Experimental and simulated investigation of the deformation behavior and microstructural evolution of Ti6554 titanium alloy during an electropulsing-assisted microtension process

Abstract

Titanium alloy formability can be noticeably improved by electrically assisted processing. In this study, uniaxial electropulsing-assisted microtensile (EAMT) tests were performed on a new high strength-ductility near β titanium alloy Ti–6Cr–5Mo-5 V–4Al (Ti6554) at electric current densities (ECDs) from 10 to 70 A/mm2. To investigate the Joule heating, mechanical response and microstructural evolution of the Ti6554 alloy during the EAMT process, the true stress strain curves, temperature, and microstructural evolution were analyzed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). A fully coupled electrothermomechanical finite element model (ETM-FEM) was developed to predict the stress and temperature and to decouple the thermal and athermal effects. The experimental results showed that the dynamic recrystallization (DRX), substructure and texture evolution can be strengthened when the ECD is less than 50 A/mm2, but that the dislocation density decreases with increasing ECD; the α precipitation and propagation of microcracks at higher ECDs can result in premature failure. Without considering the athermal effect, the predicted stress deviates from the tested data, but the predicted temperature agrees better. To elucidate the electroplasticity mechanism, the thermal expansion effect was qualified, and other athermal effects, including the skin effect, pinch effect, interaction between electrons and dislocations and phonon frequency, on the flow stress were discussed.