Study on the Interface Structure and Properties of Si ₃ N ₄ –TiB ₂ Composite Ceramics Optimized by Core–Shell Structure

Introducing titanium diboride (TiB 2 ) into silicon nitride (Si 3 N 4 ) is an effective strategy to impart electrical conductivity, but severe interfacial reaction and thermal mismatch cause increased interfacial defects and decreased performance. Therefore, it is necessary to design an effective interface control strategy. In this study, an amorphous Si 3 N 4 coating (5–8 nm) was deposited on TiB 2 particles by atomic layer deposition (ALD) to form a core–shell structure, and then Si 3 N 4 –TiB 2 composites were fabricated by hot pressing. The core–shell structure acts as a physical barrier to suppress the interfacial reaction, and the gradient layer alleviates the residual thermal stress, forming an integrated coherent interface between the two phases. Consequently, the composites maintain high relative density (> 99.6%) over a wide TiB 2 content range (5–25 wt%). At 25 wt% TiB 2 , the thermal conductivity reaches 47.8 ± 0.4 W·m −1 ·K −1 , hardness 16.6 ± 0.2 GPa, fracture toughness 9.9 ± 0.1 MPa·m 1/2 , and volume resistivity drops to (1.2 ± 0.5) × 10 9 Ω·cm (2.5 orders lower than directly mixed samples). This work provides a new strategy for developing multifunctional Si 3 N 4 ceramics with high strength, high thermal conductivity, and tailorable electrical conductivity.