Dépouillements

Cyclic twin nucleation in tin-based solder alloys / L.P. Lehman in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3546–3556 Titre : Cyclic twin nucleation in tin-based solder alloys Type de document : texte imprimé Auteurs : L.P. Lehman, Auteur ; Y. Xing, Auteur ; T. R. Bieler, Auteur Année de publication : 2011 Article en page(s) : pp. 3546–3556 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Undercooling  solidification  Nucleation  Twinning  Single  crystal  growth  Electron  backscattering  diffraction  (EBSD)  Solidification  microstructure Résumé : The microstructure and Sn crystal orientations of lead-free solder alloys such as near-eutectic SnAgCu have a significant influence on the mechanical response of a solder joint to service conditions. Thus solidification processes were examined in SnAgCu solder joints. Distinct evidence of sixfold cyclic growth twinning of Sn during solidification from the melt was observed in Sn–Ag, SAC and Sn–Cu solders. Three orientations of Sn grains, each having a common 〈1 0 0〉 direction, were found in each of these systems, though the morphologies of these cyclic twinned microstructures differed. Analysis of dendrite arm spacing in cyclically twined structures with a beach ball morphology implies that the common 〈1 0 0〉 axis intersects with the region of the nucleation event. Models are presented for two pseudo/metastable hexagonal unit cells based upon {1 0 1} or {3 0 1} twins that introduce the cyclic twinning structure at the nucleation stage. Formation of these hexagonal unit cells may be facilitated by the presence of alloy elements. Subsequent epitaxial growth of the tetragonal unit cell on this nucleus can account for all three types of morphologies observed in microstructures of Sn-rich solder alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000443 [article] Cyclic twin nucleation in tin-based solder alloys [texte imprimé] / L.P. Lehman, Auteur ; Y. Xing, Auteur ; T. R. Bieler, Auteur . - 2011 . - pp. 3546–3556. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3546–3556 Mots-clés : Undercooling  solidification  Nucleation  Twinning  Single  crystal  growth  Electron  backscattering  diffraction  (EBSD)  Solidification  microstructure Résumé : The microstructure and Sn crystal orientations of lead-free solder alloys such as near-eutectic SnAgCu have a significant influence on the mechanical response of a solder joint to service conditions. Thus solidification processes were examined in SnAgCu solder joints. Distinct evidence of sixfold cyclic growth twinning of Sn during solidification from the melt was observed in Sn–Ag, SAC and Sn–Cu solders. Three orientations of Sn grains, each having a common 〈1 0 0〉 direction, were found in each of these systems, though the morphologies of these cyclic twinned microstructures differed. Analysis of dendrite arm spacing in cyclically twined structures with a beach ball morphology implies that the common 〈1 0 0〉 axis intersects with the region of the nucleation event. Models are presented for two pseudo/metastable hexagonal unit cells based upon {1 0 1} or {3 0 1} twins that introduce the cyclic twinning structure at the nucleation stage. Formation of these hexagonal unit cells may be facilitated by the presence of alloy elements. Subsequent epitaxial growth of the tetragonal unit cell on this nucleus can account for all three types of morphologies observed in microstructures of Sn-rich solder alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000443

Mechanics of superelasticity in Ti–30Nb–(8–10)Ta–5Zr alloy / E.G. Obbard in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3557–3567 Titre : Mechanics of superelasticity in Ti–30Nb–(8–10)Ta–5Zr alloy Type de document : texte imprimé Auteurs : E.G. Obbard, Auteur ; Y.L. Hao, Auteur ; T. Akahori, Auteur Année de publication : 2011 Article en page(s) : pp. 3557–3567 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Martensitic  phase  transformation  Shape  memory  alloys  Synchrotron  radiation  Titanium  alloys  X-ray  diffraction Résumé : The superelastic behaviour of Ti–30Nb–10Ta–5Zr and Ti–30Nb–8Ta–5Zr (wt.%) biomedical alloys was investigated by tensile testing and in situ synchrotron X-ray diffraction. The phenomenological theory of martensite crystallography and texture prediction based on the Schmid law indicate that α″ in Ti–30Nb–10Ta–5Zr forms in untwinned variants. Measurement of single-crystal elastic constants using an Eshelby–Kroener–Kneer self-consistent model shows that the 10-Ta alloy has a C′ modulus 3 GPa higher than that of the 8-Ta alloy. That it nevertheless has a proof stress 35 MPa lower can be qualitatively explained by the differences in martensite crystallography. The results suggest that high tensile strength can be maintained for low modulus β-Ti in spite of martensitic transformation by optimizing transformation strains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000960 [article] Mechanics of superelasticity in Ti–30Nb–(8–10)Ta–5Zr alloy [texte imprimé] / E.G. Obbard, Auteur ; Y.L. Hao, Auteur ; T. Akahori, Auteur . - 2011 . - pp. 3557–3567. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3557–3567 Mots-clés : Martensitic  phase  transformation  Shape  memory  alloys  Synchrotron  radiation  Titanium  alloys  X-ray  diffraction Résumé : The superelastic behaviour of Ti–30Nb–10Ta–5Zr and Ti–30Nb–8Ta–5Zr (wt.%) biomedical alloys was investigated by tensile testing and in situ synchrotron X-ray diffraction. The phenomenological theory of martensite crystallography and texture prediction based on the Schmid law indicate that α″ in Ti–30Nb–10Ta–5Zr forms in untwinned variants. Measurement of single-crystal elastic constants using an Eshelby–Kroener–Kneer self-consistent model shows that the 10-Ta alloy has a C′ modulus 3 GPa higher than that of the 8-Ta alloy. That it nevertheless has a proof stress 35 MPa lower can be qualitatively explained by the differences in martensite crystallography. The results suggest that high tensile strength can be maintained for low modulus β-Ti in spite of martensitic transformation by optimizing transformation strains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000960

Observations on the effect of a magnetic field on the annealing texture and microstructure evolution in zirconium / D.A. Molodov in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3568–3581 Titre : Observations on the effect of a magnetic field on the annealing texture and microstructure evolution in zirconium Type de document : texte imprimé Auteurs : D.A. Molodov, Auteur ; N. Bozzolo, Auteur Année de publication : 2011 Article en page(s) : pp. 3568–3581 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  growth  Magnetic  annealing  Zirconium  Magnetic  anisotropy Résumé : The effect of a magnetic field on the development of texture and microstructure in cold-rolled (80%) commercially pure zirconium (Zr701) was investigated. The specifically oriented sheet specimens were annealed at 550 °C for 15, 30 and 45 min and at 700 °C for 60, 90 and 180 min in a magnetic field of 19 T and 17 T, respectively. X-ray diffraction and electron backscatter diffraction measurements were used to characterize the crystallographic texture and the grain microstructure. The results revealed that the magnetic annealing promotes grain growth in the investigated material. This becomes apparent from the faster development of specific “grain growth” texture components and the bigger mean grain size after magnetic annealing. Magnetic annealing at 700 °C resulted in asymmetry of the two major texture components that constantly increased with annealing time. This effect is attributed to a magnetic driving force for grain growth arising from the anisotropic magnetic susceptibility of zirconium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001138 [article] Observations on the effect of a magnetic field on the annealing texture and microstructure evolution in zirconium [texte imprimé] / D.A. Molodov, Auteur ; N. Bozzolo, Auteur . - 2011 . - pp. 3568–3581. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3568–3581 Mots-clés : Grain  growth  Magnetic  annealing  Zirconium  Magnetic  anisotropy Résumé : The effect of a magnetic field on the development of texture and microstructure in cold-rolled (80%) commercially pure zirconium (Zr701) was investigated. The specifically oriented sheet specimens were annealed at 550 °C for 15, 30 and 45 min and at 700 °C for 60, 90 and 180 min in a magnetic field of 19 T and 17 T, respectively. X-ray diffraction and electron backscatter diffraction measurements were used to characterize the crystallographic texture and the grain microstructure. The results revealed that the magnetic annealing promotes grain growth in the investigated material. This becomes apparent from the faster development of specific “grain growth” texture components and the bigger mean grain size after magnetic annealing. Magnetic annealing at 700 °C resulted in asymmetry of the two major texture components that constantly increased with annealing time. This effect is attributed to a magnetic driving force for grain growth arising from the anisotropic magnetic susceptibility of zirconium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001138

