Les Inscriptions à la Bibliothèque sont ouvertes en
ligne via le site: https://biblio.enp.edu.dz
Les Réinscriptions se font à :
• La Bibliothèque Annexe pour les étudiants en
2ème Année CPST
• La Bibliothèque Centrale pour les étudiants en Spécialités
A partir de cette page vous pouvez :
| Retourner au premier écran avec les recherches... |
Acta materialia |
Dépouillements
Ajouter le résultat dans votre panierDeformation processes in View the MathML source-textured nanocrystalline Mg by molecular dynamics simulation / D.H. Kim in Acta materialia, Vol. 58 N° 19 (Novembre 2010)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6217–6229
Titre : Deformation processes in View the MathML source-textured nanocrystalline Mg by molecular dynamics simulation Type de document : texte imprimé Auteurs : D.H. Kim, Auteur ; M.V. Manuel, Auteur ; F. Ebrahimi, Auteur Année de publication : 2011 Article en page(s) : pp. 6217–6229 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium Nanocrystalline Plastic deformation Molecular dynamics Résumé : Plastic deformation of nanocrystalline Mg is studied using molecular dynamics simulation. In a View the MathML source-textured structure, slip and twinning behaviors are observed during tensile loading. Various twinning and slip process are identified, with basal slip and tensile View the MathML source twinning being dominant. For grain sizes larger than ∼30 nm, basal slip occurs at a lower strain than twinning; for smaller grain sizes, twinning takes place at a lower strain than slip. For small grain sizes, the system generates partial dislocations; extended or full type dislocations are generated at high stress and large grain sizes. As the external stress increases, pyramidal 〈c + a〉 dislocations are also frequently generated, leading to a reduction in twinning activity. Whereas, under low stresses only the tensile twin is created at the grain boundaries, under high stress compressive twins are created at grain boundaries and in the interior of grains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004805 [article] Deformation processes in View the MathML source-textured nanocrystalline Mg by molecular dynamics simulation [texte imprimé] / D.H. Kim, Auteur ; M.V. Manuel, Auteur ; F. Ebrahimi, Auteur . - 2011 . - pp. 6217–6229.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6217–6229
Mots-clés : Magnesium Nanocrystalline Plastic deformation Molecular dynamics Résumé : Plastic deformation of nanocrystalline Mg is studied using molecular dynamics simulation. In a View the MathML source-textured structure, slip and twinning behaviors are observed during tensile loading. Various twinning and slip process are identified, with basal slip and tensile View the MathML source twinning being dominant. For grain sizes larger than ∼30 nm, basal slip occurs at a lower strain than twinning; for smaller grain sizes, twinning takes place at a lower strain than slip. For small grain sizes, the system generates partial dislocations; extended or full type dislocations are generated at high stress and large grain sizes. As the external stress increases, pyramidal 〈c + a〉 dislocations are also frequently generated, leading to a reduction in twinning activity. Whereas, under low stresses only the tensile twin is created at the grain boundaries, under high stress compressive twins are created at grain boundaries and in the interior of grains. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004805
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6230–6242
Titre : Deformation twinning in AZ31 : Influence on strain hardening and texture evolution Type de document : texte imprimé Auteurs : Marko Knezevic, Auteur ; Amanda Levinson, Auteur ; Ryan Harris, Auteur Année de publication : 2011 Article en page(s) : pp. 6230–6242 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium Deformation Texture Twinning EBSD Résumé : This paper describes the main results from an experimental investigation into the consequences of deformation twinning in AZ31 on various aspects of plastic deformation, including the anisotropic strain-hardening rates, the tension/compression yield asymmetry, and the evolution of crystallographic texture. It was seen that AZ31 exhibited unusually high normalized strain-hardening rates compared to α-Ti that occurred beyond the strain levels where extension twins have completely altered the underlying texture. This observation challenges the validity of the generally accepted notion in the current literature that the high strain-hardening rates in AZ31 are directly caused by extension twins. It is postulated here that the thin contraction twins are very effective in strain hardening of the alloy by restricting the slip length associated with pyramidal 〈c + a〉 slip. This new hypothesis is able to explain the major experimental observations made in this study and in the prior literature. We have also presented a new hypothesis for the physical origin of the observed differences in the thicknesses of the extension and contraction twins. The stress fields in selected matrix–twin configurations were modeled using crystal plasticity finite element models. The contraction twin View the MathML sourceView the MathML source was predicted to form an internal extension twin View the MathML sourceView the MathML source, resulting in the commonly observed “double twin” sequence. The extension twin is suggested to inhibit thickening of this double twin by loss of twin–matrix coherency. Extension twins were predicted to retain their coherency and thus thicken. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004854 [article] Deformation twinning in AZ31 : Influence on strain hardening and texture evolution [texte imprimé] / Marko Knezevic, Auteur ; Amanda Levinson, Auteur ; Ryan Harris, Auteur . - 2011 . - pp. 6230–6242.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6230–6242
Mots-clés : Magnesium Deformation Texture Twinning EBSD Résumé : This paper describes the main results from an experimental investigation into the consequences of deformation twinning in AZ31 on various aspects of plastic deformation, including the anisotropic strain-hardening rates, the tension/compression yield asymmetry, and the evolution of crystallographic texture. It was seen that AZ31 exhibited unusually high normalized strain-hardening rates compared to α-Ti that occurred beyond the strain levels where extension twins have completely altered the underlying texture. This observation challenges the validity of the generally accepted notion in the current literature that the high strain-hardening rates in AZ31 are directly caused by extension twins. It is postulated here that the thin contraction twins are very effective in strain hardening of the alloy by restricting the slip length associated with pyramidal 〈c + a〉 slip. This new hypothesis is able to explain the major experimental observations made in this study and in the prior literature. We have also presented a new hypothesis for the physical origin of the observed differences in the thicknesses of the extension and contraction twins. The stress fields in selected matrix–twin configurations were modeled using crystal plasticity finite element models. The contraction twin View the MathML sourceView the MathML source was predicted to form an internal extension twin View the MathML sourceView the MathML source, resulting in the commonly observed “double twin” sequence. The extension twin is suggested to inhibit thickening of this double twin by loss of twin–matrix coherency. Extension twins were predicted to retain their coherency and thus thicken. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004854
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6243–6248
Titre : Structural, electrical and optical properties of p-type transparent conducting SnO2 : Al film derived from thermal diffusion of Al/SnO2/Al multilayer thin films Type de document : texte imprimé Auteurs : J. Zhao, Auteur ; X.J. Zhao, Auteur ; J.M. Ni, Auteur Année de publication : 2011 Article en page(s) : pp. 6243–6248 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : p-Type SnO2 Al film Multilayer thin films Sputtering Annealing Résumé : Highly transparent, p-type conducting SnO2:Al films derived from thermal diffusion of a sandwich structure Al/SnO2/Al multilayer thin films deposited on quartz substrate have been prepared by direct current and radio-frequency magnetron sputtering using Al and SnO2 targets. The deposited films were annealed at various temperatures for different durations. The effect of thermal diffusing temperature and time on the structural, electrical and optical performances of SnO2:Al films has been studied. X-ray diffraction results show that all p-type conducting films possessed polycrystalline SnO2 with tetragonal rutile structure. Hall-effect results indicate that 450 °C for 4 h were the optimum annealing parameters for p-type SnO2:Al films, resulting in a relatively high hole concentration of 7.2 × 1018 cm−3 and a low resistivity of 0.81 Ω cm. The transmission of the p-type SnO2:Al films was above 80%. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004866 [article] Structural, electrical and optical properties of p-type transparent conducting SnO2 : Al film derived from thermal diffusion of Al/SnO2/Al multilayer thin films [texte imprimé] / J. Zhao, Auteur ; X.J. Zhao, Auteur ; J.M. Ni, Auteur . - 2011 . - pp. 6243–6248.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6243–6248
Mots-clés : p-Type SnO2 Al film Multilayer thin films Sputtering Annealing Résumé : Highly transparent, p-type conducting SnO2:Al films derived from thermal diffusion of a sandwich structure Al/SnO2/Al multilayer thin films deposited on quartz substrate have been prepared by direct current and radio-frequency magnetron sputtering using Al and SnO2 targets. The deposited films were annealed at various temperatures for different durations. The effect of thermal diffusing temperature and time on the structural, electrical and optical performances of SnO2:Al films has been studied. X-ray diffraction results show that all p-type conducting films possessed polycrystalline SnO2 with tetragonal rutile structure. Hall-effect results indicate that 450 °C for 4 h were the optimum annealing parameters for p-type SnO2:Al films, resulting in a relatively high hole concentration of 7.2 × 1018 cm−3 and a low resistivity of 0.81 Ω cm. The transmission of the p-type SnO2:Al films was above 80%. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004866
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6249–6255
Titre : Coupling of grain boundary sliding and migration within the range of boundary specialness Type de document : texte imprimé Auteurs : A.D. Sheikh-Ali, Auteur Année de publication : 2011 Article en page(s) : pp. 6249–6255 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain boundary sliding Grain boundary migration High-temperature deformation Coincidence site lattice Grain boundary dislocation Résumé : Stress-induced behavior of high-angle near-coincidence symmetric tilt boundaries has been examined in bicrystal specimens of zinc. Parameters of coupling between boundary sliding and migration were determined. The angular deviation from the coincidence misorientation within the range of boundary specialness has a noticeable effect on the sliding-to-migration ratio, called “coupling factor”. Mechanisms of coupled boundary sliding and migration based on the motion of edge-type extrinsic and intrinsic grain boundary dislocations are discussed. It has been demonstrated that the observed alteration of the coupling factor with the change in boundary misorientation is due to the change of the parameters of extrinsic secondary grain boundary dislocations. The obtained results have also shown the limitation of the coincidence site lattice/displacement shift complete lattice model for the quantitative description of the structure of near-coincidence boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004878 [article] Coupling of grain boundary sliding and migration within the range of boundary specialness [texte imprimé] / A.D. Sheikh-Ali, Auteur . - 2011 . - pp. 6249–6255.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6249–6255
Mots-clés : Grain boundary sliding Grain boundary migration High-temperature deformation Coincidence site lattice Grain boundary dislocation Résumé : Stress-induced behavior of high-angle near-coincidence symmetric tilt boundaries has been examined in bicrystal specimens of zinc. Parameters of coupling between boundary sliding and migration were determined. The angular deviation from the coincidence misorientation within the range of boundary specialness has a noticeable effect on the sliding-to-migration ratio, called “coupling factor”. Mechanisms of coupled boundary sliding and migration based on the motion of edge-type extrinsic and intrinsic grain boundary dislocations are discussed. It has been demonstrated that the observed alteration of the coupling factor with the change in boundary misorientation is due to the change of the parameters of extrinsic secondary grain boundary dislocations. The obtained results have also shown the limitation of the coincidence site lattice/displacement shift complete lattice model for the quantitative description of the structure of near-coincidence boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004878
