Plastic deformation of ultrafine-grained 2.5Y-TZP exposed to a dc electric field with an air gap

The influence on the tensile flow stress of ultrafine-grained 2.5Y-TZP at 1450 °C by a dc electric field with an air gap between the negative electrodes and the positive specimen was determined in two test procedures: Type a, in which the field is applied continuously from the very beginning up to a fixed strain ɛ ≈ 0.2 and Type b, in which the field is alternately applied and removed following the prestrain ɛ ≈ 0.2 without and with the field. A larger reduction in the flow stress by the field occurred in the Type a test compared to the Type b. Moreover, a larger reduction occurred in the Type b test when the prestrain was with a field applied compared to without. Both of these behaviors are attributed to a retardation of dynamic grain growth by the field. The reduction in the flow stress by the field in the Type b test was in accord with a decrease in the electrochemical potential for the formation of vacancies corresponding to the lattice diffusion of the rate-controlling Zr ions. sults in the present tests were in general accord with those obtained previously in which both the positive and negative electrodes made direct contact with the specimen. This indicates that neither the orientation of the field nor the presence of an air gap has significant influence on the electric field dependence of the flow stress.