Genetic design and characterization of novel ultra-high-strength stainless steels strengthened by Ni3Ti intermetallic nanoprecipitates / W. Xu in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3582–3593 Titre : Genetic design and characterization of novel ultra-high-strength stainless steels strengthened by Ni3Ti intermetallic nanoprecipitates Type de document : texte imprimé Auteurs : W. Xu, Auteur ; P.E.J. Rivera-Díaz-del-Castillo, Auteur ; Wang, W., Auteur Année de publication : 2011 Article en page(s) : pp. 3582–3593 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Maraging  steels  Stainless  steels  Thermodynamics  Precipitation  Alloy  design Résumé : A general computational alloy design approach based on thermodynamic and physical metallurgical principles, and coupled with a genetic optimization scheme, is presented. The method is applied to the design of new ultra-high-strength maraging stainless steels strengthened by Ni3Ti intermetallics. In the first design round, the alloy composition is optimized on the basis of precipitate formation at a fixed ageing temperature without considering other steps in the heat treatment. In the second round, the alloy is redesigned, applying an integrated model which allows for the simultaneous optimization of alloy composition and the ageing temperature as well as the prior austenitization temperature. The experimental characterizations of prototype alloys clearly demonstrate that alloys designed by the proposed approach achieve the desired microstructures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000114X [article] Genetic design and characterization of novel ultra-high-strength stainless steels strengthened by Ni3Ti intermetallic nanoprecipitates [texte imprimé] / W. Xu, Auteur ; P.E.J. Rivera-Díaz-del-Castillo, Auteur ; Wang, W., Auteur . - 2011 . - pp. 3582–3593. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3582–3593 Mots-clés : Maraging  steels  Stainless  steels  Thermodynamics  Precipitation  Alloy  design Résumé : A general computational alloy design approach based on thermodynamic and physical metallurgical principles, and coupled with a genetic optimization scheme, is presented. The method is applied to the design of new ultra-high-strength maraging stainless steels strengthened by Ni3Ti intermetallics. In the first design round, the alloy composition is optimized on the basis of precipitate formation at a fixed ageing temperature without considering other steps in the heat treatment. In the second round, the alloy is redesigned, applying an integrated model which allows for the simultaneous optimization of alloy composition and the ageing temperature as well as the prior austenitization temperature. The experimental characterizations of prototype alloys clearly demonstrate that alloys designed by the proposed approach achieve the desired microstructures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000114X

Role of interface morphology in the exchange-spring behavior of FePt/Fe perpendicular bilayers / F. Casoli in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3594–3601 Titre : Role of interface morphology in the exchange-spring behavior of FePt/Fe perpendicular bilayers Type de document : texte imprimé Auteurs : F. Casoli, Auteur ; F. Albertini, Auteur ; L. Nasi, Auteur Année de publication : 2011 Article en page(s) : pp. 3594–3601 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnetic  recording  thin  films  Iron  alloys  Transmission  electron  microscopy  FePt  exchange-coupled  bilayers  Interfaces Résumé : The role of interface morphology in the magnetic behavior of FePt/Fe exchange-coupled systems has been considered. Hard/soft bilayers with different interface morphologies were obtained by depositing Fe thin layers on FePt epitaxial layers with different morphologies, but all with a high degree of L10 ordering and high coercivity. It was found that the hard/soft coupling can be tuned by changing the FePt morphology, allowing tailoring of the hysteresis loops and modification of the magnetic regime at a fixed Fe thickness (from Rigid Magnet to Exchange-Spring magnet). Remarkably, all bilayer series showed a drastic reduction in coercivity with increasing Fe thickness to 3.5 nm (μ0HC ⩽ 1.1 T). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001151 [article] Role of interface morphology in the exchange-spring behavior of FePt/Fe perpendicular bilayers [texte imprimé] / F. Casoli, Auteur ; F. Albertini, Auteur ; L. Nasi, Auteur . - 2011 . - pp. 3594–3601. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3594–3601 Mots-clés : Magnetic  recording  thin  films  Iron  alloys  Transmission  electron  microscopy  FePt  exchange-coupled  bilayers  Interfaces Résumé : The role of interface morphology in the magnetic behavior of FePt/Fe exchange-coupled systems has been considered. Hard/soft bilayers with different interface morphologies were obtained by depositing Fe thin layers on FePt epitaxial layers with different morphologies, but all with a high degree of L10 ordering and high coercivity. It was found that the hard/soft coupling can be tuned by changing the FePt morphology, allowing tailoring of the hysteresis loops and modification of the magnetic regime at a fixed Fe thickness (from Rigid Magnet to Exchange-Spring magnet). Remarkably, all bilayer series showed a drastic reduction in coercivity with increasing Fe thickness to 3.5 nm (μ0HC ⩽ 1.1 T). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001151

Atom probe tomography analysis of the white etching layer in a rail track surface / J. Takahashi in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3602–3612 Titre : Atom probe tomography analysis of the white etching layer in a rail track surface Type de document : texte imprimé Auteurs : J. Takahashi, Auteur ; K. Kawakami, Auteur ; M. Ueda, Auteur Année de publication : 2011 Article en page(s) : pp. 3602–3612 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Atom  probe  Pearlitic  lamella  Cementite  decomposition  White  etching  layer  Martensite Résumé : Atomic scale characterization of the white etching layer (WEL) in a rail track surface made of pearlitic steel was performed with respect to elemental distribution using atom probe tomography. The atomic distributions of the alloying elements at various depths below the surface were analyzed inside and outside the WEL. Manganese-enriched and silicon-depleted zones corresponding to pre-existing cementite lamellae were observed in the WEL, although the cementite lamellae of the matrix pearlite had completely decomposed. The manganese-enriched and silicon-depleted zones were more distinct in the bottom region than in the topmost surface region of the WEL. The width and spacing of the zones indicated that the WEL region did not undergo heavy deformation. A temperature rise in the rail-to-wheel contact areas was predicted by friction calculation, which was confirmed through shape analysis of the manganese-enriched zones. These results support the hypothesis that martensitic transformation after rapid austenization was the origin of the WEL. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001291 [article] Atom probe tomography analysis of the white etching layer in a rail track surface [texte imprimé] / J. Takahashi, Auteur ; K. Kawakami, Auteur ; M. Ueda, Auteur . - 2011 . - pp. 3602–3612. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3602–3612 Mots-clés : Atom  probe  Pearlitic  lamella  Cementite  decomposition  White  etching  layer  Martensite Résumé : Atomic scale characterization of the white etching layer (WEL) in a rail track surface made of pearlitic steel was performed with respect to elemental distribution using atom probe tomography. The atomic distributions of the alloying elements at various depths below the surface were analyzed inside and outside the WEL. Manganese-enriched and silicon-depleted zones corresponding to pre-existing cementite lamellae were observed in the WEL, although the cementite lamellae of the matrix pearlite had completely decomposed. The manganese-enriched and silicon-depleted zones were more distinct in the bottom region than in the topmost surface region of the WEL. The width and spacing of the zones indicated that the WEL region did not undergo heavy deformation. A temperature rise in the rail-to-wheel contact areas was predicted by friction calculation, which was confirmed through shape analysis of the manganese-enriched zones. These results support the hypothesis that martensitic transformation after rapid austenization was the origin of the WEL. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001291

Use of quasi-static nanoindentation data to obtain stress–strain characteristics for metallic materials / J. Dean in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3613–3623 Titre : Use of quasi-static nanoindentation data to obtain stress–strain characteristics for metallic materials Type de document : texte imprimé Auteurs : J. Dean, Auteur ; J.M. Wheeler, Auteur ; T.W. Clyne, Auteur Année de publication : 2011 Article en page(s) : pp. 3613–3623 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoindentation  Finite  element  analysis  Creep  Non-destructive  testing Résumé : This paper concerns optimization of procedures and algorithms for extraction of stress–strain relationships from quasi-static nanoindentation experiments, using finite element method modelling. Several issues are highlighted, including the usefulness of incorporating residual indent shape in the comparisons, as well as load–displacement–time data, and the significance of creep and interfacial friction. The study is focused on extruded copper bar, using a spherical indenter and assuming transverse isotropy throughout. It is shown that, using the methodology presented here, experimental nanoindentation data could be used to estimate the yield stress and work-hardening rate, with good accuracy, i.e. the yield stress could have been obtained to a precision of about ±10%, and the work-hardening rate to about ±25%. Such inferred constitutive relations are more likely to be reliable if the comparisons are made in regimes within which creep does not significantly influence the behaviour, and in general the timescale of measurement is important. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001308 [article] Use of quasi-static nanoindentation data to obtain stress–strain characteristics for metallic materials [texte imprimé] / J. Dean, Auteur ; J.M. Wheeler, Auteur ; T.W. Clyne, Auteur . - 2011 . - pp. 3613–3623. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3613–3623 Mots-clés : Nanoindentation  Finite  element  analysis  Creep  Non-destructive  testing Résumé : This paper concerns optimization of procedures and algorithms for extraction of stress–strain relationships from quasi-static nanoindentation experiments, using finite element method modelling. Several issues are highlighted, including the usefulness of incorporating residual indent shape in the comparisons, as well as load–displacement–time data, and the significance of creep and interfacial friction. The study is focused on extruded copper bar, using a spherical indenter and assuming transverse isotropy throughout. It is shown that, using the methodology presented here, experimental nanoindentation data could be used to estimate the yield stress and work-hardening rate, with good accuracy, i.e. the yield stress could have been obtained to a precision of about ±10%, and the work-hardening rate to about ±25%. Such inferred constitutive relations are more likely to be reliable if the comparisons are made in regimes within which creep does not significantly influence the behaviour, and in general the timescale of measurement is important. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001308

