Estimation of Stress Exponent and Activation Energy for Rapid Densification of 8 mol% Yttria-Stabilized Zirconia Powder


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The rapid densification behavior of 8 mol% Y2O3-stabilized ZrO2 polycrystalline (8Y-SZP) powder compacts at the initial stage of pressure sintering (relative density (math formula) below 0.92) has been investigated using an electric current-activated/assisted sintering (ECAS) system. Data points corresponding to a fixed heating rate were extracted from the densification rate (math formula) versus ρ and math formula versus temperature (T) curves. These curves were obtained experimentally by consolidation at a fixed current. Under fixed current ECAS, the heating rate (math formula) decreases continuously over sintering time. Using a quasi- constant heating rate (CHR) method, data points were extracted to plot math formula vs. ρ, math formula vs. T, and ρ vs. T curves at a fixed math formula. The stress exponent (n), estimated from a log-log plot of grain size (d)-corrected math formula/ρ and effective stress (σeff) at 1300–1400 K, shows an almost constant value of 1. In addition, the activation energy (Q) for rapid densification, estimated from an Arrhenius plot of d-corrected math formula/ρ also shows an almost constant value of 350 kJ/mol, which is considerably lower than the previously reported value of the activation energy for Zr4+ lattice diffusion of about 440 kJ/mol. These results suggest that rapid densification of 8Y-SZP by ECAS seems to proceed by diffusional creep controlled by grain-boundary diffusion of Zr4+ ions.