Prozessentwicklung zur in-situ Herstellung von Verbundbauteilen mittels gerichteter Erstarrung von eutektischen NiAl-Legierungen

Currently, turbine blades and turbine vanes in the first turbine stage are made of Ni-base superalloys with a unique combination of high temperature properties, corrosion resistance and processability. Given that, the gas entry temperature exceeds the melting point of Ni-based superalloys in high-efficient turbines and the turbine blades have to be cooled by sophisticated cooling systems, for a further temperature increase materials with higher melting points and the necessary mechanical properties have to be found. One promising alloy class is based on the intermetallic phase NiAl with a melting point of 1638,8 °C. In this study the directional solidification of eutectic NiAl alloys to produce in-situ composites are investigated. These NiAl in-situ compo-sites consist of a NiAl matrix and reinforcing Mo fibers, respectively Cr(Mo) lamellae. Depending on fineness and orientation of the reinforcing phase anisotropic mechanical properties can be achieved. Therefore, it is essential to investigate the directional solidification on two levels. On the one hand, the microscopic solidification front with stabile, coupled eutectic growth leads to a high alignment of the reinforcing phase. On the other hand, the processing of casting parts for industry is a necessity to establish this alloy class for the application in gas turbines. This study of the directional solidification of NiAl in-situ composites includes a process window for stabile eutectic growth of the alloys NiAl-9Mo and NiAl-28Cr-6Mo. Furthermore, directional solidification on industry-orientated casting geometry is conducted and the transfer to the industrial-scale Bridgman technology is discussed