Microstructure and mechanical properties of Al2O3–YSZ spherical polycrystalline composites

The mechanical behavior and microstructure of highly densified, spherically shaped, polycrystalline Al2O3–YSZ composites, processed from pseudoboehmite powders by sol–gel is reported here. Processing was carried out by combining nanometric sized α-Al2O3 (120 nm) seeds and YSZ particles of tetragonal structure. The YSZ particles were homogeneously distributed in a coarse-grained matrix of alumina, both inside grains and along grain boundaries. Fracture surfaces, achieved by impact tests showed toughening effects of the zirconia particles. The tetragonality of the YSZ phase stability even after fracture events and fracture toughness measurements by Vickers indentation, where the crack tip interacts with YSZ particles, are all provided and discussed. The local mechanical properties, such as elastic modulus, indentation hardness and the onset of plastic deformation or fracture contact pressure of both YSZ particles and the Al2O3 matrix were quantified by nanoindentation. Evidence of coercive contact pressure was observed in YSZ from indentation stress–strain curves.