Evolution of twins and sub-boundaries at the early stage of dynamic recrystallization in a Ni-30%Fe austenitic model alloy

Evolution of twins and sub-boundaries at the early stage of dynamic recrystallization (DRX) is investigated in a Ni-30%Fe austenitic alloy. It is found that the primary nucleation of DRX is accomplished by formation of annealing twins along the bulged pre-existing grain boundaries and at the triple junctions at the early stage of deformation. With the strain increasing, the DRX nucleation due to the formation and evolution of sub-boundaries also plays a significant role. The results also indicate that the ∑9 twin boundaries are generated by mutual interactions between the encountered ∑3 twin boundaries at the initial stage. The pre-existing twin boundaries can gradually convert to general boundaries or twin steps owing to the interaction of twin boundaries with dislocations. Continuous DRX (CDRX) mechanism associated with the sub-boundaries evolution is found to be an assistant mechanism at the early stage of DRX. Besides, formation of sub-boundaries inside the growing DRX grains can stimulate a new round DRX nucleation by impeding migration of grain boundaries and making them serrated.