Development and characterization of alumina-toughened zirconia (ATZ) ceramic composites doped with a beneficiated rare-earth oxide extracted from natural ore

This work analysed the effect of the addition of rare-earth mixed oxide (RE2O3), a solid solution of Y2O3 and other rare earths benefited from a Brazilian natural ore called Xenotime, on the sintering and properties of a commercial nanopowder composed of Ce-tetragonal polycrystal zirconia (TZP) + 15 wt.% Al2O3. Powder mixtures were prepared, adding 10 wt.% of Y2O3 or 10 wt.% RE2O3 in Ce-TZP/Al2O3 powder, which were compacted and sintered at 1500 °C for 2 h. Sintered samples were characterized by X-ray diffraction, scanning electron microscopy, and relative density. Structural analyses and phase quantification were performed using the Rietveld refinement method. Mechanical characterization - Vickers hardness and fracture toughness - of the samples was carried out by Vickers indentation. The results indicated that the RE2O3 is composed of a solid Y2O3 solution with lattice parameters slightly lower than those of pure Y2O3 due to the presence of other oxides such as Yb2O3 (19.7%), Er2O3 (13.9%), or Dy2O3 (10.2%). During sintering, the oxides added to the composite were completely consumed by the Ce-TZP/Al2O3 matrix to form two different crystalline phases: ZrO2-Cubic and Y3Al5O12. As a consequence, multi-phase composites with relative density of 93.8 ± 1.2 (Y2O3 reinforced) and 94.5 ± 1.7 (RE2O3 reinforced), average hardness in the order of 10.5 GPa, and fracture toughness of 7.1–8.5 MPa m1/2 were obtained. The high fracture toughness observed was a consequence of the presence of different coupled toughening mechanisms resulting from the multiphase characteristic of these composites.