Hardness and Fracture Toughness of Alumina-Doped Tetragonal Zirconia with Different Yttria Contents

The 0.75 to 3.0 mol% Y2O3-stabilized tetragonal ZrO2 (Y-TZP) and Al2O3/Y-TZP fine-grained ceramics with 0.2 to 0.7 mass% of alumina were produced by a colloidal technique and low-temperature sintering. Trace alumina addition enhanced the densification of Y-TZP. The influence of the resulting density, microstructure, the yttria-stabilizer and the alumina content on the hardness and toughness were studied. The bulk 2.7Y-TZP ceramic with an average grain size of 110 nm reached a hardness of 13.6 GPa and fracture toughness of 11.2 MPa·m1⁄2. Y-TZP ceramics with a reduced yttria-stabilizer content were found to reach a fracture toughness of 13.8 MPa·m1⁄2 (2Y-TZP), and 14.5 MPa·m1⁄2 (1.5Y-TZP). A nano-grained alumina dispersed zirconia with 3 mol% Y2O3 with an average grain size of 97 nm was obtained, and the hardness increased to 16.8 GPa. Y-TZP/alumina ceramics with a 0.35 mass% Al2O3 were found to reach a fracture toughness of 15.7 MPa·m1⁄2 (2Y) and 15.3 MPa·m1⁄2 (1.5Y).