Effects of limiting current density and current step rate on microstructure and hardness of flash sintered MgAl2O4 ceramics

Abstract

This study investigates the effects of limiting current density and current step rate on the microstructure and hardness of current-step flash-sintered (CS-FS) disc-shaped MgAl₂O₄ ceramics. The results indicated that, unlike conventional flash sintering, the temperature of the sample during the current-step flash started at a lower initial value and subsequently increased gradually. Furthermore, the differences in oxygen vacancies between the positive and negative sides of the CS-FS-ed MgAl₂O₄ ceramics were significantly reduced. This led to the CS-FS samples exhibiting higher relative density, finer grain size, a more uniform microstructure, and increased hardness. The homogeneous microstructure resulted in consistent hardness across both sides of each CS-FS-ed sample. Additionally, as the limiting current density increased, the grain sizes near the positive and negative sides gradually enlarged, while the relative density initially increased before decreasing. A similar trend was observed when the current step rate decreased.