Enhanced superalloy dual-grain structures in which coarse-grained regions possess serrated grain boundaries

• Enhanced dual-grain structures in superalloys were fabricated via a novel strategy. • Grain boundary morphology in coarse-grained regions was tailored to be serrated. • Desired grain-size gradient was tailored by controlling the deformation condition. To provide a greater competitive advantage for dual-property turbine disks in advanced aeroengines, this study proposes a strategy for preparing enhanced dual-grain structures in which the coarse-grained regions possess serrated grain boundaries. A series of designed serration heat treatments is applied to prefabricate serrated grain boundaries, followed by deformation on samples subjected to an optimized serration heat treatment to fabricate dual-grain structures. This processing route successfully achieved pronounced microstructural gradients across the structures, optimal serrated grain boundaries in the coarse-grained regions, and effective microstructure control in the fine-grained regions. The results indicate that the amplitude and wavelength of serrated grain boundaries are negatively correlated with the cooling rate of serration heat treatment. These serrations primarily form at 1170–1050 °C and require cooling rates below 10 °C/min. Two mechanisms govern the formation of serrations, both of which are correlated with γ’ gb particle precipitation at grain boundaries. Owing to impeded grain boundary sliding and additional energy dissipation, the sample with serrated grain boundaries produced at a cooling rate of 4 °C/min shows a 49.08% increase in creep life compared to the sample with flat grain boundaries. The grain-size gradient can be effectively tailored by controlling the deformation conditions to obtain the desired dual-grain structures. The serration amplitudes in the coarse-grained regions decrease slightly during this process. Dynamic recrystallization governs microstructural evolution and completely changes the grain boundary morphology in the transition and fine-grained regions, involving multiple nucleation mechanisms. These findings offer a promising pathway for the development of advanced dual-property turbine disks.