Low temperature degradation-free zirconia through microstructure tuning by Two-Step Sintering

This study describes the microstructural evolution of a 3 mol% yttria‑stabilized zirconia during densification, comparing Conventional Sintering (CS) and Two‑Step Sintering (TSS). Monitoring the microstructural evolution revealed a reduction in grain size and less phase partitioning with TSS than with CS, which is related to a more homogeneous yttria distribution with TSS. Diffusion lengths for both CS and TSS were estimated using Fick’s laws. Since the sintered materials spend more time at high temperature in CS than in TSS, the cation diffusion lengths are longer for CS, which is consistent with the yttria distribution observed in the microstructures. Similar values of flexural strength and toughness were obtained for both TSS and CS materials. However, hydrothermal ageing tests revealed a clear improvement in the Low Temperature Degradation of the TSS sample. This difference is attributed to the diffusion‑sensitive nature of hydrothermal ageing, unlike the diffusion‑less martensitic phase change mechanism governing toughness.