Dépouillements

Reaction kinetics of Ni/Sn soldering reaction / Jens Görlich in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3187–3197 Titre : Reaction kinetics of Ni/Sn soldering reaction Type de document : texte imprimé Auteurs : Jens Görlich, Auteur ; Dietmar Baither, Auteur ; Guido Schmitz, Auteur Année de publication : 2011 Article en page(s) : pp. 3187–3197 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Phase  transformation  Soldering  reaction  Grain  boundary  diffusion  Grain  boundary  wetting  Intermetallic  compounds Résumé : Soldering between solid Ni and liquid Sn is studied, including late stages of reflow. Only during the very early stages of the process, intermetallic grains grow with a 1/3 power dependence on time. Later, kinetics clearly changes to parabolic growth, but remarkably in two subsequent regimes distinguished by different rate constants. The observed kinetics is discussed with respect to recent flux-driven ripening theory. This theory is only valid, if at all, for short reflows up to about 4 min. Transmission electron microscopy reveals the predicted scallop-like microstructure only at the very beginning. A sponge-like structure of equiaxed grains then develops, triggered by permanent nucleation of new grains at the Ni/Ni3Sn4 interface. Wetting of grain boundaries appears only up to a certain depth in the reaction zone. This remarkable behavior is explained by thermodynamic arguments. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000418 [article] Reaction kinetics of Ni/Sn soldering reaction [texte imprimé] / Jens Görlich, Auteur ; Dietmar Baither, Auteur ; Guido Schmitz, Auteur . - 2011 . - pp. 3187–3197. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3187–3197 Mots-clés : Phase  transformation  Soldering  reaction  Grain  boundary  diffusion  Grain  boundary  wetting  Intermetallic  compounds Résumé : Soldering between solid Ni and liquid Sn is studied, including late stages of reflow. Only during the very early stages of the process, intermetallic grains grow with a 1/3 power dependence on time. Later, kinetics clearly changes to parabolic growth, but remarkably in two subsequent regimes distinguished by different rate constants. The observed kinetics is discussed with respect to recent flux-driven ripening theory. This theory is only valid, if at all, for short reflows up to about 4 min. Transmission electron microscopy reveals the predicted scallop-like microstructure only at the very beginning. A sponge-like structure of equiaxed grains then develops, triggered by permanent nucleation of new grains at the Ni/Ni3Sn4 interface. Wetting of grain boundaries appears only up to a certain depth in the reaction zone. This remarkable behavior is explained by thermodynamic arguments. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000418

ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016 / P.W.J. Mckenzie in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3198–3211 Titre : ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016 : Part 1: Microstructure Type de document : texte imprimé Auteurs : P.W.J. Mckenzie, Auteur ; R. Lapovok, Auteur Année de publication : 2011 Article en page(s) : pp. 3198–3211 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Equal  channel  angular  pressing  (ECAP)  Ultrafine  grained  (UFG)  Aluminium  alloy  6016  Tensile  test  Strain  hardening Résumé : The microstructure evolution of aluminium alloy 6016 processed by equal channel angular pressing (ECAP) was investigated for different processing parameters. A number of heat treatments, including F, W, O, T4, T6 and T7, were evaluated for workability required to withstand the severe plastic deformation. It was found that this aluminium alloy had limited workability at room temperature in the F, W and T4 tempers, especially at low levels of applied back pressure, while both the O and T7 tempers can be pressed to a very high strain (∼1800%) without failure. Considering that the O temper has better utility for industry because of decreased preparation time, a complete study of microstructure after ECAP processing with and without back pressure was carried out for the O temper. The thermal stability of microstructure after 16 ECAP passes with 200 MPa of back pressure was also studied. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000522 [article] ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016 : Part 1: Microstructure [texte imprimé] / P.W.J. Mckenzie, Auteur ; R. Lapovok, Auteur . - 2011 . - pp. 3198–3211. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3198–3211 Mots-clés : Equal  channel  angular  pressing  (ECAP)  Ultrafine  grained  (UFG)  Aluminium  alloy  6016  Tensile  test  Strain  hardening Résumé : The microstructure evolution of aluminium alloy 6016 processed by equal channel angular pressing (ECAP) was investigated for different processing parameters. A number of heat treatments, including F, W, O, T4, T6 and T7, were evaluated for workability required to withstand the severe plastic deformation. It was found that this aluminium alloy had limited workability at room temperature in the F, W and T4 tempers, especially at low levels of applied back pressure, while both the O and T7 tempers can be pressed to a very high strain (∼1800%) without failure. Considering that the O temper has better utility for industry because of decreased preparation time, a complete study of microstructure after ECAP processing with and without back pressure was carried out for the O temper. The thermal stability of microstructure after 16 ECAP passes with 200 MPa of back pressure was also studied. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000522

ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016 / P.W.J. Mckenzie in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3212–3222 Titre : ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016 : Part 2: Mechanical properties and texture Type de document : texte imprimé Auteurs : P.W.J. Mckenzie, Auteur ; R. Lapovok, Auteur Année de publication : 2011 Article en page(s) : pp. 3212–3222 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Equal  channel  angular  pressing  (ECAP)  Ultrafine  grained  (UFG)  Aluminium  alloy  6016  Tensile  test  Strain  hardening Résumé : The simultaneous increase in strength and ductility of aluminium alloy 6016 processed by equal channel angular pressing (ECAP) was investigated. A complete study of microstructure, texture and mechanical properties after ECAP processing with and without back pressure was carried out for the O temper. The simultaneous increase in strength and ductility of AA6016-O with number of ECAP passes was explained by the use of back pressure during ECAP. A maximum ductility of ∼100% was obtained at the temperature of 200 °C and strain rate of 10−4 s−1, which is a significant improvement on the ductility exhibited by AA6016 (∼89%) after a conventional thermomechanical treatment at a much higher temperature of 500 °C. The mechanical behaviour was interpreted in the context of the textures developed in the material. A significant amount of texture rotation due to applied back pressure was found. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000510 [article] ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016 : Part 2: Mechanical properties and texture [texte imprimé] / P.W.J. Mckenzie, Auteur ; R. Lapovok, Auteur . - 2011 . - pp. 3212–3222. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3212–3222 Mots-clés : Equal  channel  angular  pressing  (ECAP)  Ultrafine  grained  (UFG)  Aluminium  alloy  6016  Tensile  test  Strain  hardening Résumé : The simultaneous increase in strength and ductility of aluminium alloy 6016 processed by equal channel angular pressing (ECAP) was investigated. A complete study of microstructure, texture and mechanical properties after ECAP processing with and without back pressure was carried out for the O temper. The simultaneous increase in strength and ductility of AA6016-O with number of ECAP passes was explained by the use of back pressure during ECAP. A maximum ductility of ∼100% was obtained at the temperature of 200 °C and strain rate of 10−4 s−1, which is a significant improvement on the ductility exhibited by AA6016 (∼89%) after a conventional thermomechanical treatment at a much higher temperature of 500 °C. The mechanical behaviour was interpreted in the context of the textures developed in the material. A significant amount of texture rotation due to applied back pressure was found. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000510

Relationship between dislocation density and nucleation of multicrystalline silicon / G. Stokkan in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3223–3229 Titre : Relationship between dislocation density and nucleation of multicrystalline silicon Type de document : texte imprimé Auteurs : G. Stokkan, Auteur Année de publication : 2011 Article en page(s) : pp. 3223–3229 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocations  Directional  solidification  Dendritic  growth  Grain  boundary  twin  Silicon Résumé : Dislocation density and crystal orientation were investigated for a set of multicrystalline silicon ingots grown in a pilot scale furnace. Both low and high dislocation density ingots were observed. The low dislocation density ingots showed a dominating orientation close to (2 1 1) in contrast to the high dislocation density ingots. The orientations are consistent with growth on dendritic crystals formed along the crucible bottom and dendritic crystals with an angle towards the melt, respectively. During crystal growth, the power that was dissipated to the crystallization furnace showed a marked drop shortly after the onset of crystallization for low dislocation density ingots, an indication of fast release of crystallization heat from dendritic growth. Ingots that were not dominated by a high dislocation density instead had a high occurrence of twinned areas. Favourable orientation of the [1 View the MathML source 0] vector in the growth plane is suggested to be the cause of growth dominated by multiple twin faceting. This favourable orientation existed for crystals grown from dendrites grown along the crucible bottom, and this is suggested as an explanation for why these crystals are dominated by multiple twins rather than dislocations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000056X [article] Relationship between dislocation density and nucleation of multicrystalline silicon [texte imprimé] / G. Stokkan, Auteur . - 2011 . - pp. 3223–3229. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3223–3229 Mots-clés : Dislocations  Directional  solidification  Dendritic  growth  Grain  boundary  twin  Silicon Résumé : Dislocation density and crystal orientation were investigated for a set of multicrystalline silicon ingots grown in a pilot scale furnace. Both low and high dislocation density ingots were observed. The low dislocation density ingots showed a dominating orientation close to (2 1 1) in contrast to the high dislocation density ingots. The orientations are consistent with growth on dendritic crystals formed along the crucible bottom and dendritic crystals with an angle towards the melt, respectively. During crystal growth, the power that was dissipated to the crystallization furnace showed a marked drop shortly after the onset of crystallization for low dislocation density ingots, an indication of fast release of crystallization heat from dendritic growth. Ingots that were not dominated by a high dislocation density instead had a high occurrence of twinned areas. Favourable orientation of the [1 View the MathML source 0] vector in the growth plane is suggested to be the cause of growth dominated by multiple twin faceting. This favourable orientation existed for crystals grown from dendrites grown along the crucible bottom, and this is suggested as an explanation for why these crystals are dominated by multiple twins rather than dislocations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000056X

