Calcium oxide-stabilized zirconia with high toughness, strength, aging resistance and transformation-induced plasticity

Monolithic zirconia ceramics generally present with trade-offs between toughness, strength and hydrothermal aging-resistance, highlighting the need to develop new zirconia ceramics that are better balanced for these key properties. In this study, zirconia containing 4.5 mol% calcium-oxide stabiliser (4.5Ca-TZP) was pressed from nanoparticles and pressureless sintered at 1200–1325°C. Fully dense 4.5Ca-TZP could be obtained at 1250–1275°C with a nanometric microstructure (average grain size <100 nm) and about 20 wt% cubic-zirconia. Optimal mechanical properties were reached when sintered at 1250°C and 1275°C, combining a four-point-bending (4PB) strength of 1170 ± 140 MPa with a single-edge-V-notched-beam toughness of 9.73 ± 0.45 MPa m^1/2. Furthermore, this nanometric zirconia was highly transformable, showing transformation-induced plasticity before failure with an evident deviation from linear behavior starting around 75 % of the 4PB strength. Strikingly, 4.5Ca-TZP was also aging-resistant without degradation observed after 20 hours of aging at 134°C. Additionally, its translucency was similar to that of conventional 3Y-TZPs.