Zirconia is best known among ceramics as being both hard and fracture-tough at room temperature. Additionally, its fine (sub-micron) grain size enables excellent surface finishes and the ability to hold a sharp edge. Although it retains many properties including corrosion resistance at extremely high temperatures, Zirconia does exhibit structural changes that may limit its use to perhaps only 500°C.
Zirconia is commonly blended with either Magnesium Oxide (MgO), (Calcium Oxide CaO), or Yttria (Y2O3) as a stabilizer in order to facilitate transformation toughening. This induces a partial cubic crystal structure instead of a fully tetragonal structure during initial firing, which remains metastable during cooling. Upon impact, the tetragonal structure precipitates undergo a stress induced phase transformation near an advancing crack tip. This action expands the structure as it absorbs a great deal of energy, and is the cause of the high toughness of this material. Reforming also occurs dramatically with elevated temperatures and this negatively affects strength along with 3-7% dimensional expansion.
The amount of tetragonal can be controlled by additions of the blends above to balance toughness against loss of strength. Partially Stabilised Zirconia or PSZ with about 3.5% Magnesia (MgO) is high in toughness and strength, and retains this property to elevated temperatures. They are somewhat lower in cost but also have larger grain structure. Yttria stabilised Zirconia is partially stabilised with 5.4% Yttria (Y2O3), also called Tetragonal Zirconia Polycrystal or TZP has the finest grain size. These grades exhibit the highest toughness and strength at room temperature, because they are nearly 100% tetragonal, but this degrades severely between 200 and 500°C as these irreversible crystal transformations also cause dimensional change.
Magnesia Partially Stabilised Zirconia (Z500)
Z500: A Zirconia-based material partially stabilised with Magnesia. Contains 96.5% ZrO2 and HfO2 in combination, plus 3.5% MgO and 0.50% SiO2. This ceramic exhibits enhanced mechanical properties.
Yttria Partially Stabilised Zirconia (Z900)
Z900: A Zirconia-based material partially stabilised with Yttria. Yttria partially stabilised Zirconia contains 94.0% ZrO2 and HfO2 in combination, plus 5.4% Y2O3 and 0.25% Al2O3. This ceramic exhibits enhanced mechanical properties.
Datasheets are available for Yttria Partially Stabilised Zirconia (Z900).
A very high purity Zirconia-based material, partially stabilised with Yttria, produced specifically for surgical implant devices. Contains 99.9% ZrO2 (Zirconia), Y2O3 (Yttria) and HfO2 (Hafnium Oxide) in combination. This material complies with the ISO13356-08 “Implants for Surgery -- Ceramic Materials Based on Yttria Stabilised Zirconia (Y-TZP)”
Datasheets are available for Zyranox™.
If you are interested in MTC Rugby Magnesia Partially Stabilised Zirconia (Z500), Yttria Stabilised Zirconia (z900) or Zyranox™ and would like to discover how these materials could be implemented in your sector, please contact us.