Phase-field simulation of void migration in a temperature gradient / S.Y. Hu in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3230–3237 Titre : Phase-field simulation of void migration in a temperature gradient Type de document : texte imprimé Auteurs : S.Y. Hu, Auteur ; C.H. Henager Jr., Auteur Année de publication : 2011 Article en page(s) : pp. 3230–3237 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Void  migration  Surface  and  bulk  diffusion  Vacancy  Temperature  gradient  Phase-field  model Résumé : A phase-field model simulating vacancy diffusion in a solid with a strong vacancy mobility inhomogeneity is presented. The model is used to study void migration via bulk and surface diffusion in a temperature gradient. The simulations demonstrate that voids migrate up the temperature gradient, and the migration velocity varies inversely with the void size, in agreement with theory. It is also shown that the current model has the capability to investigate the effects of surface diffusion, temperature gradient and vacancy concentration on the void migration velocity. An interesting potential application of the model is to study the kinetics of void migration and the formation of a central hole in nuclear fuels. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000571 [article] Phase-field simulation of void migration in a temperature gradient [texte imprimé] / S.Y. Hu, Auteur ; C.H. Henager Jr., Auteur . - 2011 . - pp. 3230–3237. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3230–3237 Mots-clés : Void  migration  Surface  and  bulk  diffusion  Vacancy  Temperature  gradient  Phase-field  model Résumé : A phase-field model simulating vacancy diffusion in a solid with a strong vacancy mobility inhomogeneity is presented. The model is used to study void migration via bulk and surface diffusion in a temperature gradient. The simulations demonstrate that voids migrate up the temperature gradient, and the migration velocity varies inversely with the void size, in agreement with theory. It is also shown that the current model has the capability to investigate the effects of surface diffusion, temperature gradient and vacancy concentration on the void migration velocity. An interesting potential application of the model is to study the kinetics of void migration and the formation of a central hole in nuclear fuels. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000571

Analysis by high-resolution electron microscopy of elastic strain in thick InAs layers embedded in Ga0.47In0.53As buffers on InP(0 0 1) substrate / C. Gatel in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3238–3246 Titre : Analysis by high-resolution electron microscopy of elastic strain in thick InAs layers embedded in Ga0.47In0.53As buffers on InP(0 0 1) substrate Type de document : texte imprimé Auteurs : C. Gatel, Auteur ; H. Tang, Auteur ; C. Crestou, Auteur Année de publication : 2011 Article en page(s) : pp. 3238–3246 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Epitaxial  strain  Molecular  beam  epitaxy  (MBE)  High-resolution  electron  microscopy  (HREM)  Semiconductor  compounds  Finite  element  modeling  (FEM) Résumé : Elastic strain has been investigated by transmission electron microscopy in nanometric InAs layers grown on Ga0.47In0.53As/InP(0 0 1) by molecular beam epitaxy using a residual Sb flux. Deposits of 10 and 15 monolayers of InAs (3 and 4.5 nm) remain elastically stressed with a two-dimensional growth mode. The out-of-plane strain in the layers is analyzed by cross-sectional high-resolution electron microscopy. A distortion of the substrate below and on top of the InAs layers is detected and is attributed to a significant surface relaxation effect due to thinning. Surface relaxation is modeled by three-dimensional finite element modeling. An additional relaxation effect is obtained when the sample is not infinite along the direction perpendicular to the thinning. This effect enhances the buffer distortion of the buffers below and on top of the strained layers. Taking into account thin foil effects, the experimental out-of-plane strain is in excellent agreement with the theoretical value calculated for a pure InAs layer (i.e. 0.035), demonstrating the high level of strain and stress in the layers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000777 [article] Analysis by high-resolution electron microscopy of elastic strain in thick InAs layers embedded in Ga0.47In0.53As buffers on InP(0 0 1) substrate [texte imprimé] / C. Gatel, Auteur ; H. Tang, Auteur ; C. Crestou, Auteur . - 2011 . - pp. 3238–3246. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3238–3246 Mots-clés : Epitaxial  strain  Molecular  beam  epitaxy  (MBE)  High-resolution  electron  microscopy  (HREM)  Semiconductor  compounds  Finite  element  modeling  (FEM) Résumé : Elastic strain has been investigated by transmission electron microscopy in nanometric InAs layers grown on Ga0.47In0.53As/InP(0 0 1) by molecular beam epitaxy using a residual Sb flux. Deposits of 10 and 15 monolayers of InAs (3 and 4.5 nm) remain elastically stressed with a two-dimensional growth mode. The out-of-plane strain in the layers is analyzed by cross-sectional high-resolution electron microscopy. A distortion of the substrate below and on top of the InAs layers is detected and is attributed to a significant surface relaxation effect due to thinning. Surface relaxation is modeled by three-dimensional finite element modeling. An additional relaxation effect is obtained when the sample is not infinite along the direction perpendicular to the thinning. This effect enhances the buffer distortion of the buffers below and on top of the strained layers. Taking into account thin foil effects, the experimental out-of-plane strain is in excellent agreement with the theoretical value calculated for a pure InAs layer (i.e. 0.035), demonstrating the high level of strain and stress in the layers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000777

Room-temperature equal channel angular extrusion of pure magnesium / Somjeet Biswas in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3247–3261 Titre : Room-temperature equal channel angular extrusion of pure magnesium Type de document : texte imprimé Auteurs : Somjeet Biswas, Auteur ; Satyam Suwas, Auteur Année de publication : 2011 Article en page(s) : pp. 3247–3261 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Equal  channel  angular  extrusion  (ECAE)  Electron  backscattering  diffraction  (EBSD)  Magnesium  Texture  Dynamic  recrystallization Résumé : In this paper, we demonstrate a way to impart severe plastic deformation to magnesium at room temperature to produce ultrafine grain size of ∼250 nm through equal channel angular extrusion (ECAE). The strategy to deform magnesium at lower temperature or to achieve such grain sizes has been proposed as: (i) to obtain a suitable initial orientation with high Schmid factor for basal slip and low Schmid factor for pyramidal/prismatic slip; (ii) to take advantage of low stacking fault energy of basal and high stacking fault energies of prismatic/pyramidal planes in order to relatively work-harden the basal plane with respect to the pyramidal/prismatic plane; and (iii) to lower the temperature of deformation in steps, leading to continual refinement of grains, resulting in finer grain size. The experimental as well as simulated texture of ECAE-processed samples indicate that the deformation mechanism leading to ultrafine grain size is slip-dominated. The recrystallization mechanism during ECAE has been found to be orientation-dependent. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000819 [article] Room-temperature equal channel angular extrusion of pure magnesium [texte imprimé] / Somjeet Biswas, Auteur ; Satyam Suwas, Auteur . - 2011 . - pp. 3247–3261. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3247–3261 Mots-clés : Equal  channel  angular  extrusion  (ECAE)  Electron  backscattering  diffraction  (EBSD)  Magnesium  Texture  Dynamic  recrystallization Résumé : In this paper, we demonstrate a way to impart severe plastic deformation to magnesium at room temperature to produce ultrafine grain size of ∼250 nm through equal channel angular extrusion (ECAE). The strategy to deform magnesium at lower temperature or to achieve such grain sizes has been proposed as: (i) to obtain a suitable initial orientation with high Schmid factor for basal slip and low Schmid factor for pyramidal/prismatic slip; (ii) to take advantage of low stacking fault energy of basal and high stacking fault energies of prismatic/pyramidal planes in order to relatively work-harden the basal plane with respect to the pyramidal/prismatic plane; and (iii) to lower the temperature of deformation in steps, leading to continual refinement of grains, resulting in finer grain size. The experimental as well as simulated texture of ECAE-processed samples indicate that the deformation mechanism leading to ultrafine grain size is slip-dominated. The recrystallization mechanism during ECAE has been found to be orientation-dependent. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000819

An analytical model for constitutional supercooling-driven grain formation and grain size prediction / M. Qian in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3262–3270 Titre : An analytical model for constitutional supercooling-driven grain formation and grain size prediction Type de document : texte imprimé Auteurs : M. Qian, Auteur ; P. Cao, Auteur ; M.A. Easton, Auteur Année de publication : 2011 Article en page(s) : pp. 3262–3270 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Undercooling  solidification  Heterogeneous  nucleation  Grain  growth  Grain  refining Résumé : Being able to predict the grain formation process and attendant grain size has been a central topic in solidification. Such an analytical model is presented for constitutional supercooling (CS)-driven grain formation with several simplifications. The model links the nucleation of new grains to the growth of a larger neighbouring grain. The average grain size (View the MathML source) is thus determined by two components: the minimum growth (rcs) necessary to establish sufficient CS (ΔTn) for nucleating new grains, and the spatial mean distance (View the MathML source) to the most potent available nucleants. Both spherical and planar growth fronts are considered, covering growth curvatures from small to infinite. Two distinct fundamental approaches are used, which result in identical descriptions of View the MathML source, where View the MathML source (D is the diffusion coefficient, v is the growth velocity, Q is the growth restriction factor). The model is compared with literature data produced under various conditions and demonstrated on aluminium alloys as an example. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000820 [article] An analytical model for constitutional supercooling-driven grain formation and grain size prediction [texte imprimé] / M. Qian, Auteur ; P. Cao, Auteur ; M.A. Easton, Auteur . - 2011 . - pp. 3262–3270. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3262–3270 Mots-clés : Undercooling  solidification  Heterogeneous  nucleation  Grain  growth  Grain  refining Résumé : Being able to predict the grain formation process and attendant grain size has been a central topic in solidification. Such an analytical model is presented for constitutional supercooling (CS)-driven grain formation with several simplifications. The model links the nucleation of new grains to the growth of a larger neighbouring grain. The average grain size (View the MathML source) is thus determined by two components: the minimum growth (rcs) necessary to establish sufficient CS (ΔTn) for nucleating new grains, and the spatial mean distance (View the MathML source) to the most potent available nucleants. Both spherical and planar growth fronts are considered, covering growth curvatures from small to infinite. Two distinct fundamental approaches are used, which result in identical descriptions of View the MathML source, where View the MathML source (D is the diffusion coefficient, v is the growth velocity, Q is the growth restriction factor). The model is compared with literature data produced under various conditions and demonstrated on aluminium alloys as an example. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000820

