Hot deformation behavior and microstructural evolution of as-forged Ti-44Al-8Nb-(W, B, Y) alloy with nearly lamellar microstructure

Abstract

The hot deformation behavior and microstructural evolution of as-forged Ti-44Al-8Nb-(W, B, Y) alloy with nearly lamellar structure were investigated by means of uniaxial hot compression. Its stress exponent and activation energy are 3.81 and 494 KJ/mol, respectively. The efficiencies of power dissipation and instability parameters are evaluated, and processing maps at strains of 0.12, 0.25, and 0.5 are developed. It is demonstrated that the microstructural evolution is dependent on the temperature and strain rate. Moreover, the recovery and recrystallization of γ phases as well as the spheroidization of α phases play important roles in refining the microstructure. Reasonable parameters for secondary hot working are above 1150 °C with a strain rate of less than 0.25 s−1 at a strain of 0.5. Additionally, the hot working window can be expanded to the region with lower temperature and higher strain rate at a strain of 0.12. Finally, crack-free TiAl sheets were successfully prepared by hot pack rolling. The as-rolled alloy is characterized by duplex microstructure with a mean grain size of 10 μm, exhibiting a failure strength of 1021 MPa with 0.78% ductility at room temperature. At 800 °C, the failure strength remains high: above 650 MPa.