Y2O3-partially stabilized zirconia shows various microstructures, for example, twinned, herring-bone, lenticular, domain, tweed, modulated, martensitic tetragonal structures, anti-phase boundaries and short range ordering. In order to interpret the formation mechanisms of these structures, the phase diagram of the ZrO2-Y2O3 system at low Y2O3 contents proposed by the present authors was investigated. It was concluded that cubic-tetragonal transformation in ZrO2 was para-ferroelastic second order transition and that the (cubic + tetragonal) two-phase region in the diagram was regarded as a miscibility gap. From these standpoints, the formation mechanisms of complex microstructures are also discussed.
(Received February 16, 1987)
Keywords: ceramics, ferroelastic state, miscibility gap, phase diagram, precipitation, spinodal decomposition, transformation, yttria, zirconia
* Department of Materials Processing, Faculty of Engineering, Tohoku University, Sendai 980, Japan.
** Tohoku University. Present address: Department of Metallurgy, Faculty of Engineering, The University of Tokyo, Tokyo 113, Japan.