High temperature deformation behavior of near γ-phase high Nb-containing TiAl alloy

High temperature compressive deformation behaviors of a high Nb-containing PM-TiAl alloy (Ti-45Al-7Nb-0.3 W, at.%) were investigated at temperatures ranging from 1050 degrees C to 1200 degrees C, and strain rates from 0.001 s(-1) to 1 s(-1). The microstructure mainly consists of gamma phase. The data obtained from the flow curves were employed to develop the constitutive equation, and the apparent activation energy (Q) was determined to be 414 kJ mol(-1). The size of the dynamically recrystallized grains (DRX) decreased with the increasing value of Zener-Hollomon (Z) parameter. A processing map was constructed on the basis of the flow stress, and the condition of intermediate Z (1150 degrees C, 0.1 s(-1)) was determined to be the optimum hot forging parameter for industrial productions. DRX was observed under all the deformation conditions. At high Z and intermediate Z condition, dislocation climbing and twinning accompanied by DRX can act as the main deformation mechanisms. At low Z condition, DRX becomes the dominant softening mechanism, accompanied by the bending of lamellar colonies as well as the broken of gamma grains and alpha(2) grains. (C) 2014 Elsevier Ltd. All rights reserved.