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

An assessment of fracture origins is conducted in yttria-stabilized zirconi a ceramics containing different grain sizes. As the microstructure coarsens due to the application of heat treatments, fracture origins change from si ngle pores to transformed regions at the free surface which are induced by the applied stress. The observation of an increasing size of failure origin s with microstructural coarsening lies as the underlying reason for the fin ding that specimens containing coarser microstructures and a more pronounce d 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 transforma bility 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 grain s of up to 4 mum may not necessarily undergo a spontaneous t-m transformati on upon cooling from sintering. (C) 2001 Kluwer Academic Publishers.