Dépouillements

Friction stir spot welding of single-crystal austenitic stainless steel / J. Jeon in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7439–7449 Titre : Friction stir spot welding of single-crystal austenitic stainless steel Type de document : texte imprimé Auteurs : J. Jeon, Auteur ; S. Mironov, Auteur ; Y.S. Sato, Auteur Année de publication : 2012 Article en page(s) : pp. 7439–7449 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Friction  stir  welding  Austenitic  stainless  steel  Single  crystal  Electron  backscatter  diffraction  Recrystallization Résumé : The high-resolution electron backscatter diffraction technique was employed to study the structural response of single-crystal austenitic stainless steel to friction stir spot welding. The strain-induced crystal rotations were found to be governed by simple-shear deformation. In contrast to aluminum alloys, the developed texture showed pronounced {1 1 1}〈1 1 0〉 simple-shear texture components, this effect being attributed to the suppression of cross-slip. Grain boundary development was demonstrated to be closely linked with texture evolution. During pin plunging, at relatively low temperatures, microstructural evolution was shown to be dictated by continuous recrystallization. Due to this process, the single-crystal structure was broken up into an ultrafine-grained polycrystalline aggregate with a mean grain size of ∼0.2 μm. During shoulder contacting, however, the temperature rose and discontinuous recrystallization became predominant. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006501# [article] Friction stir spot welding of single-crystal austenitic stainless steel [texte imprimé] / J. Jeon, Auteur ; S. Mironov, Auteur ; Y.S. Sato, Auteur . - 2012 . - pp. 7439–7449. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7439–7449 Mots-clés : Friction  stir  welding  Austenitic  stainless  steel  Single  crystal  Electron  backscatter  diffraction  Recrystallization Résumé : The high-resolution electron backscatter diffraction technique was employed to study the structural response of single-crystal austenitic stainless steel to friction stir spot welding. The strain-induced crystal rotations were found to be governed by simple-shear deformation. In contrast to aluminum alloys, the developed texture showed pronounced {1 1 1}〈1 1 0〉 simple-shear texture components, this effect being attributed to the suppression of cross-slip. Grain boundary development was demonstrated to be closely linked with texture evolution. During pin plunging, at relatively low temperatures, microstructural evolution was shown to be dictated by continuous recrystallization. Due to this process, the single-crystal structure was broken up into an ultrafine-grained polycrystalline aggregate with a mean grain size of ∼0.2 μm. During shoulder contacting, however, the temperature rose and discontinuous recrystallization became predominant. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006501#

Highly mobile twinned interface in 10 M modulated Ni–Mn–Ga martensite / L. Straka in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7450–7463 Titre : Highly mobile twinned interface in 10 M modulated Ni–Mn–Ga martensite : Analysis beyond the tetragonal approximation of lattice Type de document : texte imprimé Auteurs : L. Straka, Auteur ; O. Heczko, Auteur ; H. Seiner, Auteur Année de publication : 2012 Article en page(s) : pp. 7450–7463 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Microstructure  Twinning  X-ray  diffraction  Heusler  phases  Magnetic  shape  memory Résumé : The huge strains that Ni–Mn–Ga magnetic shape memory alloys can achieve are usually described in a tetragonal unit cell approximation of a five-layered modulated (10 M) crystal structure. Here we analyze the impact of a slight orthorhombic and monoclinic distortion of the 10 M structure in Ni50.2Mn28.3Ga21.5at.% single crystal. Combining dedicated experiments to probe the microstructure, structure and mechanical properties with calculation using elastic continuum theory, we prove the existence of fine a/b-laminates within modulation macrotwins of the order of 100 micrometers in size. This complex twin microstructure containing a Type II macrotwin interface is associated with an extraordinarily low twinning stress of between 0.05 and 0.3 MPa, while Type I twins exhibit twinning stress of about 1 MPa. The findings provide important guidelines for designing the martensitic microstructure for more efficient actuators. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006574 [article] Highly mobile twinned interface in 10 M modulated Ni–Mn–Ga martensite : Analysis beyond the tetragonal approximation of lattice [texte imprimé] / L. Straka, Auteur ; O. Heczko, Auteur ; H. Seiner, Auteur . - 2012 . - pp. 7450–7463. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7450–7463 Mots-clés : Microstructure  Twinning  X-ray  diffraction  Heusler  phases  Magnetic  shape  memory Résumé : The huge strains that Ni–Mn–Ga magnetic shape memory alloys can achieve are usually described in a tetragonal unit cell approximation of a five-layered modulated (10 M) crystal structure. Here we analyze the impact of a slight orthorhombic and monoclinic distortion of the 10 M structure in Ni50.2Mn28.3Ga21.5at.% single crystal. Combining dedicated experiments to probe the microstructure, structure and mechanical properties with calculation using elastic continuum theory, we prove the existence of fine a/b-laminates within modulation macrotwins of the order of 100 micrometers in size. This complex twin microstructure containing a Type II macrotwin interface is associated with an extraordinarily low twinning stress of between 0.05 and 0.3 MPa, while Type I twins exhibit twinning stress of about 1 MPa. The findings provide important guidelines for designing the martensitic microstructure for more efficient actuators. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006574

Unexpected slip mechanism induced by the reduced dimensions in silicon nanostructures / Julien Guénolé in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7464–7472 Titre : Unexpected slip mechanism induced by the reduced dimensions in silicon nanostructures : Atomistic study Type de document : texte imprimé Auteurs : Julien Guénolé, Auteur ; Sandrine Brochard, Auteur ; Julien Godet, Auteur Année de publication : 2012 Article en page(s) : pp. 7464–7472 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  Semiconductors  Plastic  deformation  Simulation Résumé : We have performed molecular dynamics simulations and first-principles calculations to investigate the first stages of plasticity in single-crystalline silicon nanostructures free of initial defects, under compressive and tensile strain along the [0 0 1] axis. In compression especially, we observe the activation of {0 1 1} planes, both in nanowires and in thin films, regardless of the temperature and the interatomic potential used. The occurrence of such an unexpected slip system can be explained by a careful investigation of the generalized stacking fault energy under different stress conditions, and the associated restoring forces. Finally, the activation of the {0 1 1} planes is shown to be an indirect consequence of the small dimensions of the nanostructures considered. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006161 [article] Unexpected slip mechanism induced by the reduced dimensions in silicon nanostructures : Atomistic study [texte imprimé] / Julien Guénolé, Auteur ; Sandrine Brochard, Auteur ; Julien Godet, Auteur . - 2012 . - pp. 7464–7472. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7464–7472 Mots-clés : Dislocation  Semiconductors  Plastic  deformation  Simulation Résumé : We have performed molecular dynamics simulations and first-principles calculations to investigate the first stages of plasticity in single-crystalline silicon nanostructures free of initial defects, under compressive and tensile strain along the [0 0 1] axis. In compression especially, we observe the activation of {0 1 1} planes, both in nanowires and in thin films, regardless of the temperature and the interatomic potential used. The occurrence of such an unexpected slip system can be explained by a careful investigation of the generalized stacking fault energy under different stress conditions, and the associated restoring forces. Finally, the activation of the {0 1 1} planes is shown to be an indirect consequence of the small dimensions of the nanostructures considered. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006161

Self-organized growth of higher manganese silicide nanowires on Si(1 1 1), (1 1 0) and (0 0 1) surfaces / Zhi-Qiang Zou in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7473–7479 Titre : Self-organized growth of higher manganese silicide nanowires on Si(1 1 1), (1 1 0) and (0 0 1) surfaces Type de document : texte imprimé Auteurs : Zhi-Qiang Zou, Auteur ; Wei-Cong Li, Auteur ; Jia-Miao Liang, Auteur Année de publication : 2012 Article en page(s) : pp. 7473–7479 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Crystal  growth  Molecular  beam  epitaxy  (MBE)  Scanning  tunneling  spectroscopy  Transmission  electron  microscopy  (TEM)  Transition  metal  silicides Résumé : Higher manganese silicide nanowires (NWs) with a large aspect ratio have been grown on three kinds of substrate, Si(1 1 1), (1 1 0) and (0 0 1), with the reactive epitaxy method at temperatures above ∼500 °C. The self-assembly of the NWs is confined along the Si〈1 1 0〉 directions, resulting in the NWs orienting with the long axis along one, two and three particular directions on the Si(1 1 0), (0 0 1) and (1 1 1) surfaces, respectively. Scanning tunneling spectroscopy and transmission electron microscopy (TEM) studies indicate unambiguously that the NWs are tetragonal MnSi1.7. The width of the NWs has a maximum or well-defined value on each kind of substrate, though the length varies greatly. In the plan-view TEM micrographs, the NWs exhibit two sets of Moiré fringes: one is along the length direction and has a large periodicity, and the other is along the width direction and has a very small periodicity. These phenomena strongly indicate that the growth of NWs is governed by a strain-driven energetic mechanism and the NW shape results from anisotropic lattice mismatch between the silicide and the Si substrate. This research paves the way towards controllable growth of the silicide NWs on silicon substrates, which may help to advance the realization of practical applications of silicide NWs in nanoelectronics. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006276 [article] Self-organized growth of higher manganese silicide nanowires on Si(1 1 1), (1 1 0) and (0 0 1) surfaces [texte imprimé] / Zhi-Qiang Zou, Auteur ; Wei-Cong Li, Auteur ; Jia-Miao Liang, Auteur . - 2012 . - pp. 7473–7479. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7473–7479 Mots-clés : Crystal  growth  Molecular  beam  epitaxy  (MBE)  Scanning  tunneling  spectroscopy  Transmission  electron  microscopy  (TEM)  Transition  metal  silicides Résumé : Higher manganese silicide nanowires (NWs) with a large aspect ratio have been grown on three kinds of substrate, Si(1 1 1), (1 1 0) and (0 0 1), with the reactive epitaxy method at temperatures above ∼500 °C. The self-assembly of the NWs is confined along the Si〈1 1 0〉 directions, resulting in the NWs orienting with the long axis along one, two and three particular directions on the Si(1 1 0), (0 0 1) and (1 1 1) surfaces, respectively. Scanning tunneling spectroscopy and transmission electron microscopy (TEM) studies indicate unambiguously that the NWs are tetragonal MnSi1.7. The width of the NWs has a maximum or well-defined value on each kind of substrate, though the length varies greatly. In the plan-view TEM micrographs, the NWs exhibit two sets of Moiré fringes: one is along the length direction and has a large periodicity, and the other is along the width direction and has a very small periodicity. These phenomena strongly indicate that the growth of NWs is governed by a strain-driven energetic mechanism and the NW shape results from anisotropic lattice mismatch between the silicide and the Si substrate. This research paves the way towards controllable growth of the silicide NWs on silicon substrates, which may help to advance the realization of practical applications of silicide NWs in nanoelectronics. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006276

Indentation size effect in nanohardness / Yu.V. Milman in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7480–7487 Titre : Indentation size effect in nanohardness Type de document : texte imprimé Auteurs : Yu.V. Milman, Auteur ; А.А. Golubenko, Auteur ; S.N. Dub, Auteur Année de publication : 2012 Article en page(s) : pp. 7480–7487 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hardness  test  Indentation  size  effect  Indentation  Nanoindentation  Plasticity Résumé : It was shown experimentally that changing the indenter load P and the indentation size does not change the total deformation during indentation (εt ≈ const.), and that fracture does not influence the scale effect. For this reason the physical nature of the scale effect is revealed better by nanoindentation and under more “clean” conditions than in uniaxial deformation tests. The indentation size effect (ISE) is revealed as the change of mechanical properties determined by indentation. It was shown that reduction of the indent size leads to both increasing hardness and decreasing plasticity, determined by indentation. The phenomenological approach to the ISE (in which the power dependence of the indenter load P on the indenter displacement of h is used) made it possible to describe the dependence of nanohardness H(P) and H(h) by simple equations. Nanohardness was determined for 21 different crystals, and parameters that enabled the size dependence of H for these crystals to be calculated were determined. It is proposed to determine nanohardness at h = const. instead of P = const. and to recalculate H using our equations for fixed values of hf = 1000 nm for metals and hf = 100 nm for hard materials. The use of the developed technique makes it possible to compare results of nanohardness tests from different sources for different indenter loads. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006021 [article] Indentation size effect in nanohardness [texte imprimé] / Yu.V. Milman, Auteur ; А.А. Golubenko, Auteur ; S.N. Dub, Auteur . - 2012 . - pp. 7480–7487. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7480–7487 Mots-clés : Hardness  test  Indentation  size  effect  Indentation  Nanoindentation  Plasticity Résumé : It was shown experimentally that changing the indenter load P and the indentation size does not change the total deformation during indentation (εt ≈ const.), and that fracture does not influence the scale effect. For this reason the physical nature of the scale effect is revealed better by nanoindentation and under more “clean” conditions than in uniaxial deformation tests. The indentation size effect (ISE) is revealed as the change of mechanical properties determined by indentation. It was shown that reduction of the indent size leads to both increasing hardness and decreasing plasticity, determined by indentation. The phenomenological approach to the ISE (in which the power dependence of the indenter load P on the indenter displacement of h is used) made it possible to describe the dependence of nanohardness H(P) and H(h) by simple equations. Nanohardness was determined for 21 different crystals, and parameters that enabled the size dependence of H for these crystals to be calculated were determined. It is proposed to determine nanohardness at h = const. instead of P = const. and to recalculate H using our equations for fixed values of hf = 1000 nm for metals and hf = 100 nm for hard materials. The use of the developed technique makes it possible to compare results of nanohardness tests from different sources for different indenter loads. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006021

