Microstructure evolutions and nucleation mechanisms of dynamic recrystallization of a powder metallurgy Ni-based superalloy during hot compression

Dynamic recrystallization (DRX) has been of great concern throughout the manufacturing processes, and it deeply affects in-service performance of powder metallurgy Ni-based disk components. Understanding the underpinning mechanisms of DRX is vital to produce the desired microstructure and mechanical properties of the superalloys. In this article, microstructure evolutions and nucleation mechanisms of DRX of an advanced Ni-based superalloy during hot deformation were studied using high resolution EBSD and TEM. The experimental results show that low angle grain boundaries were formed at low temperature and readily evolved to high angle grain boundaries with temperature increasing and/or strain rate decreasing. Effects of strain amount on DRX were examined and significant DRX was detected when the strain increased to 0.5 under conditions of 1050 °C/0.01 s−1. Three different nucleation mechanisms were found under different deformation parameters. Nucleation of DRX was strongly related to the bulged-original boundaries, which acted as the interaction barrier with mobile dislocations at relatively low temperature and strain rate of 0.1 s−1. In contrast, twining boundaries were identified as the nucleation sites at a higher temperature and strain rate of 0.01 s−1. At 1100 °C and low strain rate of 0.001 s−1, coalesced γ′ was encompassed by bulged-original boundary, where nucleation of DRX was detected.