A metallurgical approach to individually assess the rheology of alpha and beta phases of Ti-6Al-4V in the two-phase domain

An original hot torsion procedure is presented using Ti-6Al-4V in the two-phase domain. Kinetics of phase transformation are used to obtain stress-strain curves in off-equilibrium states. The individual influences of phase fraction and of temperature are quantitatively assessed in the two-phase domain. Between the two forging temperatures 1143 K (870 °C) and 1228 K (955 °C), a 95 MPa stress difference is observed. The paper shows that this flow stress drop is mainly due to thermal activation, by 80 MPa, while 15 MPa is due to the change of phase fraction. The stresses in each phase are individually assessed and stress-strain curves for each phase are obtained within the two-phase domain.