On the specific surface area of nanoporous materials / E. Detsi in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7488–7497 Titre : On the specific surface area of nanoporous materials Type de document : texte imprimé Auteurs : E. Detsi, Auteur ; E. De Jong, Auteur ; A. Zinchenko, Auteur Année de publication : 2012 Article en page(s) : pp. 7488–7497 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Specific  surface  area  Nanoporous  materials  Catalysts  Sensors  Actuators Résumé : A proper quantification of the specific surface area of nanoporous materials is necessary for a better understanding of the properties that are affected by the high surface-area-to-volume ratio of nanoporous metals, nanoporous polymers and nanoporous ceramics. In this paper we derive an analytical expression that relates the specific surface area of arbitrary nanoporous materials to their solid bulk density and ligament size. Computed specific surface areas of porous materials with regular nanopores are in good agreement with the expression derived. These regular void geometries include single and double gyroid structures, as well as materials with spherical and cylindrical nanopores. Validation of the expression for disordered nanoporous materials is performed by investigation of the specific surface areas of various nanoporous gold electrodes in the double-layer charging regime. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006008 [article] On the specific surface area of nanoporous materials [texte imprimé] / E. Detsi, Auteur ; E. De Jong, Auteur ; A. Zinchenko, Auteur . - 2012 . - pp. 7488–7497. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7488–7497 Mots-clés : Specific  surface  area  Nanoporous  materials  Catalysts  Sensors  Actuators Résumé : A proper quantification of the specific surface area of nanoporous materials is necessary for a better understanding of the properties that are affected by the high surface-area-to-volume ratio of nanoporous metals, nanoporous polymers and nanoporous ceramics. In this paper we derive an analytical expression that relates the specific surface area of arbitrary nanoporous materials to their solid bulk density and ligament size. Computed specific surface areas of porous materials with regular nanopores are in good agreement with the expression derived. These regular void geometries include single and double gyroid structures, as well as materials with spherical and cylindrical nanopores. Validation of the expression for disordered nanoporous materials is performed by investigation of the specific surface areas of various nanoporous gold electrodes in the double-layer charging regime. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006008

Atomic transport mechanisms in thin oxide films grown on zirconium by thermal oxidation, as-derived from 18O-tracer experiments / G. Bakradze in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7498–7507 Titre : Atomic transport mechanisms in thin oxide films grown on zirconium by thermal oxidation, as-derived from 18O-tracer experiments Type de document : texte imprimé Auteurs : G. Bakradze, Auteur ; L.P.H. Jeurgens, Auteur ; T. Acartürk, Auteur Année de publication : 2012 Article en page(s) : pp. 7498–7507 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Oxidation  Mechanism  Nanocrystalline  films  Zirconium  Time-of-flight  secondary  ion  mass-spectrometry Résumé : Two-stage oxidation experiments using 16O and 18O isotopes were performed to reveal the governing atomic transport mechanism(s) in thin (thickness <10 nm) oxide films grown during the initial stages of dry thermal oxidation of pure Zr at 450 K. To this end, bare (i.e. without a native oxide) Zr(0 0 0 1) and Zr single-crystalline surfaces were prepared under ultra-high vacuum conditions by a cyclic treatment of alternating ion-sputtering and in vacuo annealing steps. Next, the bare Zr surfaces were oxidized at 450 K and at pO2 = 1 × 10−4 Pa, first in 16O2(g) and subsequently in 18O2(g). The 18O-tracer depth distributions in the oxide films were recorded by time-of-flight secondary ion mass spectrometry. It was concluded that the early stage of the oxidation process is governed by oxygen transport to the metal/oxide interface through the lattice and along the grain boundaries of the nanosized oxide grains whereas, on continuing oxidation, only oxygen lattice transport controls the oxidation process. An oxide-film growth mechanism is proposed. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006124 [article] Atomic transport mechanisms in thin oxide films grown on zirconium by thermal oxidation, as-derived from 18O-tracer experiments [texte imprimé] / G. Bakradze, Auteur ; L.P.H. Jeurgens, Auteur ; T. Acartürk, Auteur . - 2012 . - pp. 7498–7507. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7498–7507 Mots-clés : Oxidation  Mechanism  Nanocrystalline  films  Zirconium  Time-of-flight  secondary  ion  mass-spectrometry Résumé : Two-stage oxidation experiments using 16O and 18O isotopes were performed to reveal the governing atomic transport mechanism(s) in thin (thickness <10 nm) oxide films grown during the initial stages of dry thermal oxidation of pure Zr at 450 K. To this end, bare (i.e. without a native oxide) Zr(0 0 0 1) and Zr single-crystalline surfaces were prepared under ultra-high vacuum conditions by a cyclic treatment of alternating ion-sputtering and in vacuo annealing steps. Next, the bare Zr surfaces were oxidized at 450 K and at pO2 = 1 × 10−4 Pa, first in 16O2(g) and subsequently in 18O2(g). The 18O-tracer depth distributions in the oxide films were recorded by time-of-flight secondary ion mass spectrometry. It was concluded that the early stage of the oxidation process is governed by oxygen transport to the metal/oxide interface through the lattice and along the grain boundaries of the nanosized oxide grains whereas, on continuing oxidation, only oxygen lattice transport controls the oxidation process. An oxide-film growth mechanism is proposed. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006124

Application of synchrotron X-ray diffraction and nanoindentation for the determination of residual stress fields around scratches / M.K. Khan in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7508–7520 Titre : Application of synchrotron X-ray diffraction and nanoindentation for the determination of residual stress fields around scratches Type de document : texte imprimé Auteurs : M.K. Khan, Auteur ; M.E. Fitzpatrick, Auteur ; S.V. Hainsworth, Auteur Année de publication : 2012 Article en page(s) : pp. 7508–7520 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoindentation  Synchrotron  radiation  X-ray  diffraction  Aluminium  alloys  Residual  stresses Résumé : Residual stresses and plastic deformation around scratches or scribe marks in ductile materials can affect fatigue life. Scratches of the order of tens of microns may convert into propagating cracks driven by tensile residual stresses at the scratch root. Probing such stresses on a small scale is experimentally challenging in engineering materials. Here we present results of a combined study using synchrotron X-ray diffraction and nanoindentation to determine the residual stresses around scratches in aluminium alloys. The extraction of residual stresses in metallic materials where there is work hardening is challenging using indentation methods, but a method is presented by which this has been achieved, and a good correlation is obtained between the results obtained using diffraction and nanoindentation. The advantage of synchrotron X-ray measurement is that it allows validation of the stresses at the same spatial scale as nanoindentation. It was found that scratches produced by a “ploughing” mechanism where there was significant plastic deformation beneath the scratch showed higher work hardening and tensile residual stresses than those produced by a “cutting” mechanism where there was little plastic deformation of the material. Little effect of fatigue cycling was seen on the peak stresses at the scratch tip. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006112 [article] Application of synchrotron X-ray diffraction and nanoindentation for the determination of residual stress fields around scratches [texte imprimé] / M.K. Khan, Auteur ; M.E. Fitzpatrick, Auteur ; S.V. Hainsworth, Auteur . - 2012 . - pp. 7508–7520. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7508–7520 Mots-clés : Nanoindentation  Synchrotron  radiation  X-ray  diffraction  Aluminium  alloys  Residual  stresses Résumé : Residual stresses and plastic deformation around scratches or scribe marks in ductile materials can affect fatigue life. Scratches of the order of tens of microns may convert into propagating cracks driven by tensile residual stresses at the scratch root. Probing such stresses on a small scale is experimentally challenging in engineering materials. Here we present results of a combined study using synchrotron X-ray diffraction and nanoindentation to determine the residual stresses around scratches in aluminium alloys. The extraction of residual stresses in metallic materials where there is work hardening is challenging using indentation methods, but a method is presented by which this has been achieved, and a good correlation is obtained between the results obtained using diffraction and nanoindentation. The advantage of synchrotron X-ray measurement is that it allows validation of the stresses at the same spatial scale as nanoindentation. It was found that scratches produced by a “ploughing” mechanism where there was significant plastic deformation beneath the scratch showed higher work hardening and tensile residual stresses than those produced by a “cutting” mechanism where there was little plastic deformation of the material. Little effect of fatigue cycling was seen on the peak stresses at the scratch tip. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006112

Synthesis of fluorine doped zinc oxide by reactive magnetron sputtering / X. Noirfalise in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7521–7529 Titre : Synthesis of fluorine doped zinc oxide by reactive magnetron sputtering Type de document : texte imprimé Auteurs : X. Noirfalise, Auteur ; T. Godfroid, Auteur ; G. Guisbiers, Auteur Année de publication : 2012 Article en page(s) : pp. 7521–7529 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Zinc  oxide  Thin  film  coating  Electrical  properties  Physical  vapour  deposition  Transparent  conductive  oxide Résumé : ZnO and fluorine doped ZnO (FZO) thin films were prepared by d.c. reactive magnetron sputtering using a zinc target in an Ar/O2(/F2) mixture. In a first attempt ZnO films were synthesized in order to optimize the matrix properties in terms of crystalline properties and transparency. The parameters studied were the d.c. power (Pdc), the total pressure (PTot) and the O2 content in the discharge (%O2). The highest grain size of ∼25 nm is obtained for Pdc = 70 W, PTot = 30 mtorr and %O2 = 7.5%. F2 was then introduced in the discharge. The influence of the presence of fluorine on the crystallographic, chemical, electrical and optical properties of the deposited films were evaluated. Our X-ray photoelectron spectroscopy and X-ray diffraction (XRD) data suggest that only a certain part of the measured fluorine atoms substitute for oxygen atoms in the ZnO structure. The rest of fluorine could be adsorbed as F2 on the grain boundaries or located in interstices of the ZnO structure. XRD data reveal a decrease in the crystallite size with an increase in the fluorine content. Above a fluorine concentration of ∼2% the FZO films become amorphous. The electrical properties have been investigated by Hall effect measurements. The optimal synthesis conditions (∼2% of fluorine in the film) were a charge carrier density of ∼1020 cm−3, an electrical resistivity of 10−2 Ω cm, and a charge mobility of 4 cm2 V s−1. Finally, all deposited FZO films had >80% transmission in the visible range. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411005544 [article] Synthesis of fluorine doped zinc oxide by reactive magnetron sputtering [texte imprimé] / X. Noirfalise, Auteur ; T. Godfroid, Auteur ; G. Guisbiers, Auteur . - 2012 . - pp. 7521–7529. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7521–7529 Mots-clés : Zinc  oxide  Thin  film  coating  Electrical  properties  Physical  vapour  deposition  Transparent  conductive  oxide Résumé : ZnO and fluorine doped ZnO (FZO) thin films were prepared by d.c. reactive magnetron sputtering using a zinc target in an Ar/O2(/F2) mixture. In a first attempt ZnO films were synthesized in order to optimize the matrix properties in terms of crystalline properties and transparency. The parameters studied were the d.c. power (Pdc), the total pressure (PTot) and the O2 content in the discharge (%O2). The highest grain size of ∼25 nm is obtained for Pdc = 70 W, PTot = 30 mtorr and %O2 = 7.5%. F2 was then introduced in the discharge. The influence of the presence of fluorine on the crystallographic, chemical, electrical and optical properties of the deposited films were evaluated. Our X-ray photoelectron spectroscopy and X-ray diffraction (XRD) data suggest that only a certain part of the measured fluorine atoms substitute for oxygen atoms in the ZnO structure. The rest of fluorine could be adsorbed as F2 on the grain boundaries or located in interstices of the ZnO structure. XRD data reveal a decrease in the crystallite size with an increase in the fluorine content. Above a fluorine concentration of ∼2% the FZO films become amorphous. The electrical properties have been investigated by Hall effect measurements. The optimal synthesis conditions (∼2% of fluorine in the film) were a charge carrier density of ∼1020 cm−3, an electrical resistivity of 10−2 Ω cm, and a charge mobility of 4 cm2 V s−1. Finally, all deposited FZO films had >80% transmission in the visible range. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411005544

Ion irradiation of novel yttrium/ytterbium-based pyrochlores / Karl R. Whittle in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7530–7537 Titre : Ion irradiation of novel yttrium/ytterbium-based pyrochlores : The effect of disorder Type de document : texte imprimé Auteurs : Karl R. Whittle, Auteur ; Mark G. Blackford, Auteur ; Robert D. Aughterson, Auteur Année de publication : 2012 Article en page(s) : pp. 7530–7537 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Radiation  damage  Pyrochlore  Oxide  dispersion  strengthened Résumé : Pyrochlores based on the general composition Ln2TiO5 (Ln2.67Ti1.33O6.67) and Ln2Ti2O7, where Ln = Y or Yb, have been irradiated through the crystalline–amorphous transition with 1 MeV Kr ions at the IVEM-TANDEM facility, Argonne National Laboratory. The results show that the Tc (critical temperature for amorphization) differs significantly between each series, e.g. for Y2TiO5 it is 589 ± 18 K and for Y2Ti2O7 665 ± 33 K. The difference suggests that recovery from damage is more rapid with increasing Ln content, i.e. a lower Tc for amorphization. These results are discussed in the context of the melting points of each phase, atomic disorder, the pyrochlore–fluorite order–disorder transition and the implications for oxide dispersion-strengthened additives. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006586 [article] Ion irradiation of novel yttrium/ytterbium-based pyrochlores : The effect of disorder [texte imprimé] / Karl R. Whittle, Auteur ; Mark G. Blackford, Auteur ; Robert D. Aughterson, Auteur . - 2012 . - pp. 7530–7537. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7530–7537 Mots-clés : Radiation  damage  Pyrochlore  Oxide  dispersion  strengthened Résumé : Pyrochlores based on the general composition Ln2TiO5 (Ln2.67Ti1.33O6.67) and Ln2Ti2O7, where Ln = Y or Yb, have been irradiated through the crystalline–amorphous transition with 1 MeV Kr ions at the IVEM-TANDEM facility, Argonne National Laboratory. The results show that the Tc (critical temperature for amorphization) differs significantly between each series, e.g. for Y2TiO5 it is 589 ± 18 K and for Y2Ti2O7 665 ± 33 K. The difference suggests that recovery from damage is more rapid with increasing Ln content, i.e. a lower Tc for amorphization. These results are discussed in the context of the melting points of each phase, atomic disorder, the pyrochlore–fluorite order–disorder transition and the implications for oxide dispersion-strengthened additives. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006586

