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In this work, zirconia powders containing 5 and 10 mol % ceria were prepared by co-precipitation method followed by doping with small amounts (< 1 mol %) of gadolinia which stabilized the tetragonal phase. X-ray diffraction and scanning electron microscopy were used for phase analysis and microstructure examination, respectively. The sintered compacts showed fine grained, dense, tough and strong ceramics. Strength up to 795.8 MPa and toughness of 17 MPa√m have been obtained. These ceramics showed higher toughness than yttria-doped tetragonal zirconia polycrystals (Y-TZP) and a higher strength than the ceria tetragonal zirconia polycrystals (Ce-TZP). The high fracture toughness was attributed to the tetragonal-to-monoclinic phase transformation which was associated with ferroelastic domain switching. The domain switching toughening has been discussed in view of Chevalier's model. Four-point bending strengths for the samples tested in the as cut state are higher than those tested in the as-sintered or the ground states.

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In this investigation, surface modification toughening of partially stabilized zirconia ceramics, by sub-eutectoid solution annealing, has been performed. The Zr0.918Mg0.068Y0.014O1.925 designated (MZY) was prepared by mixing Magnesia Partially Stabilized Zirconia (MZ9) and Yttria Tetragonal Zirconia (TZ3Y) Polycrystal commercial powders using wet ball milling. The mechanical properties and microstructure of the MZY were investigated. XRD and SEM were used for phase analysis and microstructure examination of the sintered samples’ surfaces. The fracture toughness and hardness of the sintered compacts were determined by the Vickers indentation technique. The physical and mechanical properties of MZY were compared to those of MZ9 ceramics prepared under the same conditions. The results showed that, the Yttria addition inhibited the exaggerated growth of the tetragonal precipitates during sintering. The MZY showed a maximum in the fracture toughness of 12.9 MPa√m upon sub-eutectoid solution annealing at 1000 °C for 150 h, while the tetragonal precipitates in the MZ9 lost coherence due to their spontaneous massive transformation to the monoclinic phase via the decomposition reaction.