Flow stress prediction during hot working of near-α titanium alloys

Abstract

In the aerospace industry where individual titanium forgings are of considerable cost, modelling of thermomechanical processing is employed to optimize operations. The reliable prediction of flow stress reduces the testing required to create and/or certify modified processing routes and enables forging to be performed near equipment operating limits (maximum forging loads, rates, etc.). However, the prediction of flow stress during forging of titanium alloys presents a significant challenge due to a variety of morphologies, sizes, and distributions of the phases present under hot working conditions. As a result, the flow behaviour and microstructural development of near-α titanium IMI834 under typical ingot breakdown process conditions has been investigated and a comprehensive flow stress model valid in one- and two-phase temperature regimes developed for general near-α alloys. Flow stress behaviour has been modelled using a self-consistent method, which has been developed in the literature for α + β alloys, by adapting constitutive equations to account for common alloying elements in near-α alloys. The model has been successfully validated for a number of alloys using experimental and literature data. Hot working conditions have been simulated through compression testing at temperatures of 975, 1000, 1025, 1060, and 1100 °C and strain rates of 0.1 and 1 s −1.