Transition of dynamic recrystallization mechanism during hot deformation of Incoloy 028 alloy

Dynamic recrystallization (DRX) plays significant roles in manipulating of microstructures during hot deformation and the result mechanical properties; however, the underling mechanism leading to multi scale–microstructures remains poorly understood. Here, the DRX mechanism under wide processing conditions (i.e. 950–1200 °C, 0.001–10 s⁻¹) in Incoloy 028 alloy was investigated, where the relationships among flow stress, Z parameter and grain size, as well as the evolution of characteristic microstructures (grain size, sub–grain boundaries, and high angle grain boundaries), are established. As the values of Z parameters decrease (corresponding to decreased flow stresses), three typical softening mechanisms successively occur, ranging from continuous DRX controlled by dislocation glide, discontinuous DRX dominated by dislocation motion (climb and cross/multiple slip) and grain boundary migration, to dynamic normal/abnormal grain growth resulting from grain boundary migration, with transition regions where two adjacent mechanisms occur simultaneously. Correspondingly, these above three softening mechanisms result in ultrafine, fine and coarse grains, respectively. The present findings demonstrate a comprehensive understanding of DRX mechanism over a wide range of processing conditions, and further provide a new guideline for preparing single crystals.