Microstructure and anisotropic mechanical properties of graphene nanoplatelet toughened biphasic calcium phosphate composite

Graphene nanoplatelets (GNPs) reinforced biphasic calcium phosphate (BCP) composites were prepared by hot pressing (HP). Based on in-depth mechanical test and observation of microstructure, the influence of GNPs on BCP matrix was investigated. A preferred orientation of GNPs occurred during sintering, leading to anisotropic mechanical properties. The mechanical properties of GNPs/BCP composite measured along the direction parallel to the HP direction are higher than those measured along the perpendicular direction. Parallel to the HP direction, the composite containing 1.5 wt% GNPs exhibited the maximun bending strength and fracture toughness of 151.82 MPa and 1.74 MPa m1/2, about 55% and 76% higher than those of monolithic BCP, respectively. The improvement in mechanical properties was mainly attributable to crack deflection, crack branching, bridging, pullout and fracture of GNPs. Especially GNPs can force crack to propagate not only in two but also in three dimensions.