In-situ synthesis of ß-NiAl based alloys by means of laser metal deposition

• Applicant: Professor Dr.-Ing. Christoph Leyens
• Subject Area: Materials in Sintering Processes and Generative Manufacturing Processes
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 457729030

Due to increasing material requirements of high temperature aerospace applications current state-of-the-art Ni-based superalloys need to be further developed or replaced. ß-NiAl exhibits a low density of only two thirds of comparable Ni-based super alloys. Moreover, the high melting temperature of 1638 °C, a superior thermal conductivity and an outstanding oxidation resistance at elevated temperatures of ß-NiAl make NiAl-based alloys a promising material for high temperature applications in future turbine engines. However, the unsolved issues of a limited ductility and fracture toughness at room temperature as well as a poor strength at high temperatures have prevented the transfer to industry so far. Based on already gathered knowledge the Additive Manufacturing (AM) technique laser metal deposition (LMD) was identified as a technology, which is capable of overcoming these challenges. Within the proposed research activity the advantages of near net shape manufacturing, tailored thermal process conditions and in-situ alloy modification will be investigated in detail for the processing of binary and ternary ß-NiAl based alloys.Firstly a reference pre-alloyed Ni50Al50 powder will be processed by LMD in order to gather basic knowledge about the processing of ß-NiAl alloys. Based on this the in-situ alloying of complex ß-NiAl-Ta-Cr alloys will be investigated profoundly.By processing pre-alloyed Ni50Al50 as well as the ternary elements Ta and Cr a second phase toughening shall be achieved. Key aspect is the formation of intermetallic and refractory secondary phases, which yield increased high temperature strength and improved room temperature fracture toughness. By parameter variation (e.g. laser power, feeding rate) interdependencies between the welding process and the microstructure of the deposited material will be analysed. Finally, the obtained knowledge will be used to develop graded ß-NiAl-Ta-Cr structures, which exhibit a spatially resolved amount of Laves-Phase. By this the possibility of manufacturing ß-NiAl-Ta-Cr components with locally tailored material properties will be analyzed.Within these investigations a profound analysis of the material microstructure as well as a characterization of the mechanical properties of manufactured samples will be conducted for detecting and understanding correlations between process parameters, the created microstructure and the resulting material properties. By means of high-speed imaging an analysis of phenomena within the process zone, such as a varying material specific absorption of the laser radiation will be incorporated into investigations.The overall goal is to obtain an in-depth understanding of correlations and interdependencies between the LMD in-situ alloying process, the microstructure and the material properties of binary and ternary ß-NiAl based alloys.

• DFG Programme: Research Grants