An analytical description of overall phase transformation kinetics applied to the recrystallization of pure iron / B.B. Rath in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7538–7545 Titre : An analytical description of overall phase transformation kinetics applied to the recrystallization of pure iron Type de document : texte imprimé Auteurs : B.B. Rath, Auteur ; C. S. Pande, Auteur Année de publication : 2012 Article en page(s) : pp. 7538–7545 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Annealing  Nucleation  of  recrystallization  Iron  Kinetics  Deformation  structure Résumé : Experimental studies of recrystallization in deformed single crystals of pure iron are described. The results are used to analyze various parameters associated with the time evolution of the volume fraction of the growing phase during phase transformations in this system associated with the phenomena of nucleation and growth. In addition, using the experimental results, the phenomenon has been modeled by a new approach which may provide a different, and possibly more precise, description of the kinetics of the process. The proposed analytical approach uses easily measured metallographic parameters, obtained from a systematic two-dimensional surface examination, to provide a detailed description on the time dependence of nucleation, nucleation rate, growth rate and interfacial migration and compared with the classical approach based on Kolomogrov formalism. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006641 [article] An analytical description of overall phase transformation kinetics applied to the recrystallization of pure iron [texte imprimé] / B.B. Rath, Auteur ; C. S. Pande, Auteur . - 2012 . - pp. 7538–7545. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7538–7545 Mots-clés : Annealing  Nucleation  of  recrystallization  Iron  Kinetics  Deformation  structure Résumé : Experimental studies of recrystallization in deformed single crystals of pure iron are described. The results are used to analyze various parameters associated with the time evolution of the volume fraction of the growing phase during phase transformations in this system associated with the phenomena of nucleation and growth. In addition, using the experimental results, the phenomenon has been modeled by a new approach which may provide a different, and possibly more precise, description of the kinetics of the process. The proposed analytical approach uses easily measured metallographic parameters, obtained from a systematic two-dimensional surface examination, to provide a detailed description on the time dependence of nucleation, nucleation rate, growth rate and interfacial migration and compared with the classical approach based on Kolomogrov formalism. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006641

Work hardening behavior of ultrafine-grained Mn transformation-induced plasticity steel / Seawoong Lee in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7546–7553 Titre : Work hardening behavior of ultrafine-grained Mn transformation-induced plasticity steel Type de document : texte imprimé Auteurs : Seawoong Lee, Auteur ; Seok-Jae Lee, Auteur ; Bruno C. De Cooman, Auteur Année de publication : 2012 Article en page(s) : pp. 7546–7553 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ultra-fine  grain  size  Localized  deformation  Grain  boundary  thickening Résumé : Ultrafine grain refinement by intercritical annealing at 680 °C and 640 °C was investigated in a Fe–0.05%C–6.15%Mn–1.4%Si multiphase TRIP steel. A large volume fraction of retained austenite was obtained at room temperature in both cases. Whereas a pronounced localization of the deformation during tensile testing appeared in the steel annealed at 640 °C, strain localization occurred only in the initial deformation stages in the steel annealed at 680 °C. The retained austenite was transformed to strain-induced martensite during tensile testing in the sample annealed at 680 °C. However, no martensitic transformation was observed in the sample annealed at 640 °C. The activation volume showed a sharp decrease during the tensile test and saturated to the same value in both cases. Two different dislocation structures were observed in the ferrite grains of the samples annealed intercritically at 680 °C after tensile deformation, but only the dislocation-free structure of ferrite was observed in the sample annealed at 640 °C. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006057 [article] Work hardening behavior of ultrafine-grained Mn transformation-induced plasticity steel [texte imprimé] / Seawoong Lee, Auteur ; Seok-Jae Lee, Auteur ; Bruno C. De Cooman, Auteur . - 2012 . - pp. 7546–7553. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7546–7553 Mots-clés : Ultra-fine  grain  size  Localized  deformation  Grain  boundary  thickening Résumé : Ultrafine grain refinement by intercritical annealing at 680 °C and 640 °C was investigated in a Fe–0.05%C–6.15%Mn–1.4%Si multiphase TRIP steel. A large volume fraction of retained austenite was obtained at room temperature in both cases. Whereas a pronounced localization of the deformation during tensile testing appeared in the steel annealed at 640 °C, strain localization occurred only in the initial deformation stages in the steel annealed at 680 °C. The retained austenite was transformed to strain-induced martensite during tensile testing in the sample annealed at 680 °C. However, no martensitic transformation was observed in the sample annealed at 640 °C. The activation volume showed a sharp decrease during the tensile test and saturated to the same value in both cases. Two different dislocation structures were observed in the ferrite grains of the samples annealed intercritically at 680 °C after tensile deformation, but only the dislocation-free structure of ferrite was observed in the sample annealed at 640 °C. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006057

Effect of solid solution elements on nanoindentation hardness, rate dependence, and incipient plasticity in fine grained magnesium alloys / Hidetoshi Somekawa in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7554–7563 Titre : Effect of solid solution elements on nanoindentation hardness, rate dependence, and incipient plasticity in fine grained magnesium alloys Type de document : texte imprimé Auteurs : Hidetoshi Somekawa, Auteur ; Christopher A. Schuh, Auteur Année de publication : 2012 Article en page(s) : pp. 7554–7563 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanoindentation  Magnesium  Activation  volume  Pop-in  behavior  Deformation  mechanism Résumé : The effect of solid solution alloying elements on the plastic deformation of fine grained Mg alloys was studied in five binary systems: Mg–0.3 at.% X (X = Al, Ca, Li, Y or Zn). All the alloys were produced by extrusion and had an average grain size of ∼2–3 μm. Solid solution strengthening is observed for all of the alloys subjected to hardness tests with a scale much larger than the grain size, and the efficacy of the various solutes is in line with expectations based on recent solution strengthening models. The different alloying elements also have an impact on the rate dependence of deformation, with activation volumes ranging between 20 b3 and 80 b3 being consistent with cross-slip as a rate limiting mechanism. For nanoscale indentations the yield point is identified by a pop-in event, and this event is found to have a dramatically different rate dependence and activation volume than does global plasticity. Specifically, the dislocation generation mechanism associated with pop-in has an activation volume of scale ∼0.2–1 b3, and is far less affected by solute content than is global plasticity. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006240 [article] Effect of solid solution elements on nanoindentation hardness, rate dependence, and incipient plasticity in fine grained magnesium alloys [texte imprimé] / Hidetoshi Somekawa, Auteur ; Christopher A. Schuh, Auteur . - 2012 . - pp. 7554–7563. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7554–7563 Mots-clés : Nanoindentation  Magnesium  Activation  volume  Pop-in  behavior  Deformation  mechanism Résumé : The effect of solid solution alloying elements on the plastic deformation of fine grained Mg alloys was studied in five binary systems: Mg–0.3 at.% X (X = Al, Ca, Li, Y or Zn). All the alloys were produced by extrusion and had an average grain size of ∼2–3 μm. Solid solution strengthening is observed for all of the alloys subjected to hardness tests with a scale much larger than the grain size, and the efficacy of the various solutes is in line with expectations based on recent solution strengthening models. The different alloying elements also have an impact on the rate dependence of deformation, with activation volumes ranging between 20 b3 and 80 b3 being consistent with cross-slip as a rate limiting mechanism. For nanoscale indentations the yield point is identified by a pop-in event, and this event is found to have a dramatically different rate dependence and activation volume than does global plasticity. Specifically, the dislocation generation mechanism associated with pop-in has an activation volume of scale ∼0.2–1 b3, and is far less affected by solute content than is global plasticity. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006240

Validation of void growth models using X-ray microtomography characterization of damage in dual phase steels / C. Landron in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7564–7573 Titre : Validation of void growth models using X-ray microtomography characterization of damage in dual phase steels Type de document : texte imprimé Auteurs : C. Landron, Auteur ; E. Maire, Auteur ; O. Bouaziz, Auteur Année de publication : 2012 Article en page(s) : pp. 7564–7573 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Steel  Dual  phase  Damage  X-ray  tomography  Modeling Résumé : In situ tensile tests were carried out during X-ray microtomography imaging of three steels: a single phase ferritic steel, a dual phase steel and a fully martensitic steel. Cavity growth was first quantified in the different samples as a function of strain and triaxiality. The Rice and Tracey model, a version of this model corrected by Huang, and a third version accounting for the cavity shape were then used to predict void growth evolution. It was experimentally demonstrated that for steels Huang’s correction is a real improvement to the original Rice and Tracey model. Some differences in the void growth kinetic are discussed, accounting for the microstructure and the mechanical behavior of each steel. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006239 [article] Validation of void growth models using X-ray microtomography characterization of damage in dual phase steels [texte imprimé] / C. Landron, Auteur ; E. Maire, Auteur ; O. Bouaziz, Auteur . - 2012 . - pp. 7564–7573. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7564–7573 Mots-clés : Steel  Dual  phase  Damage  X-ray  tomography  Modeling Résumé : In situ tensile tests were carried out during X-ray microtomography imaging of three steels: a single phase ferritic steel, a dual phase steel and a fully martensitic steel. Cavity growth was first quantified in the different samples as a function of strain and triaxiality. The Rice and Tracey model, a version of this model corrected by Huang, and a third version accounting for the cavity shape were then used to predict void growth evolution. It was experimentally demonstrated that for steels Huang’s correction is a real improvement to the original Rice and Tracey model. Some differences in the void growth kinetic are discussed, accounting for the microstructure and the mechanical behavior of each steel. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006239

Microstructures and deformation mechanisms of a G4 TiAl alloy produced by spark plasma sintering / H. Jabbar in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7574–7585 Titre : Microstructures and deformation mechanisms of a G4 TiAl alloy produced by spark plasma sintering Type de document : texte imprimé Auteurs : H. Jabbar, Auteur ; J.-P. Monchoux, Auteur ; M. Thomas, Auteur Année de publication : 2012 Article en page(s) : pp. 7574–7585 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Powder  consolidation  Scanning  and  transmission  electron  microscopy  Titanium  aluminides  Plastic  deformation Résumé : TiAl alloys are prepared by spark plasma sintering (SPS) using a pre-alloyed powder with the so-called G4 composition (Ti51Al47Re1W1Si0.2). SPS densifications are conducted using short and classical cycles, with various dwell temperatures. The microstructure of the products is studied by scanning and transmission electron microscopy. In particular, constituent phases, grain size, precipitates and local chemical composition are determined. A double phase γ + α2 microstructure containing B2 precipitates is found in a large range of sintering temperatures. Mechanical properties at RT and creep strength at 700 °C/300 MPa are measured. No significant improvement of the mechanical properties is obtained with respect to those of SPS-TiAl alloys previously sintered. A study of the deformation mechanisms and the effect of the microstructure on these mechanisms is performed. Hence, the strong effect of microstructural heterogeneities from the initial powder is demonstrated. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006288 [article] Microstructures and deformation mechanisms of a G4 TiAl alloy produced by spark plasma sintering [texte imprimé] / H. Jabbar, Auteur ; J.-P. Monchoux, Auteur ; M. Thomas, Auteur . - 2012 . - pp. 7574–7585. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7574–7585 Mots-clés : Powder  consolidation  Scanning  and  transmission  electron  microscopy  Titanium  aluminides  Plastic  deformation Résumé : TiAl alloys are prepared by spark plasma sintering (SPS) using a pre-alloyed powder with the so-called G4 composition (Ti51Al47Re1W1Si0.2). SPS densifications are conducted using short and classical cycles, with various dwell temperatures. The microstructure of the products is studied by scanning and transmission electron microscopy. In particular, constituent phases, grain size, precipitates and local chemical composition are determined. A double phase γ + α2 microstructure containing B2 precipitates is found in a large range of sintering temperatures. Mechanical properties at RT and creep strength at 700 °C/300 MPa are measured. No significant improvement of the mechanical properties is obtained with respect to those of SPS-TiAl alloys previously sintered. A study of the deformation mechanisms and the effect of the microstructure on these mechanisms is performed. Hence, the strong effect of microstructural heterogeneities from the initial powder is demonstrated. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006288

