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

• Internal stresses are reduced by exposure to temperatures >400°C • Temperature exposure to 500 and 800°C triggers transformation of metastable t- or c-ZrO2 to m-ZrO2 • Microcracks grow along the domain boundaries • Cracks cause a volume expansion up to 13.4 % • Coarser grit sizes transform at higher 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 ZrO 2 , causing a volume increase of up to 13.4 %. This indicates a decrease in the stabilizing effect of Ti in the meta-stable tetragonal ZrO 2 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 ZrO 2 along the c -axis and distortions in the basal plane in both tetragonal and monoclinic ZrO 2 .