Documents disponibles écrits par cet auteur

Analysis of local microstructure after shear creep deformation of a fine-grained duplex γ-TiAl alloy / D. Peter in Acta materialia, Vol. 58 N° 19 (Novembre 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6431–6443 Titre : Analysis of local microstructure after shear creep deformation of a fine-grained duplex γ-TiAl alloy Type de document : texte imprimé Auteurs : D. Peter, Auteur ; G.B. Viswanathan, Auteur ; A. Dlouhy, Auteur Année de publication : 2011 Article en page(s) : pp. 6431–6443 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Titanium  aluminides  Shear  creep  deformation  Transmission  electron  microscopy  Dislocations  Twinning Résumé : The present work characterizes the microstructure of a hot-extruded Ti–45Al–5Nb–0.2B–0.2C (at.%) alloy with a fine-grained duplex microstructure after shear creep deformation (temperature 1023 K; shear stress 175 MPa; shear deformation 20%). Diffraction contrast transmission electron microscopy (TEM) was performed to identify ordinary dislocations, superdislocations and twins. The microstructure observed in TEM is interpreted taking into account the contribution of the applied stress and coherency stresses to the overall local stress state. Two specific locations in the lamellar part of the microstructure were analyzed, where either twins or superdislocations provided c-component deformation in the L10 lattice of the γ phase. Lamellar γ grains can be in soft and hard orientations with respect to the resolved shear stress provided by the external load. The presence of twins can be rationalized by the superposition of the applied stress and local coherency stresses. The presence of superdislocations in hard γ grains represents indirect evidence for additional contributions to the local stress state associated with stress redistribution during creep. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005094 [article] Analysis of local microstructure after shear creep deformation of a fine-grained duplex γ-TiAl alloy [texte imprimé] / D. Peter, Auteur ; G.B. Viswanathan, Auteur ; A. Dlouhy, Auteur . - 2011 . - pp. 6431–6443. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6431–6443 Mots-clés : Titanium  aluminides  Shear  creep  deformation  Transmission  electron  microscopy  Dislocations  Twinning Résumé : The present work characterizes the microstructure of a hot-extruded Ti–45Al–5Nb–0.2B–0.2C (at.%) alloy with a fine-grained duplex microstructure after shear creep deformation (temperature 1023 K; shear stress 175 MPa; shear deformation 20%). Diffraction contrast transmission electron microscopy (TEM) was performed to identify ordinary dislocations, superdislocations and twins. The microstructure observed in TEM is interpreted taking into account the contribution of the applied stress and coherency stresses to the overall local stress state. Two specific locations in the lamellar part of the microstructure were analyzed, where either twins or superdislocations provided c-component deformation in the L10 lattice of the γ phase. Lamellar γ grains can be in soft and hard orientations with respect to the resolved shear stress provided by the external load. The presence of twins can be rationalized by the superposition of the applied stress and local coherency stresses. The presence of superdislocations in hard γ grains represents indirect evidence for additional contributions to the local stress state associated with stress redistribution during creep. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005094

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