Diffusionless Cubic‐to‐Tetragonal Phase Transition and Microstructural Evolution in Sintered Zirconia–Yttria Ceramics

Abstract

Microstructural changes associated with the diffusionless cubic‐to‐tetragonal phase transition ( c–t ′) in sintered ZrO 2 –Y 2 O 3 ceramics with 4 to 20 mol% Y 2 O 3 are investigated. Ceramics containing 4 to 7 mol% Y 2 O 3 that are quickly cooled from high temperatures experience cubic‐to‐tetragonal transformation by a diffusionless mechanism. The TEM diffraction pattern of the transformation product, t ′‐ZrO 2 , reveals (112) reflections that are suppressed in the c ‐ZrO 2 phase. The microstructural features of the t ′‐ZrO 2 phase include antiphase boundaries and a twinned substructure in the (112) dark‐field images. The (112) reflections result from the displacement of oxygen atoms in the lattice during phase transformation. With increasing Y 2 O 3 content, the antiphase domain size, the tetragonality of the lattice, and the intensity of the (112) reflections decrease. When the Y 2 O 3 content reaches 8 mol% or more, the (112) reflections appear, but the dark‐field image shows no antiphase boundary, and the tetragonality decreases to 1. In ceramics with 14 to 20 mol% Y 2 O 3 , no suppressed reflection appears because the c–t transformation is fully suppressed. A model of the lattice structure is calculated and the intensity of diffraction determined experimentally; on this basis, the mechanism of diffusionless c–t ’transformation is discussed.