Microstructure and mechanical properties of yttria-stabilized ZrO2/Al2O3 nanocomposite ceramics

Yttria-stabilized ZrO2/Al2O3 (abridged as YSZ/Al2O3) nanocomposite ceramics were prepared by pressureless sintering of the green sheets of the YSZ/Al2O3 nanopowders synthesized by co-precipitation method. The relative density, average grain size, and phase microstructure of the YSZ/Al2O3 nanoceramics as a function of YSZ contents were investigated. The relative densities of the YSZ/Al2O3 nanoceramics are over 95% as the YSZ contents of the YSZ/Al2O3 nanopowders are within 20–85 mol %. The average grain sizes of the ZrO2 and Al2O3 of the as-sintered YSZ/Al2O3 nanoceramics decrease with increasing YSZ content of the co-precipitated YSZ/Al2O3 nanopowders, while the content of monoclinic ZrO2 of YSZ/Al2O3 nanoceramics increases with increasing YSZ content. The presence of the second phase effectively limits a rapid grain growth of the matrix alumina. The YSZ/Al2O3 nanoceramics with an average grain sizes below 80 nm, relative density over 95%, and hardness as high as 19.8 GPa were obtained by the pressureless sintering.