Microstructure, mechanical, and thermal properties of graphene and carbon nanotube-reinforced Al 2 O 3 nanocomposites

The inherent brittleness of monolithic alumina (Al2O3) has been limiting its potential structural applications in some high performance areas, such as engine turbine components and high-temperature space materials. In the current study, effects of spark plasma sintering (SPS) parameters on the microstructure, mechanical, and thermal properties of graphene/CNTs-reinforced alumina nanocomposites were studied. In order to confirm that this was a successful process, the morphology and structure were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). With the increase of graphene contents, the fracture toughness of Al2O3 and CNTs-Al2O3 increased by 38.4% and 49.5%, respectively. Novel toughening mechanisms, such as bridging, crack deflection, and pull-out and embedded graphene, have been observed to be responsible for the significant increase in toughness. The highest thermal conductivity of 23.3 and 22.4 Wm−1 K−1 was observed for monolithic alumina and 0.4 wt% graphene & 1 wt%CNTs/Al2O3 nanocomposites, respectively. The results also revealed that the increase in temperature leads to the decrease of thermal conductivity, but leads to the increase of heat capacity of monolithic Al2O3 and the hybrid composites.