Abstract
Mixtures of powders essentially differing in their particle morphology and size were applied to prepare polycrystals in a Y2O3-ZrO2 system. An yttria–zirconia solid solution nanometric powder with a Y2O3 concentration of 3.5% was prepared by subjecting co-precipitated gels to hydrothermal treatment at 240 °C. The crystallization occurred in distilled water. The pure zirconia powders composed of elongated and sub-micrometer size particles were also manufactured through the hydrothermal treatment of pure zirconia gel, although in this case, the process took place in the NaOH solution. Mixtures of the two kinds of powder were prepared so as to produce a mean composition corresponding to an yttria concentration of 3 mol%. Compacts of this powder mixture were sintered, and changes in phase composition vs. temperature were studied using X-ray diffraction. The dilatometry measurements revealed the behavior of the powder compact during sintering. The polished surfaces revealed the microstructure of the resulting polycrystal. Additionally, the electron back scattering diffraction technique (EBSD) allowed us to identify symmetry between the observed grains. Hardness, fracture toughness, and mechanical strength measurements were also performed.
Highlights
For 40 years, tetragonal zirconia polycrystals composed of the yttria solid solution in zirconia (TZP) have been the subject of numerous investigations [1,2,3]
The pure zirconia powder crystallized in the NaOH solution and the 3.5 mol% Y2 O3 ZrO2 solid solution powder processed in the distilled water differed substantially in their specific surface area, phase composition, and crystallite size, as assessed on the X-ray reflections’ broadening
The studied system was composed of nanometric yttria–zirconia solid solution particles and sub-micrometric particles of pure zirconia
Summary
For 40 years, tetragonal zirconia polycrystals composed of the yttria solid solution in zirconia (TZP) have been the subject of numerous investigations [1,2,3]. The reason for the high fracture toughness of this material is related to the martensitic transformation of the tetragonal symmetry grains to their monoclinic form (t→m) at the crack tip advancing through the material. This consumes the transformation strain energy that would otherwise propagate the crack
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