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6256–6266
Titre : Enhanced mechanical properties due to structural changes induced by devitrification in Fe–Co–B–Si–Nb bulk metallic glass Type de document : texte imprimé Auteurs : J. Fornell, Auteur ; S. González, Auteur ; E. Rossinyol, Auteur Année de publication : 2011 Article en page(s) : pp. 6256–6266 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metallic glass Annealing Nanoindentation Transmission electron microscopy Acoustic methods Résumé : Fe36Co36B19.2Si4.8Nb4 bulk glassy rods were synthesized by copper mould casting. The effects of annealing treatments on the microstructure, elastic and mechanical properties of this alloy are investigated. Annealing below the glass transition temperature induces the formation of atomic clusters with pseudo-tenfold symmetry with a close relationship to the Fe23B6 phase. Annealing at sufficiently high temperatures promotes the formation of stable Fe2B and FeB phases and Fe(Co) solid solution. The as-cast alloy exhibits ultra-high hardness (H > 14 GPa), high reduced Young’s modulus (Er > 200 GPa) and good wear resistance. These properties are further enhanced after thermal treatments (H > 18 GPa and Er > 260 GPa are achieved in the fully crystallized sample). The mechanical hardening is accompanied with an increase of the elastic recovery and a decrease of the Poisson’s ratio. The different microstructural mechanisms responsible for these annealing-induced changes in mechanical and elastic properties are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000491X [article] Enhanced mechanical properties due to structural changes induced by devitrification in Fe–Co–B–Si–Nb bulk metallic glass [texte imprimé] / J. Fornell, Auteur ; S. González, Auteur ; E. Rossinyol, Auteur . - 2011 . - pp. 6256–6266.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6256–6266
Mots-clés : Metallic glass Annealing Nanoindentation Transmission electron microscopy Acoustic methods Résumé : Fe36Co36B19.2Si4.8Nb4 bulk glassy rods were synthesized by copper mould casting. The effects of annealing treatments on the microstructure, elastic and mechanical properties of this alloy are investigated. Annealing below the glass transition temperature induces the formation of atomic clusters with pseudo-tenfold symmetry with a close relationship to the Fe23B6 phase. Annealing at sufficiently high temperatures promotes the formation of stable Fe2B and FeB phases and Fe(Co) solid solution. The as-cast alloy exhibits ultra-high hardness (H > 14 GPa), high reduced Young’s modulus (Er > 200 GPa) and good wear resistance. These properties are further enhanced after thermal treatments (H > 18 GPa and Er > 260 GPa are achieved in the fully crystallized sample). The mechanical hardening is accompanied with an increase of the elastic recovery and a decrease of the Poisson’s ratio. The different microstructural mechanisms responsible for these annealing-induced changes in mechanical and elastic properties are discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000491X
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6267–6275
Titre : Thermal behaviors of Al-based amorphous alloys bearing nanocrystalline In particles Type de document : texte imprimé Auteurs : J. Mu, Auteur ; Z.W. Zhu, Auteur ; H.F. Zhang, Auteur Année de publication : 2011 Article en page(s) : pp. 6267–6275 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Melt-spinning Nanocrystalline materials Interface structure Melting behavior Crystallization Résumé : We successfully fabricated nanocrystalline (NC) indium (In) particles embedded in Al-based amorphous matrix. Systematic investigations indicate that thermal interaction between the NC In and the amorphous matrix significantly influences their respective thermal behaviors. The melting temperature of NC In was found to be depressed by 10–30 K, owing to the specific interfacial structure of NC In/amorphous system. The simultaneous appearance of the liquid/amorphous interface destabilizes the amorphous matrix, leading to face-centered cubic-Al precipitation at the interface of In sphere/amorphous matrix at a relatively lower temperature. This effect is attributed to the diffusion of La from the matrix to the liquid In particles. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004921 [article] Thermal behaviors of Al-based amorphous alloys bearing nanocrystalline In particles [texte imprimé] / J. Mu, Auteur ; Z.W. Zhu, Auteur ; H.F. Zhang, Auteur . - 2011 . - pp. 6267–6275.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6267–6275
Mots-clés : Melt-spinning Nanocrystalline materials Interface structure Melting behavior Crystallization Résumé : We successfully fabricated nanocrystalline (NC) indium (In) particles embedded in Al-based amorphous matrix. Systematic investigations indicate that thermal interaction between the NC In and the amorphous matrix significantly influences their respective thermal behaviors. The melting temperature of NC In was found to be depressed by 10–30 K, owing to the specific interfacial structure of NC In/amorphous system. The simultaneous appearance of the liquid/amorphous interface destabilizes the amorphous matrix, leading to face-centered cubic-Al precipitation at the interface of In sphere/amorphous matrix at a relatively lower temperature. This effect is attributed to the diffusion of La from the matrix to the liquid In particles. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004921
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6276–6281
Titre : First-principles prediction of partitioning of alloying elements between cementite and ferrite Type de document : texte imprimé Auteurs : Chaitanya Krishna Ande, Auteur ; Marcel H.F. Sluiter, Auteur Année de publication : 2011 Article en page(s) : pp. 6276–6281 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Iron Carbides Steels First-principles electron theory Partitioning Résumé : At long tempering times in steels when both cementite (Fe3C) and ferrite (body-centered cubic (bcc) Fe-rich solid solution) phases are present, alloying elements tend to segregate to either of the two phases. The elements V, Cr, Mn, Mo and W are found to partition to the cementite phase, while Al, Si, P, Co, Ni and Cu partition to ferrite. We show that partitioning of alloying elements and cementite (de)stabilization by alloying in mixtures of bcc Fe and cementite are intimately related through the introduction of a partitioning enthalpy. The formation enthalpy of alloying-element-substituted cementite is shown not to be a proper gauge for addressing these questions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004933 [article] First-principles prediction of partitioning of alloying elements between cementite and ferrite [texte imprimé] / Chaitanya Krishna Ande, Auteur ; Marcel H.F. Sluiter, Auteur . - 2011 . - pp. 6276–6281.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6276–6281
Mots-clés : Iron Carbides Steels First-principles electron theory Partitioning Résumé : At long tempering times in steels when both cementite (Fe3C) and ferrite (body-centered cubic (bcc) Fe-rich solid solution) phases are present, alloying elements tend to segregate to either of the two phases. The elements V, Cr, Mn, Mo and W are found to partition to the cementite phase, while Al, Si, P, Co, Ni and Cu partition to ferrite. We show that partitioning of alloying elements and cementite (de)stabilization by alloying in mixtures of bcc Fe and cementite are intimately related through the introduction of a partitioning enthalpy. The formation enthalpy of alloying-element-substituted cementite is shown not to be a proper gauge for addressing these questions. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004933
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6282–6293
Titre : Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2 extruded alloy Type de document : texte imprimé Auteurs : K. Hagihara, Auteur ; A. Kinoshita, Auteur ; Y. Sugino, Auteur Année de publication : 2011 Article en page(s) : pp. 6282–6293 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Plastic deformation Magnesium alloys Extrusion Fiber-reinforced composites Intermetallic compounds Résumé : The mechanical properties of Mg97Zn1Y2 extruded alloy, composed of Mg matrix phase and a long-period stacking ordered phase, the so-called LPSO phase, with a volume fraction of approximately 24%, were investigated using compression tests at room temperature. The microstructure was varied to a large degree by various heat treatments at high temperatures above 400 °C, and the relationship between the microstructure and mechanical properties was clarified. The plastic behavior of the Mg/LPSO two-phase alloy was compared with that of Mg99.2Zn0.2Y0.6 alloy, composed almost Mg-solid-solution phase, and the strengthening mechanisms at work in the Mg97Zn1Y2 extruded alloy are discussed. The existence of the LPSO phase strongly enhanced the refinement of Mg matrix grains during extrusion, which led to a large increase in yield stress through the Hall–Petch relationship. In addition, the LPSO phases, which were aligned along the direction of extrusion in the Mg97Zn1Y2 extruded alloy, acted as hardening phases, being roughly coordinated with the short-fiber reinforcement mechanism. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004945 [article] Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2 extruded alloy [texte imprimé] / K. Hagihara, Auteur ; A. Kinoshita, Auteur ; Y. Sugino, Auteur . - 2011 . - pp. 6282–6293.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6282–6293
Mots-clés : Plastic deformation Magnesium alloys Extrusion Fiber-reinforced composites Intermetallic compounds Résumé : The mechanical properties of Mg97Zn1Y2 extruded alloy, composed of Mg matrix phase and a long-period stacking ordered phase, the so-called LPSO phase, with a volume fraction of approximately 24%, were investigated using compression tests at room temperature. The microstructure was varied to a large degree by various heat treatments at high temperatures above 400 °C, and the relationship between the microstructure and mechanical properties was clarified. The plastic behavior of the Mg/LPSO two-phase alloy was compared with that of Mg99.2Zn0.2Y0.6 alloy, composed almost Mg-solid-solution phase, and the strengthening mechanisms at work in the Mg97Zn1Y2 extruded alloy are discussed. The existence of the LPSO phase strongly enhanced the refinement of Mg matrix grains during extrusion, which led to a large increase in yield stress through the Hall–Petch relationship. In addition, the LPSO phases, which were aligned along the direction of extrusion in the Mg97Zn1Y2 extruded alloy, acted as hardening phases, being roughly coordinated with the short-fiber reinforcement mechanism. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004945
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6294–6305
Titre : Formation of a high-cycle fatigue fracture surface and a crack growth mechanism of ultrafine-grained copper with different stages of microstructural evolution Type de document : texte imprimé Auteurs : M. Goto, Auteur ; S.Z. Han, Auteur ; K. Euh, Auteur Année de publication : 2011 Article en page(s) : pp. 6294–6305 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Equal channel angular pressing Fatigue crack Fracture surface Copper Misorientation Résumé : Fatigue tests were conducted on smooth specimens of ultrafine-grained copper produced by 4 and 12 passes of equal channel angular pressing (henceforth referred to as UFG4 and UFG12, respectively). A major crack was initiated from shear bands at an early stage of stressing. The UFG4 and UFG12 samples exhibited different growth behavior tendencies at a low crack growth rate (CGR). For UFG12, the CGR initially increased as the crack was extended with continued fatigue cycling, but then abruptly decreased before CGR reaching 10−6 mm/c. This drop was temporary and was gradually recovered with subsequent cycling. The drop and recovery in CGR corresponded to the transitions from planar to granular fracture surface and from granular to striated fracture surface, respectively. For UFG4, there was no temporary CGR reduction, which corresponded to the change in the fracture surfaces from a planar to striated surface without any granulated surface formation. To understand the changes in growth rate and fracture surface morphologies, a quantitative model describing the crack growth mechanism is developed in this study by considering the reversible plastic zone size and the microstructural factors. The relationship between the crack growth behavior and the formation of the fracture surface is discussed based on the model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004957 [article] Formation of a high-cycle fatigue fracture surface and a crack growth mechanism of ultrafine-grained copper with different stages of microstructural evolution [texte imprimé] / M. Goto, Auteur ; S.Z. Han, Auteur ; K. Euh, Auteur . - 2011 . - pp. 6294–6305.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6294–6305
