Hot deformation behavior of Ti-5.0Al-2.40Sn-2.02Zr-3.86Mo-3.91Cr alloy with an initial lamellar microstructure in the α plus 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 alpha + beta phase field was investigated at the temperatures of 1050-1130K (all below the beta-transus temperature) and the strain rates of 0.001-10.0 s(-1) using processing maps. The apparent activation energy of deformation was calculated to be 313 kJ mol(-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 (eta), identification of the instability regions and optimization of the alpha + beta forging process parameters. It is found that the hot deformation at low temperature has high eta value, and the microstructure obtained at high temperature is more homogeneous. The globularization process represents the moderate eta 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 (T-opi: 1130K, (epsilon) over dot(opi) : 0.001 s(-1)). Flow instability is expected to occur at a single region with a higher strain rate ((epsilon) over dot >= 3.0 s(-1)) across the temperature range (T-d: 1050-1130K) due to the possible occurrence of adiabatic shear banding or/and flow localization. (c) 2010 Elsevier B.V. All rights reserved.