Effect of DC and AC electric fields on crack healing behavior in 8 mol% yttria‐stabilized cubic zirconia polycrystal

Abstract

The effect of the flash event (FE) on microcrack healing behavior in 8 mol% yttria‐stabilized zirconia was examined at healing temperatures of 1040 and 1230°C under the direct and alternating (DC and AC) electric fields. The crack healing behavior changed depending on the factors of the electric field, healing temperature, and crack length. Although the crack healing proceeded with the temperature, the healing rate increased with the crack length, suggesting that the external energy stored as crack surface energy would provide a driving force for the crack healing. Although the crack healing occurs even under the static annealing without the electric field, the healing rate was accelerated by FE significantly more under the AC field than under the DC field. The microcracks with a length of ≈20 μm were fully healed at 1230°C only for 10 min by the FE treatment under the AC field, and the flash healing behavior was four times faster than that of the static annealing. These results suggest that the enhanced healing behavior cannot be explained only by thermal effects, and the accelerated diffusivity caused additionally by nonthermal effect under FE might contribute to the enhanced healing behavior, especially in the AC electric field.

Promoting effects of alternating current and input power on grain growth behavior of cubic ZrO2 polycrystals

“…In contrast, athermal effects that cannot be explained by temperature increments due to the Joule heating have also been suggested to promote atomic diffusivity in materials. 6 For example, high-temperature processes, such as enhanced plastic deformation, [7][8][9][10][11][12][13][14] diffusion joining, [15][16][17] and crack healing [18][19][20][21] of fully densified yttria-stabilized zirconia (YSZ) materials, have already been achieved at lower temperatures and in shorter times. Therefore, during the flash event, cation diffusion, which is regarded as the rate-controlling process in high-temperature processes, is expected to be promoted athermally by applying an electric field and current.…”