Zirconia Toughened Alumina
It is also known in industry as ATZ.
Zirconia aluminia (or zirconia toughened alumina), a combination of zirconium oxide and aluminum oxide, is part of a class of composite ceramics called AZ composites. Noted for their mechanical properties, AZ composites are commonly used in structural applications, as cutting tools, and in many medical applications. Additionally, AZ composites feature high strength, fracture toughness, elasticity, hardness, and wear resistance. Zirconia toughened alumina (ZTA), in particular, offers several key properties.
The mechanical robustness compared to alumina is attributed to the displacive phase transformation of the metastable tetragonal ziroconia grains when the material is stressed. The stress concentration at a crack tip can cause a transformation from a tetragonal crystal structure to a monoclinic one, which has an associated volume expansion of ziroconia. This volume expansion effectively pushes back the propagation of the crack and results in higher toughness and strength. 
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