Anomalous transformation-induced deformation in 〈1 1 0〉 textured Gum Metal / J.W. Morris Jr. in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3271–3280 Titre : Anomalous transformation-induced deformation in 〈1 1 0〉 textured Gum Metal Type de document : texte imprimé Auteurs : J.W. Morris Jr., Auteur ; Y. Hanlumyuang, Auteur ; M. Sherburne, Auteur Année de publication : 2011 Article en page(s) : pp. 3271–3280 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Gum  Metal  Phase  transformation  Titanium  alloys Résumé : Tensile tests on single crystals of Gum Metal (Ti–36Nb–2Ta–3Zr–0.3O (wt.%)) showed, anomalously, that while a stress-induced β(bcc) → α″(orthorhombic) transformation occurred in a crystal pulled in the 〈1 1 0〉 direction, (1) no transformation was observed in crystals pulled in the 〈1 0 0〉 or 〈1 1 1〉 directions and (2) little or no transformation occurred in severely worked rods, which are polycrystals with very strong 〈1 1 0〉 texture. Analysis of the energetics of the β → α″ transformation offers straightforward explanations: (1) an α″ precipitate has zero elastic energy if it forms as a thin plate with the habit {1 1 1.5}; a 〈1 1 0〉 tensile load significantly decreases the energy of this plate; loading along 〈1 0 0〉 or 〈1 1 1〉 is less effective; (2) while worked rods have a strong 〈1 1 0〉 axial texture, the perpendicular planes are severely distorted, increasing the elastic energy of α″ and inhibiting the transformation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000087X [article] Anomalous transformation-induced deformation in 〈1 1 0〉 textured Gum Metal [texte imprimé] / J.W. Morris Jr., Auteur ; Y. Hanlumyuang, Auteur ; M. Sherburne, Auteur . - 2011 . - pp. 3271–3280. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3271–3280 Mots-clés : Gum  Metal  Phase  transformation  Titanium  alloys Résumé : Tensile tests on single crystals of Gum Metal (Ti–36Nb–2Ta–3Zr–0.3O (wt.%)) showed, anomalously, that while a stress-induced β(bcc) → α″(orthorhombic) transformation occurred in a crystal pulled in the 〈1 1 0〉 direction, (1) no transformation was observed in crystals pulled in the 〈1 0 0〉 or 〈1 1 1〉 directions and (2) little or no transformation occurred in severely worked rods, which are polycrystals with very strong 〈1 1 0〉 texture. Analysis of the energetics of the β → α″ transformation offers straightforward explanations: (1) an α″ precipitate has zero elastic energy if it forms as a thin plate with the habit {1 1 1.5}; a 〈1 1 0〉 tensile load significantly decreases the energy of this plate; loading along 〈1 0 0〉 or 〈1 1 1〉 is less effective; (2) while worked rods have a strong 〈1 1 0〉 axial texture, the perpendicular planes are severely distorted, increasing the elastic energy of α″ and inhibiting the transformation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000087X

Formation mechanisms of cyclic saturation dislocation patterns in [0 0 1], [0 1 1] and View the MathML source copper single crystals / P. Li in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3281–3294 Titre : Formation mechanisms of cyclic saturation dislocation patterns in [0 0 1], [0 1 1] and View the MathML source copper single crystals Type de document : texte imprimé Auteurs : P. Li, Auteur ; S.X. Li, Auteur ; Z.G. Wang, Auteur Année de publication : 2011 Article en page(s) : pp. 3281–3294 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Orientation  effect  Cyclic  deformation  Copper  single  crystals  Dislocation  patterns Résumé : This work reveals the formation mechanisms of saturation dislocation patterns in three typical multiple-slip oriented [0 0 1], [0 1 1] and View the MathML source copper single crystals. Compared with the single-slip oriented copper single crystals, the three multiple-slip oriented ones show very different dislocation patterns. It was found that the dislocation patterns in cyclically saturated copper single crystals are the Labyrinth structure for [0 0 1], wall structure for [0 1 1] and cell structure for View the MathML source, respectively. Based on a two-phase structure consisting of persistent slip bands and veins for single-slip orientation, the formation mechanisms of the dislocation patterns in multiple-slip oriented crystals are proposed as follows: the formation of the complex dislocation patterns depends on the activating slip system. The easy operation of the critical secondary slip system will contribute to the formation of the Labyrinth structure. The activation of the coplanar secondary slip system will be beneficial to formation of the cell structure. If no secondary slip system is activated, the wall structure is more prone to appear. Finally, the intrinsic relationship between various dislocation patterns and face centered cubic crystal structure was established. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000881 [article] Formation mechanisms of cyclic saturation dislocation patterns in [0 0 1], [0 1 1] and View the MathML source copper single crystals [texte imprimé] / P. Li, Auteur ; S.X. Li, Auteur ; Z.G. Wang, Auteur . - 2011 . - pp. 3281–3294. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3281–3294 Mots-clés : Orientation  effect  Cyclic  deformation  Copper  single  crystals  Dislocation  patterns Résumé : This work reveals the formation mechanisms of saturation dislocation patterns in three typical multiple-slip oriented [0 0 1], [0 1 1] and View the MathML source copper single crystals. Compared with the single-slip oriented copper single crystals, the three multiple-slip oriented ones show very different dislocation patterns. It was found that the dislocation patterns in cyclically saturated copper single crystals are the Labyrinth structure for [0 0 1], wall structure for [0 1 1] and cell structure for View the MathML source, respectively. Based on a two-phase structure consisting of persistent slip bands and veins for single-slip orientation, the formation mechanisms of the dislocation patterns in multiple-slip oriented crystals are proposed as follows: the formation of the complex dislocation patterns depends on the activating slip system. The easy operation of the critical secondary slip system will contribute to the formation of the Labyrinth structure. The activation of the coplanar secondary slip system will be beneficial to formation of the cell structure. If no secondary slip system is activated, the wall structure is more prone to appear. Finally, the intrinsic relationship between various dislocation patterns and face centered cubic crystal structure was established. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000881

Modeling homogeneous precipitation with an event-based Monte Carlo method / T. Jourdan in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3295–3302 Titre : Modeling homogeneous precipitation with an event-based Monte Carlo method : Application to the case of Fe–Cu Type de document : texte imprimé Auteurs : T. Jourdan, Auteur ; J.-L. Bocquet, Auteur ; F. Soisson, Auteur Année de publication : 2011 Article en page(s) : pp. 3295–3302 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Precipitation  Kinetics  Modelling  Monte  Carlo  techniques Résumé : A precipitation model for an event-based kinetic Monte Carlo (EKMC) method is presented. It is based on atomic-scale computations of the emission and absorption rates of monomers by clusters. Clusters are considered as single objects that emit monomers close to them, at higher rates than predicted by the mean field cluster dynamics method. We show that a law based on continuous diffusion equation can be used to account for absorption, provided the reaction distances between clusters are accurately computed. The model is shown to reproduce quantitatively results obtained by atomistic kinetic Monte Carlo methods when only monomers are mobile. The kinetics obtained by EKMC is faster than the one given by cluster dynamics, which highlights the limits of such a mean-field method, especially at high solute concentrations. When applied to the precipitation of Cu in Fe, which involves the mobility of clusters, the EKMC model shows good agreement with experimental results. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000893 [article] Modeling homogeneous precipitation with an event-based Monte Carlo method : Application to the case of Fe–Cu [texte imprimé] / T. Jourdan, Auteur ; J.-L. Bocquet, Auteur ; F. Soisson, Auteur . - 2011 . - pp. 3295–3302. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3295–3302 Mots-clés : Precipitation  Kinetics  Modelling  Monte  Carlo  techniques Résumé : A precipitation model for an event-based kinetic Monte Carlo (EKMC) method is presented. It is based on atomic-scale computations of the emission and absorption rates of monomers by clusters. Clusters are considered as single objects that emit monomers close to them, at higher rates than predicted by the mean field cluster dynamics method. We show that a law based on continuous diffusion equation can be used to account for absorption, provided the reaction distances between clusters are accurately computed. The model is shown to reproduce quantitatively results obtained by atomistic kinetic Monte Carlo methods when only monomers are mobile. The kinetics obtained by EKMC is faster than the one given by cluster dynamics, which highlights the limits of such a mean-field method, especially at high solute concentrations. When applied to the precipitation of Cu in Fe, which involves the mobility of clusters, the EKMC model shows good agreement with experimental results. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000893

A study of the microstructural evolution during selective laser melting of Ti–6Al–4V / Lore Thijs in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3303–3312 Titre : A study of the microstructural evolution during selective laser melting of Ti–6Al–4V Type de document : texte imprimé Auteurs : Lore Thijs, Auteur ; Frederik Verhaeghe, Auteur ; Tom Craeghs, Auteur Année de publication : 2011 Article en page(s) : pp. 3303–3312 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Selective  laser  melting  Additive  manufacturing  Laser  treatment  Titanium  alloys  Optical  microscopy Résumé : Selective laser melting (SLM) is an additive manufacturing technique in which functional, complex parts can be created directly by selectively melting layers of powder. This process is characterized by highly localized high heat inputs during very short interaction times and will therefore significantly affect the microstructure. In this research, the development of the microstructure of the Ti–6Al–4V alloy processed by SLM and the influence of the scanning parameters and scanning strategy on this microstructure are studied by light optical microscopy. The martensitic phase is present, and due to the occurrence of epitaxial growth, elongated grains emerge. The direction of these grains is directly related to the process parameters. At high heat inputs it was also found that the intermetallic phase Ti3Al is precipitated during the process. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000090X [article] A study of the microstructural evolution during selective laser melting of Ti–6Al–4V [texte imprimé] / Lore Thijs, Auteur ; Frederik Verhaeghe, Auteur ; Tom Craeghs, Auteur . - 2011 . - pp. 3303–3312. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3303–3312 Mots-clés : Selective  laser  melting  Additive  manufacturing  Laser  treatment  Titanium  alloys  Optical  microscopy Résumé : Selective laser melting (SLM) is an additive manufacturing technique in which functional, complex parts can be created directly by selectively melting layers of powder. This process is characterized by highly localized high heat inputs during very short interaction times and will therefore significantly affect the microstructure. In this research, the development of the microstructure of the Ti–6Al–4V alloy processed by SLM and the influence of the scanning parameters and scanning strategy on this microstructure are studied by light optical microscopy. The martensitic phase is present, and due to the occurrence of epitaxial growth, elongated grains emerge. The direction of these grains is directly related to the process parameters. At high heat inputs it was also found that the intermetallic phase Ti3Al is precipitated during the process. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000090X

