Dépouillements

On intrinsic brittleness and ductility of intergranular fracture along symmetrical tilt grain boundaries in copper / Y. Cheng in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2293–2299 Titre : On intrinsic brittleness and ductility of intergranular fracture along symmetrical tilt grain boundaries in copper Type de document : texte imprimé Auteurs : Y. Cheng, Auteur ; Z.-H. Jin, Auteur ; Y.W. Zhang, Auteur Année de publication : 2011 Article en page(s) : pp. 2293–2299 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fracture  Grain  boundary  Dislocation  Atomistic  simulation Résumé : The intrinsic brittleness and ductility of intergranular fracture along a number of symmetrical [1 1 0] tilt grain boundaries (GBs) in Cu are investigated via combined atomistic and continuum studies of dislocation nucleation from an atomically sharp crack tip. In all cases investigated, the classical model of Rice predicts a directional anisotropy in that, along a given GB, brittle cleavage is favored for crack propagation in one direction while dislocation emission from the crack tip is preferred in the opposite direction. This prediction is validated by atomistic simulations of crack propagation along coherent GBs, including View the MathML source and View the MathML source. However, for incoherent GBs such as View the MathML source and View the MathML source, such directional anisotropy in intrinsic ductility is not observed; instead, we show that dislocation emission is favored in both crack propagation directions. The reason for this discrepancy is shown to be dislocation emission at a distance ahead of the crack tip along an incoherent GB, which violates the assumption in Rice’s model that dislocation emission occurs directly at the crack tip. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900812X [article] On intrinsic brittleness and ductility of intergranular fracture along symmetrical tilt grain boundaries in copper [texte imprimé] / Y. Cheng, Auteur ; Z.-H. Jin, Auteur ; Y.W. Zhang, Auteur . - 2011 . - pp. 2293–2299. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2293–2299 Mots-clés : Fracture  Grain  boundary  Dislocation  Atomistic  simulation Résumé : The intrinsic brittleness and ductility of intergranular fracture along a number of symmetrical [1 1 0] tilt grain boundaries (GBs) in Cu are investigated via combined atomistic and continuum studies of dislocation nucleation from an atomically sharp crack tip. In all cases investigated, the classical model of Rice predicts a directional anisotropy in that, along a given GB, brittle cleavage is favored for crack propagation in one direction while dislocation emission from the crack tip is preferred in the opposite direction. This prediction is validated by atomistic simulations of crack propagation along coherent GBs, including View the MathML source and View the MathML source. However, for incoherent GBs such as View the MathML source and View the MathML source, such directional anisotropy in intrinsic ductility is not observed; instead, we show that dislocation emission is favored in both crack propagation directions. The reason for this discrepancy is shown to be dislocation emission at a distance ahead of the crack tip along an incoherent GB, which violates the assumption in Rice’s model that dislocation emission occurs directly at the crack tip. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900812X

Damage evolution and domain-level anisotropy in metal/ceramic composites exhibiting lamellar microstructures / Siddhartha Roy in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2300–2312 Titre : Damage evolution and domain-level anisotropy in metal/ceramic composites exhibiting lamellar microstructures Type de document : texte imprimé Auteurs : Siddhartha Roy, Auteur ; Benjamin Butz, Auteur ; Alexander Wanner, Auteur Année de publication : 2011 Article en page(s) : pp. 2300–2312 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metal  matrix  composites  (MMC)  Compression  test  Scanning  electron  microscopy  Analytical  electron  microscopy Résumé : Aluminium/alumina composites based on ceramic preforms prepared via freeze-casting are examined. Domains composed of alternating but also interpenetrating ceramic and metallic lamellae are observed. Single-domain samples were extracted from composites processed under different conditions. In situ scanning electron microscopy analyses were carried out to investigate the damage evolution under compressive load. The composite is strong and brittle when loaded along directions parallel to the freezing direction. When compressed in other directions, the behavior is controlled by the soft metal. The plastic anisotropy is less pronounced than theoretical predictions for laminates, which is explained by the presence of bridges between the ceramic lamellae. Coating the preform with Cu or Cu2O prior to melt infiltration reduces the compressive strengths of the composites. Transmission electron microscopy analysis shows that even in the case of a Cu coating a Cu2O layer is formed during processing, weakening the interface and preventing the dissolution of Cu in the aluminium alloy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900857X [article] Damage evolution and domain-level anisotropy in metal/ceramic composites exhibiting lamellar microstructures [texte imprimé] / Siddhartha Roy, Auteur ; Benjamin Butz, Auteur ; Alexander Wanner, Auteur . - 2011 . - pp. 2300–2312. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2300–2312 Mots-clés : Metal  matrix  composites  (MMC)  Compression  test  Scanning  electron  microscopy  Analytical  electron  microscopy Résumé : Aluminium/alumina composites based on ceramic preforms prepared via freeze-casting are examined. Domains composed of alternating but also interpenetrating ceramic and metallic lamellae are observed. Single-domain samples were extracted from composites processed under different conditions. In situ scanning electron microscopy analyses were carried out to investigate the damage evolution under compressive load. The composite is strong and brittle when loaded along directions parallel to the freezing direction. When compressed in other directions, the behavior is controlled by the soft metal. The plastic anisotropy is less pronounced than theoretical predictions for laminates, which is explained by the presence of bridges between the ceramic lamellae. Coating the preform with Cu or Cu2O prior to melt infiltration reduces the compressive strengths of the composites. Transmission electron microscopy analysis shows that even in the case of a Cu coating a Cu2O layer is formed during processing, weakening the interface and preventing the dissolution of Cu in the aluminium alloy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900857X

Grain size–wear rate relationship for titanium in liquid nitrogen environment / Aditya Jain in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2313–2323 Titre : Grain size–wear rate relationship for titanium in liquid nitrogen environment Type de document : texte imprimé Auteurs : Aditya Jain, Auteur ; B. Basu, Auteur ; B.V. Manoj Kumar, Auteur Année de publication : 2011 Article en page(s) : pp. 2313–2323 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Wear  Grain  size  Tribolayer  Ti Résumé : This paper presents the results of sliding wear experiments conducted on high-purity titanium (Ti) against bearing-steel in liquid nitrogen (LN2; boiling point: 77 K) environment. Ti samples of three different grain sizes (9, 17 and 37 μm) were used to study the effect of hardness, derived from grain refinement as well as cryogenic test temperature, on the wear properties of Ti. In our experiments, a constant load of 10 N and sliding speeds of 0.67, 1.11 and 4.19 m s−1 were used. The coefficient of friction (COF) for this tribo-couple varied between ∼0.25 and ∼0.50. While a steady state was always achieved, a peak in the COF was always noted in case of coarse-grain (37 μm) Ti tested at a sliding speed of 4.19 m s−1. Under the investigated sliding conditions, the wear rate was found to be of the order of 10−3–10−4 mm3 N−1 m−1. The lowest wear rate was recorded in the fine-grain (9 μm) Ti at the highest sliding speed of 4.19 m s−1. The critical analysis of the worn surface topography reveals that the reduced wear rate was due to the formation of adherent and strain-hardened tribolayer. In order to show various dominant wear mechanisms of Ti, a qualitative map was developed in sliding speed–grain size space. Substructure evaluation revealed the formation of a dense array of deformation twins because of the plastic deformation, which often resulted in the subdivision of grains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008593 [article] Grain size–wear rate relationship for titanium in liquid nitrogen environment [texte imprimé] / Aditya Jain, Auteur ; B. Basu, Auteur ; B.V. Manoj Kumar, Auteur . - 2011 . - pp. 2313–2323. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2313–2323 Mots-clés : Wear  Grain  size  Tribolayer  Ti Résumé : This paper presents the results of sliding wear experiments conducted on high-purity titanium (Ti) against bearing-steel in liquid nitrogen (LN2; boiling point: 77 K) environment. Ti samples of three different grain sizes (9, 17 and 37 μm) were used to study the effect of hardness, derived from grain refinement as well as cryogenic test temperature, on the wear properties of Ti. In our experiments, a constant load of 10 N and sliding speeds of 0.67, 1.11 and 4.19 m s−1 were used. The coefficient of friction (COF) for this tribo-couple varied between ∼0.25 and ∼0.50. While a steady state was always achieved, a peak in the COF was always noted in case of coarse-grain (37 μm) Ti tested at a sliding speed of 4.19 m s−1. Under the investigated sliding conditions, the wear rate was found to be of the order of 10−3–10−4 mm3 N−1 m−1. The lowest wear rate was recorded in the fine-grain (9 μm) Ti at the highest sliding speed of 4.19 m s−1. The critical analysis of the worn surface topography reveals that the reduced wear rate was due to the formation of adherent and strain-hardened tribolayer. In order to show various dominant wear mechanisms of Ti, a qualitative map was developed in sliding speed–grain size space. Substructure evaluation revealed the formation of a dense array of deformation twins because of the plastic deformation, which often resulted in the subdivision of grains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008593

Studies on recrystallization of single-phase copper alloys by resistance measurements / J. Freudenberger in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2324–2329 Titre : Studies on recrystallization of single-phase copper alloys by resistance measurements Type de document : texte imprimé Auteurs : J. Freudenberger, Auteur ; A. Kauffmann, Auteur ; H. Klauß, Auteur Année de publication : 2011 Article en page(s) : pp. 2324–2329 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Recrystallization  Copper  alloys  Low  temperature  deformation Résumé : Copper-based solid solutions with different contents of solute elements (Zn, Al, Ga, Sn, Ge) were deformed at room temperature and at liquid nitrogen temperature. The recrystallization behaviour of these alloys has been investigated by means of dynamic and isothermal measurements of the resistivity (ρ). Variations of dρ/dT from View the MathML source are interpreted in terms of changes in defect densities by recovery and recrystallization. Deviations from a linear temperature dependence of the resistivity increase with increasing solute concentration. This deviation (i.e. Δρrec as determined at room temperature) also depends on the stacking fault energy γ. We observe a 1/γ2-dependency of Δρrec which is also influenced by the deformation temperature. During deformation, γ controls the possibility of storing deformation energy in the form of dislocations and deformation twins. In combination with the general trend of alloying elements to shift recrystallization to higher temperatures, the recrystallization behaviour of single-phase copper alloys has been described qualitatively. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900860X [article] Studies on recrystallization of single-phase copper alloys by resistance measurements [texte imprimé] / J. Freudenberger, Auteur ; A. Kauffmann, Auteur ; H. Klauß, Auteur . - 2011 . - pp. 2324–2329. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2324–2329 Mots-clés : Recrystallization  Copper  alloys  Low  temperature  deformation Résumé : Copper-based solid solutions with different contents of solute elements (Zn, Al, Ga, Sn, Ge) were deformed at room temperature and at liquid nitrogen temperature. The recrystallization behaviour of these alloys has been investigated by means of dynamic and isothermal measurements of the resistivity (ρ). Variations of dρ/dT from View the MathML source are interpreted in terms of changes in defect densities by recovery and recrystallization. Deviations from a linear temperature dependence of the resistivity increase with increasing solute concentration. This deviation (i.e. Δρrec as determined at room temperature) also depends on the stacking fault energy γ. We observe a 1/γ2-dependency of Δρrec which is also influenced by the deformation temperature. During deformation, γ controls the possibility of storing deformation energy in the form of dislocations and deformation twins. In combination with the general trend of alloying elements to shift recrystallization to higher temperatures, the recrystallization behaviour of single-phase copper alloys has been described qualitatively. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900860X

Towards smooth and pure iron nanowires grown by electrodeposition in self-organized alumina membranes / V. Haehnel in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2330–2337 Titre : Towards smooth and pure iron nanowires grown by electrodeposition in self-organized alumina membranes Type de document : texte imprimé Auteurs : V. Haehnel, Auteur ; S. Fähler, Auteur ; P. Schaaf, Auteur Année de publication : 2011 Article en page(s) : pp. 2330–2337 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Electrodeposition  AAO  template  Iron  nanowires  Mössbauer  spectroscopy Résumé : Due to their high aspect ratio, magnetic nanowires are interesting for various applications. Fe nanowires are of particular interest due to their high magnetization, which suggests high shape anisotropy is possible. Here, we show how the electrodeposition process can be adapted to the constraints of a high aspect ratio template in order to approach an ideal behaviour of smooth and pure Fe nanowires. An adjustment of the Fe2+ concentration and the addition of H3BO3 result in smooth and continuous nanowires; saturation polarization is achieved, together with an anisotropy field of up to 70% compared to pure Fe. Mössbauer spectroscopy reveals a negligible amount of impurities. Together with magnetic measurements we show that shape anisotropy aligns the preferential magnetization axis along the wire axis. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008611 [article] Towards smooth and pure iron nanowires grown by electrodeposition in self-organized alumina membranes [texte imprimé] / V. Haehnel, Auteur ; S. Fähler, Auteur ; P. Schaaf, Auteur . - 2011 . - pp. 2330–2337. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2330–2337 Mots-clés : Electrodeposition  AAO  template  Iron  nanowires  Mössbauer  spectroscopy Résumé : Due to their high aspect ratio, magnetic nanowires are interesting for various applications. Fe nanowires are of particular interest due to their high magnetization, which suggests high shape anisotropy is possible. Here, we show how the electrodeposition process can be adapted to the constraints of a high aspect ratio template in order to approach an ideal behaviour of smooth and pure Fe nanowires. An adjustment of the Fe2+ concentration and the addition of H3BO3 result in smooth and continuous nanowires; saturation polarization is achieved, together with an anisotropy field of up to 70% compared to pure Fe. Mössbauer spectroscopy reveals a negligible amount of impurities. Together with magnetic measurements we show that shape anisotropy aligns the preferential magnetization axis along the wire axis. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008611

Carbon supersaturation of ferrite in a nanocrystalline bainitic steel / F. G. Caballero in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2338–2343 Titre : Carbon supersaturation of ferrite in a nanocrystalline bainitic steel Type de document : texte imprimé Auteurs : F. G. Caballero, Auteur ; M. K. Miller, Auteur ; C. Garcia-Mateo, Auteur Année de publication : 2011 Article en page(s) : pp. 2338–2343 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Steels  Bainite  Three-dimensional  atom  probe  (3DAP) Résumé : The extremely slow transformation kinetics of a nanocrystalline bainitic steel allows the carbon content of the bainitic ferrite away from any carbon-enriched regions such as dislocations and boundaries to be determined by atom probe tomography as the bainite transformation progresses at 200 °C. A high level of carbon, well above that expected from para-equilibrium with austenite, has been detected in solid solution in bainitic ferrite at the early stage of transformation. Results provide strong evidence that bainite transformation is essentially displacive in nature so that the newly formed bainitic ferrite retains much of the carbon content of the parent austenite. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008623 [article] Carbon supersaturation of ferrite in a nanocrystalline bainitic steel [texte imprimé] / F. G. Caballero, Auteur ; M. K. Miller, Auteur ; C. Garcia-Mateo, Auteur . - 2011 . - pp. 2338–2343. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2338–2343 Mots-clés : Steels  Bainite  Three-dimensional  atom  probe  (3DAP) Résumé : The extremely slow transformation kinetics of a nanocrystalline bainitic steel allows the carbon content of the bainitic ferrite away from any carbon-enriched regions such as dislocations and boundaries to be determined by atom probe tomography as the bainite transformation progresses at 200 °C. A high level of carbon, well above that expected from para-equilibrium with austenite, has been detected in solid solution in bainitic ferrite at the early stage of transformation. Results provide strong evidence that bainite transformation is essentially displacive in nature so that the newly formed bainitic ferrite retains much of the carbon content of the parent austenite. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008623

Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading / M.L. Young in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2344–2354 Titre : Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading Type de document : texte imprimé Auteurs : M.L. Young, Auteur ; M.F.-X. Wagner, Auteur ; J. Frenzel, Auteur Année de publication : 2011 Article en page(s) : pp. 2344–2354 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : NiTi  shape-memory  alloys  Tensile  testing  Stress-induced  martensite  Synchrotron  radiation  Localized  deformation Résumé : An ultrafine-grained pseudoelastic NiTi shape-memory alloy wire with 50.9 at.% Ni was examined using synchrotron X-ray diffraction during in situ uniaxial tensile loading (up to 1 GPa) and unloading. Both macroscopic stress–strain measurements and volume-averaged lattice strains are reported and discussed. The loading behavior is described in terms of elasto-plastic deformation of austenite, emergence of R phase, stress-induced martensitic transformation, and elasto-plastic deformation, grain reorientation and detwinning of martensite. The unloading behavior is described in terms of stress relaxation and reverse plasticity of martensite, reverse transformation of martensite to austenite due to stress relaxation, and stress relaxation of austenite. Microscopically, lattice strains in various crystallographic directions in the austenitic B2, martensitic R, and martensitic B19′ phases are examined during loading and unloading. It is shown that the phase transformation occurs in a localized manner along the gage length at the plateau stress. Phase volume fractions and lattice strains in various crystallographic reflections in the austenite and martensite phases are examined over two transition regions between austenite and martensite, which have a width on the order of the wire diameter. Anisotropic effects observed in various crystallographic reflections of the austenitic phase are also discussed. The results contribute to a better understanding of the tensile loading behavior, both macroscopically and microscopically, of NiTi shape-memory alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008635 [article] Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading [texte imprimé] / M.L. Young, Auteur ; M.F.-X. Wagner, Auteur ; J. Frenzel, Auteur . - 2011 . - pp. 2344–2354. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2344–2354 Mots-clés : NiTi  shape-memory  alloys  Tensile  testing  Stress-induced  martensite  Synchrotron  radiation  Localized  deformation Résumé : An ultrafine-grained pseudoelastic NiTi shape-memory alloy wire with 50.9 at.% Ni was examined using synchrotron X-ray diffraction during in situ uniaxial tensile loading (up to 1 GPa) and unloading. Both macroscopic stress–strain measurements and volume-averaged lattice strains are reported and discussed. The loading behavior is described in terms of elasto-plastic deformation of austenite, emergence of R phase, stress-induced martensitic transformation, and elasto-plastic deformation, grain reorientation and detwinning of martensite. The unloading behavior is described in terms of stress relaxation and reverse plasticity of martensite, reverse transformation of martensite to austenite due to stress relaxation, and stress relaxation of austenite. Microscopically, lattice strains in various crystallographic directions in the austenitic B2, martensitic R, and martensitic B19′ phases are examined during loading and unloading. It is shown that the phase transformation occurs in a localized manner along the gage length at the plateau stress. Phase volume fractions and lattice strains in various crystallographic reflections in the austenite and martensite phases are examined over two transition regions between austenite and martensite, which have a width on the order of the wire diameter. Anisotropic effects observed in various crystallographic reflections of the austenitic phase are also discussed. The results contribute to a better understanding of the tensile loading behavior, both macroscopically and microscopically, of NiTi shape-memory alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008635

Tensile and compressive behavior of tungsten, molybdenum, tantalum and niobium at the nanoscale / Ju-Young Kim in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2355–2363 Titre : Tensile and compressive behavior of tungsten, molybdenum, tantalum and niobium at the nanoscale Type de document : texte imprimé Auteurs : Ju-Young Kim, Auteur ; Dongchan Jang, Auteur ; Julia R. Greer, Auteur Année de publication : 2011 Article en page(s) : pp. 2355–2363 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoscale  plasticity  Tension  test  Compression  test  Plastic  deformation Résumé : In situ nanomechanical tests are carried out to investigate the tensile and compressive behavior of 〈0 0 1〉-oriented body-centered cubic (bcc) metals W, Mo, Ta and Nb with nanometer dimensions. We find that the strength of these metals exhibits strong size dependence. The compressive size effect in Nb, as evaluated by the log–log slope of strength vs. nanopillar diameter, is −0.93, a factor of 2.1 greater than that for the other three metals W, Mo and Ta (−0.44). In tension, however, Ta and Nb show higher size effect slopes (−0.80 and −0.77) as compared with W and Mo (−0.58 and −0.43). We also report that while the yield strength of these metals is a strong function of size, the strain-hardening behavior does not present any size-dependent trends. We further discuss the effects of strain-rate on deformation behavior and provide transmission electron microscopy analysis of microstructural evolution in the same Mo nanopillar before and after compression. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008647 [article] Tensile and compressive behavior of tungsten, molybdenum, tantalum and niobium at the nanoscale [texte imprimé] / Ju-Young Kim, Auteur ; Dongchan Jang, Auteur ; Julia R. Greer, Auteur . - 2011 . - pp. 2355–2363. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2355–2363 Mots-clés : Nanoscale  plasticity  Tension  test  Compression  test  Plastic  deformation Résumé : In situ nanomechanical tests are carried out to investigate the tensile and compressive behavior of 〈0 0 1〉-oriented body-centered cubic (bcc) metals W, Mo, Ta and Nb with nanometer dimensions. We find that the strength of these metals exhibits strong size dependence. The compressive size effect in Nb, as evaluated by the log–log slope of strength vs. nanopillar diameter, is −0.93, a factor of 2.1 greater than that for the other three metals W, Mo and Ta (−0.44). In tension, however, Ta and Nb show higher size effect slopes (−0.80 and −0.77) as compared with W and Mo (−0.58 and −0.43). We also report that while the yield strength of these metals is a strong function of size, the strain-hardening behavior does not present any size-dependent trends. We further discuss the effects of strain-rate on deformation behavior and provide transmission electron microscopy analysis of microstructural evolution in the same Mo nanopillar before and after compression. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008647

A study of a new type of deviation from the Kurdjumov–Sachs orientation relationship in face-centered-cubic/body-centered-cubic transformation system / Y. Meng in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2364–2375 Titre : A study of a new type of deviation from the Kurdjumov–Sachs orientation relationship in face-centered-cubic/body-centered-cubic transformation system Type de document : texte imprimé Auteurs : Y. Meng, Auteur ; X.-F. Gu, Auteur ; W.-Z. Zhang, Auteur Année de publication : 2011 Article en page(s) : pp. 2364–2375 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Orientation  relationship  Habit  plane  O-line  Near-coincidence  sites  Precipitation  crystallography Résumé : Slight deviations from the Kurdjumov–Sachs orientation relationship (KS OR) are often observed in the face-centered-cubic/body-centered-cubic (fcc/bcc) transformation systems, and some can be explained on the premise of the parallelism of either the close-packed planes (CPPs) or the close-packed directions (CPDs), as suggested in many models. This work investigates a new OR which deviates from the KS OR in both the CPPs and the CPDs. This OR is determined by requiring the habit plane to contain a single set of periodic dislocations along the invariant line lying in the CPPs. The angles of the double deviation, as a function of the lattice parameter ratio, are proved to be identical. The calculated results for a stainless steel are in good agreement with the experimental observations. The habit plane for the new OR is associated with slightly lower interfacial energy than those with the ORs of single deviation, which might explain the preference by nature in the present case. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008659 [article] A study of a new type of deviation from the Kurdjumov–Sachs orientation relationship in face-centered-cubic/body-centered-cubic transformation system [texte imprimé] / Y. Meng, Auteur ; X.-F. Gu, Auteur ; W.-Z. Zhang, Auteur . - 2011 . - pp. 2364–2375. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2364–2375 Mots-clés : Orientation  relationship  Habit  plane  O-line  Near-coincidence  sites  Precipitation  crystallography Résumé : Slight deviations from the Kurdjumov–Sachs orientation relationship (KS OR) are often observed in the face-centered-cubic/body-centered-cubic (fcc/bcc) transformation systems, and some can be explained on the premise of the parallelism of either the close-packed planes (CPPs) or the close-packed directions (CPDs), as suggested in many models. This work investigates a new OR which deviates from the KS OR in both the CPPs and the CPDs. This OR is determined by requiring the habit plane to contain a single set of periodic dislocations along the invariant line lying in the CPPs. The angles of the double deviation, as a function of the lattice parameter ratio, are proved to be identical. The calculated results for a stainless steel are in good agreement with the experimental observations. The habit plane for the new OR is associated with slightly lower interfacial energy than those with the ORs of single deviation, which might explain the preference by nature in the present case. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008659

Interfacial diffusion in Cu with a gradient nanostructured surface layer / Z.B. Wang in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2376–2386 Titre : Interfacial diffusion in Cu with a gradient nanostructured surface layer Type de document : texte imprimé Auteurs : Z.B. Wang, Auteur ; K. Lu, Auteur ; G. Wilde, Auteur Année de publication : 2011 Article en page(s) : pp. 2376–2386 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanostructured  material  Surface  mechanical  attrition  treatment  Diffusion  Grain  boundaries  Twin  boundaries Résumé : A graded microstructure was produced in the surface layer of a pure Cu sample by means of surface mechanical attrition treatment (SMAT) [Wang K, Tao NR, Liu G, Lu J, Lu K. Acta Mater 2006;54:5281.]. The diffusion behavior of 63Ni in such a surface layer was investigated by the radiotracer technique at temperatures <438 K. It is shown that the effective diffusivity in the top 10 μm surface layer is more than 2 orders of magnitude higher than that along conventional high-angle grain boundaries (HAGB) in Cu of similar purity. The diffusion rate increases gradually with increasing depth up to 30–50 μm, and then decreases with further increasing depth. The enhanced diffusivities reveal higher-energy states of various interfaces in the SMAT surface layer. The excess free energy of HAGB in this layer is estimated to be ∼30% higher than that of conventional grain boundaries. An apparent retardation of the effective diffusion rate in the top 25 μm surface layer is induced by tracer leakage into numerous twin-boundary-like interfaces, while the gradual decrease in interface excess free energy correlates with the observed decrease in diffusivity in the subsurface layer at depths exceeding 50 μm. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008702 [article] Interfacial diffusion in Cu with a gradient nanostructured surface layer [texte imprimé] / Z.B. Wang, Auteur ; K. Lu, Auteur ; G. Wilde, Auteur . - 2011 . - pp. 2376–2386. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2376–2386 Mots-clés : Nanostructured  material  Surface  mechanical  attrition  treatment  Diffusion  Grain  boundaries  Twin  boundaries Résumé : A graded microstructure was produced in the surface layer of a pure Cu sample by means of surface mechanical attrition treatment (SMAT) [Wang K, Tao NR, Liu G, Lu J, Lu K. Acta Mater 2006;54:5281.]. The diffusion behavior of 63Ni in such a surface layer was investigated by the radiotracer technique at temperatures <438 K. It is shown that the effective diffusivity in the top 10 μm surface layer is more than 2 orders of magnitude higher than that along conventional high-angle grain boundaries (HAGB) in Cu of similar purity. The diffusion rate increases gradually with increasing depth up to 30–50 μm, and then decreases with further increasing depth. The enhanced diffusivities reveal higher-energy states of various interfaces in the SMAT surface layer. The excess free energy of HAGB in this layer is estimated to be ∼30% higher than that of conventional grain boundaries. An apparent retardation of the effective diffusion rate in the top 25 μm surface layer is induced by tracer leakage into numerous twin-boundary-like interfaces, while the gradual decrease in interface excess free energy correlates with the observed decrease in diffusivity in the subsurface layer at depths exceeding 50 μm. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008702

Extending cluster dynamics to concentrated and disordered alloys / F. Berthier in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2387–2398 Titre : Extending cluster dynamics to concentrated and disordered alloys : The linear-chain case Type de document : texte imprimé Auteurs : F. Berthier, Auteur ; I. Braems, Auteur ; E. Maras, Auteur Année de publication : 2011 Article en page(s) : pp. 2387–2398 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cluster  dynamics  Kinetic  Monte  Carlo  simulations  Linear  chain  Local  order  Nanowires Résumé : Cluster dynamics is often used in the multi-scale procedure to link atomistic and macroscopic approaches, in particular when modelling precipitation processes. To extend its use to concentrated alloys, it is necessary to take into account accurately the exclusion zones and their overlap. By investigating the one-dimensional case, one obtains an exact formula for these zones, and its generalization to higher dimensions is proposed. By integrating cluster fragmentation/coagulation processes into cluster dynamics equations, a perfect agreement between atomistic simulations (Kinetic Monte Carlo) and cluster dynamics is reached on the whole range of concentrations for kinetics which govern microstructure in one dimension. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008714 [article] Extending cluster dynamics to concentrated and disordered alloys : The linear-chain case [texte imprimé] / F. Berthier, Auteur ; I. Braems, Auteur ; E. Maras, Auteur . - 2011 . - pp. 2387–2398. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2387–2398 Mots-clés : Cluster  dynamics  Kinetic  Monte  Carlo  simulations  Linear  chain  Local  order  Nanowires Résumé : Cluster dynamics is often used in the multi-scale procedure to link atomistic and macroscopic approaches, in particular when modelling precipitation processes. To extend its use to concentrated alloys, it is necessary to take into account accurately the exclusion zones and their overlap. By investigating the one-dimensional case, one obtains an exact formula for these zones, and its generalization to higher dimensions is proposed. By integrating cluster fragmentation/coagulation processes into cluster dynamics equations, a perfect agreement between atomistic simulations (Kinetic Monte Carlo) and cluster dynamics is reached on the whole range of concentrations for kinetics which govern microstructure in one dimension. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008714

Three-dimensional analysis of microstructures in titanium / Hemant Sharma in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2399–2407 Titre : Three-dimensional analysis of microstructures in titanium Type de document : texte imprimé Auteurs : Hemant Sharma, Auteur ; Stefan M.C. Van Bohemen, Auteur ; Roumen H. Petrov, Auteur Année de publication : 2011 Article en page(s) : pp. 2399–2407 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : EBSD  Titanium  alloys  Grain  morphology  Serial  sectioning Résumé : Samples of Ti–4.3Fe–6.7Mo–1.5Al were isothermally annealed in the temperature range of 730–780 °C for various times to study the β–α transformation. Serial sectioning in conjunction with both optical and EBSD analyses was applied to determine the three-dimensional (3-D) morphologies of primary α phase. The 3-D analysis proved to be essential for characterization of the complex morphologies of α grains and consequently for the identification of growth behavior. It showed that nucleation of α grains takes place at β–β grain boundaries and significant branching takes place after initial growth of α grains along β–β grain boundaries. Some branches grow inside the β grain interior. The branching behavior is shown to interact with β–β grain boundaries, leading to a zig-zag morphology. The presented 3-D analysis of α grains and their influence on β–β grain boundaries clearly show that 2-D observations of the microstructural morphologies are not sufficient to adequately represent the transformation characteristics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008726 [article] Three-dimensional analysis of microstructures in titanium [texte imprimé] / Hemant Sharma, Auteur ; Stefan M.C. Van Bohemen, Auteur ; Roumen H. Petrov, Auteur . - 2011 . - pp. 2399–2407. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2399–2407 Mots-clés : EBSD  Titanium  alloys  Grain  morphology  Serial  sectioning Résumé : Samples of Ti–4.3Fe–6.7Mo–1.5Al were isothermally annealed in the temperature range of 730–780 °C for various times to study the β–α transformation. Serial sectioning in conjunction with both optical and EBSD analyses was applied to determine the three-dimensional (3-D) morphologies of primary α phase. The 3-D analysis proved to be essential for characterization of the complex morphologies of α grains and consequently for the identification of growth behavior. It showed that nucleation of α grains takes place at β–β grain boundaries and significant branching takes place after initial growth of α grains along β–β grain boundaries. Some branches grow inside the β grain interior. The branching behavior is shown to interact with β–β grain boundaries, leading to a zig-zag morphology. The presented 3-D analysis of α grains and their influence on β–β grain boundaries clearly show that 2-D observations of the microstructural morphologies are not sufficient to adequately represent the transformation characteristics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008726

