Effect of pre-deformation heat treatment on deformation behavior of near-a Ti-Fe alloy in (α+β) two-phase region

Numbers of studies on hot deformation of α+β titanium alloys, especially Ti-6AI-4V and near α alloys in (α+β) two-phase region were carried out. However, effects of initial microstructure on the deformed microstructure have not been studied well. In this study, deformation behavior and microstructure evolution of a Ti-1.5Fe alloy in (α+β) two-phase region is studied with focusing on effect of initial microstructure at different deformation temperatures and strain rates. Two different prc-deformation heat treatments were used to achieve different initial microstructure. One is quenching to room temperature after fi solutionizing at 1173K for 1.2ks and reheating to the deformation temperature providing a fine intcrlamcllar spacing and colony size in the (α+β) lamellar microstructure. The other is direct cooling to the deformation temperature after (J solutionizing resulting in a coarser lamellar structure. Hot deformation was conducted at 1108, 1073 and 948K, where corresponding equilibrium volume fractions of a phase are 15, 50 and 85%, respectively, by uniaxial compression by 50% at various initial strain rates ranged from 1 to 10^-4-1. Decrease in both intcrlamcllar spacing and colony size of initial microstructure results in promotion of dynamic reciystallization (DRX) at a given deformation condition. By increasing strain rate grain size of the rccrystallizcd a is dccrcascd. It is concludcd that critical strain needed for initiation and completion of DRX is decreased by refining the initial microstructure. Also, it is proposed that DRX of lamellar a phase is a continuous type.