Effect of DC electric field on the tensile deformation of ultrafine-grained 3Y-TZP at 1450–1600 °C

Two test types were employed to determine the effect of DC electric field E = 5–8.3 V cm⁻¹ applied in the loading direction on the tensile flow stress of 3Y-TZP (d_o = 0.44 μm) at 1450–1600 °C. In type a, the field was applied continuously throughout the tensile test; in type b, the field was alternately applied and removed during the course of the tensile test. The field reduced the flow stress in both test types, but with an appreciably larger effect in the type a tests. The field, however, had no discernable effect on the stress exponent $n=\mathrm{\partial }\log \dot{\epsilon }/\mathrm{\partial }\log \sigma$ determined by strain rate change tests. The reduction in flow stress in the type b tests reversed upon removal of the field. It was interpreted to result from both Joule heating and a decrease in the energy to form the rate-controlling Zr⁴⁺ vacancies in the space charge zone adjacent to the grain boundaries. The calculated width of the space charge zone λ (=1.5–7.8 nm) and the ratio of the applied electric potential to the reduction in stress Δϕ_a/Δσ (=18–19 μV/MPa) were in accord with predictions. The larger reduction in the flow stress in the type a tests is attributed to a greater retardation of grain growth by the field.