Study of internal strain evolution in Zircaloy-2 using polycrystalline models / C. Mareau in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3313–3325 Titre : Study of internal strain evolution in Zircaloy-2 using polycrystalline models : Comparison between a rate-dependent and a rate-independent formulation Type de document : texte imprimé Auteurs : C. Mareau, Auteur ; M.R. Daymond, Auteur Année de publication : 2011 Article en page(s) : pp. 3313–3325 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Micromechanics  Twinning  Zirconium  Homogenization  Micromechanical  modeling Résumé : In the present paper, an elasto-viscoplastic model is proposed to describe the behavior of hexagonal close-packed materials where multiple deformation modes, including plastic slip and twinning, coexist. The model assists in interpreting the experimental lattice strains whose evolution is often complex because of the many deformation modes involved. The proposed rate-dependent model is compared with a previously developed rate-independent model by studying the development of internal strains in a moderately textured Zircaloy-2 slab. The comparison shows that most of the inflexions that are experimentally observed are well reproduced by the proposed model and the qualitative and quantitative agreement is generally better with the new rate-dependent formulation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000911 [article] Study of internal strain evolution in Zircaloy-2 using polycrystalline models : Comparison between a rate-dependent and a rate-independent formulation [texte imprimé] / C. Mareau, Auteur ; M.R. Daymond, Auteur . - 2011 . - pp. 3313–3325. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3313–3325 Mots-clés : Micromechanics  Twinning  Zirconium  Homogenization  Micromechanical  modeling Résumé : In the present paper, an elasto-viscoplastic model is proposed to describe the behavior of hexagonal close-packed materials where multiple deformation modes, including plastic slip and twinning, coexist. The model assists in interpreting the experimental lattice strains whose evolution is often complex because of the many deformation modes involved. The proposed rate-dependent model is compared with a previously developed rate-independent model by studying the development of internal strains in a moderately textured Zircaloy-2 slab. The comparison shows that most of the inflexions that are experimentally observed are well reproduced by the proposed model and the qualitative and quantitative agreement is generally better with the new rate-dependent formulation. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000911

On grain growth in the presence of mobile particles / V.Yu. Novikov in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3326–3331 Titre : On grain growth in the presence of mobile particles Type de document : texte imprimé Auteurs : V.Yu. Novikov, Auteur Année de publication : 2011 Article en page(s) : pp. 3326–3331 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Grain  growth  suppression  Grain  boundary  migration  Disperse  particles  Nanocrystalline  materials Résumé : The ability of second phase particles to migrate along with grain boundaries is shown to be determined not only by the particle mobility but also by the migration rate of the grain boundary where they locate. This leads to a duality in the mobile particle behaviour: they behave as either movable or immovable depending on the boundary migration rate. In the first case, they reduce the boundary mobility; in the second one they decrease the driving force for boundary migration. It is demonstrated by numerical modeling that mobile particles with low mobility can suppress grain growth even in nanocrystalline material, the limiting grains size being several times smaller than in the case of randomly distributed immobile particles. It is also shown that the Zener solution to the problem of the grain growth retardation by disperse particles is a specific case of the proposed approach. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000923 [article] On grain growth in the presence of mobile particles [texte imprimé] / V.Yu. Novikov, Auteur . - 2011 . - pp. 3326–3331. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3326–3331 Mots-clés : Grain  growth  suppression  Grain  boundary  migration  Disperse  particles  Nanocrystalline  materials Résumé : The ability of second phase particles to migrate along with grain boundaries is shown to be determined not only by the particle mobility but also by the migration rate of the grain boundary where they locate. This leads to a duality in the mobile particle behaviour: they behave as either movable or immovable depending on the boundary migration rate. In the first case, they reduce the boundary mobility; in the second one they decrease the driving force for boundary migration. It is demonstrated by numerical modeling that mobile particles with low mobility can suppress grain growth even in nanocrystalline material, the limiting grains size being several times smaller than in the case of randomly distributed immobile particles. It is also shown that the Zener solution to the problem of the grain growth retardation by disperse particles is a specific case of the proposed approach. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000923

A micromechanical formulation for piezoelectric fiber composites with nonlinear and viscoelastic constituents / Muliana, Anastasia H. in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3332–3344 Titre : A micromechanical formulation for piezoelectric fiber composites with nonlinear and viscoelastic constituents Type de document : texte imprimé Auteurs : Muliana, Anastasia H., Auteur Année de publication : 2011 Article en page(s) : pp. 3332–3344 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Piezoelectricity  Active  composites  Micromechanical  modeling  Viscoelasticity  High  electric  field Résumé : This study presents a simplified micromechanical model to predict electromechanical behaviors of piezocomposites, having ferroelectric fibers and polymer matrix. A nonlinear electromechanical constitutive model is formulated for the ferroelectric fibers, i.e. PZT fibers. The nonlinearity is due to polarization switching in the PZT materials under high electric field and compression stress. Phenomenological models are used to represent stress–strain and polarization–electric field hysteresis responses during polarization switching. The nonlinear electromechanical constitutive relation is verified using hysteresis polarization and strain responses of PZT-51. Effective responses of piezocomposites at various fiber volume contents, generated using the simplified micromechanical model, are also compared with available experimental data. The effects of viscoelastic polymer matrix on the overall electromechanical hysteresis and creep behaviors of piezocomposites are also examined. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000935 [article] A micromechanical formulation for piezoelectric fiber composites with nonlinear and viscoelastic constituents [texte imprimé] / Muliana, Anastasia H., Auteur . - 2011 . - pp. 3332–3344. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3332–3344 Mots-clés : Piezoelectricity  Active  composites  Micromechanical  modeling  Viscoelasticity  High  electric  field Résumé : This study presents a simplified micromechanical model to predict electromechanical behaviors of piezocomposites, having ferroelectric fibers and polymer matrix. A nonlinear electromechanical constitutive model is formulated for the ferroelectric fibers, i.e. PZT fibers. The nonlinearity is due to polarization switching in the PZT materials under high electric field and compression stress. Phenomenological models are used to represent stress–strain and polarization–electric field hysteresis responses during polarization switching. The nonlinear electromechanical constitutive relation is verified using hysteresis polarization and strain responses of PZT-51. Effective responses of piezocomposites at various fiber volume contents, generated using the simplified micromechanical model, are also compared with available experimental data. The effects of viscoelastic polymer matrix on the overall electromechanical hysteresis and creep behaviors of piezocomposites are also examined. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000935

Octasilsesquioxane-reinforced DGEBA and TGDDM epoxy nanocomposites / Shanmugam Nagendiran in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3345–3356 Titre : Octasilsesquioxane-reinforced DGEBA and TGDDM epoxy nanocomposites : Characterization of thermal, dielectric and morphological properties Type de document : texte imprimé Auteurs : Shanmugam Nagendiran, Auteur ; Muthukaruppan Alagar, Auteur ; Ian Hamerton, Auteur Année de publication : 2011 Article en page(s) : pp. 3345–3356 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : DGEBA  and  TGDDM  epoxy  resins  POSS  Nanocomposites  Thermal  and  dielectric  properties Résumé : Epoxy resin nanocomposites, based on the diglycidyl ether of bisphenol-A (DGEBA) and tetraglycidyl diamino diphenyl methane (TGDDM), are prepared via in situ co-polymerization with 4,4′-diaminodiphenylsulfone (DDS) in the presence of octa-aminophenyl silsesquioxane (OAPS) at levels of up to 20 wt.% of the latter. The curing reaction involving epoxy, DDS and OAPS is investigated using Fourier transform infrared (FTIR) spectroscopy. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperatures of the polyhedral oligomeric silsesquioxane (POSS) containing nanocomposites are higher than the corresponding neat epoxy systems at lower concentrations of POSS (⩽3 wt.%). Thermogravimetric analysis indicates that the POSS–epoxy nanocomposites display high ceramic yields, suggesting improved flame retardancy. The increasing concentration of OAPS into epoxy–amine networks exhibits a decreasing trend in the values of dielectric constant compared with those values obtained from neat epoxy systems. The higher epoxy functionality present in TGDDM leads to nanocomposites which possess enhanced thermal stability and higher dielectric constants than the DGEBA-based nanocomposites. X-ray diffraction analysis reveals that the molecular level reinforcement of POSS cages occurs in both the cases of DGEBA- and TGDDM-based hybrid epoxy nanocomposites. Furthermore, homogeneous dispersion of POSS cages in the epoxy matrices is evidenced by scanning electron microscopy, which further confirms that the POSS molecule has become an integral part of the organic–inorganic inter-cross-linked network systems. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000947 [article] Octasilsesquioxane-reinforced DGEBA and TGDDM epoxy nanocomposites : Characterization of thermal, dielectric and morphological properties [texte imprimé] / Shanmugam Nagendiran, Auteur ; Muthukaruppan Alagar, Auteur ; Ian Hamerton, Auteur . - 2011 . - pp. 3345–3356. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3345–3356 Mots-clés : DGEBA  and  TGDDM  epoxy  resins  POSS  Nanocomposites  Thermal  and  dielectric  properties Résumé : Epoxy resin nanocomposites, based on the diglycidyl ether of bisphenol-A (DGEBA) and tetraglycidyl diamino diphenyl methane (TGDDM), are prepared via in situ co-polymerization with 4,4′-diaminodiphenylsulfone (DDS) in the presence of octa-aminophenyl silsesquioxane (OAPS) at levels of up to 20 wt.% of the latter. The curing reaction involving epoxy, DDS and OAPS is investigated using Fourier transform infrared (FTIR) spectroscopy. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperatures of the polyhedral oligomeric silsesquioxane (POSS) containing nanocomposites are higher than the corresponding neat epoxy systems at lower concentrations of POSS (⩽3 wt.%). Thermogravimetric analysis indicates that the POSS–epoxy nanocomposites display high ceramic yields, suggesting improved flame retardancy. The increasing concentration of OAPS into epoxy–amine networks exhibits a decreasing trend in the values of dielectric constant compared with those values obtained from neat epoxy systems. The higher epoxy functionality present in TGDDM leads to nanocomposites which possess enhanced thermal stability and higher dielectric constants than the DGEBA-based nanocomposites. X-ray diffraction analysis reveals that the molecular level reinforcement of POSS cages occurs in both the cases of DGEBA- and TGDDM-based hybrid epoxy nanocomposites. Furthermore, homogeneous dispersion of POSS cages in the epoxy matrices is evidenced by scanning electron microscopy, which further confirms that the POSS molecule has become an integral part of the organic–inorganic inter-cross-linked network systems. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000947