Mots-clés : Equal channel angular pressing Fatigue crack Fracture surface Copper Misorientation Résumé : Fatigue tests were conducted on smooth specimens of ultrafine-grained copper produced by 4 and 12 passes of equal channel angular pressing (henceforth referred to as UFG4 and UFG12, respectively). A major crack was initiated from shear bands at an early stage of stressing. The UFG4 and UFG12 samples exhibited different growth behavior tendencies at a low crack growth rate (CGR). For UFG12, the CGR initially increased as the crack was extended with continued fatigue cycling, but then abruptly decreased before CGR reaching 10−6 mm/c. This drop was temporary and was gradually recovered with subsequent cycling. The drop and recovery in CGR corresponded to the transitions from planar to granular fracture surface and from granular to striated fracture surface, respectively. For UFG4, there was no temporary CGR reduction, which corresponded to the change in the fracture surfaces from a planar to striated surface without any granulated surface formation. To understand the changes in growth rate and fracture surface morphologies, a quantitative model describing the crack growth mechanism is developed in this study by considering the reversible plastic zone size and the microstructural factors. The relationship between the crack growth behavior and the formation of the fracture surface is discussed based on the model. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004957
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6306–6316
Titre : Thermal conductivity of electron-doped CaMnO3 perovskites : Local lattice distortions and optical phonon thermal excitation Type de document : texte imprimé Auteurs : Yang Wang, Auteur ; Yu Sui, Auteur ; Xianjie Wang, Auteur Année de publication : 2011 Article en page(s) : pp. 6306–6316 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Manganite perovskite Thermal conductivity Spin-phonon scattering MnO6 distortion Optical phonon Résumé : The thermal transport properties of a series of electron-doped CaMnO3 perovskites have been investigated. Throughout the temperature range 5–300 K, phonon thermal conductivity is dominant, and both electron and spin wave contributions are negligible. The short phonon mean free paths in this system result in the relatively low thermal conductivities. The strong phonon scatterings stem from the A-site mismatch and bond-length fluctuations induced by local distortions of MnO6 octahedra. The thermal conductivity in the magnetically ordered state is enhanced as a result of the decrease in spin–phonon scattering. The results also indicate that above the magnetic ordering temperature, observable thermal excitation of optical phonons occurs. The contribution of optical phonons to thermal conductivity becomes non-negligible and is proposed to play an important role in the glass-like thermal transport behavior (i.e. positive temperature dependence of the thermal conductivity) in the paramagnetic state. These features can be understood in terms of an expression of thermal conductivity that includes both acoustic and optical phonon terms. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004969 [article] Thermal conductivity of electron-doped CaMnO3 perovskites : Local lattice distortions and optical phonon thermal excitation [texte imprimé] / Yang Wang, Auteur ; Yu Sui, Auteur ; Xianjie Wang, Auteur . - 2011 . - pp. 6306–6316.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6306–6316
Mots-clés : Manganite perovskite Thermal conductivity Spin-phonon scattering MnO6 distortion Optical phonon Résumé : The thermal transport properties of a series of electron-doped CaMnO3 perovskites have been investigated. Throughout the temperature range 5–300 K, phonon thermal conductivity is dominant, and both electron and spin wave contributions are negligible. The short phonon mean free paths in this system result in the relatively low thermal conductivities. The strong phonon scatterings stem from the A-site mismatch and bond-length fluctuations induced by local distortions of MnO6 octahedra. The thermal conductivity in the magnetically ordered state is enhanced as a result of the decrease in spin–phonon scattering. The results also indicate that above the magnetic ordering temperature, observable thermal excitation of optical phonons occurs. The contribution of optical phonons to thermal conductivity becomes non-negligible and is proposed to play an important role in the glass-like thermal transport behavior (i.e. positive temperature dependence of the thermal conductivity) in the paramagnetic state. These features can be understood in terms of an expression of thermal conductivity that includes both acoustic and optical phonon terms. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004969
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6317–6323
Titre : Mechanical properties of anatase and semi-metallic TiO2 nanotubes Type de document : texte imprimé Auteurs : Felix Schmidt-Stein, Auteur ; Stefan Thiemann, Auteur ; Steffen Berger, Auteur Année de publication : 2011 Article en page(s) : pp. 6317–6323 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : TiO2 nanotubes Semi-metallic Mechanical properties Hardness Résumé : We report for the first time on mechanical properties of anodically formed, self-organized TiO2 nanotube layers on titanium. We compare their behavior in their virgin state and after conversion to their semi-metallic form by an acetylene treatment. We show that the acetylene treatment leads to significant enhanced hardness, tensile strength and friction behavior. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004970 [article] Mechanical properties of anatase and semi-metallic TiO2 nanotubes [texte imprimé] / Felix Schmidt-Stein, Auteur ; Stefan Thiemann, Auteur ; Steffen Berger, Auteur . - 2011 . - pp. 6317–6323.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6317–6323
Mots-clés : TiO2 nanotubes Semi-metallic Mechanical properties Hardness Résumé : We report for the first time on mechanical properties of anodically formed, self-organized TiO2 nanotube layers on titanium. We compare their behavior in their virgin state and after conversion to their semi-metallic form by an acetylene treatment. We show that the acetylene treatment leads to significant enhanced hardness, tensile strength and friction behavior. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004970
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6324–6333
Titre : Optimizing load transfer in multiwall nanotubes through interwall coupling : Theory and simulation Type de document : texte imprimé Auteurs : E. M. Byrne, Auteur ; A. Letertre, Auteur ; M.A. McCarthy, Auteur Année de publication : 2011 Article en page(s) : pp. 6324–6333 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Multi-wall carbon nanotube Nanocomposite Interwall bonding Load transfer Résumé : An analytical model is developed to determine the length scales over which load is transferred from outer to inner walls of multiwall carbon nanotubes (MWCNTs) as a function of the amount of bonding between walls. The model predicts that the characteristic length for load transfer scales as View the MathML source, where t is the CNT wall spacing, E is the effective wall Young’s modulus, and View the MathML source is the average interwall shear modulus due to interwall coupling. Molecular dynamics simulations for MWCNTs with up to six walls, and with interwall coupling achieved by interwall sp3 bonding at various densities, provide data against which the model is tested. For interwall bonding having a uniform axial distribution, the analytic and simulation models agree well, showing that continuum mechanics concepts apply down to the atomic scale in this problem. The simulation models show, however, that load transfer is sensitive to natural statistical fluctuations in the spatial distribution of the interwall bonding between pairs of walls, and such fluctuations generally increase the net load transfer length needed to fully load an MWCNT. Optimal load transfer is achieved when bonding is uniformly distributed axially, and all interwall regions have the same shear stiffness, implying a linear decrease in the number of interwall bonds with distance from the outer wall. Optimal load transfer into an n-wall MWCNT is shown to occur over a length of ∼1.5nℓ. The model can be used to design MWCNTs for structural materials, and to interpret load transfer characteristics deduced from experiments on individual MWCNTs. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004982 [article] Optimizing load transfer in multiwall nanotubes through interwall coupling : Theory and simulation [texte imprimé] / E. M. Byrne, Auteur ; A. Letertre, Auteur ; M.A. McCarthy, Auteur . - 2011 . - pp. 6324–6333.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6324–6333
Mots-clés : Multi-wall carbon nanotube Nanocomposite Interwall bonding Load transfer Résumé : An analytical model is developed to determine the length scales over which load is transferred from outer to inner walls of multiwall carbon nanotubes (MWCNTs) as a function of the amount of bonding between walls. The model predicts that the characteristic length for load transfer scales as View the MathML source, where t is the CNT wall spacing, E is the effective wall Young’s modulus, and View the MathML source is the average interwall shear modulus due to interwall coupling. Molecular dynamics simulations for MWCNTs with up to six walls, and with interwall coupling achieved by interwall sp3 bonding at various densities, provide data against which the model is tested. For interwall bonding having a uniform axial distribution, the analytic and simulation models agree well, showing that continuum mechanics concepts apply down to the atomic scale in this problem. The simulation models show, however, that load transfer is sensitive to natural statistical fluctuations in the spatial distribution of the interwall bonding between pairs of walls, and such fluctuations generally increase the net load transfer length needed to fully load an MWCNT. Optimal load transfer is achieved when bonding is uniformly distributed axially, and all interwall regions have the same shear stiffness, implying a linear decrease in the number of interwall bonds with distance from the outer wall. Optimal load transfer into an n-wall MWCNT is shown to occur over a length of ∼1.5nℓ. The model can be used to design MWCNTs for structural materials, and to interpret load transfer characteristics deduced from experiments on individual MWCNTs. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004982
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6334–6344
Titre : Physical and numerical characterization of the near-eutectic permeability of aluminum–copper alloys Type de document : texte imprimé Auteurs : Ehsan Khajeh, Auteur ; Daan M. Maijer, Auteur Année de publication : 2011 Article en page(s) : pp. 6334–6344 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Permeability 3-D X-ray microtomography Modeling Microstructure Aluminum–copper alloy Résumé : The near-eutectic permeability of aluminum–copper alloys has been determined through physical and numerical modeling. The physical models are large-scale analogues of interdendritic structures produced by a rapid prototyping technique from three-dimensional (3-D) geometries obtained by X-ray microtomography. A glycerin-based solution was passed through the physical models and the permeability was calculated from measurements of the discharge flow rate and pressure drop. Mathematical models, considering the continuity and momentum equations, were developed for the corresponding unstructured meshes of the 3-D geometries used for the physical models. The numerically determined values of permeability are in good agreement with those measured. With the aid of this 3-D characterization, it is possible to distinguish between isolated liquid regions that are prevalent at high solid fractions and those liquid channels that contribute to interdendritic flow. The work presented in this study highlights the attention that must be paid to numerical calculations of fluid flow in the mushy zone and presents an alternative technique to determine permeability compared to conventional permeameters. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004994 [article] Physical and numerical characterization of the near-eutectic permeability of aluminum–copper alloys [texte imprimé] / Ehsan Khajeh, Auteur ; Daan M. Maijer, Auteur . - 2011 . - pp. 6334–6344.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6334–6344
