On the spinodal decomposition in zirconia-yttria (ZrO₂-Y₂O₃) alloys

Abstract

Structural changes in arc-melted zirconia alloys containing 4 and 5mol.% yttria (Y-PSZ) during ageing inside the two-phase region of cubic (c) and tetragonal (t) phases were investigated with transmission electron microscopy. The arc-melted and auenched Y-PSZ's consist of only tetragonal t′ phase containing many domains. Ageing inside the two-phase region of t + c sometimes produces fine modulated structures consisting of two different tetragonal phases, i.e. t ₁ and t ₂ These two-phase structures exhibit satellites in the electron diffraction pattern. It was discovered for the first time that in the early stage of ageing at lower temperatures, Y-PSZ alloy exhibits a period when the wavelength λ_m of its modulated structure remains practically constant. Furthermore, there is a linear relation between the sauare of the wave-number β² _m (β_m = 2π/λ_m) and the ageing temperature T The above experimental results strongly indicate the occurrence of spinodal decomposition (t′→t ₁ + t ₂) in Y-PSZ alloy resulting in the formation of a modulated structure. The linear relation between β² _m; and T indicates that the spinodal temperature of ZrO₂-4mol.%Y₂O₃ alloy is 1836K.