Abstract
Mechanical properties and phase structure of yttria-stabilized tetragonal zirconia polycrystals aged in air at 200° and 300°C for 25000h (about 3 years) were investigated. The bending strength and dynamic hardness of the aged samples were reduced after the aging. The remarkable tetragonal-to-monoclinic phase transformation occurred in surface and sub-surface layers of the sample within 100μm from the surface. The monoclinic phase fraction of the aged samples, especially aged at 200°C, was much larger than that of the unaged samples. The bending strength and dynamic hardness decreased drastically when the monoclinic phase fraction exceeded 60%. Several samples were collapsed during the aging at 200°C of which monoclinic phase fraction finally exceeded 65%.
