Stress jump behavior during tensile deformation assisted by pulsed current

The article is related to the study of the manifestation of the athermal electroplastic effect in the form of stress jumps on the stress-strain curve on a number of conductive materials. The aim of the work is to discover the relationship between the microstructure of the material, pulsed current modes and parameters of the stress jump, including its shape, amplitude and duration. For comparison, studies were carried out on materials that differ greatly in thermal and electrical conductivity, grain size, and amorphous-crystalline state. The methodological basis of the study was quasi-static tensile tests, accompanied by the introduction of single pulses of unipolar current of high density and duty cycle at a constant pulse duration. The high duty cycle of the pulsed current during the tension process ensured that the temperature of the samples was maintained close to room temperature. The relationship between the structure-phase state, phase transformations and grain size in the materials with the main parameters of the stress jump is shown. In a coarse-grained state, a pulsed current of high duty cycle can lead to simultaneous strengthening and increased ductility, possibly due to low-cycle strengthening. Structural refinement of alloys leads to a decrease in the electroplastic effect until it disappears in the amorphous state. In shape memory alloys that exhibit an austenitic-martensitic transformation upon heating, the direction of the stress jump changes to the opposite direction compared to the traditional one. Fractographic studies of the fracture surfaces of samples tested with and without current did not reveal structural changes, confirming the athermal nature of the electroplastic effect under the selected pulsed current modes. It is assumed that the results of the study can be used to verify various models of the electroplastic effect, as well as to select pulsed current modes to increase deformability during metal forming without significant heating.