Centre d’Élaboration de Matériaux et d’Etudes Structurales (UPR 8011)


Accueil > Recherche > PPM : Physique de la Plasticité et Métallurgie > Alliages métalliques à microstructure complexe

TiAl Alloys : Microstructure and mechanical properties

Staff : Alain Couret, Jean-Philippe Monchoux, Daniel Caillard

During the last two decades, TiAl alloys were subjected to extensive research efforts to develop applications in gas turbine engines due to their high specific Young’s modulus and strength, and to their good oxidation and burn resistances. However, they still suffer of a poor ductility at room temperature and of a weak creep resistance.

 

At CEMES, several correlated studies are under progress on theses TiAl alloys :

 

  • Development of TiAl alloys by Spark Plasma Sintering (SPS) [1, 2].

    Propriétés mécaniques d’alliages TiAl élaborés par frittage flash

    SPS is a powder metallurgy technique which allows to compact powders through the simultaneous application of direct current pulses of high intensity and of uniaxial pressure. The challenge is to produce refined microstructures to have a good creep resistance, with no large grain size which reduces tensile ductility, and without strong texture which imparts anisotropic properties. Full compaction, quite reproducible and promising mechanical properties were achieved. In particular, the tensile properties at room temperature are very promising whereas a limited creep resistance was obtained at 700°C.

 

  • Quantitative study of the formation of the lamellar microstructure [3,4].

    It is well known that the lamellar microstructure leads to the best combination of fracture toughness at room temperature and creep resistance at high temperature which is of primary importance for gas-turbines applications. Our work consists to analyse the different type of lamellar transformations which are activated during cooling and to determine the corresponding driving force and mechanisms. This work is based on quantitative analyses of lamellar microstructure, with a special attention to the distribution of the phases, orientation variants and lamellar spacing.

 

  • Study of the elementary deformation mechanisms [5,6] (Video).

    Microstructure d’un alliage lamellaire déformé à la température ambiante

    In the single phased and multiphased alloys, the deformation can occur by various types of dislocations. The deformation mechanisms for these dislocations are studied at different temperatures. It was also analysed the crossing of the interfaces. These investigations are performed by in situ straining experiments inside the transmission electron microscope and by post mortem analysis of deformed samples.

 

  • Creep of TiAl alloys [7,8].

    The creep of TiAl alloys with different chemical compositions and microstructures are studied by : i) classical creep experiments, ii) stress jumps to measure the activation parameters and iii) post mortem analysis of crept samples. The creep strength is explained in terms of microstructural parameters and elementary deformation mechanisms.

 

These studies are developed in collaboration with Snecma motors, Turboméca and DMSN/ONERA.

 

Selected publications

  1. Spark Plasma Sintering, a promising route in powder metallurgy ; application to titanium aluminide alloys MOLENAT G., THOMAS M. GALY J., COURET A. Advanced Engineering Materials, 9 N°8, 667-669, 2007
  2. Microstructure and mechanical properties of TiAl alloys consolidated by spark plasma sintering COURET A.,MOLENAT G., GALY J., THOMAS M. Intermetallics, in press, 2008
  3. Structural transformations activated during the formation of the lamellar microstructure of TiAl alloys ZGHAL S., THOMAS M, COURET, A., Intermetallics, 13, 9, 1008-1013, 2005.
  4. Phase transformations in TiAl based alloys ZGHAL S., THOMAS M, NAKA S., FINEL A., COURET, A., Acta Metall. Mater., 53, 2653-2664, 2005
  5. Interpretation of the stress dependence of creep by a mixed climb mechanism in ?-TiAl MALAPLATE J., CAILLARD D, COURET A. Phil. Mag., 3671-3687, 84, 2004.
  6. The activation and the spreading of deformation in a fully lamellar Ti-47Al-1Cr-0.2Si Alloy SINGH J.B.,MOLENAT G., SUDARARAMAN M., BANERJEE S., SAADA G., VEYSSIERE P.,COURET A. Phil. Mag., 86, 2429-2450,2006
  7. Le Contrat de Programme de Recherche TiAl : un exemple de collaboration coordonnée entre recherché académique et industrie. COURET A., GRANGE M, LASALMONIE A., BRECHET Y., BELAYGUE P. Matériaux et Techniques, 1-2, 3-12, 2004.
  8. Primary creep at 750°C of Ti48Al48Cr2Nb2 alloys elaborated by powder metallurgy and cast processes MALAPLATE J., THOMAS M., BELAYGUE P., GRANGE M., COURET A. Acta Metall. Mater., 601-611, 2006

 

Fundings

  • SPLASMAP : Spark PLAsma Sintering : Mise en œuvre d’un outil innovant pour l’élaboration de Matériaux Aéronautiques plus Performants. Action interrégionale Aquitaine et Midi-Pyrénées – Recherche et Transfert de technologie. 10 2007 – 10 - 2009
  • IRIS : Innovative manufacturing Route for Intermetallic alloys by spark plasma net Shaping Le frittage flash : une voie innovante pour l’élaboration aux cotes d’alliages intermétalliques
    ANR – Matériaux Fonctionnels et Procédés Innovants 10 2008 – 10 - 2012