Structural and Mechanical Properties of Alumina-Zirconia (ZTA) Composites with Unstabilized Zirconia Modulation

Zirconia toughened alumina (ZTA) ceramics are very promising materials for structural and biomedical applications due to their high hardness, fracture toughness, strength, corrosion and abrasion resistance and excellent biocompa-tibility. The effect of unstabilized ZrO 2 on the density, fracture toughness, microhardness, flexural strength and microstructure of some Zirconia-toughened alumina (ZTA) samples was investigated in this work. The volume percentage of unstabilized ZrO 2 was varied from 0% - 20% whereas sintering time and sintering temperature were kept constant at 2 hours and 1580˚C. The samples were fabricated from nanometer-sized (α-Al 2 O 3 : 150 nm, monoclinic ZrO 2 : 30 - 60 nm) powder raw materials by the conventional mechanical mixing process. Using a small amount of sintering aid (0.2 wt% MgO) almost 99.2% of theoretical density, 8.54 MPam ½ fracture toughness, 17.35 GPa Vickers microhardness and 495.67 MPa flexural strength were found. It was observed that the maximum flexural strength and fracture toughness was obtained for 10 vol% monoclinic ZrO 2 but maximum Vickers microhardness was achieved for 5 vol% ZrO 2 although the maximum density was found for 20 vol% ZrO 2 . It is assumed that this was happened due to addition of denser component, phase transformation of monoclinic ZrO 2 and the changes of grain size of α-Al 2 O 3 and ZrO 2