Effect of processing parameters on hot deformation behavior and microstructural evolution during hot compression of as-cast Ti60 titanium alloy

Effects of the processing parameters on the flow stress behavior and the microstructural revolution are investigated in the hot compression of as-cast Ti60 alloy. The flow stress behavior reveals greater flow softening in the two-phase field compared with that of single-phase field. In the two-phase field, flow softening is caused by break-up of lamellar α, deformation heating, flow localization and free-surface cracking. While in the single-phase field, flow softening is associated with dynamic recovery and recrystallization. In addition, the flow stress curves display discontinuous yielding, which is attributed to rapid dislocation generation and multiplication from the grain boundary. Moreover, the magnitude of yield drop is inversely proportional to the average grain size. In the α+β phase field, the distorted degree of lamellar α within the prior β grains increases with increasing strain rate and reduction, while flow instability including low localization and oxidation cracking occurs in higher strain rate (>1s^-1) and larger reduction (>60%), a small amount of recrystallized grains are observed at the prior β grain boundaries in lower strain rates (≤0.1s^-1) with reduction of 60%. In the β phase field, however, the concentration of recrystallized β grains at prior β grain boundaries is much higher than that observed during deformation in the α+β phase field. The fraction of recrystallized β grains increases with increasing temperature, reduction and decreasing strain rate. It indicates that the processing parameters have a significant influence on the deformation behavior and microstructural revolution of as-cast Ti60 titanium alloy. It is helpful for the controlling of the microstructure and the optimization of processing parameters.