ON THE BRITTLE-TO-DUCTILE TRANSITION OF Y-PSZ SINGLE-CRYSTALS

The fracture behaviour (fracture mechanisms, fracture toughness, and s trength) of yttria-partially stabilized zirconia (Y-PSZ) single crysta ls; has been investigated between room temperature and 1700 degrees C. Cleavage was the fracture mechanism acting over the entire temperatur e interval studied, with some plastic elements arising at temperatures of 1000 degrees C and above, accounting for the increasing fragmentat ion with temperature observed for the precipitation-hardened materials . Fragmentation is ensured from intel domain cleavage on {1 0 0} and { 1 1 0} planes. No subcritical cracks were observed. The strength and f acture toughness follow behaviour typical for materials with a pronoun ced brittle-to-ductile transition. After a gradual decrease between ro om temperature and 1000 degrees C, both properties show a sharp increa se under elevated temperatures, followed by a sharp decrease. This inc rease is associated with dislocation plasticity revealed in delaminati ons along {1 1 0} and {1 0 0} planes. The lower temperature limit of t he brittle-to-ductile transition was estimated as 1000 degrees C. A hi gher limit was not reached and the transition of Y-PSZ [1 0 0] single crystals into a ductile state probably occurs at about 2000-2100 degre es C. The mechanism of ductile fracture is presumably intergranular sl iding of grains, formed in the course of plastic deformation, from dom ain microstructure. (C) 1996 Elsevier Science Limited.