In situ observations of solidification processes in γ-TiAl alloys by synchrotron radiation / Olga Shuleshova in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2408–2418 Titre : In situ observations of solidification processes in γ-TiAl alloys by synchrotron radiation Type de document : texte imprimé Auteurs : Olga Shuleshova, Auteur ; Dirk Holland-Moritz, Auteur ; Wolfgang Löser, Auteur Année de publication : 2011 Article en page(s) : pp. 2408–2418 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Titanium  aluminides  Phase  transformations  Synchrotron  radiation  Thermodynamics Résumé : In situ observations of phase transformations involving melts are performed using energy-dispersive diffraction of synchrotron X-rays on electromagnetically levitated γ-TiAl alloys containing Nb. The determined primary solidification modes, confirmed by microstructure analysis, delivered new reliable data about the boundary of the α(Ti) solidification domain, which differs in the various Ti–Al–Nb phase diagram descriptions. These data have been used for a reassessment of the thermodynamic database of the ternary Ti–Al–Nb system. The new description realistically reflects the experimental findings. Liquidus and solidus temperatures determined by the pyrometric method agree fairly well with the calculated values. Direct experimental information on the nature of the reactions along the univariant lines is provided. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008738 [article] In situ observations of solidification processes in γ-TiAl alloys by synchrotron radiation [texte imprimé] / Olga Shuleshova, Auteur ; Dirk Holland-Moritz, Auteur ; Wolfgang Löser, Auteur . - 2011 . - pp. 2408–2418. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2408–2418 Mots-clés : Titanium  aluminides  Phase  transformations  Synchrotron  radiation  Thermodynamics Résumé : In situ observations of phase transformations involving melts are performed using energy-dispersive diffraction of synchrotron X-rays on electromagnetically levitated γ-TiAl alloys containing Nb. The determined primary solidification modes, confirmed by microstructure analysis, delivered new reliable data about the boundary of the α(Ti) solidification domain, which differs in the various Ti–Al–Nb phase diagram descriptions. These data have been used for a reassessment of the thermodynamic database of the ternary Ti–Al–Nb system. The new description realistically reflects the experimental findings. Liquidus and solidus temperatures determined by the pyrometric method agree fairly well with the calculated values. Direct experimental information on the nature of the reactions along the univariant lines is provided. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008738

An assessment of the contributing factors to the superior properties of a nanostructured steel using in situ high-energy X-ray diffraction / S. Cheng in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2419–2429 Titre : An assessment of the contributing factors to the superior properties of a nanostructured steel using in situ high-energy X-ray diffraction Type de document : texte imprimé Auteurs : S. Cheng, Auteur ; Y.D. Wang, Auteur ; H. Choo, Auteur Année de publication : 2011 Article en page(s) : pp. 2419–2429 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Synchrotron  high-energy  X-ray  diffraction  Nanostructured  steel  Martensitic  transformation  Luders  banding  Texture Résumé : In contrast to most nanostructured materials, outstanding mechanical property has been demonstrated in a nanostructured metastable austenitic steel, owing to the new characteristics of deformation-induced martensitic transformation. In this paper, by employing an in situ high-energy X-ray diffraction technique, we explore these characteristics by examining factors from the load partitioning, Lüders banding, to texture development. It was found that the martensitic transformation was mainly driven through Lüders band propagation. Marked load transfer takes place from austenite to martensite as Lüders band propagates, and continues into the homogeneous deformation regime. The texture development is mostly contributed by martensitic transformation, but dislocation-based plasticity also plays a role. The effective load partitioning along with the deformability of martensite promotes sample ductility. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900874X [article] An assessment of the contributing factors to the superior properties of a nanostructured steel using in situ high-energy X-ray diffraction [texte imprimé] / S. Cheng, Auteur ; Y.D. Wang, Auteur ; H. Choo, Auteur . - 2011 . - pp. 2419–2429. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2419–2429 Mots-clés : Synchrotron  high-energy  X-ray  diffraction  Nanostructured  steel  Martensitic  transformation  Luders  banding  Texture Résumé : In contrast to most nanostructured materials, outstanding mechanical property has been demonstrated in a nanostructured metastable austenitic steel, owing to the new characteristics of deformation-induced martensitic transformation. In this paper, by employing an in situ high-energy X-ray diffraction technique, we explore these characteristics by examining factors from the load partitioning, Lüders banding, to texture development. It was found that the martensitic transformation was mainly driven through Lüders band propagation. Marked load transfer takes place from austenite to martensite as Lüders band propagates, and continues into the homogeneous deformation regime. The texture development is mostly contributed by martensitic transformation, but dislocation-based plasticity also plays a role. The effective load partitioning along with the deformability of martensite promotes sample ductility. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900874X

Effect of a high magnetic field on the Al–Al3Ni fiber eutectic during directional solidification / Xi Li in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2430–2441 Titre : Effect of a high magnetic field on the Al–Al3Ni fiber eutectic during directional solidification Type de document : texte imprimé Auteurs : Xi Li, Auteur ; Yves Fautrelle, Auteur ; Zhongming Ren, Auteur Année de publication : 2011 Article en page(s) : pp. 2430–2441 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : High  magnetic  field  Al–Al3Ni  fiber  eutectic  Eutectic  fiber  spacing  Preferred  orientation  relationship Résumé : The effect of a high magnetic field on the morphology and preferred orientation relationship of the Al–Al3Ni fiber eutectic has been investigated during directional solidification. Results indicate that an application of a high magnetic field has decreased the eutectic spacing and caused the appearance of the band-like structure. Moreover, it has been found that a high magnetic field has changed the preferred orientation relationship of the Al–Al3Ni eutectic. Indeed, the application of a 12 T high magnetic field has caused the preferred orientation relationship of the Al{3 3 1}//Al3Ni{0 0 1}; Al [1 1 0]//Al3Ni[0 1 0] in the case of no magnetic field to transfer into the Al{0 0 1}//Al3Ni{1 0 2}; Al[1 0 2]// Al3Ni[0 1 0]. Further, in order to investigate the nucleation and growing mechanism of the Al–Al3Ni eutectic, the growth and morphology relationships between the Al–Al3Ni eutectic and the primary Al and Al3Ni phases have been investigated during volume and directional solidification, respectively. It has been found that the growth and orientation of the primary Al3Ni phase and the heating flow extraction direction have determined the growth of the Al–Al3Ni eutectic. This implies that the Al–Al3Ni eutectic growth may be capable of being controlled by adjusting the alignment of the Al3Ni eutectic phase and the heating flow extraction direction. The above experimental results have been discussed from the effect of a high magnetic field on the diffusion process and the epitaxial growth of the eutectic. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008751 [article] Effect of a high magnetic field on the Al–Al3Ni fiber eutectic during directional solidification [texte imprimé] / Xi Li, Auteur ; Yves Fautrelle, Auteur ; Zhongming Ren, Auteur . - 2011 . - pp. 2430–2441. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2430–2441 Mots-clés : High  magnetic  field  Al–Al3Ni  fiber  eutectic  Eutectic  fiber  spacing  Preferred  orientation  relationship Résumé : The effect of a high magnetic field on the morphology and preferred orientation relationship of the Al–Al3Ni fiber eutectic has been investigated during directional solidification. Results indicate that an application of a high magnetic field has decreased the eutectic spacing and caused the appearance of the band-like structure. Moreover, it has been found that a high magnetic field has changed the preferred orientation relationship of the Al–Al3Ni eutectic. Indeed, the application of a 12 T high magnetic field has caused the preferred orientation relationship of the Al{3 3 1}//Al3Ni{0 0 1}; Al [1 1 0]//Al3Ni[0 1 0] in the case of no magnetic field to transfer into the Al{0 0 1}//Al3Ni{1 0 2}; Al[1 0 2]// Al3Ni[0 1 0]. Further, in order to investigate the nucleation and growing mechanism of the Al–Al3Ni eutectic, the growth and morphology relationships between the Al–Al3Ni eutectic and the primary Al and Al3Ni phases have been investigated during volume and directional solidification, respectively. It has been found that the growth and orientation of the primary Al3Ni phase and the heating flow extraction direction have determined the growth of the Al–Al3Ni eutectic. This implies that the Al–Al3Ni eutectic growth may be capable of being controlled by adjusting the alignment of the Al3Ni eutectic phase and the heating flow extraction direction. The above experimental results have been discussed from the effect of a high magnetic field on the diffusion process and the epitaxial growth of the eutectic. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008751

Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples / H. Cheng in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2442–2451 Titre : Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples : Effect of Y-doping Type de document : texte imprimé Auteurs : H. Cheng, Auteur ; H.S. Caram, Auteur ; W.E. Schiesser, Auteur Année de publication : 2011 Article en page(s) : pp. 2442–2451 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Oxidation  Grain-boundary  diffusion  Ceramics  Grain  boundaries  Dopants Résumé : Novel wedge-geometry, dual-layer alumina samples, both undoped and 500 ppm Y3+-doped, were studied in the temperature regime 1250–1400 °C to determine the effect of Y3+ on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants (k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by a factor of ∼5 (at 1300 °C), and increases the corresponding activation enthalpy for oxidation from 407 ± 20 to 486 ± 34 kJ mol−1. Microstructural observations suggested that yttrium also slows Ni outward diffusion. A comparison of the different k values revealed that, at 1300 °C, the presence of Ni alone enhances transport by a factor of ∼2 relative to undoped alumina. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008763 [article] Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples : Effect of Y-doping [texte imprimé] / H. Cheng, Auteur ; H.S. Caram, Auteur ; W.E. Schiesser, Auteur . - 2011 . - pp. 2442–2451. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2442–2451 Mots-clés : Oxidation  Grain-boundary  diffusion  Ceramics  Grain  boundaries  Dopants Résumé : Novel wedge-geometry, dual-layer alumina samples, both undoped and 500 ppm Y3+-doped, were studied in the temperature regime 1250–1400 °C to determine the effect of Y3+ on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants (k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by a factor of ∼5 (at 1300 °C), and increases the corresponding activation enthalpy for oxidation from 407 ± 20 to 486 ± 34 kJ mol−1. Microstructural observations suggested that yttrium also slows Ni outward diffusion. A comparison of the different k values revealed that, at 1300 °C, the presence of Ni alone enhances transport by a factor of ∼2 relative to undoped alumina. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008763

Out-of-plane stresses arising from grain interactions in textured thin films / Aaron M. Vodnick in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2452–2463 Titre : Out-of-plane stresses arising from grain interactions in textured thin films Type de document : texte imprimé Auteurs : Aaron M. Vodnick, Auteur ; David E. Nowak, Auteur ; Stephane Labat, Auteur Année de publication : 2011 Article en page(s) : pp. 2452–2463 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thin  films  X-ray  diffraction  Synchrotron  radiation  Mechanical  properties Résumé : Face-centered-cubic thin films often have mixed (1 1 1)/(1 0 0) fiber texture. These orientations can have very different in-plane stiffnesses, leading to the possibility of significant stress inhomogeneities. Previous X-ray studies appeared to confirm this, reporting much higher stresses in (1 1 1)- than (1 0 0)-oriented grains. In those studies, the stress in the film normal direction was assumed to be zero everywhere, but Poisson effects suggest that out-of-plane stresses may be significant. Here, an X-ray data analysis that allows for out-of-plane stresses is presented and applied to X-ray data taken from a Cu film. The in-plane stress is shown to be homogeneous, and significant out-of-plane stresses arise. This analysis is shown to be more accurate and more consistent with the microstructure than previous methods. Consideration of inhomogeneous triaxial stress states is seen to be critical to understanding mechanical behavior of films with mixed fiber texture. Models for yielding and texture development are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008775 [article] Out-of-plane stresses arising from grain interactions in textured thin films [texte imprimé] / Aaron M. Vodnick, Auteur ; David E. Nowak, Auteur ; Stephane Labat, Auteur . - 2011 . - pp. 2452–2463. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2452–2463 Mots-clés : Thin  films  X-ray  diffraction  Synchrotron  radiation  Mechanical  properties Résumé : Face-centered-cubic thin films often have mixed (1 1 1)/(1 0 0) fiber texture. These orientations can have very different in-plane stiffnesses, leading to the possibility of significant stress inhomogeneities. Previous X-ray studies appeared to confirm this, reporting much higher stresses in (1 1 1)- than (1 0 0)-oriented grains. In those studies, the stress in the film normal direction was assumed to be zero everywhere, but Poisson effects suggest that out-of-plane stresses may be significant. Here, an X-ray data analysis that allows for out-of-plane stresses is presented and applied to X-ray data taken from a Cu film. The in-plane stress is shown to be homogeneous, and significant out-of-plane stresses arise. This analysis is shown to be more accurate and more consistent with the microstructure than previous methods. Consideration of inhomogeneous triaxial stress states is seen to be critical to understanding mechanical behavior of films with mixed fiber texture. Models for yielding and texture development are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008775

On the mechanism of twin formation in Fe–Mn–C TWIP steels / H. Idrissi in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2464–2476 Titre : On the mechanism of twin formation in Fe–Mn–C TWIP steels Type de document : texte imprimé Auteurs : H. Idrissi, Auteur ; K. Renard, Auteur ; L. Ryelandt, Auteur Année de publication : 2011 Article en page(s) : pp. 2464–2476 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : TWIP  steels  Dislocations  Twinning  mechanisms  Transmission  electron  microscopy Résumé : Although it is well known that Fe–Mn–C TWIP steels exhibit high work-hardening rates, the elementary twinning mechanisms controlling the plastic deformation of these steels have still not been characterized. The aim of the present study is to analyse the extended defects related to the twinning occurrence using transmission electron microscopy. Based on these observations, the very early stage of twin nucleation can be attributed to the pole mechanism with deviation proposed by Cohen and Weertman or to the model of Miura, Takamura and Narita, while the twin growth is controlled by the pole mechanism proposed by Venables. High densities of sessile Frank dislocations are observed within the twins at the early stage of deformation, which can affect the growth and the stability of the twins, but also the strength of these twins and their interactions with the gliding dislocations present in the matrix. This experimental evidence is discussed and compared to recent results in order to relate the defects analysis to the macroscopic behaviour of this category of material. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008787 [article] On the mechanism of twin formation in Fe–Mn–C TWIP steels [texte imprimé] / H. Idrissi, Auteur ; K. Renard, Auteur ; L. Ryelandt, Auteur . - 2011 . - pp. 2464–2476. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2464–2476 Mots-clés : TWIP  steels  Dislocations  Twinning  mechanisms  Transmission  electron  microscopy Résumé : Although it is well known that Fe–Mn–C TWIP steels exhibit high work-hardening rates, the elementary twinning mechanisms controlling the plastic deformation of these steels have still not been characterized. The aim of the present study is to analyse the extended defects related to the twinning occurrence using transmission electron microscopy. Based on these observations, the very early stage of twin nucleation can be attributed to the pole mechanism with deviation proposed by Cohen and Weertman or to the model of Miura, Takamura and Narita, while the twin growth is controlled by the pole mechanism proposed by Venables. High densities of sessile Frank dislocations are observed within the twins at the early stage of deformation, which can affect the growth and the stability of the twins, but also the strength of these twins and their interactions with the gliding dislocations present in the matrix. This experimental evidence is discussed and compared to recent results in order to relate the defects analysis to the macroscopic behaviour of this category of material. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008787

Effects of temperature on structure and mobility of the 〈1 0 0〉 edge dislocation in body-centred cubic iron / D.A. Terentyev in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2477–2482 Titre : Effects of temperature on structure and mobility of the 〈1 0 0〉 edge dislocation in body-centred cubic iron Type de document : texte imprimé Auteurs : D.A. Terentyev, Auteur ; Yu. N. Osetsky, Auteur ; D. J. Bacon, Auteur Année de publication : 2011 Article en page(s) : pp. 2477–2482 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bcc  metals  Dislocation  loops  Hardening  〈1  0〉  dislocation Résumé : Dislocation segments with Burgers vector b = 〈1 0 0〉 are formed during deformation of body-centred-cubic (bcc) metals by the interaction between dislocations with b = 1/2〈1 1 1〉. Such segments are also created by reactions between dislocations and dislocation loops in irradiated bcc metals. The obstacle resistance produced by these segments on gliding dislocations is controlled by their mobility, which is determined in turn by the atomic structure of their cores. The core structure of a straight 〈1 0 0〉 edge dislocation is investigated here by atomic-scale computer simulation for α-iron using three different interatomic potentials. At low temperature the dislocation has a non-planar core consisting of two 1/2〈1 1 1〉 fractional dislocations with atomic disregistry spread on planes inclined to the main glide plane. Increasing temperature modifies this core structure and so reduces the critical applied shear stress for glide of the 〈1 0 0〉 dislocation. It is concluded that the response of the 〈1 0 0〉 edge dislocation to temperature or applied stress determines specific reaction pathways occurring between a moving dislocation and 1/2〈1 1 1〉 dislocation loops. The implications of this for plastic flow in unirradiated and irradiated ferritic materials are discussed and demonstrated by examples. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008817 [article] Effects of temperature on structure and mobility of the 〈1 0 0〉 edge dislocation in body-centred cubic iron [texte imprimé] / D.A. Terentyev, Auteur ; Yu. N. Osetsky, Auteur ; D. J. Bacon, Auteur . - 2011 . - pp. 2477–2482. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2477–2482 Mots-clés : Bcc  metals  Dislocation  loops  Hardening  〈1  0〉  dislocation Résumé : Dislocation segments with Burgers vector b = 〈1 0 0〉 are formed during deformation of body-centred-cubic (bcc) metals by the interaction between dislocations with b = 1/2〈1 1 1〉. Such segments are also created by reactions between dislocations and dislocation loops in irradiated bcc metals. The obstacle resistance produced by these segments on gliding dislocations is controlled by their mobility, which is determined in turn by the atomic structure of their cores. The core structure of a straight 〈1 0 0〉 edge dislocation is investigated here by atomic-scale computer simulation for α-iron using three different interatomic potentials. At low temperature the dislocation has a non-planar core consisting of two 1/2〈1 1 1〉 fractional dislocations with atomic disregistry spread on planes inclined to the main glide plane. Increasing temperature modifies this core structure and so reduces the critical applied shear stress for glide of the 〈1 0 0〉 dislocation. It is concluded that the response of the 〈1 0 0〉 edge dislocation to temperature or applied stress determines specific reaction pathways occurring between a moving dislocation and 1/2〈1 1 1〉 dislocation loops. The implications of this for plastic flow in unirradiated and irradiated ferritic materials are discussed and demonstrated by examples. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008817

