Microstructure Evolution in GH4169 Alloy during Cross-Wedge Rolling

The morphology, content, and distribution of the delta phase in GH4169 alloy have important effects on the performance of parts. To study the evolution of the delta phase during the cross-wedge rolling of GH4169 alloy, the microstructure and phase structure were characterized using scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Furthermore, the interaction mechanism between the delta phase and dynamic recrystallization during cross-wedge rolling was investigated. The experimental results showed that the fracture and dissolution of the delta phase gradually extended from the surface to the center of GH4169 alloy rolled parts. The initial acicular delta phase on the surface and at the core of the rolled piece gradually fractured and dissolved into short rods/granules, and the degree of spheroidization gradually increased as the section shrinkage rate increased. Varying microstructures were obtained at different positions of the rolled piece owing to nonuniform plastic deformation induced by cross-wedge rolling. During deformation, dislocations piled up near the delta phase and formed high-density dislocation cells, promoting dynamic recrystallization nucleation. The necklace-like microstructure was characterized by insufficient dynamic recrystallization, while the fine homogenous microstructure was derived from full dynamic recrystallization as the section shrinkage rate increased to 82%.