Effects of electric current on the plastic deformation behavior of pure copper, iron, and titanium

Uniaxial tension tests were performed on pure polycrystalline copper, iron, and titanium specimens with various applied constant (dc) current levels and at matching temperatures, i.e., zero current with temperature histories matched to the current tests. The experiments achieved uniform strain, current density, and temperature conditions along the specimen gage length for unambiguous interpretation of the test data. The results showed non-thermal current effects only with the titanium; 20% reduction in ultimate strength with respect to the strength from the matching temperature tests was observed as well as significant inhomogeneous grain growth. No discernable changes in microstructure were observed in specimens deformed at matching temperatures or with applied current but no deformation (matching temperatures). The electron-wind and local Joule heating mechanisms for electrically-assisted deformation (EAD) do not produce effects large enough to explain the observed titanium results. Dislocation scattering by thermal phonons and electrons associated with the radial and axial heat fluxes generated in the titanium tensile specimens with bulk Joule heating is suggested as a potential mechanism for the observed EAD effects. The experimental results and the possible link to thermal phonon/electron scattering suggests several new avenues of research for understanding EAD of metals.