Hard and tough Al₂O₃-SiC-CNT hybrid ceramic nanocomposite produced by molecular level mixing and spark plasma sintering

This work reports a simultaneous improvement in both the hardness and toughness of an alumina Al₂O₃-SiC-CNTs hybrid ceramic nanocomposite. The nanocomposite powder was synthesized using sonication and molecular level mixing (MLM) and was sintered at 1500, 1550, and 1600 °C for 10 min by the spark plasma sintering (SPS) method. The influence of sintering temperature on the microstructure and properties was investigated. The dispersion of silicon carbide (SiC) nanoparticles and carbon nanotubes (CNT) in the powder and consolidated samples was characterized using a field emission scanning electron microscope equipped with energy dispersive spectroscopy. The microhardness and fracture toughness of the samples were measured using a hardness tester. The synthesized nanopowder and the consolidated samples revealed a uniform distribution of the SiC and CNT reinforcements. The relative density of the sintered samples increased from 90.36 to 98.91% as a result of an increase in sintering temperature from 1500 to 1600 °C. The Al₂O₃-5SiC-1CNTs sample, which was sintered at 1600 °C for 10 min, possessed the highest hardness and fracture toughness values of 23.32 GPa and 7.10 MPa.m^1/2, respectively. This finding constitutes an increase in the hardness and fracture toughness of 25.65 and 96.67%, respectively, compared to monolithic alumina sintered at 1500 °C for 10 min.