Impact of γ′(Ni3(Al,Ti)) phase on dynamic recrystallization of a Ni-based disk superalloy during isothermal compression

The present work aims at investigating the impact of gamma '(Ni-3(Al,Ti)) phase on the dynamic recrystallization (DRX) behavior of a Ni-based turbine disk superalloy FGH4096 during hot compression. Two different treatments were selected to obtain gamma ' phase with different size and morphology. For the first treatment by slow cooling rate after solution treatment the coarsening of gamma ' phases occurred with morphologies of dendrites, fireworks and long strips, and simultaneously the grain boundaries of microstructure were serrated. The second heat treatment yielded alloy with fine and round shape gamma ' phase. During sub-solvus compression, both the peak flow stress and the critical strain for the initiation of DRX for the alloy with coarse gamma ' phase were lower than that of the alloy with fine gamma ' phase. The volume fraction of DRX grains for the alloy samples with coarse gamma ' phase was higher than that of samples with fine gamma ' phase particles. Secondary electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to find the reason for this phenomenon, and finally dislocation induced coarse gamma ' phase DRX nucleation mechanism was proposed. (C) 2016 Elsevier B.V. All rights reserved.