Hot Deformation Behavior of Fe-microalloyed Ti-6Al-4V Based on Experiments and Calculations

Hot deformation behaviors of Ti-6Al-4V-0.35Fe were studied, which is significant to improve plastic deformation ability of titanium alloys. In experiment, we used a Gleeble 3800 thermo-mechanical simulator to obtain the relationship between thermomechanical parameters and flow stress in a range of temperatures (800~950ºC) and strain rates (0.001~10 s^-1). The single-peak profiles of the flow curves indicate that dynamic recrystallization (DRX) mechanism dominates the deformation. TEM analysis indicates that the grain size in DRX changes under different deformation temperatures, and finer grains are formed at relatively lower temperature due to the dynamic globularization. The dislocation walls are formed in subgrain boundaries due to dislocation slipping-climbing. The Avrami-type DRX model and the strain compensated multivariable regression model were applied to fit the experimental stress-strain data during hot deformation. A comparative study between these two types of constitutive models was conducted to represent the flow behavior. It is found that both models have good accuracy in predicting the flow stress of Ti-6Al-4V-0.35Fe alloy. A processing map based on dynamic material model (DMM) at the strain of 0.8 (steady-state flow stage) was established to identify the flow instability regions and stability regions. The strain rate range of stability region is 0.001~0.6 s^-1 which has been expanded compared to the range of 0.0003~0.1 s^-1 of Ti-6Al-4V. Optimal hot working parameters are confirmed to be 920~950ºC and 0.001~0.005 s^-1, and nearly complete DRX has taken place. Our results indicate that hot working property of Fe-microalloyed Ti-6Al-4V is better than that of Ti-6Al-4V alloy in 800~950ºC temperature scale, and processing cost is decreased.