Abnormal dynamic recrystallization behavior of a nickel based superalloy during hot deformation

Abstract

The dependence of hot deformation behavior and microstructure evolution of IN718 alloy on strain rate were studied by isothermal compression experiments. The tests were performed under the strain rates range of 10−2 s−1 ∼ 20 s−1 up to true strain of 1.2 at 1000 °C. Two peak value of the flow stress curve is observed at intermediate strain rate of 1 s−1, which is different from the single-peak dynamic recrystallization (DRX) behavior. The microstructure characterization reveals that fine and uniform DRX grains are easily obtained both at lower and higher strain rates, while the smaller DRX grain size and elongated original grains with lower fraction of DRX exhibits at strain rate of 1 s−1. The lower accumulated stored energy is detected by Kernal Average Misorientation (KAM) map at the strain rate of 1 s−1, which serves as strong obstacle to the migration of grain boundaries, thus restricts the nucleation and growth of DRX. In addition, the formation of twin boundaries (including ∑3, ∑9 and ∑27 boundaries) during the hot deformation depend on the DRX grains size and the driving force which is sensitive to the strain rate.