Multifunctional Si₃N₄-skeleton-reinforced graphite flake composites with preferred orientation integrate excellent mechanical, thermophysical, and electromagnetic shielding properties

Si₃N₄-skeleton-reinforced graphite flake (GF/Si₃N₄) composites with preferred orientation were fabricated using a combination of vacuum infiltration and plasma-activated sintering to produce highly oriented graphite-based composites with excellent strength, favorable thermal conductivity, low thermal expansion, and effective electromagnetic shielding properties. The impact of Si₃N₄ content on the microstructure, bending strength, thermophysical properties, and electromagnetic shielding effectiveness of the composites was systematically examined. The composites exhibited reasonable anisotropy (Lotgering factor f > 93 %), endowing them with high thermal conductivity in the basal plane direction of the GF. The formation of SiC at the Si₃N₄/GF interface increased the interfacial bonding and effectively suppressed the thermal expansion of GF perpendicular to the basal plane from ∼28 × 10⁻⁶/K to ∼8 × 10⁻⁶/K. The composite with 21 vol.% Si₃N₄ exhibited the optimal properties, including a satisfactory bending strength of 128 MPa, good thermal conductivity of 247 W/m/K, a suitable thermal expansion of 9.4 × 10⁻⁶/K, and good electromagnetic interference shielding effectiveness of 30 dB. Hence, the fabricated GF/Si₃N₄ composites demonstrate significant potential as high-orientation graphite-based composites for multifunctional thermal management.