Behavior and modeling of high temperature deformation of an α plus 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 degrees C) and strain rates (0.001-1 s(-1)) up to a height reduction of 50%. Microstructure observations in alpha + beta and single beta phase fields showed the globularization of the platelet alpha and dynamic recovery of beta, 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 Prasad's 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 degrees C and epsilon > 0.1 s(-1) was suggested and height reduction bigger than 50% was needed to get a further recrystallized microstructure. (C) 2012 Elsevier B.V. All rights reserved.