Effect of Test Temperature on Tensile Behavior of Ti-5Al-5V-2Mo-1Cr-1Fe (α+β) Titanium Alloy with Initial Microstructures in Hot Forged and Heat Treated Conditions

Ti-5Al-5V-2Mo-1Cr-1Fe (Ti-55211) is another popular (α+β)-Ti alloy which exhibits good hardenability and high strength due to the formation of α′ martensite. In the present study, this alloy in the as-forged and heat treated conditions was investigated to evaluate the tensile behavior as a function of test temperature (from room temperature to near its β transus). There was significant loss of ductility with a marginal improvement in tensile strength at room temperature upon heat treating the as-forged alloy near the β transus temperature. This is attributed to the solid solution strengthening, formation of α′ laths, change in shape and distribution of α phase during heat treatment. The alloy in both as-forged and heat treated conditions exhibited typical superplasticity characteristics with large elongations to failure (~ 200 to 230 pct) associated with high strain rate sensitivity values (0.2 to 0.4) at the testing temperature near its β transus. Microstructural investigation revealed that the morphology of the α-phase gets transformed from lamellar or acicular into equiaxed/globular with random deformation texture in both conditions during tensile deformation near β transus. It was found that the mode of deformation operating at temperature of 1123 K was found to be dynamic recrystallization (DRX) of α-phase, whereas dynamic recovery (DRV) of β-phase occurred at 1173 K.