The γ′-hardened Cobalt-base superalloys are a very new class of materials (discovered in 2006), which however share some elementary properties with the well-established Nickel-base superalloys. The main application area of these Ni-base alloys are turbine blades and discs in aircraft engines and stationary gas turbines. In regions where the highest temperatures occur, they are often used in single crystalline form. By avoiding grain boundaries and orienting the turbine blades along specific crystal directions, diffusion processes can be decelerated and thermal stresses can be reduced. One obvious similarity is the microstructure, which consists of a face centered cubic matrix containing a high volume fraction (ca. 70%) of coherent precipitates with usually cuboidal morphology. Despite many similarities, Co-base superalloys show also a number of essential differences to the established superalloys, which helps to get a more profound understanding of their outstanding properties. One of these differences is the sign of the lattice misfit, which is positive in Co-base superalloys, i.e. the lattice parameter of the precipitates is larger than the one of the matrix phase. Most Ni-base superalloys possess a negative lattice misfit.
This project is embedded in the collaborative research center SFB/TR 103
“From Atoms to Turbine Blades – a Scientific Approach for Developing the Next Generation of Single Crystal Superalloys”. One goal is to investigate, how the new γ′-hardened Co-base superalloys can compete with Ni-base superalloys or conventional solid solution and carbide strengthened Co-base superalloys. In this project (B3) new alloys are designed and investigated concerning
- segregation behavior, diffusivity, partitioning behavior and solid solution hardening of possible alloying elements
- microstructure- and phase stability
- γ/γ′-lattice misfit
- mechanical properties at high temperatures and deformation mechanisms
The integration in the scientific framework of the SFB/TR 103 additionally enables access to state-of-the art research equipment like 3D atom probe tomography (project A4) or high resolution TEM (A7). Moreover two further groups focus on oxidation and corrosion (A5) and develop potential protective coatings (B6) for the alloys designed in this project.