Improving low-temperature degradation resistance in 3-mol% yttria-stabilized zirconia by flash sintering

This study demonstrates the effectiveness of current-ramp flash sintering in producing near-full-density 3-mol% yttria-stabilized tetragonal zirconia ceramics with improved resistance to low-temperature degradation (LTD) compared to conventionally sintered samples. LTD, driven by the spontaneous tetragonal-to-monoclinic phase transformation in humid environments, results in surface microcracking and gradual loss of structural integrity. A comparative analysis of near-full-density samples with similar grain sizes (∼0.37 μm) reveals that the thickness of the monoclinic surface layer was suppressed by half compared to that of conventionally sintered counterparts after 60 h of hydrothermal aging at 140 °C. Conventional sintering, which involves prolonged thermal exposure, induces yttrium segregation, leading to the formation of yttrium-rich cubic and yttrium-depleted tetragonal phases. This compositional inhomogeneity destabilizes the tetragonal phase, making it more prone to LTD. In contrast, flash sintering enables rapid densification within minutes under applied electric field and current, effectively suppressing yttrium segregation and significantly enhancing resistance to LTD.