Crystallography of the Tetragonal to Monoclinic Transformation in MgO‐Partially‐Stabilized Zirconia

Abstract

The structure of monoclinic ZrO2 particles dispersed in MgO‐partially‐stabilized zirconia has been examined systematically using transmission electron microscopy and electron micro‐diffraction. In both particles transformed athermally and those transformed under stress, the product of the martensitic tetragonal to monoclinic transformation comprises parallel variants of the monoclinic structure. The monoclinic domains extend either parallel or normal to the original precipitate habit plane and, to within the accuracy of the technique, adjacent pairs are twin related. For particles with domains parallel to the particle habit plane the boundary between variants is (001)m and the orientation relationship between tetragonal and monoclinic lattices is such that (001)m‖ (001)t and [100]m‖ [100]t. In particles with transverse domains, the domain boundaries are parallel to (100)m, and the orientation relationship is given by (100)m‖ (100)t and [001]m‖ [001]t. In each case the lattice correspondence implied between parent and product lattices is such that the cm axis is parallel to the Cm axis. The microcracking associated with transformed particles appears closely related to the substructure adopted by the particles and the origin of this microcracking is briefly discussed.