Dynamic recrystallization mechanisms operating in a Ni–20%Cr alloy under hot-to-warm working / N. Dudova in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3624–3632 Titre : Dynamic recrystallization mechanisms operating in a Ni–20%Cr alloy under hot-to-warm working Type de document : texte imprimé Auteurs : N. Dudova, Auteur ; A. Belyakov, Auteur ; T. Sakai, Auteur Année de publication : 2011 Article en page(s) : pp. 3624–3632 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hot  and  warm  working  Electron  microscopy  Nickel  alloys  Dynamic  recrystallization  Ultrafine  grained  microstructure Résumé : The structural mechanisms responsible for the development of new grains in a Ni–20%Cr alloy during hot-to-warm working were studied in compression at temperatures of 500–950 °C. A bilinear relationship between the flow stresses and the dynamic grain sizes was obtained with an inflection point at 7 × 10−3G. The dynamic grain size can be related to the flow stress through power-law functions with grain size exponents of −0.7 and −0.25 for low and high flow stresses, respectively. The variation of the stress versus grain size dependence is attributed to the change in mechanisms of new grain development from discontinuous to continuous reactions with increasing flow stress. The former is associated with the grain boundary bulging and the latter is related to a strain-induced phenomenon involving the development of large angular misorientations between deformation subgrains after large strains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000131X [article] Dynamic recrystallization mechanisms operating in a Ni–20%Cr alloy under hot-to-warm working [texte imprimé] / N. Dudova, Auteur ; A. Belyakov, Auteur ; T. Sakai, Auteur . - 2011 . - pp. 3624–3632. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3624–3632 Mots-clés : Hot  and  warm  working  Electron  microscopy  Nickel  alloys  Dynamic  recrystallization  Ultrafine  grained  microstructure Résumé : The structural mechanisms responsible for the development of new grains in a Ni–20%Cr alloy during hot-to-warm working were studied in compression at temperatures of 500–950 °C. A bilinear relationship between the flow stresses and the dynamic grain sizes was obtained with an inflection point at 7 × 10−3G. The dynamic grain size can be related to the flow stress through power-law functions with grain size exponents of −0.7 and −0.25 for low and high flow stresses, respectively. The variation of the stress versus grain size dependence is attributed to the change in mechanisms of new grain development from discontinuous to continuous reactions with increasing flow stress. The former is associated with the grain boundary bulging and the latter is related to a strain-induced phenomenon involving the development of large angular misorientations between deformation subgrains after large strains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000131X

Density change upon crystallization of amorphous Zr–Cu–Al thin films / Qiang Guo in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3633–3641 Titre : Density change upon crystallization of amorphous Zr–Cu–Al thin films Type de document : texte imprimé Auteurs : Qiang Guo, Auteur ; Peter K. Liaw, Auteur ; Philip D. Rack, Auteur Année de publication : 2011 Article en page(s) : pp. 3633–3641 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metallic  glasses  Crystallization  Thin  films Résumé : Systematic deflection measurements with micro-cantilevers and a combinatorial-deposition method have been used to investigate the density change upon crystallization of amorphous Zr–Cu–Al thin films. It is found that, in general, the density change decreases from Cu-/Al-rich compositions to Zr-rich compositions, and the previously reported good glass-forming compositions are found to correspond to global minima of the density change inside respective local eutectic systems. Furthermore, we propose that the general trend of density change as a function of alloy compositions discovered in this work may have implications for the macroscopic plasticity of metallic glasses. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001321 [article] Density change upon crystallization of amorphous Zr–Cu–Al thin films [texte imprimé] / Qiang Guo, Auteur ; Peter K. Liaw, Auteur ; Philip D. Rack, Auteur . - 2011 . - pp. 3633–3641. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3633–3641 Mots-clés : Metallic  glasses  Crystallization  Thin  films Résumé : Systematic deflection measurements with micro-cantilevers and a combinatorial-deposition method have been used to investigate the density change upon crystallization of amorphous Zr–Cu–Al thin films. It is found that, in general, the density change decreases from Cu-/Al-rich compositions to Zr-rich compositions, and the previously reported good glass-forming compositions are found to correspond to global minima of the density change inside respective local eutectic systems. Furthermore, we propose that the general trend of density change as a function of alloy compositions discovered in this work may have implications for the macroscopic plasticity of metallic glasses. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001321

The formation of randomly textured magnesium alloy sheet through rapid solidification / N. Stanford in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3642–3654 Titre : The formation of randomly textured magnesium alloy sheet through rapid solidification Type de document : texte imprimé Auteurs : N. Stanford, Auteur ; D. Phelan, Auteur Année de publication : 2011 Article en page(s) : pp. 3642–3654 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Rapid  solidification  Magnesium  alloys  Texture  Strip  casting Résumé : The rapid solidification of three magnesium-based alloys has been carried out on copper substrates with four tailored surface morphologies. Increasing surface roughness improved the wetting characteristics of the substrates, as did coating with carbon. Of the alloys tested, AZ31 showed inferior wetting behaviour due to the formation of alumina oxides at the interface between the melt and the copper substrate. This behaviour was obviated by the addition of calcium to the melt. The pure magnesium castings all produced a strongly columnar region and showed a weak crystallographic texture. The alloy castings produced weakly columnar regions with an essentially random texture. The alloys cast onto the carbon-coated substrates produced a fully equiaxed microstructure due to the inhibition of heterogeneous nucleation on the substrate surface. It is demonstrated that a randomly textured microstructure with equiaxed grains can be produced through rapid solidification and the implications of this microstructure for the ductility of magnesium sheet is discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001333 [article] The formation of randomly textured magnesium alloy sheet through rapid solidification [texte imprimé] / N. Stanford, Auteur ; D. Phelan, Auteur . - 2011 . - pp. 3642–3654. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3642–3654 Mots-clés : Rapid  solidification  Magnesium  alloys  Texture  Strip  casting Résumé : The rapid solidification of three magnesium-based alloys has been carried out on copper substrates with four tailored surface morphologies. Increasing surface roughness improved the wetting characteristics of the substrates, as did coating with carbon. Of the alloys tested, AZ31 showed inferior wetting behaviour due to the formation of alumina oxides at the interface between the melt and the copper substrate. This behaviour was obviated by the addition of calcium to the melt. The pure magnesium castings all produced a strongly columnar region and showed a weak crystallographic texture. The alloy castings produced weakly columnar regions with an essentially random texture. The alloys cast onto the carbon-coated substrates produced a fully equiaxed microstructure due to the inhibition of heterogeneous nucleation on the substrate surface. It is demonstrated that a randomly textured microstructure with equiaxed grains can be produced through rapid solidification and the implications of this microstructure for the ductility of magnesium sheet is discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001333

