Development of thermomechanical processing routes for the targeted microstructure modification of multi-crystalline CoNiGa shape memory materials

• Applicants: Professor Dr.-Ing. Philipp Junker; Professor Dr.-Ing. Hans Jürgen Maier
• Subject Area: Mechanics ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560578888

High-temperature shape memory alloys (HT-SMA) made of cobalt-nickel-gallium (CoNiGa) offer excellent shape memory properties as single crystals. However, the economically much more attractive multi-crystalline CoNiGa-SMAs exhibit very high inter-crystalline stresses due to strongly direction-dependent transformation strains, which lead to rapid crack formation and very low functional stability. The objective of the research project is to develop process routes that enable the production of CoNiGa shape memory materials by thermomechanical treatment with a customized microstructure that leads to low intercrystalline stresses during phase transformation and thus exhibits high functional stability. In preliminary work, promising structures with few very large grains and parallel grain boundaries have already been produced by a combination of extrusion and heat treatment. Within the project, the microstructural processes will now be simulated, leading to a deeper understanding of the process and enabling the process route to be designed on the basis of the required target microstructure. Multi-crystalline CoNiGa materials will be thermomechanically treated using a combination of extrusion and post-heat treatment, crystallographically and microstructurally characterized and their mechanical and functional properties evaluated. Finally, the findings will be used to transfer the principle to another alloy system. The multi-crystalline CoNiGa-FGL with high functional stability produced in the project are intended to lay the foundation for qualifying the promising properties of single-crystalline materials for use in the high-temperature range (for example as pseudo-elastic high-temperature damper elements). At present, the enormous technical and economic challenges of monocrystalline materials stand in the way of such an application.

• DFG Programme: Research Grants