Ultrafast high-temperature sintering (UHS) vs. conventional sintering of 3YSZ: Microstructure and properties

Doped-zirconia finds several applications as strucutral material and in different electrochemical devices; moreover, it is considered a model ceramic system. The consolidation of 3 mol% Y2O3 stabilized ZrO2 (3YSZ) by rapid sintering (flash processes) has yielded unusual properties like higher hardness and thinner electrochemical grain boundaries. To explore the effect of high heating rate and distinguish it from field-induced phenomena, we investigated and compared UHS (Ultrafast high-temperature sintering) with conventional heating with and without an electric field. The results show that: i) UHS allows ultra-rapid consolidation (<30 s) of YSZ nanopowders (≈20 nm) with a densification pathway different from conventional sintering in terms of microstructural evolution (UHS allows a grain size reduction by more than 60% at a fixed desnity level); ii) the electric field plays a minor role in sintering, microstructure evolution, and properties; iii) UHS does not affect the hardness and the grain boundary electrochemical properties of the sintered bodies. Whereas similarities can be pointed out between UHS and flash-related techniques in terms of accelerated densification and microstructure, the final properties are rather different with UHS YSZ being more similar to conventional sintering.