EBSD studies of the stress-induced B2–B19′ martensitic transformation in NiTi tubes under uniaxial tension and compression / S.C. Mao in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3357–3366 Titre : EBSD studies of the stress-induced B2–B19′ martensitic transformation in NiTi tubes under uniaxial tension and compression Type de document : texte imprimé Auteurs : S.C. Mao, Auteur ; J.F. Luo, Auteur ; Z. Zhang, Auteur Année de publication : 2011 Article en page(s) : pp. 3357–3366 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Shape  memory  alloys  (SMA)  Martensitic  phase  transformation  Electron  backscattering  diffraction  (EBSD)  In  situ Résumé : In situ electron backscattering diffraction (EBSD) investigations were conducted on polycrystalline NiTi tube specimens during tensile and compressive deformation. The long-range cooperative and catalytic martensitic transformation under tension induces the transformation to proceed in the form of helical Lüders band. Propagation of the band is closely related to the spatial distribution of the orientations of individual grains. In uniaxial compression, the larger variation in Schmid factors, and consequently the larger variation in the critical transformation stresses among grains, leads to a homogeneous martensitic transformation, and therefore the absence of the Lüders band. To interpret the observed tension–compression asymmetry, a crystallographic model of the critical transformation stress and transformation strain for polycrystalline NiTi under tension and compression is proposed. The model defines three crystallographic regions: tension-favorable, compression-favorable and neutral zones. The orientation population in which tensile strains are larger than compressive strains is much higher than that of orientations with higher compressive strains. For resolved shear stress, orientation populations favoring tension and compression do not show any great difference. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000959 [article] EBSD studies of the stress-induced B2–B19′ martensitic transformation in NiTi tubes under uniaxial tension and compression [texte imprimé] / S.C. Mao, Auteur ; J.F. Luo, Auteur ; Z. Zhang, Auteur . - 2011 . - pp. 3357–3366. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3357–3366 Mots-clés : Shape  memory  alloys  (SMA)  Martensitic  phase  transformation  Electron  backscattering  diffraction  (EBSD)  In  situ Résumé : In situ electron backscattering diffraction (EBSD) investigations were conducted on polycrystalline NiTi tube specimens during tensile and compressive deformation. The long-range cooperative and catalytic martensitic transformation under tension induces the transformation to proceed in the form of helical Lüders band. Propagation of the band is closely related to the spatial distribution of the orientations of individual grains. In uniaxial compression, the larger variation in Schmid factors, and consequently the larger variation in the critical transformation stresses among grains, leads to a homogeneous martensitic transformation, and therefore the absence of the Lüders band. To interpret the observed tension–compression asymmetry, a crystallographic model of the critical transformation stress and transformation strain for polycrystalline NiTi under tension and compression is proposed. The model defines three crystallographic regions: tension-favorable, compression-favorable and neutral zones. The orientation population in which tensile strains are larger than compressive strains is much higher than that of orientations with higher compressive strains. For resolved shear stress, orientation populations favoring tension and compression do not show any great difference. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000959

Phase transformations in nickel sulphide / Oussama Yousfi in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3367–3380 Titre : Phase transformations in nickel sulphide : Microstructures and mechanisms Type de document : texte imprimé Auteurs : Oussama Yousfi, Auteur ; Patricia Donnadieu, Auteur ; Bréchet, Yves, Auteur Année de publication : 2011 Article en page(s) : pp. 3367–3380 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel  sulphides  Phase  transformation  Microstructure  Massive  transformation  Diffusive  transformation Résumé : Nickel sulphide inclusions are known to be responsible for delayed fracture in tempered glasses due to phase transformation within the inclusion. Microstructural identification of the phase transformation mechanisms in the Ni–S system close to the NiS composition were carried out on a series of partially transformed states. Observations allow to investigate the morphological evolution during transformation, the phase orientation relationships and the first stages of the transformation were investigated by optical microscopy, electron backscatter diffraction, and scanning and transmission electron microscopy. The transformation mechanisms change significantly with the change in sulphur content of the α-NiS phase. Massive transformation is observed for near-stoichiometric composition. For overstoichiometric composition, the transformation is controlled by a long-range diffusion mechanism. The influence of stoichiometry and impurities (Fe) on the microstructural evolution and transformation mechanisms has also been studied. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000972 [article] Phase transformations in nickel sulphide : Microstructures and mechanisms [texte imprimé] / Oussama Yousfi, Auteur ; Patricia Donnadieu, Auteur ; Bréchet, Yves, Auteur . - 2011 . - pp. 3367–3380. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3367–3380 Mots-clés : Nickel  sulphides  Phase  transformation  Microstructure  Massive  transformation  Diffusive  transformation Résumé : Nickel sulphide inclusions are known to be responsible for delayed fracture in tempered glasses due to phase transformation within the inclusion. Microstructural identification of the phase transformation mechanisms in the Ni–S system close to the NiS composition were carried out on a series of partially transformed states. Observations allow to investigate the morphological evolution during transformation, the phase orientation relationships and the first stages of the transformation were investigated by optical microscopy, electron backscatter diffraction, and scanning and transmission electron microscopy. The transformation mechanisms change significantly with the change in sulphur content of the α-NiS phase. Massive transformation is observed for near-stoichiometric composition. For overstoichiometric composition, the transformation is controlled by a long-range diffusion mechanism. The influence of stoichiometry and impurities (Fe) on the microstructural evolution and transformation mechanisms has also been studied. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000972

Role of additives in LiBH4–MgH2 reactive hydride composites for sorption kinetics / U. Bösenberg in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3381–3389 Titre : Role of additives in LiBH4–MgH2 reactive hydride composites for sorption kinetics Type de document : texte imprimé Auteurs : U. Bösenberg, Auteur ; J.W. Kim, Auteur ; D. Gosslar, Auteur Année de publication : 2011 Article en page(s) : pp. 3381–3389 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hydrogen  storage  Nanocomposites  Heterogeneous  nucleation  of  phase  transformations  Phase  transformation  kinetics Résumé : The influence of additives on the reaction kinetics and microstructure refinement in LiBH4–MgH2 composites is investigated in detail. Indications of the rate-limiting processes during the reactions are obtained by comparison of the measured reaction kinetics with simulations with one specific rate-limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in situ X-ray diffraction measurements. During desorption, the hydrogen is released at a constant rate, which is possibly correlated with the one-dimensional growth of MgB2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of microstructure on the reaction kinetics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000984 [article] Role of additives in LiBH4–MgH2 reactive hydride composites for sorption kinetics [texte imprimé] / U. Bösenberg, Auteur ; J.W. Kim, Auteur ; D. Gosslar, Auteur . - 2011 . - pp. 3381–3389. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3381–3389 Mots-clés : Hydrogen  storage  Nanocomposites  Heterogeneous  nucleation  of  phase  transformations  Phase  transformation  kinetics Résumé : The influence of additives on the reaction kinetics and microstructure refinement in LiBH4–MgH2 composites is investigated in detail. Indications of the rate-limiting processes during the reactions are obtained by comparison of the measured reaction kinetics with simulations with one specific rate-limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in situ X-ray diffraction measurements. During desorption, the hydrogen is released at a constant rate, which is possibly correlated with the one-dimensional growth of MgB2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of microstructure on the reaction kinetics. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000984

Spark plasma sintering of a commercially available granulated zirconia powder / Guillaume Bernard-Granger in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3390–3399 Titre : Spark plasma sintering of a commercially available granulated zirconia powder : Comparison with hot-pressing Type de document : texte imprimé Auteurs : Guillaume Bernard-Granger, Auteur ; Ahmed Addad, Auteur ; Gilbert Fantozzi, Auteur Année de publication : 2011 Article en page(s) : pp. 3390–3399 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ceramics  Sintering  Transmission  electron  microscopy  (TEM)  Electrical  resistivity/conductivity Résumé : A commercially available granulated TZ3Y powder has been sintered by hot-pressing (HP). The “grain size/relative density” relationship, referred to here as the “sintering path”, has been established for a constant value of the heating rate (25 °C min−1) and a constant value of the macroscopic applied pressure (100 MPa). It has then been compared to that obtained previously on the same powder but sintered by spark plasma sintering (SPS, heating rate of 50 °C min−1, same applied macroscopic pressure). By coupling the analysis of a sintering law (derived from creep rate equations) and comparative observations of sintered samples using transmission electron microscopy, a hypothesis about the densification mechanism(s) involved in SPS and HP has been proposed. Slight differences in the densification mechanisms lead to scars in the microstructure that explain the higher total ionic conductivity measured, in the temperature range 300–550 °C, when SPS is used for sintering. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000996 [article] Spark plasma sintering of a commercially available granulated zirconia powder : Comparison with hot-pressing [texte imprimé] / Guillaume Bernard-Granger, Auteur ; Ahmed Addad, Auteur ; Gilbert Fantozzi, Auteur . - 2011 . - pp. 3390–3399. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3390–3399 Mots-clés : Ceramics  Sintering  Transmission  electron  microscopy  (TEM)  Electrical  resistivity/conductivity Résumé : A commercially available granulated TZ3Y powder has been sintered by hot-pressing (HP). The “grain size/relative density” relationship, referred to here as the “sintering path”, has been established for a constant value of the heating rate (25 °C min−1) and a constant value of the macroscopic applied pressure (100 MPa). It has then been compared to that obtained previously on the same powder but sintered by spark plasma sintering (SPS, heating rate of 50 °C min−1, same applied macroscopic pressure). By coupling the analysis of a sintering law (derived from creep rate equations) and comparative observations of sintered samples using transmission electron microscopy, a hypothesis about the densification mechanism(s) involved in SPS and HP has been proposed. Slight differences in the densification mechanisms lead to scars in the microstructure that explain the higher total ionic conductivity measured, in the temperature range 300–550 °C, when SPS is used for sintering. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000996

Influence of cluster mobility on Cu precipitation in α-Fe / T. Jourdan in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3400–3405 Titre : Influence of cluster mobility on Cu precipitation in α-Fe : A cluster dynamics modeling Type de document : texte imprimé Auteurs : T. Jourdan, Auteur ; F. Soisson, Auteur ; E. Clouet, Auteur Année de publication : 2011 Article en page(s) : pp. 3400–3405 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Precipitation  Kinetics  Modeling  Monte  Carlo  techniques Résumé : A cluster dynamics model has been parametrized to quantitatively reproduce results obtained by atomistic kinetic Monte Carlo (AKMC) modeling on the precipitation of Cu in α-Fe under thermal aging. The cluster mobility, highlighted by AKMC, is shown to have a significant effect on the precipitation kinetics and can reconcile the experimentally observed fast kinetics with the relatively low diffusivity of Cu monomers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000100X [article] Influence of cluster mobility on Cu precipitation in α-Fe : A cluster dynamics modeling [texte imprimé] / T. Jourdan, Auteur ; F. Soisson, Auteur ; E. Clouet, Auteur . - 2011 . - pp. 3400–3405. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3400–3405 Mots-clés : Precipitation  Kinetics  Modeling  Monte  Carlo  techniques Résumé : A cluster dynamics model has been parametrized to quantitatively reproduce results obtained by atomistic kinetic Monte Carlo (AKMC) modeling on the precipitation of Cu in α-Fe under thermal aging. The cluster mobility, highlighted by AKMC, is shown to have a significant effect on the precipitation kinetics and can reconcile the experimentally observed fast kinetics with the relatively low diffusivity of Cu monomers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000100X

