HiGh spEed TuRbinE cAsing produced by powDer HIP technologY

Executive Summary:

The next generation of aeronautic engines aims at continuously improving performances and efficiency, reducing at the same time emissions. However, increasing this temperature severely stresses the turbine constitutive materials. Current casing constitutive materials are designed to work at ca. 650° C and superalloys like Inconel 718 or Waspaloy are typically used. Different aeronautic propulsion producers have different strategies to develop more efficient turbines, but they are all trying to find materials and manufacturing routes capable to provide casings which can readily operate at 700 to 800° C. Besides the requirement on maximum operating temperature casing constitutive materials are also requested to have high stiffness, so as to guarantee the maintenance of accurate clearances between the rotatory and stationary parts of turbines. Materials capable to provide such characteristics are indeed available on the market, e.g. Astroloy, but with major problems in terms of workability.

Astroloy is characterized by an higher amount of Ti + Al alloying elements with respect to Waspaloy and the increased content of these elements gives the possibility to develop a higher fraction of gamma prime precipitates which are responsible for the improved properties at high temperature. At the same time increased Ti and Al additions provide poorer forgeability for Astroloy material. Therefore, although appealing service performances can be achieved by designing with Astroloy, there is of course a strong industrial interest to apply alternative near net shape processing routes to form such an alloy, so as to increase cost efficiency of manufacturing and reduce the environmental impact of the overall component processing.

Within this project the Consortium:

1. Has successfully applied the powder Near Net Shape Hot Isostatic Pressing (NNSHIP) manufacturing route to the fabrication of two Astroloy turbine casings for high speed turbine.
2. Has optimised the material usage reducing material waste: the NNSHIP to design process has been optimised so as to provide a semi-finished part very close to the final casing profile component (1.5 mm overstock) thus reducing as much as possible the machining efforts.
3. Has fine tuned a post heat treatment to fully exploit the Astroloy potential thermal/mechanical resistance for casing application and done a complete and certified mechanical characterization.
4. Has developed a modelling of thermal densification and rheological properties of the powders with simulation tools to simulate the NNSHIP process and being able to adapt the process when component change its design.