Deformation behaviour and microstructure evolution of Ti-2.3Al-2.6Zr alloy in the temperature range of 700–1000 °C

Abstract

Ti-2.3Al-2.6Zr alloy was hot deformed at temperatures from 700 to 1000 °C and strain rates from 10−2 −30 s−1. The uniaxial compression tests were conducted in vacuum to a true strain of 1 for this alloy. Strain rate sensitivity was calculated from the true stress- true strain data and plotted as contour plots to generate the strain rate sensitivity map. The hot working condition of this model α-Ti alloy was optimized by using the strain rate sensitivity map. The optimized hot workability domains were identified for α-phase as (a) 780–900 °C at strain rate of 10−2 to 0.3 s−1 and (b) 825–900 °C at strain rate of 3–30 s−1. The domain of hot processing condition for β-phase was found at 930–1000 °C for all strain rates. In α-phase domain the strain rate sensitivity was about 0.3, the stress exponent was 4.3 and the activation energy for deformation was 285 kJ mol−1 whereas in β-phase domain the strain rate sensitivity was about 0.34, the stress exponent was 5.3 and the activation energy for deformation was 210 kJ mol−1. These deformation parameters suggest the deformation process to be a dislocation based mechanism. Samples deformed within the high strain rate sensitivity domains showed microstructural features of dynamic recrystallization. In α-phase fine equiaxed recrystallized grains with high angle boundaries were observed. Deformation at 900 °C and 0.01 s−1 resulted in fully recrystallized equiaxed grains in the α-phase, whereas the β-phase showed lamellar grain morphology with very fine recrystallized grains.