Flash spark plasma sintering of 3YSZ: Introducing structural and microstructural heterogeneity by high heating rates

Yttria stabilized zirconia (3 mol% YSZ) ceramics were prepared by Flash-SPS at various temperatures ranging from 700 degrees to 2060 degrees C using heating rates ⁓11,000 degrees C/min, and leading to densification in seconds. The influence of peak temperature on microstructure is then analyzed and displays unusual sintering trajectory. Densification shows a maximum of 91 % around 1600 degrees C and further decreases with increasing sintering temperature. The structural and microstructural homogeneities are assessed, showing the presence of remaining monoclinic phase from starting powder in the core of the pellets, even after sintering at 2060 degrees C, suggesting strong thermal gradient. This also results in grain size and morphology heterogeneity. This work aims at showing the importance of assessing homogeneity over the whole sample volume, especially for ultra-rapid sintering techniques.