What is in this article?:
- Space-Age Alloys Take Off in â€śHypergravityâ€ť
- Gravity's pull
- Lighter aircraft-grade alloys
- Applications for aerospace turbine structures
- Low-ductility problems in casting
- Achieving hypergravity
Researchers at the European Space Agency (ESA) helped in the development of an alloy that is critical to an emerging series of aerospace applications, a material that reportedly is twice as light as conventional nickel-based super alloys, with comparably good properties for strength and heat-resistance. Creating this alloy is very difficult, however. The production process demands particular capabilities that ESA made available to product engineers, namely the ability to conduct research under all types of gravity.
Aircraft and jet engine designers, as well as airlines, want component and system designs that will reduce aircraft weight, in order to save fuel costs, but without sacrificing engine performance or flight safety. According to ESA, cutting an aircraft’s weight by 1% will save up to 1.5% in fuel volume. For commercial airlines, this savings could reduce operating costs. For passengers, it might result in cheaper fares and more direct routes. A reduced environmental impact would be another benefit, ESA indicated.
Aerospace engineers understand that titanium aluminide (TiAl) alloys offer weight savings over the Ni-based super alloys in standard use for jet engines. TiAl, is a lightweight intermetallic that resists oxidation and heat, but its tensile strength is low. It is particularly difficult to cast, because of the trouble maintaining conditions for thorough mold filling and reliable solidification.
Engineers note that one specific titanium aluminide compound, gamma TiAl, has strong mechanical properties and oxidation- and corrosion-resistance at elevated temperatures: it can withstand extreme temperatures up to 800°C. These factors indicate TiAl-based alloys have a strong potential to increase the thrust-to-weight ratio in an aircraft engine, specifically in low-pressure turbine blades and high-pressure compressor blades. By contrast, Ni-based superalloys reportedly are nearly twice as dense as TiAl-based alloys.
The use of TiAl in aerospace structures is a relatively recent development: jet engine designer/manufacturer GE Aviation chose TiAl for turbine blades in its GEnx engine, which is installed in the Boeing 787 Dreamliner and Boeing 747-8 cargo jets.
There are some investment casting foundries capable of producing TiAl for low-pressure turbines, but the volumes are low due to the production difficulties, and the commercial applications of the material exceeds its availability. Over 1 million turbine blades will be manufactured in the coming decade, according to ESA, and using TiAl would reduce the components’ weight by 45% over current standard materials.
The alloy’s benefits may be significant to automaking as well as aerospace applications, the R&D source stated.
Although it is possible to produce the alloys in laboratory conditions, casting it into turbine blades or other critical shapes required by aircraft engine builders is not simple. ESA scientists worked to address the production problem through the Impress project. The Intermetallic Materials Processing in Relation to Earth and Space Solidification (Impress) project investigates materials processing, structures, and properties of new higher-performance intermetallic alloys for industrial applications, such as turbine blades and catalytic powders. It is a joint effort between the European Commission and ESA.
ESA is an intergovernmental agency that conducts research into issues critical to space exploration. With 20 member states and headquartered in Paris, ESA has a staff of over 2,000 and an annual budget of about $5.38 billion.