Effect of dc on the Formability of Ti–6Al–4V

Abstract

Recent research has demonstrated that the mechanical properties of metals are altered when an electrical current is passed through the material. These studies suggest that titanium alloys, due to their low formability and need for dramatic improvement, should be subjected to additional study. The research presented herein further investigates the use of electricity to aid in the bulk deformation of Ti–6Al–4V under tensile and compressive loads. Extensive testing is presented, which documents the changes that occur in the formability of titanium due to the presence of an electrical current at varying current densities. Using carefully designed experiments, this study also characterizes and isolates the effect of resistive heating from the overall effect due to the electrical flow. This study clearly indicates that electrical flow affects the material beyond that which can be explained through resistive heating. The results demonstrate that an applied electrical current within the material during mechanical loading can greatly decrease the force needed to deform the titanium while also dramatically enhancing the degree to which it can be worked without fracturing. Isothermal testing further demonstrates that the changes are significantly beyond that which can be accounted for due to increases in the titanium’s temperature. The results are also supported by data from tests using pulsed and discontinuously applied current. Furthermore, current densities are identified that cause an enhanced formability behavior to occur. Overall, this work fully demonstrates that an electrical current can be used to significantly improve the formability of Ti–6Al–4V and that these improvements far exceed that which can be explained by resistive heating.

The Effect of Electric Current on Metals

“…Moreover, this theory is also in agreement with Ross et al where isothermal tests were performed at temperature greater than that reached in the electrical tests [18]. The results from this work showed that the isothermal testing did not create near the flow stress reductions or the increases in fracture strain as compared to the electrical tests.…”

“…Ductile fracture begins by the nucleation, growth, and coalescence of micro-voids. The micro-voids are formed when a high [18] stress induces separation of the material at grain boundaries or at small impurity particles (Fig. 3.10b).…”

A review of electrically-assisted manufacturing

“…Ross et al 39 reported that the forgeability of Ti6Al4V was clearly enhanced by a continuous electric current. Bunget et al 71 suggested that electroplasticity and Joule heating can be separated in energy modeling, which was confirmed in Perkins' studies on Al6061 specimens, in order to analyze and predict electroplastic behavior in the EA forging process.…”

“…Also, according to Dzialo et al, 38 the temperature increase obtained during electrically assisted compression of copper alloys was lower than that during a hot working process at the same reduction of stress. Ross et al 39 suggested isolatable effects due to electricity such as Joule heating, kinetic energy (pushing dislocations), and retained stress-strain energy, while reporting that a higher resistivity of material induced a greater electroplastic effect. Salandro et al 40,41 assumed that the electric current during deformation produced only heating and deformation energy.…”

High temperature deformation behavior of the TC6 titanium alloy under the uniform DC electric field

“…Fortunately, a considerable literature [1][2][3][4][5][6][7][8] has reported that the application of electric current, electric field or high density DC current pulses on metals may produce significant changes in the mechanical properties, which provide a possible way to improve the metal's mechanical performance instead of the conventional heat-treatment methods. To this end, Joseph et al [4] investigated the effect of an "electron wind" on the mechanical properties of aluminum.…”