Three different alumina-zirconia composites: Sintering, microstructure and mechanical properties

Two commercial 3 mol% yttria-partially stabilized zirconia powders, with 0.3 wt% Al2O3 (Y-PSZA) and without Al2O3 (Y-PSZ), and a Zr (IV) precursor were used to produce alumina (Al2O3)-zirconia (ZrO2) slip cast composites. The influence of both the zirconia content and the reduction of zirconia particle size on the sintering behavior, microstructure development and mechanical properties were investigated. The increase in the zirconia content from 10.5 to 22 vol% increased the hardness; whereas, above 22 vol% ZrO2 the hardness decreased. A significant increase in the fracture toughness with increasing the ZrO2 content over 22 vol% was obtained by the stress-induced phase transformation. The flaw size limited the strength below 22 vol%; whereas, above 22 vol% ZrO2 the strength was controlled by the stress-activated phase transformation. For 10.5 vol% ZrO2, the smaller ZrO2 grains produced by using the Zr (IV) precursor were more effective in preventing the Al2O3 grain growth resulting in higher hardness. However, the tetragonal-monoclinic (t-m) transformation of some unstabilized ZrO2 grains during cooling reduced Young's modulus and fracture toughness.