Surfaces, interfaces and phase transitions in Al–In monotectic alloys / I. Kaban in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3406–3414 Titre : Surfaces, interfaces and phase transitions in Al–In monotectic alloys Type de document : texte imprimé Auteurs : I. Kaban, Auteur ; S. Curiotto, Auteur ; D. Chatain, Auteur Année de publication : 2011 Article en page(s) : pp. 3406–3414 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Al–In  Monotectic  Complete  wetting  Surface  transition  Density Résumé : Surface and bulk liquid phase transitions are measured by a unique method currently used to determine surface and interfacial tension of liquid alloys. Focusing on the Al–In system, the location of the liquid miscibility gap was determined from the critical to the monotectic temperatures. The surface tensions of nine liquid alloys, the interfacial tension between coexisting liquids and their densities were measured as a function of temperature. Implementing the bulk data extracted from the asymmetric miscibility gap into a sub-regular model reproduced the experimental surface and interfacial tensions. The wetting temperature was estimated to lie well below the monotectic temperature. The micrometer thickness of the In-rich films which wet the surface of the Al-rich liquid phase after solidification is suggested to be due to the growth of the equilibrium wetting film by diffusion from the Al-rich phase during cooling. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001011 [article] Surfaces, interfaces and phase transitions in Al–In monotectic alloys [texte imprimé] / I. Kaban, Auteur ; S. Curiotto, Auteur ; D. Chatain, Auteur . - 2011 . - pp. 3406–3414. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3406–3414 Mots-clés : Al–In  Monotectic  Complete  wetting  Surface  transition  Density Résumé : Surface and bulk liquid phase transitions are measured by a unique method currently used to determine surface and interfacial tension of liquid alloys. Focusing on the Al–In system, the location of the liquid miscibility gap was determined from the critical to the monotectic temperatures. The surface tensions of nine liquid alloys, the interfacial tension between coexisting liquids and their densities were measured as a function of temperature. Implementing the bulk data extracted from the asymmetric miscibility gap into a sub-regular model reproduced the experimental surface and interfacial tensions. The wetting temperature was estimated to lie well below the monotectic temperature. The micrometer thickness of the In-rich films which wet the surface of the Al-rich liquid phase after solidification is suggested to be due to the growth of the equilibrium wetting film by diffusion from the Al-rich phase during cooling. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001011

Comparing properties of substrate-constrained and freestanding epitaxial Ni–Mn–Ga films / Anja Backen in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3415–3421 Titre : Comparing properties of substrate-constrained and freestanding epitaxial Ni–Mn–Ga films Type de document : texte imprimé Auteurs : Anja Backen, Auteur ; Srinivasa R. Yeduru, Auteur ; Manfred Kohl, Auteur Année de publication : 2011 Article en page(s) : pp. 3415–3421 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnetic  shape  memory  alloy  Epitaxial  Thin  films  Interfaces  Ni–Mn–Ga Résumé : In order to use the magnetic shape memory alloy Ni–Mn–Ga with its high achievable strain of up to 10% for microactuators, freestanding epitaxial films are required. Here we show that these conditions can be fulfilled when using chromium as a sacrificial layer. The low misfit towards Ni–Mn–Ga enables epitaxial growth. Furthermore, Cr can afterwards be removed selectively by wet-chemical etching and during deposition no significant interdiffusion is observed. The structure, microstructure and magnetic properties of micrometer thick films are not affected by the etching process. Films are ferromagnetic at room temperature and we observe the coexistence of non-modulated (NM) and seven layered modulated (14 M) martensite. Tensile stress–strain measurement of a freestanding bridge reveals a broad strain plateau of 12% at a twinning stress of 25 MPa, indicating reorientation of NM variants. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001023 [article] Comparing properties of substrate-constrained and freestanding epitaxial Ni–Mn–Ga films [texte imprimé] / Anja Backen, Auteur ; Srinivasa R. Yeduru, Auteur ; Manfred Kohl, Auteur . - 2011 . - pp. 3415–3421. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3415–3421 Mots-clés : Magnetic  shape  memory  alloy  Epitaxial  Thin  films  Interfaces  Ni–Mn–Ga Résumé : In order to use the magnetic shape memory alloy Ni–Mn–Ga with its high achievable strain of up to 10% for microactuators, freestanding epitaxial films are required. Here we show that these conditions can be fulfilled when using chromium as a sacrificial layer. The low misfit towards Ni–Mn–Ga enables epitaxial growth. Furthermore, Cr can afterwards be removed selectively by wet-chemical etching and during deposition no significant interdiffusion is observed. The structure, microstructure and magnetic properties of micrometer thick films are not affected by the etching process. Films are ferromagnetic at room temperature and we observe the coexistence of non-modulated (NM) and seven layered modulated (14 M) martensite. Tensile stress–strain measurement of a freestanding bridge reveals a broad strain plateau of 12% at a twinning stress of 25 MPa, indicating reorientation of NM variants. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001023

Thermodynamic evaluation of hypereutectic Al–Si (A390) alloy with addition of Mg / Alireza Hekmat-Ardakan in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3422–3428 Titre : Thermodynamic evaluation of hypereutectic Al–Si (A390) alloy with addition of Mg Type de document : texte imprimé Auteurs : Alireza Hekmat-Ardakan, Auteur ; Frank Ajersch, Auteur Année de publication : 2011 Article en page(s) : pp. 3422–3428 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thermodynamic  Factsage  Aluminum  alloys  Eutectic  solidification  Magnesium Résumé : This paper presents the thermodynamic evaluation of A390 hypereutectic Al–Si alloy (Al–17% Si–4.5% Cu–0.5% Mg) and alloys up to 10% Mg, using the Factsage® software. Two critical compositions were detected at 4.2% and 7.2% Mg where the temperatures of the liquidus, the start of the binary and of the ternary eutectic reaction are changed. These critical compositions show differences in the formation of Mg2Si intermetallic particles during the solidification interval. For compositions up to 4.2% Mg, the Mg2Si intermetallic phase first appears in the ternary eutectic zone. With Mg contents between 4.2% and 7.2%, Mg2Si particle appears in both the binary and ternary eutectic reactions. Above 7.2% Mg, it solidifies as a primary phase and also during the binary and ternary reactions. The calculated liquid fraction vs. temperature curves also showed a decrease of the eutectic formation temperature (knee point temperature) with the addition of Mg content up to 4.2% Mg. This temperature becomes almost constant up to 10% Mg. The calculation of eutectic formation temperature shows a good agreement with differential scanning calorimetry (DSC) tests. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001035 [article] Thermodynamic evaluation of hypereutectic Al–Si (A390) alloy with addition of Mg [texte imprimé] / Alireza Hekmat-Ardakan, Auteur ; Frank Ajersch, Auteur . - 2011 . - pp. 3422–3428. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3422–3428 Mots-clés : Thermodynamic  Factsage  Aluminum  alloys  Eutectic  solidification  Magnesium Résumé : This paper presents the thermodynamic evaluation of A390 hypereutectic Al–Si alloy (Al–17% Si–4.5% Cu–0.5% Mg) and alloys up to 10% Mg, using the Factsage® software. Two critical compositions were detected at 4.2% and 7.2% Mg where the temperatures of the liquidus, the start of the binary and of the ternary eutectic reaction are changed. These critical compositions show differences in the formation of Mg2Si intermetallic particles during the solidification interval. For compositions up to 4.2% Mg, the Mg2Si intermetallic phase first appears in the ternary eutectic zone. With Mg contents between 4.2% and 7.2%, Mg2Si particle appears in both the binary and ternary eutectic reactions. Above 7.2% Mg, it solidifies as a primary phase and also during the binary and ternary reactions. The calculated liquid fraction vs. temperature curves also showed a decrease of the eutectic formation temperature (knee point temperature) with the addition of Mg content up to 4.2% Mg. This temperature becomes almost constant up to 10% Mg. The calculation of eutectic formation temperature shows a good agreement with differential scanning calorimetry (DSC) tests. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001035

Kinetics of Ag3Sn growth in Ag–Sn–Ag system during transient liquid phase soldering process / J.F. Li in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3429–3443 Titre : Kinetics of Ag3Sn growth in Ag–Sn–Ag system during transient liquid phase soldering process Type de document : texte imprimé Auteurs : J.F. Li, Auteur ; P. A. Agyakwa, Auteur ; C.M. Johnson, Auteur Année de publication : 2011 Article en page(s) : pp. 3429–3443 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Transient  liquid  phase  (TLP)  soldering  Interface  Intermetallic  compounds  Kinetics  Differential  scanning  calorimetry  (DSC) Résumé : The kinetics of the interfacial reaction of a thin layer of Sn sandwiched between two pieces of Ag foil has been investigated at temperatures of 260 °C, 300 °C and 340 °C. A time dependence of the form t1/n with n = 3 was obtained for the kinetics of both the consumption of the Sn remaining and the thickening growth of the Ag3Sn scallops formed between Sn and Ag. Such a result can be explained well using the model of grain boundary/molten channel-controlled growth of intermetallic compounds. In this case, the diffusion of Ag atoms through the molten channels existing between the previously formed Ag3Sn scallops is the controlling mechanism for the kinetics. We also report here the derived kinetic constants including reaction constants and the associated activation energy for guiding the practical transient liquid phase soldering of the Ag–Sn–Ag system. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001047 [article] Kinetics of Ag3Sn growth in Ag–Sn–Ag system during transient liquid phase soldering process [texte imprimé] / J.F. Li, Auteur ; P. A. Agyakwa, Auteur ; C.M. Johnson, Auteur . - 2011 . - pp. 3429–3443. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3429–3443 Mots-clés : Transient  liquid  phase  (TLP)  soldering  Interface  Intermetallic  compounds  Kinetics  Differential  scanning  calorimetry  (DSC) Résumé : The kinetics of the interfacial reaction of a thin layer of Sn sandwiched between two pieces of Ag foil has been investigated at temperatures of 260 °C, 300 °C and 340 °C. A time dependence of the form t1/n with n = 3 was obtained for the kinetics of both the consumption of the Sn remaining and the thickening growth of the Ag3Sn scallops formed between Sn and Ag. Such a result can be explained well using the model of grain boundary/molten channel-controlled growth of intermetallic compounds. In this case, the diffusion of Ag atoms through the molten channels existing between the previously formed Ag3Sn scallops is the controlling mechanism for the kinetics. We also report here the derived kinetic constants including reaction constants and the associated activation energy for guiding the practical transient liquid phase soldering of the Ag–Sn–Ag system. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001047

