Deformation and dynamic recrystallization behavior of a high Nb containing TiAl alloy

The hot deformation and dynamic recrystalliztion (DRX) behavior of a high Nb containing TiAl alloy were studied using hot uniaxial compression tests. The tests were conducted at temperatures of 1000-1150 degrees C and strain rates of 0.001-0.5 s (1). Due to high Nb additions, this alloy possesses a wide hot-working window. The stress-strain curve exhibits peak stress at low strain followed by dynamic softening and steady-state flow. The dependence of the peak stress on the deformation temperature and strain rate can well be expressed by a hyperbolic-sine type equation. The activation energy, Q, was measured to be 427 kJ/mol (4.3 eV) and the stress exponent was measured as 4.16. Based on the conventional strain hardening rate curves (d sigma/d epsilon versus sigma), the characteristic points including the critical strain for DRX initiation (epsilon(c)) and the strain for peak stress (epsilon(p)) were identified to express the evolution of DRX and epsilon(c) is 0.92 times epsilon(p). In order to characterize the evolution of DRX volume fraction, 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 alloys. Besides, the role of beta phase and the softening mechanism during hot deformation were discussed in detail. (C) 2012 Elsevier B.V. All rights reserved.