Mechanisms of grain refinement and abnormal grain growth of GH4169 superalloy during axial rotary forging and following solution treatment

This study investigates the microstructural evolution and mechanisms of grain refinement and abnormal grain growth (AGG) in GH4169 superalloy during axial rotary forging (ARF). Combining finite element simulation and experimental characterization, the effects of deformation degrees on strain distribution and recrystallization behavior were analyzed. Results reveal that, during the ARF process, there is an obvious gradient distribution of strain and temperature, with different deformation patterns in different regions. These differences lead to distinct microstructural evolution in various regions of the workpiece. Grain refinement occurs through coupled mechanisms: during the ARF process, the upper surface cools due to contact with the die, suppressing recrystallization. The high-density dislocations generated by deformation promote δ phase nucleation at grain boundaries and other regions, pinning the grain boundaries and suppressing axial growth. Meanwhile, the substructures within the grains facilitate the refinement of grains during solution treatment. In the central region, recrystallized grains initially nucleate and grow at triple junctions to maintain strain compatibility between adjacent grains. Strain-induced boundary migration (SIBM) drives twin boundaries to bend and transform into high-angle grain boundaries, segmenting the grains. Discontinuous dynamic recrystallization (DDRX), twinning-induced dynamic recrystallization (TDRX) and continuous dynamic recrystallization (CDRX) contribute to grain refinement through grain fragmentation and interface nucleation, respectively. The coupling of multiple mechanisms leads to overall microstructural refinement. Excessive deformation triggers AGG during solution treatment, attributed to uneven δ-phase distribution causing non-uniform grain boundary pinning and preferential growth of high-stored-energy grains. This work clarifies the microstructural control mechanisms in ARF, providing insights for optimizing processing parameters to achieve fine-grained microstructures and avoid AGG in GH4169 components for aerospace applications.