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

Abstract

In this study, the mechanical properties and microstructural evolution of the pre-strained titanium alloy Ti‐6Al‐4V 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 α'/α'' martensite phases were formed in the β phase after the HDPEC treatment, which is possibly related to the high cooling rate and diffusion of the V element (β phase stabilizer element). Specifically, at the current condition of 250 A/mm2 for 20 ms, some tiny martensite phases precipitated in the β 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.