Effect of synthesized yttrium aluminum garnet (YAG) additives on the physical and the mechanical properties of zirconia toughened alumina (ZTA) composites

Abstract

Yttrium aluminium garnet (YAG) nano powder was synthesised from yttria powder and aluminium isopropoxide via the sol-gel method and then calcined at 1500°C for 2 hours to obtain a pure YAG phase. Zirconia-toughened alumina (ZTA) composites containing 15% zirconia were mechanically mixed, then 10, 20 and 30 wt.% nano-synthesised YAG powder were added and mixed with ZTA powder. All four composites were fired at four sintering temperatures starting from 1575°C, with 25°C intervals. The lower apparent porosity and high bulk density were achieved at 1675°C, where X-ray diffraction analysis, microstructure and mechanical properties were carried out. In this study, a ZTA composite with 10% YAG additives exhibited a maximum flexural strength of 396.5 MPa and a fracture toughness of 3.95 MPa.m0.5. Such properties were achieved due to their low apparent porosity and the maintaining of zirconia in the tetragonal phase after sintering. It was found that YAG addition enhanced the mechanical properties of ZTA, as it is located at the grain boundaries and acts as inclusions, which can change the path of crack propagation and improve the fracture toughness of the sintered sample through the crack deflection mechanism.