High-throughput investigation of novel ternary NiTi shape memory alloys by means of in-situ alloy formation during Laser Directed Energy Deposition of Metal Powders

• Applicants: Dr. Jan Haubrich; Professor Dr.-Ing. Michael Schmidt
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 554643239

Despite numerous newly developed shape memory alloys (SMA), the shape memory properties of binary NiTi alloys are still state of the art. However, their application possibilities are limited by their low operating temperatures, which are primarily determined by the phase transformation temperatures. These temperature intervals and the resulting functional properties are strongly influenced by the chemical composition of the SMA and can also be specifically adapted to the respective application. In the field of additive manufacturing, NiTi-based SMAs have so far hardly been processed using laser powder deposition (DED-LB/M). As a result, many process-material property relationships are still not understood. The main objective of the research project is to investigate NiTi-based alloy systems for the generation of high-temperature shape memory structures using DED-LB/M. These alloy systems should have increased transformation temperatures of > 100 °C and ensure an improved long-term stability of the shape memory effect under cyclic loading. To adapt the functional properties, the binary NiTi system is modified by in-situ alloying with a third alloy component (M). In addition to binary NiTi as a reference and NiTiHf as the most technically relevant high-temperature FGL to date, NiTiSc, a NiTi-M alloy system that has hardly been researched to date, is being considered. For all three alloy systems, suitable composition ranges will first be determined using CALPHAD. According to the respective alloy composition, test specimens will then be generated and analyzed in high-throughput investigations using the DED-LB/M and in-situ alloy formation from elemental powders. The aim is to gain an understanding of the relationships between the process management and the thermal process conditions in DED-LB/M of NiTi, NiTiHf and NiTiSc, the resulting residual stresses, defect formation and the microstructural, mechanical and shape memory properties of the structures generated. Selective element evaporation and defect formation are to be prevented through thermal process control and the use of beam shaping. Furthermore, heat treatments are developed on the basis of the calculated phase diagrams in order to be able to subsequently adapt or restore the functional properties. In-situ HEXRD experiments with synchrotron radiation at DESY are planned to investigate the phase transformation. The dynamic long-term behavior of the test structures will be analyzed on a testing device for thermomechanical high-temperature tests.

• DFG Programme: Research Grants