Process parameter dependent recrystallization behaviour of a ferritic ODS alloy

This thesis focuses on the investigation of the dynamic recrystallization (DRX) behavior of a ferritic oxide dispersion strengthened (ODS) FeAlOY alloy, designed as a sustainable alternative to conventional high-temperature materials. With a significantly reduced content of critical raw materials, such as nickel and cobalt, the FeAlOY system presents a promising candidate for future energy-related applications. These include components in gas turbines operating with hydrogen-based fuels, where high mechanical strength, oxidation resistance, and long-term thermal stability are required. The alloy was produced by mechanical alloying (MA) of elemental Fe, Al, Cr, and ($Y_{2}O_{3}$ powders under two distinct processing conditions: room temperature (RT) milling and a combination of room and cryogenic temperature (CT) milling. Subsequent hot rolling consolidated the powders into sheets, followed by hot compression tests performed using the Gleeble 3800-GTC system. Various strain rates and temperatures were applied to simulate industrial hot forming processes and to study their influence on grain size- and particle evolution. Detailed microstructural analys were conducted using scanning electron microscopy (SEM). An automated Python-based image analysis tool developed in-house enabled precise quantification of oxide particle size distributions and phase fractions. A systematic investigation of grain growth and oxide particle growth was conducted, taking the particle-pinning effect into account. Additionally, a semi-empirical Zener-Hollomon-based model was applied and optimized to predict the recrystallized grain size under varying thermomechanical conditions. Due to its low initial grain size of about 150 nm after rolling, results reveal a low but significant dependence of recrystallized grain size and oxide particle size on the applied strain rate and temperature. Higher strain rates led to finer grain structures as a result of increased dislocation density and the associated rise in recrystallization driving force. However, local inhomogeneities and variations in oxide particle distribution introduced deviations from model predictions. A semi-empirical grain size model was evaluated and despite inherent limitations, particularly regarding particle-related effects, demonstrated acceptable predictive capability within the investigated parameter range. The study shows that mechanical alloying parameters, oxide dispersion, and thermomechanical processing critically influence the final microstructure and properties of FeAlOY. These findings provide a valuable contribution towards the process optimization and industrial application of ODS ferritic alloys in demanding high-temperature environments.