Mineralogical and microstructural changes in fused cast Ti-stabilized alumina-zirconia eutectic ceramics at elevated temperatures

Ti-stabilized alumina-zirconia eutectic ceramics produced by fusion-casting are characterized to investigate microstructural mechanisms at elevated temperatures and to explain the self-sharpening effect. Scanning electron microscopy (SEM) images show fine-grained lamellar eutectic microstructures with well-defined domains. After thermal annealing at 800 °C, distinct cracks formed along the domain boundaries. Thermal analyses and powder X-ray diffraction (pXRD), using Rietveld evaluation, confirmed that the cracks are triggered by the phase transformation from meta-stable tetragonal to monoclinic ZrO2, causing a volume increase of up to 13.4 %. This indicates a decrease in the stabilizing effect of Ti in the meta-stable tetragonal ZrO2 starting from 669 °C, and subsequently triggering the phase transformation. Additionally, structural analysis of pXRD data reveals internal stresses within the crystal lattice, showing expansion of tetragonal ZrO2 along the c-axis and distortions in the basal plane in both tetragonal and monoclinic ZrO2.