Spheroidization and dynamic recrystallization mechanisms of a novel HIPed P/M superalloy during hot deformation

The spheroidization behavior of γ′ phase and dynamic recrystallization (DRX) mechanisms of a novel HIPed powder metallurgy (P/M) superalloy deformed at high temperatures (1080−1170 ℃) and different strain rates (1–0.001 s−1) are investigated. The results show that the spheroidization behavior of γ' phase and DRX mechanisms are greatly influenced by deformation condition. The coarse γ′Ⅰ phase promotes the DRX process, while the fine spherical γ'Ⅲ phase results in the formation of sub-grain boundaries. Thus, the grains are refined. During hot deformation, some coarse γ′Ⅰ and γ′ⅠⅠ phases transform into the fine spherical γ'Ⅲ phases, while some initial γ'Ⅲ phases gradually diminish. Besides, the spheroidization rates of γ′Ⅰ, γ′Ⅱ and γ'Ⅲ phases increase with the increase of strain rate. The low DRX volume fraction and refined grains with the average size of 2.27 µm are obtained at 1110 ℃/1 s−1. It is attributed to the fact that the DRX nucleation is obviously enhanced and the pinning effects of spherical γ′Ⅲ phases on dislocations accelerate the formation of sub-grains. In addition, the discontinuous DRX is the main DRX mechanism of this novel P/M superalloy.