Flash viscous flow sintering of nanostructured amorphous ZrO2-Y2O3 composite ceramics starting from a partially amorphous precursor powder

Nanostructured amorphous composites are novel materials comprising nano-sized crystal phases embedded in an amorphous matrix, but often necessitating ultra-high-pressure molding for preparation. In this study, nanostructured amorphous ZrO2-Y2O3 composite ceramics were rapidly prepared for the first time using flash viscous flow sintering without the application of pressure. The relative density of the ZY ceramics increased with increasing current density, and ZY composite ceramics with relative density of 86%-97% were prepared by FS in a short time of 60 s under 700 V/cm with 0.16-0.56 A/cm2. Furthermore, the sintering activities in FS were compared between partially amorphous powder and crystalline powder. The ceramics prepared by flash sintering of partially amorphous powder show a much higher relative density than that from crystalline powder, suggesting that partially amorphous powder achieves easier densification than crystalline powder in flash sintering under given current density and power dissipation. This phenomenon was attributable to the differing sintering mechanisms between the two materials, i.e., solid-state sintering for crystalline powder and viscous flow sintering for partially amorphous powder.