Recrystallization During Thermo-Mechanical Fatigue of Two High-Generation Ni-Based Single Crystal Superalloys

Ni-based single crystal superalloys are widely used for turbine engine blades because of their excellent high-temperature mechanical properties. Thermo-mechanical fatigue (TMF) is a complex deformation process that combines strain and temperature effects. This process is also considered as a deformation method related to the working conditions of aviation turbine blades. Therefore, understanding the deformation mechanism of materials undergoing TMF is important for extending the service life of aviation turbine blades. Here, third-generation and fourth-generation single crystal superalloys that experienced TMF deformation are investigated by SEM and TEM, including aberration-corrected STEM. The results show the formation of deformation twins on different {111} planes of the single crystal superalloys. In addition, a large number of recrystallized grains are found in parallel twin lamellae or around the intersection of twin lamellae. The grain boundary of recrystallized grains is primarily composed of twin boundaries, low-angle grain boundaries, and large-angle grain boundaries generated by twin intersections. Furthermore, the twinning boundaries after deformation are analyzed using aberration-corrected TEM. Consequently, the process of twinning-induced dynamic recrystallization is comprehensively understood, which improved the TMF fracture mechanism of single crystal high-temperature alloys. These results improve the understanding of the deformation mechanism of single crystal superalloys under service conditions.