Athermal charge effect of improving the plasticity of metals: first-principles study

High plasticity is one of the most required factors when manipulating metals. Among several methods that have been industrially used to increase the plasticity of metals, plasticity induced by an electric current flow, which is called electro-plasticity, is widely used, but its physical origin has not been fully understood. It was suggested that Joule heating due to electric currents would cause a temperature rise leading to high plasticity observed in several metals. Recent studies have, however, revealed that such Joule heating may not be enough to increase a local temperature to induce high plasticity. Here we propose that the electro-plasticity is induced by modified electronic structures due to the charge doping effect. Our study suggests that the effect of charge doping causes phonon softening at certain frequencies due to bond weakening. We also consider the effects of charge doping on stacking fault in metals. It is found that the energy barrier for the slipping process of metal planes is reduced by excess charges accumulating near the slip plane during the stacking fault process. It is the athermal effect rather than a thermal one that induces electro-plasticity caused by phonon softening and charge accumulation.