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 range 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.
Highlights
Structure weight reducing is an important development direction of aeronautics and astronautics aircrafts
Each specimen was heated to the deformation temperature at a rate of 5 ◦ C/s, soaked for 5 min, compressed to an engineering strain of 50%, and quenched immediately to preserve the as-deformed microstructure
The positive ismole less fraction than 45%, completely through completely the β phasethrough field. The of this mole fraction of Al is less than 45%, it solidifies completely through the β phase field
Summary
Structure weight reducing is an important development direction of aeronautics and astronautics aircrafts. The novel lightweight and heat resisting structural material is urgently demanded. TiAl alloy is expected to become a substitute for nickel-based superalloys in several high temperature applications because of its low density, high strength, and excellent high temperature performance, and the working temperature could be up to 650–800 ◦ C [1,2]. Due to its poor ductility and narrow thermal processing window, the production of large-size and high-quality TiAl components from ingot material presents significant difficulties [3]. The application of TiAl alloy is limited. TiAl alloys containing the β phase show much better hot workability than (γ + α2 ) TiAl alloys, even enabling the production of
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