Effect of TiO2 addition on the sintering behavior, hardness and fracture toughness of an ultrafine alumina

The effect of TiO₂ addition (0–4.0 wt%) on the sintering behavior and mechanical properties of an ultrafine (150 nm) alumina–5 wt% zirconia powder has been investigated. TiO₂ is a beneficial additive, resulting in lower sintering temperature and higher sintered density. The grain growth is shown to be enhanced simultaneously after TiO₂ addition. At higher amounts of TiO₂ addition and at higher sintering temperature, the formation of secondary phases of ZrTiO₄ or Al₂TiO₅, which has lower elastic moduli compared with alumina, reduces the hardness of the sintered bulk from 19.3 to 17.9 GPa. The lager grain size and the transition of fracture mode to fully intergranular due to the TiO₂ addition seem to improve the toughness from 4.4 to 5.2 MPa m^1/2.