Electric Field-Assisted Sintering in Comparison with the Hot Pressing of Yttria-Stabilized Zirconia

This study aims at comparing hot pressing (HP) and the electric field-assisted sintering technique (FAST) of 8 mol% yttria-stabilized zirconia (8YSZ). Three different ionic conductive nano- and submicron powders were investigated, with a median particle size of 20-30, 51-65, and 150 nm, respectively. Processing parameters were kept identical for both sintering methods: sample geometry, heating schedule, applied pressure, and atmosphere. Investigations of densification and microstructural characterization reveal that under the same conditions FAST and HP sintered samples behave similarly. The analysis of the sintering curves shows that the densification mechanism is the same for both sintering methods (grain-boundary diffusion). An increase of the heating rate up to 150 K/min does not modify the densification mechanism. The sintering trajectory reveals that grain size depends only on density and not on the sintering method and grains have no preferential orientation. Secondary ion mass spectroscopy shows that both types of specimens are contaminated with carbon only superficially. Measurements of the electrical conductivity at high temperature show no significant difference between HP and FAST samples.