Spheroidization of the lamellar microstructure in Ti–6Al–4V alloy during warm deformation and annealing

The spheroidization behavior of an α colony microstructure in Ti–6Al–4V alloy during warm working and subsequent annealing at 600 and 800 °C was established. The principal features of microstructure evolution were found to be temperature dependent. At 800 °C transformation of the lamellar microstrucuture into a globular one was associated primarily with the classical boundary splitting mechanism followed by further spheroidization of α particles by means of termination migration. For thick α lamellae, however, new grains were formed due to continuous dynamic recrystallization during deformation, but spheroidization per se was limited. A decrease in temperature to 600 °C resulted in increased shear strains, lower diffusivity, and a decrease in the volume fraction of the β phase. Consequently, the thin β interlayers transformed relatively quickly into separate particles while α became the matrix phase. Evolution of the α phase during deformation/annealing at 600 °C was associated with continuous dynamic recrystallization with only limited dynamic or static spheroidization. Static spheroidization kinetics during annealing following warm working were explained in the context of approximate models of boundary splitting and termination migration.

► Spheroidization of lamelar microstructure in Ti–6Al–4V alloy during warm working/annealing.
► At 800 °C boundary splitting and termination migration mechanisms are mainly operated.
► At 600 °C β interlayers transform into separate particles while α becomes matrix.
► Evolution of α is related to continuous recrystallization at both temperatures.