Micromechanical properties and microstructures of AC and DC flash-sintered alumina

Alumina (α-Al2O3), one of the most widely used structural ceramics for industrial applications, requires high temperature and long sintering time to achieve a fully dense structure through conventional pressureless consolidation and sintering methods. Recently, several attempts have been made to reduce sintering time and temperature of Al2O3 through the application of electric field with limited success. In this study, alternating current (AC) and direct current (DC) flash sintering techniques were employed to obtain high-density Al2O3 within 10 min. The density of flash-sintered (FS) specimens was greater than the specimens prepared by the pressureless sintering technique (hereinafter designated as conventional sintering) at the same temperature for 10 h. Furthermore, AC technique can reduce the electric field necessary for flash sintering substantially comparing to the DC flash sintering. The microindentation measurements reveal that the AC-FS Al2O3 provides the highest fracture toughness and a high hardness among all sintered specimens. The improved mechanical properties of AC-FS Al2O3 are attributed to defects, such as dislocations as well as stacking faults observed in the FS specimens. This study provides a fresh perspective on the low-energy manufacturing of structural ceramics with improved properties.