Preparation of Gd2Zr2O7 nanoceramics by flash sintering and two-step flash sintering

Preparation of Gd2Zr2O7 nanoceramics using a simple and low energy-consuming approach is significant for their wide range of applications. In this work, flash sintering (FS) and two-step flash sintering (TSFS) were first utilized to prepare Gd2Zr2O7 nanoceramics. The effects of electric field intensity and current limit on the densification and grain growth were investigated. The grain size was decreased with the increase of electric field intensity. Meanwhile, both grain size and density were increased with the increase of current limit. The Gd2Zr2O7 nanoceramics with an average grain size of 98 nm and a relative density of 92.8% were prepared by FS. By contrast, the Gd2Zr2O7 nanoceramics with the higher relative densities of 96.3-97.5% and the smaller average grain sizes of 85-90 nm were prepared by TSFS. Compared to FS, TSFS can achieve suppressed grain growth and fast densification. The as-prepared Gd2Zr2O7 nanoceramics showed excellent hardness and fracture toughness. The sample breakage caused by current localization can be avoided by controlling the current ramp after the occurrence of the flash event.