Flow behavior and constitutive model for Ni–20.0Cr–2.5Ti–1.5Nb–1.0Al superalloy compressed below γ′-transus temperature

Hot deformation behavior of Ni–20.0Cr–2.5Ti–1.5Nb–1.0Al superalloy has been investigated at the temperatures of 940–1060 ̊C (all below nominal γ′-transus temperature of 1080 °C) and strain rates of 0.001–1.0 s−1. The results show that true stress–true strain curves exhibit a peak stress at a small strain, after which the flow stress decreases monotonically until high strains, showing a dynamic flow softening. The flow stress consists of four different stages, viz., work-hardening, stable, softening and steady stage. Flow stress decreases with increasing temperature and decreasing strain rate. The constitutive equation represented as a function of temperature, strain rate and true strain was developed, which gives an accurate and precise estimate of flow stress. Hot deformation should be carried out under condition of (Topi: 1020 °C, ε ˙ opi :     1.0  s − 1 ) obtain fine homogeneous microstructure.