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

The twinning evolution of a typical nickel-based superalloy was investigated by means of isothermal compression tests in the temperature range of 960-1160 degrees C and strain rate range of 0.001-1.s(-1). During hot deformation, the original 3 boundaries lost their 3 misorientation due to crystal rotations, while lots of new Sigma 3 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 3 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 Sigma 3 boundaries. On the other hand, the higher deformation temperature and lower strain rate would also lead to the lower fraction of incoherent 3 boundaries, the reason of which was also discussed.