Constitutive modeling and hot processing map of Ti551 alloy in the α+β two-phase region

As a base material for additive forging processes, a novel titanium alloy Ti551 had been used to conduct hot compression via a Gleeble 3500 thermo-mechanical simulator, and then flow stress curves were obtained over a strain rate range of 0.001～ 10 s⁻¹ and a temperature range of 700～ 900 ℃ in this study. The flow stress curves were fitted using a strain-compensated Arrhenius model and an artificial neural network model, respectively. The strain-stress curves indicate that during deformation in the two-phase region, the flow stress of the Ti551 alloy exhibits a typical post-peak softening behavior under medium-to-low temperatures and high strain rates. Compared with predicated results from the strain-compensated model, the artificial neural network model gives higher prediction accuracy and lower average absolute relative error under low-temperature and high strain-rate conditions, with a correlation coefficient R of 0.9922 and a mean average absolute relative error of 6.3%. Based on the constructed hot processing map of the Ti551 alloy deformed in the two-phase region, the plastic instability domains under different strain conditions were identified. The lower limit of equivalent strain rate during forging in the α+β two-phase region should be no less than 0.01 s⁻¹, corresponding to an actual forging speed of not less than 10 mm/s, and that the final forging temperature should be no lower than 750 ℃. These finds can help design practical forging parameters and numerical simulation of Ti551 alloy in the α+β two-phase region.