Effect of an electric field on the plastic deformation and fracture of polycrystalline NaCl

The influence of an electric field E ≤ 0.1 MV/m on the plastic flow and fracture of cast polycrystalline NaCl was determined in compression at room temperature. Without an electric field the major slip system was deduced to be 110 〈 110 〉, with impurity-cation-vacancy dipoles being the short-range obstacles to dislocation motion. The initial strain hardening rate was similar in magnitude to that for Stage II in single crystals; its decrease with strain was attributed to cross slip. Plastic flow preceded fracture, which was intergranular without an electric field. The yield, flow and fracture stresses and the strain hardening coefficient decreased with electric field, an approximately 50% decrease occurring at E = 0.1 MV/m. This field is one-to-two orders of magnitude lower than had previously been found to produce significant effects in NaCl single crystals. The fracture mode with the field was mixed cleavage and intergranular. It is concluded that the major effect of the electric field was to enhance cross slip, thereby reducing the rate of strain hardening and in turn the flow and fracture stresses.