Flow behavior and microstructural evolution in nickel during hot deformation

The hot deformation behavior of pure nickel with coarse, columnar grains in the temperature range of 950-1150 degrees C at intervals of 50 degrees C and in the strain rate range of 0.001-10.000s(-1) at intervals of one order of magnitude was investigated by isothermal hot compressive testing with the compression ratio of 70%. The results reveal that the strain rate and the temperature strongly affect the flow stress during hot deformation and that flow stress increases with the increase in strain rate while decreases with temperature increasing. Moreover, the relationship among flow stress, strain rate and temperature can be represented by the Zener-Hollomon parameter with the calculated apparent activation energy of 312.403kJmol(-1), and the variation of activation energy is sensitive to strain rate rather than temperature. In addition, the dynamic recrystallization (DRX) analysis reveals that the DRX behavior of nickel is evidently affected by both deformation temperature and strain rate and that the distinct mechanisms of nucleation are the bulging of serrated grain boundaries and the development of twinning.