Microstructures and shape memory characteristics of dual-phase Co–Ni–Ga high-temperature shape memory alloys / Yan Li in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3655–3663 Titre : Microstructures and shape memory characteristics of dual-phase Co–Ni–Ga high-temperature shape memory alloys Type de document : texte imprimé Auteurs : Yan Li, Auteur ; Yan Xin, Auteur ; Liang Chai, Auteur Année de publication : 2011 Article en page(s) : pp. 3655–3663 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Co–Ni–Ga  Dual  phases  Shape  memory  alloys  Martensitic  phase  transformation  Fracture Résumé : The influence of microstructure on mechanical properties and shape memory characteristics of Co–Ni–Ga high-temperature shape memory alloys were investigated in this study. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were employed to detect the microstructures. We found that these alloys were composed of dual phases, a non-modulated tetragonal L10 martensite and a face-centered cubic (fcc) γ phase. The martensite was twinned and well self-accommodated. The γ phase was a Co-based solid solution with 30% lower hardness than martensite. Although the fracture mode was intergranular, the strength and plasticity of the alloys increased markedly with the increasing volume fraction of the γ phase. The presence of the γ phase in grain boundaries rather than in the martensite is favorable to shape memory recovery. This was revealed by the maximum shape recovery strain over 5.0% that was obtained in the Co46Ni25Ga29 alloy, with the γ phase formed mainly in grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001461 [article] Microstructures and shape memory characteristics of dual-phase Co–Ni–Ga high-temperature shape memory alloys [texte imprimé] / Yan Li, Auteur ; Yan Xin, Auteur ; Liang Chai, Auteur . - 2011 . - pp. 3655–3663. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3655–3663 Mots-clés : Co–Ni–Ga  Dual  phases  Shape  memory  alloys  Martensitic  phase  transformation  Fracture Résumé : The influence of microstructure on mechanical properties and shape memory characteristics of Co–Ni–Ga high-temperature shape memory alloys were investigated in this study. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were employed to detect the microstructures. We found that these alloys were composed of dual phases, a non-modulated tetragonal L10 martensite and a face-centered cubic (fcc) γ phase. The martensite was twinned and well self-accommodated. The γ phase was a Co-based solid solution with 30% lower hardness than martensite. Although the fracture mode was intergranular, the strength and plasticity of the alloys increased markedly with the increasing volume fraction of the γ phase. The presence of the γ phase in grain boundaries rather than in the martensite is favorable to shape memory recovery. This was revealed by the maximum shape recovery strain over 5.0% that was obtained in the Co46Ni25Ga29 alloy, with the γ phase formed mainly in grain boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001461

Diffusivities of an Al–Fe–Ni melt and their effects on the microstructure during solidification / Lijun Zhang in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3664–3675 Titre : Diffusivities of an Al–Fe–Ni melt and their effects on the microstructure during solidification Type de document : texte imprimé Auteurs : Lijun Zhang, Auteur ; Yong Du, Auteur ; Ingo Steinbach, Auteur Année de publication : 2011 Article en page(s) : pp. 3664–3675 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Al–Fe–Ni  melt  Diffusion  Atomic  mobility  Microstructure  Solidification Résumé : A systematical investigation of the diffusivities in an Al–Fe–Ni melt was presented. Based on the experimental and theoretical data about diffusivities, the temperature- and composition-dependent atomic mobilities were evaluated for the elements in Al–Ni, Al–Fe, Fe–Ni and Al–Fe–Ni melts via an effective approach. Most of the reported diffusivities can be reproduced well by the obtained atomic mobilities. In particular, for the first time the ternary diffusivity of the liquid in a ternary system is described in conjunction with the established atomic mobilities. The effect of the atomic mobilities in a liquid on microstructure and microsegregation during solidification was demonstrated with one Al–Ni binary alloy. The simulation results indicate that accurate databases of mobilities in the liquid phase are much needed for the quantitative simulation of microstructural evolution during solidification by using various approaches, including DICTRA and the phase-field method. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001473 [article] Diffusivities of an Al–Fe–Ni melt and their effects on the microstructure during solidification [texte imprimé] / Lijun Zhang, Auteur ; Yong Du, Auteur ; Ingo Steinbach, Auteur . - 2011 . - pp. 3664–3675. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3664–3675 Mots-clés : Al–Fe–Ni  melt  Diffusion  Atomic  mobility  Microstructure  Solidification Résumé : A systematical investigation of the diffusivities in an Al–Fe–Ni melt was presented. Based on the experimental and theoretical data about diffusivities, the temperature- and composition-dependent atomic mobilities were evaluated for the elements in Al–Ni, Al–Fe, Fe–Ni and Al–Fe–Ni melts via an effective approach. Most of the reported diffusivities can be reproduced well by the obtained atomic mobilities. In particular, for the first time the ternary diffusivity of the liquid in a ternary system is described in conjunction with the established atomic mobilities. The effect of the atomic mobilities in a liquid on microstructure and microsegregation during solidification was demonstrated with one Al–Ni binary alloy. The simulation results indicate that accurate databases of mobilities in the liquid phase are much needed for the quantitative simulation of microstructural evolution during solidification by using various approaches, including DICTRA and the phase-field method. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001473

SMIG model / F. Mompiou in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3676–3689 Titre : SMIG model : A new geometrical model to quantify grain boundary-based plasticity Type de document : texte imprimé Auteurs : F. Mompiou, Auteur ; M. Legros, Auteur ; D. Caillard, Auteur Année de publication : 2011 Article en page(s) : pp. 3676–3689 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  boundary  Coupled  shear-migration  Geometrical  modelling Résumé : Stress-assisted grain boundary migration is a mechanism that has proven active in polycrystals but that relies on a limited number of models. Those models do not apply to general grain boundaries and often fail to reproduce the intensity of the coupling between the migration distance and the produced shear strain. Recently a new geometrical model, entitled the shear migration geometrical (SMIG) model, that is valid for all tilt boundaries has been introduced to account for the low coupling factors observed experimentally. In the present work we propose, on the basis of this model, (i) to determine, for a given tilt grain boundary, the number of possible coupling modes and (ii) to evaluate the shuffling needed to rearrange atoms as the grain boundary migrates. We will show that, for a given grain boundary defined by a misorientation angle and a grain boundary plane, it is almost always possible to find a coupling mode implying the shuffling of up to 20 atoms, supposedly without long-range diffusion. This characteristic is of prime importance in polycrystals where collective grain boundary motions are required to accommodate strain. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001485 [article] SMIG model : A new geometrical model to quantify grain boundary-based plasticity [texte imprimé] / F. Mompiou, Auteur ; M. Legros, Auteur ; D. Caillard, Auteur . - 2011 . - pp. 3676–3689. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3676–3689 Mots-clés : Grain  boundary  Coupled  shear-migration  Geometrical  modelling Résumé : Stress-assisted grain boundary migration is a mechanism that has proven active in polycrystals but that relies on a limited number of models. Those models do not apply to general grain boundaries and often fail to reproduce the intensity of the coupling between the migration distance and the produced shear strain. Recently a new geometrical model, entitled the shear migration geometrical (SMIG) model, that is valid for all tilt boundaries has been introduced to account for the low coupling factors observed experimentally. In the present work we propose, on the basis of this model, (i) to determine, for a given tilt grain boundary, the number of possible coupling modes and (ii) to evaluate the shuffling needed to rearrange atoms as the grain boundary migrates. We will show that, for a given grain boundary defined by a misorientation angle and a grain boundary plane, it is almost always possible to find a coupling mode implying the shuffling of up to 20 atoms, supposedly without long-range diffusion. This characteristic is of prime importance in polycrystals where collective grain boundary motions are required to accommodate strain. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001485

The influence of indenter tip rounding on the indentation size effect / Xiao Guang Qiao in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3690–3700 Titre : The influence of indenter tip rounding on the indentation size effect Type de document : texte imprimé Auteurs : Xiao Guang Qiao, Auteur ; Marco J. Starink, Auteur ; Nong Gao, Auteur Année de publication : 2011 Article en page(s) : pp. 3690–3700 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ultrafine-grained  (UFG)  aluminium  Nanoindentation  Geometrically  necessary  dislocations  Tip  rounding  effect Résumé : A model was developed to interpret the indentation size effect (ISE). The model considers the tip wear effect, causing a rounded tip, the plastic zone size and various strengthening contributions, including geometrically necessary dislocations, pre-existing statistically stored dislocations and grain size. It is shown that the shape of the worn tip can be effectively determined through calibration experiments. The model is applied to predict dislocation densities, and shows a good correspondence with published data on dislocation densities in copper single crystals. The predicted ISE is shown to be in good correspondence with published data on a range of metals, and an improvement over existing models is demonstrated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001497 [article] The influence of indenter tip rounding on the indentation size effect [texte imprimé] / Xiao Guang Qiao, Auteur ; Marco J. Starink, Auteur ; Nong Gao, Auteur . - 2011 . - pp. 3690–3700. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3690–3700 Mots-clés : Ultrafine-grained  (UFG)  aluminium  Nanoindentation  Geometrically  necessary  dislocations  Tip  rounding  effect Résumé : A model was developed to interpret the indentation size effect (ISE). The model considers the tip wear effect, causing a rounded tip, the plastic zone size and various strengthening contributions, including geometrically necessary dislocations, pre-existing statistically stored dislocations and grain size. It is shown that the shape of the worn tip can be effectively determined through calibration experiments. The model is applied to predict dislocation densities, and shows a good correspondence with published data on dislocation densities in copper single crystals. The predicted ISE is shown to be in good correspondence with published data on a range of metals, and an improvement over existing models is demonstrated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001497

