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

The grain growth behavior during an AC flash event was examined in 8 mol% yttria-stabilized cubic zirconia (8Y-CSZ) polycrystals. The effects of current/power densities on the grain growth behavior were investigated in 8Y-CSZ samples with different specific surface areas at a constant sample temperature and applied field strength. The grain growth rate of flash-treated 8Y-CSZ was 300 times faster than that of heat-treated 8Y-CSZ at the same sample temperature in the absence of an electric current/field, suggesting that the promoted grain growth cannot be ascribed only to a thermal effect but also to an athermal effect occurring during the AC flash event. Moreover, the grain growth during the flash treatment strongly depends on the applied current/power densities and grain size; in particular, the grain growth showed enhancements with increasing applied current/power densities and for relatively small grain sizes. This result suggests that the grain boundary diffusivity of cations, which are regarded as the rate-controlling species for grain growth, could be accelerated by tuning the current/power densities during the flash event. The grain growth mechanism was characterized using a grain growth exponent (n) value of 4.8 for the flash treatment at high current/power densities and using a conventional value of n = 3 under normal heat treatment conditions. The dependence of the grain growth behavior on the AC current/power density suggests that because the cation diffusivity is accelerated due to the formation of numerous point defects during the AC flash event, the grain growth mechanism might depend on the current/power densities and differ from that of conventional grain growth.