GeO<SUB>2</SUB>-doping Dependence of High Temperature Superplastic Behavior in 3Y-TZP

Abstract

Superplastic behavior in a fine-grained, GeO2-doped 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) with the dopant level of 0.2—3 mol% was examined at 1400°C under an initial strain rate of 1.3 × 10−4 s−1. Microstructure and chemical composition at the grain boundaries was examined by high-resolution electron microscopy (HREM) combined with an X-ray energy dispersive spectrometer (EDS). No secondary phase was observed along the grain boundaries, though EDS analysis indicated the segregation of Ge cations along the grain boundaries. The Ge content at the grain boundaries tends to increase with increasing the total amount of GeO2 addition, but saturate over the doping level of 2 mol%. Dependence of flow stress reduction on the total amount of GeO2 addition has a good correlation with Ge content at the grain boundaries. This fact indicates that the GeO2-doping effect on the flow stress in 3Y-TZP is caused mainly from the grain boundary segregation of Ge cations.