Synthesis of metallic glass composites using phase separation phenomena / H. J. Chang in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2483–2491 Titre : Synthesis of metallic glass composites using phase separation phenomena Type de document : texte imprimé Auteurs : H. J. Chang, Auteur ; W. Yook, Auteur ; E.S. Park, Auteur Année de publication : 2011 Article en page(s) : pp. 2483–2491 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metallic  glass  Phase  separation  Composite  Spinodal  decomposition Résumé : Phase separation phenomena in metallic glass systems have been explored by thermodynamic calculation and experimental method in the present study. Miscibility gap and spinodal curve for liquid phase in Gd–Ti–Al–Co/Cu systems have been calculated using the CALPHAD method. Based on the calculation result, various types of phase separation phenomena have been observed experimentally. Basically two types of structure are observed: interconnected-type structure by spinodal decomposition; and droplet-type structure by nucleation and growth mechanism. Multi-step phase separation occurs during cooling from the liquid, forming a hierarchical length scale composite structure. Depending on the glass-forming ability of the separated liquid phase, amorphous/amorphous or amorphous/crystalline composite structure can be obtained. The present study shows that there are several factors such as critical temperature, asymmetry and composition range of the spinodal curve which affect scale and morphology of the microstructure after phase separation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008829 [article] Synthesis of metallic glass composites using phase separation phenomena [texte imprimé] / H. J. Chang, Auteur ; W. Yook, Auteur ; E.S. Park, Auteur . - 2011 . - pp. 2483–2491. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2483–2491 Mots-clés : Metallic  glass  Phase  separation  Composite  Spinodal  decomposition Résumé : Phase separation phenomena in metallic glass systems have been explored by thermodynamic calculation and experimental method in the present study. Miscibility gap and spinodal curve for liquid phase in Gd–Ti–Al–Co/Cu systems have been calculated using the CALPHAD method. Based on the calculation result, various types of phase separation phenomena have been observed experimentally. Basically two types of structure are observed: interconnected-type structure by spinodal decomposition; and droplet-type structure by nucleation and growth mechanism. Multi-step phase separation occurs during cooling from the liquid, forming a hierarchical length scale composite structure. Depending on the glass-forming ability of the separated liquid phase, amorphous/amorphous or amorphous/crystalline composite structure can be obtained. The present study shows that there are several factors such as critical temperature, asymmetry and composition range of the spinodal curve which affect scale and morphology of the microstructure after phase separation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008829

Microstructure evolution of 6061 O Al alloy during ultrasonic consolidation / E. Mariani in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - 2492–2503 Titre : Microstructure evolution of 6061 O Al alloy during ultrasonic consolidation : An insight from electron backscatter diffraction Type de document : texte imprimé Auteurs : E. Mariani, Auteur ; E. Ghassemieh, Auteur Année de publication : 2011 Article en page(s) : 2492–2503 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Electron  backscatter  diffraction  (EBSD)  Ultrasonic  consolidation  (UC)  Recrystallized  microstructure  Continuous  dynamic  recrystallization  (CDRX)  Aluminium  alloys Résumé : 6061 O Al alloy foils were welded to form monolithic and SiC fibre-embedded samples using the ultrasonic consolidation (UC) process. Contact pressures of 135, 155 and 175 MPa were investigated at 20 kHz frequency, 50% of the oscillation amplitude, 34.5 mm s−1 sonotrode velocity and 20 °C. Deformed microstructures were analysed using electron backscatter diffraction (EBSD). At all contact pressures deformation occurs by non-steady state dislocation glide. Dynamic recovery is active in the upper and lower foils. Friction at the welding interface, instantaneous internal temperatures (0.5–0.8 of the melting temperature, Tm), contact pressure and fast strain rates result in transient microstructures and grain size reduction by continuous dynamic recrystallization (CDRX) within the bonding zone. Bonding occurs by local grain boundary migration, which allows diffusion and atom interlocking across the contact between two clean surfaces. Textures weaken with increasing contact pressure due to increased strain hardening and different grain rotation rates. High contact pressures enhance dynamic recovery and CDRX. Deformation around the fibre is intense within 50 μm and extends to 450 μm from it. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008830 [article] Microstructure evolution of 6061 O Al alloy during ultrasonic consolidation : An insight from electron backscatter diffraction [texte imprimé] / E. Mariani, Auteur ; E. Ghassemieh, Auteur . - 2011 . - 2492–2503. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - 2492–2503 Mots-clés : Electron  backscatter  diffraction  (EBSD)  Ultrasonic  consolidation  (UC)  Recrystallized  microstructure  Continuous  dynamic  recrystallization  (CDRX)  Aluminium  alloys Résumé : 6061 O Al alloy foils were welded to form monolithic and SiC fibre-embedded samples using the ultrasonic consolidation (UC) process. Contact pressures of 135, 155 and 175 MPa were investigated at 20 kHz frequency, 50% of the oscillation amplitude, 34.5 mm s−1 sonotrode velocity and 20 °C. Deformed microstructures were analysed using electron backscatter diffraction (EBSD). At all contact pressures deformation occurs by non-steady state dislocation glide. Dynamic recovery is active in the upper and lower foils. Friction at the welding interface, instantaneous internal temperatures (0.5–0.8 of the melting temperature, Tm), contact pressure and fast strain rates result in transient microstructures and grain size reduction by continuous dynamic recrystallization (CDRX) within the bonding zone. Bonding occurs by local grain boundary migration, which allows diffusion and atom interlocking across the contact between two clean surfaces. Textures weaken with increasing contact pressure due to increased strain hardening and different grain rotation rates. High contact pressures enhance dynamic recovery and CDRX. Deformation around the fibre is intense within 50 μm and extends to 450 μm from it. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008830

Mechanical properties at the nanometer scale of GDC and YSZ used as electrolytes for solid oxide fuel cells / M. Morales in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2504–2509 Titre : Mechanical properties at the nanometer scale of GDC and YSZ used as electrolytes for solid oxide fuel cells Type de document : texte imprimé Auteurs : M. Morales, Auteur ; J.J. Roa, Auteur ; X. G. Capdevila, Auteur Année de publication : 2011 Article en page(s) : pp. 2504–2509 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : SOFC  Gadolinia  doped-ceria  Yttria-stabilized  zirconia  Mechanical  properties  Nanoindentation Résumé : The Young’s modulus (E), hardness (H) and fracture toughness (KIC) of various compositions of gadolinia doped-ceria (GDC, GdxCe1−xO2−x/2, 0.1 ⩽ x ⩽ 0.2) and yttria-stabilized zirconia (YSZ, Y0.08Zr0.92O1.96) electrolytes were investigated by nanoindentation. All samples were produced by the sol–gel method, formed by uniaxial pressure and sintered at 1400 °C. In order to determine the mechanical properties, a Berkovich diamond tip was employed at applied loads of 5, 10, 30, 100 and 500 mN. The results were interpreted by the Oliver–Pharr method and values of KIC were determined using the method of Palmqvist cracks. The residual imprints were observed by field emission scanning electron microscopy. The results obtained showed that the H, E and KIC of GDC decreased with increasing gadolinia concentration, due to the oxygen vacancies generated by the dopant addition. As a result, the mechanical properties of GDC were significantly lower than those of YSZ electrolyte. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008842 [article] Mechanical properties at the nanometer scale of GDC and YSZ used as electrolytes for solid oxide fuel cells [texte imprimé] / M. Morales, Auteur ; J.J. Roa, Auteur ; X. G. Capdevila, Auteur . - 2011 . - pp. 2504–2509. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2504–2509 Mots-clés : SOFC  Gadolinia  doped-ceria  Yttria-stabilized  zirconia  Mechanical  properties  Nanoindentation Résumé : The Young’s modulus (E), hardness (H) and fracture toughness (KIC) of various compositions of gadolinia doped-ceria (GDC, GdxCe1−xO2−x/2, 0.1 ⩽ x ⩽ 0.2) and yttria-stabilized zirconia (YSZ, Y0.08Zr0.92O1.96) electrolytes were investigated by nanoindentation. All samples were produced by the sol–gel method, formed by uniaxial pressure and sintered at 1400 °C. In order to determine the mechanical properties, a Berkovich diamond tip was employed at applied loads of 5, 10, 30, 100 and 500 mN. The results were interpreted by the Oliver–Pharr method and values of KIC were determined using the method of Palmqvist cracks. The residual imprints were observed by field emission scanning electron microscopy. The results obtained showed that the H, E and KIC of GDC decreased with increasing gadolinia concentration, due to the oxygen vacancies generated by the dopant addition. As a result, the mechanical properties of GDC were significantly lower than those of YSZ electrolyte. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008842

LaMg11 with a giant unit cell synthesized by hydrogen metallurgy: Crystal structure and hydrogenation behavior / Roman V. Denys in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2510–2519 Titre : LaMg11 with a giant unit cell synthesized by hydrogen metallurgy: Crystal structure and hydrogenation behavior Type de document : texte imprimé Auteurs : Roman V. Denys, Auteur ; Andrey A. Poletaev, Auteur ; Jan Ketil Solberg, Auteur Année de publication : 2011 Article en page(s) : pp. 2510–2519 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Powder  processing  Synchrotron  X-ray  diffraction  Hydrides  Magnesium  alloys  Hydrogen  storage Résumé : We have successfully applied a hydrogen metallurgy synthesis to yield LaMg12−x intermetallic at 500 °C. During a vacuum thermal desorption from the LaH3–MgH2 nanocomposite prepared by reactive ball milling in H2, hydrogen desorption from the La dihydride occurred via a mechanism of cooperative phase transformation at temperatures being 400° lower than the desorption from pure LaH2. The crystal structure of the intermetallic was determined by synchrotron X-ray diffraction (SR XRD). The orthorhombic LaMg12−x has a giant unit cell, the volume of which exceeds 8000 Å3. In situ SR XRD studies showed the fine details of the hydrogen desorption process with several parallel and consecutive transformation steps. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008957 [article] LaMg11 with a giant unit cell synthesized by hydrogen metallurgy: Crystal structure and hydrogenation behavior [texte imprimé] / Roman V. Denys, Auteur ; Andrey A. Poletaev, Auteur ; Jan Ketil Solberg, Auteur . - 2011 . - pp. 2510–2519. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2510–2519 Mots-clés : Powder  processing  Synchrotron  X-ray  diffraction  Hydrides  Magnesium  alloys  Hydrogen  storage Résumé : We have successfully applied a hydrogen metallurgy synthesis to yield LaMg12−x intermetallic at 500 °C. During a vacuum thermal desorption from the LaH3–MgH2 nanocomposite prepared by reactive ball milling in H2, hydrogen desorption from the La dihydride occurred via a mechanism of cooperative phase transformation at temperatures being 400° lower than the desorption from pure LaH2. The crystal structure of the intermetallic was determined by synchrotron X-ray diffraction (SR XRD). The orthorhombic LaMg12−x has a giant unit cell, the volume of which exceeds 8000 Å3. In situ SR XRD studies showed the fine details of the hydrogen desorption process with several parallel and consecutive transformation steps. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008957

Comparison of residual microstructures associated with impact craters in Al–Sc and Al–Ti alloys / Yicong Ye in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2520–2526 Titre : Comparison of residual microstructures associated with impact craters in Al–Sc and Al–Ti alloys Type de document : texte imprimé Auteurs : Yicong Ye, Auteur ; Peijie Li, Auteur ; L.S. Novikov, Auteur Année de publication : 2011 Article en page(s) : pp. 2520–2526 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminium  alloys  High-speed  impact  Microstructure  Precipitation Résumé : Al–Sc and Al–Ti semi-infinite targets were impacted by high-speed projectiles with velocities of 0.8, 2 and 4 km s−1, respectively. The results show that deep columned craters with hemispherical bottoms were formed in the Al–Ti target, while near-hemispheroidal or relatively shallower craters formed in the Al–Sc alloy. It is concluded that different microstructures of Al–Sc and Al–Ti alloys, including different grain sizes and secondary particles precipitated in the matrix, result in their having greatly different capabilities of resisting impact. Residual microstructures of different samples are further discussed. It is possible that, due to the very large amount of energy imported into the target by high-speed impact, secondary Al3Sc lost its coherency and consequently recrystallization occurred. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008969 [article] Comparison of residual microstructures associated with impact craters in Al–Sc and Al–Ti alloys [texte imprimé] / Yicong Ye, Auteur ; Peijie Li, Auteur ; L.S. Novikov, Auteur . - 2011 . - pp. 2520–2526. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2520–2526 Mots-clés : Aluminium  alloys  High-speed  impact  Microstructure  Precipitation Résumé : Al–Sc and Al–Ti semi-infinite targets were impacted by high-speed projectiles with velocities of 0.8, 2 and 4 km s−1, respectively. The results show that deep columned craters with hemispherical bottoms were formed in the Al–Ti target, while near-hemispheroidal or relatively shallower craters formed in the Al–Sc alloy. It is concluded that different microstructures of Al–Sc and Al–Ti alloys, including different grain sizes and secondary particles precipitated in the matrix, result in their having greatly different capabilities of resisting impact. Residual microstructures of different samples are further discussed. It is possible that, due to the very large amount of energy imported into the target by high-speed impact, secondary Al3Sc lost its coherency and consequently recrystallization occurred. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008969

Dynamic grain growth and particle coarsening in Al–3.5Cu / O.V. Rofman in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2527–2534 Titre : Dynamic grain growth and particle coarsening in Al–3.5Cu Type de document : texte imprimé Auteurs : O.V. Rofman, Auteur ; P.S. Bate, Auteur Année de publication : 2011 Article en page(s) : pp. 2527–2534 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  growth  Coarsening  Aluminium Résumé : Grain growth and particle coarsening in Al–3.5Cu at a temperature of 450 °C has been studied. Plastic deformation of this Zener-pinned system at strain rates of 10−3 and 10−4 s−1 led to an increase in both the grain growth and particle coarsening rates. The results of mechanical tests and metallography, including in situ studies, showed that the material was deforming primarily by intragranular slip. The dynamic grain growth was ascribed to the geometric effect of deformation on the Zener pinning, and the rate sensitivity of the growth to the dynamic particle coarsening. The principal effect of deformation on particle coarsening was concluded to be increased diffusion due to the dislocation content. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008970 [article] Dynamic grain growth and particle coarsening in Al–3.5Cu [texte imprimé] / O.V. Rofman, Auteur ; P.S. Bate, Auteur . - 2011 . - pp. 2527–2534. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2527–2534 Mots-clés : Grain  growth  Coarsening  Aluminium Résumé : Grain growth and particle coarsening in Al–3.5Cu at a temperature of 450 °C has been studied. Plastic deformation of this Zener-pinned system at strain rates of 10−3 and 10−4 s−1 led to an increase in both the grain growth and particle coarsening rates. The results of mechanical tests and metallography, including in situ studies, showed that the material was deforming primarily by intragranular slip. The dynamic grain growth was ascribed to the geometric effect of deformation on the Zener pinning, and the rate sensitivity of the growth to the dynamic particle coarsening. The principal effect of deformation on particle coarsening was concluded to be increased diffusion due to the dislocation content. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008970

