Serrated flow behavior and microstructure evolution of Inconel 625 superalloy during plane-strain compression with different strain rates

Strain rate played an important role in the forming process of metal and alloy. In the present work, the effect of strain rate on deformation behavior and microstructure evolution of thermal-rolled Inconel 625 superalloy were systematically investigated by plane-strain compression (PSC) test at 1000 °C, and the strain rate range changed from 1 × 10⁻³ s⁻¹ to 5 s⁻¹. Obvious serrations occurred in strain rate range of 5 s⁻¹ - 0.05 s⁻¹ and transformed from type A to type A+B, and type B with decreasing of strain rate. Microscopic observations from transmission electron microscopy (TEM) indicated that type A and type B serration were related to slip bands nucleation-propagation, and carbon atoms-dislocations interaction, respectively. Electron backscatter diffraction (EBSD) technique and TEM were used to study the dynamic recrystallization (DRX) behavior during PSC. As the strain rates were greater than 5 s⁻¹, DRX process was accelerated because of high deformed stored energy and adiabatic heating. This is undoubtedly a meaningful find to refine grain size and improve thermal processing efficiency. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) have been confirmed to occur simultaneously during the deformation process, but CDRX played a minor role in DRX nucleation. Texture evolution characteristics were also related to strain rate. Nearly random texture distribution was obtained as the strain rate above 0.5 s⁻¹. Obvious Cu, E, S and Cube textures appeared in the strain rate range of 0.1 s⁻¹–10⁻² s⁻¹. Grain orientations showed random distribution at the strain rate of 10⁻³ s⁻¹. Moreover,<001> direction should be considered as preferred crystallographic orientations to recrystallization nucleation.