Mechanism for Densification of Yttria-Stabilized Tetragonal Zirconia Powder by Electric Current-Activated/Assisted Sintering

Abstract

The effect of electric current-activated/assisted sintering (ECAS) on the densification of a mechanically milled 3Y-TZP ceramic powder was investigated. The changes in temperature (T) and relative density (ρ) with time during ECAS under a uniaxial pressure of 90.5 MPa in a closed die were measured for different heating conditions. From the results, densification rate (\\dotρ) vs. T and \\dotρ vs. ρ curves were interpolated for different fixed heating-rates (\\dotT) of 0.1 to 2.0 K/s. Although the values of \\dotρ at fixed temperatures or relative densities increased with increasing \\dotT, the values of T and ρ corresponding to the peaks of \\dotρ were almost constant at 1300 K and 0.8, respectively, irrespective of \\dotT. The stress exponent (n) estimated from log-log plots of \\dotρ and the effective stress (σeff) increased monotonically with increasing T; however, the values of n re-estimated using σeff compensated for threshold stress (σ0) were approximately 2, irrespective of T. In addition, the activation energy (Q) estimated from the (σeff−σ0) vs. 1⁄T Arrhenius plot was 450±20 kJ/mol. These values of n and Q were similar to those for creep experiments reported by Melendo et al., which suggests that densification of 3Y-TZP powder compacts by ECAS proceeds through grain boundary sliding affected by σ0 as well as creep deformation in the intermediate stress region.