Hot deformation behavior and microstructural evolution characteristics of Ti-44Al-5V-1Cr alloy containing (γ + α2 + B2) phases

Abstract

The hot deformation behavior and microstructural evolution of Ti-44Al-5V-1Cr alloy were investigated by hot compression tests at temperatures of 1000-1250 C and strain rates of 0.001-1 s-1. It was indicated that the dependence of peak stress on deformation temperature and strain rate could be accurately described by a hyperbolic sine type equation. The activation energy, Q, was estimated to be 632 kJ/mol. The hot processing map was developed at different strains on the basis of dynamic materials modeling and the Murty criteria. As a result, the instability zones occurred in the regions of low temperature (<1050 C) and a high strain rate (>0.1 s-1). The flow soft mechanism of the instability regions is stress relaxation caused by localization deformation at lamellar boundaries. Dynamic recrystallization is the mainly refining and spheroidizing mechanism of lamellar microstructures. The optimum hot working condition of as-cast TiAl alloy occurs in the temperature range of 1175-1225˚C and the strain rate ra ge 0.05-0.1 s-1. The large-size TiAl alloy rectangular bars with crack-free appearance were successfully prepared by hot extrusion. After annealing, the fine and uniform microstructure with excellent deformation ability was obtained.