Ultrasonic-Induced Phase Redistribution and Acoustic Hardening for Rotary Ultrasonic Roller Burnished Ti-6Al-4V

Ultrasonic energy can promote the dislocation motion in ultrasonic-assisted machining. The phase redistribution of Ti-6Al-4V alloy will occur in ultrasonic-assisted machining with appropriate ultrasonic powers. The variations of the volume fractions of β-Ti and α-Ti influence the microhardness on the processed surface. In the present paper, various rotary ultrasonic roller burnishing experiments were conducted to investigate the ultrasonic-induced phase redistribution of Ti-6Al-4V at different ultrasonic powers. The volume fractions of β-Ti and α-Ti were measured by X-ray diffraction. SEM images of the processed surfaces were used to analyze the microstructure evolution and grain refinement of Ti-6Al-4V at various ultrasonic powers. Then, the distributions of local misorientation, texture and grain boundary were observed by EBSD. The results indicated that the microhardness approached the maximum value on the processed surface while the volume fraction of β-Ti reached its maximum value. Finally, the modified phenomenological model was applied to elucidate the relationship among the microhardness, the phase volume fractions and the grain refinement. The fitting degree for microhardness between the modified phenomenological model prediction and experimental measurement was 92.2 pct.