Fundamental investigations of the use of powder mixtures and the influence of starting material and process parameters on the solidification sequence and the microstructure formation process of ferritic and austenitic steels during powder bed-based melting of metals using a laser beam

• Applicants: Professor Dr.-Ing. Arne Röttger; Professor Dr. Jan T. Sehrt
• Subject Area: Materials in Sintering Processes and Generative Manufacturing Processes ; Mechanical Properties of Metallic Materials and their Microstructural Origins ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553317883

This research proposal fundamentally investigates the processing of ferritic and austenitic stainless steels by powder bed fusion (PBF) of metallic (M) materials from powder mixtures of the binary and ternary systems using a laser beam (LB). If the use of base powder mixtures enables the production of a large number of different microstructures compared to the use of a single pre-alloyed, gas-atomized powder, this results in many unanswered scientific and technological questions. These relate to the laser-metal powder interaction, the formation of melt pools with a homogeneous chemical composition, the microstructure formation process during the solidification and subsequent transformations in the solid state because of the recurring heat input, and the chemical and mechanical properties associated with this microstructure. To answer this multitude of scientific and technological questions and to derive alloy compositions that can be processed into low-defect samples using PBF, a corresponding Schaeffler diagram for PBF-LB/M-processing of stainless steels will be derived, inspired by welding technology. The phase-field and Scheil-Gulliver-method will describe the microstructure formation process during solidification as a function of chemical composition and solidification rate. The influence of multiple heat inputs due to the layered material built-up process can be estimated by diffusion calculations. The simulations are validated through experimental investigations. For this purpose, remelting experiments are carried out, whereby the microstructure, the forming phases, and the associated properties are characterized with the aid of nanoindentation, in-situ X-ray diffraction, and electron microscopy (EBSD, EDS). With the help of this knowledge, the Schaeffler diagram known from welding technology can be adapted for the PBF-LB/M-processing of stainless steels. In parallel with these investigations, questions regarding the processing of powder mixtures need to be answered. In addition to the basic characterization of the powder properties and their behavior during processing, the characterization of the powder layer that has formed and its remelting by varying the exposure parameters and the atmosphere must be examined. The investigations will focus on the laser-metal powder interaction, the generation of melt pools with a homogeneous chemical composition by appropriate measures (wobbling, multiple exposures, particle size adjustment), and the associated targeted influence on the microstructure formation via process engineering measures. In a superordinate work package, the acquired knowledge is to be summarized and applied as an example for the PBF-LB/M-processing of ferritic and austenitic steel with advanced mechanical and chemical properties.

• DFG Programme: Research Grants