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

The rapid densification behavior of 8 mol% Y 2 O 3 ‐stabilized ZrO 2 polycrystalline (8 Y ‐ SZP ) powder compacts at the initial stage of pressure sintering (relative density (ρ · ) 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 (ρ · ) versus ρ andρ ·versus temperature ( T ) curves. These curves were obtained experimentally by consolidation at a fixed current. Under fixed current ECAS , the heating rate (T · ) decreases continuously over sintering time. Using a quasi‐ constant heating rate ( CHR ) method, data points were extracted to plotρ ·vs. ρ,ρ ·vs. T , and ρ vs. T curves at a fixedT · . The stress exponent ( n ), estimated from a log‐log plot of grain size ( d )‐correctedρ · /ρ and effective stress (σ eff ) 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 ‐correctedρ · /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 Zr 4+ lattice diffusion of about 440 kJ/mol. These results suggest that rapid densification of 8 Y ‐ SZP by ECAS seems to proceed by diffusional creep controlled by grain‐boundary diffusion of Zr 4+ ions.