Influence of Strain Rate on the Interactions Between Precipitation and Recrystallization during Hot Deformation of Ni-Based Superalloy Nimonic 80A

Abstract

The interactions between precipitation and dynamic recrystallization of nickel-based superalloy Nimonic 80A were investigated by conducting hot compression and stress relaxation tests in the temperature interval of 900-1000 °C and strain rates 0.001-1 s−1. Analysis of the stress–strain curves indicated a peak strain followed by a softening trend, indicative of the occurrence of dynamic recrystallization at 900, 925, 950, and 975 °C for all strain rates. However, as the temperature increase, the peak strain tends to fade out, so that the flow stress curves were flattened, and the peak strain vanished for tests at 1000 °C. The values of activation energy of the material were determined as 1185 kJ mol−1. The deformed microstructures were characterized using optical and field-emission scanning electron microscopes. The results show that, at low temperatures and high strain rates (900 °C and 1 s−1), the dominant work softening mechanism was continuous dynamic recrystallization. In contrast, as the temperature increased and the strain rate decreased, the dominant work softening mechanism changed to discontinuous dynamic recrystallization. The influence of strain rate and the role of gamma prime precipitation on the progress of recrystallization were analyzed and quantified.