Eignung des Verfahrens der gerichteten Erstarrung zur Herstellung von Gasturbinenschaufeln aus der intermetallischen NiAl-Legierung FG75

摘要

In times of increasing environmental pollution and rising energy costs there is a constant pursuit for prospects to improve the efficiency of gas and steam turbine combined cycle power plants. This can be realized by higher gas turbine inlet temperatures in combined cycle power plants. These increased process temperatures in both the gas and steam turbine, however, lead to higher material loads. Hereby, today’s high temperature components such as turbine blades almost exclusively made of Ni-base alloys are at their metallurgical and alloying limits. Currently, there are a multitude of research projects, which aim to examine alternative high-temperature materials for use in combined-cycle power plants. Amongst others, NiAl alloys are investigated as a possible substitute material for Ni-base alloys. The present research mainly work deals with the vacuum casting of the intermetallic NiAl alloy IC75. The focuses of this research are the development of ceramic cores for investment casting of NiAl alloys, the upscaling of the component sizes up to the production scale and the development of process the technology for directional solidification of the intermetallic alloy IC75. The implementation of these functions is represented by two turbine blade geometries. In the development of the core technology are mainly considered two aspects the core materials and the manufacture of filigree, thin-walled cores. The cores must survive all stages of the manufacturing process and the high thermal stresses during casting. Previously to this work the casted IC75 samples do not exceed the maximum size of a cigarette packet. The Upscaling of the component size up to real turbine blade dimensions increase the challenge concerning the investment casting process for nickel-aluminum alloys. The casting weights and the thermal stress during casting are significantly higher, which is especially evident in the directional solidification of these components. The directional solidification of IC75 yields better high temperature properties compared to the standard equiaxed casting process. Therefore, the directional solidification of IC75 components on industrial scale is the next logical step in the development of the casting technology. The studies for the directional solidification contain the elaboration of an appropriate process parameter window, the measurement of high temperature tensile strength and the cast of the dummy turbine blades.