Toughening of yttria-stabilised tetragonal zirconia ceramics

Current knowledge of toughening mechanisms in zirconia ceramics is reviewed, with particular emphasis on the transformation toughening of yttria-stabilised polycrystalline tetragonal zirconia (Y-TZP). The physics and mechanics of transformation toughening are discussed, but the main aim is to provide a comprehensive understanding of the role of the metastable tetragonal zirconia phase on stress induced transformation toughening. The focus is on the microstructural variables governing the stability of tetragonal zirconia in the context of transformation toughening. The potential for additional toughening contributions from microcracking and ferroelastic toughening is briefly addressed and the coupling of toughening mechanisms is also discussed. Finally, a perspective on the future development of Y-TZP-based high toughness materials is given.