Flow characteristics and constitutive modeling for elevated temperature deformation of a high Nb containing TiAl alloy

The hot deformation behavior of a high Nb containing TiAl alloy with a nominal composition of Ti-42Al-8Nb-(W, B, Y) was investigated at temperatures ranging from 1000 C to 1150 C and strain rates from 10^-3 s ^-1 to 0.5 s^-1 on a Gleeble thermo-simulation machine. The work hardening regime and flow softening behavior of the alloy were analyzed in detail. The results revealed that the onset of dynamic recrystallization (DRX) was quite easy for the present alloy, whereas the dynamic recovery (DRV) was impeded during the hot deformation. The DRX kinetics was studied by Avrami-type equation. The low Avrami exponents of the proposed equation indicate a lower recrystallization rate compared to ordinary metals and alloys. Based on the classical hyperbolic-sine law and the kinematics of DRX, the constitutive equations of the work hardening-recovery period (i.e. flow stress before the peak) and flow softening process (i.e. flow curve after the peak stress) were established for the present alloy, respectively. Comparisons between the experimental and calculated results revealed that except the severely cracked specimens, the stress-strain curves predicted by the established model are in good agreement with experimental results.