Deformation mechanism and microstructure evolution of TC4 alloy during ultrasonic energy field-assisted deformation

Ultrasonic vibration-assisted compression tests on TC4 alloy are performed at room temperature under various deformation and ultrasonic conditions. The influence of strain rate and Ultrasonic Energy Field (UEF) on plastic deformation behaviors and microstructure evolution is analyzed. The experimental results indicate that the flow stress exhibits a decreasing trend either with the decrease of strain rate or the application of UEF. As the strain rate increases, the slip system activity is impaired with the deceleration of dislocation motion. The uneven intragranular deformation takes place, and the grain structure shows the severe elongation characteristics. With the application of UEF, the high activity of slip system enhances dislocation motion, and boosts the formation of soft orientations $<0001>$ in basal plane and $<10\overline{1}0>$ in prismatic plane, which further facilitates dislocation multiplication and uniform dislocation distribution. Moreover, due to high input ultrasonic energy, the highly active dislocations are rearranged into subgrain boundaries and are subsequently evolved into grain boundaries. Many new fine grains are formed around the initial large grains, and the UEF shows a positive effect on grain refinement. Additionally, grain rotation toward the soft orientations is promoted under the application of UEF, resulting in the formation of $<0001>//\text{ND}$ and $<10\overline{1}0>//\text{ND}$ textures.