Microstructure and mechanical properties of SiCf/SiC composites with a hybrid BN interphases

Boron nitride (BN), due to its layered structure and excellent thermal stability, is a preferred interphase material for silicon carbide fiber-reinforced silicon carbide matrix composites (SiC f /SiC) used in aero-engine applications. In this study, a hybrid icBN interphase was fabricated within 2D SiC f /SiC composites using a combination of in-situ and chemical vapor infiltration (CVI) techniques. For comparison, control groups featuring single iBN interphases (fabricated by in-situ method) and single cBN interphases (fabricated by CVI) were also prepared. The microstructures of the composites were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Interfacial and macroscopic mechanical properties of 2D SiC f /iBN/SiC, 2D SiC f /cBN/SiC, and 2D SiC f /icBN/SiC composites were compared to evaluate the influence of interphase design on interfacial behavior and overall mechanical performance. The cBN interphase, despite its minimal thickness (∼180 nm), demonstrated the highest interfacial bonding strength (2532.63 MPa) and interfacial shear strength (113.20 MPa), attributed to its high crystallinity and irregular serrated interface. In contrast, the iBN interphase, with a thickness of ∼240 nm, exhibited the weakest bonding, with an interfacial bonding strength of 1463.46 MPa and shear strength of 27.71 MPa. The icBN interphase showed intermediate properties, with a bonding strength of 1629.86 MPa. Its failure mode was characterized by partial debonding and crack deflection, with cracks arrested at the iBN/cBN interface. Macroscopic mechanical performance closely followed interfacial behavior. The cBN-interphase composite exhibited the highest tensile strength (341.22 MPa) and flexural strength (585.4 MPa), whereas the iBN-interphase composite, with the weakest bonding, recorded a tensile strength of 211.2 MPa. The icBN-interphase composite demonstrated intermediate performance with a tensile strength of 254.0 MPa.