated by PO2 values above 103 Pa, where oxygen permeation proceeded by aluminum diffusion from regions of lower to higher PO2, lutetium had little effect on aluminum diffusion and migrated together with aluminum, resulting in precipitation and growth of Al5Lu3O12 particles on the higher PO2 surface. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007654 [article] The effect of lutetium dopant on oxygen permeability of alumina polycrystals under oxygen potential gradients at ultra-high temperatures [texte imprimé] / Tsuneaki Matsudaira, Auteur ; Masashi Wada, Auteur ; Tomohiro Saitoh, Auteur . - 2011 . - pp. 1544–1553. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1544–1553 Mots-clés : Alumina  Oxygen  permeation  Oxygen  potential  gradient  Diffusion  Grain  boundary Résumé : The oxygen permeability of undoped and lutetia-doped polycrystalline alumina wafers that were exposed to oxygen potential gradients was evaluated at temperatures up to 1973 K. The main diffusion species during oxygen permeation through the alumina grain boundaries were found to depend on oxygen partial O2 pressures (PO2), which created oxygen potential gradients. Under oxygen potential gradients generated by PO2 values below 10−3 Pa, where oxygen permeation occurred by oxygen diffusion from regions of higher to lower PO2, segregated lutetium at the grain boundaries suppressed only the mobility of oxygen in the wafers, without affecting the oxygen permeation mechanism. By contrast, under oxygen potential gradients generated by PO2 values above 103 Pa, where oxygen permeation proceeded by aluminum diffusion from regions of lower to higher PO2, lutetium had little effect on aluminum diffusion and migrated together with aluminum, resulting in precipitation and growth of Al5Lu3O12 particles on the higher PO2 surface. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007654

The structure and mechanical and tribological properties of TiBCN nanocomposite coatings / Jianliang Lin in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1554–1564 Titre : The structure and mechanical and tribological properties of TiBCN nanocomposite coatings Type de document : texte imprimé Auteurs : Jianliang Lin, Auteur ; John J. Moore, Auteur ; Brajendra Mishra, Auteur Année de publication : 2011 Article en page(s) : pp. 1554–1564 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : TiBCN  coating  Nanocomposite  coating  Nanocrystalline  coating  Pulsed  magnetron  sputtering  Wear Résumé : TiBCN nanocomposite coatings were deposited in a closed field unbalanced magnetron sputtering system using pulsed magnetron sputtering of a TiBC compound target with various Ar/N2 mixtures. TiBCN coatings were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, Rockwell C indentation and ball-on-disk wear tests. The coatings with a nitrogen content of less than 8 at.% exhibited superhardness values in the range of 44–49 GPa, but also showed poor adhesion and low wear resistance. Improvements in the coating adhesion, H/E ratio and wear resistance were achieved together with a decrease in the coating hardness to 35–45 GPa as the N content in the coatings was increased from 8 to 15 at.%. The microstructure of the coatings changed from a nano-columnar to a nanocomposite structure in which 5–8 nm nanocrystalline Ti(B,C) and Ti(N,C) compounds were embedded in an amorphous matrix consisting of BN, free carbon and CN phases. With a further increase in the N content in the coatings to levels greater than 20 at.%, the inter-particle spacing of the nanocrystalline compounds increased significantly due to the formation of a large amount of the amorphous BN phase, which also led to low hardness and poor wear resistance of the TiBCN coatings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007666 [article] The structure and mechanical and tribological properties of TiBCN nanocomposite coatings [texte imprimé] / Jianliang Lin, Auteur ; John J. Moore, Auteur ; Brajendra Mishra, Auteur . - 2011 . - pp. 1554–1564. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1554–1564 Mots-clés : TiBCN  coating  Nanocomposite  coating  Nanocrystalline  coating  Pulsed  magnetron  sputtering  Wear Résumé : TiBCN nanocomposite coatings were deposited in a closed field unbalanced magnetron sputtering system using pulsed magnetron sputtering of a TiBC compound target with various Ar/N2 mixtures. TiBCN coatings were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, Rockwell C indentation and ball-on-disk wear tests. The coatings with a nitrogen content of less than 8 at.% exhibited superhardness values in the range of 44–49 GPa, but also showed poor adhesion and low wear resistance. Improvements in the coating adhesion, H/E ratio and wear resistance were achieved together with a decrease in the coating hardness to 35–45 GPa as the N content in the coatings was increased from 8 to 15 at.%. The microstructure of the coatings changed from a nano-columnar to a nanocomposite structure in which 5–8 nm nanocrystalline Ti(B,C) and Ti(N,C) compounds were embedded in an amorphous matrix consisting of BN, free carbon and CN phases. With a further increase in the N content in the coatings to levels greater than 20 at.%, the inter-particle spacing of the nanocrystalline compounds increased significantly due to the formation of a large amount of the amorphous BN phase, which also led to low hardness and poor wear resistance of the TiBCN coatings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007666

Discrete dislocation dynamics simulations of plasticity at small scales / Caizhi Zhou in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1565–1577 Titre : Discrete dislocation dynamics simulations of plasticity at small scales Type de document : texte imprimé Auteurs : Caizhi Zhou, Auteur ; S. Bulent Biner, Auteur ; Richard LeSar, Auteur Année de publication : 2011 Article en page(s) : pp. 1565–1577 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  dynamics  Size  effects  Plasticity Résumé : Discrete dislocation dynamics simulations in three dimensions have been used to examine the role of dislocation multiplication and mobility on the plasticity in small samples under uniaxial compression. To account for the effects of the free surfaces a boundary-element method, with a superposition technique, was employed. Cross-slip motion of the dislocation was also included, and found to be critical to the modeling of the dislocation behavior. To compare directly with recent experiments on micropillars, simulation samples at small volumes were created by cutting them from bulk three-dimensional simulations, leading to a range of initial dislocation structures. Application was made to single-crystal nickel samples. Comparison of the simulation results and the experiments are excellent, finding essentially identical behavior. Examination of details of the dislocation mechanism illuminates many features unique to small samples and points directly to the importance of both the surface forces and cross-slip in understanding small-scale plasticity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007678 [article] Discrete dislocation dynamics simulations of plasticity at small scales [texte imprimé] / Caizhi Zhou, Auteur ; S. Bulent Biner, Auteur ; Richard LeSar, Auteur . - 2011 . - pp. 1565–1577. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1565–1577 Mots-clés : Dislocation  dynamics  Size  effects  Plasticity Résumé : Discrete dislocation dynamics simulations in three dimensions have been used to examine the role of dislocation multiplication and mobility on the plasticity in small samples under uniaxial compression. To account for the effects of the free surfaces a boundary-element method, with a superposition technique, was employed. Cross-slip motion of the dislocation was also included, and found to be critical to the modeling of the dislocation behavior. To compare directly with recent experiments on micropillars, simulation samples at small volumes were created by cutting them from bulk three-dimensional simulations, leading to a range of initial dislocation structures. Application was made to single-crystal nickel samples. Comparison of the simulation results and the experiments are excellent, finding essentially identical behavior. Examination of details of the dislocation mechanism illuminates many features unique to small samples and points directly to the importance of both the surface forces and cross-slip in understanding small-scale plasticity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007678

Mapping of crack tip strains and twinned zone in a hexagonal close packed zirconium alloy / M. Kerr in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1578–1588 Titre : Mapping of crack tip strains and twinned zone in a hexagonal close packed zirconium alloy Type de document : texte imprimé Auteurs : M. Kerr, Auteur ; M.R. Daymond, Auteur ; R. A. Holt, Auteur Année de publication : 2011 Article en page(s) : pp. 1578–1588 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Synchrotron  diffraction  Fracture  Twinning  Zirconium  Micro-mechanical  modeling Résumé : This paper describes the use of synchrotron X-ray diffraction to map crack tip strain field evolution and initiation of twinning under applied load in a fatigue pre-cracked zirconium alloy. Compact tension specimens were machined in two orientations from a textured rolled plate and loaded along the normal direction and the transverse direction to rolling. Residual strains due to fatigue and the strains introduced at applied KI of approximately 10 and 30 MPa√m were measured for the two specimen orientations. Maps of the region of twinned material were determined. The experimental data is compared to finite element (FE) calculations for the crack tip strain fields and a prediction of the size of the twinned region using a multiscale model based on combining an FE approach with an elastoplastic self-consistent polycrystalline plasticity model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900768X [article] Mapping of crack tip strains and twinned zone in a hexagonal close packed zirconium alloy [texte imprimé] / M. Kerr, Auteur ; M.R. Daymond, Auteur ; R. A. Holt, Auteur . - 2011 . - pp. 1578–1588. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1578–1588 Mots-clés : Synchrotron  diffraction  Fracture  Twinning  Zirconium  Micro-mechanical  modeling Résumé : This paper describes the use of synchrotron X-ray diffraction to map crack tip strain field evolution and initiation of twinning under applied load in a fatigue pre-cracked zirconium alloy. Compact tension specimens were machined in two orientations from a textured rolled plate and loaded along the normal direction and the transverse direction to rolling. Residual strains due to fatigue and the strains introduced at applied KI of approximately 10 and 30 MPa√m were measured for the two specimen orientations. Maps of the region of twinned material were determined. The experimental data is compared to finite element (FE) calculations for the crack tip strain fields and a prediction of the size of the twinned region using a multiscale model based on combining an FE approach with an elastoplastic self-consistent polycrystalline plasticity model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900768X

On the nature of displacement bursts during nanoindentation of ultrathin Ni films on sapphire / E. Rabkin in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1589–1598 Titre : On the nature of displacement bursts during nanoindentation of ultrathin Ni films on sapphire Type de document : texte imprimé Auteurs : E. Rabkin, Auteur ; J.K. Deuschle, Auteur ; B. Baretzky, Auteur Année de publication : 2011 Article en page(s) : pp. 1589–1598 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoindentation  Grain  boundaries  Thin  films Résumé : Quasi-static nanoindentation tests were performed on polycrystalline Ni films sputter deposited on basal plane-oriented sapphire substrates. In the majority of tests a combined elasto-plastic response of the film was observed, without detectable displacement bursts during loading. In some of the tests a single large displacement burst was observed slightly below or at the maximal load (75 or 50 μN). The residual plastic depth of the corresponding indents was close to the film thickness. These large displacement bursts were interpreted as manifestations of intergranular brittle fracture in the indented region. The strength of the disclination-type defect at the triple junctions leading to brittle fracture at the grain boundaries was estimated based on the theory of strain gradient plasticity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007691 [article] On the nature of displacement bursts during nanoindentation of ultrathin Ni films on sapphire [texte imprimé] / E. Rabkin, Auteur ; J.K. Deuschle, Auteur ; B. Baretzky, Auteur . - 2011 . - pp. 1589–1598. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1589–1598 Mots-clés : Nanoindentation  Grain  boundaries  Thin  films Résumé : Quasi-static nanoindentation tests were performed on polycrystalline Ni films sputter deposited on basal plane-oriented sapphire substrates. In the majority of tests a combined elasto-plastic response of the film was observed, without detectable displacement bursts during loading. In some of the tests a single large displacement burst was observed slightly below or at the maximal load (75 or 50 μN). The residual plastic depth of the corresponding indents was close to the film thickness. These large displacement bursts were interpreted as manifestations of intergranular brittle fracture in the indented region. The strength of the disclination-type defect at the triple junctions leading to brittle fracture at the grain boundaries was estimated based on the theory of strain gradient plasticity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007691

