Transformation toughening in zirconia-containing ceramics

The recognition of the potential for enhanced fracture toughness that can b e derived from controlled, stress-activated tetragonal (t) to monoclinic (r n) transformation in ZrO2-based ceramics ushered in a new era in the develo pment of the mechanical properties of engineering ceramics and provided a m ajor impetus for broader-ranging research into the toughening mechanisms av ailable to enhance the fracture properties of brittle-matrix materials. ZrO 2-based systems have remained a major focal point for research as developme nts in understanding of the crystallography of the t --> m transformation h ave led to more-complete descriptions of the origins of transformation toug hening and definition of the features required of a transformation-tougheni ng system, In parallel, there have been significant advances in the design and control of microstructure required to optimize mechanical properties in materials developed commercially. This review concentrates on the science of the t --> m transformation in ZrO2 and its application in the modeling o f transformation-toughening behavior, while also summarizing the microstruc tural control needed to use the benefits in ZrO2-toughened ceramics.