Dynamic recrystallization kinetics of a powder metallurgy Ti-22Al-25Nb alloy during hot compression

The flow behavior of a P/M Ti-22Al-25Nb alloy was evaluated by applying a series of compression tests to a height reduction of 50% performed within the temperature range of 950-1070 degrees C using strain rate range of 0.001-1 s(-1). The dynamic reaystallization (DRX) behavior at elevated temperature was evaluated by the modified Avrami type equation based on stress-strain data. By means of conventional hyperbolic sine function, the activation energies for DRX were estimated to be 1053.06 kJ/mol in the (alpha(2)+beta/B2+O) phase region and 734.77 kJ/mol in the (alpha 2+B2) phase region, respectively. The critical strain (epsilon(c)) for the onset of DRX, the strain for peak stress (epsilon(p)) and the strain for maximum softening rate (epsilon*) under different deformation conditions were identified according to the strain hardening rate curves. The DRX kinetics model was proposed to characterize the evolution of DRX volume fraction, which revealed that the DRX exhibited the 'slow-rapid-slow' evolution with the increasing strain. It was also found that the process of DRX was promoted by decreasing strain rate and increasing deformation temperature. Moreover, the microstructure examination results indicated that the theoretical prediction results were shown to be in good agreement with the statistical results. Finally, the continuous dynamic reaystallization (CDRX) was identified to be the DRX mechanism by referring to a transmission electron microscope (TEM) observation. (C) 2014 Elsevier B.V. All rights reserved.