Hot-pressed graphene nanoplatelets or/and zirconia reinforced hybrid alumina nanocomposites with improved toughness and mechanical characteristics

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This work explains the synergistic contribution of graphene nanoplatelets (GNP) and zirconia ceramic nanoparticles (ZrO2) on the microstructure, mechanical performance and ballistic properties of the alumina (Al2O3) ceramic hybrid nanocomposites. Over the benchmarked monolithic alumina, the hot-pressed hybrid nanocomposite microstructure demonstrated 68% lower grain size due to grain pinning phenomenon by the homogenously distributed reinforcing GNP (0.5 wt%) and zirconia (4 wt%) inclusions. Moreover, the hybrid nanocomposite manifested 155% better fracture toughness (KIC) and 17% higher microhardness as well as 88% superior ballistic trait over the monolithic alumina, respectively. The superior mechanical and ballistic performance of the hybrid nanocomposites was attributed to the combined role of zirconia nanoparticles and GNP nanomaterial in refining the microstructure and inducing idiosyncratic strengthening/toughening mechanisms. Extensive combined electron microscopy revealed complicated physical interlocking of the GNP into the microstructure as well as excellent bonding of the GNP with alumina at their interface in the hybrid nanocomposites. We also probed the efficiency of the pull-out and crack-bridging toughening mechanisms through proven quantitative methods. Based on the information extracted from the in-depth SEM/TEM investigation, we outlined schematic models for understating the reinforcing ability as well as toughening mechanisms in the hybrid nanocomposites and meticulously discussed. The hot-pressed hybrid nanocomposites owning high toughness and hardness may have applications in advanced armor technology.