Influence of MgO Pre-Calcination on Microstructural Evolution in Mg-Partially Stabilized Zirconia

Z irconia (Z rO2) stabilized with magnesia (MgO) exhibits excellent mechanical properties, which are influenced by its thermal history. These arise from phase formation in partially stabilized zirconia (PSZ), where ZrO2 exists in cubic, tetragonal and monoclinic phases, stabilized by the addition of M gO. This study examined Mg-PSZ ceramics with 9.25 and 14.5 mol% MgO, sintered at 1500° and 1720°C for 3 h in air, revealing variations in phase composition and microstructure. To assess the effect of M gO morphology, M gO was added either in its raw form or pre-calcined at 1200°C for 2 h. This pre-treatment aimed to modify the powder characteristics and enhance densification. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction were used to analyse phase transformations during pressureless sintering. Pre-calcination significantly impacted the density and microstructure, with the final ceramics reaching 87% to 98% of their theoretical density. Samples with 14.5 mol% MgO showed predominant cubic phases, consistent with the 1720°C sintering temperature. It is evident that polygonal MgO-cubic precipitates form on cubic ZrO2 grains without any post-sintering aging treatment, highlighting the role of pre-calcined MgO in the microstructural evolution. These results support the potential of Mg-PSZ ceramics for high-stress engineering applications.