Determination of the Jackson–Hunt constants of the In–In2Bi eutectic alloy based on in situ observation of its solidification dynamics / S. Akamatsu in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7586–7591 Titre : Determination of the Jackson–Hunt constants of the In–In2Bi eutectic alloy based on in situ observation of its solidification dynamics Type de document : texte imprimé Auteurs : S. Akamatsu, Auteur ; S. Bottin-Rousseau, Auteur ; G. Faivre, Auteur Année de publication : 2012 Article en page(s) : pp. 7586–7591 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Eutectic  solidification  Directional  solidification  Solidification  microstructures Résumé : We present a real-time observation study of lamellar patterns in thin-sample directional solidification of a near-eutectic In–In2Bi metallic alloy. The spacing range of stability is shown to extend from about 0.9λJH to 2.2λJH, where λJH is the Jackson–Hunt minimum undercooling spacing, in agreement with what was observed earlier in transparent eutectics. We analyze the time evolution of non-uniform spacing distributions using a previously established semi-empirical “spacing-diffusion” law [Akamatsu et al., Metal. Mater. Trans. A 35 (2004) 1815]. We obtain a quantitative estimate of the Jackson–Hunt constants and other material parameters relevant to eutectic growth, among which and D = 505 ± 75 μm2 s−1, where V is the solidification speed, and D is the solute diffusion coefficient in the liquid. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006136 [article] Determination of the Jackson–Hunt constants of the In–In2Bi eutectic alloy based on in situ observation of its solidification dynamics [texte imprimé] / S. Akamatsu, Auteur ; S. Bottin-Rousseau, Auteur ; G. Faivre, Auteur . - 2012 . - pp. 7586–7591. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7586–7591 Mots-clés : Eutectic  solidification  Directional  solidification  Solidification  microstructures Résumé : We present a real-time observation study of lamellar patterns in thin-sample directional solidification of a near-eutectic In–In2Bi metallic alloy. The spacing range of stability is shown to extend from about 0.9λJH to 2.2λJH, where λJH is the Jackson–Hunt minimum undercooling spacing, in agreement with what was observed earlier in transparent eutectics. We analyze the time evolution of non-uniform spacing distributions using a previously established semi-empirical “spacing-diffusion” law [Akamatsu et al., Metal. Mater. Trans. A 35 (2004) 1815]. We obtain a quantitative estimate of the Jackson–Hunt constants and other material parameters relevant to eutectic growth, among which and D = 505 ± 75 μm2 s−1, where V is the solidification speed, and D is the solute diffusion coefficient in the liquid. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006136

Microstructure and high-temperature deformation behavior of Al2O3–TiO2 obtained from ultra-high-pressure densification of metastable powders / J. Suffner in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7592–7601 Titre : Microstructure and high-temperature deformation behavior of Al2O3–TiO2 obtained from ultra-high-pressure densification of metastable powders Type de document : texte imprimé Auteurs : J. Suffner, Auteur ; T. Scherer, Auteur ; D. Wang, Auteur Année de publication : 2012 Article en page(s) : pp. 7592–7601 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Sintering  Nanocomposite  Superplasticity  Ceramics  Crystallization Résumé : Metastable alumina composite powders with 13 wt.% titania were produced by plasma spraying using liquid nitrogen quenched substrates. The material consisted of a mixture of Al2O3 in a distorted spinel structure and a large amount of amorphous phases. High-pressure–high-temperature sintering below the crystallization temperature of the amorphous phase yielded a crystalline/amorphous composite that was used for creep experiments. During heating to the desired testing temperature, crystallization occurred and an in situ composite composed of corundum and rutile was obtained. This material exhibited superior deformation behavior compared to conventionally processed alumina materials. Comparably low temperatures of 1100 °C could be utilized to achieve plastic deformation of the material under a pressure of 50 MPa. Coble grain boundary creep with n = 1 and a low activation energy for diffusion of 390 kJ mol−1 was assumed to be the deformation mechanism. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006628 [article] Microstructure and high-temperature deformation behavior of Al2O3–TiO2 obtained from ultra-high-pressure densification of metastable powders [texte imprimé] / J. Suffner, Auteur ; T. Scherer, Auteur ; D. Wang, Auteur . - 2012 . - pp. 7592–7601. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7592–7601 Mots-clés : Sintering  Nanocomposite  Superplasticity  Ceramics  Crystallization Résumé : Metastable alumina composite powders with 13 wt.% titania were produced by plasma spraying using liquid nitrogen quenched substrates. The material consisted of a mixture of Al2O3 in a distorted spinel structure and a large amount of amorphous phases. High-pressure–high-temperature sintering below the crystallization temperature of the amorphous phase yielded a crystalline/amorphous composite that was used for creep experiments. During heating to the desired testing temperature, crystallization occurred and an in situ composite composed of corundum and rutile was obtained. This material exhibited superior deformation behavior compared to conventionally processed alumina materials. Comparably low temperatures of 1100 °C could be utilized to achieve plastic deformation of the material under a pressure of 50 MPa. Coble grain boundary creep with n = 1 and a low activation energy for diffusion of 390 kJ mol−1 was assumed to be the deformation mechanism. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006628

Analysis of Ti–Ni–Hf shape memory alloys by combinatorial nanocalorimetry / Yahya Motemani in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7602–7614 Titre : Analysis of Ti–Ni–Hf shape memory alloys by combinatorial nanocalorimetry Type de document : texte imprimé Auteurs : Yahya Motemani, Auteur ; Patrick J. McCluskey, Auteur ; Chunwang Zhao, Auteur Année de publication : 2012 Article en page(s) : pp. 7602–7614 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thin  film  Calorimetry  Martensitic  transformation  Thermal  cycling  High-temperature  shape  memory  alloy Résumé : The martensitic transformation in Ti–Ni–Hf thin films with ultra-fine grain structure has been analyzed as a function of composition using a high-throughput array of nanocalorimeters. The martensite–austenite transformation temperature is significantly lower than in bulk Ti–Ni–Hf, but increases linearly with Hf content at a rate comparable to bulk Ti–Ni–Hf. The response to high-temperature cycling (22 °C < T < 850 °C) changes with Ni concentration. For Ni ⩽ 47 at.%, the transformation temperature increases during high-temperature cycling because precipitation of (Ti1−x, Hfx)2Ni enriches the surrounding matrix in Hf; for Ni ⩾ 47.7 at.%, precipitation of the same phase gradually suppresses the transformation. Low-temperature cycling (22 °C < T < 450 °C) causes the transformation temperature to initially decrease and then stabilize. Relaxation of internal stresses by dislocations generated during thermal cycling is suggested as the active mechanism. Thermal cycling stability of the films is improved compared to previous studies on bulk Ti–Ni–Hf. This is attributed to the very small grain size (18 ± 5 nm) of the samples. Alloys with superior thermal cycling stability are identified and the ability to control the transformation temperature through multiple thermal cycling is demonstrated. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100601X [article] Analysis of Ti–Ni–Hf shape memory alloys by combinatorial nanocalorimetry [texte imprimé] / Yahya Motemani, Auteur ; Patrick J. McCluskey, Auteur ; Chunwang Zhao, Auteur . - 2012 . - pp. 7602–7614. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7602–7614 Mots-clés : Thin  film  Calorimetry  Martensitic  transformation  Thermal  cycling  High-temperature  shape  memory  alloy Résumé : The martensitic transformation in Ti–Ni–Hf thin films with ultra-fine grain structure has been analyzed as a function of composition using a high-throughput array of nanocalorimeters. The martensite–austenite transformation temperature is significantly lower than in bulk Ti–Ni–Hf, but increases linearly with Hf content at a rate comparable to bulk Ti–Ni–Hf. The response to high-temperature cycling (22 °C < T < 850 °C) changes with Ni concentration. For Ni ⩽ 47 at.%, the transformation temperature increases during high-temperature cycling because precipitation of (Ti1−x, Hfx)2Ni enriches the surrounding matrix in Hf; for Ni ⩾ 47.7 at.%, precipitation of the same phase gradually suppresses the transformation. Low-temperature cycling (22 °C < T < 450 °C) causes the transformation temperature to initially decrease and then stabilize. Relaxation of internal stresses by dislocations generated during thermal cycling is suggested as the active mechanism. Thermal cycling stability of the films is improved compared to previous studies on bulk Ti–Ni–Hf. This is attributed to the very small grain size (18 ± 5 nm) of the samples. Alloys with superior thermal cycling stability are identified and the ability to control the transformation temperature through multiple thermal cycling is demonstrated. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100601X

Effects of Yb and Zr microalloying additions on the microstructure and mechanical properties of dilute Al–Sc alloys / Marsha E. Van Dalen in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7615–7626 Titre : Effects of Yb and Zr microalloying additions on the microstructure and mechanical properties of dilute Al–Sc alloys Type de document : texte imprimé Auteurs : Marsha E. Van Dalen, Auteur ; Thomas Gyger, Auteur ; David C. Dunand, Auteur Année de publication : 2012 Article en page(s) : pp. 7615–7626 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminum  alloys  Nucleation  Precipitation  Coarsening  Creep Résumé : It is known that Zr and Yb partition to the Al3Sc precipitates created during aging when microalloyed separately in dilute binary Al–Sc alloys. Addition of Zr delays precipitate coarsening, thereby improving the coarsening resistance of the ternary Al-Sc-Zr alloys. Addition of Yb increases the resistance against dislocation climb, thereby improving the creep resistances of the ternary Al-Sc-Yb alloys. A combination of microhardness, creep, and atom probe tomography measurements provide evidence that these effects of Zr and Yb additions are cumulative in quaternary dilute Al–Sc–Yb–Zr alloys: Yb increases their creep resistance at 300 °C compared with ternary Al–Sc–Zr alloys and Zr improves their coarsening resistance at 300 °C compared with ternary Al–Sc–Yb alloys. Additionally, excellent coarsening resistance is observed at 350 and 375 °C. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006562 [article] Effects of Yb and Zr microalloying additions on the microstructure and mechanical properties of dilute Al–Sc alloys [texte imprimé] / Marsha E. Van Dalen, Auteur ; Thomas Gyger, Auteur ; David C. Dunand, Auteur . - 2012 . - pp. 7615–7626. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7615–7626 Mots-clés : Aluminum  alloys  Nucleation  Precipitation  Coarsening  Creep Résumé : It is known that Zr and Yb partition to the Al3Sc precipitates created during aging when microalloyed separately in dilute binary Al–Sc alloys. Addition of Zr delays precipitate coarsening, thereby improving the coarsening resistance of the ternary Al-Sc-Zr alloys. Addition of Yb increases the resistance against dislocation climb, thereby improving the creep resistances of the ternary Al-Sc-Yb alloys. A combination of microhardness, creep, and atom probe tomography measurements provide evidence that these effects of Zr and Yb additions are cumulative in quaternary dilute Al–Sc–Yb–Zr alloys: Yb increases their creep resistance at 300 °C compared with ternary Al–Sc–Zr alloys and Zr improves their coarsening resistance at 300 °C compared with ternary Al–Sc–Yb alloys. Additionally, excellent coarsening resistance is observed at 350 and 375 °C. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006562

Effect of residual stresses on the onset of yielding in a Zr-based metallic glass / L. Wang in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7627–7633 Titre : Effect of residual stresses on the onset of yielding in a Zr-based metallic glass Type de document : texte imprimé Auteurs : L. Wang, Auteur ; H. Bei, Auteur ; Y.F. Gao, Auteur Année de publication : 2012 Article en page(s) : pp. 7627–7633 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Residual  stresses  Onset  of  yielding  Metallic  glasses  Nanoindentation  Glass  transition Résumé : Indentation experiments were performed on as-cast and elastically-bent-and-constrained Zr-based metallic glass samples to investigate the effect of strain rate and residual stresses on the onset of yielding in the material. The critical shear stress for the onset of yielding in the as-cast sample was found to be insensitive to the applied strain rate. By contrast, in the elastically-stressed sample, the maximum contact pressure from the Hertzian stress field at the onset of yielding was found to largely decrease under tensile residual stress, but only slightly increase under compressive residual stress. Despite the different residual stresses, the effective shear stress, i.e. the superimposition of residual and Hertzian stress fields, for the onset of yielding in the Zr-based metallic glass was essentially a constant. The constancy of the effective stress for the onset of yielding was discussed in light of a critical excess volume associated with the atomic structure upon loading. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006665 [article] Effect of residual stresses on the onset of yielding in a Zr-based metallic glass [texte imprimé] / L. Wang, Auteur ; H. Bei, Auteur ; Y.F. Gao, Auteur . - 2012 . - pp. 7627–7633. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7627–7633 Mots-clés : Residual  stresses  Onset  of  yielding  Metallic  glasses  Nanoindentation  Glass  transition Résumé : Indentation experiments were performed on as-cast and elastically-bent-and-constrained Zr-based metallic glass samples to investigate the effect of strain rate and residual stresses on the onset of yielding in the material. The critical shear stress for the onset of yielding in the as-cast sample was found to be insensitive to the applied strain rate. By contrast, in the elastically-stressed sample, the maximum contact pressure from the Hertzian stress field at the onset of yielding was found to largely decrease under tensile residual stress, but only slightly increase under compressive residual stress. Despite the different residual stresses, the effective shear stress, i.e. the superimposition of residual and Hertzian stress fields, for the onset of yielding in the Zr-based metallic glass was essentially a constant. The constancy of the effective stress for the onset of yielding was discussed in light of a critical excess volume associated with the atomic structure upon loading. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006665

