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

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 (rho) 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 ((rho) over dot) vs. T and (rho) over dot vs. rho curves were interpolated for different fixed heating-rates ((T) over dot) of 0.1 to 2.0 K/s. Although the values of (rho) over dot at fixed temperatures or relative densities increased with increasing (T) over dot, the values of T and rho corresponding to the peaks of (rho) over dot were almost constant at 1300 K and 0.8, respectively, irrespective of (T) over dot. The stress exponent (n) estimated from log-log plots of (rho) over dot and the effective stress (sigma(eff)) increased monotonically with increasing T; however, the values of n re-estimated using sigma(eff) compensated for threshold stress (sigma(0)) were approximately 2, irrespective of T. In addition, the activation energy (Q) estimated from the (sigma(eff) - sigma(0)) 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 sigma(0) as well as creep deformation in the intermediate stress region. [doi:10.2320/matertrans.M2011104]