Crystallographic orientation and stress-amplitude dependence of damping in the martensite phase in textured Ti–Nb–Al shape memory alloy / T. Inamura in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2535–2544 Titre : Crystallographic orientation and stress-amplitude dependence of damping in the martensite phase in textured Ti–Nb–Al shape memory alloy Type de document : texte imprimé Auteurs : T. Inamura, Auteur ; Y. Yamamoto, Auteur ; H. Hosoda, Auteur Année de publication : 2011 Article en page(s) : pp. 2535–2544 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dynamic  mechanical  analysis  Shape  memory  alloys  Titanium  alloys  Damping  Martensitic  phase  transformation Résumé : The low-frequency damping (tanδ) of a strongly textured β-titanium shape memory alloy (SMA) was investigated by a dynamic mechanical analysis (DMA) in a tensile mode together with a tensile test and a crystallographic analysis of the transformation. In addition to the high background of tanδ in martensite, a broad tanδ peak with a relaxation-like character was found in the martensite phase similar to the Ti–Ni SMAs. There was a critical stress for the broad peak that corresponds to the stress to complete the martensite variant reorientation, whereas the high background of tanδ had no critical stress. This implies that the broad peak is generated through the long-range motion of twin boundaries. A guideline to estimate the orientation dependence of damping in textured SMAs is also proposed using the interaction energy between the external stress and the transformation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008982 [article] Crystallographic orientation and stress-amplitude dependence of damping in the martensite phase in textured Ti–Nb–Al shape memory alloy [texte imprimé] / T. Inamura, Auteur ; Y. Yamamoto, Auteur ; H. Hosoda, Auteur . - 2011 . - pp. 2535–2544. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2535–2544 Mots-clés : Dynamic  mechanical  analysis  Shape  memory  alloys  Titanium  alloys  Damping  Martensitic  phase  transformation Résumé : The low-frequency damping (tanδ) of a strongly textured β-titanium shape memory alloy (SMA) was investigated by a dynamic mechanical analysis (DMA) in a tensile mode together with a tensile test and a crystallographic analysis of the transformation. In addition to the high background of tanδ in martensite, a broad tanδ peak with a relaxation-like character was found in the martensite phase similar to the Ti–Ni SMAs. There was a critical stress for the broad peak that corresponds to the stress to complete the martensite variant reorientation, whereas the high background of tanδ had no critical stress. This implies that the broad peak is generated through the long-range motion of twin boundaries. A guideline to estimate the orientation dependence of damping in textured SMAs is also proposed using the interaction energy between the external stress and the transformation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008982

Effect of equal-channel angular pressing routes on high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy / Yang Gon Kim in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2545–2554 Titre : Effect of equal-channel angular pressing routes on high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy Type de document : texte imprimé Auteurs : Yang Gon Kim, Auteur ; Young Gun Ko, Auteur ; Dong Hyuk Shin, Auteur Année de publication : 2011 Article en page(s) : pp. 2545–2554 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminum  alloy  Ultra-fine  grain  Equal-channel  angular  pressing  Adiabatic  shear  band Résumé : The effect of equal-channel angular pressing (ECAP) route on the high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy was investigated. The 8-pass ECAPed specimens deformed via three different routes consisted of ultra-fine grains 0.5 μm in size, and contained a considerable amount of second-phase particles, which were fragmented and distributed in the matrix. In the torsion tests, the maximum shear stress significantly increased with increasing number of ECAP passes, while the maximum shear stress and fracture shear strain were lowest in the specimen deformed via route A among the three 8-pass ECAPed specimens. Observation of the deformed area beneath the fractured surface revealed the adiabatic shear bands of 100 μm in width in the specimen deformed via route A, which minimized the maximum shear stress and fracture shear strain, whereas they were hardly formed in the specimens deformed via route B or C. The formation of adiabatic shear bands was explained in terms of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008994 [article] Effect of equal-channel angular pressing routes on high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy [texte imprimé] / Yang Gon Kim, Auteur ; Young Gun Ko, Auteur ; Dong Hyuk Shin, Auteur . - 2011 . - pp. 2545–2554. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2545–2554 Mots-clés : Aluminum  alloy  Ultra-fine  grain  Equal-channel  angular  pressing  Adiabatic  shear  band Résumé : The effect of equal-channel angular pressing (ECAP) route on the high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy was investigated. The 8-pass ECAPed specimens deformed via three different routes consisted of ultra-fine grains 0.5 μm in size, and contained a considerable amount of second-phase particles, which were fragmented and distributed in the matrix. In the torsion tests, the maximum shear stress significantly increased with increasing number of ECAP passes, while the maximum shear stress and fracture shear strain were lowest in the specimen deformed via route A among the three 8-pass ECAPed specimens. Observation of the deformed area beneath the fractured surface revealed the adiabatic shear bands of 100 μm in width in the specimen deformed via route A, which minimized the maximum shear stress and fracture shear strain, whereas they were hardly formed in the specimens deformed via route B or C. The formation of adiabatic shear bands was explained in terms of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008994

The effect of the orientation of the basal plane on the mechanical loss in magnesium matrix composites studied by mechanical spectroscopy / A. S. M. F. Chowdhury in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2555–2563 Titre : The effect of the orientation of the basal plane on the mechanical loss in magnesium matrix composites studied by mechanical spectroscopy Type de document : texte imprimé Auteurs : A. S. M. F. Chowdhury, Auteur ; D. Mari, Auteur ; R. Schaller, Auteur Année de publication : 2011 Article en page(s) : pp. 2555–2563 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Liquid  infiltration  Metal  matrix  composites  Magnesium  Damping  Mechanical  spectroscopy Résumé : In metal matrix composites, thermal stresses are relaxed by either interface debonding, crack propagation or dislocation motion. The present paper shows that in the case of a magnesium matrix, interface thermal stresses are relaxed by dislocation motion in the basal plane (0 0 1) of the hexagonal structure. Different specimens were processed by a gas pressure infiltration method and the metallic matrix was oriented with respect to the interface by the Bridgman technique. Mechanical spectroscopy experiments show that the damping as well as the evolution of the relative shear modulus depend strongly on the orientation of the basal plane. The results are in good agreement with the theoretical model. The calculations show that the orientation of the glide plane influences the coupling between the thermal stress and the applied mechanical stress. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009008 [article] The effect of the orientation of the basal plane on the mechanical loss in magnesium matrix composites studied by mechanical spectroscopy [texte imprimé] / A. S. M. F. Chowdhury, Auteur ; D. Mari, Auteur ; R. Schaller, Auteur . - 2011 . - pp. 2555–2563. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2555–2563 Mots-clés : Liquid  infiltration  Metal  matrix  composites  Magnesium  Damping  Mechanical  spectroscopy Résumé : In metal matrix composites, thermal stresses are relaxed by either interface debonding, crack propagation or dislocation motion. The present paper shows that in the case of a magnesium matrix, interface thermal stresses are relaxed by dislocation motion in the basal plane (0 0 1) of the hexagonal structure. Different specimens were processed by a gas pressure infiltration method and the metallic matrix was oriented with respect to the interface by the Bridgman technique. Mechanical spectroscopy experiments show that the damping as well as the evolution of the relative shear modulus depend strongly on the orientation of the basal plane. The results are in good agreement with the theoretical model. The calculations show that the orientation of the glide plane influences the coupling between the thermal stress and the applied mechanical stress. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009008

Effects of drawing on the tensile fracture strength and its reliability of small-sized metallic glasses / Wu, Y. in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2564–2576 Titre : Effects of drawing on the tensile fracture strength and its reliability of small-sized metallic glasses Type de document : texte imprimé Auteurs : Wu, Y., Auteur ; H.H. Wu, Auteur ; X.D. Hui, Auteur Année de publication : 2011 Article en page(s) : pp. 2564–2576 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metallic  glasses  Drawing  Tension  test  Strength  reliability Résumé : The effects of drawing on the structure and mechanical properties of a Co-based metallic glass under tension were thoroughly investigated. Surface changes induced by drawing, including removal of surface flaws, surface chemical homogenization and generation of compressive residual stress tend to increase the fracture strength, whilst open volumes created during drawing, particularly nano-voids, are likely to soften the wires. Initially, the surface changes are decisive factors, but as drawing proceeds, the open volumes gradually become dominant, yielding a maximum fracture strength in the wires with an area reduction ratio of 22%. Moreover, it was found that the fracture strength reliability was enhanced by the drawing, which is due not only to the surface perfection but also to the increase of plastic deformation capability, manifested by the decrease in the activation energy of individual shear transformation zones. Our results imply that the drawing technique could be a promising approach to continuously producing small-sized glassy wires with improved overall properties. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900901X [article] Effects of drawing on the tensile fracture strength and its reliability of small-sized metallic glasses [texte imprimé] / Wu, Y., Auteur ; H.H. Wu, Auteur ; X.D. Hui, Auteur . - 2011 . - pp. 2564–2576. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2564–2576 Mots-clés : Metallic  glasses  Drawing  Tension  test  Strength  reliability Résumé : The effects of drawing on the structure and mechanical properties of a Co-based metallic glass under tension were thoroughly investigated. Surface changes induced by drawing, including removal of surface flaws, surface chemical homogenization and generation of compressive residual stress tend to increase the fracture strength, whilst open volumes created during drawing, particularly nano-voids, are likely to soften the wires. Initially, the surface changes are decisive factors, but as drawing proceeds, the open volumes gradually become dominant, yielding a maximum fracture strength in the wires with an area reduction ratio of 22%. Moreover, it was found that the fracture strength reliability was enhanced by the drawing, which is due not only to the surface perfection but also to the increase of plastic deformation capability, manifested by the decrease in the activation energy of individual shear transformation zones. Our results imply that the drawing technique could be a promising approach to continuously producing small-sized glassy wires with improved overall properties. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964540900901X

Effect of switching stresses on domain evolution during quasi-static crack growth in a ferroelastic single crystal / Peter Neumeister in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2577–2584 Titre : Effect of switching stresses on domain evolution during quasi-static crack growth in a ferroelastic single crystal Type de document : texte imprimé Auteurs : Peter Neumeister, Auteur ; Hannes Kessler, Auteur ; Herbert Balke, Auteur Année de publication : 2011 Article en page(s) : pp. 2577–2584 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fracture  toughening  Ferroelastic  domain  switching  Switching  stress  Ferroelastic  single  crystal Résumé : The present paper demonstrates the effect of switching stresses on domain evolution and fracture toughening during quasi-static crack growth in elastically isotropic ferroelastic single crystals with transversally isotropic ferroelastic strains. With a simple switching algorithm and crack propagation procedure, domain evolution is simulated in an exemplary material with semi-infinite crack under mode I loading, starting from a mono-domain configuration. Domain reorientation is found to be strongly affected by switching stresses, which therefore have to be considered in the context of domain evolution modelling and fracture toughening. Before the onset of crack growth a needle-like domain is formed at the tip of the stationary crack, but this does not effect the crack tip stress intensity factor. Elongation of this domain during the onset of crack growth causes a large increase of the fracture toughness. Domain separation in a later stage results in toughness reduction. The subsequent domain evolution indicates a periodic formation of needle-like domains as observed in soft ferroelastic materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009021 [article] Effect of switching stresses on domain evolution during quasi-static crack growth in a ferroelastic single crystal [texte imprimé] / Peter Neumeister, Auteur ; Hannes Kessler, Auteur ; Herbert Balke, Auteur . - 2011 . - pp. 2577–2584. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2577–2584 Mots-clés : Fracture  toughening  Ferroelastic  domain  switching  Switching  stress  Ferroelastic  single  crystal Résumé : The present paper demonstrates the effect of switching stresses on domain evolution and fracture toughening during quasi-static crack growth in elastically isotropic ferroelastic single crystals with transversally isotropic ferroelastic strains. With a simple switching algorithm and crack propagation procedure, domain evolution is simulated in an exemplary material with semi-infinite crack under mode I loading, starting from a mono-domain configuration. Domain reorientation is found to be strongly affected by switching stresses, which therefore have to be considered in the context of domain evolution modelling and fracture toughening. Before the onset of crack growth a needle-like domain is formed at the tip of the stationary crack, but this does not effect the crack tip stress intensity factor. Elongation of this domain during the onset of crack growth causes a large increase of the fracture toughness. Domain separation in a later stage results in toughness reduction. The subsequent domain evolution indicates a periodic formation of needle-like domains as observed in soft ferroelastic materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009021

Phase transformation in an yttrium–hydrogen system studied by TEM / K. Wang in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2585–2597 Titre : Phase transformation in an yttrium–hydrogen system studied by TEM Type de document : texte imprimé Auteurs : K. Wang, Auteur ; J.R. Hattrick-Simpers, Auteur ; L. A. Bendersky, Auteur Année de publication : 2011 Article en page(s) : pp. 2585–2597 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Yttrium  hydride  Phase  transformation  Thin-films  TEM  Ordering  of  hydrogen Résumé : Phase transformations in Pd-capped epitaxial yttrium films grown on (0 0 0 1) sapphire substrates covered with a Ti buffer layer and hydrogenated for different times were studied using transmission electron microscopy (TEM). For short hydrogen charging times, the phase transformation from α-Y to β-YH2 is associated with the nucleation and growth of two orientational variants, which after coalescence form twin-related lamellae of the β-YH2 phase with twin interfaces parallel to the substrate plane. Shockley partial dislocations are present at the twin boundaries; their glides during phase transformation are responsible for the formation of the twin lamellae. Superlattice reflections were observed for β-YH2, and the existence of a new long-range ordered superstoichiometric YH2+x phase was suggested. A structural model of the ordering based on the occupation of octahedral interstitial sites by H in a doubled cell of Y-face-centered cubic was offered. For samples hydrogenated for longer times, β-YH2-to-γ-YH3 phase transformation was accompanied by cracking along the twin boundaries, which eventually developed into a network of pores and caused significant swelling of the films. No γ-YH3 phase was observed directly in TEM because of its unstable nature under the high vacuum of a microscope column. The fully transformed YH3 films have over a 60% increase in its thickness, which is mostly accounted for by the high volume fraction of pores. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009033 [article] Phase transformation in an yttrium–hydrogen system studied by TEM [texte imprimé] / K. Wang, Auteur ; J.R. Hattrick-Simpers, Auteur ; L. A. Bendersky, Auteur . - 2011 . - pp. 2585–2597. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2585–2597 Mots-clés : Yttrium  hydride  Phase  transformation  Thin-films  TEM  Ordering  of  hydrogen Résumé : Phase transformations in Pd-capped epitaxial yttrium films grown on (0 0 0 1) sapphire substrates covered with a Ti buffer layer and hydrogenated for different times were studied using transmission electron microscopy (TEM). For short hydrogen charging times, the phase transformation from α-Y to β-YH2 is associated with the nucleation and growth of two orientational variants, which after coalescence form twin-related lamellae of the β-YH2 phase with twin interfaces parallel to the substrate plane. Shockley partial dislocations are present at the twin boundaries; their glides during phase transformation are responsible for the formation of the twin lamellae. Superlattice reflections were observed for β-YH2, and the existence of a new long-range ordered superstoichiometric YH2+x phase was suggested. A structural model of the ordering based on the occupation of octahedral interstitial sites by H in a doubled cell of Y-face-centered cubic was offered. For samples hydrogenated for longer times, β-YH2-to-γ-YH3 phase transformation was accompanied by cracking along the twin boundaries, which eventually developed into a network of pores and caused significant swelling of the films. No γ-YH3 phase was observed directly in TEM because of its unstable nature under the high vacuum of a microscope column. The fully transformed YH3 films have over a 60% increase in its thickness, which is mostly accounted for by the high volume fraction of pores. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009033