Mots-clés : Permeability 3-D X-ray microtomography Modeling Microstructure Aluminum–copper alloy Résumé : The near-eutectic permeability of aluminum–copper alloys has been determined through physical and numerical modeling. The physical models are large-scale analogues of interdendritic structures produced by a rapid prototyping technique from three-dimensional (3-D) geometries obtained by X-ray microtomography. A glycerin-based solution was passed through the physical models and the permeability was calculated from measurements of the discharge flow rate and pressure drop. Mathematical models, considering the continuity and momentum equations, were developed for the corresponding unstructured meshes of the 3-D geometries used for the physical models. The numerically determined values of permeability are in good agreement with those measured. With the aid of this 3-D characterization, it is possible to distinguish between isolated liquid regions that are prevalent at high solid fractions and those liquid channels that contribute to interdendritic flow. The work presented in this study highlights the attention that must be paid to numerical calculations of fluid flow in the mushy zone and presents an alternative technique to determine permeability compared to conventional permeameters. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410004994
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6345–6357
Titre : The effect of oxygen on transitional Marangoni flow in laser spot welding Type de document : texte imprimé Auteurs : C.X. Zhao, Auteur ; C. Kwakernaak, Auteur ; Y. Pan, Auteur Année de publication : 2011 Article en page(s) : pp. 6345–6357 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Weld pool Instability Flow motions Laser spot welding Visualization Résumé : Owing to its significant influence in heat and mass transfer, liquid metal flow during stationary laser welding has been studied for different concentrations of oxygen in the surrounding environment. Two predominant types of surface flow motion are observed: an inward flow, corresponding to a positive surface tension temperature gradient, and an outward flow, corresponding to a negative gradient. Time-dependent changes in oxygen concentration at the surface are observed to flip the surface tension temperature gradient from negative to positive under appropriate shielding conditions. The oxygen concentration affects not only the flow motion, but also the laser absorption coefficient, which increases with increasing environmental oxygen concentration. It is shown here that the evolution of dissolved oxygen in the weld pool as a function of temperature can have a profound influence on the fluid flow and hence on energy transport. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005008 [article] The effect of oxygen on transitional Marangoni flow in laser spot welding [texte imprimé] / C.X. Zhao, Auteur ; C. Kwakernaak, Auteur ; Y. Pan, Auteur . - 2011 . - pp. 6345–6357.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6345–6357
Mots-clés : Weld pool Instability Flow motions Laser spot welding Visualization Résumé : Owing to its significant influence in heat and mass transfer, liquid metal flow during stationary laser welding has been studied for different concentrations of oxygen in the surrounding environment. Two predominant types of surface flow motion are observed: an inward flow, corresponding to a positive surface tension temperature gradient, and an outward flow, corresponding to a negative gradient. Time-dependent changes in oxygen concentration at the surface are observed to flip the surface tension temperature gradient from negative to positive under appropriate shielding conditions. The oxygen concentration affects not only the flow motion, but also the laser absorption coefficient, which increases with increasing environmental oxygen concentration. It is shown here that the evolution of dissolved oxygen in the weld pool as a function of temperature can have a profound influence on the fluid flow and hence on energy transport. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005008
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6358–6370
Titre : Solidification of metal foams Type de document : texte imprimé Auteurs : M. Mukherjee, Auteur ; F. Garcia-Moreno, Auteur ; J. Banhart, Auteur Année de publication : 2011 Article en page(s) : pp. 6358–6370 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Metal foam Solidification expansion Phase transformation Blowing agent Diffusion Résumé : Expansion and contraction phenomena during solidification of liquid metal foams were studied. Such foams were processed by mixing metal powders with TiH2 powder and compacting the resulting blends, after which the compacted powders were melted. The subsequent foaming process was monitored in situ by X-ray radioscopy. An intermediate expansion stage during solidification was observed. This solidification expansion (SE) could be linked to phase transformations in the alloy. SE was found to depend mainly on the time spent at the foaming temperature before cooling (holding time), the cooling rate and the alloy composition. The interplay between gas shrinkage, solidification shrinkage, gas production by the blowing agent and gas losses due to out-diffusion was identified as the main reason for SE. While the blowing agent had a major influence on SE, gas dissolved in the metal also played a role, since some SE was observed in foams blown without TiH2 by pure pressure manipulation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000501X [article] Solidification of metal foams [texte imprimé] / M. Mukherjee, Auteur ; F. Garcia-Moreno, Auteur ; J. Banhart, Auteur . - 2011 . - pp. 6358–6370.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6358–6370
Mots-clés : Metal foam Solidification expansion Phase transformation Blowing agent Diffusion Résumé : Expansion and contraction phenomena during solidification of liquid metal foams were studied. Such foams were processed by mixing metal powders with TiH2 powder and compacting the resulting blends, after which the compacted powders were melted. The subsequent foaming process was monitored in situ by X-ray radioscopy. An intermediate expansion stage during solidification was observed. This solidification expansion (SE) could be linked to phase transformations in the alloy. SE was found to depend mainly on the time spent at the foaming temperature before cooling (holding time), the cooling rate and the alloy composition. The interplay between gas shrinkage, solidification shrinkage, gas production by the blowing agent and gas losses due to out-diffusion was identified as the main reason for SE. While the blowing agent had a major influence on SE, gas dissolved in the metal also played a role, since some SE was observed in foams blown without TiH2 by pure pressure manipulation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000501X
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6371–6378
Titre : Sputter-deposited Cu/Cu(O) multilayers exhibiting enhanced strength and tunable modulus Type de document : texte imprimé Auteurs : J. P. Chu, Auteur ; Y.-C. Wang, Auteur Année de publication : 2011 Article en page(s) : pp. 6371–6378 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Sputtering deposition Multilayer thin film Nanoindentation AES Secondary ion mass spectroscopy Résumé : By means of brief pauses in radiofrequency (RF) sputter deposition between individual layers, ultrathin copper oxide layers were formed through adsorption in the Cu/Cu multilayers. Their mechanical properties were compared with the Cu/Cu(O) multilayers whose oxide layers were deliberately deposited between copper layers. The mechanical hardness value of the Cu/Cu(O) multilayers approached that of nanostructured copper thin films. The Young’s modulus of the multilayers was tunable, in accordance with the elasticity theories of composites. In addition, the Hall–Petch slope of the RF sputter-deposited Cu monolayers indicated that their theoretical strength approached the shear modulus of copper. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005021 [article] Sputter-deposited Cu/Cu(O) multilayers exhibiting enhanced strength and tunable modulus [texte imprimé] / J. P. Chu, Auteur ; Y.-C. Wang, Auteur . - 2011 . - pp. 6371–6378.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6371–6378
Mots-clés : Sputtering deposition Multilayer thin film Nanoindentation AES Secondary ion mass spectroscopy Résumé : By means of brief pauses in radiofrequency (RF) sputter deposition between individual layers, ultrathin copper oxide layers were formed through adsorption in the Cu/Cu multilayers. Their mechanical properties were compared with the Cu/Cu(O) multilayers whose oxide layers were deliberately deposited between copper layers. The mechanical hardness value of the Cu/Cu(O) multilayers approached that of nanostructured copper thin films. The Young’s modulus of the multilayers was tunable, in accordance with the elasticity theories of composites. In addition, the Hall–Petch slope of the RF sputter-deposited Cu monolayers indicated that their theoretical strength approached the shear modulus of copper. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005021
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6379–6384
Titre : The effect of microalloying additions of Au on the natural ageing of Al–Cu Type de document : texte imprimé Auteurs : B. Klobes, Auteur ; O. Balarisi, Auteur ; M. Liu, Auteur Année de publication : 2011 Article en page(s) : pp. 6379–6384 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminium alloys Al–Cu–Au Ageing Positron annihilation XANES Résumé : The influence of microalloying additions of Au to the binary Al–Cu system is investigated utilizing hardness measurements, positron annihilation spectroscopy and X-ray absorption spectroscopy. No room temperature ageing could be observed in the case of the ternary Al–Cu–Au alloy. Instead, quenched-in vacancies were trapped by Au atoms and thus could not catalyse the decomposition of the alloy. However, artificial ageing dissolves the complexes of Au and vacancies. A comparison between experimental and calculated absorption spectra shows that Au atoms did not agglomerate significantly during either natural or artificial ageing. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005033 [article] The effect of microalloying additions of Au on the natural ageing of Al–Cu [texte imprimé] / B. Klobes, Auteur ; O. Balarisi, Auteur ; M. Liu, Auteur . - 2011 . - pp. 6379–6384.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6379–6384
Mots-clés : Aluminium alloys Al–Cu–Au Ageing Positron annihilation XANES Résumé : The influence of microalloying additions of Au to the binary Al–Cu system is investigated utilizing hardness measurements, positron annihilation spectroscopy and X-ray absorption spectroscopy. No room temperature ageing could be observed in the case of the ternary Al–Cu–Au alloy. Instead, quenched-in vacancies were trapped by Au atoms and thus could not catalyse the decomposition of the alloy. However, artificial ageing dissolves the complexes of Au and vacancies. A comparison between experimental and calculated absorption spectra shows that Au atoms did not agglomerate significantly during either natural or artificial ageing. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005033
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6385–6392
Titre : A new method for evaluating the plastic properties of materials through instrumented frictional sliding tests Type de document : texte imprimé Auteurs : S. C. Bellemare, Auteur ; M. Dao, Auteur ; S. Suresh, Auteur Année de publication : 2011 Article en page(s) : pp. 6385–6392 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Scratch test Elasto-plastic properties Small-volume materials and devices Reverse algorithm Friction Résumé : Frictional normal contact probing methods involving instrumented, depth-sensing indentation can be used to estimate the mechanical properties of small-volume structures and materials such as thin films and components of micro-electro-mechanical systems. This paper describes a new method for estimating the plastic properties, i.e. the yield strength and strain hardening exponent, of ductile materials from the topography of scratches formed by a conical tip during an instrumented, depth-sensing frictional sliding test. The proposed reverse analysis (or inverse analysis) uses dimensionless functions derived from computational simulations to extract plastic properties from an instrumented scratch response performed on a standard, commercially available instrument. Sensitivity analysis indicates that an experimental error of 5% in the scratch hardness or the pile-up height induces an error of <22% in the estimated strain hardening exponent. Laboratory experiments illustrate how two aluminum alloy tempers of the same indentation hardness have significantly different pile-up as a result of different strain hardening. Comparative results between the frictional sliding test and traditional tensile tests showed reasonable agreement for a total of 11 metallic alloys evaluated. These results confirm the potential usefulness of the proposed method as an engineering tool to probe plastic properties of small-volume materials and confined structures where it is difficult to obtain reliable estimates of mechanical properties by other means. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005045 [article] A new method for evaluating the plastic properties of materials through instrumented frictional sliding tests [texte imprimé] / S. C. Bellemare, Auteur ; M. Dao, Auteur ; S. Suresh, Auteur . - 2011 . - pp. 6385–6392.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6385–6392
