Influence of the special behavior of interpass retention-relaxation on the softening mechanism of precipitation strengthened GH99 alloy during multi-pass hot deformation

This study investigates the hot deformation behavior of the GH99 alloy for hypersonic missile airfoils at 1020 °C-1170 °C and 0.001s-1-1 s-1 by single-pass hot compression experiments. Based on the establishment of the constitutive equation, thermal processing map, and dynamic recrystallization kinetic model, it elucidates the influence of the second phase strengthening on dynamic recrystallization (DRX). It determines the optimal hot deformation parameters of the GH99 alloy. Moreover, through designing different multi-pass hot compression experiments, we investigated the relaxation characteristics of the organization properties during the water quenching-cooling-holding process in the interpass and the influence of the interpass retention-relaxation behavior on the DRX mechanism. The results show that the water quenching process increases the rheological stress of the second pass compression, and the nucleation of discontinuously dominates the organization dynamically recrystallized (DDRX), supplemented by continuously dynamically recrystallized (CDRX); the static recrystallization (SRX) occurring in the high-temperature retention stage of the interpass can effectively reduce the rheological stress. The organization is characterized by the growth of recrystallized grains during the subsequent deformation process. With the prolongation of the high-temperature retention time, the number of recrystallized grains and the dislocation density increase.