Mechanical and electromagnetic interference shielding properties of in-situ grown Si₃N₄nw synergistic defective-graphene reinforced alumina ceramics

Ceramic matrix composites have versatile application potential but are astricted by brittleness and single function. It can be ameliorated assisted by reinforcements, but the uneven distribution of reinforcements seriously limits the reinforcing efficiency. In this work, the layered porous skeleton of alumina (Al₂O₃) and silicon dioxide (SiO₂) was prepared, then defective-graphene (DG) and silicon nitride nanowires (Si₃N₄nw) were successively grown in-situ in the skeleton (Al₂O₃/SiO₂-G-Si₃N₄nw) to concurrently strength and toughen, as well as endow Al₂O₃ ceramic with electromagnetic interference (EMI) shielding performance. Subsequently, Al₂O₃/SiO₂-G-Si₃N₄nw preform was sintered to construct a uniform Si₃N₄nw synergistic DG enhancement network. The optimum flexural strength and fracture toughness of the sintered ceramic reached 388.52 MPa and 11.29 MPa m^1/2, respectively. This was mainly since DG can fine the ceramic grains, induce crack deflection and furcation, while the uniformly distributed Si₃N₄nw consumed additional energy during the pull-out process. In addition, the EMI shielding effectiveness of the sintered ceramics in X-band was up to 31.77 dB, which is mainly attributed to the conductive loss, dipole polarization loss and interfacial polarization loss of DG. Remarkably, this work provides an idea for efficient strengthening, toughening and integration of structure and function.