Mots-clés : Scratch test Elasto-plastic properties Small-volume materials and devices Reverse algorithm Friction Résumé : Frictional normal contact probing methods involving instrumented, depth-sensing indentation can be used to estimate the mechanical properties of small-volume structures and materials such as thin films and components of micro-electro-mechanical systems. This paper describes a new method for estimating the plastic properties, i.e. the yield strength and strain hardening exponent, of ductile materials from the topography of scratches formed by a conical tip during an instrumented, depth-sensing frictional sliding test. The proposed reverse analysis (or inverse analysis) uses dimensionless functions derived from computational simulations to extract plastic properties from an instrumented scratch response performed on a standard, commercially available instrument. Sensitivity analysis indicates that an experimental error of 5% in the scratch hardness or the pile-up height induces an error of <22% in the estimated strain hardening exponent. Laboratory experiments illustrate how two aluminum alloy tempers of the same indentation hardness have significantly different pile-up as a result of different strain hardening. Comparative results between the frictional sliding test and traditional tensile tests showed reasonable agreement for a total of 11 metallic alloys evaluated. These results confirm the potential usefulness of the proposed method as an engineering tool to probe plastic properties of small-volume materials and confined structures where it is difficult to obtain reliable estimates of mechanical properties by other means. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005045
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6393–6403
Titre : Mapping the parent austenite orientation reconstructed from the orientation of martensite by EBSD and its application to ausformed martensite Type de document : texte imprimé Auteurs : Goro Miyamoto, Auteur ; Naomichi Iwata, Auteur ; Naoki Takayama, Auteur Année de publication : 2011 Article en page(s) : pp. 6393–6403 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Lath martensite Electron backscattering diffraction Austenite Steels Orientation relationship Résumé : A new method is developed for reconstruction of the local orientation of the parent austenite based on the orientation of lath martensite measured by electron backscattered diffraction. The local orientation of austenite was obtained by least squares fitting as the difference between the experimental data and the predicted martensite orientation was minimal, assuming the specific orientation relationship (OR) between martensite and the parent austenite. First, the average OR between austenite and lath martensite was precisely determined and it was shown that both close packed planes and directions between martensite and the parent austenite deviated by more than 1° in low carbon martensite. The quality of the reconstructed austenite orientation map depended strongly on the OR used for the calculation. When Kurdjumov–Sachs (K–S) or Nishiyama–Wasserman (N–W) ORs were used the austenite orientation was frequently mis-indexed as a twin orientation with respect to the true orientation because of the mirror symmetry of (0 1 1)α stacking in the K–S or N–W ORs. In contrast, the frequency of mis-indexing was significantly reduced by using the measured OR, where the close packed planes and directions were not parallel. The deformation structure in austenite was successfully reconstructed by applying the proposed method to ausformed martensite in low carbon steel. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005057 [article] Mapping the parent austenite orientation reconstructed from the orientation of martensite by EBSD and its application to ausformed martensite [texte imprimé] / Goro Miyamoto, Auteur ; Naomichi Iwata, Auteur ; Naoki Takayama, Auteur . - 2011 . - pp. 6393–6403.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6393–6403
Mots-clés : Lath martensite Electron backscattering diffraction Austenite Steels Orientation relationship Résumé : A new method is developed for reconstruction of the local orientation of the parent austenite based on the orientation of lath martensite measured by electron backscattered diffraction. The local orientation of austenite was obtained by least squares fitting as the difference between the experimental data and the predicted martensite orientation was minimal, assuming the specific orientation relationship (OR) between martensite and the parent austenite. First, the average OR between austenite and lath martensite was precisely determined and it was shown that both close packed planes and directions between martensite and the parent austenite deviated by more than 1° in low carbon martensite. The quality of the reconstructed austenite orientation map depended strongly on the OR used for the calculation. When Kurdjumov–Sachs (K–S) or Nishiyama–Wasserman (N–W) ORs were used the austenite orientation was frequently mis-indexed as a twin orientation with respect to the true orientation because of the mirror symmetry of (0 1 1)α stacking in the K–S or N–W ORs. In contrast, the frequency of mis-indexing was significantly reduced by using the measured OR, where the close packed planes and directions were not parallel. The deformation structure in austenite was successfully reconstructed by applying the proposed method to ausformed martensite in low carbon steel. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005057
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6404–6410
Titre : Segregation-induced grain boundary electrical potential in ionic oxide materials : A first principles model Type de document : texte imprimé Auteurs : D. Gómez-García, Auteur ; Juan J. Meléndez, Auteur ; Robert L. González-Romero, Auteur Année de publication : 2011 Article en page(s) : pp. 6404–6410 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ceramics Grain boundary defects Segregation Analytical methods Résumé : A first principles continuum analytical model for cationic segregation to the grain boundaries in complex ceramic oxides is presented. The model permits one to determine the electric charge density and the segregation-induced electric potential profiles through the grain and can be extrapolated to the range of nanostructured grain sizes. The theoretical predictions are compared with existing data for yttria-stabilized tetragonal zirconia polycrystals. The implications for physical properties (mainly high temperature plasticity and hardening behaviour) are then discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005069 [article] Segregation-induced grain boundary electrical potential in ionic oxide materials : A first principles model [texte imprimé] / D. Gómez-García, Auteur ; Juan J. Meléndez, Auteur ; Robert L. González-Romero, Auteur . - 2011 . - pp. 6404–6410.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6404–6410
Mots-clés : Ceramics Grain boundary defects Segregation Analytical methods Résumé : A first principles continuum analytical model for cationic segregation to the grain boundaries in complex ceramic oxides is presented. The model permits one to determine the electric charge density and the segregation-induced electric potential profiles through the grain and can be extrapolated to the range of nanostructured grain sizes. The theoretical predictions are compared with existing data for yttria-stabilized tetragonal zirconia polycrystals. The implications for physical properties (mainly high temperature plasticity and hardening behaviour) are then discussed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005069
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6411–6420
Titre : Role of severe plastic deformation on the cyclic reversibility of a Ti50.3Ni33.7Pd16 high temperature shape memory alloy Type de document : texte imprimé Auteurs : B. Kockar, Auteur ; K. C. Atli, Auteur ; Ma, J., Auteur Année de publication : 2011 Article en page(s) : pp. 6411–6420 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : TiNiPd High temperature shape memory alloys Severe plastic deformation Equal channel angular extrusion Equal channel angular pressing Résumé : The present work focuses on the effect of microstructural refinement on the thermo-mechanical cyclic stability of a Ti50.3Ni33.7Pd16 high temperature shape memory alloy (HTSMA) which was severe plastically deformed using equal channel angular extrusion (ECAE). The grain/subgrain size of the high temperature austenite phase was refined down to about 100 nm, the lowest reported to date in HTSMAs. The increase in strength differential between the onset of transformation and the macroscopic plastic yielding after ECAE led to a notable enhancement in the cyclic stability during isobaric cooling–heating experiments. The reduction in irrecoverable strain levels was attributed to the increase in critical stress for dislocation slip due to the microstructural refinement during the ECAE process. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005070 [article] Role of severe plastic deformation on the cyclic reversibility of a Ti50.3Ni33.7Pd16 high temperature shape memory alloy [texte imprimé] / B. Kockar, Auteur ; K. C. Atli, Auteur ; Ma, J., Auteur . - 2011 . - pp. 6411–6420.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6411–6420
Mots-clés : TiNiPd High temperature shape memory alloys Severe plastic deformation Equal channel angular extrusion Equal channel angular pressing Résumé : The present work focuses on the effect of microstructural refinement on the thermo-mechanical cyclic stability of a Ti50.3Ni33.7Pd16 high temperature shape memory alloy (HTSMA) which was severe plastically deformed using equal channel angular extrusion (ECAE). The grain/subgrain size of the high temperature austenite phase was refined down to about 100 nm, the lowest reported to date in HTSMAs. The increase in strength differential between the onset of transformation and the macroscopic plastic yielding after ECAE led to a notable enhancement in the cyclic stability during isobaric cooling–heating experiments. The reduction in irrecoverable strain levels was attributed to the increase in critical stress for dislocation slip due to the microstructural refinement during the ECAE process. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005070
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6421–6430
Titre : Reinforcement architectures and thermal fatigue in diamond particle-reinforced aluminum Type de document : texte imprimé Auteurs : M. Schöbel, Auteur ; H.P. Degischer, Auteur ; S. Vaucher, Auteur Année de publication : 2011 Article en page(s) : pp. 6421–6430 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Particulate reinforced composites Neutron diffraction Synchrotron radiation computed tomography Thermal cycling Internal stresses Résumé : Aluminum reinforced by 60 vol.% diamond particles has been investigated as a potential heat sink material for high power electronics. Diamond (CD) is used as reinforcement contributing its high thermal conductivity (TC ≈ 1000 W mK−1) and low coefficient thermal expansion (CTE ≈ 1 ppm K−1). An Al matrix enables shaping and joining of the composite components. Interface bonding is improved by limited carbide formation induced by heat treatment and even more by SiC coating of diamond particles. An AlSi7 matrix forms an interpenetrating composite three-dimensional (3D) network of diamond particles linked by Si bridges percolated by a ductile α-Al matrix. Internal stresses are generated during temperature changes due to the CTE mismatch of the constituents. The stress evolution was determined in situ by neutron diffraction during thermal cycling between room temperature and 350 °C (soldering temperature). Tensile stresses build up in the Al/CD composites: during cooling <100 MPa in a pure Al matrix, but around 200 MPa in the Al in an AlSi7 matrix. Compressive stresses build up in Al during heating of the composite. The stress evolution causes changes in the void volume fraction and interface debonding by visco-plastic deformation of the Al matrix. Thermal fatigue damage has been revealed by high resolution synchrotron tomography. An interconnected diamond–Si 3D network formed with an AlSi7 matrix promises higher stability with respect to cycling temperature exposure. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005082 [article] Reinforcement architectures and thermal fatigue in diamond particle-reinforced aluminum [texte imprimé] / M. Schöbel, Auteur ; H.P. Degischer, Auteur ; S. Vaucher, Auteur . - 2011 . - pp. 6421–6430.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6421–6430
