ABSTRACT
This chapter presents a coherent picture of the state-of-the-art in zirconia crystallography and its general physical properties, phase transformations, alloy additives, and composite systems. It describes the crystal chemistry and the properties of zirconia which make it such an attractive material for use in transformation-toughening systems. Prior to 1975, partially stabilized zirconia (PSZ) materials consisted of monoclinic zirconia precipitates dispersed in a cubic-stabilized-zirconia matrix. Very small “unconstrained” particles of tetragonal zirconia are known to exist in the Free State at room temperature. The existence of the pure stoichiometric cubic zirconia form, above 2360°C, is probably of academic interest, but has been questioned for sometime on a number of grounds. Martensite transformations are of great industrial importance and have been studied in metallic systems for some time. The twin mode of transformation also suggests for zirconia-toughened ceramics systems, as with Magnesium-PSZ, the transforming particle is pursuing a route which will minimize its shape change during the transformation.