A crystallographic model of fcc/bcc martensitic nucleation and growth / J-B. Yang in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1599–1606 Titre : A crystallographic model of fcc/bcc martensitic nucleation and growth Type de document : texte imprimé Auteurs : J-B. Yang, Auteur ; Z.-G. Yang, Auteur ; Y. Nagai, Auteur Année de publication : 2011 Article en page(s) : pp. 1599–1606 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Martensitic  phase  transformation  Heterogeneous  nucleation  of  phase  transformations  Analytical  methods Résumé : A crystallographic model of face-centered cubic/body-centered cubic martensitic nucleation and growth has been developed in which the glissile martensitic interface is described in terms of discrete transformation and misfit dislocations within the framework of the Frank–Bilby equation. In the present model heterogeneous nucleation of a martensitic embryo occurs spontaneously by dissociation of an existing perfect dislocation under certain conditions, such as the catalysis on grain boundaries. Autocatalytic dislocation is proposed to be responsible for embryo growth, then nucleation and subsequent growth of a single embryo can be regarded as an autocatalytic process. As a natural result the crystallographic features of grown martensite are consistent with the phenomenological theory of martensite crystallography. Martensitic nucleation in this model agrees with many experimental observations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007708 [article] A crystallographic model of fcc/bcc martensitic nucleation and growth [texte imprimé] / J-B. Yang, Auteur ; Z.-G. Yang, Auteur ; Y. Nagai, Auteur . - 2011 . - pp. 1599–1606. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1599–1606 Mots-clés : Martensitic  phase  transformation  Heterogeneous  nucleation  of  phase  transformations  Analytical  methods Résumé : A crystallographic model of face-centered cubic/body-centered cubic martensitic nucleation and growth has been developed in which the glissile martensitic interface is described in terms of discrete transformation and misfit dislocations within the framework of the Frank–Bilby equation. In the present model heterogeneous nucleation of a martensitic embryo occurs spontaneously by dissociation of an existing perfect dislocation under certain conditions, such as the catalysis on grain boundaries. Autocatalytic dislocation is proposed to be responsible for embryo growth, then nucleation and subsequent growth of a single embryo can be regarded as an autocatalytic process. As a natural result the crystallographic features of grown martensite are consistent with the phenomenological theory of martensite crystallography. Martensitic nucleation in this model agrees with many experimental observations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007708

Modelling and analysis of the oxidation influence on creep behaviour of thin-walled structures of the single-crystal nickel-base superalloy René N5 at 980 °C / Matthias Bensch in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1607–1617 Titre : Modelling and analysis of the oxidation influence on creep behaviour of thin-walled structures of the single-crystal nickel-base superalloy René N5 at 980 °C Type de document : texte imprimé Auteurs : Matthias Bensch, Auteur ; Johannes Preußner, Auteur ; Rainer Hüttner, Auteur Année de publication : 2011 Article en page(s) : pp. 1607–1617 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Creep  Oxidation  Modelling  Thin-walled  structures  Nickel  alloy Résumé : Creep test results of thin-walled specimens of the single-crystal nickel-base superalloy René N5 at 980 °C under vacuum as well as under air show different creep properties depending on material thickness and atmosphere. The differences in creep strength and strain were analysed based on a creep-oxidation model. The model specifies the primary and secondary creep stages of thin-walled specimens by a sequence of layers. The model takes different zones affected by oxidation into account. Four layers were experimentally observed and considered in the model: oxide layer, γ′-free layer, γ′-reduced layer and the two-phase substrate in the sample as centre. Material parameters for growth laws of each layer were identified both by experimental analyses and by thermodynamic simulations. The final creep-oxidation model characterizes the creep behaviour of samples with small thicknesses and low initial stress with high accuracy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900771X [article] Modelling and analysis of the oxidation influence on creep behaviour of thin-walled structures of the single-crystal nickel-base superalloy René N5 at 980 °C [texte imprimé] / Matthias Bensch, Auteur ; Johannes Preußner, Auteur ; Rainer Hüttner, Auteur . - 2011 . - pp. 1607–1617. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1607–1617 Mots-clés : Creep  Oxidation  Modelling  Thin-walled  structures  Nickel  alloy Résumé : Creep test results of thin-walled specimens of the single-crystal nickel-base superalloy René N5 at 980 °C under vacuum as well as under air show different creep properties depending on material thickness and atmosphere. The differences in creep strength and strain were analysed based on a creep-oxidation model. The model specifies the primary and secondary creep stages of thin-walled specimens by a sequence of layers. The model takes different zones affected by oxidation into account. Four layers were experimentally observed and considered in the model: oxide layer, γ′-free layer, γ′-reduced layer and the two-phase substrate in the sample as centre. Material parameters for growth laws of each layer were identified both by experimental analyses and by thermodynamic simulations. The final creep-oxidation model characterizes the creep behaviour of samples with small thicknesses and low initial stress with high accuracy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900771X

Experimental and microstructural characterization of simultaneous creep, plasticity and phase transformation in Ti50Pd40Ni10 high-temperature shape memory alloy / Parikshith K. Kumar in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1618–1628 Titre : Experimental and microstructural characterization of simultaneous creep, plasticity and phase transformation in Ti50Pd40Ni10 high-temperature shape memory alloy Type de document : texte imprimé Auteurs : Parikshith K. Kumar, Auteur ; Dimitris C. Lagoudas, Auteur Année de publication : 2011 Article en page(s) : pp. 1618–1628 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Creep  test  Shape  memory  alloys  (SMAs)  Martensitic  phase  transformation  Transmission  electron  microscopy  (TEM)  Viscoplasticity Résumé : The influence of viscoplastic phenomena on the transformation behavior of a Ti50Pd40Ni10 high-temperature shape memory alloy (HTSMA) is investigated by thermomechanical testing followed by transmission electron microscopy (TEM). An ingot of the alloy is fabricated by vacuum arc melting and processed by hot rolling. Cylindrical specimens for compression testing are cut from the rolled bar and standard creep tests and thermally induced phase transformation tests are conducted using a custom high-temperature setup. Thin sections are prepared from the specimens before and after the thermomechanical tests and their microstructure is studied using TEM. The thermomechanical test results show that irrecoverable strains generated due to creep and transformation-induced plasticity impact the actuation performance of the HTSMA. The results from the microstructural study indicate different microstructural changes due to the two irrecoverable strains (plastic and viscoplastic) generated during the course of transformation. Both these mechanisms in turn affect the actuation behavior in different ways. The results from the thermomechanical testing and the microstructural observations indicate that the irrecoverable strain generated due to creep does not seem to affect the transformation behavior or the rate-independent irrecoverable strain (generated in part due to retained martensite). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007812 [article] Experimental and microstructural characterization of simultaneous creep, plasticity and phase transformation in Ti50Pd40Ni10 high-temperature shape memory alloy [texte imprimé] / Parikshith K. Kumar, Auteur ; Dimitris C. Lagoudas, Auteur . - 2011 . - pp. 1618–1628. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1618–1628 Mots-clés : Creep  test  Shape  memory  alloys  (SMAs)  Martensitic  phase  transformation  Transmission  electron  microscopy  (TEM)  Viscoplasticity Résumé : The influence of viscoplastic phenomena on the transformation behavior of a Ti50Pd40Ni10 high-temperature shape memory alloy (HTSMA) is investigated by thermomechanical testing followed by transmission electron microscopy (TEM). An ingot of the alloy is fabricated by vacuum arc melting and processed by hot rolling. Cylindrical specimens for compression testing are cut from the rolled bar and standard creep tests and thermally induced phase transformation tests are conducted using a custom high-temperature setup. Thin sections are prepared from the specimens before and after the thermomechanical tests and their microstructure is studied using TEM. The thermomechanical test results show that irrecoverable strains generated due to creep and transformation-induced plasticity impact the actuation performance of the HTSMA. The results from the microstructural study indicate different microstructural changes due to the two irrecoverable strains (plastic and viscoplastic) generated during the course of transformation. Both these mechanisms in turn affect the actuation behavior in different ways. The results from the thermomechanical testing and the microstructural observations indicate that the irrecoverable strain generated due to creep does not seem to affect the transformation behavior or the rate-independent irrecoverable strain (generated in part due to retained martensite). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007812

Microtexture tracking in hot-deformed polycrystalline aluminium / R. Quey in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1629–1642 Titre : Microtexture tracking in hot-deformed polycrystalline aluminium : Experimental results Type de document : texte imprimé Auteurs : R. Quey, Auteur ; D. Piot, Auteur ; J.H. Driver, Auteur Année de publication : 2011 Article en page(s) : pp. 1629–1642 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Microstructure  Plastic  deformation  Deformation  structure  Electron  backscattering  diffraction  (EBSD)  Aluminium  alloys Résumé : A split sample of Al–0.1%Mn has been deformed by a series of compression tests in a channel-die at 400 °C to a final strain of 1.6. The orientations of 176 grains in a View the MathML source internal surface were followed by high-resolution electron backscatter diffraction at four different strains to compare with crystal plasticity models. Typically 3000 orientations per grain were used to quantify the average lattice rotations of each grain together with their orientation spreads (termed microtexture tracking). The average orientations tend towards the standard β-fibre plane-strain compression texture components, albeit with some variations. The in-grain orientation spreads develop strongly at first, then tend to saturate at high strains. Finally, the influence of grain environment on lattice rotation is examined by means of the rotation “variability at constant orientation”. On average and at the beginning of the deformation, two grains of the same initial orientation, but different neighbours, would rotate by angles that vary by 25% and axes separated by 37°; their orientations at ε=1.2 would vary by 12°. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007824 [article] Microtexture tracking in hot-deformed polycrystalline aluminium : Experimental results [texte imprimé] / R. Quey, Auteur ; D. Piot, Auteur ; J.H. Driver, Auteur . - 2011 . - pp. 1629–1642. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1629–1642 Mots-clés : Microstructure  Plastic  deformation  Deformation  structure  Electron  backscattering  diffraction  (EBSD)  Aluminium  alloys Résumé : A split sample of Al–0.1%Mn has been deformed by a series of compression tests in a channel-die at 400 °C to a final strain of 1.6. The orientations of 176 grains in a View the MathML source internal surface were followed by high-resolution electron backscatter diffraction at four different strains to compare with crystal plasticity models. Typically 3000 orientations per grain were used to quantify the average lattice rotations of each grain together with their orientation spreads (termed microtexture tracking). The average orientations tend towards the standard β-fibre plane-strain compression texture components, albeit with some variations. The in-grain orientation spreads develop strongly at first, then tend to saturate at high strains. Finally, the influence of grain environment on lattice rotation is examined by means of the rotation “variability at constant orientation”. On average and at the beginning of the deformation, two grains of the same initial orientation, but different neighbours, would rotate by angles that vary by 25% and axes separated by 37°; their orientations at ε=1.2 would vary by 12°. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007824