Mots-clés : Particulate reinforced composites Neutron diffraction Synchrotron radiation computed tomography Thermal cycling Internal stresses Résumé : Aluminum reinforced by 60 vol.% diamond particles has been investigated as a potential heat sink material for high power electronics. Diamond (CD) is used as reinforcement contributing its high thermal conductivity (TC ≈ 1000 W mK−1) and low coefficient thermal expansion (CTE ≈ 1 ppm K−1). An Al matrix enables shaping and joining of the composite components. Interface bonding is improved by limited carbide formation induced by heat treatment and even more by SiC coating of diamond particles. An AlSi7 matrix forms an interpenetrating composite three-dimensional (3D) network of diamond particles linked by Si bridges percolated by a ductile α-Al matrix. Internal stresses are generated during temperature changes due to the CTE mismatch of the constituents. The stress evolution was determined in situ by neutron diffraction during thermal cycling between room temperature and 350 °C (soldering temperature). Tensile stresses build up in the Al/CD composites: during cooling <100 MPa in a pure Al matrix, but around 200 MPa in the Al in an AlSi7 matrix. Compressive stresses build up in Al during heating of the composite. The stress evolution causes changes in the void volume fraction and interface debonding by visco-plastic deformation of the Al matrix. Thermal fatigue damage has been revealed by high resolution synchrotron tomography. An interconnected diamond–Si 3D network formed with an AlSi7 matrix promises higher stability with respect to cycling temperature exposure. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005082
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6431–6443
Titre : Analysis of local microstructure after shear creep deformation of a fine-grained duplex γ-TiAl alloy Type de document : texte imprimé Auteurs : D. Peter, Auteur ; G.B. Viswanathan, Auteur ; A. Dlouhy, Auteur Année de publication : 2011 Article en page(s) : pp. 6431–6443 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Titanium aluminides Shear creep deformation Transmission electron microscopy Dislocations Twinning Résumé : The present work characterizes the microstructure of a hot-extruded Ti–45Al–5Nb–0.2B–0.2C (at.%) alloy with a fine-grained duplex microstructure after shear creep deformation (temperature 1023 K; shear stress 175 MPa; shear deformation 20%). Diffraction contrast transmission electron microscopy (TEM) was performed to identify ordinary dislocations, superdislocations and twins. The microstructure observed in TEM is interpreted taking into account the contribution of the applied stress and coherency stresses to the overall local stress state. Two specific locations in the lamellar part of the microstructure were analyzed, where either twins or superdislocations provided c-component deformation in the L10 lattice of the γ phase. Lamellar γ grains can be in soft and hard orientations with respect to the resolved shear stress provided by the external load. The presence of twins can be rationalized by the superposition of the applied stress and local coherency stresses. The presence of superdislocations in hard γ grains represents indirect evidence for additional contributions to the local stress state associated with stress redistribution during creep. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005094 [article] Analysis of local microstructure after shear creep deformation of a fine-grained duplex γ-TiAl alloy [texte imprimé] / D. Peter, Auteur ; G.B. Viswanathan, Auteur ; A. Dlouhy, Auteur . - 2011 . - pp. 6431–6443.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6431–6443
Mots-clés : Titanium aluminides Shear creep deformation Transmission electron microscopy Dislocations Twinning Résumé : The present work characterizes the microstructure of a hot-extruded Ti–45Al–5Nb–0.2B–0.2C (at.%) alloy with a fine-grained duplex microstructure after shear creep deformation (temperature 1023 K; shear stress 175 MPa; shear deformation 20%). Diffraction contrast transmission electron microscopy (TEM) was performed to identify ordinary dislocations, superdislocations and twins. The microstructure observed in TEM is interpreted taking into account the contribution of the applied stress and coherency stresses to the overall local stress state. Two specific locations in the lamellar part of the microstructure were analyzed, where either twins or superdislocations provided c-component deformation in the L10 lattice of the γ phase. Lamellar γ grains can be in soft and hard orientations with respect to the resolved shear stress provided by the external load. The presence of twins can be rationalized by the superposition of the applied stress and local coherency stresses. The presence of superdislocations in hard γ grains represents indirect evidence for additional contributions to the local stress state associated with stress redistribution during creep. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005094
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6444–6451
Titre : Elastic anisotropy and extreme Poisson’s ratios in single crystals Type de document : texte imprimé Auteurs : Zoe A.D. Lethbridge, Auteur ; Richard I. Walton, Auteur ; Arnaud S.H. Marmier, Auteur Année de publication : 2011 Article en page(s) : pp. 6444–6451 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Mechanical properties Elastic behaviour Oxides Layered structures Metal and alloys Résumé : The relationship between elastic anisotropy and extreme Poisson’s ratio behaviour (either positive or negative) in single-crystalline materials has been investigated using experimentally determined single-crystal elastic constants for a wide range of solid materials. This makes use of a recently proposed elastic anisotropy index that is applicable to all crystal symmetries. For many real materials we find a striking correlation between the value of the elastic anisotropy index and the magnitudes of maximum and minimum Poisson’s ratios this is independent of crystal symmetry. This structure–property relationship provides new examples of auxetics and shows that negative Poisson’s ratios are actually not uncommon among many classes of inorganic (and organic) materials, including elemental metals, alloys, ionic solids, molecular solids and giant covalent networks. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005100 [article] Elastic anisotropy and extreme Poisson’s ratios in single crystals [texte imprimé] / Zoe A.D. Lethbridge, Auteur ; Richard I. Walton, Auteur ; Arnaud S.H. Marmier, Auteur . - 2011 . - pp. 6444–6451.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6444–6451
Mots-clés : Mechanical properties Elastic behaviour Oxides Layered structures Metal and alloys Résumé : The relationship between elastic anisotropy and extreme Poisson’s ratio behaviour (either positive or negative) in single-crystalline materials has been investigated using experimentally determined single-crystal elastic constants for a wide range of solid materials. This makes use of a recently proposed elastic anisotropy index that is applicable to all crystal symmetries. For many real materials we find a striking correlation between the value of the elastic anisotropy index and the magnitudes of maximum and minimum Poisson’s ratios this is independent of crystal symmetry. This structure–property relationship provides new examples of auxetics and shows that negative Poisson’s ratios are actually not uncommon among many classes of inorganic (and organic) materials, including elemental metals, alloys, ionic solids, molecular solids and giant covalent networks. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005100
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6452–6463
Titre : Texture development in near-α Ti friction stir welds Type de document : texte imprimé Auteurs : R.W. Fonda, Auteur ; K.E. Knipling, Auteur Année de publication : 2011 Article en page(s) : pp. 6452–6463 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Friction stir welding Shear texture Titanium alloys Electron backscattering diffraction (EBSD) Résumé : The microstructures and crystallographic textures produced during friction stir welding of the near-α Ti-5111 titanium alloy were characterized as a function of welding speed. The textures produced were compared with ideal hexagonal close packed (hcp) shear textures and with predicted textures of hcp Burgers variants of ideal body-centered cubic (bcc) shear textures, showing that the deposited welds are dominated by the hcp P1 and bcc D1 textures. The hcp P1 shear texture was dominant at slow weld speeds, while the bcc D1 shear texture was dominant at the fast weld speed. This variation appears to result from a poor transmission of the shear deformation from the rotating tool to the deposited weld that develops at faster welding speeds. These observations are compared to other studies of friction stir welds in hcp and bcc materials reported in the literature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005112 [article] Texture development in near-α Ti friction stir welds [texte imprimé] / R.W. Fonda, Auteur ; K.E. Knipling, Auteur . - 2011 . - pp. 6452–6463.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6452–6463
Mots-clés : Friction stir welding Shear texture Titanium alloys Electron backscattering diffraction (EBSD) Résumé : The microstructures and crystallographic textures produced during friction stir welding of the near-α Ti-5111 titanium alloy were characterized as a function of welding speed. The textures produced were compared with ideal hexagonal close packed (hcp) shear textures and with predicted textures of hcp Burgers variants of ideal body-centered cubic (bcc) shear textures, showing that the deposited welds are dominated by the hcp P1 and bcc D1 textures. The hcp P1 shear texture was dominant at slow weld speeds, while the bcc D1 shear texture was dominant at the fast weld speed. This variation appears to result from a poor transmission of the shear deformation from the rotating tool to the deposited weld that develops at faster welding speeds. These observations are compared to other studies of friction stir welds in hcp and bcc materials reported in the literature. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005112
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6464–6473
Titre : Evolution of structure and free volume in symmetric tilt grain boundaries during dislocation nucleation Type de document : texte imprimé Auteurs : Garritt J. Tucker, Auteur ; Mark A. Tschopp, Auteur ; David L. McDowell, Auteur Année de publication : 2011 Article en page(s) : pp. 6464–6473 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain boundaries Dislocations Molecular dynamics Free volume Plastic deformation Résumé : Grain boundary evolution in copper bicrystals is investigated during uniaxial tension at 10 K. Grain boundary structures are generated using molecular statics employing an embedded atom method potential, followed by molecular dynamics simulation at a constant 1 × 109 s−1 strain rate. Interfacial free volume is continuously measured during boundary deformation, and its evolution is investigated both prior to and during grain boundary dislocation nucleation. Free volume provides valuable insight into atomic-scale processes associated with stress-induced grain boundary deformation. Different boundary structures are investigated in this work to analyze the role of interface structure, stress state and initial free volume on dislocation nucleation. The results indicate that the free volume influences interfacial deformation through modified atomic-scale processes, and grain boundaries containing particular free volume distributions show a greater propensity for collective atomic migration during inelastic deformation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005124 [article] Evolution of structure and free volume in symmetric tilt grain boundaries during dislocation nucleation [texte imprimé] / Garritt J. Tucker, Auteur ; Mark A. Tschopp, Auteur ; David L. McDowell, Auteur . - 2011 . - pp. 6464–6473.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6464–6473
