Preparation And Properties Of High Performance Carbon / Carbon Composites

Carbon/carbon composite is a composite material which is made by adding carbon fiber as reinforcement phase to different carbon matrix and prepared after high temperature heat treatment.Different carbon structure between fiber and matrix gives it different mechanical properties from other composite materials.It is a layered composite material which can still maintain excellent mechanical properties in high temperature environment,and has been widely used in many fields.With the development of science and technology,aerospace,military,civil engineering and other fields put forward higher requirements for high temperature bending and shear properties of carbon/carbon composites.Therefore,it is more and more important to prepare carbon/carbon composites with excellent mechanical properties.However,the traditional process of carbon/carbon composites prepared by polymer or organic gas is prone to stress cracks or ring cracks,which leads to the poor mechanical properties of the composites.In this paper,the diamond matrix precursor is made of Dongli T300-1k carbon fiber cloth.The carbon fiber cloth of certain size is stacked in the same direction.The nano diamond powder is deposited in the carbon fiber preform by liquid-phase impregnation and chemical infiltration.The content of diamond powder in the preform is controlled by controlling the concentration of impregnation solution of the precursor of nano diamond,which is beneficial to the content of diamond powder in the preform The diamond particles are mechanically linked with the surface of carbon fiber similar to"tree scar",and then sintered by plasma discharge reaction to obtain high performance carbon/carbon composite.The method is simple and will not damage the structure of carbon fiber.The microstructure and fracture of the composite were observed by SEM and HRTEM.The phase analysis was carried out by X-ray diffraction(XRD)and Raman.The bending and shear properties of the composite were tested on the universal testing machine,and the best addition and sintering pressure of nano diamond were determined.The change of the hybrid mode of carbon atoms before and after sintering of composite materials was characterized by X-ray photoelectron spectroscopy(XPS),and the sintering mechanism between fiber and matrix was analyzed.The main results are as follows:The nano graphite onion balls,which were transformed by reaction sintering,were used as binder in the preform to consolidate the original fiber silk and fiber cloth into a layered reinforced structure.The volume expansion during the transformation from diamond to graphite structure promotes the consolidation of composite.Based on the results of XPS and phase analysis and HRTEM,the interface between the fiber and the matrix was enhanced by the formation of sp~3 hybrid bond between carbon fiber and nano graphite onion.The content of nano diamond powder in the preform is 40 wt.%.When the sintering pressure is 40MPa,the bending strength of the composite is the highest,reaching 1206.5MPa.The composite fiber with more than 40 wt.%has strong bonding with the matrix,and the aggregate inside the composite reduces the mechanical properties of the composite.The sintering pressure above 40 MPa has damage to the fiber structure,which also weakens the mechanical properties of the composite.For layered composite,the binding effect of fiber and matrix is too weak or too strong,but the mechanical properties of the composite materials are reduced,and the appropriate interface bonding is more favorable for the mechanical properties of the composite.