Hot deformation behavior of Ti-5.0Al-2.40Sn-2.02Zr-3.86Mo-3.91Cr alloy with an initial lamellar microstructure in the α+β phase field

Hot deformation behavior of Ti-5.0Al-2.40Sn-2.02Zr-3.86Mo-3.91Cr alloy with an initial lamellar microstructure in the α+β phase field was investigated at the temperatures of 1050-1130K (all below the β-transus temperature) and the strain rates of 0.001-10.0s-1using processing maps. The apparent activation energy of deformation was calculated to be 313kJmol-1, and a constitutive equation by which the flow stress is represented as a function of strain rate and deformation temperature was developed. A processing map was constructed based on the experimental data for evaluation of the efficiency of power dissipation (η), identification of the instability regions and optimization of the α+β forging process parameters. It is found that the hot deformation at low temperature has high η value, and the microstructure obtained at high temperature is more homogeneous. The globularization process represents the moderate η value and contributes to the grain refinement. In order to obtain the homogeneous microstructure with fine grain, hot deformation should be carried out under the condition of (Topi: 1130K, ε̇opi:0.001 s-1). Flow instability is expected to occur at a single region with a higher strain rate (ε̇≥3.0 s-1) across the temperature range (Td: 1050-1130K) due to the possible occurrence of adiabatic shear banding or/and flow localization.