A systematic study on thermo-mechanical behavior, processing maps and recrystallization mechanism of Incoloy825 superalloy during hot compression

Abstract

This study conducted isothermal hot compression experiments on Incoloy825 superalloy, spanning temperatures from 1000 to 1150 °C, strain rates from 0.01 to 10 s−1, and a true strain of 0.69. Employing Electron Backscatter Diffraction and Transmission Electron Microscopy for characterization, the research systematically explored the alloy's thermal-mechanical behavior, hot processing maps, microstructural evolution, and dynamic recrystallization (DRX) mechanisms during hot deformation. True stress-strain curves were obtained for various deformation conditions, corrected, and used to establish a highly precise constitutive model. A hot processing map was constructed using the Dislocation Migration Model theory. Through comparative analysis with microstructures, it identified the optimal hot processing parameters for Incoloy825 superalloy within the range of 1110–1150 °C, 0.01–0.3 s−1, and 3.3–10 s−1. Microstructural analysis revealed a positive correlation between temperature and the extent of DRX in the alloy, with an acceleration in the transformation from Low-Angle Grain Boundaries (LAGB) to High-Angle Grain Boundaries (HAGB). The temperature of 1100 °C served as a critical point for the influence of strain rate on the microstructure. Below this temperature, DRX and HAGB proportions initially decreased and then increased with higher strain rates, while at higher temperatures, they directly correlated with strain rates. The study also investigated DRX mechanisms, determining Dynamic Discontinuous Recrystallization (DDRX) as the primary mechanism, more active at higher temperatures and strain rates. Continuous Dynamic Recrystallization (CDRX) served as a supplementary mechanism, especially in high-temperature and low-strain-rate deformation. Twins acted as favorable nucleation sites for DRX, facilitating both DDRX and Twin-DRX (TDRX) processes in Incoloy825 superalloy.