Behavior and modeling of high temperature deformation of an α + β titanium alloy

The deformation behavior of as-cast ATI 425 titanium alloy was studied using isothermal, constant strain rate compression carried out on a Gleeble-3500 testing system under conditions of varying temperature (950–1150 °C) and strain rates (0.001–1 s−1) up to a height reduction of 50%. Microstructure observations in α + β and single β phase fields showed the globularization of the platelet α and dynamic recovery of β, respectively. Constitutive equation describing the flow stress as a function of the processing parameters was proposed in the form of Arrhenius-type relationship. The calculated apparent activation energy of 155 ± 15 kJ/mol suggested a dislocation climb/slip controlled deformation mechanism. Processing map was generated according to dynamic material model and Prasadʹs instability criterion. Domains with peak efficiency >0.48 and flow instability were investigated and the evidences of deformation in these regions were identified and validated through microstructure observations. For ingot breakdown, deformation at T > 1100 °C and ε ˙ > 0.1  s − 1 was suggested and height reduction bigger than 50% was needed to get a further recrystallized microstructure.