Investigation of mechanical and microstructural characteristics of Ti–45Nb undergoing transversal ultrasonic vibration-assisted upsetting

Abstract

Abstract Numbers of researchers have investigated the mechanism of the acoustic softening effect and applied it in the plastic forming field. Inadequacy discussion, nevertheless, softening effect has been focused on the volume effect, seldom considering the surface effect. In this study, a transverse ultrasonic vibration-assisted upsetting system was developed to compress the aeronautical material Ti–45Nb cylinder. A similar acoustic softening effect was obtained comparing with the existing softening mechanism as the amplitude is lower than 34 μm or under slow compression rates, whereas the reduction of flow stress is not only contributed by the volume effect when the amplitude is larger than 34 μm and with higher compression rates, which is co-caused by volume effect and surface effect. Besides, the influences of amplitude and vernation time on residual hardening effect were analyzed. To reveal the effect of the different acoustic softening mechanisms on texture evolution with a higher compression rate, Electron backscatter diffraction (EBSD) was used to disclose the evolution characterizations of grain size, misorientation angle, and texture under different amplitude. The results show that the number of the low angle grain boundary and sub-grain in the tested area has a positive relationship with the deformation and amplitude, especially the specimens under amplitudes of 38 μm and 46 μm. Besides, the acoustic residual hardening effect of Ti–45Nb is caused by the increase of dislocation density and grain refinement under ultrasonic vibration.