Structure and Properties of Y2O3-Doped Al2O3-MWCNT Nanocomposites Prepared by Pressureless Sintering and Hot-Pressing

This study describes the combined effects of multi-walled carbon nanotubes (CNTs) additions and Y2O3 doping on the microstructures and mechanical properties of Al2O3-CNT nanocomposites fabricated by pressureless and hot-press sintering processes. A uniform dispersion of CNTs within the Al2O3 matrix was successfully attained via a combined approach using surfactant, sonication, and adequate period of incubation. Small amounts (1 wt.%) of Y2O3, as dopants, significantly affected the densification and properties of pressureless sintered monolithic Al2O3 and its nanocomposites at low CNT concentrations (< 1 wt.%); however, they hardly showed any improvement at higher CNT contents. As opposed to the pressureless sintering, pressures applied during high temperature sintering in combination with the Y2O3 doping contributed in generating a homogenous microstructure and improved the densities (7 and 15%) and microhardness (11 and 12%) of Al2O3 reinforced with higher CNT contents (2 and 5 wt.%), respectively. Adding on, hot-pressed Y2O3-doped Al2O3 reinforced with 2 and 5 wt.% CNTs showed higher hardness (19 and 70%), flexural strength (10 and 5%), and fracture toughness (26 and 11%), respectively, compared to similar but CNT-free samples. These results showed that pressure-assisted sintering and Y2O3 are promising for the fabrication of CNT-reinforced Al2O3 nanocomposites, especially at higher CNT concentrations.