Ultrahigh deformability of Ti-6Al-4V assisted by high-density pulsed electric current treatment

In this study, the mechanical properties and microstructural evolution of the pre-strained titanium alloy Ti-6Al4V under high-density pulsed electric current (HDPEC) treatment were investigated. The results showed that the HDPEC treatment successfully restored the plastic deformation or strain hardening of the pre-strained Ti-6Al-4V without deteriorating its strength. In addition, multi-HDPEC treatments were conducted to examine the cumulative effect on plastic recovery, and ultrahigh deformability with an increasing rate of 287% was achieved at a current density of 250 A/mm2 for 20 ms. Microstructural characterization indicated that dislocations and the associated sub-grain boundaries were remarkably reduced after the HDPEC treatment, contributing to ductility enhancement. Additionally, the rapidly heat-treated sample with a thermal history curve similar to that of the HDPEC-treated samples did not show obvious microstructural changes, indicating that the athermal effect of the HDPEC treatment plays an important role in modifying the microstructure of the material. The alpha'/alpha" martensite phases were formed in the beta phase after the HDPEC treatment, which is possibly related to the high cooling rate and diffusion of the V element (beta phase stabilizer element). Specifically, at the current condition of 250 A/mm2 for 20 ms, some tiny martensite phases precipitated in the beta phase without heavily deteriorating the microstructure and mechanical properties. Therefore, owing to its low cost and high efficiency, the HDPEC treatment can be applied to Ti-alloy components with internal plastic deformation to realize rapid restoration or achieve long service periods without significantly altering the microstructure.