Macro-micro behaviors of Ti–22Al–26Nb alloy under near isothermal electrically-assisted tension

Abstract

To reveal the non-thermal effect of electric current in macro-micro behaviors Ti–22Al–26Nb alloy sheet with bimodal initial structure, electrically-assisted (EA) near isothermal tensile tests and thermally-assisted (TA) tensile tests have been conducted comparatively at equivalent temperatures by adjusting the applied current-time curve. The stress responses, morphological evolution of constituent phases and the phase transformation behaviors have been characterized by means of EBSD and TEM. Result shows that EA tension is more effective in reducing deformation resistance, while TA tension plays a more important role in plasticity enhancement. The overall electrically-induced stress drop in EA tension increases monotonically with current density, but its non-thermal component first decreases with current density and then increases significantly from the critical value of 12.40A/mm2 in EA tension. The variation of the non-thermal stress drop during EA deformation is attributed to the competition between softening effect and strengthening effect of the electric current, viz. electric current causes softening effect by activating dislocation slip and inducing dislocation annihilation on one hand, and the electrically-driven dynamic precipitation of nanoscale O laths and dynamic globularization of O lamellae leads to additional strengthening effect on the other hand. Moreover, electric current promotes the process of O→B2 phase transformation from both thermodynamic and kinetic at 16.01–20.87 A/mm2.