CYCLIC BEHAVIOUR AND ROOM TEMPERATURE MICROMECHANISMS OF 3Y-TZP CERAMICS AT SUBMICRON AND NANOCRYSTALLINE LEVELS

Abstract— The cyclic behaviour and micromechanisms of 3Y-TZP ceramics were investigated at a stress ratio, R , of 0.1 and a frequency of 0.1 Hz at room temperature for both nanocrystalline (100nm) and submicron polycrystalline (0.35μm) 3Y-TZP ceramics. The nanocrystalline material displayed cyclic softening, but the submicron polycrystalline material displayed cyclic hardening. The cyclic hardening resulted mainly from saturation of tetragonal to monoclinic phase transformation which induced a higher internal stress in the material; the cyclic softening resulted partly from the formation of microcracks along the grain boundary of the tetragonal phase.
Superplastic deformation was first found by the Scanning Electron Microscope and the Atomic Force Microscope (AFM) in some micro-areas of the fatigue fracture surface of the nanocrystalline material. Furthermore it was observed by AFM that there were a large number of slip lines and an early stage for the formation of an extrusion on the side edge of the fracture. From this it was deduced that the micromechanism of local superplasticity resulted from the slip motion of dislocation.