Tensile Flow Behavior of Ti-6Al-4V Alloy from Room to Intermediate Temperatures

The tensile flow behavior of Ti-6A-4V in a bimodal alpha plus transformed beta microstructural condition has been evaluated at a strain rate of 10⁻³ s⁻¹ over the temperature range from room temperature to 325 °C. The strain-hardening behavior is examined using log–log and differential (rate of work hardening) plots of true stress versus true plastic strain. Double-slope behavior in the log–log plot suggests the presence of two distinct mechanisms during tensile deformation in different strain regimes. The true stress versus true plastic strain plots are fitted using constitutive equations such as Hollomon, Swift and Ludwigson. The temperature dependence of yield, tensile stress and work hardening is analyzed. It is found that the work-hardening exponents and rates increase with increasing temperature. This suggests a possible dynamic strain aging (DSA) behavior. This is further confirmed by the presence of Type C serrations in the stress–strain curve at 300 °C. An estimation of the velocity of dislocation in the DSA regimes with respect to the moving solute indicates that the interstitial oxygen is responsible for the DSA behavior. The associated mechanism is one of the hopping of solute atoms from the compression to the tensile region in the vicinity of the dislocation core.