Correlation among composition, microstructure and mechanical properties of ZrO₂(Y₂O₃)/Al₂O₃ composite ceramics

The aim of this work is to correlate the microstructure of alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) composites with the Vickers hardness, flexural strength and fracture toughness. The monoclinic zirconia (m-ZrO₂) phase has completely been transformed into tetragonal zirconia (t-ZrO₂) phase for Al₂O₃ content. The presence of 3 mol% yttria-stabilised zirconia (3YSZ) particles on the grain boundaries effectively limits a rapid grain growth of the Al₂O₃ grains. The average grain sizes of pure Al₂O₃ and 3YSZ as well as Al₂O₃ and t-ZrO₂ in the 3YSZ + 40 wt% Al₂O₃composite were 3.78 μm, 1.82 μm, 0.89 μm and 0.83 μm, respectively. The 3YSZ + 40 wt% Al₂O₃ composite showed maximum flexural strength of 395 MPa, fracture toughness of 5.6 MPa.m^1/2 and intermediate Vickers hardness of 15.01 GPa with the highly dense microstructure consisting of higher t-ZrO₂ grains of the critical size, which make it suitable for dental applications.