Analysis of structural integrity and functional properties of hybrid additively manufactured functionally graded Fe-36Ni Invar alloy using wire-based directed energy deposition processes

• Applicants: Dr.-Ing. Johannes Günther; Dr.-Ing. Thomas Wegener
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Materials in Sintering Processes and Generative Manufacturing Processes
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 575239423

The Fe-36Ni alloy Invar is known for its low coefficient of thermal expansion (CTE) and good mechanical properties in cryogenic environments. Due to its unique properties, Invar is commonly used as a high precision and highly reliable material in components where superior dimensional stabilities are required in a wide temperature range. Since Invar reveals high ductility and relatively low thermal conductivity, conventional machining of complex geometries is highly challenging and accompanied by high costs and tool wear. Additive manufacturing (AM) processes are promising candidates to overcome these challenges. Compared to powder-bed-based AM processes, wire-based directed energy deposition (DED) offers advantages in terms of material efficiency, the cost of the available precursor materials and the achievable build rates. In addition, these processes are significantly less restricted in terms of build chamber and component size. An analysis of the current state of research shows that there are no comprehensive analyses of the process-microstructure-property relationships of Invar manufactured using wire and laser-based DED processes. Previous investigations show that the microstructures and, thus, the mechanical properties are characterized by significant differences depending on the DED process and the relevant process parameters. Since many components made of Invar are subjected to complex load scenarios in practice during operation, the structural integrity under cyclic loads must also be investigated. An analysis of the state of the art moreover demonstrates that there are no systematic investigations into the thermal-cyclical stability of the Invar effect (regardless of the manufacturing route). Initial examinations clearly indicate a degradation of the CTE as a result of multi-step heat treatments. In light of this research gap, the present project was designed. The overall aim of the project is the structured, comprehensive analysis of the process-microstructure-property relationships in the additive manufacturing of an Fe-36Ni Invar alloy using wire-based DED processes. Both, laser- and arc-based DED processes are considered. By specifically influencing and locally adapting the microstructure through a combination of both technologies, the material is also to be optimized to external loads using hybrid additive manufacturing. In addition to a cross-scale microstructure analysis, the investigations will focus on an evaluation of the mechanical properties, in particular the deformation behavior under cyclic loading, as well as the thermal expansion behavior and its stability under thermal cycling.

• DFG Programme: Research Grants