Mots-clés : Grain boundaries Dislocations Molecular dynamics Free volume Plastic deformation Résumé : Grain boundary evolution in copper bicrystals is investigated during uniaxial tension at 10 K. Grain boundary structures are generated using molecular statics employing an embedded atom method potential, followed by molecular dynamics simulation at a constant 1 × 109 s−1 strain rate. Interfacial free volume is continuously measured during boundary deformation, and its evolution is investigated both prior to and during grain boundary dislocation nucleation. Free volume provides valuable insight into atomic-scale processes associated with stress-induced grain boundary deformation. Different boundary structures are investigated in this work to analyze the role of interface structure, stress state and initial free volume on dislocation nucleation. The results indicate that the free volume influences interfacial deformation through modified atomic-scale processes, and grain boundaries containing particular free volume distributions show a greater propensity for collective atomic migration during inelastic deformation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005124
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6474–6486
Titre : Elastic properties of hard cobalt boride composite nanoparticles Type de document : texte imprimé Auteurs : A. Rinaldi, Auteur ; M.A. Correa-Duarte, Auteur ; V. Salgueirino-Maceira, Auteur Année de publication : 2011 Article en page(s) : pp. 6474–6486 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Core-shell nanoparticles Transition metal Intermetallics Nanomechanics Mechanical properties Résumé : This paper reports on the determination of elastic and hardness properties of Co–B composite nanoparticles (CNP). Co boride materials is usually known for their functional properties (hydrogen catalysis, magnetism, corrosion, biomedics), but nanoscale dimensions also bring significant mechanical properties. In situ compression tests of 70–150 nm core–shell silica-coated Co2B CNP (Composite nanoparticles) were performed for the first time with a nanoindenter in the load range 30–300 μN. The CNP modulus is comparable with the bulk material (ECNP = 159–166 GPa), but the hardness is as much as 5 times higher (∼4.5 ± 1.0 GPA). Both modulus and hardness (to a lesser extent) are found to increase with the applied pressure. The paper first addresses the limitations of ordinary contact analysis intended for single-phase NP, and then presents a hybrid Oliver–Pharr strategy suitable for CNP, where numerical modeling overcomes issues related to anisotropy and heterogenety of the composite nanostructure that hinder the direct application of basic contact models. An alternative regression-based approach for estimating modulus and hardness is also considered for comparison. The importance of the model selection for the contact area A for accurate modulus and hardness results is emphasized. Besides typical Hertzian, geometrical and cylindrical area models, a new one is formulated from a “rigid-sphere” approximation, which turned out to perform best and consistently in this study, on a par with the cylindrical model. Finally, evidence of the magnetic nature of CNP and, unexpectedly, reverse plasticity is provided. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005239 [article] Elastic properties of hard cobalt boride composite nanoparticles [texte imprimé] / A. Rinaldi, Auteur ; M.A. Correa-Duarte, Auteur ; V. Salgueirino-Maceira, Auteur . - 2011 . - pp. 6474–6486.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6474–6486
Mots-clés : Core-shell nanoparticles Transition metal Intermetallics Nanomechanics Mechanical properties Résumé : This paper reports on the determination of elastic and hardness properties of Co–B composite nanoparticles (CNP). Co boride materials is usually known for their functional properties (hydrogen catalysis, magnetism, corrosion, biomedics), but nanoscale dimensions also bring significant mechanical properties. In situ compression tests of 70–150 nm core–shell silica-coated Co2B CNP (Composite nanoparticles) were performed for the first time with a nanoindenter in the load range 30–300 μN. The CNP modulus is comparable with the bulk material (ECNP = 159–166 GPa), but the hardness is as much as 5 times higher (∼4.5 ± 1.0 GPA). Both modulus and hardness (to a lesser extent) are found to increase with the applied pressure. The paper first addresses the limitations of ordinary contact analysis intended for single-phase NP, and then presents a hybrid Oliver–Pharr strategy suitable for CNP, where numerical modeling overcomes issues related to anisotropy and heterogenety of the composite nanostructure that hinder the direct application of basic contact models. An alternative regression-based approach for estimating modulus and hardness is also considered for comparison. The importance of the model selection for the contact area A for accurate modulus and hardness results is emphasized. Besides typical Hertzian, geometrical and cylindrical area models, a new one is formulated from a “rigid-sphere” approximation, which turned out to perform best and consistently in this study, on a par with the cylindrical model. Finally, evidence of the magnetic nature of CNP and, unexpectedly, reverse plasticity is provided. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005239
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6487–6494
Titre : Material-dependent representative plastic strain for the prediction of indentation hardness Type de document : texte imprimé Auteurs : Nathan A. Branch, Auteur ; Ghatu Subhash, Auteur ; Nagaraj K. Arakere, Auteur Année de publication : 2011 Article en page(s) : pp. 6487–6494 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Representative plastic strain Hardness Plastic deformation Finite element modeling Résumé : The definition of representative plastic strain induced by a Vickers indent has received considerable attention in recent years. Previous reports have attempted to define a universal value that was independent of a material’s plastic response. However, the work presented here will show that a material-dependent representative plastic strain is valid in the conversion of flow stress to indentation hardness. This representative plastic strain is the volume average plastic strain within the plastic zone of Vickers indentation. The increase in indentation hardness within the plastic zones of macro-indents was experimentally determined by micro-Vickers indentation and then compared with that predicted by finite element modeling, which utilizes the proposed representative plastic strain. It was further shown that the representative plastic strain defined here is independent of yield strength, elastic modulus and magnitude of prior plastic deformation for both linear and power law strain hardening materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005240 [article] Material-dependent representative plastic strain for the prediction of indentation hardness [texte imprimé] / Nathan A. Branch, Auteur ; Ghatu Subhash, Auteur ; Nagaraj K. Arakere, Auteur . - 2011 . - pp. 6487–6494.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6487–6494
Mots-clés : Representative plastic strain Hardness Plastic deformation Finite element modeling Résumé : The definition of representative plastic strain induced by a Vickers indent has received considerable attention in recent years. Previous reports have attempted to define a universal value that was independent of a material’s plastic response. However, the work presented here will show that a material-dependent representative plastic strain is valid in the conversion of flow stress to indentation hardness. This representative plastic strain is the volume average plastic strain within the plastic zone of Vickers indentation. The increase in indentation hardness within the plastic zones of macro-indents was experimentally determined by micro-Vickers indentation and then compared with that predicted by finite element modeling, which utilizes the proposed representative plastic strain. It was further shown that the representative plastic strain defined here is independent of yield strength, elastic modulus and magnitude of prior plastic deformation for both linear and power law strain hardening materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005240
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6495–6503
Titre : Design and fabrication of compositionally graded inorganic oxide thin films : Mechanical, optical and permeation characteristics Type de document : texte imprimé Auteurs : Y.-H. Choi, Auteur ; X. Bulliard, Auteur ; A. Benayad, Auteur Année de publication : 2011 Article en page(s) : pp. 6495–6503 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Functionally graded materials Thin films Interface structure Sputtering Toughness Résumé : Different types of inorganic oxide films composed of a chemical composition gradient single layer were designed, fabricated and characterized. Compositionally graded thin films were created by power-controlled co-sputtering of alumina (Al2O3) and silica (SiO2) at room temperature, allowing the structural design of the film to be tailored at the nanometer scale. Two distinct graded thin films were fabricated: one with a compositionally asymmetric structure consisting of a SiO2-rich bottom interface and a Al2O3-rich top surface, and the other with a compositionally balanced sandwich structure consisting of both the top surface and bottom interface rich in SiO2 and a core rich in Al2O3 (referred to as SGS for ‘sandwich graded structure’). Smoothly graded thin films without interfacial boundaries were verified by Auger electron spectroscopy profiles. X-ray photoelectron spectroscopy demonstrated that the Al2O3/SiO2 graded structures consisted of Si–O and Al–O bonds, as well as Al–O–Si bonds in the transition layer. Neat Al2O3 or SiO2 and their graded ones were all investigated for their mechanical, optical and permeation properties. A SGS thin film presented the best mechanical stability (i.e., about three times improved film toughness of a neat Al2O3 single layer), demonstrating that balanced internal stresses and alternating bonding structures, achieved via a graded structure without interfaces, are crucial for enhancing mechanical stability. Furthermore, neat and graded thin films exhibited the similar level of optical transmittance and the permeation properties for the graded films were well matched with the behaviors of mechanical stability. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005252 [article] Design and fabrication of compositionally graded inorganic oxide thin films : Mechanical, optical and permeation characteristics [texte imprimé] / Y.-H. Choi, Auteur ; X. Bulliard, Auteur ; A. Benayad, Auteur . - 2011 . - pp. 6495–6503.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6495–6503
Mots-clés : Functionally graded materials Thin films Interface structure Sputtering Toughness Résumé : Different types of inorganic oxide films composed of a chemical composition gradient single layer were designed, fabricated and characterized. Compositionally graded thin films were created by power-controlled co-sputtering of alumina (Al2O3) and silica (SiO2) at room temperature, allowing the structural design of the film to be tailored at the nanometer scale. Two distinct graded thin films were fabricated: one with a compositionally asymmetric structure consisting of a SiO2-rich bottom interface and a Al2O3-rich top surface, and the other with a compositionally balanced sandwich structure consisting of both the top surface and bottom interface rich in SiO2 and a core rich in Al2O3 (referred to as SGS for ‘sandwich graded structure’). Smoothly graded thin films without interfacial boundaries were verified by Auger electron spectroscopy profiles. X-ray photoelectron spectroscopy demonstrated that the Al2O3/SiO2 graded structures consisted of Si–O and Al–O bonds, as well as Al–O–Si bonds in the transition layer. Neat Al2O3 or SiO2 and their graded ones were all investigated for their mechanical, optical and permeation properties. A SGS thin film presented the best mechanical stability (i.e., about three times improved film toughness of a neat Al2O3 single layer), demonstrating that balanced internal stresses and alternating bonding structures, achieved via a graded structure without interfaces, are crucial for enhancing mechanical stability. Furthermore, neat and graded thin films exhibited the similar level of optical transmittance and the permeation properties for the graded films were well matched with the behaviors of mechanical stability. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005252
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6504–6512
Titre : Thermal stability of nanocomposite metals : In situ observation of anomalous residual stress relaxation during annealing under synchrotron radiation Type de document : texte imprimé Auteurs : J. B. Dubois, Auteur ; L. Thilly, Auteur ; P.O. Renault, Auteur Année de publication : 2011 Article en page(s) : pp. 6504–6512 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanostructures In situ annealing Residual stresses X-ray diffraction Synchrotron Résumé : The thermal stability of nanocomposite metals (a nanostructured copper matrix embedding niobium nanotubes) is investigated via time-resolved in situ annealing under synchrotron high-energy X-rays. The diffraction peak profile analysis demonstrates that internal-stress relaxation begins in the Nb nanotubes at a temperature far below the bulk recrystallization temperature and follows size-specific regimes originating from a proximity effect with the nanostructured Cu matrix: the increased Cu–Nb interface surface disrupts internal-stress relaxation processes, confirming the larger thermal resistance of nanostructured materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005276 [article] Thermal stability of nanocomposite metals : In situ observation of anomalous residual stress relaxation during annealing under synchrotron radiation [texte imprimé] / J. B. Dubois, Auteur ; L. Thilly, Auteur ; P.O. Renault, Auteur . - 2011 . - pp. 6504–6512.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6504–6512
