Mechanism-based assessment of the influence of powder production and process parameters on the microstructure and the deformation behavior of SLM-compacted C + N steels in air and in corrosive environments

• Applicants: Dr.-Ing. Nils Ellendt, since 7/2022; Professor Dr.-Ing. Frank Walther; Professor Dr.-Ing. Sebastian Weber, since 3/2023
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 372290567

In the research project "Mechanism-based assessment of the influence of powder production and process parameters on the microstructure and the deformation behavior of SLM-compressed C + N steels in air and in a corrosive environment", fundamental relationships between the production of N-alloyed starting powder, the microstructure formation process during the L-PBF processing (Laser-Powder Bed Fusion) of N-alloyed steels and the properties associated with them, could be understood. During the research project, a number of new scientific questions were raised, which are now to be answered within the continuation project requested here.The overarching goal of the renewal application is to create a deeper understanding of the microstructure formation mechanisms and the associated properties of nitrogen-alloyed austenites and duplex steels processed by L-PBF. For this purpose, the project takes an integral approach, in which the powder production and the L-PBF processing of the produced powders, as well as post processing steps and the characterization of the resulting microstructures and properties are regarded. In particular, investigations concerning the interactions between single powder particles during flowing of the powder will be used to explain the global powder properties and will be correlated to the powder production and conditioning parameters. Based on this, suitable powder properties will be derived for the L-PBF process. In this context, the influence of recycling of the powders will be also investigated. Furthermore, the solidification sequences of nitrogen-alloyed austenites and duplex steels depending on their chromium and nickel equivalents are of special interest considering the process specific thermal conditions during L-PBF. Thereby, fundamental knowledge shall be gathered on the relation of primary solidification mode, phase formation kinetics, defect formation and the resulting material properties. Additionally, the influence of post processing steps using enhanced pressure (HIP) or partly melting of the material (SLPS) on the microstructure and the properties of the nitrogen-alloyed steels will be determined. In order to characterize the material properties, cyclic testing will be performed in air and in corrosive media, focusing on the failure sequence and the initiation and propagation of cracks in L-PBF-built duplex steels. According to the expertise of the project partners, the characterization of the mechanical and chemical properties of the investigated steels considers the complete process chain.

• DFG Programme: Research Grants
• Ehemalige Antragsteller: Professor Dr.-Ing. Werner Theisen, until 3/2023; Dr.-Ing. Volker Uhlenwinkel, until 7/2022