The formation of nanograin structures and accelerated room-temperature theta precipitation in a severely deformed Al–4 wt.% Cu alloy / Y. Huang in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1643–1657 Titre : The formation of nanograin structures and accelerated room-temperature theta precipitation in a severely deformed Al–4 wt.% Cu alloy Type de document : texte imprimé Auteurs : Y. Huang, Auteur ; J.D. Robson, Auteur ; P.B. Prangnell, Auteur Année de publication : 2011 Article en page(s) : pp. 1643–1657 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Severe  plastic  deformation  (SPD)  Nanocrystalline  Accelerated  ageing  Theta  phase  Nucleation Résumé : The grain size achievable and long-term stability of a severely deformed aluminium copper alloy have been investigated when copper is used in solution to inhibit recovery. It is shown that copper is more effective than magnesium in inhibiting dynamic recovery. A grain width of only ∼70 nm was obtained in an Al–4 wt.% Cu alloy, after processing by equal-channel angular extrusion to a strain of εeff = 10, resulting in a lamellar nanograin structure. However, post-processing, the severely deformed solid solution was found to be unstable at room temperature and copious precipitation of θ occurred at grain boundaries within the deformed state, leading to recovery of the deformation structure and a loss of strength. The solute level fell to equilibrium within ∼9 months. The precipitation kinetics were shown to occur at many orders of magnitude higher than can be predicted by classical nucleation and growth theory. The reasons for this discrepancy are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007836 [article] The formation of nanograin structures and accelerated room-temperature theta precipitation in a severely deformed Al–4 wt.% Cu alloy [texte imprimé] / Y. Huang, Auteur ; J.D. Robson, Auteur ; P.B. Prangnell, Auteur . - 2011 . - pp. 1643–1657. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1643–1657 Mots-clés : Severe  plastic  deformation  (SPD)  Nanocrystalline  Accelerated  ageing  Theta  phase  Nucleation Résumé : The grain size achievable and long-term stability of a severely deformed aluminium copper alloy have been investigated when copper is used in solution to inhibit recovery. It is shown that copper is more effective than magnesium in inhibiting dynamic recovery. A grain width of only ∼70 nm was obtained in an Al–4 wt.% Cu alloy, after processing by equal-channel angular extrusion to a strain of εeff = 10, resulting in a lamellar nanograin structure. However, post-processing, the severely deformed solid solution was found to be unstable at room temperature and copious precipitation of θ occurred at grain boundaries within the deformed state, leading to recovery of the deformation structure and a loss of strength. The solute level fell to equilibrium within ∼9 months. The precipitation kinetics were shown to occur at many orders of magnitude higher than can be predicted by classical nucleation and growth theory. The reasons for this discrepancy are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007836

Influence of directional strength-to-stiffness on the elastic–plastic transition of fcc polycrystals under uniaxial tensile loading / S.L. Wong in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1658–1678 Titre : Influence of directional strength-to-stiffness on the elastic–plastic transition of fcc polycrystals under uniaxial tensile loading Type de document : texte imprimé Auteurs : S.L. Wong, Auteur ; P.R. Dawson, Auteur Année de publication : 2011 Article en page(s) : pp. 1658–1678 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Finite  element  analysis  Elastic  behavior  Plastic  deformation  Yield  phenomena Résumé : Crystal-based finite element simulations have been conducted on virtual face-centered cubic polycrystals under uniaxial tensile loading to study the influence of single crystal elastic anisotropy on the elastic–plastic transition behavior exhibited by the lattice strains. The lattice strain response is examined for different sets of crystals corresponding to different crystallographic fibers. The lattice strain response observed in the elastic–plastic transition is related to crystals associated with different crystallographic fibers yielding on average at different levels of the macroscopic stress. The lattice strain behavior is determined by a combination of the elastic and plastic anisotropies of the single crystals, which is quantified using the directional strength-to-stiffness ratio. The directional strength-to-stiffness ratio for a single crystal and a crystallographic fiber are introduced and they are used to explain the deviation of the lattice strains from linear behavior in the elastic–plastic transition leading up to fully developed plasticity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007848 [article] Influence of directional strength-to-stiffness on the elastic–plastic transition of fcc polycrystals under uniaxial tensile loading [texte imprimé] / S.L. Wong, Auteur ; P.R. Dawson, Auteur . - 2011 . - pp. 1658–1678. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1658–1678 Mots-clés : Finite  element  analysis  Elastic  behavior  Plastic  deformation  Yield  phenomena Résumé : Crystal-based finite element simulations have been conducted on virtual face-centered cubic polycrystals under uniaxial tensile loading to study the influence of single crystal elastic anisotropy on the elastic–plastic transition behavior exhibited by the lattice strains. The lattice strain response is examined for different sets of crystals corresponding to different crystallographic fibers. The lattice strain response observed in the elastic–plastic transition is related to crystals associated with different crystallographic fibers yielding on average at different levels of the macroscopic stress. The lattice strain behavior is determined by a combination of the elastic and plastic anisotropies of the single crystals, which is quantified using the directional strength-to-stiffness ratio. The directional strength-to-stiffness ratio for a single crystal and a crystallographic fiber are introduced and they are used to explain the deviation of the lattice strains from linear behavior in the elastic–plastic transition leading up to fully developed plasticity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007848

The effect of film thickness on the failure strain of polymer-supported metal films / Nanshu Lu in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1679–1687 Titre : The effect of film thickness on the failure strain of polymer-supported metal films Type de document : texte imprimé Auteurs : Nanshu Lu, Auteur ; Zhigang Suo, Auteur ; Joost J. Vlassak, Auteur Année de publication : 2011 Article en page(s) : pp. 1679–1687 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metal  films  Failure  strain  Thickness  Yield  strength  Texture Résumé : We perform uniaxial tensile tests on polyimide-supported copper films with a strong (1 1 1) fiber texture and with thicknesses varying from 50 nm to 1 μm. Films with thicknesses below 200 nm fail by intergranular fracture at elongations of only a few percent. Thicker films rupture by ductile transgranular fracture and local debonding from the substrate. The failure strain for transgranular fracture exhibits a maximum for film thicknesses around 500 nm. The transgranular failure mechanism is elucidated by performing finite element simulations that incorporate a cohesive zone along the film/substrate interface. As the film thickness increases from 200 to 500 nm, a decrease in the yield stress of the film makes it more difficult for the film to debond from the substrate, thus increasing the failure strain. As the thickness increases beyond 500 nm, however, the fraction of (1 0 0) grains in the (1 1 1)-textured films increases. On deformation, necking and debonding initiate at the (1 0 0) grains, leading to a reduction in the failure strain of the films. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900785X [article] The effect of film thickness on the failure strain of polymer-supported metal films [texte imprimé] / Nanshu Lu, Auteur ; Zhigang Suo, Auteur ; Joost J. Vlassak, Auteur . - 2011 . - pp. 1679–1687. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1679–1687 Mots-clés : Metal  films  Failure  strain  Thickness  Yield  strength  Texture Résumé : We perform uniaxial tensile tests on polyimide-supported copper films with a strong (1 1 1) fiber texture and with thicknesses varying from 50 nm to 1 μm. Films with thicknesses below 200 nm fail by intergranular fracture at elongations of only a few percent. Thicker films rupture by ductile transgranular fracture and local debonding from the substrate. The failure strain for transgranular fracture exhibits a maximum for film thicknesses around 500 nm. The transgranular failure mechanism is elucidated by performing finite element simulations that incorporate a cohesive zone along the film/substrate interface. As the film thickness increases from 200 to 500 nm, a decrease in the yield stress of the film makes it more difficult for the film to debond from the substrate, thus increasing the failure strain. As the thickness increases beyond 500 nm, however, the fraction of (1 0 0) grains in the (1 1 1)-textured films increases. On deformation, necking and debonding initiate at the (1 0 0) grains, leading to a reduction in the failure strain of the films. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900785X

