Hot deformation characteristics of Alloy 617B nickel-based superalloy: A study using processing map

Abstract

The deformation behavior of Alloy 617B was investigated by the isothermal compression test at temperature range of 1120–1210 °C with strain rates of 0.01–20 s−1 on a Gleeble-1500 thermo-mechanical simulator. The approach of processing map was used to reveal the hot workability and microstructural evolution during hot deformation. The temperature correction was invited here for high strain rate condition to get more accurate processing map. The results show that the processing parameters have significant effects on power dissipation efficiency and instability factors. The unsafe domains are detected at the high strain rate (>10 s−1) condition and is characterized by uneven microstructure and high density twins, which should be avoided in hot working process. The optimum hot working condition are obtained in the temperature range of 1120–1165 °C and strain rate scope of 0.01–0.1 s−1 with the peak power dissipation efficiency of 48%. Another domain of 1170–1210 °C and 0.1–4.5 s−1 can also be chosen as the optimal working condition at large strains (>0.8). In these two optimum domains, the original grains are substituted by fine dynamic recrystallization (DRX) grains and DRX is the main power dissipation mechanism. The dominant nucleation mechanism of DRX in the safe domain is the bulging of original grain boundaries accompanied with twining, which is the feature of discontinuous dynamic recrystallization (DDRX). Some characteristics of continuous dynamic recrystallization (CDRX) can also be found when deformed at strain rate of 1 s−1, although it can only be considered as an assistant nucleation mechanism.