Anomalous strengthening effect in tension accompanied by impulse current
The work is related to the study of external influences on the deformation behavior of metallic materials. On the basis of literary sources, the effects accompanying the passage of a pulsed current and related structure changes in the metals and alloys are briefly considered. A special role in the contribution of each effect belongs to the current mode (direct, pulse) and regimes (density, off-duty factor), as well to the material. The results of our own studies of the interaction of pulsed current with a large off-duty factor (Q ≥ 10<sup>3</sup>) and plastic deformation by quasi-static tension in materials of different physical nature are presented: pure metals (titanium and aluminum), shape memory TiNi alloys with reversible martensitic transformation (stoichiometric and behind stoichiometric composition), ferrite-pearlitic (ST3) and stainless austenitic (0Kh18N10T) steels. A pulsed current with a density above the critical and high off-duty factor is used, which makes it possible to observe the electroplastic effect in the form of stress drops with a minimum thermal effect. In contrast to the well-known classical manifestation of the electroplastic effect in the form of a decrease in flow stresses and an increase in plasticity, a manifestation of anomalous strengthening from several tens to hundreds of MPa is demonstrated. It is assumed that the reasons of visible effects are external and internal factors - high off-duty factor, thermomechanical cycling, change in the dislocation mechanism of deformation, martensitic transformation, structure refinement, dissolution of particles of excess phases. With a decrease in the off-duty factor (increasing the frequency of the pulsed current to 10<sup>3</sup> Hz) and transition from single pulse to multi-pulse current, the hardening effects are replaced by the traditional decrease in flow stresses due to the thermal effect of the current.