Phase-resolved fatigue damage mechanisms of duplex steels processed by laser-directed energy deposition

• Applicants: Professor Dr.-Ing. Arne Röttger; Professor Dr.-Ing. Frank Walther
• Subject Area: Materials in Sintering Processes and Generative Manufacturing Processes ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 554750747

According to the current state of research, basic studies have looked into the processing of duplex steels using laser-based AM methods (L-PBF, DED-L). Still, their main focus has been on determining the best process parameters and post-processing techniques to produce microstructures that are dense and closely resemble a phase set of 50/50 ferrite/austenite. Common duplex steel alloys are shown to be of limited utility for laser-based additive manufacturing (AM) techniques. A precise understanding of the microstructure creation process in the solid state and during the solidification of duplex steels, contingent on the chemical composition, solidification rate, and alternate reheating, is necessary for material development (Röttger, FUW). Moreover, further investigation is required to accurately characterize the phase-resolved and related bulk characteristics. Additional information on the phase-resolved damage development of multi-phase materials, such as the duplex steels under consideration under static and cyclic loads, is an important topic for research. For AM-processed duplex steels, the effects of dislocation density and local phase stability on local fracture propagation and related microstructural alterations have not been thoroughly discussed (Walther, WPT). The proposal's goals include a wide range of topics, including surface treatments, failure mechanisms, fatigue behavior, material characterization, and modeling. Together, they offer a thorough strategy for enhancing fatigue resistance in diverse duplex steel alloys. Gaining a basic understanding of the dynamics of phase formation in both the melt and the solid will also help lay the groundwork for future efforts to derive comparable alloy ideas for AM. The project is designed to consider the applicants' strengths in a synergistic approach (FUW: alloy development, WPT: material characterization). FUW will produce samples in this manner to be analyzed at WPT. The standard materials 1.4362 and 1.4462 in WP 1 are used at the beginning of the project to facilitate direct sample characterization at WPT. Additionally, by following this protocol, it will be possible to compare some of the results with findings from previous studies. The second year will concentrate on an optimized alloy for the DED process (1.4462 mod, mod: modification), assuming broad conclusions about a powerful alloy design might be drawn from it.

• DFG Programme: Research Grants