Zirconia is renowned among ceramics for its hardness and fracture toughness at room temperature. Its fine, sub-micron grain size allows for excellent surface finishes and the ability to maintain a sharp edge.

While zirconia retains properties like corrosion resistance at very high temperatures, it undergoes structural changes that limit its use to temperatures around 500 °C. As this temperature is approached, zirconia also becomes electrically conductive.

To enhance its performance, zirconia is often blended with stabilizers such as MgO, CaO, or Yttria. These stabilizers enable transformation toughening by inducing a partial cubic crystal structure during initial firing, which remains metastable upon cooling. When a crack forms, the tetragonal precipitates undergo a stress-induced phase transformation, expanding the structure and absorbing significant energy. This process is responsible for zirconia’s high toughness. However, at elevated temperatures, this transformation causes dramatic reforming, negatively affecting strength and causing 3-7% dimensional expansion. The amount of tetragonal phase can be adjusted by varying the stabilizer blend to balance toughness with strength retention.

Zirconia PSZ: Partially stabilized zirconia (PSZ) with approximately 10% MgO is cream-colored and offers high toughness, retaining this property at elevated temperatures. PSZ is more cost-effective but has a larger grain structure.

Zirconia TZP: Tetragonal zirconia polycrystal (TZP) with about 3% Yttria has the finest grain size and the highest toughness at room temperature due to its nearly 100% tetragonal structure. However, this toughness degrades significantly between 200 and 500 °C, as irreversible crystal transformations cause dimensional changes.