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

Abstract

This study aims at comparing hot pressing (HP) and the electric field-assisted sintering technique (FAST) of 8 mol% yttriastabilized 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. II. Experimental Procedure(1) FAST and HP Experiments All experiments were made with HP (model HPW 150/200-2200-100-LA) and FAST (FCT HP D 25/1) equipments were D. Clarke-contributing editor This work was financially supported by the Deutsche Forschungsgemeinschaft (Emmy Noether Program GU993-1/1).

Two step sintering of cubic yttria stabilized zirconia using Field Assisted Sintering Technique/Spark Plasma Sintering

“…Nevertheless, according to sintering trajectories obtained from free sintering or even standard FAST/SPS experiments, it would be expected that an increase in density from 98% to 99% would give rise to more pronounced grain growth. 13,14 Finally, as a reminder, no effect of electric field is expected under the present conditions, as it was highlighted in a previous …”

“…Indeed, the grain size of pressure-filtrated sample heated at 1150 • C without low-temperature second step is already limited to about 200 nm. Langer et al 13 performed FAST/SPS experiments with the same powder dry pressed, applying single step sintering cycle under constant pressure and heating rate of 15 • C/min. The grain size for a density of 65% was already 190 nm and the maximal grain size for a density of 99% was evaluated to 2.47 m, i.e.…”

“…Nevertheless, if pressure limits grain growth compared to free sintering, coarsening is still observed for densities larger than 95%. 13,14 High heating rates have been effective in reducing grain growth by minimizing the time a sample is exposed to low temperature at which coarsening mechanisms are active. 15 By increasing the pressure up to 800 MPa, [16][17][18] it is possible to dramatically reduce the temperature required for full densification, as other deformation mechanisms such as dislocation motion may become active.…”

“…study comparing FAST/SPS to hot pressing,13 even if interesting grain growth behaviour could recently be evidenced under current flow 20. …”

Densification of zirconium nitride by spark plasma sintering and high voltage electric discharge consolidation: A comparative analysis

“…Many efforts are currently dedicated to the individuation and modeling of densification mechanisms of ceramic materials under SPS conditions [32,[38][39][40][41][42][43], while equations capable of reliable describing consolidation kinetics for HVEDC procedures have not been developed.…”