Diffusion kinetics in aluminium–gold bond contacts from first-principles density functional calculations / Christian M. Ulrich in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7634–7644 Titre : Diffusion kinetics in aluminium–gold bond contacts from first-principles density functional calculations Type de document : texte imprimé Auteurs : Christian M. Ulrich, Auteur ; Adham Hashibon, Auteur ; Jiřı´ Svoboda, Auteur Année de publication : 2012 Article en page(s) : pp. 7634–7644 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bonding  Diffusion  Intermetallic  compounds  Al–Au  Growth  kinetics Résumé : A common joining method in microelectronics is thermosonic bonding of gold wires to aluminium pads deposited on the integrated circuit. In the interface between the wire and the pad a number of intermetallic compounds AlxAuy can develop, which significantly affect the mechanical properties and corrosion resistance of the bonds. Based on Onsager’s extremal principle of irreversible thermodynamics, the present paper describes the evolution of the intermetallic phases. This macroscopic model contains several thermodynamic and kinetic parameters, some of which are not available from databases. As an alternative to often cumbersome experiments, density functional theory is applied to calculate the formation energies of the phases and of atomic vacancies, as well as the vacancy migration energies in AlAu4. To derive tracer diffusion coefficients from the atomistic vacancy jump rates, one must take peculiarities of the AlAu4 lattice into account: the vacancy migration energy between certain gold sites is found to be rather low, but these low-energy jumps are arranged in closed triangles and, therefore, do not provide paths for long-range diffusion of gold atoms. However, together with two other types of jumps with still moderate migration energies, a contiguous network of diffusion paths for gold becomes possible. Since the diffusion of aluminium in AlAu4 requires the generation of high- energy anti-site defects (at least temporarily), aluminium is expected to move very slowly, but no final solution is provided. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100588X [article] Diffusion kinetics in aluminium–gold bond contacts from first-principles density functional calculations [texte imprimé] / Christian M. Ulrich, Auteur ; Adham Hashibon, Auteur ; Jiřı´ Svoboda, Auteur . - 2012 . - pp. 7634–7644. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7634–7644 Mots-clés : Bonding  Diffusion  Intermetallic  compounds  Al–Au  Growth  kinetics Résumé : A common joining method in microelectronics is thermosonic bonding of gold wires to aluminium pads deposited on the integrated circuit. In the interface between the wire and the pad a number of intermetallic compounds AlxAuy can develop, which significantly affect the mechanical properties and corrosion resistance of the bonds. Based on Onsager’s extremal principle of irreversible thermodynamics, the present paper describes the evolution of the intermetallic phases. This macroscopic model contains several thermodynamic and kinetic parameters, some of which are not available from databases. As an alternative to often cumbersome experiments, density functional theory is applied to calculate the formation energies of the phases and of atomic vacancies, as well as the vacancy migration energies in AlAu4. To derive tracer diffusion coefficients from the atomistic vacancy jump rates, one must take peculiarities of the AlAu4 lattice into account: the vacancy migration energy between certain gold sites is found to be rather low, but these low-energy jumps are arranged in closed triangles and, therefore, do not provide paths for long-range diffusion of gold atoms. However, together with two other types of jumps with still moderate migration energies, a contiguous network of diffusion paths for gold becomes possible. Since the diffusion of aluminium in AlAu4 requires the generation of high- energy anti-site defects (at least temporarily), aluminium is expected to move very slowly, but no final solution is provided. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100588X

Coarsening by network restructuring in model nanoporous gold / Kedarnath Kolluri in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp 7645–7653 Titre : Coarsening by network restructuring in model nanoporous gold Type de document : texte imprimé Auteurs : Kedarnath Kolluri, Auteur ; Michael J. Demkowicz, Auteur Année de publication : 2012 Article en page(s) : pp 7645–7653 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Coarsening  Foams  Nanoporous  metals  Modeling Résumé : Using atomistic modeling, we show that restructuring of the network of interconnected ligaments causes coarsening in a model of nanoporous gold. The restructuring arises from the collapse of some ligaments onto neighboring ones and is enabled by localized plasticity at ligaments and nodes. This mechanism may explain the occurrence of enclosed voids and reduction in volume in nanoporous metals during their synthesis. An expression is developed for the critical ligament radius below which coarsening by network restructuring may occur spontaneously, setting a lower limit to the ligament dimensions of nanofoams. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006148 [article] Coarsening by network restructuring in model nanoporous gold [texte imprimé] / Kedarnath Kolluri, Auteur ; Michael J. Demkowicz, Auteur . - 2012 . - pp 7645–7653. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp 7645–7653 Mots-clés : Coarsening  Foams  Nanoporous  metals  Modeling Résumé : Using atomistic modeling, we show that restructuring of the network of interconnected ligaments causes coarsening in a model of nanoporous gold. The restructuring arises from the collapse of some ligaments onto neighboring ones and is enabled by localized plasticity at ligaments and nodes. This mechanism may explain the occurrence of enclosed voids and reduction in volume in nanoporous metals during their synthesis. An expression is developed for the critical ligament radius below which coarsening by network restructuring may occur spontaneously, setting a lower limit to the ligament dimensions of nanofoams. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006148

Fatigue threshold R-curves predict small crack fatigue behavior of bridging toughened materials / S. Gallops in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7654–7661 Titre : Fatigue threshold R-curves predict small crack fatigue behavior of bridging toughened materials Type de document : texte imprimé Auteurs : S. Gallops, Auteur ; T. Fett, Auteur ; J. W. Ager III, Auteur Année de publication : 2012 Article en page(s) : pp. 7654–7661 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fatigue  Fracture  Toughness  Crack  bridging Résumé : Small crack fatigue is a widely recognized problem in the fatigue of materials; however, there has been limited progress in developing methods to predict small crack fatigue behavior. In this paper small crack effects due to crack bridging are addressed. A fatigue threshold R-curve was measured for a 99.5% pure polycrystalline alumina using standard compact tension specimens and was used (i) to determine the bridging stress profile for the material and (ii) to make fatigue endurance strength predictions for realistic semi-elliptical surface cracks. Furthermore, it has been shown that the fatigue threshold R-curve can equivalently be determined by measuring the bridging stress distribution, in this case using fluorescence spectroscopy, using only a long crack compact tension specimen without the need for difficult small crack experiments. It is expected that this method will be applicable to a wide range of bridging toughened materials, including composites, toughened ceramics, intermetallics, and multi-phase materials. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100615X [article] Fatigue threshold R-curves predict small crack fatigue behavior of bridging toughened materials [texte imprimé] / S. Gallops, Auteur ; T. Fett, Auteur ; J. W. Ager III, Auteur . - 2012 . - pp. 7654–7661. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7654–7661 Mots-clés : Fatigue  Fracture  Toughness  Crack  bridging Résumé : Small crack fatigue is a widely recognized problem in the fatigue of materials; however, there has been limited progress in developing methods to predict small crack fatigue behavior. In this paper small crack effects due to crack bridging are addressed. A fatigue threshold R-curve was measured for a 99.5% pure polycrystalline alumina using standard compact tension specimens and was used (i) to determine the bridging stress profile for the material and (ii) to make fatigue endurance strength predictions for realistic semi-elliptical surface cracks. Furthermore, it has been shown that the fatigue threshold R-curve can equivalently be determined by measuring the bridging stress distribution, in this case using fluorescence spectroscopy, using only a long crack compact tension specimen without the need for difficult small crack experiments. It is expected that this method will be applicable to a wide range of bridging toughened materials, including composites, toughened ceramics, intermetallics, and multi-phase materials. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100615X

Unexpected influence of Mn addition on the creep properties of a cast Mg–2Al–2Ca (mass%) alloy / T. Homma in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7662–7672 Titre : Unexpected influence of Mn addition on the creep properties of a cast Mg–2Al–2Ca (mass%) alloy Type de document : texte imprimé Auteurs : T. Homma, Auteur ; S. Nakawaki, Auteur ; K. Oh-ishi, Auteur Année de publication : 2012 Article en page(s) : pp. 7662–7672 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium  alloy  Creep  Guinier–Preston  zone  Transmission  electron  microscopy  Atom  probe Résumé : The addition of 0.3% Mn to a Mg–2Al–2Ca (mass%) alloy improves the minimum creep rate by one order of magnitude compared with the Mn-free alloy. Network-shaped Mg2Ca (C14 structure) and (Mg,Al)2Ca (C36 structure) compounds coexist in the interdendritic regions, while plate-shaped Al2Ca (C15 structure) phases are dispersed in the matrix. Ordered Guinier–Preston (GP) zones form dynamically on the basal plane of the α-Mg matrix during creep deformation. The number density of the fine GP zones in the Mn-containing alloy was found to be higher than that in the Mn-free alloy. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006264 [article] Unexpected influence of Mn addition on the creep properties of a cast Mg–2Al–2Ca (mass%) alloy [texte imprimé] / T. Homma, Auteur ; S. Nakawaki, Auteur ; K. Oh-ishi, Auteur . - 2012 . - pp. 7662–7672. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7662–7672 Mots-clés : Magnesium  alloy  Creep  Guinier–Preston  zone  Transmission  electron  microscopy  Atom  probe Résumé : The addition of 0.3% Mn to a Mg–2Al–2Ca (mass%) alloy improves the minimum creep rate by one order of magnitude compared with the Mn-free alloy. Network-shaped Mg2Ca (C14 structure) and (Mg,Al)2Ca (C36 structure) compounds coexist in the interdendritic regions, while plate-shaped Al2Ca (C15 structure) phases are dispersed in the matrix. Ordered Guinier–Preston (GP) zones form dynamically on the basal plane of the α-Mg matrix during creep deformation. The number density of the fine GP zones in the Mn-containing alloy was found to be higher than that in the Mn-free alloy. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006264

Plastic deformation mechanisms of fcc single crystals at small scales / Caizhi Zhou in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7673–7682 Titre : Plastic deformation mechanisms of fcc single crystals at small scales Type de document : texte imprimé Auteurs : Caizhi Zhou, Auteur ; Irene J. Beyerlein, Auteur ; Richard LeSar, Auteur Année de publication : 2012 Article en page(s) : pp. 7673–7682 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  dynamics  Size  effects  Small  scales  Dislocation  starvation  Cross-slip Résumé : Three-dimensional (3-D) dislocation dynamics simulations were employed to examine the fundamental mechanisms of plasticity in small-scale face-centered cubic single crystals. Guided by the simulation results, we examined two distinct modes of behavior that reflect the dominant physical mechanisms of plastic deformation at small scales. We found that the residence lifetimes of internal dislocation sources formed by cross-slip decrease as the system size decreases. Below a critical sample size (which depends on the initial density of dislocations) the dislocation loss rate exceeds the multiplication rate, leading to the loss of internal dislocation sources. In this case nucleation of surface dislocations is required to provide dislocations for deformation and the “starvation hardening” mechanism becomes the dominant deformation process. When the sample is larger than a critical size multiplication of internal dislocation sources provides the dominant mechanism for plastic flow. As the strain is increased the rising dislocation density leads to reactions that shut off these sources, creating “exhaustion hardening”. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006094 [article] Plastic deformation mechanisms of fcc single crystals at small scales [texte imprimé] / Caizhi Zhou, Auteur ; Irene J. Beyerlein, Auteur ; Richard LeSar, Auteur . - 2012 . - pp. 7673–7682. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7673–7682 Mots-clés : Dislocation  dynamics  Size  effects  Small  scales  Dislocation  starvation  Cross-slip Résumé : Three-dimensional (3-D) dislocation dynamics simulations were employed to examine the fundamental mechanisms of plasticity in small-scale face-centered cubic single crystals. Guided by the simulation results, we examined two distinct modes of behavior that reflect the dominant physical mechanisms of plastic deformation at small scales. We found that the residence lifetimes of internal dislocation sources formed by cross-slip decrease as the system size decreases. Below a critical sample size (which depends on the initial density of dislocations) the dislocation loss rate exceeds the multiplication rate, leading to the loss of internal dislocation sources. In this case nucleation of surface dislocations is required to provide dislocations for deformation and the “starvation hardening” mechanism becomes the dominant deformation process. When the sample is larger than a critical size multiplication of internal dislocation sources provides the dominant mechanism for plastic flow. As the strain is increased the rising dislocation density leads to reactions that shut off these sources, creating “exhaustion hardening”. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006094

