Effect of initial microstructure on plastic flow behaviour during isothermal forging of Ti–10V–2Fe–3Al

The plastic flow behaviour and microstructural development during isothermal forging was determined for near beta alloy Ti–10V–2Fe–3Al. Two different initial microstructures were employed: (i) a beta forged billet with a large prior beta grain size with Widmanstätten alpha platelets; and (ii) an alpha–beta forged billet with prior globular primary alpha. The beta forged condition exhibited a peak stress followed by intense flow softening, which is attributed to the break up of the Widmanstätten alpha platelets. Evidence suggests that peak hardening at low strains is due to dislocation pile-ups at alpha platelet/subgrain beta interfaces and subsequent flow softening is attributed to the transmission of beta phase through the alpha platelets. A strain rate ‘jump’ test investigation provided sufficient evidence to suggest that there is a transition from dislocation dominant deformation mechanisms at high strains rates to diffusional dominant deformation at low strain rates in Ti–10V–2Fe–3Al during forging.