The recognition of the potential for enhanced fracture toughness that can be derived from controlled, stress-activated tetragonal (t) to monoclinic (m) transformation in ZrO 2 -based ceramics ushered in a new era in the development of the mechanical properties of engineering ceramics and provided a major impetus for broader-ranging research into the toughening mechanisms available to enhance the fracture properties of brittle-matrix materials. ZrO 2 -based systems have remained a major focal point for research as developments in understanding of the crystallography of the t 3 m transformation have led to more-complete descriptions of the origins of transformation toughening and definition of the features required of a transformation-toughening 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 3 m transformation in ZrO 2 and its application in the modeling of transformation-toughening behavior, while also summarizing the microstructural control needed to use the benefits in ZrO 2 -toughened ceramics.

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A simple and accurate method of determining foil thickness is described. The method makes use of measurements of the spacing of intensity oscillations in convergent beam diffraction patterns obtained with commercial scanning transmission electron microscopes. Extension of the technique to determination of extinction distances and anomalous absorption parameters required for the two‐beam dynamical theory is outlined briefly.

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