A study of the densification mechanisms during spark plasma sintering of zirconium (oxy-)carbide powders / M. Gendre in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2598–2609 Titre : A study of the densification mechanisms during spark plasma sintering of zirconium (oxy-)carbide powders Type de document : texte imprimé Auteurs : M. Gendre, Auteur ; A. Maître, Auteur ; G. Trolliard, Auteur Année de publication : 2011 Article en page(s) : pp. 2598–2609 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Carboreduction  Densification  mechanism  Zirconium  oxycarbide  Modeling  SPS Résumé : Zirconium oxycarbide powders with controlled composition ZrC0.94O0.05 were synthesized using the carboreduction of zirconia. They were further subjected to spark plasma sintering (SPS) under several applied loads (25, 50, 100 MPa). The densification mechanism of zirconium oxycarbide powders during the SPS was studied. An analytical model derived from creep deformation studies of ceramics was successfully applied to determine the mechanisms involved during the final stage of densification. These mechanisms were elucidated by evaluating the stress exponent (n) and the apparent activation energy (Ea) from the densification rate law. It was concluded that at low macroscopic applied stress (25 MPa), an intergranular glide mechanism (n ⩽ 2) governs the densification process, while a dislocation motion mechanism (n ⩾ 3) operates at higher applied load (100 MPa). Transmission electron microscopy observations confirm theses results. The samples treated at low applied stress appear almost free of dislocations, whereas samples sintered at high applied stress present a high dislocation density, forming sub-grain boundaries. High values of apparent activation energy (e.g. 687–774 kJ mol−1) are reached irrespective of the applied load, indicating that both mechanisms mentioned above are assisted by the zirconium lattice diffusion which thus appears to be the rate-limiting step for densification. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009045 [article] A study of the densification mechanisms during spark plasma sintering of zirconium (oxy-)carbide powders [texte imprimé] / M. Gendre, Auteur ; A. Maître, Auteur ; G. Trolliard, Auteur . - 2011 . - pp. 2598–2609. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2598–2609 Mots-clés : Carboreduction  Densification  mechanism  Zirconium  oxycarbide  Modeling  SPS Résumé : Zirconium oxycarbide powders with controlled composition ZrC0.94O0.05 were synthesized using the carboreduction of zirconia. They were further subjected to spark plasma sintering (SPS) under several applied loads (25, 50, 100 MPa). The densification mechanism of zirconium oxycarbide powders during the SPS was studied. An analytical model derived from creep deformation studies of ceramics was successfully applied to determine the mechanisms involved during the final stage of densification. These mechanisms were elucidated by evaluating the stress exponent (n) and the apparent activation energy (Ea) from the densification rate law. It was concluded that at low macroscopic applied stress (25 MPa), an intergranular glide mechanism (n ⩽ 2) governs the densification process, while a dislocation motion mechanism (n ⩾ 3) operates at higher applied load (100 MPa). Transmission electron microscopy observations confirm theses results. The samples treated at low applied stress appear almost free of dislocations, whereas samples sintered at high applied stress present a high dislocation density, forming sub-grain boundaries. High values of apparent activation energy (e.g. 687–774 kJ mol−1) are reached irrespective of the applied load, indicating that both mechanisms mentioned above are assisted by the zirconium lattice diffusion which thus appears to be the rate-limiting step for densification. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009045

Strain mapping in a deformation-twinned nanocrystalline Pd grain / H. Rösner in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2610–2620 Titre : Strain mapping in a deformation-twinned nanocrystalline Pd grain Type de document : texte imprimé Auteurs : H. Rösner, Auteur ; N. Boucharat, Auteur ; K.A. Padmanabhan, Auteur Année de publication : 2011 Article en page(s) : pp. 2610–2620 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Strain  mapping  Nanocrystalline  plasticity  Twinning  High-resolution  electron  microscopy Résumé : Strain in a deformation-twinned nanocrystalline Pd sample of about 24 nm grain size was mapped by means of geometric phase analysis based on an individual high-resolution transmission electron microscopy image. The in-plane components of the strain tensor were calculated and charted. Strains with magnitudes of about 0.8% were found in the grain interior. Twins and matrix were significantly distorted relative to each other (by about 3° on average) and showed a strong rotation gradient from top to bottom, revealing that the whole grain is bent. An estimate of the strain energy stored in the Pd grain yielded a value of View the MathML source. Based on the strain distribution observed, a temporal deformation scenario has been developed. In our judgement, deformation twins had formed first and subsequently dislocations were activated, most likely by the misfit strain/stress concentrations generated by the twins themselves. The interaction of the dislocations with the twin boundaries left behind Shockley partials and this accounted for the strain concentrations finally observed along the twin boundaries. It is concluded that in the temporal evolution of deformation in a nanocrystalline material, twinning must be by far the fastest deformation mode, which accounts for the abundance of deformation twins, especially at high strain rates. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009057 [article] Strain mapping in a deformation-twinned nanocrystalline Pd grain [texte imprimé] / H. Rösner, Auteur ; N. Boucharat, Auteur ; K.A. Padmanabhan, Auteur . - 2011 . - pp. 2610–2620. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2610–2620 Mots-clés : Strain  mapping  Nanocrystalline  plasticity  Twinning  High-resolution  electron  microscopy Résumé : Strain in a deformation-twinned nanocrystalline Pd sample of about 24 nm grain size was mapped by means of geometric phase analysis based on an individual high-resolution transmission electron microscopy image. The in-plane components of the strain tensor were calculated and charted. Strains with magnitudes of about 0.8% were found in the grain interior. Twins and matrix were significantly distorted relative to each other (by about 3° on average) and showed a strong rotation gradient from top to bottom, revealing that the whole grain is bent. An estimate of the strain energy stored in the Pd grain yielded a value of View the MathML source. Based on the strain distribution observed, a temporal deformation scenario has been developed. In our judgement, deformation twins had formed first and subsequently dislocations were activated, most likely by the misfit strain/stress concentrations generated by the twins themselves. The interaction of the dislocations with the twin boundaries left behind Shockley partials and this accounted for the strain concentrations finally observed along the twin boundaries. It is concluded that in the temporal evolution of deformation in a nanocrystalline material, twinning must be by far the fastest deformation mode, which accounts for the abundance of deformation twins, especially at high strain rates. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009057

The origin of stresses in magnetron-sputtered thin films with zone T structures / R. Daniel in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2621–2633 Titre : The origin of stresses in magnetron-sputtered thin films with zone T structures Type de document : texte imprimé Auteurs : R. Daniel, Auteur ; K.J. Martinschitz, Auteur ; J. Keckes, Auteur Année de publication : 2011 Article en page(s) : pp. 2621–2633 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cr  CrN  Residual  stress  Film  growth  Structure Résumé : In order to understand the origin of the residual stress state in thin films and its thickness dependence, the structure–stress relation of magnetron-sputtered Cr and CrN layers with thicknesses ranging from 100 nm to 3 μm was investigated in detail. Based on correlations between the layer-thickness-dependent grain size, texture and morphology and the magnitude of the intrinsic and thermal components of the residual stress, a model is proposed that explains the origin of internal stresses of thin polycrystalline films with zone T structures. The model was further extended for the CrN/Cr dual-layer system, where the CrN top layer is epitaxially aligned with the underlying highly (2 0 0)-oriented Cr interlayer. It is shown for the first time that both the intrinsic and thermal stress components are thickness-dependent, which is associated with the layer microstructure. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009069 [article] The origin of stresses in magnetron-sputtered thin films with zone T structures [texte imprimé] / R. Daniel, Auteur ; K.J. Martinschitz, Auteur ; J. Keckes, Auteur . - 2011 . - pp. 2621–2633. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2621–2633 Mots-clés : Cr  CrN  Residual  stress  Film  growth  Structure Résumé : In order to understand the origin of the residual stress state in thin films and its thickness dependence, the structure–stress relation of magnetron-sputtered Cr and CrN layers with thicknesses ranging from 100 nm to 3 μm was investigated in detail. Based on correlations between the layer-thickness-dependent grain size, texture and morphology and the magnitude of the intrinsic and thermal components of the residual stress, a model is proposed that explains the origin of internal stresses of thin polycrystalline films with zone T structures. The model was further extended for the CrN/Cr dual-layer system, where the CrN top layer is epitaxially aligned with the underlying highly (2 0 0)-oriented Cr interlayer. It is shown for the first time that both the intrinsic and thermal stress components are thickness-dependent, which is associated with the layer microstructure. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009069

Atom probe study of sodium distribution in polycrystalline Cu(In,Ga)Se2 thin film / E. Cadel in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2634–2637 Titre : Atom probe study of sodium distribution in polycrystalline Cu(In,Ga)Se2 thin film Type de document : texte imprimé Auteurs : E. Cadel, Auteur ; N. Barreau, Auteur ; J. Kessler, Auteur Année de publication : 2011 Article en page(s) : pp. 2634–2637 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thin  film  solar  cell  Atom  probe  Sodium  Grain  boundary Résumé : This article reports the first investigations of CuIn1−xGaxSe2 (CIGSe) polycrystalline thin films by means of atom probe tomography. Attention is focused on the distribution of Na atoms within the films. Both Na-containing and Na-free CIGSe thin films have been investigated. When Na is available during the CIGSe coevaporation, it is observed to be mainly segregated at the grain boundaries of the films; however, it is also detected within the grains of CIGSe at very low concentration. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009070 [article] Atom probe study of sodium distribution in polycrystalline Cu(In,Ga)Se2 thin film [texte imprimé] / E. Cadel, Auteur ; N. Barreau, Auteur ; J. Kessler, Auteur . - 2011 . - pp. 2634–2637. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2634–2637 Mots-clés : Thin  film  solar  cell  Atom  probe  Sodium  Grain  boundary Résumé : This article reports the first investigations of CuIn1−xGaxSe2 (CIGSe) polycrystalline thin films by means of atom probe tomography. Attention is focused on the distribution of Na atoms within the films. Both Na-containing and Na-free CIGSe thin films have been investigated. When Na is available during the CIGSe coevaporation, it is observed to be mainly segregated at the grain boundaries of the films; however, it is also detected within the grains of CIGSe at very low concentration. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009070

Scaling the response of microscale compression molding of elemental Cu in the presence of dynamic recrystallization / Fanghua Mei in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2638–2645 Titre : Scaling the response of microscale compression molding of elemental Cu in the presence of dynamic recrystallization Type de document : texte imprimé Auteurs : Fanghua Mei, Auteur ; Ke Chen, Auteur ; J. Jiang, Auteur Année de publication : 2011 Article en page(s) : pp. 2638–2645 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Compression  test  Copper  High-temperature  deformation  Dynamic  recrystallization  Molding Résumé : Replication of metallic high-aspect-ratio microscale structures by direct compression molding is a promising microfabrication technique. In this paper, the micromolding response of elemental Cu is measured as a function of molding temperature. Companion tensile testing of macroscale Cu specimens was carried out at the corresponding molding temperatures. Microstructures of tensile tested macroscale Cu specimens and molded Cu specimens were characterized by combining focused ion beam (FIB) sectioning and imaging with ion-induced secondary electrons (ISEs). At all temperatures tested, measured tensile stress–strain curves for Cu show clear evidence for the occurrence of dynamic recrystallization (DRX) within macroscale tensile specimens. Additional FIB sectioning and imaging with ISEs of molded Cu specimens provide microstructural evidence for the occurrence of DRX during molding. The present results show that, even in the presence of DRX, an appropriate one-parameter scaling continues to reduce the molding response to a universal function independent of the molding temperature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009082 [article] Scaling the response of microscale compression molding of elemental Cu in the presence of dynamic recrystallization [texte imprimé] / Fanghua Mei, Auteur ; Ke Chen, Auteur ; J. Jiang, Auteur . - 2011 . - pp. 2638–2645. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2638–2645 Mots-clés : Compression  test  Copper  High-temperature  deformation  Dynamic  recrystallization  Molding Résumé : Replication of metallic high-aspect-ratio microscale structures by direct compression molding is a promising microfabrication technique. In this paper, the micromolding response of elemental Cu is measured as a function of molding temperature. Companion tensile testing of macroscale Cu specimens was carried out at the corresponding molding temperatures. Microstructures of tensile tested macroscale Cu specimens and molded Cu specimens were characterized by combining focused ion beam (FIB) sectioning and imaging with ion-induced secondary electrons (ISEs). At all temperatures tested, measured tensile stress–strain curves for Cu show clear evidence for the occurrence of dynamic recrystallization (DRX) within macroscale tensile specimens. Additional FIB sectioning and imaging with ISEs of molded Cu specimens provide microstructural evidence for the occurrence of DRX during molding. The present results show that, even in the presence of DRX, an appropriate one-parameter scaling continues to reduce the molding response to a universal function independent of the molding temperature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009082

Double twinning in Ni–Mn–Ga–Co / K. Rolfs in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2646–2651 Titre : Double twinning in Ni–Mn–Ga–Co Type de document : texte imprimé Auteurs : K. Rolfs, Auteur ; M. Chmielus, Auteur ; R.C. Wimpory, Auteur Année de publication : 2011 Article en page(s) : pp. 2646–2651 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Heusler  phases  Neutron  diffraction  Twinning  Plastic  deformation Résumé : Magnetic shape-memory alloys tend to deform via magnetic-field-induced and stress-induced twin-boundary motion. The rather low martensite transformation temperature of ternary Ni–Mn–Ga limits the operating temperature for potential applications. By alloying 5 at.% cobalt, the martensite transformation temperature and the Curie temperature was increased from 70 and 110 °C respectively up to 160 °C. In the single crystalline samples two non-modulated structures with tetragonal and orthorhombic lattices were found. The non-modulated orthorhombic structure has similar lattice parameters to the pseudo-orthorhombic 14M Ni–Mn–Ga phase. The single crystal specimen with the non-modulated orthorhombic structure exhibited a cyclic permutation of all three crystallographic axes in response to uniaxial loading. The parallelepiped-shaped sample was compressed repeatedly in all three directions. While maximizing work done by the load during deformation required three different martensite variants to result from deformation in three different directions, only two different martensite variants were found. The analysis of the sample shape revealed two variants mutually related through cyclic permutation of the lattice parameters, which cannot result from a single twinning event. The cyclic permutation is discussed in the light of Crocker’s double twinning mechanism. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009094 [article] Double twinning in Ni–Mn–Ga–Co [texte imprimé] / K. Rolfs, Auteur ; M. Chmielus, Auteur ; R.C. Wimpory, Auteur . - 2011 . - pp. 2646–2651. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2646–2651 Mots-clés : Heusler  phases  Neutron  diffraction  Twinning  Plastic  deformation Résumé : Magnetic shape-memory alloys tend to deform via magnetic-field-induced and stress-induced twin-boundary motion. The rather low martensite transformation temperature of ternary Ni–Mn–Ga limits the operating temperature for potential applications. By alloying 5 at.% cobalt, the martensite transformation temperature and the Curie temperature was increased from 70 and 110 °C respectively up to 160 °C. In the single crystalline samples two non-modulated structures with tetragonal and orthorhombic lattices were found. The non-modulated orthorhombic structure has similar lattice parameters to the pseudo-orthorhombic 14M Ni–Mn–Ga phase. The single crystal specimen with the non-modulated orthorhombic structure exhibited a cyclic permutation of all three crystallographic axes in response to uniaxial loading. The parallelepiped-shaped sample was compressed repeatedly in all three directions. While maximizing work done by the load during deformation required three different martensite variants to result from deformation in three different directions, only two different martensite variants were found. The analysis of the sample shape revealed two variants mutually related through cyclic permutation of the lattice parameters, which cannot result from a single twinning event. The cyclic permutation is discussed in the light of Crocker’s double twinning mechanism. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009094

The deformation of Gum Metal through in situ compression of nanopillars / E.A. Withey in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2652–2665 Titre : The deformation of Gum Metal through in situ compression of nanopillars Type de document : texte imprimé Auteurs : E.A. Withey, Auteur ; A.M. Minor, Auteur ; D. C. Chrzan, Auteur Année de publication : 2011 Article en page(s) : pp. 2652–2665 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Compression  test  Titanium  TEM  Gum  Metal Résumé : The name “Gum Metal” has been given to a set of β-Ti alloys that achieve exceptional elastic elongation and, with appropriate preparation, appear to deform by a dislocation-free mechanism triggered by elastic instability at the limit of strength. We have studied the compressive deformation of these materials with in situ nanocompression in a quantitative stage in a transmission electron microscope. The samples studied are cylindrical nanopillars 80–250 nm in diameter. The deformation pattern is monitored in real time using bright-field microscopy, dark-field microscopy or electron diffraction. Interesting results include the following: (i) nanopillars approach, and in several examples appear to reach, ideal strength; (ii) in contrast to conventional crystalline materials, there is no substantial “size effect” in pillar strength; (iii) the deformation mode is fine-scale with respect to the sample dimension, even in pillars of 100 nm size; (iv) shear bands (“giant faults”) do form in some tests, but only after yield and plastic deformation; and (v) a martensitic transformation to the base-centered orthorhombic α′′ phase is sometimes observed, but is an incidental feature of the deformation rather than a significant cause of it. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009100 [article] The deformation of Gum Metal through in situ compression of nanopillars [texte imprimé] / E.A. Withey, Auteur ; A.M. Minor, Auteur ; D. C. Chrzan, Auteur . - 2011 . - pp. 2652–2665. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2652–2665 Mots-clés : Compression  test  Titanium  TEM  Gum  Metal Résumé : The name “Gum Metal” has been given to a set of β-Ti alloys that achieve exceptional elastic elongation and, with appropriate preparation, appear to deform by a dislocation-free mechanism triggered by elastic instability at the limit of strength. We have studied the compressive deformation of these materials with in situ nanocompression in a quantitative stage in a transmission electron microscope. The samples studied are cylindrical nanopillars 80–250 nm in diameter. The deformation pattern is monitored in real time using bright-field microscopy, dark-field microscopy or electron diffraction. Interesting results include the following: (i) nanopillars approach, and in several examples appear to reach, ideal strength; (ii) in contrast to conventional crystalline materials, there is no substantial “size effect” in pillar strength; (iii) the deformation mode is fine-scale with respect to the sample dimension, even in pillars of 100 nm size; (iv) shear bands (“giant faults”) do form in some tests, but only after yield and plastic deformation; and (v) a martensitic transformation to the base-centered orthorhombic α′′ phase is sometimes observed, but is an incidental feature of the deformation rather than a significant cause of it. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009100