BiFeO3 thin films of (1 1 1)-orientation deposited on SrRuO3 buffered Pt/TiO2/SiO2/Si(1 0 0) substrates / Jiagang Wu in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1688–1697 Titre : BiFeO3 thin films of (1 1 1)-orientation deposited on SrRuO3 buffered Pt/TiO2/SiO2/Si(1 0 0) substrates Type de document : texte imprimé Auteurs : Jiagang Wu, Auteur ; John Wang, Auteur Année de publication : 2011 Article en page(s) : pp. 1688–1697 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : BiFeO3  thin  films  (1  1  1)  Orientation  Ferroelectric  properties  Dielectric  relaxation  Conduction  mechanism Résumé : BiFeO3 (BFO) thin films of varying degrees of (1 1 1) orientation were successfully grown on SrRuO3-buffered Pt/TiO2/SiO2/Si(1 0 0) substrates by off-axis radio-frequency magnetron sputtering. They demonstrate much enhanced ferroelectric behavior, including a much enhanced remnant polarization (2Pr ∼ 197.1 μC cm−2 at 1 kHz) measured by positive-up negative-down (PUND), at an optimized deposition temperature of 590 °C. The effects of film deposition temperature on the degree of (1 1 1) orientation, film texture, ferroelectric behavior, leakage current and fatigue endurance of the BFO thin films were systematically investigated. While the degree of (1 1 1) orientation is optimized at 590 °C, the defect concentration in the film increases steadily with increasing deposition temperature, as demonstrated by the dependence of leakage behavior on the deposition temperature. The polarization behavior is shown to strongly depend on the degree of (1 1 1) orientation for the BFO thin film. Oxygen vacancies are shown to involve in the conduction and dielectric relaxation of the BFO thin films deposited at different temperatures, as demonstrated by their dielectric and conduction behavior as a function of both temperature (in the range 294–514 K) and frequency (in the range 10−1–106 Hz). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007861 [article] BiFeO3 thin films of (1 1 1)-orientation deposited on SrRuO3 buffered Pt/TiO2/SiO2/Si(1 0 0) substrates [texte imprimé] / Jiagang Wu, Auteur ; John Wang, Auteur . - 2011 . - pp. 1688–1697. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1688–1697 Mots-clés : BiFeO3  thin  films  (1  1  1)  Orientation  Ferroelectric  properties  Dielectric  relaxation  Conduction  mechanism Résumé : BiFeO3 (BFO) thin films of varying degrees of (1 1 1) orientation were successfully grown on SrRuO3-buffered Pt/TiO2/SiO2/Si(1 0 0) substrates by off-axis radio-frequency magnetron sputtering. They demonstrate much enhanced ferroelectric behavior, including a much enhanced remnant polarization (2Pr ∼ 197.1 μC cm−2 at 1 kHz) measured by positive-up negative-down (PUND), at an optimized deposition temperature of 590 °C. The effects of film deposition temperature on the degree of (1 1 1) orientation, film texture, ferroelectric behavior, leakage current and fatigue endurance of the BFO thin films were systematically investigated. While the degree of (1 1 1) orientation is optimized at 590 °C, the defect concentration in the film increases steadily with increasing deposition temperature, as demonstrated by the dependence of leakage behavior on the deposition temperature. The polarization behavior is shown to strongly depend on the degree of (1 1 1) orientation for the BFO thin film. Oxygen vacancies are shown to involve in the conduction and dielectric relaxation of the BFO thin films deposited at different temperatures, as demonstrated by their dielectric and conduction behavior as a function of both temperature (in the range 294–514 K) and frequency (in the range 10−1–106 Hz). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007861

Thermal behavior of Ni (99.967% and 99.5% purity) deformed to an ultra-high strain by high pressure torsion / H.W. Zhang in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1698–1707 Titre : Thermal behavior of Ni (99.967% and 99.5% purity) deformed to an ultra-high strain by high pressure torsion Type de document : texte imprimé Auteurs : H.W. Zhang, Auteur ; X. Huang, Auteur ; R. Pippan, Auteur Année de publication : 2011 Article en page(s) : pp. 1698–1707 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Discontinuous  recrystallization  Continuous  recrystallization  Nickel  Stored  energy  Plastic  deformation Résumé : Polycrystalline Ni of two purities (99.967% (4N) and 99.5% (2N)) was deformed to an ultra-high strain of εvM = 100 (εvM, von Mises strain) by high pressure torsion at room temperature. The 4N and 2N samples at this strain are nanostructured with an average boundary spacing of ∼100 nm, a high density of dislocations and a large fraction of high angle boundaries (>15°) of 0.68–0.74, as determined by transmission electron microscopy, and 0.8–0.83, as determined by electron backscattering diffraction. The deformed samples were annealed isochronally for 1 h at temperatures from 100 to 600 °C, and the evolution of the structural parameters (boundary spacing, average boundary misorientation angle and the fraction of high angle boundaries), crystallographic texture and hardness were determined. Based on microstructural parameters the energy stored in the deformed state was estimated to be 14 MPa and 24 MPa for 4N Ni and 2N Ni, respectively. The isochronal annealing leads to a drop in hardness in three stages: a relatively small decrease at low temperatures (recovery), followed by a rapid decrease at intermediate temperatures (recrystallization) and a slow decrease at high temperature (grain growth). Both recovery and recrystallization of the 2N Ni are strongly retarded by the presence of impurities reducing the mobility of boundaries. In the recrystallization stage, changes in hardness, microstructure and texture show that the 4N Ni recrystallizes discontinuously, in spite of a large fraction of high angle boundaries in the deformed state. This finding contradicts previous experiments and theory, which suggest that recrystallization is continuous when the fraction of high angle boundaries is high. In the 2N Ni, the observations suggest that some structural coarsening (continuous recrystallization) may take place simultaneously with discontinuous recrystallization. The findings emphasize the importance of alloying, which can delay the process of recovery and recrystallization and thereby enable tailoring of the microstructure and properties through an optimized annealing treatment. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007873 [article] Thermal behavior of Ni (99.967% and 99.5% purity) deformed to an ultra-high strain by high pressure torsion [texte imprimé] / H.W. Zhang, Auteur ; X. Huang, Auteur ; R. Pippan, Auteur . - 2011 . - pp. 1698–1707. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1698–1707 Mots-clés : Discontinuous  recrystallization  Continuous  recrystallization  Nickel  Stored  energy  Plastic  deformation Résumé : Polycrystalline Ni of two purities (99.967% (4N) and 99.5% (2N)) was deformed to an ultra-high strain of εvM = 100 (εvM, von Mises strain) by high pressure torsion at room temperature. The 4N and 2N samples at this strain are nanostructured with an average boundary spacing of ∼100 nm, a high density of dislocations and a large fraction of high angle boundaries (>15°) of 0.68–0.74, as determined by transmission electron microscopy, and 0.8–0.83, as determined by electron backscattering diffraction. The deformed samples were annealed isochronally for 1 h at temperatures from 100 to 600 °C, and the evolution of the structural parameters (boundary spacing, average boundary misorientation angle and the fraction of high angle boundaries), crystallographic texture and hardness were determined. Based on microstructural parameters the energy stored in the deformed state was estimated to be 14 MPa and 24 MPa for 4N Ni and 2N Ni, respectively. The isochronal annealing leads to a drop in hardness in three stages: a relatively small decrease at low temperatures (recovery), followed by a rapid decrease at intermediate temperatures (recrystallization) and a slow decrease at high temperature (grain growth). Both recovery and recrystallization of the 2N Ni are strongly retarded by the presence of impurities reducing the mobility of boundaries. In the recrystallization stage, changes in hardness, microstructure and texture show that the 4N Ni recrystallizes discontinuously, in spite of a large fraction of high angle boundaries in the deformed state. This finding contradicts previous experiments and theory, which suggest that recrystallization is continuous when the fraction of high angle boundaries is high. In the 2N Ni, the observations suggest that some structural coarsening (continuous recrystallization) may take place simultaneously with discontinuous recrystallization. The findings emphasize the importance of alloying, which can delay the process of recovery and recrystallization and thereby enable tailoring of the microstructure and properties through an optimized annealing treatment. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007873

Compressive plasticity and toughness of a Ti-based bulk metallic glass / X.J. Gu in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1708–1720 Titre : Compressive plasticity and toughness of a Ti-based bulk metallic glass Type de document : texte imprimé Auteurs : X.J. Gu, Auteur ; S.J. Poon, Auteur ; G.J. Shiflet, Auteur Année de publication : 2011 Article en page(s) : pp. 1708–1720 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metallic  glasses  Titanium  alloys  Compressive  plasticity  Toughness Résumé : The effects of changes in sample dimensions on the compressive plasticity and fracture toughness/energy have been determined for Ti40Zr25Cu12Ni3Be20 bulk metallic glass (BMG). Changes in sample dimensions alone produced widely different values for compressive plasticity. While these were correlated with changes to the measured Poisson’s ratio for samples of the same composition cast into different sample sizes, significant effects of testing conditions apart from the Poisson’s ratio on the measured compressive plasticity are also demonstrated. Fracture toughness testing on the same material/size that exhibited zero compressive plasticity produced both notch and fatigue pre-cracked toughness in excess of 100 MPa m1/2, while a size effect on the magnitude of toughness was similarly demonstrated. Discussions on the source(s) of the size effect on toughness are provided in addition to demonstrating that exceptional toughness can be obtained in this BMG which exhibits essentially zero compressive plasticity under certain test conditions. The apparent critical Poisson’s ratio for plasticity/toughness is thus different in these very different types of tests. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007885 [article] Compressive plasticity and toughness of a Ti-based bulk metallic glass [texte imprimé] / X.J. Gu, Auteur ; S.J. Poon, Auteur ; G.J. Shiflet, Auteur . - 2011 . - pp. 1708–1720. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1708–1720 Mots-clés : Metallic  glasses  Titanium  alloys  Compressive  plasticity  Toughness Résumé : The effects of changes in sample dimensions on the compressive plasticity and fracture toughness/energy have been determined for Ti40Zr25Cu12Ni3Be20 bulk metallic glass (BMG). Changes in sample dimensions alone produced widely different values for compressive plasticity. While these were correlated with changes to the measured Poisson’s ratio for samples of the same composition cast into different sample sizes, significant effects of testing conditions apart from the Poisson’s ratio on the measured compressive plasticity are also demonstrated. Fracture toughness testing on the same material/size that exhibited zero compressive plasticity produced both notch and fatigue pre-cracked toughness in excess of 100 MPa m1/2, while a size effect on the magnitude of toughness was similarly demonstrated. Discussions on the source(s) of the size effect on toughness are provided in addition to demonstrating that exceptional toughness can be obtained in this BMG which exhibits essentially zero compressive plasticity under certain test conditions. The apparent critical Poisson’s ratio for plasticity/toughness is thus different in these very different types of tests. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007885

The high-strain-rate dynamic response of boron carbide-based composites / S. Hayun in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1721–1731 Titre : The high-strain-rate dynamic response of boron carbide-based composites : The effect of microstructure Type de document : texte imprimé Auteurs : S. Hayun, Auteur ; M. P. Dariel, Auteur ; N. Frage, Auteur Année de publication : 2011 Article en page(s) : pp. 1721–1731 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Reaction  bonded  boron  carbide  Microstructure  High  strain  rate  Hugoniot  elastic  limit  Spall Résumé : The dynamic high-strain-rate behavior of boron carbide-based composites with similar phase composition yet different microstructural features, namely, amount of residual silicon, average grain size and morphology of the SiC particles, was investigated as a function of the planar impact strength. The composites consisted of boron carbide preforms (compacted or partly sintered powder) with or without free carbon addition, infiltrated with molten silicon. The dynamic response of the composites depends strongly on the amount of residual silicon, on the average size of the boron carbide grains, and on the morphology of the SiC particles. The preliminary sintering of the preforms exerts no effect on the dynamic properties of the composites. The deformation and failure mechanisms under dynamic loading are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007897 [article] The high-strain-rate dynamic response of boron carbide-based composites : The effect of microstructure [texte imprimé] / S. Hayun, Auteur ; M. P. Dariel, Auteur ; N. Frage, Auteur . - 2011 . - pp. 1721–1731. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1721–1731 Mots-clés : Reaction  bonded  boron  carbide  Microstructure  High  strain  rate  Hugoniot  elastic  limit  Spall Résumé : The dynamic high-strain-rate behavior of boron carbide-based composites with similar phase composition yet different microstructural features, namely, amount of residual silicon, average grain size and morphology of the SiC particles, was investigated as a function of the planar impact strength. The composites consisted of boron carbide preforms (compacted or partly sintered powder) with or without free carbon addition, infiltrated with molten silicon. The dynamic response of the composites depends strongly on the amount of residual silicon, on the average size of the boron carbide grains, and on the morphology of the SiC particles. The preliminary sintering of the preforms exerts no effect on the dynamic properties of the composites. The deformation and failure mechanisms under dynamic loading are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007897

