CE08 - Matériaux métalliques et inorganiques et procédés associés

Design of more environmentally resistant TiAl alloys – DEMENTIAL

Submission summary

The aim of this project is to design new TiAl alloys exhibiting improved resistance to high temperature exposures in air, which are the typical service conditions of key applications in the aeronautical sector (turbine blades). As a matter of fact, this issue is at the heart of the current concerns which aim at extending the industrial use of intermetallics in these applications. A major limitation for this deals with the oxygen penetration, which is found to have a very negative impact on mechanical properties at room and high temperatures. To limit this detrimental effect, an alloy design strategy will be implemented, on the basis of theoretical approaches followed by experimental validations. Moreover, the methodology developed will exhibit a marked multi-scale character, the theoretical and experimental approaches concerning the atomic, microscopic and macroscopic levels. Therefore, a research project in several steps will be addressed:

(i) A large number of alloying elements (about 30), acting as traps in the O diffusion mechanisms, will be defined on the basis of first-principles calculations. This will allow to choose the 10 elements which will potentially diminish with the highest efficiency the O penetration kinetics. A particular interest will be laid on Y, Zr and W elements, which have been identified as promising in the bibliography. The equilibrium microstructures of the corresponding alloys will then be simulated by ThermoCalc, and model alloys processed by casting. On these materials, concentration profiles of 18O isotopes by SIMS will allow, for the first time, to determine experimental values of diffusion coefficients, and to quantify the trapping effect predicted by the calculations.

(ii) The effect of the interfaces in the diffusion phenomena, which can be significant, will be evidenced on materials exhibiting either large and oriented grains (grown by Bridgman technique), or small grains (processed by spark plasma sintering). These results will provide valued indications on the most favorable microstructures limiting O penetration.

(iii) From these model experiments, two alloy compositions will be selected, for deeper investigations and at larger scale. For this purpose, these alloys will be produced by powder metallurgy route (processing by foundry, gas atomization, then densification by spark plasma sintering), with a special care concerning the microstructure optimization.

(iv) The obtained materials will be mechanically tested after O penetration, including tension at room temperature, fatigue at high temperature, and creep. The results will thus allow to select an optimized alloy regarding exposures at high temperatures in O-rich environments.

(v) Finally, to provide a physical basis, the microscopic plasticity and damaging mechanisms in the presence of O will be characterized by advanced microscopy techniques, like in situ TEM, or micropillar compression tests.

At the end of the project, an industrial valorization could be proposed, which would be in line with the current context of incentives for limitation of greenhouse gas emissions. Therefore, the development of intermetallic TiAl materials which would exhibit a higher performance compared to Ni-based alloys, would contribute to the consolidation of the French aeronautical sector in the international competition.

Project coordination

Jean-Philippe MONCHOUX (CENTRE D'ELABORATION DE MATERIAUX ET D'ETUDES STRUCTURALES)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CEMES CENTRE D'ELABORATION DE MATERIAUX ET D'ETUDES STRUCTURALES
Safran
CIRIMAT CENTRE INTERUNIVERSITAIRE DE RECHERCHE ET D'INGÉNIÉRIE DES MATÉRIAUX
ONERA (DMAS) Département Matériaux et Structures - ONERA

Help of the ANR 618,291 euros
Beginning and duration of the scientific project: - 48 Months

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