Structural evolution and physical properties of Bi1−xGdxFeO3 ceramics / J.B. Li in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3701–3708 Titre : Structural evolution and physical properties of Bi1−xGdxFeO3 ceramics Type de document : texte imprimé Auteurs : J.B. Li, Auteur ; G.H. Rao, Auteur ; Xiao, Y., Auteur Année de publication : 2011 Article en page(s) : pp. 3701–3708 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bi-based  magnetoelectric  perovskites  Crystal  structure  Phase  transformation  X-ray  diffraction Résumé : The crystal structure and physical properties of Bi1−xGdxFeO3 ceramics with x ≤ 0.5 have been studied by X-ray diffraction, differential scanning calorimetry, dielectric and magnetic measurements. Bi1−xGdxFeO3 compounds crystallize at room temperature in R3c structure for x < 0.08 and in Pbnm structure for x ≥ 0.3. The R3c phase transforms to the Pbnm phase as temperature increases. Temperature-dependent dielectric response and low-temperature X-ray diffraction indicate a phase transition of the Pbnm phase at low-temperature. Detailed structural analysis indicates that the interaction between Bi and O plays an important role in the evolution of structure and physical properties. A phase diagram is constructed to illustrate the physical property–composition–temperature relations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001527 [article] Structural evolution and physical properties of Bi1−xGdxFeO3 ceramics [texte imprimé] / J.B. Li, Auteur ; G.H. Rao, Auteur ; Xiao, Y., Auteur . - 2011 . - pp. 3701–3708. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3701–3708 Mots-clés : Bi-based  magnetoelectric  perovskites  Crystal  structure  Phase  transformation  X-ray  diffraction Résumé : The crystal structure and physical properties of Bi1−xGdxFeO3 ceramics with x ≤ 0.5 have been studied by X-ray diffraction, differential scanning calorimetry, dielectric and magnetic measurements. Bi1−xGdxFeO3 compounds crystallize at room temperature in R3c structure for x < 0.08 and in Pbnm structure for x ≥ 0.3. The R3c phase transforms to the Pbnm phase as temperature increases. Temperature-dependent dielectric response and low-temperature X-ray diffraction indicate a phase transition of the Pbnm phase at low-temperature. Detailed structural analysis indicates that the interaction between Bi and O plays an important role in the evolution of structure and physical properties. A phase diagram is constructed to illustrate the physical property–composition–temperature relations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001527

A mean-field micromechanical model of thermal-ratcheting behavior in short fiber-reinforced metal matrix composites / Hideaki Tsukamoto in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3709–3717 Titre : A mean-field micromechanical model of thermal-ratcheting behavior in short fiber-reinforced metal matrix composites Type de document : texte imprimé Auteurs : Hideaki Tsukamoto, Auteur Année de publication : 2011 Article en page(s) : pp. 3709–3717 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metal  matrix  composites  (MMCs)  Thermal  ratcheting  Internal  stress  Micromechanical  modeling Résumé : Thermal-ratcheting behavior in short fiber-reinforced metal matrix composites has been investigated. The internal stresses due to mismatch in thermal expansion coefficients between the fiber and matrix in the composites can introduce anomalous deformation under thermal-cycling conditions with or without external mechanical loads. This study has resulted in a more comprehensive understanding of such thermal-ratcheting behavior in short fiber-reinforced composites subject to a wide range of external uniaxial loads based on a mean-field micromechanical model considering the local mass transfer by diffusion along the fiber–matrix interface. The validity of the model has been verified through systematic experiments with directionally solidified Al–Al3Ni eutectic composites. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001539 [article] A mean-field micromechanical model of thermal-ratcheting behavior in short fiber-reinforced metal matrix composites [texte imprimé] / Hideaki Tsukamoto, Auteur . - 2011 . - pp. 3709–3717. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3709–3717 Mots-clés : Metal  matrix  composites  (MMCs)  Thermal  ratcheting  Internal  stress  Micromechanical  modeling Résumé : Thermal-ratcheting behavior in short fiber-reinforced metal matrix composites has been investigated. The internal stresses due to mismatch in thermal expansion coefficients between the fiber and matrix in the composites can introduce anomalous deformation under thermal-cycling conditions with or without external mechanical loads. This study has resulted in a more comprehensive understanding of such thermal-ratcheting behavior in short fiber-reinforced composites subject to a wide range of external uniaxial loads based on a mean-field micromechanical model considering the local mass transfer by diffusion along the fiber–matrix interface. The validity of the model has been verified through systematic experiments with directionally solidified Al–Al3Ni eutectic composites. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001539

Thermodynamic theory of dislocation-mediated plasticity / J.S. Langer in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3718–3732 Titre : Thermodynamic theory of dislocation-mediated plasticity Type de document : texte imprimé Auteurs : J.S. Langer, Auteur ; Eran Bouchbinder, Auteur ; Turab Lookman, Auteur Année de publication : 2011 Article en page(s) : pp. 3718–3732 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  theory  Hardening  Thermodynamics Résumé : We reformulate the theory of polycrystalline plasticity, in externally driven, nonequilibrium situations, by writing equations of motion for the flow of energy and entropy associated with dislocations. Within this general framework, and using a minimal model of thermally assisted depinning with essentially only one adjustable parameter, we find that our theory fits the strain-hardening data for Cu over a wide range of temperatures and six decades of strain rate. We predict the transition between stage II and stage III hardening, including the observation that this transition occurs at smaller strains for higher temperatures. We also explain why strain-rate hardening is very weak up to large rates; and, with just one additional number, we accurately predict the crossover to power-law rate hardening in the strong-shock regime. Our analysis differs in several important respects from conventional dislocation-mediated continuum theories. We provide some historical background and discuss our rationale for these differences. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001540 [article] Thermodynamic theory of dislocation-mediated plasticity [texte imprimé] / J.S. Langer, Auteur ; Eran Bouchbinder, Auteur ; Turab Lookman, Auteur . - 2011 . - pp. 3718–3732. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3718–3732 Mots-clés : Dislocation  theory  Hardening  Thermodynamics Résumé : We reformulate the theory of polycrystalline plasticity, in externally driven, nonequilibrium situations, by writing equations of motion for the flow of energy and entropy associated with dislocations. Within this general framework, and using a minimal model of thermally assisted depinning with essentially only one adjustable parameter, we find that our theory fits the strain-hardening data for Cu over a wide range of temperatures and six decades of strain rate. We predict the transition between stage II and stage III hardening, including the observation that this transition occurs at smaller strains for higher temperatures. We also explain why strain-rate hardening is very weak up to large rates; and, with just one additional number, we accurately predict the crossover to power-law rate hardening in the strong-shock regime. Our analysis differs in several important respects from conventional dislocation-mediated continuum theories. We provide some historical background and discuss our rationale for these differences. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001540

