Morphology of Tetragonal Precipitates in Partially Stabilized ZrO2

Tetragonal ( t ) ZrO₂ precipitates in Mg-, Ca-, and Y-partially-stabilized ZrO₂ (Mg-PSZ, Ca-PSZ, Y-PSZ) have different habit planes and different morphologies. These differences arise because of differences in lattice parameters of precipitate and cubic ( c ) ZrO₂ matrix in the three systems. The approximate {001} habit plane and oblate spheroid precipitate morphology observed in Mg-PSZ are explained in terms of anisotropic elasticity using the theory of Khachaturyan. The aspect ratio of ∼5 of these particles is used to calculate a c/t interfacial energy of ∼0.15 J·m^–2. The aligned equiaxed precipitates observed in Ca-PSZ and the twinned colonies observed in Y-PSZ can also be explained using this theory and arise from interactions between strain fields during coarsening; the aligned particles in Ca-PSZ may actually represent an intermediate state before the formation of colonies in this system.