Investigation on the hot deformation behavior of powder metallurgy TiAl-based alloy using 3D processing map

摘要

The deformation behavior of the powder metallurgy Ti-47Al-2Nb-2Cr alloy in hot working process was researched by the isothermal compression tests performed in the deformation temperature range of 950-1200 degrees C and the strain rate range of 0.001-0.1 s(-1) with true strain of 0.8. The constitutive equation which presented the flow stress as a function of the strain rate and deformation temperature was established for hot deformation of this alloy. The hot deformation apparent activation energy was calculated to be 337.501 kj-mol(-1). The 3D processing maps were developed on the basis of experimental data and dynamic material model theory for the identification of the instability regions and optimization of hot processing parameters. It was found that the dynamic recrystallization of powder metallurgy Ti-47Al-2Nb-2Cr alloy occurs at two domains, one occurs in the temperature range of 1040-1060 degrees C and strain rates of 0.001-0.0015 s(-1), with peak efficiency of power dissipation of 55.0% occurring at about 1050 degrees C/0.001 s(-1), the other occurs in the temperature range of 1180-1200 degrees C and strain rate of 0.003-0.01 s(-1) with peak power dissipation efficiency of 48.8% occurring at about 1200 degrees C/0.001 s(-1), which suggested that these domains can be considered as the optimum processing window for hot working of this alloy. Meanwhile, the flow instability domain was found to occur at strain rates higher than 0.01 s(-1) with the microstructural observation of the grain boundary cracks, which has to be kept away during hot processing in pursuit of achieving the desired mechanical properties. (C) 2014 Elsevier Inc. All rights reserved.