Zirconia toughened alumina (ZTA) materials offer improved strength and toughness at slightly reduced hardness compared to alumina. ZTA is used in commodities such as cutting tools but also in high performance biomedical applications where excellent mechanical properties and reliabilty are crucial. While the basic reinforcement mechanisms: transformation toughening, microcracking and residual stress and their relation to composition are basically understood, producing excellent ZTA is still an issue.
ZTA materials based on unstabilized and stabilized zirconia were manufactured from different alumina and zirconia starting powders, different stabilizer contents and compounding processes and characterized with respect to mechanical properties, phase composition and microstructure. The effects of processing and composition are demonstrated.
In fully dense materials of nominally identical composition powder selection has a strong effect on mechanical properties with strength and toughness values varying by up to 50%. The aim to reach a tailored size distribution of zirconia in the microstructure to maximize transformation toughening depends on the selection of the “right” zirconia powder and a proper homogenization process. A sinter to size strategy to adjust the microstructure by  overfiring is of limited value.
In case of ZTA materials with a zirconia fraction at or over the percolation threshold stabilizer has to be added. It is shown that in such materials homogeneity is even more important to avoid over-stabilization and manufacture materials with a combination of high strength and toughness and a limited content of monoclinic phase.