Effects of silanization of C/C composites and grafting of h-BN fillers on the microstructure and interfacial properties of CVI-based C/C-BN composites

A low-density carbon/carbon (C/C) composite/silane coupling agent/hexagonal boron nitride (h-BN) hybrid reinforcement was prepared by grafting polyethyleneimine (PEI)-encapsulated modified h-BN fillers onto a carbon fiber surface using 3-aminopropyltriethoxysilane (APS) as the connection to improve the distribution uniformity of h-BN fillers in quasi-three-dimensional reinforcements and the interfacial properties between the fibers/pyrocarbon (PyC) in the C/C-BN composites obtained after densification by chemical vapor infiltration (CVI). The microstructure and chemical components of the hybrid reinforcement were investigated. The transmission electron microscopy (TEM) sample was prepared using a focused-ion beam (FIB) for the h-BN/PyC interfacial zone. The interlaminar shear strength (ILSS) and impact toughness were analyzed to inspect the composites' interfacial properties. The results show that APS and h-BN are uniformly grafted on the fiber surface in the chopped fiber web inside the C/C composite without a density gradient, and agglomeration occurred and significantly increasing the fiber surface roughness. The highly ordered h-BN basal plane may affect the order degree of PyC near the h-BN/PyC interface. The addition of h-BN reduces the PyC texture near it, causing the annular cracks to disappear gradually. The lower PyC texture and the rougher fiber surface strengthen the interfacial bond of the fiber/matrix. Consequently, the ILSS strength of the C/C-BN composites first increases and then decreases as the h-BN filler content increases and is always higher than that of the C/C composite, while the addition of h-BN fillers weakens its impact toughness. When the h-BN content in the C/C-BN composite is 10 vol %, the ILSS of the C/C-BN composites was 15.6% higher than that of the C/C composites. However, when the hBN content is excessive (15 vol%), the densely grafted h-BN will bridge each other, reducing the subsequent CVI densification efficiency to form a loose interface, causing a decrease in the shear strength.

Automated summary

This study prepared a low-density carbon/carbon (C/C) composite/silane coupling agent/hexagonal boron nitride (h-BN) hybrid reinforcement by grafting polyethyleneimine (PEI)-encapsulated modified h-BN fillers onto a carbon fiber surface using 3-aminopropyltriethoxysilane (APS). The results showed that the addition of h-BN can enhance the interfacial bond of fiber/matrix in the C/C-BN composites, while weakening the impact toughness. When the h-BN content in the C/C-BN composite is 10%, the ILSS of the composite was 15.6% higher compared to the C/C composites, but excessive h-BN content can lead to a loose interface and a decrease in shear strength.