Surface softening mechanism based on microstructure analyses under ultrasonic impact condition for Ti-17 titanium alloy

Ultrasonic impact significantly influences the mechanical properties and flow stress of Ti-17 titanium alloy. In this study, compression tests on Ti-17 titanium alloy were conducted under ultrasonic impact conditions, varying ultrasonic amplitudes and compression rates. The flow stress, surface elemental content, microhardness, and microstructure of Ti-17 titanium alloy were tested, and the softening mechanism of Ti-17 titanium alloy under ultrasonic impact conditions was investigated. The results indicate that the softening mechanism of Ti-17 titanium alloy involved ultrasonic softening combined with stress superposition. Ultrasonic impact leads to a higher distribution of grain orientation differences, alters the distribution of small-angle grain boundaries, and changes the distribution of surface phases, resulting in a reduced density of α phases. The geometrically necessary dislocation density at the surface increases, and the average grain size decreases from 2.91 μm to 2.73 μm. The Brass-type texture essentially disappears, transforming mainly into a Copper-type texture {112}<11-1>, with the maximum pole density decreasing from 73.98 to 39.88.