Technologische Entwicklung zur Herstellung von near-net shape Niederdruckturbinenschaufeln aus dem intermetallischen Werkstoff Titanaluminid im Feinguss

Doctoral thesis German OPEN
Kättlitz, Oliver (2014)
  • Publisher: Giesserei Institut, RWTH Aachen
  • Subject: Titanaluminide | Feinguss | Turbinenschaufel | Schleuderguss | Technik | titanium aluminide | investment casting | turbine blade | centrifugal casting
    • ddc: ddc:600

Global air traffic is predicted to rise long-term (2012-2031) at an annual rate of almost 5%, signifying a 100% increase in passenger and freight volumes over the next 15-20 years. In view of the environmental consequences, 2011 saw the release by the EU of Vision Flightpath 2050, which sets ambitious goals for pollution and noise reduction (including a 75% reduction in CO2, taking the year 2000 as benchmark). A potential CO2 emission saving in the order of 15-20% is achievable simply by stepping up the efficiency and optimizing the weight of aircraft jet en-gines. One promising option for achieving these targets is the substitution of the very heavy iron and nickel-based super alloys currently in use for high temperature applications by new, lighter materials. Alongside the general weight-saving achievable, this development will also enable an increase in the response times for movable components by up to 50%. The current work focuses on titanium aluminide alloys based on gamma-TiAl and alpha2-Ti3Al, which combine the attributes „light, corrosion-protected and extremely tough“. The application potential of this material at moderate to high temperatures (500°C-800°C) makes it a particularly attractive option for manufacturing rotating turbine blades and wheels. The main barrier to the general introduction of TiAl components is the nature of this material: very hard and brittle, and, in a melt, extremely reactive. Cost-effective manufacture of TiAl low pressure turbine blades on the industrial scale is achievable by the near-net shape casting approach. The manufacture of single near net shape prototypes using centrifugal casting has already been successfully demonstrated. However, transferring this approach to industrial standard has not hitherto been possible. Starting from the current technological platform already achieved, this work aims to develop a stable and reproducible manufacturing process chain, thus laying the foundation for future series casting of near-net shape TiAl low pressure turbine blades (up to approx. 300 mm in length) for jet engines. This will enable the transfer of the huge potential of this difficult-to-process intermetallic material to a broad field of application within the aerospace industry. This calls for close investigation of component, material and the various process steps as a complex, rather than in isolation. Alongside the fundamental definition of a casting concept and corresponding process parameters, and the subsequent technology transfer to production plant specifically developed for the production of TiAl components, an essential focus of the technology development within the scope of this paper is an all-round optimization of the casting process. Not only the melt flow up to the shell mould but also mould-filling of the cavities is covered in this research. It is demonstrated that modelling a complex, thin-walled blade geometry is only achievable by goal-oriented adaptation of the crucible tilt process and the gating and feeder technology. Verification of the suitability of both the ceramic material and furnace used in being able to meet the dimensional tolerances demanded then provides the basis for the production of a small series of 600 turbine blades, the setting up of which is based on bringing together knowledge previously obtained. Verification of a stable and reproducible process chain is executed by evaluating process stability and component quality.
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