On the influence of trace elements on the high temperature properties of single crystal Ni-base superalloys (T07*)

• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Glass, Ceramics and Derived Composites
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 190389738

Single crystal Ni-base superalloys (SX) are used for turbine blades, which operate at temperatures above 1000°C where they must withstand mechanical loads and high temperature corrosion. SX have complex compositions, they can contain more than 10 alloying elements. There is a need to master the recycling of SX turbine blades, not only because it allows cost reductions, but also, because the topic of sustainable metallurgy is of utmost importance. Most importantly, the availability of strategic elements is of concern. Ex-service blades can be remelted, directionally solidified and newly heat treated. This unavoidably leads to an unintended increase of new elements (trace elements) in small quantities, which can affect critical material properties. The scientific objective of the present project is to find out, how far this can be tolerated and where a limit has to be drawn. The present project focusses on the trace elements Li, Mg and Si, which are expected to play a more important role as trace elements in the future and for which only limited information exists. Applying an ingot metallurgy processing route, a master melt of a CMSX4 type SX alloy will be processed (melting, directional solidification, multiple step heat treatment) with and without small amounts of Li, Mg and Si. Moreover, six actual blades will be considered (two new and four ex-service blades), which will be characterized across length scales and then subjected to the ingot metallurgy based recycling procedure. Analytical electron microscopy (scanning and transmission electron microscopy) will be used to study the influence of the three trace elements on nano-/microstructural evolution during directional solidification and heat treatments. The effect of the trace elements on high temperature properties will be investigated, focusing on creep, thermal fatigue and high temperature oxidation.

• DFG Programme: CRC/Transregios (Transfer Project)
• Subproject of: TRR 103: From Atoms to Turbine Blades - A Scientific Approach for Developing the Next Generation of Single Crystal Superalloys
• Applicant Institution: Ruhr-Universität Bochum
• Business and Industry: MTU Aero Engines AG
• Project Heads: Professor Dr.-Ing. Gunther Eggeler; Professor Dr.-Ing. Jan Frenzel