HRTEM and EELS study of aluminum nitride in nanostructured Al 5083/B4C processed via cryomilling / Y. Li in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1732–1740 Titre : HRTEM and EELS study of aluminum nitride in nanostructured Al 5083/B4C processed via cryomilling Type de document : texte imprimé Auteurs : Y. Li, Auteur ; W. Liu, Auteur ; V. Ortalan, Auteur Année de publication : 2011 Article en page(s) : pp. 1732–1740 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : High-resolution  electron  microscopy  (HREM)  Electron  energy  loss  spectroscopy  (EELS)  Transmission  electron  microscopy  (TEM)  Particulate  reinforced  composites  Metal  matrix  composites  (MMC) Résumé : The presence of aluminum nitride in nanostructured aluminum metal matrix composites was studied by high resolution transmission electron microscopy, electron energy loss spectroscopy, energy dispersive X-ray spectroscopy analysis and electron microscopy simulations. Three types of aluminum nitride structures were identified; predominantly, one layer of N atoms occupies the tetrahedral interstitial positions in the Al lattice, the frequency of which varies as a function of spatial location. The second and third were in the form of hexagonal and possibly cubic aluminum nitride particles with particle sizes on the order of 15–20 nm. The results suggest that the aluminum nitride phase evolves from intermediate transitional structures that involve N atoms in the Al lattice. The aluminum nitride phases frequently contained O and Mg, which preferentially segregate in close proximity to the reinforcement particles. First-principle calculations were used to describe the influence of O and Mg on the adsorption of N. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007940 [article] HRTEM and EELS study of aluminum nitride in nanostructured Al 5083/B4C processed via cryomilling [texte imprimé] / Y. Li, Auteur ; W. Liu, Auteur ; V. Ortalan, Auteur . - 2011 . - pp. 1732–1740. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1732–1740 Mots-clés : High-resolution  electron  microscopy  (HREM)  Electron  energy  loss  spectroscopy  (EELS)  Transmission  electron  microscopy  (TEM)  Particulate  reinforced  composites  Metal  matrix  composites  (MMC) Résumé : The presence of aluminum nitride in nanostructured aluminum metal matrix composites was studied by high resolution transmission electron microscopy, electron energy loss spectroscopy, energy dispersive X-ray spectroscopy analysis and electron microscopy simulations. Three types of aluminum nitride structures were identified; predominantly, one layer of N atoms occupies the tetrahedral interstitial positions in the Al lattice, the frequency of which varies as a function of spatial location. The second and third were in the form of hexagonal and possibly cubic aluminum nitride particles with particle sizes on the order of 15–20 nm. The results suggest that the aluminum nitride phase evolves from intermediate transitional structures that involve N atoms in the Al lattice. The aluminum nitride phases frequently contained O and Mg, which preferentially segregate in close proximity to the reinforcement particles. First-principle calculations were used to describe the influence of O and Mg on the adsorption of N. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007940

Decoupled structural and non-collinear magnetic phase transitions in Fe(ND3)2PO4 / Belén F. Alfonso in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1741–1749 Titre : Decoupled structural and non-collinear magnetic phase transitions in Fe(ND3)2PO4 Type de document : texte imprimé Auteurs : Belén F. Alfonso, Auteur ; Camino Trobajo, Auteur ; Carmen Piqué, Auteur Année de publication : 2011 Article en page(s) : pp. 1741–1749 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Iron  phosphates  Structural  phase  transition  Heat  capacity  measurements  Magnetic  properties Résumé : Interest in Fe(ND3)2PO4, one of the first three-dimensional structurally linked solids forming Fe–ND3 bonds, has been renewed recently due to the observation of structural and magnetic phase transitions. This paper reports powder neutron diffraction experiments which show that Fe(ND3)2PO4 crystallizes at room temperature in an orthorhombic (Pnma) crystal structure, but that below Tt = 226(5) K the crystal progressively adopts a monoclinic (P21/n) structure via a continuous phase transition, as observed from heat capacity measurements in the temperature range 250–100 K. In addition, neutron diffraction experiments suggest that the magnetic structure is non-collinear with an incommensurate propagation vector View the MathML source, with τ ∼ 0.04 reciprocal lattice units (rlus), and that the magnitude of the Fe(III) magnetic moments is close to μFe = 4.5 μB at T = 2 K, describing a helimagnetic arrangement. To the best of our knowledge, this is an unprecedented magnetic ordering in an iron phosphate lattice. We argue that the proposed magnetic ordering can be explained by means of a model of superexchange interactions involving Fe–O–P–O–Fe paths. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007952 [article] Decoupled structural and non-collinear magnetic phase transitions in Fe(ND3)2PO4 [texte imprimé] / Belén F. Alfonso, Auteur ; Camino Trobajo, Auteur ; Carmen Piqué, Auteur . - 2011 . - pp. 1741–1749. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1741–1749 Mots-clés : Iron  phosphates  Structural  phase  transition  Heat  capacity  measurements  Magnetic  properties Résumé : Interest in Fe(ND3)2PO4, one of the first three-dimensional structurally linked solids forming Fe–ND3 bonds, has been renewed recently due to the observation of structural and magnetic phase transitions. This paper reports powder neutron diffraction experiments which show that Fe(ND3)2PO4 crystallizes at room temperature in an orthorhombic (Pnma) crystal structure, but that below Tt = 226(5) K the crystal progressively adopts a monoclinic (P21/n) structure via a continuous phase transition, as observed from heat capacity measurements in the temperature range 250–100 K. In addition, neutron diffraction experiments suggest that the magnetic structure is non-collinear with an incommensurate propagation vector View the MathML source, with τ ∼ 0.04 reciprocal lattice units (rlus), and that the magnitude of the Fe(III) magnetic moments is close to μFe = 4.5 μB at T = 2 K, describing a helimagnetic arrangement. To the best of our knowledge, this is an unprecedented magnetic ordering in an iron phosphate lattice. We argue that the proposed magnetic ordering can be explained by means of a model of superexchange interactions involving Fe–O–P–O–Fe paths. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007952

Kinetics of isothermal phase transformations above and below the peritectic temperature / G. Boussinot in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1750–1760 Titre : Kinetics of isothermal phase transformations above and below the peritectic temperature : Phase-field simulations Type de document : texte imprimé Auteurs : G. Boussinot, Auteur ; E. A. Brener, Auteur ; D.E. Temkin, Auteur Année de publication : 2011 Article en page(s) : pp. 1750–1760 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Peritectic  phase  diagram  Phase-field  model  Triple  junction  Liquid-film-migration Résumé : We present phase-field simulations of isothermal phase transformations in the peritectic system below and above the peritectic temperature. The physical processes involved are of different natures, involving either a triple junction or a liquid-film-migration (LFM) mechanism. Below the peritectic temperature, one of the solid phases steadily grows along the other. Above the peritectic temperature the phase transformation proceeds via the LFM mechanism. To the best of our knowledge, this mechanism has not been discussed in the literature as a generic process of phase transitions in peritectic systems. In addition to the LFM process, we also simulate melting along the solid–solid interface. Finally, we make a simplified linear stability analysis of the liquid film, supporting our simulation results. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007964 [article] Kinetics of isothermal phase transformations above and below the peritectic temperature : Phase-field simulations [texte imprimé] / G. Boussinot, Auteur ; E. A. Brener, Auteur ; D.E. Temkin, Auteur . - 2011 . - pp. 1750–1760. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1750–1760 Mots-clés : Peritectic  phase  diagram  Phase-field  model  Triple  junction  Liquid-film-migration Résumé : We present phase-field simulations of isothermal phase transformations in the peritectic system below and above the peritectic temperature. The physical processes involved are of different natures, involving either a triple junction or a liquid-film-migration (LFM) mechanism. Below the peritectic temperature, one of the solid phases steadily grows along the other. Above the peritectic temperature the phase transformation proceeds via the LFM mechanism. To the best of our knowledge, this mechanism has not been discussed in the literature as a generic process of phase transitions in peritectic systems. In addition to the LFM process, we also simulate melting along the solid–solid interface. Finally, we make a simplified linear stability analysis of the liquid film, supporting our simulation results. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007964

Role of transverse temperature gradients in the generation of lamellar eutectic solidification patterns / Mikaël Perrut in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1761–1769 Titre : Role of transverse temperature gradients in the generation of lamellar eutectic solidification patterns Type de document : texte imprimé Auteurs : Mikaël Perrut, Auteur ; Andrea Parisi, Auteur ; Silvère Akamatsu, Auteur Année de publication : 2011 Article en page(s) : pp. 1761–1769 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Eutectic  solidification  Solidification  microstructure  Directional  solidification  Phase  field  modeling Résumé : In directional solidification, a sample is pulled in an externally imposed temperature gradient. When the pulling direction and the temperature gradient are not perfectly aligned, a transverse temperature gradient is generated in the sample. We investigate the dynamics of lamellar eutectic patterns, both by experimental observations and by numerical simulations, and find that it is dramatically affected by a transverse gradient. Whereas, in its absence, the labyrinth patterns that are formed in the initial stage of solidification persist over the entire duration of the experiments, a transverse temperature gradient induces a drift of the pattern which rapidly generates a regular array of lamellae. The drift speed is found to be consistently larger than expected from the normal growth hypothesis, both in simulations and experiments. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007976 [article] Role of transverse temperature gradients in the generation of lamellar eutectic solidification patterns [texte imprimé] / Mikaël Perrut, Auteur ; Andrea Parisi, Auteur ; Silvère Akamatsu, Auteur . - 2011 . - pp. 1761–1769. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1761–1769 Mots-clés : Eutectic  solidification  Solidification  microstructure  Directional  solidification  Phase  field  modeling Résumé : In directional solidification, a sample is pulled in an externally imposed temperature gradient. When the pulling direction and the temperature gradient are not perfectly aligned, a transverse temperature gradient is generated in the sample. We investigate the dynamics of lamellar eutectic patterns, both by experimental observations and by numerical simulations, and find that it is dramatically affected by a transverse gradient. Whereas, in its absence, the labyrinth patterns that are formed in the initial stage of solidification persist over the entire duration of the experiments, a transverse temperature gradient induces a drift of the pattern which rapidly generates a regular array of lamellae. The drift speed is found to be consistently larger than expected from the normal growth hypothesis, both in simulations and experiments. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007976