Effect of Cu on the evolution of precipitation in an Fe–Cr–Ni–Al–Ti maraging steel / Ronald Schnitzer in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3733–3741 Titre : Effect of Cu on the evolution of precipitation in an Fe–Cr–Ni–Al–Ti maraging steel Type de document : texte imprimé Auteurs : Ronald Schnitzer, Auteur ; Michael Schober, Auteur ; Silvia Zinner, Auteur Année de publication : 2011 Article en page(s) : pp. 3733–3741 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Maraging  steel  Atom  probe  tomography  Precipitates  Aging Résumé : The evolution of precipitates in an Fe–Cr–Ni–Al–Ti stainless maraging steel alloyed with Cu was investigated during aging at 525 °C. Atom probe tomography was used to reveal the development of precipitates and to determine their chemical composition. Two types of precipitates were observed to form during the aging process. Based on their chemical composition these are assumed to be NiAl B2 and Ni3(Ti,Al) (η-phase). The two phases of precipitates were found to develop independently of each other and the addition of Cu was found to accelerate precipitation. However, the effect of Cu on the nucleation of these phases is different: on the one hand, in the case of NiAl, Cu is incorporated and thus reduces the activation energy by reducing the lattice misfit; on the other hand, Cu acts as a nucleation site for the precipitation of Ni3(Ti,Al) by forming independent Cu clusters. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001552 [article] Effect of Cu on the evolution of precipitation in an Fe–Cr–Ni–Al–Ti maraging steel [texte imprimé] / Ronald Schnitzer, Auteur ; Michael Schober, Auteur ; Silvia Zinner, Auteur . - 2011 . - pp. 3733–3741. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3733–3741 Mots-clés : Maraging  steel  Atom  probe  tomography  Precipitates  Aging Résumé : The evolution of precipitates in an Fe–Cr–Ni–Al–Ti stainless maraging steel alloyed with Cu was investigated during aging at 525 °C. Atom probe tomography was used to reveal the development of precipitates and to determine their chemical composition. Two types of precipitates were observed to form during the aging process. Based on their chemical composition these are assumed to be NiAl B2 and Ni3(Ti,Al) (η-phase). The two phases of precipitates were found to develop independently of each other and the addition of Cu was found to accelerate precipitation. However, the effect of Cu on the nucleation of these phases is different: on the one hand, in the case of NiAl, Cu is incorporated and thus reduces the activation energy by reducing the lattice misfit; on the other hand, Cu acts as a nucleation site for the precipitation of Ni3(Ti,Al) by forming independent Cu clusters. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001552

Stick–slip behavior of serrated flow during inhomogeneous deformation of bulk metallic glasses / Florian H. Dalla Torre in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3742–3750 Titre : Stick–slip behavior of serrated flow during inhomogeneous deformation of bulk metallic glasses Type de document : texte imprimé Auteurs : Florian H. Dalla Torre, Auteur ; David Klaumünzer, Auteur ; Robert Maaß, Auteur Année de publication : 2011 Article en page(s) : pp. 3742–3750 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bulk  metallic  glasses  Serrated  flow  Viscosity  Shear  banding  Acoustic  emission Résumé : Accurate compression tests with a piezoelectric load cell and an acquisition rate of up to 10 kHz were performed on a Zr-based bulk metallic glass in the temperature range 210–320 K at a strain rate of 10−3 s−1. Information about the stress drop magnitude and the associated size of shear displacements as a function of temperature and strain provides detailed insights into the shear band characteristics, which can be described by a stick–slip process. The average shear slip displacement is on average about 1–2 μm, irrespective of temperature, whereas the associated slip time (or stress drop time) increases from ∼1 ms at 320 K to ∼0.4 s at 213 K, yielding values on the deformation kinetics and the shear viscosity. Scanning electron microscopy investigations on shear surfaces and in situ acoustic emission measurements provide further understanding into the complex multistep shear slip process. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001564 [article] Stick–slip behavior of serrated flow during inhomogeneous deformation of bulk metallic glasses [texte imprimé] / Florian H. Dalla Torre, Auteur ; David Klaumünzer, Auteur ; Robert Maaß, Auteur . - 2011 . - pp. 3742–3750. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3742–3750 Mots-clés : Bulk  metallic  glasses  Serrated  flow  Viscosity  Shear  banding  Acoustic  emission Résumé : Accurate compression tests with a piezoelectric load cell and an acquisition rate of up to 10 kHz were performed on a Zr-based bulk metallic glass in the temperature range 210–320 K at a strain rate of 10−3 s−1. Information about the stress drop magnitude and the associated size of shear displacements as a function of temperature and strain provides detailed insights into the shear band characteristics, which can be described by a stick–slip process. The average shear slip displacement is on average about 1–2 μm, irrespective of temperature, whereas the associated slip time (or stress drop time) increases from ∼1 ms at 320 K to ∼0.4 s at 213 K, yielding values on the deformation kinetics and the shear viscosity. Scanning electron microscopy investigations on shear surfaces and in situ acoustic emission measurements provide further understanding into the complex multistep shear slip process. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001564

Martensite structure in Ti–Ni–Hf–Cu quaternary alloy ribbons containing (Ti,Hf)2Ni precipitates / X.L. Meng in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3751–3763 Titre : Martensite structure in Ti–Ni–Hf–Cu quaternary alloy ribbons containing (Ti,Hf)2Ni precipitates Type de document : texte imprimé Auteurs : X.L. Meng, Auteur ; W. Cai, Auteur ; Y.D. Fu, Auteur Année de publication : 2011 Article en page(s) : pp. 3751–3763 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ti–Ni–Hf–Cu  alloy  Microstructure  Martensite  Precipitates  Transmission  electron  microscopy Résumé : The martensite structure in a Ti36Ni44Hf15Cu5 ribbon annealed at different temperatures is investigated. When the annealing temperature is <873 K, spherical (Ti,Hf)2Ni particles 20–40 nm in diameter precipitate in the grain interior. Transmission electron microscopy analysis shows that (0 0 1) compound twins are dominant in the ribbon containing homogeneously distributed (Ti,Hf)2Ni precipitates. When the annealing temperature is 773 K, the boundaries between the martensite domains with the (0 0 1) twins are blurry and vague. When the annealing temperature is 873 K, four types of boundaries among the martensite domains are found: {1 1 1}, (0 0 1)//{1 1 1}, {1 1 3} and (1 1 0)//{1 1 3} types. When the annealing temperature is 973 K, the (0 1 1) twins become dominant, and the martensite variants show mainly spear-like and mosaic-like morphologies. However, martensite domains with (0 0 1) twins also exist around the coarse (Ti,Hf)2Ni precipitates. Fine (Ti,Hf)2Ni precipitates should be responsible for the improvement in shape memory effect and the superelasticity of Ti–Ni–Hf–Cu ribbons. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001606 [article] Martensite structure in Ti–Ni–Hf–Cu quaternary alloy ribbons containing (Ti,Hf)2Ni precipitates [texte imprimé] / X.L. Meng, Auteur ; W. Cai, Auteur ; Y.D. Fu, Auteur . - 2011 . - pp. 3751–3763. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3751–3763 Mots-clés : Ti–Ni–Hf–Cu  alloy  Microstructure  Martensite  Precipitates  Transmission  electron  microscopy Résumé : The martensite structure in a Ti36Ni44Hf15Cu5 ribbon annealed at different temperatures is investigated. When the annealing temperature is <873 K, spherical (Ti,Hf)2Ni particles 20–40 nm in diameter precipitate in the grain interior. Transmission electron microscopy analysis shows that (0 0 1) compound twins are dominant in the ribbon containing homogeneously distributed (Ti,Hf)2Ni precipitates. When the annealing temperature is 773 K, the boundaries between the martensite domains with the (0 0 1) twins are blurry and vague. When the annealing temperature is 873 K, four types of boundaries among the martensite domains are found: {1 1 1}, (0 0 1)//{1 1 1}, {1 1 3} and (1 1 0)//{1 1 3} types. When the annealing temperature is 973 K, the (0 1 1) twins become dominant, and the martensite variants show mainly spear-like and mosaic-like morphologies. However, martensite domains with (0 0 1) twins also exist around the coarse (Ti,Hf)2Ni precipitates. Fine (Ti,Hf)2Ni precipitates should be responsible for the improvement in shape memory effect and the superelasticity of Ti–Ni–Hf–Cu ribbons. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001606

