HYDROTHERMAL STABILITY OF YTTRIA-DOPED AND CERIA-DOPED TETRAGONAL ZIRCONIA ALUMINA COMPOSITES

Changes in the crystalline phase and microstructure resulting from hydrothermal ageing of Y-TZP, (Y, Ce)-TZP, Y-TZP-Al2O3 composites and (Y, Ce)-TZP-Al2O3 composites were invesitaged under hydrothermal conditions at 180-degrees-C and 1 MPa. Although (Y, Ce)-TZP showed no tetragonal-to-monoclinic (t --> m) phase transformation during low-temperature ageing in air as compared with 3Y-TZP, the tetragonal phase of (Y, Ce)-TZP easily transformed to monoclinic phase by ageing under hydrothermal condition. This t --> m phase transformation invaded the inside of the body accompanied by microcraks. (Y, Ce)-TZP-Al2O3 composites were resistant to phase transformation during hydrothermal ageing.