Sintering behavior of 8YSZ-Ni cermet: Comparison between conventional, FST/SPS, and flash sintering

Abstract

Cermets are ceramic metal composites. The metallic phase in the cermet typically undergoes oxidation during sintering in air. Electric field-assisted sintering processes such as field-assisted sintering technology/spark plasma sintering (FAST/SPS) and flash involves very high heating rates, short processing time and low processing temperature. The main aim of this work was to see if field-assisted sintering techniques can prevent the oxidation of the metallic phase in the cermet. Sintering behavior of 8YSZ-5 wt.% Ni cermet was studied by three different techniques namely; conventional sintering, FAST/SPS and flash sintering. Phases and microstructure were analyzed through X-ray diffraction and scanning electron microscopy, respectively. Temperature and time required for sintering the samples via FAST/SPS and flash sintering was significantly lower than that during conventional sintering. In addition, we found limited grain growth during FAST/SPS and flash sintering. During conventional sintering in reducing atmosphere (Ar and vacuum), Ni particles retained their elemental state, however the extent of densification was poor in the cermet. FAST/SPS in argon and vacuum resulted in almost complete densification (relative density > 97%) and Ni particles were retained in their elemental state in the cermet. During flash sintering in air, the samples sintered to a high densification (relative density ∼98%), however, Ni particles were completely oxidized.