Preferentially oriented SiC/graphene composites for enhanced mechanical and thermal properties

Dense SiC ceramics with a high alignment of graphene nanoplatelets (GNPs) were fabricated via a liquid-phase hot pressing (HP) process. The effects of GNPs on the phase composition, microstructure evolutions, mechanical and thermal properties of SiC ceramics were analyzed in detail. As the GNPs content increased from 0 to 3 wt %, the density and hardness of the SiC/GNPs composites decreased monotonically, whereas the flexural strength, fracture toughness and thermal conductivity increased initially and then decreased. The decrease in density and hardness is due to the low density and low hardness of GNPs themselves. The increase in thermal conductivity is mainly due to electron thermal transmission and the widening effect of phonon thermal transmission channel by the textured GNPs. The main strengthening and toughening mechanisms include fine grain strengthening, dislocation strengthening, crack bridging, crack deflection and crack termination. The SiC/GNPs composites sintered under uniaxial pressure condition (HP) display anisotropic thermal and mechanical properties. The anisotropic thermal conductivities of the SiC/GNPs composites are likely due to in plane GNPs parallel to the direction of heat flow, while through plane GNPs are perpendicular to the direction of heat flow. The anisotropy in mechanical properties of the SiC/GNPs composites are due to the through plane GNPs preferentially oriented to intersect the cracks, while the in plane GNPs preferentially oriented to parallel the cracks.