Structure, phase composition and properties of vacuum pressureless sintered ZrO2-based composites reinforced with carbon nanotubes

Abstract

Abstract In this work, composites based on 3 mol. % yttria-stabilized zirconia (3YSZ) with additives of 1, 5 and 10 wt. % multi-walled carbon nanotubes (MWCNT) were investigated. Samples were obtained by cold pressing followed by vacuum pressureless sintering at a temperature of 1500 °C. It was found that MWCNTs retain their structure after high-temperature sintering, they are located along the zirconia grain boundaries and they lead a grain refining effect for zirconia matrix. Nanotubes can significantly affect the phase composition of composites. Additives 5 wt. % and 10 wt. % MWCNT partially limits the monoclinic-tetragonal phase transition of ZrO2 and leads to the formation of a new phase of zirconium carbide. An increase of MWCNTs content in composites leads to a smooth decrease of the relative density from 99.2 % to 81.2 %. To obtain fully dense 3YSZ/MWCNT composites, longer sintering at higher temperatures is required compared to the conditions for sintering 3YSZ ceramics without additives.