Electroplastic Effect in Titanium Alloys Under Tension

Abstract

The electroplastic effect (EPE) is a phenomenon which consists in a decrease in the strain resistance and enhancement of the plasticity of metals under the effect of the electric current of a sufficiently high density [1]. This study aims to compare the deformation behavior of single-phase commercially pure titanium Grade 4 and two-phase VT6 alloy under tension and external heating with the introduction of a pulsed current. Current of various pulse ratios and densities is supplied to the grips of the tensile testing machine from a pulse generator. To estimate the relative contribution of the electroplastic effect during passage of current to the reduction of flow stresses, the materials are also exposed to external heating. The microstructure of the samples in the sample head and in the vicinity of the fracture region in the longitudinal section is studied using optical microscopy. The electroplastic effect in the studied materials is manifested on the tensile curve through individual jumps in the downward flow stress at a high pulse ratio, whereas at a low current pulse ratio a decrease in the flow stress and strain hardening and increase in the plasticity are observed. It is shown that the tension of the sample under the effect of current results in a greater decrease in the flow stresses than that observed under external heating at the same temperature for both materials. This confirms the athermal nature of the pulsed current effect. The critical density of the high pulse ratio current (q = 5000) capable of providing manifestation of the electroplastic effect is two times lower for the VT6 alloy than for the pure titanium Grade 4. Under the same pulsed current modes, the flow stresses for VT6 decrease more than for Grade 4. The pulsed current of high pulse ratio caused an anomalous hardening effect in the VT6 alloy, but the physical nature of this effect requires an additional study. The pulsed current modes used in the study did not lead to any structural changes noticeable under optical magnification in the samples under tension, except for the disappearance of twins and separation of the impurity particles in Grade 4 and spheroidization of grains in VT6.