Phase transformations and induced volume changes in a nitrided ternary Fe–3%Cr–0.345%C alloy / S. Jegou in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2666–2676 Titre : Phase transformations and induced volume changes in a nitrided ternary Fe–3%Cr–0.345%C alloy Type de document : texte imprimé Auteurs : S. Jegou, Auteur ; L. Barrallier, Auteur ; R. Kubler, Auteur Année de publication : 2011 Article en page(s) : pp. 2666–2676 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nitriding  Iron  alloys  Residual  stresses  Phase  transformations  Precipitation Résumé : Phase transformations during nitriding of a ternary carbon iron-based alloy Fe–3%Cr–0.345%C were studied, aiming for a better understanding of residual stresses generation and evolution. The relationship between the precipitation of Cr7C3 carbides and CrN nitrides, the induced volume change and the mechanical properties were investigated at three distinct depths of the diffusion zone. The relaxation of residual stresses arose through phase transformations according to the diffusion of nitrogen but also of carbon. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009112 [article] Phase transformations and induced volume changes in a nitrided ternary Fe–3%Cr–0.345%C alloy [texte imprimé] / S. Jegou, Auteur ; L. Barrallier, Auteur ; R. Kubler, Auteur . - 2011 . - pp. 2666–2676. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2666–2676 Mots-clés : Nitriding  Iron  alloys  Residual  stresses  Phase  transformations  Precipitation Résumé : Phase transformations during nitriding of a ternary carbon iron-based alloy Fe–3%Cr–0.345%C were studied, aiming for a better understanding of residual stresses generation and evolution. The relationship between the precipitation of Cr7C3 carbides and CrN nitrides, the induced volume change and the mechanical properties were investigated at three distinct depths of the diffusion zone. The relaxation of residual stresses arose through phase transformations according to the diffusion of nitrogen but also of carbon. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009112

A closer look at the local responses of twin and grain boundaries in Cu to stress at the nanoscale with possible transition from the P–H to the inverse P–H relation / L. Yue in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2677–2684 Titre : A closer look at the local responses of twin and grain boundaries in Cu to stress at the nanoscale with possible transition from the P–H to the inverse P–H relation Type de document : texte imprimé Auteurs : L. Yue, Auteur ; H. Zhang, Auteur ; D.Y. Li, Auteur Année de publication : 2011 Article en page(s) : pp. 2677–2684 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nano-twinning  Nano-grains  Inverse  Petch–Hall  relation  Molecular  dynamics  Simulation Résumé : Nanocrystalline copper is considered to be a candidate for electrical contacts for dynamic systems because of its intrinsic conductivity and enhanced fretting resistance. However, the enhanced electron scattering at high-density grain boundaries significantly deteriorates the overall conductivity of nanocrystalline copper. Recent studies suggest that nanosized twin boundaries in copper might be a solution to such a dilemma. To better understand the general mechanical behavior of nanotwin boundaries, we conducted molecular dynamics simulation studies to investigate responses of both nanotwin and nanograin boundaries in copper to stress at the nanoscale, particularly in the critical range of 5–25 nm where the inverse Petch–Hall relation (P–H) may occur in nanocrystalline copper. The obtained results suggest that the twin boundary blocks dislocation movement more effectively and the degree of emitting dislocations under stress is considerably lower than that of grain boundary, leading to superior mechanical behavior. The inverse P–H relation is not applicable to the nanotwinned system. It is also demonstrated that the inverse P–H relation occurring in nanograined materials does not necessarily result from grain boundary sliding. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000029 [article] A closer look at the local responses of twin and grain boundaries in Cu to stress at the nanoscale with possible transition from the P–H to the inverse P–H relation [texte imprimé] / L. Yue, Auteur ; H. Zhang, Auteur ; D.Y. Li, Auteur . - 2011 . - pp. 2677–2684. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2677–2684 Mots-clés : Nano-twinning  Nano-grains  Inverse  Petch–Hall  relation  Molecular  dynamics  Simulation Résumé : Nanocrystalline copper is considered to be a candidate for electrical contacts for dynamic systems because of its intrinsic conductivity and enhanced fretting resistance. However, the enhanced electron scattering at high-density grain boundaries significantly deteriorates the overall conductivity of nanocrystalline copper. Recent studies suggest that nanosized twin boundaries in copper might be a solution to such a dilemma. To better understand the general mechanical behavior of nanotwin boundaries, we conducted molecular dynamics simulation studies to investigate responses of both nanotwin and nanograin boundaries in copper to stress at the nanoscale, particularly in the critical range of 5–25 nm where the inverse Petch–Hall relation (P–H) may occur in nanocrystalline copper. The obtained results suggest that the twin boundary blocks dislocation movement more effectively and the degree of emitting dislocations under stress is considerably lower than that of grain boundary, leading to superior mechanical behavior. The inverse P–H relation is not applicable to the nanotwinned system. It is also demonstrated that the inverse P–H relation occurring in nanograined materials does not necessarily result from grain boundary sliding. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000029

Understanding the mechanical reinforcement of uniformly dispersed multiwalled carbon nanotubes in alumino-borosilicate glass ceramic / Amartya Mukhopadhyay in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2685–2697 Titre : Understanding the mechanical reinforcement of uniformly dispersed multiwalled carbon nanotubes in alumino-borosilicate glass ceramic Type de document : texte imprimé Auteurs : Amartya Mukhopadhyay, Auteur ; Bryan T. T. Chu, Auteur ; Malcolm L.H. Green, Auteur Année de publication : 2011 Article en page(s) : pp. 2685–2697 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Carbon  nanotubes  Nanocomposites  Fracture  toughness  Crack  bridging  Fibre-reinforced  composites Résumé : The improvement of mechanical properties of carbon nanotube–reinforced polycrystalline ceramic or glass matrix composites was limited in earlier studies by the difficulties in producing a good dispersion of carbon nanotubes. Additionally, a proper understanding of the reinforcing mechanisms, if any, affecting the mechanical properties of ceramics containing carbon nanotubes is still lacking. We report here the effects of a good dispersion of as much as 10 wt.% multiwalled carbon nanotubes (MWCNTs) on the mechanical properties of dense alumino-borosilicate glass ceramics (ABS) prepared by an ultrasonication-assisted sol–gel technique followed by hot pressing (950 °C; 2 h; Ar atmosphere). The fracture toughness and flexural strength of the nanocomposites increased with increasing MWCNT content up to 10 wt.%. The ABS–10 wt.% MWCNT nanocomposite possessed nearly double the strength of the unreinforced ABS, accompanied by ∼150% improvement in fracture toughness. However, a further increase in MWCNT content to 15 wt.% resulted in a modest deterioration of the mechanical properties due to agglomeration of the MWCNTs. The carbon nanotubes have been observed to bridge crack openings of the order of ∼100 nm and the experimental evidence, along with theoretical analysis, showed that crack bridging provided the major contribution towards the improvement in fracture toughness. Debonding between the MWCNTs and the matrix appeared to occur in the matrix, away from the actual interface. However, the absence of significant pull-out of broken sections of the MWCNTs during fracture, due to failure of the bridging CNTs being predominantly at the crack plane, indicates that further toughening may be available if this mechanism can be activated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000042 [article] Understanding the mechanical reinforcement of uniformly dispersed multiwalled carbon nanotubes in alumino-borosilicate glass ceramic [texte imprimé] / Amartya Mukhopadhyay, Auteur ; Bryan T. T. Chu, Auteur ; Malcolm L.H. Green, Auteur . - 2011 . - pp. 2685–2697. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2685–2697 Mots-clés : Carbon  nanotubes  Nanocomposites  Fracture  toughness  Crack  bridging  Fibre-reinforced  composites Résumé : The improvement of mechanical properties of carbon nanotube–reinforced polycrystalline ceramic or glass matrix composites was limited in earlier studies by the difficulties in producing a good dispersion of carbon nanotubes. Additionally, a proper understanding of the reinforcing mechanisms, if any, affecting the mechanical properties of ceramics containing carbon nanotubes is still lacking. We report here the effects of a good dispersion of as much as 10 wt.% multiwalled carbon nanotubes (MWCNTs) on the mechanical properties of dense alumino-borosilicate glass ceramics (ABS) prepared by an ultrasonication-assisted sol–gel technique followed by hot pressing (950 °C; 2 h; Ar atmosphere). The fracture toughness and flexural strength of the nanocomposites increased with increasing MWCNT content up to 10 wt.%. The ABS–10 wt.% MWCNT nanocomposite possessed nearly double the strength of the unreinforced ABS, accompanied by ∼150% improvement in fracture toughness. However, a further increase in MWCNT content to 15 wt.% resulted in a modest deterioration of the mechanical properties due to agglomeration of the MWCNTs. The carbon nanotubes have been observed to bridge crack openings of the order of ∼100 nm and the experimental evidence, along with theoretical analysis, showed that crack bridging provided the major contribution towards the improvement in fracture toughness. Debonding between the MWCNTs and the matrix appeared to occur in the matrix, away from the actual interface. However, the absence of significant pull-out of broken sections of the MWCNTs during fracture, due to failure of the bridging CNTs being predominantly at the crack plane, indicates that further toughening may be available if this mechanism can be activated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000042

Substitutional diffusion in multicomponent solids with non-ideal sources and sinks for vacancies / F.D. Fischer in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2698–2707 Titre : Substitutional diffusion in multicomponent solids with non-ideal sources and sinks for vacancies Type de document : texte imprimé Auteurs : F.D. Fischer, Auteur ; J. Svoboda, Auteur Année de publication : 2011 Article en page(s) : pp. 2698–2707 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Substitutional  diffusion  Vacancies  Annihilation  Residual  stresses  Non-equilibrium  process Résumé : Based on previous work by the authors the diffusion equations for a multicomponent solid are derived. Generation and annihilation of vacancies are described by an evolution law which is directly coupled with an eigenstrain rate. Manning’s correlation factor f is used in the kinetic factor for diffusion of vacancies. In addition to presentation of the diffusion equations, a rigorous treatment of the boundary conditions, assuming no or an ideal source and sink for vacancies at the surface, is presented. As an instructive example development of the site fractions of the components and the eigenstress state are demonstrated for a multicomponent chemically inhomogeneous layer on a substrate. Both the role of nonlinear terms and the correlation factor f in the diffusion equations are studied. Computational procedures to calculate to the proper boundary conditions are also outlined. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000066 [article] Substitutional diffusion in multicomponent solids with non-ideal sources and sinks for vacancies [texte imprimé] / F.D. Fischer, Auteur ; J. Svoboda, Auteur . - 2011 . - pp. 2698–2707. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2698–2707 Mots-clés : Substitutional  diffusion  Vacancies  Annihilation  Residual  stresses  Non-equilibrium  process Résumé : Based on previous work by the authors the diffusion equations for a multicomponent solid are derived. Generation and annihilation of vacancies are described by an evolution law which is directly coupled with an eigenstrain rate. Manning’s correlation factor f is used in the kinetic factor for diffusion of vacancies. In addition to presentation of the diffusion equations, a rigorous treatment of the boundary conditions, assuming no or an ideal source and sink for vacancies at the surface, is presented. As an instructive example development of the site fractions of the components and the eigenstress state are demonstrated for a multicomponent chemically inhomogeneous layer on a substrate. Both the role of nonlinear terms and the correlation factor f in the diffusion equations are studied. Computational procedures to calculate to the proper boundary conditions are also outlined. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000066

Experimental and computational study on the effect of yttrium on the phase stability of sputtered Cr–Al–Y–N hard coatings / F. Rovere in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2708–2715 Titre : Experimental and computational study on the effect of yttrium on the phase stability of sputtered Cr–Al–Y–N hard coatings Type de document : texte imprimé Auteurs : F. Rovere, Auteur ; D. Music, Auteur ; J.M. Schneider, Auteur Année de publication : 2011 Article en page(s) : pp. 2708–2715 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : CrAlN  Phase  stability  Ab  initio  OpenMX Résumé : The effect of Y incorporation into cubic Cr–Al–N (B1) was studied using ab initio calculations, X-ray diffraction and energy-dispersive X-ray analysis of sputtered quaternary nitride films. The data obtained indicate that the Y incorporation shifts the critical Al content, where the hexagonal (B4) structure is stable, to lower values. The calculated critical Al contents of x ≈ 0.75 for Cr1−xAlxN and x ≈ 0.625 for Cr1−x−yAlxYyN with y = 0.125 are consistent with experimentally obtained values of x = 0.69 for Cr1−xAlxN and x = 0.68 and 0.61 for Cr1−x−yAlxYyN with y = 0.02 and 0.06, respectively. This may be understood based on the electronic structure. Both Cr and Al can randomly be substituted by Y. The substitution of Cr by Y increases the phase stability due to depletion of non-bonding (anti-bonding) states, while the substitution of Al by Y decreases the phase stability mainly due to lattice strain. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000008X [article] Experimental and computational study on the effect of yttrium on the phase stability of sputtered Cr–Al–Y–N hard coatings [texte imprimé] / F. Rovere, Auteur ; D. Music, Auteur ; J.M. Schneider, Auteur . - 2011 . - pp. 2708–2715. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2708–2715 Mots-clés : CrAlN  Phase  stability  Ab  initio  OpenMX Résumé : The effect of Y incorporation into cubic Cr–Al–N (B1) was studied using ab initio calculations, X-ray diffraction and energy-dispersive X-ray analysis of sputtered quaternary nitride films. The data obtained indicate that the Y incorporation shifts the critical Al content, where the hexagonal (B4) structure is stable, to lower values. The calculated critical Al contents of x ≈ 0.75 for Cr1−xAlxN and x ≈ 0.625 for Cr1−x−yAlxYyN with y = 0.125 are consistent with experimentally obtained values of x = 0.69 for Cr1−xAlxN and x = 0.68 and 0.61 for Cr1−x−yAlxYyN with y = 0.02 and 0.06, respectively. This may be understood based on the electronic structure. Both Cr and Al can randomly be substituted by Y. The substitution of Cr by Y increases the phase stability due to depletion of non-bonding (anti-bonding) states, while the substitution of Al by Y decreases the phase stability mainly due to lattice strain. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000008X

