Deformation behavior and microstructure in the low-frequency vibration upsetting of titanium alloy

Low-frequency vibration-assisted metal plastic forming is a novel promising technology, adopting a high-pressure-capability device compared to the ultrasonic vibration system. This work focuses on the low-frequency vibration assisted upsetting (LFVAU) process of Ti45Nb, to reduce the flow stress and crack initialization in the cold deformation of titanium alloy. The results show that the flow stress is significantly reduced by applying the vibration, and this stress reduction phenomenon becomes more obvious with larger frequency and amplitude. The vibration promotes the dislocation movement and grain rotation, resulting in dislocation annihilation in the shear band but dislocation concentration and low-angle grain boundary formation near the grain boundary in the large deformation zone. Therefore, more homogenous deformation occurred in LFVAU compared to the conventional quasi static upset (QUS) specimen, though the grain size is similar in the cylinders after QSU and LFVAU. Based on the above research results, the application of low-frequency vibration assisted processing technology in the field of aerospace will help to improve the plastic deformation quality, especially the riveting quality for Ti45Nb.