Interface thermodynamics of ultra-thin, amorphous oxide overgrowths on AlMg alloys / E. Panda in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1770–1781 Titre : Interface thermodynamics of ultra-thin, amorphous oxide overgrowths on AlMg alloys Type de document : texte imprimé Auteurs : E. Panda, Auteur ; L.P.H. Jeurgens, Auteur ; E. J. Mittemeijer, Auteur Année de publication : 2011 Article en page(s) : pp. 1770–1781 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Interface  energy  Thermodynamics  Alloy  oxidation  Amorphous  oxides  Ultra-thin  oxide  films Résumé : A thermodynamic model has been presented for the prediction of the type of initial, amorphous oxide overgrowth (i.e. am-Al2O3, am-MgO or am-MgAl2O4) on bare AlMg substrates as a function of the Mg alloying element content at the substrate/oxide interface, the growth temperature and the oxide-film thickness (up to 5 nm). On the basis of the macroscopic atom approach, expressions have been derived for the estimation of the energies of the interfaces between the AlMg substrate and the competing am-Al2O3, am-MgO and am-MgAl2O4 overgrowths. For all cases a strong driving force has been revealed for the interfacial (chemical) segregation of Mg. am-Al2O3 was found to be the most stable amorphous oxide phase on the AlMg substrate for T < 610 K; its relatively high stability is governed by a relatively low interface energy. The model predictions are in good agreement with corresponding experimental results on the chemical constitution of ultra-thin amorphous oxide films grown on Al- and Mg-based alloy substrates in the temperature range of 300–400 K. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007988 [article] Interface thermodynamics of ultra-thin, amorphous oxide overgrowths on AlMg alloys [texte imprimé] / E. Panda, Auteur ; L.P.H. Jeurgens, Auteur ; E. J. Mittemeijer, Auteur . - 2011 . - pp. 1770–1781. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1770–1781 Mots-clés : Interface  energy  Thermodynamics  Alloy  oxidation  Amorphous  oxides  Ultra-thin  oxide  films Résumé : A thermodynamic model has been presented for the prediction of the type of initial, amorphous oxide overgrowth (i.e. am-Al2O3, am-MgO or am-MgAl2O4) on bare AlMg substrates as a function of the Mg alloying element content at the substrate/oxide interface, the growth temperature and the oxide-film thickness (up to 5 nm). On the basis of the macroscopic atom approach, expressions have been derived for the estimation of the energies of the interfaces between the AlMg substrate and the competing am-Al2O3, am-MgO and am-MgAl2O4 overgrowths. For all cases a strong driving force has been revealed for the interfacial (chemical) segregation of Mg. am-Al2O3 was found to be the most stable amorphous oxide phase on the AlMg substrate for T < 610 K; its relatively high stability is governed by a relatively low interface energy. The model predictions are in good agreement with corresponding experimental results on the chemical constitution of ultra-thin amorphous oxide films grown on Al- and Mg-based alloy substrates in the temperature range of 300–400 K. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007988

A model of grain fragmentation based on lattice curvature / László S. Tóth in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1782–1794 Titre : A model of grain fragmentation based on lattice curvature Type de document : texte imprimé Auteurs : László S. Tóth, Auteur ; Yuri Estrin, Auteur ; Rimma Lapovok, Auteur Année de publication : 2011 Article en page(s) : pp. 1782–1794 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  fragmentation  Severe  plastic  deformation  Texture  development  Strain-hardening  Misorientation  distribution Résumé : A new model is proposed that aims to capture within a single modelling frame all the main microstructural features of a severe plastic deformation process. These are: evolution of the grain size distribution, misorientation distribution, crystallographic texture and the strain-hardening of the material. The model is based on the lattice curvature that develops in all deformed grains. The basic assumption is that lattice rotation within an individual grain is impeded near the grain boundaries by the constraining effects of the neighbouring grains, which gives rise to lattice curvature. On that basis, a fragmentation scheme is developed which is integrated in the Taylor viscoplastic polycrystal model. Dislocation density evolution is traced for each grain, which includes the contribution of geometrically necessary dislocations associated with lattice curvature. The model is applied to equal-channel angular pressing. The role of texture development is shown to be an important element in the grain fragmentation process. Results of this modelling give fairly precise predictions of grain size and grain misorientation distribution. The crystallographic textures are well reproduced and the strength of the material is also reliably predicted based on the modelling of dislocation density evolution coupled with texture development. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900799X [article] A model of grain fragmentation based on lattice curvature [texte imprimé] / László S. Tóth, Auteur ; Yuri Estrin, Auteur ; Rimma Lapovok, Auteur . - 2011 . - pp. 1782–1794. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1782–1794 Mots-clés : Grain  fragmentation  Severe  plastic  deformation  Texture  development  Strain-hardening  Misorientation  distribution Résumé : A new model is proposed that aims to capture within a single modelling frame all the main microstructural features of a severe plastic deformation process. These are: evolution of the grain size distribution, misorientation distribution, crystallographic texture and the strain-hardening of the material. The model is based on the lattice curvature that develops in all deformed grains. The basic assumption is that lattice rotation within an individual grain is impeded near the grain boundaries by the constraining effects of the neighbouring grains, which gives rise to lattice curvature. On that basis, a fragmentation scheme is developed which is integrated in the Taylor viscoplastic polycrystal model. Dislocation density evolution is traced for each grain, which includes the contribution of geometrically necessary dislocations associated with lattice curvature. The model is applied to equal-channel angular pressing. The role of texture development is shown to be an important element in the grain fragmentation process. Results of this modelling give fairly precise predictions of grain size and grain misorientation distribution. The crystallographic textures are well reproduced and the strength of the material is also reliably predicted based on the modelling of dislocation density evolution coupled with texture development. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900799X

Evolution of solute clustering in Al–Cu–Mg alloys during secondary ageing / R.K.W. Marceau in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1795–1805 Titre : Evolution of solute clustering in Al–Cu–Mg alloys during secondary ageing Type de document : texte imprimé Auteurs : R.K.W. Marceau, Auteur ; G. Sha, Auteur ; R.N. Lumley, Auteur Année de publication : 2011 Article en page(s) : pp. 1795–1805 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminium  alloys  Age  hardening  Solute  clustering  Secondary  ageing  Atom  probe  tomography Résumé : The evolution of an atomistic-level nanostructure during the early stages of secondary ageing of a rapid hardening Al–1.1Cu–1.7Mg (at.%) alloy has been characterized by a combination of atom probe tomography (APT) and transmission electron microscopy. Quantitative APT analysis reveals key changes in the evolution of solute clusters during secondary ageing (T6I4 condition) that correlate with secondary hardness increments. The microstructures that cause peak hardness differ between the T6 and T6I4 tempers – the former is a result of solute clustering as well as the precipitation of GPB zones and S phase, whereas in the latter, secondary ageing promotes only the formation of solute clusters. Cu–Mg clusters with high Mg:Cu ratio have the most strengthening potency during secondary ageing in T6I4 heat treatment. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008003 [article] Evolution of solute clustering in Al–Cu–Mg alloys during secondary ageing [texte imprimé] / R.K.W. Marceau, Auteur ; G. Sha, Auteur ; R.N. Lumley, Auteur . - 2011 . - pp. 1795–1805. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1795–1805 Mots-clés : Aluminium  alloys  Age  hardening  Solute  clustering  Secondary  ageing  Atom  probe  tomography Résumé : The evolution of an atomistic-level nanostructure during the early stages of secondary ageing of a rapid hardening Al–1.1Cu–1.7Mg (at.%) alloy has been characterized by a combination of atom probe tomography (APT) and transmission electron microscopy. Quantitative APT analysis reveals key changes in the evolution of solute clusters during secondary ageing (T6I4 condition) that correlate with secondary hardness increments. The microstructures that cause peak hardness differ between the T6 and T6I4 tempers – the former is a result of solute clustering as well as the precipitation of GPB zones and S phase, whereas in the latter, secondary ageing promotes only the formation of solute clusters. Cu–Mg clusters with high Mg:Cu ratio have the most strengthening potency during secondary ageing in T6I4 heat treatment. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008003

Nanoscale characterisation and clustering mechanism in an Fe–Y2O3 model ODS alloy processed by reactive ball milling and annealing / M. Brocq in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1806–1814 Titre : Nanoscale characterisation and clustering mechanism in an Fe–Y2O3 model ODS alloy processed by reactive ball milling and annealing Type de document : texte imprimé Auteurs : M. Brocq, Auteur ; B. Radiguet, Auteur ; J.-M. Le Breton, Auteur Année de publication : 2011 Article en page(s) : pp. 1806–1814 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Oxide  dispersion  strengthened  steel  Mechanical  milling  Tomographic  atom  probe  X-ray  diffraction  Mössbauer  spectroscopy Résumé : Reactive ball milling and annealing is proposed as a new production method for oxide dispersion strengthened (ODS) steels. A highly concentrated Fe–38 atm.% Y2O3 ODS model alloy was processed by reactive ball milling and annealing of YFe3 and Fe2O3 powders so as to induce the chemical reaction 2YFe3 + Fe2O3 → 8Fe + Y2O3. The model alloy was characterised after milling and annealing by complementary techniques, including atom probe tomography. Ball milling up to the stationary state results in the formation of two metastable nanometric interconnected phases: super-saturated α-iron and an yttrium and oxygen rich phase. Annealing leads the system towards equilibrium through: (i) a chemical evolution of each phase to nearly pure α-Fe and Y2O3 oxide slightly sub-stoichiometric in oxygen; and (ii) growth of the phases. A pure iron matrix reinforced by nanometric Y2O3 particles was successfully synthesised by reactive ball milling and annealing. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008015 [article] Nanoscale characterisation and clustering mechanism in an Fe–Y2O3 model ODS alloy processed by reactive ball milling and annealing [texte imprimé] / M. Brocq, Auteur ; B. Radiguet, Auteur ; J.-M. Le Breton, Auteur . - 2011 . - pp. 1806–1814. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1806–1814 Mots-clés : Oxide  dispersion  strengthened  steel  Mechanical  milling  Tomographic  atom  probe  X-ray  diffraction  Mössbauer  spectroscopy Résumé : Reactive ball milling and annealing is proposed as a new production method for oxide dispersion strengthened (ODS) steels. A highly concentrated Fe–38 atm.% Y2O3 ODS model alloy was processed by reactive ball milling and annealing of YFe3 and Fe2O3 powders so as to induce the chemical reaction 2YFe3 + Fe2O3 → 8Fe + Y2O3. The model alloy was characterised after milling and annealing by complementary techniques, including atom probe tomography. Ball milling up to the stationary state results in the formation of two metastable nanometric interconnected phases: super-saturated α-iron and an yttrium and oxygen rich phase. Annealing leads the system towards equilibrium through: (i) a chemical evolution of each phase to nearly pure α-Fe and Y2O3 oxide slightly sub-stoichiometric in oxygen; and (ii) growth of the phases. A pure iron matrix reinforced by nanometric Y2O3 particles was successfully synthesised by reactive ball milling and annealing. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008015

