Low‐Temperature Processing and Mechanical Properties of Zirconia and Zirconia–Alumina Nanoceramics

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Abstract
The 1.5‐ to 3‐mol%‐Y2O3‐stabilized tetragonal ZrO2 (Y‐TZP) and Al2O3/Y‐TZP nanocomposite ceramics with 1 to 5 wt% of alumina were produced by a colloidal technique and low‐temperature sintering. The influence of the ceramic processing conditions, resulting density, microstructure, and the alumina content on the hardness and toughness were determined. The densification of the zirconia (Y‐TZP) ceramic at low temperatures was possible only when a highly uniform packing of the nanoaggregates was achieved in the green compacts. The bulk nanostructured 3‐mol%‐yttria‐stabilized zirconia ceramic with an average grain size of 112 nm was shown to reach a hardness of 12.2 GPa and a fracture toughness of 9.3 MPa·m1/2. The addition of alumina allowed the sintering process to be intensified. A nanograined bulk alumina/zirconia composite ceramic with an average grain size of 94 nm was obtained, and the hardness increased to 16.2 GPa. Nanograined tetragonal zirconia ceramics with a reduced yttria‐stabilizer content were shown to reach fracture toughnesses between 12.6–14.8 MPa·m1/2 (2Y‐TZP) and 11.9–13.9 MPa·m1/2 (1.5Y‐TZP).