Characterization of discontinuous yielding phenomenon in isothermal compression of TC8 titanium alloy
(School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, China)
Abstract: The discontinuous yielding phenomenon (DYP) during high temperature deformation was investigated based on the isothermal compression of TC8 titanium alloy. The DYP of TC8 titanium alloy was characterized by quantifying the yield drop of the DYP (？σUL) and ending strain of flow oscillation (εOSC) based on the flow stress-strain curves, and then the effect of deformation parameters on the ？σUL and εOSC values was analyzed. The results show that the ？σUL and εOSC values increase with the increase of strain rate. The effect of deformation temperature on the ？σUL value depends on the strain rate. Finally, the transmission electron microscope (TEM) observation shows the evidence for the dynamic theory, which ascribes the DYP to the generation of mobile dislocation at the grain boundary. Meanwhile, the optical microscope (OM) observation shows that both the primary α grain and β grain become smaller with the increase of strain, which well interprets the effect of deformation parameters on the ？σUL and εOSC values.
Key words: titanium alloy; flow stress; discontinuous yielding; dynamic theory