Mechanical behaviour of nanoporous superalloy membranes / J. Rösler in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1815–1828 Titre : Mechanical behaviour of nanoporous superalloy membranes Type de document : texte imprimé Auteurs : J. Rösler, Auteur ; O. Näth, Auteur Année de publication : 2011 Article en page(s) : pp. 1815–1828 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanostructure  Cellular  materials  Nickel  alloys  Elastic  behaviour  Fracture Résumé : The mechanical behaviour of nanoporous superalloy membranes is analysed for the first time and discussed in conjunction with their microstructure, consisting of ligaments of the γ′ phase and channel-like pores a few hundred nanometers wide. Tensile tests and vibrating reed experiments are performed to determine the mechanical properties. It is shown that they are strongly dependent on the processing procedure, the orientation of the γ′ ligaments and interdendritic heterogeneities. A microstructural model of the membrane materials is then used to analyse the findings in more detail and rationalize the observed elastic behaviour. Following these results, unique metallic membrane materials can be produced, combining excellent strength on a macroscopic scale with extremely fine porosity on a microscopic scale. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008039 [article] Mechanical behaviour of nanoporous superalloy membranes [texte imprimé] / J. Rösler, Auteur ; O. Näth, Auteur . - 2011 . - pp. 1815–1828. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1815–1828 Mots-clés : Nanostructure  Cellular  materials  Nickel  alloys  Elastic  behaviour  Fracture Résumé : The mechanical behaviour of nanoporous superalloy membranes is analysed for the first time and discussed in conjunction with their microstructure, consisting of ligaments of the γ′ phase and channel-like pores a few hundred nanometers wide. Tensile tests and vibrating reed experiments are performed to determine the mechanical properties. It is shown that they are strongly dependent on the processing procedure, the orientation of the γ′ ligaments and interdendritic heterogeneities. A microstructural model of the membrane materials is then used to analyse the findings in more detail and rationalize the observed elastic behaviour. Following these results, unique metallic membrane materials can be produced, combining excellent strength on a macroscopic scale with extremely fine porosity on a microscopic scale. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008039

Volume and enthalpy relaxation in Zr55Cu30Ni5Al10 bulk metallic glass / O. Haruyama in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1829–1836 Titre : Volume and enthalpy relaxation in Zr55Cu30Ni5Al10 bulk metallic glass Type de document : texte imprimé Auteurs : O. Haruyama, Auteur ; Y. Nakayama, Auteur ; R. Wada, Auteur Année de publication : 2011 Article en page(s) : pp. 1829–1836 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bulk  metallic  glass  Zr55Cu30Ni5Al10  Volume  relaxation  Enthalpy  relaxation  Two-component  model Résumé : The structural relaxation in a Zr55Cu30Ni5Al10 bulk metallic glass was investigated by volume and enthalpy relaxation at various temperatures. The relaxation kinetics was well described by a stretched exponential relaxation function, Φ(t)=exp[-(t/τ)β]. The Kohlrausch index, β, ranged from 0.35 to 0.69, while the temperature dependence of relaxation time, τ was best fitted by the Vogel–Fulcher–Tanmmann formula, τ(T)=τ0exp[D∗T0/(T-T0)], with τ0 = 1.1 × 10−14 s, D∗ = 44.2 and T0 = 311 K. Atomic volumes in the equilibrium liquid region were measured by the electrostatic levitation method and these volumes, together with volumes of relaxed glasses, were better described by the Cohen–Grest model than by the Cohen–Turnbull model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008040 [article] Volume and enthalpy relaxation in Zr55Cu30Ni5Al10 bulk metallic glass [texte imprimé] / O. Haruyama, Auteur ; Y. Nakayama, Auteur ; R. Wada, Auteur . - 2011 . - pp. 1829–1836. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1829–1836 Mots-clés : Bulk  metallic  glass  Zr55Cu30Ni5Al10  Volume  relaxation  Enthalpy  relaxation  Two-component  model Résumé : The structural relaxation in a Zr55Cu30Ni5Al10 bulk metallic glass was investigated by volume and enthalpy relaxation at various temperatures. The relaxation kinetics was well described by a stretched exponential relaxation function, Φ(t)=exp[-(t/τ)β]. The Kohlrausch index, β, ranged from 0.35 to 0.69, while the temperature dependence of relaxation time, τ was best fitted by the Vogel–Fulcher–Tanmmann formula, τ(T)=τ0exp[D∗T0/(T-T0)], with τ0 = 1.1 × 10−14 s, D∗ = 44.2 and T0 = 311 K. Atomic volumes in the equilibrium liquid region were measured by the electrostatic levitation method and these volumes, together with volumes of relaxed glasses, were better described by the Cohen–Grest model than by the Cohen–Turnbull model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008040

Characterizing short-range vs. long-range spatial correlations in dislocation distributions / Juliette Chevy in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1837–1849 Titre : Characterizing short-range vs. long-range spatial correlations in dislocation distributions Type de document : texte imprimé Auteurs : Juliette Chevy, Auteur ; Claude Fressengeas, Auteur ; Mikhail Lebyodkin, Auteur Année de publication : 2011 Article en page(s) : pp. 1837–1849 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  dynamics  Self-organization  Spatial  correlation  Hard  X-ray  diffraction Résumé : Hard X-ray diffraction experiments have provided evidence of a strongly heterogeneous distribution of dislocation densities along the axis of cylindrical ice single crystals oriented for basal slip in torsion creep. The dislocation arrangements showed a complex scale-invariant character, which was analyzed by means of statistical and multifractal techniques. A trend to decreasing autocorrelation of the dislocation distribution was observed as deformation proceeds. At low strain levels, long-range spatial correlations control the distribution, but short-range correlations in relation with cross-slip progressively prevail when strain increases. This trend was reproduced by a model based on field dislocation dynamics, a theory accounting for both long-range elastic interactions and short-range interactions through transport of dislocation densities. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008064 [article] Characterizing short-range vs. long-range spatial correlations in dislocation distributions [texte imprimé] / Juliette Chevy, Auteur ; Claude Fressengeas, Auteur ; Mikhail Lebyodkin, Auteur . - 2011 . - pp. 1837–1849. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1837–1849 Mots-clés : Dislocation  dynamics  Self-organization  Spatial  correlation  Hard  X-ray  diffraction Résumé : Hard X-ray diffraction experiments have provided evidence of a strongly heterogeneous distribution of dislocation densities along the axis of cylindrical ice single crystals oriented for basal slip in torsion creep. The dislocation arrangements showed a complex scale-invariant character, which was analyzed by means of statistical and multifractal techniques. A trend to decreasing autocorrelation of the dislocation distribution was observed as deformation proceeds. At low strain levels, long-range spatial correlations control the distribution, but short-range correlations in relation with cross-slip progressively prevail when strain increases. This trend was reproduced by a model based on field dislocation dynamics, a theory accounting for both long-range elastic interactions and short-range interactions through transport of dislocation densities. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008064

On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys / T. Simon in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1850–1860 Titre : On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys Type de document : texte imprimé Auteurs : T. Simon, Auteur ; A. Kröger, Auteur ; C. Somsen, Auteur Année de publication : 2011 Article en page(s) : pp. 1850–1860 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : NiTi  Martensitic  transformations  Dislocation  multiplication  mechanism  Martensite  variants  Dislocations Résumé : In situ and post-mortem diffraction contrast transmission electron microscopy (TEM) was used to study the multiplication of dislocations during a thermal martensitic forward and reverse transformation in a NiTi shape memory alloy single crystal. An analysis of the elongated dislocation loops which formed during the transformation was performed. It is proposed that the stress field of an approaching martensite needle activates an in-grown dislocation segment and generates characteristic narrow and elongated dislocation loops which expand on {1 1 0}B2 planes parallel to {0 0 1}B19′ compound twin planes. The findings are compared with TEM results reported in the literature for NiTi and other shape memory alloys. It is suggested that the type of dislocation multiplication mechanism documented in the present study is generic and that it can account for the increase in dislocation densities during thermal and stress-induced martensitic transformations in other shape memory alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008076 [article] On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys [texte imprimé] / T. Simon, Auteur ; A. Kröger, Auteur ; C. Somsen, Auteur . - 2011 . - pp. 1850–1860. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1850–1860 Mots-clés : NiTi  Martensitic  transformations  Dislocation  multiplication  mechanism  Martensite  variants  Dislocations Résumé : In situ and post-mortem diffraction contrast transmission electron microscopy (TEM) was used to study the multiplication of dislocations during a thermal martensitic forward and reverse transformation in a NiTi shape memory alloy single crystal. An analysis of the elongated dislocation loops which formed during the transformation was performed. It is proposed that the stress field of an approaching martensite needle activates an in-grown dislocation segment and generates characteristic narrow and elongated dislocation loops which expand on {1 1 0}B2 planes parallel to {0 0 1}B19′ compound twin planes. The findings are compared with TEM results reported in the literature for NiTi and other shape memory alloys. It is suggested that the type of dislocation multiplication mechanism documented in the present study is generic and that it can account for the increase in dislocation densities during thermal and stress-induced martensitic transformations in other shape memory alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008076

