Preparation and mechanical properties of graphene-reinforced alumina-matrix composites

Monolithic Al₂O₃ and graphene-reinforced Al₂O₃ ceramic-matrix nanocomposites were fabricated with the help of spark plasma sintering (SPS). Density, hardness, bending strength, fracture toughness and microstructure of the sintered samples were studied. The contents of graphene were 0–1.6 wt%. The strengthening and toughening mechanisms of the composites were discussed in detail. The results showed that the density of the composites varied from 99.7% to 98.7%. 0.4–1.6 wt% of graphene was homogeneously distributed in the matrix. The structural stability of graphene was analyzed by Raman spectroscopy. The bending strength of the nanocomposite reached the maximum when graphene content was 0.4 wt%. The fracture toughness of the composites also increased when the addition of graphene was between 0.4 and 1.6 wt% as compared to monolithic alumina. Different types of toughening mechanisms were observed including; micro-cracks, graphene pull-out, crack deflection and crack bridging.