On the power density at the onset for flash sintering in ceramic composites

Flash sintering is usually said to be activated in a narrow range of power density regardless of the onset flash temperature and material. However, the typical logarithmic scale employed in the flash power plots could hide some finer tendencies in the flash onset conditions. Herein, we investigated the flash onset in YSZ/Al2O3 composites taking into account the power density normalized to the total composite (won-comp) and the conductive phase volume (won-YSZ). The results show that at the flash onset (i) won-YSZ strongly increases with the Al2O3 amount in the composite, (ii) won-comp weakly depends on the composite composition, and (iii) both won-comp and won-YSZ increase with the flash onset temperature (which is a function of the electric field). The results offer new light on the mechanisms of flash ignition and a new insight on the power required to activate the phenomenon, which appears to be consistent with a thermally-driven process. © 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.