Effect of Initial Grain Size on Crack Healing Behavior under DC Electric Field of Zirconia (8Y‐CSZ) Ceramic

Abstract

The effect of initial grain size on the flash event was examined in microcrack healing behavior under DC electric field in fine‐ and coarse‐grained 8 mol% Y2O3‐stabilized cubic ZrO2 (8Y‐CSZ) polycrystals. The healing behavior depends strongly on the initial grain size and is apparently accelerated in fine‐grained 8Y‐CSZ than in coarse‐grained one. Since the crack healing under the flash event is higher than that of static annealing treatment without the electric field, the enhanced healing phenomena cannot be explained only by the thermal effect caused by Joule heating, but nonthermal effects caused by the flash event. The grain size‐dependent healing behavior indicates that the grain boundaries play an important role in the flash event and the flash healing would be accelerated through the field/current‐enhanced diffusional processes, especially through the grain boundary diffusivity of the cations.

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

“…A similar grain‐size‐dependent flash effect was confirmed in other high‐temperature processes. In our recent study, the crack healing behavior of 8Y‐CSZ during the flash event was strongly dependent on the initial grain size; the crack healing effect was considerably enhanced for a fine grain size of 0.8 μm compared with that for a coarse grain size of 2.4 μm 19 . The grain‐size‐dependent healing behavior indicated that the grain boundaries play an important role in the flash event and the crack healing would be accelerated via field/current‐enhanced diffusional processes.…”

“…In our recent study, the crack healing behavior of 8Y-CSZ during the flash event was strongly dependent on the initial grain size; the crack healing effect was considerably enhanced for a fine grain size of 0.8 μm compared with that for a coarse grain size of 2.4 μm. 19 The grainsize-dependent healing behavior indicated that the grain boundaries play an important role in the flash event and the crack healing would be accelerated via field/current-enhanced diffusional processes. These results suggest that the athermal effects due to the flash event may activate the grain boundary diffusivity of cations and that the effect of the promoting grain boundary diffusivity might also depend on the current/power densities.…”

“…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.…”