Effect of solid solution additives on the densification and creep of granular ceramics

The effect of solid solution additives on the densification and creep of granular ceramics was investigated for a model system consisting of CeO2 solid solutions with Y2O3 as the additive. In the sintering of powder compacts at 1,150 C, the densification rate of CeO2 at a given density decreased significantly with increasing Y3+ concentration. The reduction in the densification rate reached a factor of ∼100 for a Y3+ concentration of 6 at.%. Creep of dense specimens was investigated at constant strain rates of 10-5 and 10-4 s-1 in air at 1,200 C. After compensation for differences in grain size, the creep rate was also found to decrease significantly with increasing Y3+ concentration. If the creep rate is assumed to be controlled by a mechanism of grain boundary diffusion, then the magnitude of the decrease is in good agreement with that observed in the sintering experiments. The results strongly indicate that it may be possible to predict changes in the steady-state creep behavior from observed changes in the sintering behavior provided that matter transport occurs by the same mechanism. They also indicate that the solid solution approach may have considerable merit for controlling the creep resistance of rare earth oxides that commonly have a high solubility for many cations