Effect of deformation parameters on twinning evolution during hot deformation in a typical nickel-based superalloy

Abstract

The twinning evolution of a typical nickel-based superalloy was investigated by means of isothermal compression tests in the temperature range of 960–1160°C and strain rate range of 0.001–1s−1. During hot deformation, the original Σ3 boundaries lost their Σ3 misorientation due to crystal rotations, while lots of new Σ3 boundaries were formed mainly by growth accidents. With the increasing temperature and decreasing strain rate, the distributions of twin boundaries became more and more uniform, while the length and width of twin boundaries increased in size. In particular, the existing twins promoted the formation of more additional stacking error, and resulted in the occurrence of twinning adjacent to the existing twins, which coalesced with the existing twins and increased the twin width. Moreover, the fraction and density of Σ3 boundaries increased with the increasing deformation temperature and decreasing strain rate firstly, and then they decreased again. At the higher temperature and lower strain rate, the accelerating grain growth inhibited the occurrence of twinning, leading to the decreasing fraction and density of Σ3 boundaries. On the other hand, the higher deformation temperature and lower strain rate would also lead to the lower fraction of incoherent Σ3 boundaries, the reason of which was also discussed.