Motivation and objectives
Rising demands on engines in the aerospace industry require high engine inlet temperatures in modern gas turbines in order to increase the efficiency. Single-crystal nickel-based Superalloys were developed in order to meet these rising demands and confer high pressure turbine blades with the necessary wear resistance at high temperatures. The blades of the high pressure turbine are subject to significant wear due to the high mechanical strain under extreme conditions, which appears in the form of cracks in the single-crystal substrate material. There are no approaches for the restoration of the original material properties since the repair of cracks and erosions by polycrystalline laser cladding can be applied only to a limited extent. The aim of the sub-project is the restoration of defect, single-crystal high pressure turbine blades.

Results
In the first funding period different possibilities of repair were evaluated with the aim of widening the scope of existing repair areas. The regeneration of defects parallel to the primary dendrite orientation were studied with the hypothesis that after the formation of cracks, the single-crystal substrate materials can be restored by means of laser metal deposition that maintains a particular temperature gradient. The generated knowledge was used in the second funding period to enable the development of a method for the successful extension of directional solidification of the deposited material in defects perpendicular to the primary dendrite orientation

Current research and outlook
For the current funding period, the constructed hypothesis is that the required single-crystal structure of the deposited material can only be restored, but also influenced specifically in a further step. By developing appropriate heat treatment methods of the regenerated material and an adaptation of the regeneration process, it is possible to influence the microstructure with regard to its thermomechanical properties with the aim of adjusting these properties to match those of the substrate material. The adaptation of the process involves the integration of results from other sub-projects with the aim of optimizing the regeneration sequence within and between the process cells.