Hot Deformation Behavior of As-Cast Ti-6554 Alloy with Different Grain Morphologies

The hot workability of titanium alloy ingot is closely related to the morphology and size of initial grains. Based on the Gleeble thermal simulation experiment, the hot deformation behavior of equiaxed and columnar grains of Ti-6554 alloy ingot at deformation temperature of 950–1050 ℃ and strain rate of 0.01–1 s−1 was studied. The flow stress decreases with the increase of temperature or the decrease of strain rate. The strain modified Arrhenius constitutive model of equiaxed and columnar crystalline alloys was established by linear regression and polynomial fitting methods. And the predicted results were in good agreement with the experimental values. The results of microstructure evolution show that the density of grain boundary in unit volume of columnar crystal sample is higher. And the flow stress is greater than that of equiaxed crystal sample under the same deformation condition. With the increase of deformation temperature and the decrease of strain rate, the columnar crystal samples are more prone to DRX (dynamic recrystallization) than the equiaxed crystal samples. The equiaxed grains are transformed from serrated grain boundaries to bulged grain boundaries and regenerated into DRX grains. The columnar grains expands into a larger area of DRX region based on DRX strips or bulged grain boundaries.