Processing of different alumina–zirconia composites by slip casting

Abstract

Two Al2O3–ZrO2 mixture preparation routes: classical powder mixing and addition of a Zr (IV) precursor solution to a well dispersed Al2O3 suspension, were used to produce alumina (Al2O3)–zirconia (ZrO2) slip cast composites. For the conventional powder mixing route, two commercial 3 mol% yttria-partially stabilized zirconia powders, 0.3 wt% Al2O3-doped (Al-doped Y-PSZ) and without Al2O3 (Y-PSZ), were employed. The influence of the zirconia content and the solid loading on the rheological properties of concentrated aqueous Al2O3–ZrO2 slips were investigated. The density of green samples was studied and related to the degree of slip dispersion. In addition, the influence of the processing conditions on the density and microstructure development of sintered samples were investigated. By using the Zr (IV) precursor route, nano-sized ZrO2 (ZN) particles homogeneously distributed on the Al2O3 particle surfaces were obtained; however, it let to aggregates of some Al2O3 particles with very fine ZrO2 uniformly distributed. The viscosity and yield stress values of Al2O3–ZN suspensions were markedly higher than those of Al2O3–Al-doped Y-PSZ and Al2O3–Y-PSZ ones, for all the compositions and solid loading studied and resulted in a less dense packing of cast samples. However, for the composite with 10.5 vol% ZN a high sintered density and a smaller ZrO2 grain size distribution compared with the conventional powder mixing route could be obtained.