Reasons For The Good Toughness Of (YSZ) Zirconia Ceramics

The high toughness of (3mol% YSZ) zirconia ceramics is primarily attributed to its unique microstructure and material properties, especially the transformation toughening mechanism. Here are the key reasons why zirconia ceramics exhibit good toughness:

1. Transformation Toughening: The tetragonal or monoclinic phases in zirconia ceramics can transform into the volumetrically expansive cubic phase under stress. This phase transformation not only absorbs energy to slow down crack propagation but also generates a compressive stress field at the crack tip, thereby enhancing the material's toughness.

2. Crack Propagation Inhibition: The volume expansion associated with the phase transformation introduces microcracks in the material. These microcracks help to disperse stress concentrations and prevent further crack extension, thereby improving the material's fracture toughness.

3. Yttria Stabilization: Zirconia ceramics are typically stabilized with yttrium oxide (Y2O3) to maintain their structure, and this stabilized zirconia (YSZ) has better toughness and crack resistance. The addition of yttrium helps to suppress phase transformations at high temperatures, maintaining the stability and toughness of the material.

4. Grain Size: A smaller grain size contributes to the increased toughness of zirconia ceramics. Small grains effectively impede crack propagation because the spread of cracks at grain boundaries is hindered.

5. Elastic Modulus: Zirconia ceramics have a high elastic modulus, which means they resist deformation when subjected to external forces. A high elastic modulus helps the material to remain intact under impact or bending, reducing the risk of brittle fracture.

6. Fracture Toughness: Zirconia ceramics have high fracture toughness, which is a result of the combined action of transformation toughening and microcrack toughening mechanisms, making the material less prone to catastrophic fracture under applied forces.