Multi-scale modeling of elastic response of three-dimensional voxel-based microstructure datasets using novel DFT-based knowledge systems / Giacomo Landi in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2716–2725 Titre : Multi-scale modeling of elastic response of three-dimensional voxel-based microstructure datasets using novel DFT-based knowledge systems Type de document : texte imprimé Auteurs : Giacomo Landi, Auteur ; Stephen R. Niezgoda, Auteur ; Surya R. Kalidindi, Auteur Année de publication : 2011 Article en page(s) : pp. 2716–2725 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Microstructure  Elastic  response  Multi-scale  modeling  Discrete  Fourier  transforms Résumé : In this paper, we present a novel approach for predicting the elastic fields in three-dimensional voxel-based microstructure datasets subjected to uniform periodic boundary conditions. This new formalism has its theoretical roots in the statistical continuum theories developed originally by Kroner. However, in the approach described by Kroner the terms in the series were established by selecting a reference medium and numerically evaluating a complex series of nested convolution integrals. This approach is largely hampered by the principal value problem and exhibits high sensitivity to the properties of the selected reference medium. In the present work, we have recast the same series expressions into much more computationally efficient representations using discrete Fourier transforms (DFTs). The main advantage of the new DFT-based framework is that it allows easy calibration of Kroner’s expansions to results from finite element methods, thereby overcoming all of the main obstacles associated with the principal value problem and the need to select a reference medium. Consequently, the DFT-based approach presented here produces much more accurate predictions. In this paper the new mathematical formalism is first presented in a generalized framework, and its viability is then demonstrated for a selected class of two phase composites. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000108 [article] Multi-scale modeling of elastic response of three-dimensional voxel-based microstructure datasets using novel DFT-based knowledge systems [texte imprimé] / Giacomo Landi, Auteur ; Stephen R. Niezgoda, Auteur ; Surya R. Kalidindi, Auteur . - 2011 . - pp. 2716–2725. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2716–2725 Mots-clés : Microstructure  Elastic  response  Multi-scale  modeling  Discrete  Fourier  transforms Résumé : In this paper, we present a novel approach for predicting the elastic fields in three-dimensional voxel-based microstructure datasets subjected to uniform periodic boundary conditions. This new formalism has its theoretical roots in the statistical continuum theories developed originally by Kroner. However, in the approach described by Kroner the terms in the series were established by selecting a reference medium and numerically evaluating a complex series of nested convolution integrals. This approach is largely hampered by the principal value problem and exhibits high sensitivity to the properties of the selected reference medium. In the present work, we have recast the same series expressions into much more computationally efficient representations using discrete Fourier transforms (DFTs). The main advantage of the new DFT-based framework is that it allows easy calibration of Kroner’s expansions to results from finite element methods, thereby overcoming all of the main obstacles associated with the principal value problem and the need to select a reference medium. Consequently, the DFT-based approach presented here produces much more accurate predictions. In this paper the new mathematical formalism is first presented in a generalized framework, and its viability is then demonstrated for a selected class of two phase composites. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000108

The effect of platinum on Al diffusion kinetics in β-NiAl / Kristen A. Marino in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2726–2737 Titre : The effect of platinum on Al diffusion kinetics in β-NiAl : Implications for thermal barrier coating lifetime Type de document : texte imprimé Auteurs : Kristen A. Marino, Auteur ; Emily A. Carter, Auteur Année de publication : 2011 Article en page(s) : pp. 2726–2737 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Diffusion  Nickel  aluminides  Platinum  Kinetics  Density  functional  theory Résumé : First-principles density functional theory calculations are used to study Al diffusion in β-NiAl. The activation energy and diffusion constant pre-exponential factors are calculated for five previously postulated Al diffusion mechanisms: next-nearest-neighbor Al jumps, the triple defect mechanism and three variants of the six-jump cycle mechanism beginning with an Al vacancy. We predict that the triple defect mechanism has the lowest activation energy and is the mechanism by which Al diffusion occurs in NiAl. In order to elucidate why Pt has a beneficial effect on thermal barrier coating lifetime, the effect of Pt on each of these mechanisms is also examined. In all cases, Pt decreases the diffusion activation energy, which should enhance Al diffusion in the coatings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000011X [article] The effect of platinum on Al diffusion kinetics in β-NiAl : Implications for thermal barrier coating lifetime [texte imprimé] / Kristen A. Marino, Auteur ; Emily A. Carter, Auteur . - 2011 . - pp. 2726–2737. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2726–2737 Mots-clés : Diffusion  Nickel  aluminides  Platinum  Kinetics  Density  functional  theory Résumé : First-principles density functional theory calculations are used to study Al diffusion in β-NiAl. The activation energy and diffusion constant pre-exponential factors are calculated for five previously postulated Al diffusion mechanisms: next-nearest-neighbor Al jumps, the triple defect mechanism and three variants of the six-jump cycle mechanism beginning with an Al vacancy. We predict that the triple defect mechanism has the lowest activation energy and is the mechanism by which Al diffusion occurs in NiAl. In order to elucidate why Pt has a beneficial effect on thermal barrier coating lifetime, the effect of Pt on each of these mechanisms is also examined. In all cases, Pt decreases the diffusion activation energy, which should enhance Al diffusion in the coatings. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000011X

Polydimensional modelling of dendritic growth and microsegregation in multicomponent alloys / Sebastian C. Michelic in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2738–2751 Titre : Polydimensional modelling of dendritic growth and microsegregation in multicomponent alloys Type de document : texte imprimé Auteurs : Sebastian C. Michelic, Auteur ; Jörg M. Thuswaldner, Auteur ; Christian Bernhard, Auteur Année de publication : 2011 Article en page(s) : pp. 2738–2751 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cellular  automaton  Microsegregation  Multicomponent  solidification Résumé : Various models for simulating dendritic solidification have been proposed in the past. However, those models based on cellular automata (adopting the virtual front-tracking (VFT) concept) are often only suitable for the consideration of one alloying element. As typical industrial alloys are constituted of numerous alloying elements, the application of these models to practical alloys is therefore rather limited. In order to overcome this drawback, a new, modified VFT model, which allows for the treatment of several alloying elements in the low Péclet number regime, is presented. By a new and effective approach, based on a functional extrapolation of the concentration gradient, we are able to study dendritic growth in multicomponent Fe–C–Si–Mn–P–S alloys. Comparisons with well-established analytical models confirm the correctness of the model; results for free and constrained dendritic growth effectively demonstrate the capabilities of this new model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000248 [article] Polydimensional modelling of dendritic growth and microsegregation in multicomponent alloys [texte imprimé] / Sebastian C. Michelic, Auteur ; Jörg M. Thuswaldner, Auteur ; Christian Bernhard, Auteur . - 2011 . - pp. 2738–2751. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2738–2751 Mots-clés : Cellular  automaton  Microsegregation  Multicomponent  solidification Résumé : Various models for simulating dendritic solidification have been proposed in the past. However, those models based on cellular automata (adopting the virtual front-tracking (VFT) concept) are often only suitable for the consideration of one alloying element. As typical industrial alloys are constituted of numerous alloying elements, the application of these models to practical alloys is therefore rather limited. In order to overcome this drawback, a new, modified VFT model, which allows for the treatment of several alloying elements in the low Péclet number regime, is presented. By a new and effective approach, based on a functional extrapolation of the concentration gradient, we are able to study dendritic growth in multicomponent Fe–C–Si–Mn–P–S alloys. Comparisons with well-established analytical models confirm the correctness of the model; results for free and constrained dendritic growth effectively demonstrate the capabilities of this new model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000248

Transformation kinetics for surface and bulk nucleation / Elena Villa in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2752–2768 Titre : Transformation kinetics for surface and bulk nucleation Type de document : texte imprimé Auteurs : Elena Villa, Auteur ; Paulo R. Rios, Auteur Année de publication : 2011 Article en page(s) : pp. 2752–2768 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Microstructure  Analytical  methods  Phase  transformations  Kinetics  Recrystallization Résumé : A rigorous mathematical approach based on the causal cone and stochastic geometry concepts is used to derive new exact expressions for transformation kinetics theory. General expressions for the mean volume density and the volume fraction are derived for both surface and bulk nucleation in a general Borel subset of R3. In practice, probably any specimen shape of engineering interest is going to be a Borel set. An expression is also derived for the important case of polyhedral shape, in which surface nucleation may take place on the faces, edges and vertices of the polyhedron as well as within the bulk. Moreover, explicit expressions are given for surface and bulk nucleation for three specific shapes of engineering relevance: two parallel planes, an infinitely long cylinder and a sphere. Superposition is explained in detail and it permits the treatment of situations in which surface and bulk nucleation take place simultaneously. The new exact expressions presented here result in a significant increase in the number of exactly solvable cases available to formal kinetics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000261 [article] Transformation kinetics for surface and bulk nucleation [texte imprimé] / Elena Villa, Auteur ; Paulo R. Rios, Auteur . - 2011 . - pp. 2752–2768. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2752–2768 Mots-clés : Microstructure  Analytical  methods  Phase  transformations  Kinetics  Recrystallization Résumé : A rigorous mathematical approach based on the causal cone and stochastic geometry concepts is used to derive new exact expressions for transformation kinetics theory. General expressions for the mean volume density and the volume fraction are derived for both surface and bulk nucleation in a general Borel subset of R3. In practice, probably any specimen shape of engineering interest is going to be a Borel set. An expression is also derived for the important case of polyhedral shape, in which surface nucleation may take place on the faces, edges and vertices of the polyhedron as well as within the bulk. Moreover, explicit expressions are given for surface and bulk nucleation for three specific shapes of engineering relevance: two parallel planes, an infinitely long cylinder and a sphere. Superposition is explained in detail and it permits the treatment of situations in which surface and bulk nucleation take place simultaneously. The new exact expressions presented here result in a significant increase in the number of exactly solvable cases available to formal kinetics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000261

The thermal explosion synthesis of AlNi monitored by neutron thermodiffractometry / X. Turrillas in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2769–2777 Titre : The thermal explosion synthesis of AlNi monitored by neutron thermodiffractometry Type de document : texte imprimé Auteurs : X. Turrillas, Auteur ; M.J. Mas-Guindal, Auteur ; T.C. Hansen, Auteur Année de publication : 2011 Article en page(s) : pp. 2769–2777 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel  aluminides  Neutron  diffraction  Nucleation  and  growth  Thermodiffraction Résumé : The synthesis of AlNi from thermally activated equimolar powder mixtures of aluminium and nickel was monitored in situ and acquired diffraction patterns every 2 s or less. The analysis of diffraction patterns View the MathML source permitted establishment of its kinetics, which could be modeled according to an equation expressed as kt=[α/(1-α)]3/2. From 1530 to View the MathML source an activation energy of 9 ± 2 kJ mol−1 was estimated. Also, the crystallite size evolution on cooling was established to vary from ≈14 nm at 1530 °C to ≈28 nm at 180 °C. Finally, the reaction was found to occur through the melting of aluminium and the subsequent dissolving of nickel to form the polycrystalline single-phase product, AlNi. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000273 [article] The thermal explosion synthesis of AlNi monitored by neutron thermodiffractometry [texte imprimé] / X. Turrillas, Auteur ; M.J. Mas-Guindal, Auteur ; T.C. Hansen, Auteur . - 2011 . - pp. 2769–2777. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2769–2777 Mots-clés : Nickel  aluminides  Neutron  diffraction  Nucleation  and  growth  Thermodiffraction Résumé : The synthesis of AlNi from thermally activated equimolar powder mixtures of aluminium and nickel was monitored in situ and acquired diffraction patterns every 2 s or less. The analysis of diffraction patterns View the MathML source permitted establishment of its kinetics, which could be modeled according to an equation expressed as kt=[α/(1-α)]3/2. From 1530 to View the MathML source an activation energy of 9 ± 2 kJ mol−1 was estimated. Also, the crystallite size evolution on cooling was established to vary from ≈14 nm at 1530 °C to ≈28 nm at 180 °C. Finally, the reaction was found to occur through the melting of aluminium and the subsequent dissolving of nickel to form the polycrystalline single-phase product, AlNi. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000273

Evolution of deformation mechanisms of Ti–22.4Nb–0.73Ta–2Zr–1.34O alloy during straining / Y. Yang in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2778–2787 Titre : Evolution of deformation mechanisms of Ti–22.4Nb–0.73Ta–2Zr–1.34O alloy during straining Type de document : texte imprimé Auteurs : Y. Yang, Auteur ; S.Q. Wu, Auteur ; G.P. Li, Auteur Année de publication : 2011 Article en page(s) : pp. 2778–2787 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Titanium  alloys  Compression  test  Plastic  deformation  Multi-peak  stress  oscillations Résumé : The plastic deformation behavior of Ti–22.4Nb–0.73Ta–2Zr–1.34O alloy was investigated by compression testing at room temperature. The multi-peak stress oscillations of the true stress–strain curve, characterized by a stress plateau, initial strain-hardening, followed by strain-softening and a second strain-hardening stages, is observed in a titanium alloy for the first time. The experimental results show that the above four-stage plastic deformation behavior is caused by a change in the dominant deformation mechanisms. At the stress plateau stage, the alloy deforms via multiple plastic deformation mechanisms. The initial strain hardening is caused mainly by tangling of dislocations. Subsequent strain softening is due to the formation of kink bands. The second strain hardening corresponds to the formation of shear bands. The above results suggest that the dominant deformation mechanisms of Ti–Nb–Ta–Zr–O alloys are related not only to the stability of the β phase, but also to the extent of plastic deformation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000297 [article] Evolution of deformation mechanisms of Ti–22.4Nb–0.73Ta–2Zr–1.34O alloy during straining [texte imprimé] / Y. Yang, Auteur ; S.Q. Wu, Auteur ; G.P. Li, Auteur . - 2011 . - pp. 2778–2787. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2778–2787 Mots-clés : Titanium  alloys  Compression  test  Plastic  deformation  Multi-peak  stress  oscillations Résumé : The plastic deformation behavior of Ti–22.4Nb–0.73Ta–2Zr–1.34O alloy was investigated by compression testing at room temperature. The multi-peak stress oscillations of the true stress–strain curve, characterized by a stress plateau, initial strain-hardening, followed by strain-softening and a second strain-hardening stages, is observed in a titanium alloy for the first time. The experimental results show that the above four-stage plastic deformation behavior is caused by a change in the dominant deformation mechanisms. At the stress plateau stage, the alloy deforms via multiple plastic deformation mechanisms. The initial strain hardening is caused mainly by tangling of dislocations. Subsequent strain softening is due to the formation of kink bands. The second strain hardening corresponds to the formation of shear bands. The above results suggest that the dominant deformation mechanisms of Ti–Nb–Ta–Zr–O alloys are related not only to the stability of the β phase, but also to the extent of plastic deformation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000297

X-ray diffraction study of the phase purity, order and texture of ductile B2 intermetallics / R.P. Mulay in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2788–2796 Titre : X-ray diffraction study of the phase purity, order and texture of ductile B2 intermetallics Type de document : texte imprimé Auteurs : R.P. Mulay, Auteur ; J.A. Wollmershauser, Auteur ; M.A. Heisel, Auteur Année de publication : 2011 Article en page(s) : pp. 2788–2796 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ductility  Intermetallics  Ordering  Preferred  orientation  Dislocations Résumé : Representatives (AgY, CuY, AgEr, CuDy, MgY and MgCe) of the newly discovered family of ductile stoichiometric B2 intermetallic (metal–rare-earth element, MR) compounds were characterized by X-ray diffraction, to determine if their anomalous ductility is related to an exceptional level of phase purity, lack of chemical ordering or a strong crystallographic texture. Brittle NiAl served as an anti-type in this study. We found that all of the rare-earth compounds, except MgY, have a significant volume fraction (∼5–20 vol.%) of second phases (M2R intermetallics and R2O3 oxides), which has not been reported in previous studies of these materials. The most ductile of observed MR compounds, AgY, is highly ordered. A moderate texture was observed in AgY, which may explain its higher ductility (using polycrystal modeling) as compared to other MR compounds. However, the intrinsic polycrystalline ductility of these compounds in the randomly textured state (like that observed in CuY) still has no specific, definitive explanation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000406 [article] X-ray diffraction study of the phase purity, order and texture of ductile B2 intermetallics [texte imprimé] / R.P. Mulay, Auteur ; J.A. Wollmershauser, Auteur ; M.A. Heisel, Auteur . - 2011 . - pp. 2788–2796. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2788–2796 Mots-clés : Ductility  Intermetallics  Ordering  Preferred  orientation  Dislocations Résumé : Representatives (AgY, CuY, AgEr, CuDy, MgY and MgCe) of the newly discovered family of ductile stoichiometric B2 intermetallic (metal–rare-earth element, MR) compounds were characterized by X-ray diffraction, to determine if their anomalous ductility is related to an exceptional level of phase purity, lack of chemical ordering or a strong crystallographic texture. Brittle NiAl served as an anti-type in this study. We found that all of the rare-earth compounds, except MgY, have a significant volume fraction (∼5–20 vol.%) of second phases (M2R intermetallics and R2O3 oxides), which has not been reported in previous studies of these materials. The most ductile of observed MR compounds, AgY, is highly ordered. A moderate texture was observed in AgY, which may explain its higher ductility (using polycrystal modeling) as compared to other MR compounds. However, the intrinsic polycrystalline ductility of these compounds in the randomly textured state (like that observed in CuY) still has no specific, definitive explanation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000406

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