Fracture variability and R-curve behavior in yttria-stabilized zirconia ceramics

An assessment of fracture origins is conducted in yttria-stabilized zirconia ceramics containing different grain sizes. As the microstructure coarsens due to the application of heat treatments, fracture origins change from single pores to transformed regions at the free surface which are induced by the applied stress. The observation of an increasing size of failure origins with microstructural coarsening lies as the underlying reason for the finding that specimens containing coarser microstructures and a more pronounced R-curve behavior do not fail at larger stresses. A fracture model is used to link the strength variability of a fully tetragonal zirconia containing a small grain size to its pore size distribution. The increased transformability of zirconia ceramics with coarser tetragonal grains is evaluated by means of quantitative phase analysis, characterizations of fracture surface morphology, and R-curve assessments. It is confirmed that tetragonal grains of up to 4 mum may not necessarily undergo a spontaneous t-m transformation upon cooling from sintering. (C) 2001 Kluwer Academic Publishers.