The control of interfacial bonding state and optimization of mechanical properties of Si₃N_4f/BN/Si₃N₄ composites via different synthesis technologies

Silicon nitride fibers-reinforced silicon nitride matrix (Si₃N_4f/BN/Si₃N₄) composites with a BN interphase were fabricated by chemical vapor infiltration (CVI) and precursor infiltration pyrolysis (PIP). It is shown that PIP Si₃N_4f/BN/Si₃N₄ composites possessed better mechanical properties and achieved effectively interface debonding and fiber pull-out, whose flexural strength and fracture toughness can achieve 189 ± 17 MPa and 5.6 ± 0.6 MPa·m^1/2, about twice and 1.5 times as much as those of CVI Si₃N_4f/BN/Si₃N₄ composites, respectively. Combining the micro-nano mechanical and macro-mechanical properties investigations, it is revealed that weakening the interfacial bond and achieving proper modulus matching relationship between fibers and matrix by PIP process could remarkably increase the mechanical properties of the Si₃N_4f/BN/Si₃N₄ composites, compared with CVI process.