Mots-clés : Nanostructures In situ annealing Residual stresses X-ray diffraction Synchrotron Résumé : The thermal stability of nanocomposite metals (a nanostructured copper matrix embedding niobium nanotubes) is investigated via time-resolved in situ annealing under synchrotron high-energy X-rays. The diffraction peak profile analysis demonstrates that internal-stress relaxation begins in the Nb nanotubes at a temperature far below the bulk recrystallization temperature and follows size-specific regimes originating from a proximity effect with the nanostructured Cu matrix: the increased Cu–Nb interface surface disrupts internal-stress relaxation processes, confirming the larger thermal resistance of nanostructured materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005276
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6513–6525
Titre : Direct evidence for stress-induced texture evolution and grain growth of silver thin films upon thermal treatment and self-ion bombardment Type de document : texte imprimé Auteurs : Matteo Seita, Auteur ; Christina M. Pecnik, Auteur ; Stephan Frank, Auteur Année de publication : 2011 Article en page(s) : pp. 6513–6525 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ion beam processing Crystal growth Thin films Abnormal grain growth Texture Résumé : Common failure mechanisms in microelectronics, such as electromigration, creep and fatigue, can be positively influenced by microstructure optimization. In this paper a combination of post-deposition heat treatment and self-ion bombardment is proposed as a valid candidate to gain control over the microstructure of (1 1 1) fiber textured thin silver films. Irradiation can induce a strong in-plane texture and hence lead to biaxially textured films through a process of selective grain growth. Moreover, we report microstructural stability of the irradiated regions over a wide range of temperatures (up to 600 °C), in contrast to non-irradiated portions of the film, which underwent abnormal growth of the (1 0 0) out-of-plane oriented grains, and a consequent texture change, at temperatures as low as 195 °C. The thermal stress induced in the film upon heat treatment was quantified in situ and its role in texture change elucidated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005288 [article] Direct evidence for stress-induced texture evolution and grain growth of silver thin films upon thermal treatment and self-ion bombardment [texte imprimé] / Matteo Seita, Auteur ; Christina M. Pecnik, Auteur ; Stephan Frank, Auteur . - 2011 . - pp. 6513–6525.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6513–6525
Mots-clés : Ion beam processing Crystal growth Thin films Abnormal grain growth Texture Résumé : Common failure mechanisms in microelectronics, such as electromigration, creep and fatigue, can be positively influenced by microstructure optimization. In this paper a combination of post-deposition heat treatment and self-ion bombardment is proposed as a valid candidate to gain control over the microstructure of (1 1 1) fiber textured thin silver films. Irradiation can induce a strong in-plane texture and hence lead to biaxially textured films through a process of selective grain growth. Moreover, we report microstructural stability of the irradiated regions over a wide range of temperatures (up to 600 °C), in contrast to non-irradiated portions of the film, which underwent abnormal growth of the (1 0 0) out-of-plane oriented grains, and a consequent texture change, at temperatures as low as 195 °C. The thermal stress induced in the film upon heat treatment was quantified in situ and its role in texture change elucidated. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005288
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6526–6534
Titre : Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt Type de document : texte imprimé Auteurs : H. Men, Auteur ; B. Jiang, Auteur ; Z. Fan, Auteur Année de publication : 2011 Article en page(s) : pp. 6526–6534 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nucleation Oxide Grain refinement Magnesium alloy Résumé : It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005306 [article] Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt [texte imprimé] / H. Men, Auteur ; B. Jiang, Auteur ; Z. Fan, Auteur . - 2011 . - pp. 6526–6534.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6526–6534
Mots-clés : Nucleation Oxide Grain refinement Magnesium alloy Résumé : It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005306
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6535–6541
Titre : Dislocation drag at the nanoscale Type de document : texte imprimé Auteurs : Christopher R. Weinberger, Auteur Année de publication : 2011 Article en page(s) : pp. 6535–6541 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation mobility Nanostructure Plastic deformation Résumé : The mobility of dislocations is shown to be a size-dependent phenomenon. When dislocations intersect free surfaces, the mobility decreases as the dislocation length decreases, suggesting that dislocation motion in small structures may be more difficult. This increased drag may be related to surface forces acting where the dislocation intersects the free surface or from altered dislocation–phonon interactions. Mobility, however, is not as dependent on the film thickness and converges rapidly to bulk values. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005318 [article] Dislocation drag at the nanoscale [texte imprimé] / Christopher R. Weinberger, Auteur . - 2011 . - pp. 6535–6541.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6535–6541
Mots-clés : Dislocation mobility Nanostructure Plastic deformation Résumé : The mobility of dislocations is shown to be a size-dependent phenomenon. When dislocations intersect free surfaces, the mobility decreases as the dislocation length decreases, suggesting that dislocation motion in small structures may be more difficult. This increased drag may be related to surface forces acting where the dislocation intersects the free surface or from altered dislocation–phonon interactions. Mobility, however, is not as dependent on the film thickness and converges rapidly to bulk values. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005318
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6542–6553
Titre : Nucleation, growth and impingement modes deduced from isothermally and isochronally conducted phase transformations : Calorimetric analysis of the crystallization of amorphous Zr50Al10Ni40 Type de document : texte imprimé Auteurs : F. Liu, Auteur ; H. Nitsche, Auteur ; F. Sommer, Auteur Année de publication : 2011 Article en page(s) : pp. 6542–6553 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nucleation Growth Impingement Crystallization kinetics Résumé : The crystallization kinetics of amorphous Zr50Al10Ni40, as measured by means of both isothermal and isochronal differential scanning calorimetry, were evaluated using a new procedure involving application of a modular analytical model to provide a complete description of the phase-transformation kinetics, in combination with a preceding analysis of the transformation-rate maximum. The power of detailed analysis of the position of the transformation-rate maximum, as a function of the transformed fraction, was demonstrated by identification of the operating impingement mode. On this basis, the kinetic parameters governing the crystallization kinetics could then be determined quantitatively using the modular analytical model. The crystallization governing mechanisms could be varied by appropriate control of the crystallization conditions. The results obtained are consistent with the microstructural evolution, as observed by transmission electron microscopy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005331 [article] Nucleation, growth and impingement modes deduced from isothermally and isochronally conducted phase transformations : Calorimetric analysis of the crystallization of amorphous Zr50Al10Ni40 [texte imprimé] / F. Liu, Auteur ; H. Nitsche, Auteur ; F. Sommer, Auteur . - 2011 . - pp. 6542–6553.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6542–6553
Mots-clés : Nucleation Growth Impingement Crystallization kinetics Résumé : The crystallization kinetics of amorphous Zr50Al10Ni40, as measured by means of both isothermal and isochronal differential scanning calorimetry, were evaluated using a new procedure involving application of a modular analytical model to provide a complete description of the phase-transformation kinetics, in combination with a preceding analysis of the transformation-rate maximum. The power of detailed analysis of the position of the transformation-rate maximum, as a function of the transformed fraction, was demonstrated by identification of the operating impingement mode. On this basis, the kinetic parameters governing the crystallization kinetics could then be determined quantitatively using the modular analytical model. The crystallization governing mechanisms could be varied by appropriate control of the crystallization conditions. The results obtained are consistent with the microstructural evolution, as observed by transmission electron microscopy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005331
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6554–6564
Titre : Simulations of stress-induced twinning and de-twinning : A phase field model Type de document : texte imprimé Auteurs : ShenYang Hu, Auteur ; Chuck H. Henager Jr, Auteur ; Long-Qing Chen, Auteur Année de publication : 2011 Article en page(s) : pp. 6554–6564 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Phase field method Partial dislocation Deformation twin Polycrystal deformation Résumé : Twinning in certain metals or under certain conditions is a major plastic deformation mode. Here we present a phase field model to describe twin formation and evolution in a polycrystalline fcc metal under loading and unloading. The model assumes that twin nucleation, growth and de-twinning is a process of partial dislocation nucleation and slip on successive habit planes. Stacking fault energies, energy pathways (γ surfaces), critical shear stresses for the formation of stacking faults and dislocation core energies are used to construct the thermodynamic model. The simulation results demonstrate that the model is able to predict the nucleation of twins and partial dislocations, as well as the morphology of the twin nuclei, and to reasonably describe twin growth and interaction. The twin microstructures at grain boundaries are in agreement with experimental observation. It was found that de-twinning occurs during unloading in the simulations, however, a strong dependence of twin structure evolution on loading history was observed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005343 [article] Simulations of stress-induced twinning and de-twinning : A phase field model [texte imprimé] / ShenYang Hu, Auteur ; Chuck H. Henager Jr, Auteur ; Long-Qing Chen, Auteur . - 2011 . - pp. 6554–6564.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6554–6564
Mots-clés : Phase field method Partial dislocation Deformation twin Polycrystal deformation Résumé : Twinning in certain metals or under certain conditions is a major plastic deformation mode. Here we present a phase field model to describe twin formation and evolution in a polycrystalline fcc metal under loading and unloading. The model assumes that twin nucleation, growth and de-twinning is a process of partial dislocation nucleation and slip on successive habit planes. Stacking fault energies, energy pathways (γ surfaces), critical shear stresses for the formation of stacking faults and dislocation core energies are used to construct the thermodynamic model. The simulation results demonstrate that the model is able to predict the nucleation of twins and partial dislocations, as well as the morphology of the twin nuclei, and to reasonably describe twin growth and interaction. The twin microstructures at grain boundaries are in agreement with experimental observation. It was found that de-twinning occurs during unloading in the simulations, however, a strong dependence of twin structure evolution on loading history was observed. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005343
Exemplaires
| Code-barres | Cote | Support | Localisation | Section | Disponibilité |
|---|---|---|---|---|---|
| aucun exemplaire | |||||
