YTTRIA-CERIA STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTALS - SINTERING, GRAIN-GROWTH AND GRAIN-BOUNDARY SEGREGATION

An analysis is presented of grain growth and densification of yttria-ceria stabilized tetragonal zirconia polycrystals (Y,Ce-TZPs) using both isothermal and non-isothermal techniques. The characteristics of Y, Ce- TZPs are compared to those of Y-TZP and Ce-TZP and the effect of increasing ceria concentration at constant yttria content is evaluated. During non-isothermal sintering two regimes are distinguished. below 900-1000-degrees-C the neck area increases strongly by surface diffusion accompanied by only very little densification and grain growth, in the temperature interval 900-1000-degrees-C to 1200-degrees-C the materials densify to 95% of the theoretical density via a grain boundary diffusion mechanism and grain growth accelerates. Dense materials with grain sizes of 0.15-0.20 mum can be prepared by isothermal sintering at 1100-1150-degrees-C In Y, Ce-TZP it is yttrium that segregates to the grain boundaries at 1150-1400-degrees-C. The yttrium content of the grain boundaries in Y, Ce-TZP is independent of temperature and ceria-concentration under the investigated experimental conditions. Grain growth in dense TZP is controlled by a solute drag mechanism at elevated temperatures (> 1200-degrees-C); this drag is highest for Y-TZP, absent for Ce-TZP and. moderate for Y, Ce-TZP.