Targeted modification of the material properties of compositionally complex alloys by integrated heat treatment in the additive manufacturing process

• Applicants: Professor Dr.-Ing. Cemal Esen; Professor Dr. Jan T. Sehrt; Professor Dr.-Ing. Sebastian Weber
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 548385228

Additive manufacturing (AM) enables the generation of complex components with special features such as the integration of functional structures, the processing of (multi-material) components with graded properties or the use of hybrid manufacturing processes. Steels in the Fe-Cr-Ni base system are proven materials for metalworking additive manufacturing processes. Compared to established austenitic and soft-martensitic grades, so-called "controlled transformation steels", which belong to the compositionally complex alloys (CCA), promise significantly higher strength, which can be achieved by multi-stage heat treatment, as well as very good AM processability. This group of materials, which is new in the AM field, is therefore used a model material for process-integrated heat/cryogen treatment in the two established AM processes for metals Powder Bed Fusion - Laser Beam/Metal (PBF-LB/M) and Directed Energy Deposition - Laser Beam/Metal/powder (DED-LB/M/powder). Both processes are widely used, but show great differences in the heat balance as well as in the formation of the melt pools (e.g. melt pool size, volumes, geometry) and consequently also in the microstructure. Furthermore, the processes differ in the degree of feasible component complexity and size as well as in the accessibility and thus the possibility of heat/cryogenic treatment in the process. Within the scope of this research project, suitable alloy compositions are first developed with CALPHAD (CALculation of PHAse Diagrams) and produced as metal powders by means of VIGA (Vacuum inert gas atomization). These CCAs exhibit a specifically adjusted phase stability of the gamma-phase compared to alpha-martensite, so that the local properties and phase fractions can be influenced in a defined manner via the heat balance in the AM process and can be investigated ex-situ. The integrated heat treatment has the advantage that internal areas of the component can be treated in a targeted manner and, in contrast to the downstream heat treatment, are not dependent on a predefined temperature gradient due to the cooling medium used. In addition, the extent to which local adjustment of the microstructure is possible regarding graded properties in the component is being investigated. The successful implementation of this approach suggests a transfer to other metallic materials that benefit from a heat/cryogenic treatment integrated into the AM process.

• DFG Programme: Research Grants