Effect of internal oxidation on wear behavior of ultrafine-grained Nb–Zr / G. Purcek in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7683–7694 Titre : Effect of internal oxidation on wear behavior of ultrafine-grained Nb–Zr Type de document : texte imprimé Auteurs : G. Purcek, Auteur ; O. Saray, Auteur ; F. Rubitschek, Auteur Année de publication : 2012 Article en page(s) : pp. 7683–7694 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Niobium–zirconium  alloys  Severe  plastic  deformation  Ultrafine-grained  materials  Thermal  oxidation  Wear  behavior Résumé : The influence of surface modification by internal oxidation on dry sliding wear behavior of ultrafine-grained (UFG) Nb–Zr was investigated using a pin-on-disc type tribometer. The results show that improvement in strength by grain refinement via equal-channel angular pressing/extrusion has no substantial effect on the wear resistance of the non-oxidized UFG samples as compared to the coarse-grained material. This was attributed to the complex wear mechanisms operating in this alloy, such as adhesion leading to smearing, tribo-chemical reactions resulting in strong oxidative wear and also abrasion bringing about scratches and deep grooves. However, internal oxidation by heat-treatment significantly improved the wear resistance of Nb–Zr, especially under low to medium applied pressures due to the hardened diffusion zone with ZrO2 nanoparticles formed in the subsurface layer. Moreover, the improvement was more pronounced in the UFG material, which is attributed to increased diffusion in the UFG microstructure. When the applied pressure was increased above 0.5 MPa, however, the wear rate increased considerably due to the elimination of the hardened subsurface layer. Still, even under high pressures, the oxidized samples demonstrated lower weight loss as compared to non-oxidized samples. Based on the investigations of the worn surfaces, it was determined that internal oxidation mostly eliminates the complex wear mechanisms operational in the non-oxidized samples, especially under low/medium loads. Improvement in wear properties by internal oxidation along with enhanced mechanical properties and previously demonstrated good biocompatibility and superior fatigue performance make internally oxidized UFG NbZr a promising candidate for biomedical applications in the human body. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006033 [article] Effect of internal oxidation on wear behavior of ultrafine-grained Nb–Zr [texte imprimé] / G. Purcek, Auteur ; O. Saray, Auteur ; F. Rubitschek, Auteur . - 2012 . - pp. 7683–7694. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7683–7694 Mots-clés : Niobium–zirconium  alloys  Severe  plastic  deformation  Ultrafine-grained  materials  Thermal  oxidation  Wear  behavior Résumé : The influence of surface modification by internal oxidation on dry sliding wear behavior of ultrafine-grained (UFG) Nb–Zr was investigated using a pin-on-disc type tribometer. The results show that improvement in strength by grain refinement via equal-channel angular pressing/extrusion has no substantial effect on the wear resistance of the non-oxidized UFG samples as compared to the coarse-grained material. This was attributed to the complex wear mechanisms operating in this alloy, such as adhesion leading to smearing, tribo-chemical reactions resulting in strong oxidative wear and also abrasion bringing about scratches and deep grooves. However, internal oxidation by heat-treatment significantly improved the wear resistance of Nb–Zr, especially under low to medium applied pressures due to the hardened diffusion zone with ZrO2 nanoparticles formed in the subsurface layer. Moreover, the improvement was more pronounced in the UFG material, which is attributed to increased diffusion in the UFG microstructure. When the applied pressure was increased above 0.5 MPa, however, the wear rate increased considerably due to the elimination of the hardened subsurface layer. Still, even under high pressures, the oxidized samples demonstrated lower weight loss as compared to non-oxidized samples. Based on the investigations of the worn surfaces, it was determined that internal oxidation mostly eliminates the complex wear mechanisms operational in the non-oxidized samples, especially under low/medium loads. Improvement in wear properties by internal oxidation along with enhanced mechanical properties and previously demonstrated good biocompatibility and superior fatigue performance make internally oxidized UFG NbZr a promising candidate for biomedical applications in the human body. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006033

Dislocation density evolution and interactions in crystalline materials / P. Shanthraj in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7695–7702 Titre : Dislocation density evolution and interactions in crystalline materials Type de document : texte imprimé Auteurs : P. Shanthraj, Auteur ; M.A. Zikry, Auteur Année de publication : 2012 Article en page(s) : pp. 7695–7702 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  density  Computational  model  Crystal  plasticity  Localization Résumé : Dislocation density-based evolution formulations that are related to a heterogeneous microstructure and are physically representative of different crystalline interactions have been developed. The balance between the generation and annihilation of dislocations, through glissile and forest interactions at the slip system level, is taken as the basis for the evolution of mobile and immobile dislocation densities. The evolution equations are coupled to a multiple slip crystal plasticity formulation, and a framework is established that relates it to a general class of crystallographies and deformation modes. Specialized finite element (FE) methodologies have then been used to investigate how certain dislocation density activities, such as dislocation density interactions and immobilization, are directly related to strain hardening and microstructure evolution. The predictions are validated with channel die compressed (CDC) experiments, and are consistent with inelastic deformation modes of fcc metals. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006185 [article] Dislocation density evolution and interactions in crystalline materials [texte imprimé] / P. Shanthraj, Auteur ; M.A. Zikry, Auteur . - 2012 . - pp. 7695–7702. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7695–7702 Mots-clés : Dislocation  density  Computational  model  Crystal  plasticity  Localization Résumé : Dislocation density-based evolution formulations that are related to a heterogeneous microstructure and are physically representative of different crystalline interactions have been developed. The balance between the generation and annihilation of dislocations, through glissile and forest interactions at the slip system level, is taken as the basis for the evolution of mobile and immobile dislocation densities. The evolution equations are coupled to a multiple slip crystal plasticity formulation, and a framework is established that relates it to a general class of crystallographies and deformation modes. Specialized finite element (FE) methodologies have then been used to investigate how certain dislocation density activities, such as dislocation density interactions and immobilization, are directly related to strain hardening and microstructure evolution. The predictions are validated with channel die compressed (CDC) experiments, and are consistent with inelastic deformation modes of fcc metals. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006185

Growth of dislocation clusters during directional solidification of multicrystalline silicon ingots / B. Ryningen in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7703–7710 Titre : Growth of dislocation clusters during directional solidification of multicrystalline silicon ingots Type de document : texte imprimé Auteurs : B. Ryningen, Auteur ; G. Stokkan, Auteur ; M. Kivambe, Auteur Année de publication : 2012 Article en page(s) : pp. 7703–7710 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Crystal  growth  Dislocation  structure  Dislocations  Silicon  Directional  solidification Résumé : Highly detrimental dislocation clusters are frequently observed in lab-scale as well as industrially produced multicrystalline silicon ingots for solar cell applications. This paper presents an investigation of dislocation clusters and how they develop over the whole height of a pilot-scale ingot. A 12-kg ingot, cast in a pilot-scale directional solidification furnace using a standard slip cast silica crucible and standard coating containing silicon nitride powder, was studied with respect to dislocation clusters. Dislocation clusters originating from grain boundaries were identified and followed from an early stage to the top of the ingot. One possible model for growth and multiplication of the dislocations in the clusters during solidification where slip on the 〈1 1 0〉 system must be allowed is described in detail. Another possible mechanism is also discussed. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100629X [article] Growth of dislocation clusters during directional solidification of multicrystalline silicon ingots [texte imprimé] / B. Ryningen, Auteur ; G. Stokkan, Auteur ; M. Kivambe, Auteur . - 2012 . - pp. 7703–7710. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7703–7710 Mots-clés : Crystal  growth  Dislocation  structure  Dislocations  Silicon  Directional  solidification Résumé : Highly detrimental dislocation clusters are frequently observed in lab-scale as well as industrially produced multicrystalline silicon ingots for solar cell applications. This paper presents an investigation of dislocation clusters and how they develop over the whole height of a pilot-scale ingot. A 12-kg ingot, cast in a pilot-scale directional solidification furnace using a standard slip cast silica crucible and standard coating containing silicon nitride powder, was studied with respect to dislocation clusters. Dislocation clusters originating from grain boundaries were identified and followed from an early stage to the top of the ingot. One possible model for growth and multiplication of the dislocations in the clusters during solidification where slip on the 〈1 1 0〉 system must be allowed is described in detail. Another possible mechanism is also discussed. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100629X

Appearance of dislocation-mediated and twinning-induced plasticity in an engineering-grade FeMnNiCr alloy / D. Geissler in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7711–7723 Titre : Appearance of dislocation-mediated and twinning-induced plasticity in an engineering-grade FeMnNiCr alloy Type de document : texte imprimé Auteurs : D. Geissler, Auteur ; J. Freudenberger, Auteur ; A. Kauffmann, Auteur Année de publication : 2012 Article en page(s) : pp. 7711–7723 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : TWIP  Deformation  twinning  Slip  Stacking  fault  Stacking  fault  energy Résumé : By comparing the microstructural and texture evolution with tensile stress–strain response of an Fe–24Mn–7Ni–8Cr (mass%) alloy, a slip-dominated deformation process and, at a later stage of deformation, twinning-induced plasticity are observed. The occurrence of deformation twinning is texture sensitive and occurs only in the 〈1 1 1〉 fibre texture component. Based on these experimental observations, a model is presented, which reflects an orientational and configurational peculiarity of face-centred cubic stacking faults bordered by two Shockley partials. With this model, the onset point of stacking fault growth, i.e. movement of the leading partial and stopping of the trailing partial, is evaluated. This point reflects the formation of twins in the sense that a twin is regarded as an arrangement of stacking faults on every consecutive slip plane. Furthermore, based on the tensile test results, a model-compatible description of the mechanical behaviour is shown and a reasonable stacking fault energy of about 8 mJ m−2 is calculated for the onset of partial dislocation breakaway, i.e. the onset of deformation twinning. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006173 [article] Appearance of dislocation-mediated and twinning-induced plasticity in an engineering-grade FeMnNiCr alloy [texte imprimé] / D. Geissler, Auteur ; J. Freudenberger, Auteur ; A. Kauffmann, Auteur . - 2012 . - pp. 7711–7723. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7711–7723 Mots-clés : TWIP  Deformation  twinning  Slip  Stacking  fault  Stacking  fault  energy Résumé : By comparing the microstructural and texture evolution with tensile stress–strain response of an Fe–24Mn–7Ni–8Cr (mass%) alloy, a slip-dominated deformation process and, at a later stage of deformation, twinning-induced plasticity are observed. The occurrence of deformation twinning is texture sensitive and occurs only in the 〈1 1 1〉 fibre texture component. Based on these experimental observations, a model is presented, which reflects an orientational and configurational peculiarity of face-centred cubic stacking faults bordered by two Shockley partials. With this model, the onset point of stacking fault growth, i.e. movement of the leading partial and stopping of the trailing partial, is evaluated. This point reflects the formation of twins in the sense that a twin is regarded as an arrangement of stacking faults on every consecutive slip plane. Furthermore, based on the tensile test results, a model-compatible description of the mechanical behaviour is shown and a reasonable stacking fault energy of about 8 mJ m−2 is calculated for the onset of partial dislocation breakaway, i.e. the onset of deformation twinning. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006173

Interfacial disconnections at Sb2Te3 precipitates in PbTe / N.A. Heinz in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7724–7735 Titre : Interfacial disconnections at Sb2Te3 precipitates in PbTe : Mechanisms of strain accommodation and phase transformation at a tetradymite/rocksalt telluride interface Type de document : texte imprimé Auteurs : N.A. Heinz, Auteur ; T. Ikeda, Auteur ; G.J. Snyder, Auteur Année de publication : 2012 Article en page(s) : pp. 7724–7735 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Interface  structure  Phase  transformations  Dislocations  High-resolution  transmission  electron  microscopy  (HRTEM)  Thermoelectric  materials Résumé : Understanding the structure and formation mechanisms of interfaces between different telluride phases is important to the development of thermoelectric nanocomposites. Here, we investigate the interfacial structure of tetradymite precipitates in a rocksalt telluride matrix, focusing in particular on precipitates of Sb2Te3 in PbTe. Using high-resolution transmission electron microscopy, we investigate the structure and arrangement of interfacial disconnections—i.e. interfacial steps possessing dislocation character—observed in this system. Our analyses provide insight concerning the roles of these defects in accommodating the large interfacial misfit (6.7%) in this system and in mediating the transformation from the rocksalt to the tetradymite structure. Our observations also suggest how such interfacial disconnections could arise through the dissociation of crystal lattice dislocations that accommodate the misfit on initially flat segments of the interface. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006203 [article] Interfacial disconnections at Sb2Te3 precipitates in PbTe : Mechanisms of strain accommodation and phase transformation at a tetradymite/rocksalt telluride interface [texte imprimé] / N.A. Heinz, Auteur ; T. Ikeda, Auteur ; G.J. Snyder, Auteur . - 2012 . - pp. 7724–7735. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7724–7735 Mots-clés : Interface  structure  Phase  transformations  Dislocations  High-resolution  transmission  electron  microscopy  (HRTEM)  Thermoelectric  materials Résumé : Understanding the structure and formation mechanisms of interfaces between different telluride phases is important to the development of thermoelectric nanocomposites. Here, we investigate the interfacial structure of tetradymite precipitates in a rocksalt telluride matrix, focusing in particular on precipitates of Sb2Te3 in PbTe. Using high-resolution transmission electron microscopy, we investigate the structure and arrangement of interfacial disconnections—i.e. interfacial steps possessing dislocation character—observed in this system. Our analyses provide insight concerning the roles of these defects in accommodating the large interfacial misfit (6.7%) in this system and in mediating the transformation from the rocksalt to the tetradymite structure. Our observations also suggest how such interfacial disconnections could arise through the dissociation of crystal lattice dislocations that accommodate the misfit on initially flat segments of the interface. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006203

