Titanium aluminide alloys with high temperature mechanical properties for a low pressure turbine blade of jet engines.

Titanium aluminide alloys have been known well as a light weight heat resistant materials. Recently, cast or forged titanium aluminide alloys have been applied to a low pressure turbine blade to improve fuel efficient of jet engines. Up to establish the technologies of the low pressure turbine blade produced by the titanium aluminide, there were a lot of challenges. One of them was to optimize the mechanical properties for the application, because brittleness of the titanium aluminide is inferior to that of conventional metallic materials, which are Fe, Ni and Ti based alloys. Through the tough challenges, the titanium aluminide has been recognized as a heat resistant material for the jet engines. Daido Steel has been produced cast titanium aluminide turbine wheels for an automotive turbocharger since 1999. In order to apply to the various turbine wheels which operating temperature rises up to 1000 ^oC, several alloys (DAT-TA series) with　high temperature mechanical properties were developed. Further, the casting, melting and brazing technologies were also developed. The alloys focus on enhancing of creep strength, fatigue property and oxidation resistance at high temperature.　Although they are used in as-cast condition for the turbine wheel, the mechanical properties can also be controlled by heat treatment for customer requirements. For example, a HIP treatment is an effective approach to improve reliability and ductility. However, it should be taken careful that the high temperature strength may remarkably deteriorate by the HIP treatment due to changing of the microstructure, which are expansion of a lamellar spacing, formation of an equiaxed gamma phase and coarsening of precipitations. Even though our developed alloys for the turbine wheel have not been used yet for a low pressure turbine blade of the jet engines, they could contribute as well as on the requirement of the higher temperature applications.