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

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

Nonlinear dynamic behavior of a rigid rotor supported by hydrostatic squeeze film dampers / A Bouzidane, in Transactions of the ASME . Journal of tribology, Vol. 130 N° 4 (Octobre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 N° 4 (Octobre 2008) . - 9 p. Titre : Nonlinear dynamic behavior of a rigid rotor supported by hydrostatic squeeze film dampers Type de document : texte imprimé Auteurs : A Bouzidane,, Auteur ; M. Thomas, Auteur ; Lakis, A. A., Auteur Article en page(s) : 9 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Hydrostatics  Viscosity  Bearings  Dampers  Rotors  Vibration  Force  Pressure  Film  thickness  Flow  (Dynamics) Résumé : This research project aims to study the nonlinear dynamic behavior of a rigid rotor supported by hydrostatic squeeze film dampers (HSFDs). The investigated HSFD consists of four hydrostatic bearing flat pads fed by capillary restrictors. A nonlinear hydrostatic squeeze film damper model is developed, and the results are compared with those obtained using a linear approach. The effect of unbalance eccentricity on the vibration response and the transmitted force of the HSFD are investigated using the linear and nonlinear models. The results show good agreement between the linear and nonlinear methods when the unbalance force is small. However, as the unbalance forces become larger, the results obtained using the linear models cease to be representative of the real behavior of rotor dynamics and a nonlinear approach must be conducted. The effects of supply pressure, viscosity, pressure ratio, and rotational speed on the response and the force transmitted to the HSFD are investigated using a nonlinear approach. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468091 [article] Nonlinear dynamic behavior of a rigid rotor supported by hydrostatic squeeze film dampers [texte imprimé] / A Bouzidane,, Auteur ; M. Thomas, Auteur ; Lakis, A. A., Auteur . - 9 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 N° 4 (Octobre 2008) . - 9 p. Mots-clés : Hydrostatics  Viscosity  Bearings  Dampers  Rotors  Vibration  Force  Pressure  Film  thickness  Flow  (Dynamics) Résumé : This research project aims to study the nonlinear dynamic behavior of a rigid rotor supported by hydrostatic squeeze film dampers (HSFDs). The investigated HSFD consists of four hydrostatic bearing flat pads fed by capillary restrictors. A nonlinear hydrostatic squeeze film damper model is developed, and the results are compared with those obtained using a linear approach. The effect of unbalance eccentricity on the vibration response and the transmitted force of the HSFD are investigated using the linear and nonlinear models. The results show good agreement between the linear and nonlinear methods when the unbalance force is small. However, as the unbalance forces become larger, the results obtained using the linear models cease to be representative of the real behavior of rotor dynamics and a nonlinear approach must be conducted. The effects of supply pressure, viscosity, pressure ratio, and rotational speed on the response and the force transmitted to the HSFD are investigated using a nonlinear approach. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468091