SHOCK COMPRESSION EQUATION OF STATE AND DYNAMIC DEFORMATION MECHANISM OF ADDITIVE MANUFACTURED Ti6Al4V TITANIUM ALLOY

The additive manufacturing (AM) process has the advantages of rapid prototyping and controllable structure, and has broad application prospects. However, the research on the dynamic properties of alloy materials manufactured by additive manufacturing is far from adequate. Due to the wide application of Ti6Al4V alloy in the field of national defense and aerospace, in this paper, the additive manufactured and forged Ti6Al4V titanium alloy was studied. The plate impact experiment with different impact velocities was carried out on two kinds of titanium alloys by using the one-stage light gas gun system. In the impact experiment, the particle velocity and the shock wave velocity of the free surface were obtained by means of the photon Doppler velocimetry (PDV) system and the impedance matching technology. The Hugoniot equation of state of the two titanium alloys was established. Furthermore, to reveal the dynamic deformation mechanism of alloys, transmission electron microscopy (TEM) and electron back-scattering diffraction (EBSD) were conducted to characterize the microstructure of the deformed samples. Both alloys were found to have high phase transformation thresholds ( > 7.90 GPa for forged alloys and > 7.87 GPa for additively manufactured alloys) and high Hugoniot elastic limit HEL (2.56 GPa for forged alloys and 2.78 GPa for additively manufactured alloys). Both the plastic deformation mechanism of the Ti6Al4V alloys is mainly controlled by dislocation slip. The forged alloy produces slip bands in the late deformation stage. The phase interface between the lamellar α phase and β phase of the additively manufactured alloy acts as a reinforcement that hinders dislocation movement in the later stage of deformation, then the dislocation line slips from the α phase across the phase interface to another adjacent α phase, and the dislocation slip across the phase interface requires a larger stress input, which results in higher HEL value than that the forged alloy.