Improved Fracture Toughness and Crack Arrest Ability of Graphene–Alumina Nanocomposite

In this work, high fracture toughness graphene–alumina composite was developed through a novel chemical method using boehmite and graphene, which is followed by extrusion and consolidation. The mixed precursors were consolidated by sintering at 1550 °C in a nitrogen atmosphere. The plate-like structures of boehmite form α-alumina; meanwhile, graphene particles at the grain boundaries hinder the growth of alumina grains. The graphene reinforcement was bonded to α-alumina matrix by van der Waals forces. The XRD pattern reveals the presence of graphene with a plane (002) along with α-alumina. Properties such as fracture toughness (5.6 ± 0.01 MPa m^0.5), Vickers hardness (1872 ± 25 kgf/mm²) and true density (3.8 g/cm³) were achieved in 0.5 wt.% graphene–alumina composite when compared to α-alumina with fracture toughness (5.3 ± 0.1 MPa m^0.5), Vickers hardness (1984 ± 28 kgf/mm²) and true density (3.91 g/cm³). The bridging and deviation of cracks in 0.5 wt.% graphene–alumina composite are attributed to the anchoring and dissipation of energy during crack growth, which enhances the fracture toughness, whereas α-alumina exhibits failure caused by linear crack propagation. Meanwhile, the slight decrease in Vickers hardness and true density of 0.5 wt.% graphene–alumina composite is due to the tribological and low-density properties of graphene. The obtained properties of composite could be suitable in high-temperature, wear-resistant applications such as crucibles, bearings, etc.