Improving the surface hardness of zirconia toughened alumina (ZTA) composites by surface treatment with a boehmite sol

This paper reports a novel way of enhancing the hardness of a zirconia-toughened alumina (ZTA) composite with a zirconia content of 20 vol% by surface treatments with a boehmite sol. More specifically, a ZTA composite was first prepared by heat-treating a mixture of alumina and zirconia powders containing Cr2O3 and SrAl11CrO19, as a reinforcement at 1400 °C for 1 h, and then infiltrating them with the boehmite sol, followed by heat-treatment at 1650 °C for 1 h to densify them. This treatment led to a significant increase in the surface hardness of the ZTA composite, which was attributed mainly to an increase in the volume fraction of an alumina phase with greater hardness, whereas the flexural strength and fracture toughness decreased slightly. The Vickers hardness, flexural strength and fracture toughness were 17.1 ± 2.5 GPa, 738 ± 88 MPa and 4.2 ± 0.11 MPa m1/2, respectively.