Effects of amorphous phase and yttrium on flash sintering and microstructures of ZrO2–SiO2 ceramic nanocomposites

Flash sintering has been used to consolidate a wide range of ceramics and ceramic composites. However, flash sintering of ceramic nanocomposite with a substantial amorphous phase is rarely studied. Meanwhile, the effects of yttrium addition on the flash sintering behaviors and microstructures of ZrO 2 -based ceramic nanocomposite remain unknown. Herein, ZrO 2 -SiO 2 crystalline-amorphous ceramic nanocomposites (CACNs) with different contents of amorphous phase and two types of yttrium dopants were sintered by flash sintering. Results showed that the content of amorphous phase (SiO 2 ) had significant effects on the flash sintering behavior. The CACN with 65 mol% SiO 2 was nonflash sinterable due to the high electric resistivity of SiO 2 , whereas, the CACN with 45 mol% SiO 2 can be flash sintered to high densification within 35 seconds. The flash-sintered CACNs consisted of ZrO 2 nanocrystallites distributed in an amorphous SiO 2 matrix. Flash sintering enhanced the tetragonal-to-monoclinic phase transformation of ZrO 2 . In addition, influences of yttrium dopant on CACNs were also investigated. Yttrium dopants can rapidly dissolve in ZrO 2 lattices and show a tetragonal phase stabilization effect during flash sintering. Firework-like ZrO 2 microcrystallites formed by dendritic growth were observed close to the cathode region, which was attributed to athermal electric field effects and the formation and aggregation of oxygen vacancies at the cathode region. The results would provide guidance for fabricating CACNs via flash sintering.