Comment on “Artificial neural network modeling of mechanical alloying process for synthesizing of metal matrix nanocomposite powders” by Dashtbayazi et al. [Mater. Sci. Eng. A 466 (2007) 274]

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 m1/2.