Grain size effect on anisotropic acoustoplasticity of rolled α-Ti during ultrasonic vibration-assisted compression

Ultrasonic vibration (UV) assisted forming is a promising way to manufacture high-performance metallic components. However, the acoustoplasticity of alpha-Ti is affected by the coupling effect of grain size and plastic anisotropy, making the UV-assisted forming process complicated and hard to control. In this research, UVassisted compression tests were conducted on rolling textured alpha-Ti specimens with different grain sizes and orientations. The deformed microstructure was observed, and the grain size effect on the anisotropic acoustoplasticity was analyzed. The results indicate that the ultrasonic softening effect on alpha-Ti was anisotropic and grain size related. The higher ultrasonic softening fraction in coarse-grained materials indicates that the ultrasonic effect is more effective. Coarse grains provide longer dislocation mean free path and more room for dislocation storage, and reduce the resistance for nucleation and growth of twins. Meanwhile, the Hall-Petch effect on ND specimens is more considerable than that on RD and TD. The ultrasonic weakening of Hall-Petch effect was observed in all three orientations, and the weakening effect is less effective on ND specimens induced by the directionality of ultrasonic softening. Furthermore, A grain size-related acoustoplasticity model considering the coupling effect of ultrasonic softening and the Hall-Petch was developed, which can well predict the acoustoplasticity of alpha-Ti. These findings provide a fundamental understanding of the grain size effect on the anisotropic acoustoplasticity of alpha-Ti in UV-assisted forming process.