Hot working behaviour of experimental Ti-4.5Al-1 V-3Fe alloy with initial lamellar microstructure

Abstract

Isothermal compression testing was carried out on newly developed low-cost (α + β) Ti-4.5Al-1 V-3Fe alloy with lamellar initial microstructure using a Gleeble 3500 thermomechanical simulator. The tests were performed under different conditions of strain rate (0.001, 0.01, 0.1, 1 and 10 s −1), deformation temperature (750, 800, 850, 900 and 950 °C) and a constant total strain of 0.6. Stress-strain analysis, constitutive constant calculations, processing maps and microstructural validation were used to understand the hot working behaviour of the alloys and the underlying softening mechanisms. The results show that the deformation behaviour was significantly influenced by the deformation parameters. Two main softening mechanisms, which have been reported in existing commercial alloys with a fully lamellar structure, also controlled the deformation behaviour of the Ti-4.5Al-1 V-3Fe alloy. Lath bending and rotation caused flow softening at low temperatures and high strain rates, while dynamic globularisation led to flow softening at the higher temperatures and low strain rates. The optimum condition for hot working of the alloy in the safe deformation region was found at ~890–905 °C and 0.003–0.01 s −1. The region of instability identified at ~875–930 °C/0.15–0.4 s −1 should be avoided during hot working to prevent flow localisation, shear cracks, cavitation and other instabilities that may arise.