Leoben knowhow for environmentally friendly aircraft engines 

The requirements to next generation aircrafts are enormous: the planes are to be quieter, more fuel-efficient and substantially more environmentally friendly. A materials system developed at the Department of Physical Metallurgy and Materials Testing of Montanuniversität Leoben (University of Leoben) in the working group of Univ.-Prof. Dr. Helmut Clemens and Ass.-Prof. Dr. Svea Mayer now contributes to the achievement of this demanding scientific and technical goal. The tailor-made material will soon prove itself in use in the Airbus A320neo.

“The new material belongs to the class of inter-metallic titanium aluminides (TiAl), i.e. is a compound of several metals coordinated at the atomic level”, explains Prof. Clemens. The portions of titanium and aluminium atoms are set at a particular ratio. “Thus, a so-called inter-metallic compound with an orderly crystalline structure results”, continues the Leoben materials scientist. “Each atom sits in a particular spot.”

That is the characteristic of titanium aluminides, which is responsible for its particular properties. Engine manufacturers worldwide are looking for possibilities to increase the efficiency of their drive aggregates, and for that they have their eyes set on TiAl. So far, however, this innovative lightweight construction material has been hardly formable and workable, since it has a brittle material behaviour. This has changed, thanks to the inter-disciplinary research work of the leading German engine manufacturer MTU Aero Engines together with the scientists of Montanuniversität Leoben, materials suppliers, a smithy and further specialists. The result is the so-called geared turbofan (GTF™) of the US aerospace company Pratt & Whitney, a partner of MTU. The first aeroplanes equipped with these particularly environmentally friendly and economical engines are to take off in the last quarter of 2015.

“Titanium aluminides are currently advancing into the domain of heavy nickel alloys as the most successful alternative”, emphasises Dr. Jörg Eßlinger, Manager of Material Engineering at MTU. The weight of the new TiAl material is only half that of the nickel base alloy used so far, but has comparable properties up to approx. 800 degrees Celsius.

The alloying concept of the new material was launched at the University of Leoben. Within the scope of fundamental research programmes, material scientists were also able to solve the most difficult mystery, namely how to bring TiAl into the shape of a blade. “The material is very hard to form”, says Clemens. Casting is not possible, since therewith, the desired mechanical properties for the GTF drive are not achieved. Thus, they concentrated on forging. But this, too, was anything but mundane, because the material is hardly formable on conventional forging aggregates. Applying new theoretical development concepts as well as using state-of-the-art experimental testing methods, ultimately it could be determined, which phase composition is best suited for forming. “With thermodynamic calculations, it was explored, in which temperature range and using which phase configuration forging may take place”, explains Clemens. “The forging process may now be undertaken on conventional forming machines – and that is the actual revolution.” In order to provide the material with the suitable mechanical properties, together with the partners, special heat treatment processes were developed, which now make this promising class of materials “ready for take-off”.

For further information:
Univ. Prof. Helmut Clemens
E-mail: helmut.clemens@unileoben.ac.at
Tel.: +43 3842/402-4200, Mobile: +43 650 402 4201