Low-furnace-temperature flash sintering of tetragonal 1.5-mol% YSZ: Role of particle necking on grain growth

This study presents a strategy to achieve over 99% relative density in monophasic tetragonal 1.5-mol% yttria-stabilized zirconia (1.5YSZ) polycrystalline ceramics via current-ramp flash (CRF) sintering at furnace temperatures as low as 600°C. While 1.5YSZ exhibits high toughness, it is prone to cracking due to spontaneous tetragonal-to-monoclinic (T → M) phase transformation when grain sizes exceed a critical threshold. The proposed strategy combines preheating with multi-step CRF sintering, where preheating promotes particle neck growth, a key mechanism enabling flash sintering at lower furnace temperatures. Without preheating, flash sintering at furnace temperatures below 1100°C resulted in accelerated grain growth and spontaneous T → M transformation, driven by current localization at poorly developed particle necks. In contrast, incorporating preheating under identical flash sintering conditions reduced grain size by nearly half with minimal change in sample temperature. This strategy lowers furnace temperatures by over 50% compared to conventional sintering methods and significantly accelerates densification. Moreover, it integrates efficiently into existing ceramic manufacturing workflows, which often include calcination to produce moderately dense bodies.