Effect of multi-pass deformation on microstructure evolution of spark plasma sintered TC4 titanium alloy

The TC4 titanium alloy powder test piece was prepared by spark plasma sintering. The multi-pass hot deformation of the TC4 titanium alloy was tested by using the Gleeble-1500 experiment machine. Measurement of relative density, X-ray diffraction, optical microscopy, scanning electron microscopy and electron backscatter diffraction were carried out for the TC4 titanium alloy. In order to reveal the evolution of the microstructure, describing its changes systematically is necessary, which has become the focus of this article. The results show that after multi-pass hot deformation, the relative density of the TC4 titanium alloy could reach 99.93%. With the increase in deformation and decrease in temperature, the beta-transformed phase was retained, and many fine beta-transformed phases were formed between two adjacent lamellar alpha. During the one-pass hot deformation, the rapid increase in relative density was the main reason for the instability of the flow stress in the stress-strain curve. For two-pass and three-pass hot deformations, more features of dynamic recrystallization and the characteristics of dynamic recovery at high strain rates (5 s(-1)) could be found. The size of the grains was about 15 mu m after the three-pass hot deformation.