The nickel (Ni) alloy Inconel® 718 (IN® 718) is conventionally used for manufacture of the turbine exhaust case. A novel high-temperature Ni-based alloy, the Ni-Cr-Co Alloy B, has been identified as an alternative and enabler material for a lighter-weight case. However, its effective implementation relies on improvements in castability and weldability to overcome the current minimum wall thickness limitation of 2 mm for a lighter structure. Scientists are developing the requisite modelling tools and experimental techniques to achieve goals related to these issues with the EU-funded project 'High-temperature Ni-based super alloy casting process advancement' (HITECAST). A numerical simulator of the casting process together with experimental studies of castability limitations of the Alloy B are enabling optimisation of the casting process and the post-casting heat treatment to improve weldability. Investigators have made excellent progress on all fronts during the first project period. 3D geometrical models were developed for implementation in casting process simulations. This led to the definition of experimental trials for casting of both the new alloy and the conventional material. The microstructure and mechanical properties of Alloy B samples produced with optimised technical parameters have been characterised. In addition, the team proceeded to welding trials to optimise the welding process as well as the weld repair process. Preliminary data confirm the potential of the HAYNES® 282 alloy in the manufacture of large, thin-walled sections of structural components. HITECAST casting and welding technology promises to enable full exploitation of a novel, high-temperature Ni alloy in a lighter and improved engine structures. Reducing the wall thickness and thus weight will have major impact on fuel consumption and emissions, helping industry meet ambitious objectives for more environmentally friendly aircraft engines.
Nickel alloy, turbine exhaust case, casting process, weldability, wall thickness limitation