High performance fiber-reinforced ceramic matrix composites have excellent properties such as light weight, high strength, and high temperature resistance, which can replace traditional superalloys as high-temperature structural materials in the aerospace field. During its preparation and cooling process, due to the mismatch of the thermal expansion coefficient between the fiber and the ceramic matrix, the internal interface of the composite material is often subject to greater thermal stress, which in turn leads to the degradation of its service performance. The current conventional solution is to introduce a cracked carbon intermediate layer on the surface of the fiber by chemical vapor deposition to form a good stress gradient and reduce stress damage. However, the chemical vapor deposition method consumes high energy, high cost, and requires high equipment. Therefore, it is necessary to develop a simple and efficient new intermediate layer preparation process.
Researcher Huang Qing from ZKNB Institute of Composite Materials has recently developed an easy-to-operate and low-cost method for preparing cracked carbon interlayer. The method uses phenolic resin as the raw material, and uniformly coats the cracked carbon layer on the surface of the carbon fiber by the impregnation cracked carbon method. At the same time, the method also uses carbon nanotubes to enhance the intermediate layer to obtain a new multi-layer silicon carbide composite material, revealing the influence of different nanometers and micrometers on the mechanical properties and microstructure of the composite material.
The research results show that when carbon nanotubes are introduced into the cracked carbon intermediate layer, the tensile strength and work of fracture of the carbon fiber/cracked carbon/silicon carbide tow composite material are significantly improved compared with the composite material without carbon nanotubes. Increased by 54.9% and 130.3%, respectively. At the same time, the microscopic morphology of the fracture of the tensile sample of the composite material showed that the surface of the broken fiber showed carbon fiber/cracked carbon, carbon nanotube/cracked carbon, and cracked carbon/matrix. A phenomenon of synergistic toughening of the interface.
The above research reveals the mechanism of performance improvement of this type of composite material: in the process of preparing carbon fiber reinforced silicon carbide composites by the precursor impregnation and pyrolysis (PIP) process, when carbon nanotubes exist at the cracked carbon/cracked carbon interface, they can To the effect of interface lubrication, it can reduce the interface thermal stress caused by the mismatch of the thermal expansion coefficient of carbon fiber and cracked carbon, so it can improve the strength; at the same time, the existence of carbon nanotubes improves the toughening ability of the cracked carbon intermediate layer itself, adding The crack propagation path leads to an increase in the work of fracture; when carbon nanotubes exist at the two interfaces of carbon fiber/cracked carbon and cracked carbon/matrix, the composite material is compared with the composite material without carbon nanotubes. The strength and the effect of improving the work of fracture are not obvious. This work proves the importance of fiber reinforced composite interface design and carving.