The Effects of Simultaneous Addition of Chromium Oxide (Cr2O3) and Niobium Oxide (Nb2O5) on Microstructures and the Zirconia Phase Stability of Al2O3-10%ZrO2 Composite

The present research aimed to study the effects of simultaneous and separate addition of niobium oxide and chromium oxide on microstructures, the tetragonal zirconia phase stability, and sintered density of alumina-zirconia composite. The powder metallurgy method was used to prepare the powder of desired composites. To this end, alumina and zirconia powders (with a constant weight of 10%) were used as the main materials and 1% niobium oxide and 0.6% chromium oxide powders were applied as additives. Powdered composite samples were centrally pressurized into a mold and then were sintered at 1300-1500°C. The phases were identified using the X-ray diffraction and microstructures were studied by a scanning electron microscope. Sintered density, hardness, grain size, and the number of zirconia phases were also calculated. The results showed that hardness and sintered density substantially increase with the addition of niobium oxide and chromium oxide, as the density and hardness of the sample containing 1% niobium oxide and 0.6% chromium oxide powders were obtained 3.72 g/cm3 and 1263 HV, respectively. The density and hardness of samples increased with the addition of niobium oxide and chromium oxide. In addition, the simultaneous addition of niobium oxide and chromium oxide to alumina-zirconia composite reduced the sintering temperature by 100°C. The alumina grain size increased with the addition of a certain weight percent of niobium oxide and chromium oxide. However, the effects of niobium oxide were greater, as it caused the growth of alumina grains and instability of the tetragonal zirconia phase.