Modelling of dominant softening mechanisms for Ti-6Al-4V in steady state hot forming conditions

In this paper a set of mechanism-based unified elastic-viscoplastic constitutive equations has been used to model the mechanisms of plastic flow softening for the two-phase titanium alloy Ti-6Al-4V in hot forming conditions. Globularisation of the secondary (lamellar) alpha phase, dislocation density, plastic deformation induced temperature increase and phase transformation during deformation have been modelled. Hot compression tests were conducted on Ti-6Al-4V samples at different temperatures in a range of 1093K-1293K and at different strain rates in the range of 0.1s^-1-10s^-1. The material parameters were determined by using the hot compression test results and by using an Evolutionary Programming (EP)-based optimisation method. Based on the set of constitutive equations, stress-strain relationships for Ti-6Al-4V at different temperatures and strain rates were predicted. Good agreements between the experimental and computed results were obtained in steady state hot forming deformation conditions.