Effect of initial mixed grain microstructure state of deformed Ni-based superalloy on its refinement behavior during two-stage annealing treatment

The effect of initial mixed grain microstructure state of deformed Ni-based superalloy on its refinement behavior during two-stage annealing treatment was investigated. Firstly, the deformed specimens with different initial mixed grain microstructure states were obtained by different hot compression experiments. Then, two-stage heat treatment experiments including aging treatments (AT) for precipitating delta phase and subsequent recrystallization annealing treatments (RT) to refine mixed grains were carried out. The results show that the deformation energy and dynamic recrystallization (DRX) degree are the main initial microstructure factors that affect the refinement behavior of deformed mixed grains. The deformation energy was estimated by the area under the stress-strain curve (S) due to the proportional relationship between them. When S is high, the recrystallization rate during the RT is high, and the final annealed grain is uniform and fine. When S is medium, the recrystallization rate is determined by DRX degree. The recrystallization rate is low and the final annealed grain is nonuniform when DRX degree is high. However, when DRX degree is low, the recrystallization rate is quick and final annealed grains are coarse but uniform. Besides, it is found that besides deformation energy, the competition relationship between static recrystallization (SRX) nucleation and breakage of delta phase affects the dissolution of delta phase during the RT. When the SRX nuclei form at delta phase boundary, the corresponding delta phase is protected.

Automated summary

The initial mixed grain microstructure state of deformed Ni-based superalloy significantly affects its refinement behavior during two-stage annealing treatment, mainly determined by deformation energy and dynamic recrystallization (DRX) degree. Higher deformation energy leads to faster recrystallization rate and finer final annealed grains. The competition between static recrystallization (SRX) nucleation and breakage of delta phase also plays a role in affecting the dissolution of delta phase during annealing treatment.