Elastic properties of surfaces on nanoparticles / Wilhelm G. Wolfer in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7736–7743 Titre : Elastic properties of surfaces on nanoparticles Type de document : texte imprimé Auteurs : Wilhelm G. Wolfer, Auteur Année de publication : 2012 Article en page(s) : pp. 7736–7743 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Elastic  properties  Lattice  strains  Nanoparticles  Surface  stress Résumé : Lattice parameter changes in nanoparticles can be used to determine the surface stress of solids. In the past a Laplace–Young relationship has been employed to interpret the lattice parameter changes as a function of the particle size. In the meantime, however, atomistic calculations revealed a purely mechanical origin of the surface stress that is consistent with elasticity theory for solid surfaces as developed by Gurtin and Murdoch. In this theory the equilibrium distance for surface atoms may differ from that in the bulk solid, and the elastic properties of the surface layer may also deviate from bulk values. We apply this Gurtin–Murdoch theory to spherical nanoparticles and reanalyze past data as well as results from recent theoretical calculations on lattice parameter changes, thereby enabling us to determine surface properties commensurate with the mechanical interpretation of surface stress. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006100 [article] Elastic properties of surfaces on nanoparticles [texte imprimé] / Wilhelm G. Wolfer, Auteur . - 2012 . - pp. 7736–7743. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7736–7743 Mots-clés : Elastic  properties  Lattice  strains  Nanoparticles  Surface  stress Résumé : Lattice parameter changes in nanoparticles can be used to determine the surface stress of solids. In the past a Laplace–Young relationship has been employed to interpret the lattice parameter changes as a function of the particle size. In the meantime, however, atomistic calculations revealed a purely mechanical origin of the surface stress that is consistent with elasticity theory for solid surfaces as developed by Gurtin and Murdoch. In this theory the equilibrium distance for surface atoms may differ from that in the bulk solid, and the elastic properties of the surface layer may also deviate from bulk values. We apply this Gurtin–Murdoch theory to spherical nanoparticles and reanalyze past data as well as results from recent theoretical calculations on lattice parameter changes, thereby enabling us to determine surface properties commensurate with the mechanical interpretation of surface stress. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006100

Structure, shear resistance and interaction with point defects of interfaces in Cu–Nb nanocomposites synthesized by severe plastic deformation / M.J. Demkowicz in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7744–7756 Titre : Structure, shear resistance and interaction with point defects of interfaces in Cu–Nb nanocomposites synthesized by severe plastic deformation Type de document : texte imprimé Auteurs : M.J. Demkowicz, Auteur ; L. Thilly, Auteur Année de publication : 2012 Article en page(s) : pp. 7744–7756 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Severe  plastic  deformation  Nanocomposite  Interface  structure  Slip  Molecular  dynamics Résumé : Atomistic modeling is used to investigate the shear resistance and interaction with point defects of a Cu–Nb interface found in nanocomposites synthesized by severe plastic deformation. The shear resistance of this interface is highly anisotropic: in one direction shearing occurs at stresses <1200 MPa, while in the other it does not occur at all. The binding energy of vacancies, interstitials and He impurities to this interface depends sensitively on the binding location, but there is no point defect delocalization, nor does this interface contain any constitutional defects. These behaviors are markedly dissimilar from a different Cu–Nb interface found in magnetron sputtered composites. The dissimilarities may, however, be explained by quantitative differences in the detailed structure of these two interfaces. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006318 [article] Structure, shear resistance and interaction with point defects of interfaces in Cu–Nb nanocomposites synthesized by severe plastic deformation [texte imprimé] / M.J. Demkowicz, Auteur ; L. Thilly, Auteur . - 2012 . - pp. 7744–7756. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7744–7756 Mots-clés : Severe  plastic  deformation  Nanocomposite  Interface  structure  Slip  Molecular  dynamics Résumé : Atomistic modeling is used to investigate the shear resistance and interaction with point defects of a Cu–Nb interface found in nanocomposites synthesized by severe plastic deformation. The shear resistance of this interface is highly anisotropic: in one direction shearing occurs at stresses <1200 MPa, while in the other it does not occur at all. The binding energy of vacancies, interstitials and He impurities to this interface depends sensitively on the binding location, but there is no point defect delocalization, nor does this interface contain any constitutional defects. These behaviors are markedly dissimilar from a different Cu–Nb interface found in magnetron sputtered composites. The dissimilarities may, however, be explained by quantitative differences in the detailed structure of these two interfaces. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006318

Deposition of alumina thin film by dual magnetron sputtering / W. Engelhart in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7757–7767 Titre : Deposition of alumina thin film by dual magnetron sputtering : Is it γ-Al2O3? Type de document : texte imprimé Auteurs : W. Engelhart, Auteur ; W. Dreher, Auteur ; O. Eibl, Auteur Année de publication : 2012 Article en page(s) : pp. 7757–7767 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thin  films  Nanostructure  Ceramic  material  Microstructures  Alumina Résumé : Alumina thin films were deposited by reactive dual magnetron sputtering at 550 °C on cemented carbide substrates. A Young’s modulus of 315 GPa and a Vickers hardness of 2348 were determined by nanoindentation and were compared to reference materials. The crystal structure of such films is usually referred to as γ-Al2O3; however, the crystal structure of cubic γ-Al2O3 is not well defined, not even for bulk materials. The alumina grain size of the films was about 50 nm as measured by dark-field imaging in a transmission electron microscope. The energy-filtered electron diffraction patterns were segmented: one part showed an amorphous intensity distribution, not known for γ-Al2O3, the other part contained reflections arranged in rings, the brightest of which had lattice spacings of the (4 0 0) and (4 4 0) reflections of γ-Al2O3. Therefore, the structure of the thin films is referred to as pseudo γ-Al2O3. This nomenclature expresses that this phase is different from γ-Al2O3 but among the Al2O3 phases is most closely related to this phase. Differences between the two crystal structures are highlighted and discussed with respect to lattice spacings, intensities of the various reflections, chemical composition and other physical properties. The pseudo γ-Al2O3 films contained an Al/Ar mole fraction ratio of about 17 as determined by energy-dispersive X-ray spectroscopy. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006252 [article] Deposition of alumina thin film by dual magnetron sputtering : Is it γ-Al2O3? [texte imprimé] / W. Engelhart, Auteur ; W. Dreher, Auteur ; O. Eibl, Auteur . - 2012 . - pp. 7757–7767. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7757–7767 Mots-clés : Thin  films  Nanostructure  Ceramic  material  Microstructures  Alumina Résumé : Alumina thin films were deposited by reactive dual magnetron sputtering at 550 °C on cemented carbide substrates. A Young’s modulus of 315 GPa and a Vickers hardness of 2348 were determined by nanoindentation and were compared to reference materials. The crystal structure of such films is usually referred to as γ-Al2O3; however, the crystal structure of cubic γ-Al2O3 is not well defined, not even for bulk materials. The alumina grain size of the films was about 50 nm as measured by dark-field imaging in a transmission electron microscope. The energy-filtered electron diffraction patterns were segmented: one part showed an amorphous intensity distribution, not known for γ-Al2O3, the other part contained reflections arranged in rings, the brightest of which had lattice spacings of the (4 0 0) and (4 4 0) reflections of γ-Al2O3. Therefore, the structure of the thin films is referred to as pseudo γ-Al2O3. This nomenclature expresses that this phase is different from γ-Al2O3 but among the Al2O3 phases is most closely related to this phase. Differences between the two crystal structures are highlighted and discussed with respect to lattice spacings, intensities of the various reflections, chemical composition and other physical properties. The pseudo γ-Al2O3 films contained an Al/Ar mole fraction ratio of about 17 as determined by energy-dispersive X-ray spectroscopy. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006252

Microstructure optimization to achieve high coercivity in anisotropic Nd–Fe–B thin films / W. B. Cui in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7768–7775 Titre : Microstructure optimization to achieve high coercivity in anisotropic Nd–Fe–B thin films Type de document : texte imprimé Auteurs : W. B. Cui, Auteur ; Y.K. Takahashi, Auteur ; K. Hono, Auteur Année de publication : 2012 Article en page(s) : pp. 7768–7775 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Permanent  magnets  Nd–Fe–B  thin  films  Coercivity  Transmission  electron  microscopy Résumé : A high coercivity of 2.35 MA m−1 (29.5 kOe) is demonstrated using perpendicular anisotropy Nd–Fe–B films. Single layer columnar grown Nd–Fe–B thin films with a coercivity comparable with that of sintered magnets (1.11 MA m−1, 14.0 kOe) were used as the starting film. The coercivity was doubled by annealing films capped with Nd, Nd/Cu, and Nd/Ag layers. Transmission electron microscopy indicated that the Nd2Fe14B columnar grains were isolated by a Nd-rich grain boundary phase formed by diffusion of the capped layers into the grain boundaries of the polycrystalline Nd–Fe–B films. The temperature dependence of coercivity was lower than that of commercial sintered magnets. The coercivity of the Nd/Cu diffusion processed sample at 473 K was 0.979 MA m−1 (12.3 kOe), which is higher than that of Nd10Dy4Fe80B6 sintered magnets. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006331 [article] Microstructure optimization to achieve high coercivity in anisotropic Nd–Fe–B thin films [texte imprimé] / W. B. Cui, Auteur ; Y.K. Takahashi, Auteur ; K. Hono, Auteur . - 2012 . - pp. 7768–7775. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7768–7775 Mots-clés : Permanent  magnets  Nd–Fe–B  thin  films  Coercivity  Transmission  electron  microscopy Résumé : A high coercivity of 2.35 MA m−1 (29.5 kOe) is demonstrated using perpendicular anisotropy Nd–Fe–B films. Single layer columnar grown Nd–Fe–B thin films with a coercivity comparable with that of sintered magnets (1.11 MA m−1, 14.0 kOe) were used as the starting film. The coercivity was doubled by annealing films capped with Nd, Nd/Cu, and Nd/Ag layers. Transmission electron microscopy indicated that the Nd2Fe14B columnar grains were isolated by a Nd-rich grain boundary phase formed by diffusion of the capped layers into the grain boundaries of the polycrystalline Nd–Fe–B films. The temperature dependence of coercivity was lower than that of commercial sintered magnets. The coercivity of the Nd/Cu diffusion processed sample at 473 K was 0.979 MA m−1 (12.3 kOe), which is higher than that of Nd10Dy4Fe80B6 sintered magnets. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006331

In situ formation of crystalline flakes in Mg-based metallic glass composites by controlled inoculation / Wanqiang Xu in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7776–7786 Titre : In situ formation of crystalline flakes in Mg-based metallic glass composites by controlled inoculation Type de document : texte imprimé Auteurs : Wanqiang Xu, Auteur ; Rongkun Zheng, Auteur ; Kevin J. Laws, Auteur Année de publication : 2012 Article en page(s) : pp. 7776–7786 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Casting  Metallic  glasses  Magnesium  Heterogeneous  nucleation  Phase  transformations Résumé : In situ bulk metallic glass (BMG) composites generally contain a crystalline phase(s) that forms throughout the amorphous matrix during cooling from the melt. The presence of the crystalline phase in these materials is known to improve both ductility and toughness. In this study the nucleation and growth behaviour of crystalline α-Mg flakes during casting of a series of Mg–Cu–Y–Zn glass forming alloys were investigated. It was demonstrated that the α-Mg phase nucleates preferentially on the surface of micron-sized yttria (Y2O3) particles that form in the melt during casting and subsequently grow in preferential crystallographic directions to generate an intimate distribution of interwoven flakes throughout the amorphous matrix. High resolution transmission electron microscopy revealed that a thin (∼5 nm) intermediate Cu layer forms at the particle–flake interface resulting in full coherency with both the particle and flake, thereby resulting in well-defined orientation relationships. The formation of this intermediate layer is argued to be the necessary precursor for nucleation of Mg flakes at the Y2O3 particles in a manner similar to that found for the preferential nucleation at TiB2 particles in conventional Al alloys. The overall effect of this intermediate layer is a reduction in the interfacial energy between the particle and nucleus, thereby lowering the thermodynamic barrier for nucleation. In general terms, inoculation controlled formation of a crystalline phase throughout an amorphous matrix in selected glass forming compositions may be a viable means of generating the desired two phase structure for generating high strength BMG composites exhibiting suitable ductility. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006215# [article] In situ formation of crystalline flakes in Mg-based metallic glass composites by controlled inoculation [texte imprimé] / Wanqiang Xu, Auteur ; Rongkun Zheng, Auteur ; Kevin J. Laws, Auteur . - 2012 . - pp. 7776–7786. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7776–7786 Mots-clés : Casting  Metallic  glasses  Magnesium  Heterogeneous  nucleation  Phase  transformations Résumé : In situ bulk metallic glass (BMG) composites generally contain a crystalline phase(s) that forms throughout the amorphous matrix during cooling from the melt. The presence of the crystalline phase in these materials is known to improve both ductility and toughness. In this study the nucleation and growth behaviour of crystalline α-Mg flakes during casting of a series of Mg–Cu–Y–Zn glass forming alloys were investigated. It was demonstrated that the α-Mg phase nucleates preferentially on the surface of micron-sized yttria (Y2O3) particles that form in the melt during casting and subsequently grow in preferential crystallographic directions to generate an intimate distribution of interwoven flakes throughout the amorphous matrix. High resolution transmission electron microscopy revealed that a thin (∼5 nm) intermediate Cu layer forms at the particle–flake interface resulting in full coherency with both the particle and flake, thereby resulting in well-defined orientation relationships. The formation of this intermediate layer is argued to be the necessary precursor for nucleation of Mg flakes at the Y2O3 particles in a manner similar to that found for the preferential nucleation at TiB2 particles in conventional Al alloys. The overall effect of this intermediate layer is a reduction in the interfacial energy between the particle and nucleus, thereby lowering the thermodynamic barrier for nucleation. In general terms, inoculation controlled formation of a crystalline phase throughout an amorphous matrix in selected glass forming compositions may be a viable means of generating the desired two phase structure for generating high strength BMG composites exhibiting suitable ductility. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006215#

