Y2O3 - containing tetragonal ZrO2 polycrystals (Y-TZP) are prepared by wet chemical methods. This results in sinterreactive ceramics with grain sizes down to 0.1µm. The aging behaviour in air and water at high temperatures has been studied by X-ray diffraction. Important factors on aging are Y-concentration, impurity level and grain size. Y-TZP with 6.1 mol% YO1.5 and a grain size of 0.1µm do not show degradation to monoclinic phase even after 5 hours at 450 K in water
Yttria-stabilized zirconia powders were prepared in the composition range of 3 to 13 at% yttria. The hydrolysis-gel precipitation technique was used, starting from metal alkoxides or chlorides. In the composition range between 5 and 10 at% yttria, the materials sintered at 1250°C have a fully tetragonal structure. The density was higher than 95% and the grain sizes can be varied between 0.1 and 0.5um depending on the preparation conditions. The fracture toughness KIC amounts 6 to 11 MPamh but is not dependent on the composition. The transformation toughening mechanism and the properties of the tetragonal phase itself play an important role in the increase of KIC compared with cubic materials. The magnitude of the oxygen-ion conductivity value is comparable with that for cubic materials.
Dense tetragonal zirconia-yttria ceramics has been prepared with grain sizes between 0.1 and 0.5 µm. The fracture toughness and flexure strength at room temperature are independent on grain size and composition in the tetragonal phase region with YO1.5 larger than 5 at.%. The ageing rate of the mechanical properties increases with increasing grain size, but for samples with grains of 0.1 um no ageing is observed. The bulk and grain boundary resistivities are 1.5-2 times higher than in cubic materials. A low impurity level decreases the grain boundary resistivity while the bulk resistivity is hardly affected
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