Structure of Cs0.5[Nb2.5W2.5O14] analysed by focal-series reconstruction and crystallographic image processing / Juri Barthel in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3764–3772 Titre : Structure of Cs0.5[Nb2.5W2.5O14] analysed by focal-series reconstruction and crystallographic image processing Type de document : texte imprimé Auteurs : Juri Barthel, Auteur ; Thomas E. Weirich, Auteur ; Gerhard Cox, Auteur Année de publication : 2011 Article en page(s) : pp. 3764–3772 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : High-resolution  transmission  electron  microscopy  (HRTEM)  Focal-series  reconstruction  Crystallographic  image  processing  (CIP)  Density  functional  theory  (DFT) Résumé : The structure of the oxygen sub-lattice in Cs0.5[Nb2.5W2.5O14] is investigated for the first time by advanced electron-optical methods. Since Cs0.5[Nb2.5W2.5O14] resembles the crystal structure of the so-called M1 phase of Mo–V–Nb–Te–O, which is the best catalyst for the selective oxidation of propane to acrylic acid, the structure analysis of the oxygen sub-lattice can contribute substantially to a better understanding of this catalytic process. The so far only partially known structure of the complex metal oxide Cs0.5[Nb2.5W2.5O14] is investigated by combining modern methods of high-resolution transmission electron microscopy with crystallographic image processing techniques. Average atom positions in the a–b plane are determined from the phase of the exit-plane wave function, which was numerically reconstructed from a focal series of spherical-aberration-corrected electron micrographs. The experimentally determined atom positions agree well with a structure model obtained by first-principles calculations for the underlying M5O14 (M = Nb, W) framework. Moreover, several deviations from the periodic structure, which may influence the catalytic properties of the structurally similar M1 phase, are observed. The obtained results demonstrate that aberration-corrected high-resolution transmission electron microscopy is a reliable alternative for the analysis of periodic structures, in particular when traditional methods for crystallographic structure determination like XRD or neutron diffraction cannot be applied. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001618 [article] Structure of Cs0.5[Nb2.5W2.5O14] analysed by focal-series reconstruction and crystallographic image processing [texte imprimé] / Juri Barthel, Auteur ; Thomas E. Weirich, Auteur ; Gerhard Cox, Auteur . - 2011 . - pp. 3764–3772. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3764–3772 Mots-clés : High-resolution  transmission  electron  microscopy  (HRTEM)  Focal-series  reconstruction  Crystallographic  image  processing  (CIP)  Density  functional  theory  (DFT) Résumé : The structure of the oxygen sub-lattice in Cs0.5[Nb2.5W2.5O14] is investigated for the first time by advanced electron-optical methods. Since Cs0.5[Nb2.5W2.5O14] resembles the crystal structure of the so-called M1 phase of Mo–V–Nb–Te–O, which is the best catalyst for the selective oxidation of propane to acrylic acid, the structure analysis of the oxygen sub-lattice can contribute substantially to a better understanding of this catalytic process. The so far only partially known structure of the complex metal oxide Cs0.5[Nb2.5W2.5O14] is investigated by combining modern methods of high-resolution transmission electron microscopy with crystallographic image processing techniques. Average atom positions in the a–b plane are determined from the phase of the exit-plane wave function, which was numerically reconstructed from a focal series of spherical-aberration-corrected electron micrographs. The experimentally determined atom positions agree well with a structure model obtained by first-principles calculations for the underlying M5O14 (M = Nb, W) framework. Moreover, several deviations from the periodic structure, which may influence the catalytic properties of the structurally similar M1 phase, are observed. The obtained results demonstrate that aberration-corrected high-resolution transmission electron microscopy is a reliable alternative for the analysis of periodic structures, in particular when traditional methods for crystallographic structure determination like XRD or neutron diffraction cannot be applied. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001618

Polarization fatigue in Pb(In0.5Nb0.5)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals / Shujun Zhang in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3773–3780 Titre : Polarization fatigue in Pb(In0.5Nb0.5)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals Type de document : texte imprimé Auteurs : Shujun Zhang, Auteur ; Jun Luo, Auteur ; Fei Li, Auteur Année de publication : 2011 Article en page(s) : pp. 3773–3780 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ferroelectricity  Piezoelectricity  Fatigue  Internal  stresses  Perovskite  crystal Résumé : Electric fatigue tests have been conducted on pure and manganese-modified Pb(In0.5Nb0.5)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystals along different crystallographic directions. Polarization degradation was observed to suddenly occur above 50–100 bipolar cycles in 〈1 1 0〉 oriented samples, while 〈0 0 1〉 oriented samples exhibited almost fatigue free characteristics. The fatigue behavior was investigated as a function of orientation, magnitude of the electric field and manganese dopant. It was found that 〈0 0 1〉 oriented PIN–PMN–PT crystals were fatigue free, due to its small domain size, being on the order of 1 μm. The 〈1 1 0〉 direction exhibited a strong electrical fatigue behavior due to mechanical degradation. Micro/macro cracks developed in fatigued 〈1 1 0〉 oriented single crystals. Fatigue and cracks were the result of strong anisotropic piezoelectric stress and non-180° domain switching, which completely locked the non-180° domains. Furthermore, manganese-modified PIN–PMN–PT crystals were found to show improved fatigue behavior due to an enhanced coercive field. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001631 [article] Polarization fatigue in Pb(In0.5Nb0.5)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals [texte imprimé] / Shujun Zhang, Auteur ; Jun Luo, Auteur ; Fei Li, Auteur . - 2011 . - pp. 3773–3780. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3773–3780 Mots-clés : Ferroelectricity  Piezoelectricity  Fatigue  Internal  stresses  Perovskite  crystal Résumé : Electric fatigue tests have been conducted on pure and manganese-modified Pb(In0.5Nb0.5)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystals along different crystallographic directions. Polarization degradation was observed to suddenly occur above 50–100 bipolar cycles in 〈1 1 0〉 oriented samples, while 〈0 0 1〉 oriented samples exhibited almost fatigue free characteristics. The fatigue behavior was investigated as a function of orientation, magnitude of the electric field and manganese dopant. It was found that 〈0 0 1〉 oriented PIN–PMN–PT crystals were fatigue free, due to its small domain size, being on the order of 1 μm. The 〈1 1 0〉 direction exhibited a strong electrical fatigue behavior due to mechanical degradation. Micro/macro cracks developed in fatigued 〈1 1 0〉 oriented single crystals. Fatigue and cracks were the result of strong anisotropic piezoelectric stress and non-180° domain switching, which completely locked the non-180° domains. Furthermore, manganese-modified PIN–PMN–PT crystals were found to show improved fatigue behavior due to an enhanced coercive field. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001631

High-temperature strength of compacted sub-micrometer aluminium powder / C. Poletti in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3781–3789 Titre : High-temperature strength of compacted sub-micrometer aluminium powder Type de document : texte imprimé Auteurs : C. Poletti, Auteur ; M. Balog, Auteur ; F. Simancik, Auteur Année de publication : 2011 Article en page(s) : pp. 3781–3789 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Powder  consolidation  Aluminium  Ultrafine-grained  microstructure  High-temperature  deformation  Grain  boundary  structure Résumé : Aluminium powders with a mean particle size of around 1 μm were compacted by cold isostatic pressing (CIP) and additional forging. The specimens are characterized by hot compression tests, dilatometry and metallography. A 3D interconnected structure of alumina films <5 nm in thickness is observed by transmission electron microscopy and field emission gun scanning electron microscopy; it is associated with the natural oxide skin which covers every aluminium powder and occupies around 3 vol.%. The compression tests are carried out in the range of 350–520 °C at strain rates of 0.003–3 s−1. The compressive strength was 100–150 and 130–180 MPa for the CIPed and forged samples, respectively. The low strain rate sensitivity m (<0.08) suggests that the alumina network forms a barrier, which suppresses any restoration mechanism across the grain boundaries as well as grain boundary sliding during hot deformation. The high strength of such compacted sub-micron Al powder is attributed to the conservation of a 3D alumina closed cell network filled with elastoplastic aluminium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001667 [article] High-temperature strength of compacted sub-micrometer aluminium powder [texte imprimé] / C. Poletti, Auteur ; M. Balog, Auteur ; F. Simancik, Auteur . - 2011 . - pp. 3781–3789. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3781–3789 Mots-clés : Powder  consolidation  Aluminium  Ultrafine-grained  microstructure  High-temperature  deformation  Grain  boundary  structure Résumé : Aluminium powders with a mean particle size of around 1 μm were compacted by cold isostatic pressing (CIP) and additional forging. The specimens are characterized by hot compression tests, dilatometry and metallography. A 3D interconnected structure of alumina films <5 nm in thickness is observed by transmission electron microscopy and field emission gun scanning electron microscopy; it is associated with the natural oxide skin which covers every aluminium powder and occupies around 3 vol.%. The compression tests are carried out in the range of 350–520 °C at strain rates of 0.003–3 s−1. The compressive strength was 100–150 and 130–180 MPa for the CIPed and forged samples, respectively. The low strain rate sensitivity m (<0.08) suggests that the alumina network forms a barrier, which suppresses any restoration mechanism across the grain boundaries as well as grain boundary sliding during hot deformation. The high strength of such compacted sub-micron Al powder is attributed to the conservation of a 3D alumina closed cell network filled with elastoplastic aluminium. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001667