Orientation dependence of twinning and strain hardening behaviour of a high manganese twinning induced plasticity steel with polycrystalline structure / H. Beladi in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7787–7799 Titre : Orientation dependence of twinning and strain hardening behaviour of a high manganese twinning induced plasticity steel with polycrystalline structure Type de document : texte imprimé Auteurs : H. Beladi, Auteur ; I.B. Timokhina, Auteur ; Y. Estrin, Auteur Année de publication : 2012 Article en page(s) : pp. 7787–7799 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Twinning  induced  plasticity  steel  Mechanical  twinning  Strain  hardening  Taylor  factor  Dynamic  strain  ageing Résumé : The twinning induced plasticity steel 0.6 C–18 Mn–1.5 Al (wt.%) employed in this study exhibited a strength of about 1 GPa, combined with a large uniform elongation of over 60% at moderate strain rates. This excellent combination of tensile mechanical properties was shown to be a result of complex dynamic strain-induced microstructural reactions, including dislocation glide, dislocation dissociation, stacking fault formation, dynamic recovery, mechanical twinning and dynamic strain ageing. The contribution of each of these processes was discussed with respect to the strain hardening behaviour. An important observation was that the propensity for mechanical twinning in a particular grain strongly depends on its crystallographic orientation and is clearly correlated with the magnitude of the corresponding Taylor factor. The current results reveal that the development of partial dislocations and stacking faults at an early stage of straining and the consequent interaction of gliding dislocations with stacking fault interfaces enhances the strain hardening rate. Subsequent or concurrent initiation of mechanical twins also contributes to strain hardening through a dynamic Hall–Petch effect limiting the dislocation mean free path and consequently enhancing dislocation storage. Dynamic strain ageing (DSA) took place at a late stage of deformation, adding to strain hardening. DSA is a factor reducing ductility by promoting strain localization. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006069 [article] Orientation dependence of twinning and strain hardening behaviour of a high manganese twinning induced plasticity steel with polycrystalline structure [texte imprimé] / H. Beladi, Auteur ; I.B. Timokhina, Auteur ; Y. Estrin, Auteur . - 2012 . - pp. 7787–7799. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7787–7799 Mots-clés : Twinning  induced  plasticity  steel  Mechanical  twinning  Strain  hardening  Taylor  factor  Dynamic  strain  ageing Résumé : The twinning induced plasticity steel 0.6 C–18 Mn–1.5 Al (wt.%) employed in this study exhibited a strength of about 1 GPa, combined with a large uniform elongation of over 60% at moderate strain rates. This excellent combination of tensile mechanical properties was shown to be a result of complex dynamic strain-induced microstructural reactions, including dislocation glide, dislocation dissociation, stacking fault formation, dynamic recovery, mechanical twinning and dynamic strain ageing. The contribution of each of these processes was discussed with respect to the strain hardening behaviour. An important observation was that the propensity for mechanical twinning in a particular grain strongly depends on its crystallographic orientation and is clearly correlated with the magnitude of the corresponding Taylor factor. The current results reveal that the development of partial dislocations and stacking faults at an early stage of straining and the consequent interaction of gliding dislocations with stacking fault interfaces enhances the strain hardening rate. Subsequent or concurrent initiation of mechanical twins also contributes to strain hardening through a dynamic Hall–Petch effect limiting the dislocation mean free path and consequently enhancing dislocation storage. Dynamic strain ageing (DSA) took place at a late stage of deformation, adding to strain hardening. DSA is a factor reducing ductility by promoting strain localization. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006069

A phase field study of strain energy effects on solute–grain boundary interactions / Tae Wook Heo in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7800–7815 Titre : A phase field study of strain energy effects on solute–grain boundary interactions Type de document : texte imprimé Auteurs : Tae Wook Heo, Auteur ; Saswata Bhattacharyya, Auteur ; Long-Qing Chen, Auteur Année de publication : 2012 Article en page(s) : pp. 7800–7815 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  boundary  segregation  Solute  drag  effect  Elastic  strain  energy  Phase  field  model Résumé : We have studied strain-induced solute segregation at a grain boundary and the solute drag effect on boundary migration using a phase field model integrating grain boundary segregation and grain structure evolution. The elastic strain energy of a solid solution due to the atomic size mismatch and the coherency elastic strain energy caused by the inhomogeneity of the composition distribution are obtained using Khachaturyan’s microelasticity theory. Strain-induced grain boundary segregation at a static planar boundary is studied numerically and the equilibrium segregation composition profiles are validated using analytical solutions. We then systematically studied the effect of misfit strain on grain boundary migration with solute drag. Our theoretical analysis based on Cahn’s analytical theory shows that enhancement of the drag force with increasing atomic size mismatch stems from both an increase in grain boundary segregation due to the strain energy reduction and misfit strain relaxation near the grain boundary. The results were analyzed based on a theoretical analysis in terms of elastic and chemical drag forces. The optimum condition for solute diffusivity to maximize the drag force under a given driving force was identified. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006227 [article] A phase field study of strain energy effects on solute–grain boundary interactions [texte imprimé] / Tae Wook Heo, Auteur ; Saswata Bhattacharyya, Auteur ; Long-Qing Chen, Auteur . - 2012 . - pp. 7800–7815. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7800–7815 Mots-clés : Grain  boundary  segregation  Solute  drag  effect  Elastic  strain  energy  Phase  field  model Résumé : We have studied strain-induced solute segregation at a grain boundary and the solute drag effect on boundary migration using a phase field model integrating grain boundary segregation and grain structure evolution. The elastic strain energy of a solid solution due to the atomic size mismatch and the coherency elastic strain energy caused by the inhomogeneity of the composition distribution are obtained using Khachaturyan’s microelasticity theory. Strain-induced grain boundary segregation at a static planar boundary is studied numerically and the equilibrium segregation composition profiles are validated using analytical solutions. We then systematically studied the effect of misfit strain on grain boundary migration with solute drag. Our theoretical analysis based on Cahn’s analytical theory shows that enhancement of the drag force with increasing atomic size mismatch stems from both an increase in grain boundary segregation due to the strain energy reduction and misfit strain relaxation near the grain boundary. The results were analyzed based on a theoretical analysis in terms of elastic and chemical drag forces. The optimum condition for solute diffusivity to maximize the drag force under a given driving force was identified. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006227

Severe deformation twinning in pure copper by cryogenic wire drawing / A. Kauffmann in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7816–7823 Titre : Severe deformation twinning in pure copper by cryogenic wire drawing Type de document : texte imprimé Auteurs : A. Kauffmann, Auteur ; J. Freudenberger, Auteur ; D. Geissler, Auteur Année de publication : 2012 Article en page(s) : pp. 7816–7823 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Deformation  twinning  Copper  Low-temperature  deformation  Stress  state  Resolved  shear  stress Résumé : The effect of low-temperature on the active deformation mechanism is studied in pure copper. For this purpose, cryogenic wire drawing at liquid nitrogen temperature (77 K) was performed using molybdenum disulfide lubrication. Microstructural investigation and texture analysis revealed severe twin formation in the cryogenically drawn copper, with a broad twin size distribution. The spacing of the observed deformation twins ranges from below 100 nm, as reported in previous investigations, up to several micrometers. The extent of twin formation, which is significantly higher when compared to other cryo-deformation techniques, is discussed with respect to the state of stress and the texture evolution during wire drawing. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006197 [article] Severe deformation twinning in pure copper by cryogenic wire drawing [texte imprimé] / A. Kauffmann, Auteur ; J. Freudenberger, Auteur ; D. Geissler, Auteur . - 2012 . - pp. 7816–7823. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7816–7823 Mots-clés : Deformation  twinning  Copper  Low-temperature  deformation  Stress  state  Resolved  shear  stress Résumé : The effect of low-temperature on the active deformation mechanism is studied in pure copper. For this purpose, cryogenic wire drawing at liquid nitrogen temperature (77 K) was performed using molybdenum disulfide lubrication. Microstructural investigation and texture analysis revealed severe twin formation in the cryogenically drawn copper, with a broad twin size distribution. The spacing of the observed deformation twins ranges from below 100 nm, as reported in previous investigations, up to several micrometers. The extent of twin formation, which is significantly higher when compared to other cryo-deformation techniques, is discussed with respect to the state of stress and the texture evolution during wire drawing. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006197

Sensitivity of deformation twinning to grain size in titanium and magnesium / Alireza Ghaderi in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7824–7839 Titre : Sensitivity of deformation twinning to grain size in titanium and magnesium Type de document : texte imprimé Auteurs : Alireza Ghaderi, Auteur ; Matthew R. Barnett, Auteur Année de publication : 2012 Article en page(s) : pp. 7824–7839 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Twinning  Grain  size  Titanium  Magnesium Résumé : The impact of grain size on deformation twinning in commercial purity titanium and magnesium alloy Mg–3Al–1Zn (AZ31) is investigated. Tensile tests were carried out for the titanium samples; compression testing was employed for the magnesium specimens. Average values of the true twin length, true twin thickness and the number density of twins were determined using stereology. A key difference between these two materials is that twinning contributes little to the plastic strain in the titanium while it accounts for nearly all of the early plastic strain in the magnesium. In some respects (e.g. volume fraction and number density) the phenomenology of twinning differed between the two materials, while in others (e.g. twin shape and size) both materials showed a similar response. It is found that in both materials, twins span the entirety of their parent grains only for grain sizes less than ∼30 μm. Both the nucleation density per unit of nucleating interface (i.e. grain and twin boundaries) and the aspect ratio of twins scale with applied stress. The impact of grain size on twin volume fraction is modelled analytically. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006550 [article] Sensitivity of deformation twinning to grain size in titanium and magnesium [texte imprimé] / Alireza Ghaderi, Auteur ; Matthew R. Barnett, Auteur . - 2012 . - pp. 7824–7839. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7824–7839 Mots-clés : Twinning  Grain  size  Titanium  Magnesium Résumé : The impact of grain size on deformation twinning in commercial purity titanium and magnesium alloy Mg–3Al–1Zn (AZ31) is investigated. Tensile tests were carried out for the titanium samples; compression testing was employed for the magnesium specimens. Average values of the true twin length, true twin thickness and the number density of twins were determined using stereology. A key difference between these two materials is that twinning contributes little to the plastic strain in the titanium while it accounts for nearly all of the early plastic strain in the magnesium. In some respects (e.g. volume fraction and number density) the phenomenology of twinning differed between the two materials, while in others (e.g. twin shape and size) both materials showed a similar response. It is found that in both materials, twins span the entirety of their parent grains only for grain sizes less than ∼30 μm. Both the nucleation density per unit of nucleating interface (i.e. grain and twin boundaries) and the aspect ratio of twins scale with applied stress. The impact of grain size on twin volume fraction is modelled analytically. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006550

The strength of chemical bonds in solids and liquids / D.B. Miracle in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7840–7854 Titre : The strength of chemical bonds in solids and liquids Type de document : texte imprimé Auteurs : D.B. Miracle, Auteur ; G.B. Wilks, Auteur ; A.G. Dahlman, Auteur Année de publication : 2012 Article en page(s) : pp. 7840–7854 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thermodynamics  Metals  and  alloys  Bond  energy Résumé : The strengths of chemical bonds between atoms are accurately measured and widely available for molecular gases, but an established method of quantifying bond strengths in liquids and solids is not available, and the strengths of these bonds are generally unknown. A new term, the condensed bond enthalpy (CBE), is proposed to specify the energy contained in bonds between atoms in condensed states. An approach to estimating these bond strengths is developed by combining classical thermodynamic concepts with measured heats of formation and crystallographic data. A nearly complete set of elemental CBE and a selection of CBE between unlike metal atom pairs are produced using the method described here. Elemental bond enthalpies generally range from about −0.1 eV to −1.3 eV, and bonds between unlike atoms studied here range from about −0.6 eV to −1.1 eV. The validity and utility of these values are demonstrated by using them to estimate enthalpies of fusion and surface energies in elemental metals and heats of formation of ternary intermetallic compounds. Predicted enthalpies are generally within experimental errors for all three comparisons. Bond enthalpies are found to have a mild but systematic dependence on chemistry and atomic structure in some of the binary systems studied here, but are essentially independent of the atomic environment in other systems. The uncertainty in εij values (±4%) is small enough to enable classical approximations, but is inadequate when higher precision is needed. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006306 [article] The strength of chemical bonds in solids and liquids [texte imprimé] / D.B. Miracle, Auteur ; G.B. Wilks, Auteur ; A.G. Dahlman, Auteur . - 2012 . - pp. 7840–7854. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7840–7854 Mots-clés : Thermodynamics  Metals  and  alloys  Bond  energy Résumé : The strengths of chemical bonds between atoms are accurately measured and widely available for molecular gases, but an established method of quantifying bond strengths in liquids and solids is not available, and the strengths of these bonds are generally unknown. A new term, the condensed bond enthalpy (CBE), is proposed to specify the energy contained in bonds between atoms in condensed states. An approach to estimating these bond strengths is developed by combining classical thermodynamic concepts with measured heats of formation and crystallographic data. A nearly complete set of elemental CBE and a selection of CBE between unlike metal atom pairs are produced using the method described here. Elemental bond enthalpies generally range from about −0.1 eV to −1.3 eV, and bonds between unlike atoms studied here range from about −0.6 eV to −1.1 eV. The validity and utility of these values are demonstrated by using them to estimate enthalpies of fusion and surface energies in elemental metals and heats of formation of ternary intermetallic compounds. Predicted enthalpies are generally within experimental errors for all three comparisons. Bond enthalpies are found to have a mild but systematic dependence on chemistry and atomic structure in some of the binary systems studied here, but are essentially independent of the atomic environment in other systems. The uncertainty in εij values (±4%) is small enough to enable classical approximations, but is inadequate when higher precision is needed. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006306

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