SUBEUTECTOID DEGRADATION OF YTTRIA-STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTAL AND CERIA-DOPED YTTRIA-STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTAL CERAMICS

Yttria-doped tetragonal zirconia containing 2 and 3 mol% Y2O3 (Y-TZP), and CeO2-doped Y-TZP containing 0 to 12 mol% CeO2 were sintered at 1350-degrees-C in a tetragonal single-phase field for 2 h in air, and the degradation behavior at low temperature in air and in hot water was observed. X-ray photoelectron spectroscopy studies on the surface of hydrothermally treated samples show evidence for the formation of a YO(OH) species, along with the simultaneous formation of purely tetragonal zirconia nuclei that retain their coherence in the Y-TZP matrix. Above a critical size, the tetragonal nuclei spontaneously transform to a monoclinic structure, giving rise to macro- and microcracking. The strong tetragonal grains degrade to produce a spalling phenomenon that facilitates further degradation. Y-TZP ceramics alloyed with adequate amounts of CeO2 show no tetragonal-to-monoclinic transformation after hydrothermal treatment.