Phase separation and hydrothermal degradation of 3 mol% y2O 3-ZrO2 ceramics

Abstract

Phase separation and hydrothermal degradation in 3 mol% Y2O 3-stabilized tetragonal ZrO2 polycrystal (3Y-TZP) were studied by X-ray diffractometry. The Rietveld analysis showed that crystal structure of sintered body remarkably changes at high temperature. The sintered body is phase separated into high and low yttrium region with increasing sintering temperature. Both regions are assigned to the tetragonal phase. The high yttrium region can be analyzed using tetragonal phase model with c / a ≅ 1. The amount of monoclinic phase induced by hydrothermal degradation increased with increasing degradation time. Aging kinetics of tetragonal to monoclinic phase transition was analyzed with Johnson-Mehl-Avrami equation. Fraction of transformable phase evaluated with the equation is in good agreement with the fraction of low yttrium region determined with the Rietveld analysis. The quantitative analyses clearly show that the low yttrium region selectively transforms into monoclinic phase under the hydrothermal condition, while the high yttrium region does not transform. Transformable fraction during the hydrothermal condition in 3Y-TZP ceramics is governed by the amount of low yttrium region. The formation of low yttrium region due to phase separation is responsible for hydrothermal degradation in sintered body.