Optimizing the mechanical properties of Si₃N_4f/Si₃N₄ composites by tailoring the BN interphase structure

Two-dimensional (2D) silicon nitride fiber-reinforced silicon nitride (Si₃N_4f/Si₃N₄) composites were fabricated with four types of boron nitride (BN) interphases: in situ BN (i-BN), chemical vapor infiltration BN (CVI-BN), and two of their combinations. The microstructure and thickness of these interphases were characterized, and their effects on the mechanical properties of the composites were investigated. The composites incorporating i-BN with a 2-cycle CVI-BN interphase (iBN-2CVIBN) exhibited optimal mechanical properties, with corresponding flexural strength, fracture toughness, and tensile strength of 187 ± 23 MPa, 6.1 ± 0.6 MPa·m^1/2, and 77 ± 7 MPa, respectively. The interfacial shear strength and mechanical stability of the BN interphase were analyzed. Finally, the mechanism by which the BN interphase structure affects the mechanical properties of Si₃N_4f/Si₃N₄ composites was discussed in depth from the perspective of residual stress. This work provides novel insights for designing high-performance Si₃N_4f/Si₃N₄ composites.