Influence of Ni on martensitic phase transformations in NiTi shape memory alloys / J. Frenzel in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3444–3458 Titre : Influence of Ni on martensitic phase transformations in NiTi shape memory alloys Type de document : texte imprimé Auteurs : J. Frenzel, Auteur ; E.P. George, Auteur ; A. Dlouhy, Auteur Année de publication : 2011 Article en page(s) : pp. 3444–3458 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : NiTi  shape  memory  alloys  Phase  transformation  temperatures  Thermodynamics  Vacuum  arc  melting  Hysteresis  width Résumé : High-precision data on phase transformation temperatures in NiTi, including numerical expressions for the effect of Ni on MS, MF, AS, AF and T0, are obtained, and the reasons for the large experimental scatter observed in previous studies are discussed. Clear experimental evidence is provided confirming the predictions of Tang et al. 1999 [19] regarding deviations from a linear relation between the thermodynamic equilibrium temperature and Ni concentration. In addition to affecting the phase transition temperatures, increasing Ni contents are found to decrease the width of thermal hysteresis and the heat of transformation. These findings are rationalized on the basis of the crystallographic data of Prokoshkin et al. 2004 [68] and the theory of Ball and James [25]. The results show that it is important to document carefully the details of the arc-melting procedure used to make shape memory alloys and that, if the effects of processing are properly accounted for, precise values for the Ni concentration of the NiTi matrix can be obtained. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001059 [article] Influence of Ni on martensitic phase transformations in NiTi shape memory alloys [texte imprimé] / J. Frenzel, Auteur ; E.P. George, Auteur ; A. Dlouhy, Auteur . - 2011 . - pp. 3444–3458. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3444–3458 Mots-clés : NiTi  shape  memory  alloys  Phase  transformation  temperatures  Thermodynamics  Vacuum  arc  melting  Hysteresis  width Résumé : High-precision data on phase transformation temperatures in NiTi, including numerical expressions for the effect of Ni on MS, MF, AS, AF and T0, are obtained, and the reasons for the large experimental scatter observed in previous studies are discussed. Clear experimental evidence is provided confirming the predictions of Tang et al. 1999 [19] regarding deviations from a linear relation between the thermodynamic equilibrium temperature and Ni concentration. In addition to affecting the phase transition temperatures, increasing Ni contents are found to decrease the width of thermal hysteresis and the heat of transformation. These findings are rationalized on the basis of the crystallographic data of Prokoshkin et al. 2004 [68] and the theory of Ball and James [25]. The results show that it is important to document carefully the details of the arc-melting procedure used to make shape memory alloys and that, if the effects of processing are properly accounted for, precise values for the Ni concentration of the NiTi matrix can be obtained. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001059

Neutron Larmor diffraction measurements for materials science / J. Repper in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3459–3467 Titre : Neutron Larmor diffraction measurements for materials science Type de document : texte imprimé Auteurs : J. Repper, Auteur ; T. Keller, Auteur ; M. Hofmann, Auteur Année de publication : 2011 Article en page(s) : pp. 3459–3467 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Larmor  diffraction  Neutron  diffraction  Precipitation  Nickel  alloys Résumé : Neutron Larmor diffraction (LD) is a high-resolution diffraction technique based on the Larmor precession of polarized neutrons. In contrast to conventional diffraction, LD does not depend on the accurate measurement of Bragg angles, and thus the resolution is independent of the beam collimation and monochromaticity. At present, a relative resolution for the determination of the crystal lattice spacing d of Δd/d∼10-6 is achieved, i.e. at least one order of magnitude superior to conventional neutron or X-ray techniques. This work is a first step to explore the application of LD to high-resolution problems in the analysis of residual stresses, where both the accurate measurement of absolute d values and the possibility of measuring type II and III stresses may provide additional information beyond those accessible by conventional diffraction techniques. Data obtained from Inconel 718 samples are presented. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001060 [article] Neutron Larmor diffraction measurements for materials science [texte imprimé] / J. Repper, Auteur ; T. Keller, Auteur ; M. Hofmann, Auteur . - 2011 . - pp. 3459–3467. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3459–3467 Mots-clés : Larmor  diffraction  Neutron  diffraction  Precipitation  Nickel  alloys Résumé : Neutron Larmor diffraction (LD) is a high-resolution diffraction technique based on the Larmor precession of polarized neutrons. In contrast to conventional diffraction, LD does not depend on the accurate measurement of Bragg angles, and thus the resolution is independent of the beam collimation and monochromaticity. At present, a relative resolution for the determination of the crystal lattice spacing d of Δd/d∼10-6 is achieved, i.e. at least one order of magnitude superior to conventional neutron or X-ray techniques. This work is a first step to explore the application of LD to high-resolution problems in the analysis of residual stresses, where both the accurate measurement of absolute d values and the possibility of measuring type II and III stresses may provide additional information beyond those accessible by conventional diffraction techniques. Data obtained from Inconel 718 samples are presented. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001060

Cu deficiency in multi-stage co-evaporated Cu(In,Ga)Se2 for solar cells applications / R. Caballero in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3468–3476 Titre : Cu deficiency in multi-stage co-evaporated Cu(In,Ga)Se2 for solar cells applications : Microstructure and Ga in-depth alloying Type de document : texte imprimé Auteurs : R. Caballero, Auteur ; V. Izquierdo-Roca, Auteur ; X. Fontané, Auteur Année de publication : 2011 Article en page(s) : pp. 3468–3476 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Cu  content  Cu(In,Ga)Se2  thin  films  Raman  spectroscopy  Scanning  electron  microscopy  Solar  cells Résumé : The objective of this work is to study the influence of the maximum Cu content during the deposition of Cu(In,Ga)Se2 (CIGSe) by multi-stage co-evaporation on the phases present in the final film, the film structure and the electrical properties of resulting solar cell devices. The variation of the composition is controlled by the Cu content in stage 2 of the deposition process. The different phases are identified by Raman spectroscopy. The in-depth Ga gradient distribution is investigated by in-depth resolved Raman scattering and secondary neutral mass spectroscopy. The morphology of the devices is studied by scanning electron microscopy. Efficiencies of 9.2% are obtained for ordered-vacancy-compound-based cells with a Cu/(In + Ga) ratio = 0.35, showing the system’s flexibility. This work supports the current growth model: a small amount of Cu excess during the absorber process is required to obtain a quality microstructure and high performance devices. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001072 [article] Cu deficiency in multi-stage co-evaporated Cu(In,Ga)Se2 for solar cells applications : Microstructure and Ga in-depth alloying [texte imprimé] / R. Caballero, Auteur ; V. Izquierdo-Roca, Auteur ; X. Fontané, Auteur . - 2011 . - pp. 3468–3476. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3468–3476 Mots-clés : Cu  content  Cu(In,Ga)Se2  thin  films  Raman  spectroscopy  Scanning  electron  microscopy  Solar  cells Résumé : The objective of this work is to study the influence of the maximum Cu content during the deposition of Cu(In,Ga)Se2 (CIGSe) by multi-stage co-evaporation on the phases present in the final film, the film structure and the electrical properties of resulting solar cell devices. The variation of the composition is controlled by the Cu content in stage 2 of the deposition process. The different phases are identified by Raman spectroscopy. The in-depth Ga gradient distribution is investigated by in-depth resolved Raman scattering and secondary neutral mass spectroscopy. The morphology of the devices is studied by scanning electron microscopy. Efficiencies of 9.2% are obtained for ordered-vacancy-compound-based cells with a Cu/(In + Ga) ratio = 0.35, showing the system’s flexibility. This work supports the current growth model: a small amount of Cu excess during the absorber process is required to obtain a quality microstructure and high performance devices. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001072

Interphase boundary structure and accommodation mechanism of lenticular martensite in Fe–Ni alloys / A. Shibata in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3477–3492 Titre : Interphase boundary structure and accommodation mechanism of lenticular martensite in Fe–Ni alloys Type de document : texte imprimé Auteurs : A. Shibata, Auteur ; T. Furuhara, Auteur ; T. Maki, Auteur Année de publication : 2011 Article en page(s) : pp. 3477–3492 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Martensitic  transformation  Interface  structure  TEM  HREM  Lenticular  martensite Résumé : This study investigates the interphase boundary structures of lenticular martensites in Fe–33Ni and Fe–31Ni, and discusses the accommodation mechanism for transformation strain. Despite the large difference in the macroscopic morphology of the interphase boundary, the nature of interfacial dislocations in both alloys is almost the same; there are two sets of screw dislocations with a/2 [View the MathML source View the MathML source 1]M and a/2 [1 View the MathML source 1]M Burgers vectors on the interphase boundary. On the basis of the array of interfacial dislocations, the shear planes of dislocations with a/2 [View the MathML source View the MathML source 1]M and a/2 [1 View the MathML source 1]M Burgers vectors were determined to be (1 1 2)M (=(1 0 1)A) and (View the MathML source 1 2)M (=(0 1 1)A). Two sets of interfacial dislocations accommodate the atomistic misfit strain due to the change in the stacking sequence and the shape of parallel close packed planes. The macroscopic transformation strain and elastic strain energy of lenticular martensite are also reduced by the presence of the observed lattice invariant deformations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001084 [article] Interphase boundary structure and accommodation mechanism of lenticular martensite in Fe–Ni alloys [texte imprimé] / A. Shibata, Auteur ; T. Furuhara, Auteur ; T. Maki, Auteur . - 2011 . - pp. 3477–3492. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3477–3492 Mots-clés : Martensitic  transformation  Interface  structure  TEM  HREM  Lenticular  martensite Résumé : This study investigates the interphase boundary structures of lenticular martensites in Fe–33Ni and Fe–31Ni, and discusses the accommodation mechanism for transformation strain. Despite the large difference in the macroscopic morphology of the interphase boundary, the nature of interfacial dislocations in both alloys is almost the same; there are two sets of screw dislocations with a/2 [View the MathML source View the MathML source 1]M and a/2 [1 View the MathML source 1]M Burgers vectors on the interphase boundary. On the basis of the array of interfacial dislocations, the shear planes of dislocations with a/2 [View the MathML source View the MathML source 1]M and a/2 [1 View the MathML source 1]M Burgers vectors were determined to be (1 1 2)M (=(1 0 1)A) and (View the MathML source 1 2)M (=(0 1 1)A). Two sets of interfacial dislocations accommodate the atomistic misfit strain due to the change in the stacking sequence and the shape of parallel close packed planes. The macroscopic transformation strain and elastic strain energy of lenticular martensite are also reduced by the presence of the observed lattice invariant deformations. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001084