Structural and morphological modification of PDMS thick film surfaces by ion implantation with the formation of strain-induced buckling domains / B.R. Winton in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1861–1867 Titre : Structural and morphological modification of PDMS thick film surfaces by ion implantation with the formation of strain-induced buckling domains Type de document : texte imprimé Auteurs : B.R. Winton, Auteur ; M. Ionescu, Auteur ; S.X. Dou, Auteur Année de publication : 2011 Article en page(s) : pp. 1861–1867 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Implantation  Atomic  force  microscopy  Scanning  electron  microscopy  X-ray  diffraction  Elastomeric  polymers Résumé : Elastomer films with three-dimensional features self-organized into coherent and semi-coherent buckling domains were created by implanting different species of metal ions and combinations thereof, using a metal evaporation ion source, into quality polydimethylsiloxane films. As a result of the implantation process, functionalized discrete regions of strain-induced surface buckling were created, taking the forms of domains of parallel surface waves, semi-ordered regions and disordered regions. In addition, deep, strain-induced, V-shaped cracks were observed to penetrate well into the elastomer matrix. Characterization was via optical microscopy, X-ray diffraction, atomic force microscopy and high-resolution scanning electron microscopy (SEM) in the form of field emission SEM. It was found that controlling the localized strain by altering the metal ion species can control the frequency of the V-shaped cracks and the properties of the buckled areas. These observations and possible mechanisms for the formation of the cracks and domains are discussed in this paper. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008088 [article] Structural and morphological modification of PDMS thick film surfaces by ion implantation with the formation of strain-induced buckling domains [texte imprimé] / B.R. Winton, Auteur ; M. Ionescu, Auteur ; S.X. Dou, Auteur . - 2011 . - pp. 1861–1867. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1861–1867 Mots-clés : Implantation  Atomic  force  microscopy  Scanning  electron  microscopy  X-ray  diffraction  Elastomeric  polymers Résumé : Elastomer films with three-dimensional features self-organized into coherent and semi-coherent buckling domains were created by implanting different species of metal ions and combinations thereof, using a metal evaporation ion source, into quality polydimethylsiloxane films. As a result of the implantation process, functionalized discrete regions of strain-induced surface buckling were created, taking the forms of domains of parallel surface waves, semi-ordered regions and disordered regions. In addition, deep, strain-induced, V-shaped cracks were observed to penetrate well into the elastomer matrix. Characterization was via optical microscopy, X-ray diffraction, atomic force microscopy and high-resolution scanning electron microscopy (SEM) in the form of field emission SEM. It was found that controlling the localized strain by altering the metal ion species can control the frequency of the V-shaped cracks and the properties of the buckled areas. These observations and possible mechanisms for the formation of the cracks and domains are discussed in this paper. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008088

Positron annihilation studies of the interaction between oxygen impurities and nanovoids in neutron-irradiated vanadium / Z. Tang in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1868–1875 Titre : Positron annihilation studies of the interaction between oxygen impurities and nanovoids in neutron-irradiated vanadium Type de document : texte imprimé Auteurs : Z. Tang, Auteur ; T. Rewcharoon, Auteur ; Y. Nagai, Auteur Année de publication : 2011 Article en page(s) : pp. 1868–1875 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Positron  annihilation  (PAL)  Radiation  effects  Vacancies  Transition  metals Résumé : Vanadium samples with controlled oxygen impurity of up to 2460 at. ppm were irradiated with fast neutrons to a fluency of View the MathML source at 150 °C. The irradiation-induced nanovoids and the interaction between the defects and the oxygen impurities are studied systematically by combining the positron lifetime technique, the coincidence Doppler broadening technique and the first-principles calculations. The nanovoids are seen to be decorated with the oxygen impurities, which play a significant role in the dynamic processes of the formation of the nanovoids by irradiation and their subsequent recovery by post-irradiation annealing. The decoration with oxygen impurities not only enhances the nanovoid formation but also stabilizes them during low-temperature annealing (<400 °C). The oxygen impurities dissociate from the nanovoids by annealing above 400 °C and the irradiation-induced nanovoids recover on the annealing at 650 °C. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900809X [article] Positron annihilation studies of the interaction between oxygen impurities and nanovoids in neutron-irradiated vanadium [texte imprimé] / Z. Tang, Auteur ; T. Rewcharoon, Auteur ; Y. Nagai, Auteur . - 2011 . - pp. 1868–1875. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1868–1875 Mots-clés : Positron  annihilation  (PAL)  Radiation  effects  Vacancies  Transition  metals Résumé : Vanadium samples with controlled oxygen impurity of up to 2460 at. ppm were irradiated with fast neutrons to a fluency of View the MathML source at 150 °C. The irradiation-induced nanovoids and the interaction between the defects and the oxygen impurities are studied systematically by combining the positron lifetime technique, the coincidence Doppler broadening technique and the first-principles calculations. The nanovoids are seen to be decorated with the oxygen impurities, which play a significant role in the dynamic processes of the formation of the nanovoids by irradiation and their subsequent recovery by post-irradiation annealing. The decoration with oxygen impurities not only enhances the nanovoid formation but also stabilizes them during low-temperature annealing (<400 °C). The oxygen impurities dissociate from the nanovoids by annealing above 400 °C and the irradiation-induced nanovoids recover on the annealing at 650 °C. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900809X

The mechanical size effect as a mean-field breakdown phenomenon / Eralp Demir in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1876–1886 Titre : The mechanical size effect as a mean-field breakdown phenomenon : Example of microscale single crystal beam bending Type de document : texte imprimé Auteurs : Eralp Demir, Auteur ; Dierk Raabe, Auteur ; Franz Roters, Auteur Année de publication : 2011 Article en page(s) : pp. 1876–1886 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Size  effect  Electron  backscattering  diffraction  (EBSD)  Bending  Copper  Crystal  plasticity Résumé : Single crystalline copper beams with thicknesses between 0.7 and 5 μm are manufactured with a focused ion beam technique and bent in a nanoindenter. The yield strengths of the beams show a mechanical size effect (smaller-is-stronger). The geometrically necessary dislocation (GND) densities estimated from misorientation maps do not explain the observed size effect. Also, accumulation of GNDs principally requires pre-straining. We hence introduce a mean-field breakdown theory and generalize it to small-scale mechanical tests other than bending. The mean-field breakdown limit is defined in terms of a microstructural correlation measure (characteristic dislocation bow-out length) below which the local availability of dislocation sources and not the density of GNDs dominates the mechanical size effect. This explains why a size dependence can occur for samples that are not pre-strained (by using a very small critical strain to define the yield strength). After pre-straining, when GNDs build up, they can contribute to the flow stress. The mean-field breakdown theory can also explain the large scatter typically observed in small-scale mechanical tests as the availability of sufficiently soft sources at scales around or below the correlation length does not follow statistical laws but highly depends on the position where the probe is taken. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008106 [article] The mechanical size effect as a mean-field breakdown phenomenon : Example of microscale single crystal beam bending [texte imprimé] / Eralp Demir, Auteur ; Dierk Raabe, Auteur ; Franz Roters, Auteur . - 2011 . - pp. 1876–1886. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1876–1886 Mots-clés : Size  effect  Electron  backscattering  diffraction  (EBSD)  Bending  Copper  Crystal  plasticity Résumé : Single crystalline copper beams with thicknesses between 0.7 and 5 μm are manufactured with a focused ion beam technique and bent in a nanoindenter. The yield strengths of the beams show a mechanical size effect (smaller-is-stronger). The geometrically necessary dislocation (GND) densities estimated from misorientation maps do not explain the observed size effect. Also, accumulation of GNDs principally requires pre-straining. We hence introduce a mean-field breakdown theory and generalize it to small-scale mechanical tests other than bending. The mean-field breakdown limit is defined in terms of a microstructural correlation measure (characteristic dislocation bow-out length) below which the local availability of dislocation sources and not the density of GNDs dominates the mechanical size effect. This explains why a size dependence can occur for samples that are not pre-strained (by using a very small critical strain to define the yield strength). After pre-straining, when GNDs build up, they can contribute to the flow stress. The mean-field breakdown theory can also explain the large scatter typically observed in small-scale mechanical tests as the availability of sufficiently soft sources at scales around or below the correlation length does not follow statistical laws but highly depends on the position where the probe is taken. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008106

Characterization of titanium aluminide alloy components fabricated by additive manufacturing using electron beam melting / L.E. Murr in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1887–1894 Titre : Characterization of titanium aluminide alloy components fabricated by additive manufacturing using electron beam melting Type de document : texte imprimé Auteurs : L.E. Murr, Auteur ; S.M. Gaytan, Auteur ; A. Ceylan, Auteur Année de publication : 2011 Article en page(s) : pp. 1887–1894 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Electron  beam  methods  Titanium  aluminides  SEM  TEM  XRD Résumé : Intermetallic, γ-TiAl, equiaxed, small-grain (∼2 μm) structures with lamellar γ/α2-Ti3Al colonies with average spacing of 0.6 μm have been fabricated by additive manufacturing using electron beam melting (EBM) of precursor, atomized powder. The residual microindentation (Vickers) hardness (HV) averaged 4.1 GPa, corresponding to a nominal yield strength of ∼1.4 GPa (∼HV/3), and a specific yield strength of 0.37 GPa cm3 g−1 (for a density of 3.76 g cm−3), in contrast to 0.27 GPa cm3 g−1 for EBM-fabricated Ti–6Al–4V components. These results demonstrate the potential to fabricate near net shape and complex titanium aluminide products directly using EBM technology in important aerospace and automotive applications. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008118 [article] Characterization of titanium aluminide alloy components fabricated by additive manufacturing using electron beam melting [texte imprimé] / L.E. Murr, Auteur ; S.M. Gaytan, Auteur ; A. Ceylan, Auteur . - 2011 . - pp. 1887–1894. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1887–1894 Mots-clés : Electron  beam  methods  Titanium  aluminides  SEM  TEM  XRD Résumé : Intermetallic, γ-TiAl, equiaxed, small-grain (∼2 μm) structures with lamellar γ/α2-Ti3Al colonies with average spacing of 0.6 μm have been fabricated by additive manufacturing using electron beam melting (EBM) of precursor, atomized powder. The residual microindentation (Vickers) hardness (HV) averaged 4.1 GPa, corresponding to a nominal yield strength of ∼1.4 GPa (∼HV/3), and a specific yield strength of 0.37 GPa cm3 g−1 (for a density of 3.76 g cm−3), in contrast to 0.27 GPa cm3 g−1 for EBM-fabricated Ti–6Al–4V components. These results demonstrate the potential to fabricate near net shape and complex titanium aluminide products directly using EBM technology in important aerospace and automotive applications. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008118

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