| • Development of TiAl alloys by Spark
Plasma Sintering [1, 2].
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. |
Mechanical properties of various alloys sintered
by SPS. The ductility of the duplex and double phased alloys is
remarkable for TiAl alloys |
• 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).
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.
|
References:
1. Spark Plasma Sintering, a promising route in powder metallurgy
; application to titanium aluminide alloys
MOLENAT G., THOMAS M. GALY J., COURET A.
2. Advanced Engineering Materials, 9 N°8, 667-669, 2007Microstructure
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
Contracts :
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
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