Kinetics of dislocations in pure Fe / D. Caillard in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3493–3503 Titre : Kinetics of dislocations in pure Fe : Part I. In situ straining experiments at room temperature Type de document : texte imprimé Auteurs : D. Caillard, Auteur Année de publication : 2011 Article en page(s) : pp. 3493–3503 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Iron  Dislocation  mobility  Plastic  deformation  Thermally  activated  processes Résumé : In situ straining experiments have been carried out in pure Fe, in order to determine the geometry and the kinetics of dislocation glide at room temperature. Straight screw dislocations glide slowly in {1 1 0} elemental slip planes, at a velocity proportional to their length, whereas curved non-screw parts are highly mobile. The exact loop shape can yield the local stress as well as the difference of core energy between pure screw and near-screw orientations. The velocity–stress dependence of screws has been measured at the scale of a single dislocation source, and compared with macroscopic activation areas. The results are discussed in terms of the kink-pair mechanism. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001096 [article] Kinetics of dislocations in pure Fe : Part I. In situ straining experiments at room temperature [texte imprimé] / D. Caillard, Auteur . - 2011 . - pp. 3493–3503. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3493–3503 Mots-clés : Iron  Dislocation  mobility  Plastic  deformation  Thermally  activated  processes Résumé : In situ straining experiments have been carried out in pure Fe, in order to determine the geometry and the kinetics of dislocation glide at room temperature. Straight screw dislocations glide slowly in {1 1 0} elemental slip planes, at a velocity proportional to their length, whereas curved non-screw parts are highly mobile. The exact loop shape can yield the local stress as well as the difference of core energy between pure screw and near-screw orientations. The velocity–stress dependence of screws has been measured at the scale of a single dislocation source, and compared with macroscopic activation areas. The results are discussed in terms of the kink-pair mechanism. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001096

Kinetics of dislocations in pure Fe / D. Caillard in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3504–3515 Titre : Kinetics of dislocations in pure Fe : Part II. In situ straining experiments at low temperature Type de document : texte imprimé Auteurs : D. Caillard, Auteur Année de publication : 2011 Article en page(s) : pp. 3504–3515 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Iron  Dislocation  mobility  Plastic  deformation  Thermally  activated  mechanisms Résumé : In situ straining experiments have been carried out at low temperature in pure Fe, in order to study the change of mechanism occurring at around 250 K. The local stress necessary to move individual screw dislocations is in good agreement with the macroscopic yield stress at various temperatures. In the lower temperature range, straight screw segments have a jerky motion in {1 1 0} planes, at variance from the steady motion observed near room temperature. The distributions of waiting times in locked positions, and jump distances, the temperature variation of the average jump distance, and the stress/temperature variation of the macroscopic activation areas, are inconsistent with the kink-pair mechanism observed above 250 K. They have been interpreted in terms of a locking–unlocking mechanism, already proposed in hexagonal-closed-packed metals. Under such conditions, the change of mechanism at 250 K can account for the surprisingly low value of the flow stress extrapolated to 0 K (much lower than the theoretical Peierls stress). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001102 [article] Kinetics of dislocations in pure Fe : Part II. In situ straining experiments at low temperature [texte imprimé] / D. Caillard, Auteur . - 2011 . - pp. 3504–3515. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3504–3515 Mots-clés : Iron  Dislocation  mobility  Plastic  deformation  Thermally  activated  mechanisms Résumé : In situ straining experiments have been carried out at low temperature in pure Fe, in order to study the change of mechanism occurring at around 250 K. The local stress necessary to move individual screw dislocations is in good agreement with the macroscopic yield stress at various temperatures. In the lower temperature range, straight screw segments have a jerky motion in {1 1 0} planes, at variance from the steady motion observed near room temperature. The distributions of waiting times in locked positions, and jump distances, the temperature variation of the average jump distance, and the stress/temperature variation of the macroscopic activation areas, are inconsistent with the kink-pair mechanism observed above 250 K. They have been interpreted in terms of a locking–unlocking mechanism, already proposed in hexagonal-closed-packed metals. Under such conditions, the change of mechanism at 250 K can account for the surprisingly low value of the flow stress extrapolated to 0 K (much lower than the theoretical Peierls stress). DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001102

Plastic anisotropy of γ-TiAl revealed by axisymmetric indentation / C. Zambaldi in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3516–3530 Titre : Plastic anisotropy of γ-TiAl revealed by axisymmetric indentation Type de document : texte imprimé Auteurs : C. Zambaldi, Auteur ; D. Raabe, Auteur Année de publication : 2011 Article en page(s) : pp. 3516–3530 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Instrumented  indentation  EBSD  AFM  Crystal  plasticity  AuCu  prototype Résumé : Single crystals of γ-TiAl cannot be grown in the near-stoichiometric compositions that are present inside two-phase γ/α2-microstructures with attractive mechanical properties. Therefore, the single-crystal constitutive behavior of γ-TiAl was studied by nanoindentation experiments in single-phase regions of these γ/α2-microstructures. The experiments were characterized by orientation microscopy and atomic force microscopy to quantify the orientation-dependent mechanical response during nanoindentation. Further, they were analyzed by a three-dimensional crystal plasticity finite element model that incorporated the deformation behavior of γ-TiAl. The spatially resolved activation of competing deformation mechanisms during indentation was used to assess their relative strengths. A convention was defined to unambiguously relate any indentation axis to a crystallographic orientation. Experiments and simulations were combined to study the orientation-dependent surface pile-up. The characteristic pile-up topographies were simulated throughout the unit triangle of γ-TiAl and represented graphically in the newly introduced inverse pole figure of pile-up patterns. Through this approach, easy activation of ordinary dislocation glide in stoichiometric γ-TiAl was confirmed independently from dislocation observation by transmission electron microscopy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001114 [article] Plastic anisotropy of γ-TiAl revealed by axisymmetric indentation [texte imprimé] / C. Zambaldi, Auteur ; D. Raabe, Auteur . - 2011 . - pp. 3516–3530. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3516–3530 Mots-clés : Instrumented  indentation  EBSD  AFM  Crystal  plasticity  AuCu  prototype Résumé : Single crystals of γ-TiAl cannot be grown in the near-stoichiometric compositions that are present inside two-phase γ/α2-microstructures with attractive mechanical properties. Therefore, the single-crystal constitutive behavior of γ-TiAl was studied by nanoindentation experiments in single-phase regions of these γ/α2-microstructures. The experiments were characterized by orientation microscopy and atomic force microscopy to quantify the orientation-dependent mechanical response during nanoindentation. Further, they were analyzed by a three-dimensional crystal plasticity finite element model that incorporated the deformation behavior of γ-TiAl. The spatially resolved activation of competing deformation mechanisms during indentation was used to assess their relative strengths. A convention was defined to unambiguously relate any indentation axis to a crystallographic orientation. Experiments and simulations were combined to study the orientation-dependent surface pile-up. The characteristic pile-up topographies were simulated throughout the unit triangle of γ-TiAl and represented graphically in the newly introduced inverse pole figure of pile-up patterns. Through this approach, easy activation of ordinary dislocation glide in stoichiometric γ-TiAl was confirmed independently from dislocation observation by transmission electron microscopy. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001114

On the characteristics of substructure development through dynamic recrystallization / Hossein Beladi in Acta materialia, Vol. 58 N° 9 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3531–3541 Titre : On the characteristics of substructure development through dynamic recrystallization Type de document : texte imprimé Auteurs : Hossein Beladi, Auteur ; Pavel Cizek, Auteur ; Peter D. Hodgson, Auteur Année de publication : 2011 Article en page(s) : pp. 3531–3541 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dynamic  recrystallization  Substructure  Austenite  Hot  torsion  Crystallographic  texture Résumé : Substructure development in an austenitic Ni–30%Fe model alloy was investigated within a dynamic recrystallization (DRX) regime. The substructure characteristics of the deformed matrix and DRX grains were markedly different regardless of the grain size and orientation. The former largely displayed ‘organized’, banded subgrain arrangements with alternating misorientations, resulting from a limited number of active slip systems. In contrast, the substructure of DRX grains was generally more ‘random’ and exhibited complex subgrain/cell arrangements characterized by local accumulation of misorientations, suggesting multiple slip. The proposed mechanism of the unique substructure development within DRX grains suggests that the DRX nuclei, forming along pre-existing grain boundaries and triple points, essentially represent grain boundary regions, which experience multiple slip to preserve the compatibility with neighbouring deformed grains. This results in the formation of a complex cell/subgrain structure, which progressively extends as the grain boundary regions expand outwards during DRX growth. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001126 [article] On the characteristics of substructure development through dynamic recrystallization [texte imprimé] / Hossein Beladi, Auteur ; Pavel Cizek, Auteur ; Peter D. Hodgson, Auteur . - 2011 . - pp. 3531–3541. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 9 (Mai 2010) . - pp. 3531–3541 Mots-clés : Dynamic  recrystallization  Substructure  Austenite  Hot  torsion  Crystallographic  texture Résumé : Substructure development in an austenitic Ni–30%Fe model alloy was investigated within a dynamic recrystallization (DRX) regime. The substructure characteristics of the deformed matrix and DRX grains were markedly different regardless of the grain size and orientation. The former largely displayed ‘organized’, banded subgrain arrangements with alternating misorientations, resulting from a limited number of active slip systems. In contrast, the substructure of DRX grains was generally more ‘random’ and exhibited complex subgrain/cell arrangements characterized by local accumulation of misorientations, suggesting multiple slip. The proposed mechanism of the unique substructure development within DRX grains suggests that the DRX nuclei, forming along pre-existing grain boundaries and triple points, essentially represent grain boundary regions, which experience multiple slip to preserve the compatibility with neighbouring deformed grains. This results in the formation of a complex cell/subgrain structure, which progressively extends as the grain boundary regions expand outwards during DRX growth. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001126

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