Characterization of hot deformation behavior and optimization of hot workability for GH4698 superalloy

The hot compressive behavior of GH4698 superalloy is examined in the temperature range of 950-1100 degrees C and strain rate range of 0.001-1 s-1. The observations from the flow stress curves reveal work hardening and dy-namic recovery features at the beginning of the deformation, which leads to rapid increase in the true stress. After the true stress exceeds its peak level, the dynamic softening induced by dynamic recrystallization (DRX) becomes dominant, and the true stress gradually drops until a relatively stable stress level. Considering the coupled impact of temperature and strain rate, an improved Zhu-Ou-Popov (ZOP) model is proposed to char-acterize the hot deformation behavior of the tested superalloy. The results verify the accuracy of the improved ZOP model for reproducing the hot deformation behavior of the tested superalloy with a correlation coefficient as high as 0.9721. Additionally, the processing maps are established according to the dynamic material model. Furthermore, the microstructural evolution is examined to validate the feasibility of the established processing maps. The results reveal that the processing maps can be decomposed into three domains: an unstable region, a stable region with low power dissipation, and a stable region with high power dissipation. The main instability regions are 950-1050 degrees C, 0.04-1 s-1 and 1095-1100 degrees C, 0.1-0.22 s- 1, where obvious microcracks and mixed grains can be observed. The stable zone with low power dissipation consists of three parts: 1040-1100 degrees C, 0.1-1 s- 1 and small DRX grains are the predominant microstructures. The stable region with high power dissipation is observed at 1010-1100 degrees C and 0.001-0.1 s- 1, where the DRX grains are found to be fine and uniform, and it is the optimal hot working window to achieve the desired performance of the tested superalloy. , 1040-1100 degrees C, 0.02-0.1 s- 1; 950-1065 degrees C, 0.001-0.04 s- 1. In these regions, the primary elongated grains