On the infiltration mode during fabrication of aluminium composite / Peng Yu in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3790–3797 Titre : On the infiltration mode during fabrication of aluminium composite Type de document : texte imprimé Auteurs : Peng Yu, Auteur ; Ma Qian, Auteur ; Ling Li, Auteur Année de publication : 2011 Article en page(s) : pp. 3790–3797 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Infiltration  Al  alloy  Slug  flow  Eutectic Résumé : Porous Al 6061–2Mg–1Sn–3nylon preforms were nitrided and subsequently infiltrated with Al–Si and Al–Si–Mg alloys at different temperatures. Different infiltration modes were identified and confirmed by numerical simulation. When infiltration happens under conditions close to the eutectic points, it proceeds in the conventional slug flow mode with a well-defined infiltration front. However, as the infiltration conditions depart from the eutectic points, the infiltration mode changes gradually to extreme non-slug flow, where the infiltrant preferentially fills small pores irrespective of their distance from the infiltrant entrance, leading to homogeneous infiltrated structures without any infiltration front. The occurrence of different infiltration modes can be attributed to the competition between thermodynamic and kinetic factors. Extreme non-slug flow occurs under thermodynamically favourable conditions where the preform is well wetted by an infiltrant with sufficient fluidity. In contrast, slug flow occurs under kinetically favourable conditions when the low infiltration temperature at the eutectic points makes mass transport difficult. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001679 [article] On the infiltration mode during fabrication of aluminium composite [texte imprimé] / Peng Yu, Auteur ; Ma Qian, Auteur ; Ling Li, Auteur . - 2011 . - pp. 3790–3797. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3790–3797 Mots-clés : Infiltration  Al  alloy  Slug  flow  Eutectic Résumé : Porous Al 6061–2Mg–1Sn–3nylon preforms were nitrided and subsequently infiltrated with Al–Si and Al–Si–Mg alloys at different temperatures. Different infiltration modes were identified and confirmed by numerical simulation. When infiltration happens under conditions close to the eutectic points, it proceeds in the conventional slug flow mode with a well-defined infiltration front. However, as the infiltration conditions depart from the eutectic points, the infiltration mode changes gradually to extreme non-slug flow, where the infiltrant preferentially fills small pores irrespective of their distance from the infiltrant entrance, leading to homogeneous infiltrated structures without any infiltration front. The occurrence of different infiltration modes can be attributed to the competition between thermodynamic and kinetic factors. Extreme non-slug flow occurs under thermodynamically favourable conditions where the preform is well wetted by an infiltrant with sufficient fluidity. In contrast, slug flow occurs under kinetically favourable conditions when the low infiltration temperature at the eutectic points makes mass transport difficult. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001679

Kinetics of mechanically induced anatase-to-rutile phase transformations under inelastic impact conditions / Emilio Napolitano in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3798–3804 Titre : Kinetics of mechanically induced anatase-to-rutile phase transformations under inelastic impact conditions Type de document : texte imprimé Auteurs : Emilio Napolitano, Auteur ; Gabriele Mulas, Auteur ; Stefano Enzo, Auteur Année de publication : 2011 Article en page(s) : pp. 3798–3804 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Mechanical  milling  Crystalline  oxides  Phase  transformation  kinetics Résumé : This work investigates the kinetics of the anatase-to-rutile phase transformation of TiO2 powders during ball milling. Two elementary stages are observed, namely the transformation of anatase to the TiO2 II phase and of this latter to rutile. Such consecutive reactions were studied under inelastic impact regimes. Based on a suitable modeling of transformation kinetics, the fraction of powder processed on average at each collision was estimated. The mass of powder involved in phase transformation and microstructural refinement processes at each collision was then worked out by a systematic variation of the powder charge inside the reactor. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001692 [article] Kinetics of mechanically induced anatase-to-rutile phase transformations under inelastic impact conditions [texte imprimé] / Emilio Napolitano, Auteur ; Gabriele Mulas, Auteur ; Stefano Enzo, Auteur . - 2011 . - pp. 3798–3804. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3798–3804 Mots-clés : Mechanical  milling  Crystalline  oxides  Phase  transformation  kinetics Résumé : This work investigates the kinetics of the anatase-to-rutile phase transformation of TiO2 powders during ball milling. Two elementary stages are observed, namely the transformation of anatase to the TiO2 II phase and of this latter to rutile. Such consecutive reactions were studied under inelastic impact regimes. Based on a suitable modeling of transformation kinetics, the fraction of powder processed on average at each collision was estimated. The mass of powder involved in phase transformation and microstructural refinement processes at each collision was then worked out by a systematic variation of the powder charge inside the reactor. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001692

Topological characteristics of plane sections of polycrystals / Gregory S. Rohrer in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3805–3814 Titre : Topological characteristics of plane sections of polycrystals Type de document : texte imprimé Auteurs : Gregory S. Rohrer, Auteur ; Herbert M. Miller, Auteur Année de publication : 2011 Article en page(s) : pp. 3805–3814 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Topology  Microstructure  Grain  boundaries  Grain  boundary  junctions  Twin  grain  boundaries Résumé : Homology metrics have been used to assess the connectivity of grain boundary networks in plane sections of polycrystals. The analysis is based on orientation maps, and four characteristic microstructure types were examined: SrTiO3 microstructures with normal and bimodal grain size distributions and two Ni microstructures with different concentrations of Σ3 grain boundaries. The inverse connectivity, defined as the ratio of the number of independent pieces of the network to the number of closed loops, is proposed as a metric for the extent to which certain types of grain boundaries are connected. The variation in inverse connectivity with disorientation threshold, below which boundaries are excluded from the network, produces distinct signatures for the different microstructures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001734 [article] Topological characteristics of plane sections of polycrystals [texte imprimé] / Gregory S. Rohrer, Auteur ; Herbert M. Miller, Auteur . - 2011 . - pp. 3805–3814. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3805–3814 Mots-clés : Topology  Microstructure  Grain  boundaries  Grain  boundary  junctions  Twin  grain  boundaries Résumé : Homology metrics have been used to assess the connectivity of grain boundary networks in plane sections of polycrystals. The analysis is based on orientation maps, and four characteristic microstructure types were examined: SrTiO3 microstructures with normal and bimodal grain size distributions and two Ni microstructures with different concentrations of Σ3 grain boundaries. The inverse connectivity, defined as the ratio of the number of independent pieces of the network to the number of closed loops, is proposed as a metric for the extent to which certain types of grain boundaries are connected. The variation in inverse connectivity with disorientation threshold, below which boundaries are excluded from the network, produces distinct signatures for the different microstructures. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001734

Growth morphologies in peritectic solidification of Fe–C: A phase-field study / Abhik Choudhury in Acta materialia, Vol. 58 N° 10 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3815–3823 Titre : Growth morphologies in peritectic solidification of Fe–C: A phase-field study Type de document : texte imprimé Auteurs : Abhik Choudhury, Auteur ; Britta Nestler, Auteur ; Abhishek Telang, Auteur Année de publication : 2011 Article en page(s) : pp. 3815–3823 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Phase  field  Diffusion  Peritectic  Nucleation  Surface  energy Résumé : We use a thermodynamically consistent multi-phase, multi-component phase-field model, where the evolution equations for the different fields are derived from an entropy functional, for simulating peritectic growth structures in two and three dimensions. Different solidification morphologies are obtained in the computations and the characteristic properties of the growth forms are discussed. The phase-field method allows for a prediction of the surface energies in the three-phase system δ-ferrite, γ-austenite and liquid based on comparison between experimentally observed and simulated structures. Additionally an investigation of possible nucleation sites in evolving domains is presented and its dependence on the solid–solid surface energy is examined. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001758 [article] Growth morphologies in peritectic solidification of Fe–C: A phase-field study [texte imprimé] / Abhik Choudhury, Auteur ; Britta Nestler, Auteur ; Abhishek Telang, Auteur . - 2011 . - pp. 3815–3823. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 10 (Juin 2010) . - pp. 3815–3823 Mots-clés : Phase  field  Diffusion  Peritectic  Nucleation  Surface  energy Résumé : We use a thermodynamically consistent multi-phase, multi-component phase-field model, where the evolution equations for the different fields are derived from an entropy functional, for simulating peritectic growth structures in two and three dimensions. Different solidification morphologies are obtained in the computations and the characteristic properties of the growth forms are discussed. The phase-field method allows for a prediction of the surface energies in the three-phase system δ-ferrite, γ-austenite and liquid based on comparison between experimentally observed and simulated structures. Additionally an investigation of possible nucleation sites in evolving domains is presented and its dependence on the solid–solid surface energy is examined. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001758

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