The effect of hydrothermal treatment on the phasestability, microstructure and mechanical properties of tetragonal zirconiaceramics stabilized with 3 mol% yttria was studied. At temperatures of 140-260_Cthe tetragonal phase transformed into monoclinic zirconia. The degree oftransformation increased with increasing temperature and time of ageing. Changesin the microstructure and mechanical properties were observed for the samplesused at temperatures of 180_C and higher. The thickness of transformed layerincreased with increasing temperature and at 260_C it reached a thickness of170 µm after 10 hours. The changes in mechanical properties (hardness andfracture toughness) corresponded to the structural changes in the materialcaused by hydrothermal ageing. Temperatures of 180_C and higher were criticalfor the mechanical and structural properties of the material.
