Preparation And Properties Of SiC Ceramic Matrix Composites Reinforced By Carbon Fiber Surface Modification

Compared with ceramic materials,carbon fiber reinforced silicon carbide ceramic matrix(Cf/SiC)composites have better strength-density ratio,temperature resistance and thermal shock resistance,and have broad prospects for development in aerospace field.For Cf/SiC composites,how to improve their fracture toughness is a common problem.The traditional method is to introduce pyrolytic carbon(PyC)interfacial layer to improve the fracture toughness in the preparation of composites.However,due to the strong chemical inertia on the surface of carbon fibers,the wettability between the fibers and the matrix is affected.Therefore,the best solution is surface modification of carbon fibers to improve the interfacial bonding properties of composites.Based on the above ideas,this topic firstly uses multi-molecular coupling agent to modify carbon fibers and graphene oxide(GO)separately.GO is grafted onto the surface of carbon fibers through chemical reactions of different active groups of multi-functional coupling agents.It is found that after GO is grafted on the surface of carbon fibers,high-energy chemical bonds are formed between carbon fibers,silane coupling agents and GO,which can effectively prevent GO.The breakage of fibers is mainly manifested in the decrease of contact angle by 51%,the increase of surface energy by 146.5%,the increase of tensile strength by 4.4%,and the increase of modulus by 7.5%.At the same time,the introduction of GO can effectively increase the surface roughness of fibers,thus improving the interfacial mechanical interlocking performance,making the interfacial shear strength(IFSS)increase by 64.5%,effectively improving the interfacial bonding performance between fibers and matrix.Secondly,a uniform and controllable PyC layer was prepared on the surface of carbon fibers by impregnation and pyrolysis,using phenolic resin precursor solution.The effects of modification of carbon fibers on the uniformity and thickness of PyC layer were studied.The results show that the graphitization degree of carbon fibers decreases with the increase of pyrolysis temperature,and the structural defects increase.The tensile strength decreases with the increase of pyrolysis temperature.Therefore,the optimum pyrolysis temperature of PyC layer is 700 degree C.The thickness of PyC layer on the surface of GO-grafted carbon fibers increased,and the oxidation resistance of the prepared Cf/PyC samples increased by 7.4%.Finally,carbon fiber reinforced SiC ceramic matrix composites were prepared by PIP method.The effects of GO grafting on carbon fiber surface and PyC layer preparation onCf/SiC composites were studied.The results show that the introduction of GO and PyC layers can deflect the matrix cracks and produce obvious fiber pull-out phenomenon,which effectively improves the interface bonding between the fibers and the matrix.With the addition of GO and the increase of PyC interlayer thickness,the graphitization degree,oxidation resistance and tensile strength of Cf/SiC composites increase.The tensile strength of Cf/SiC composites increases by 47.8%,63.4% and 172.4% respectively compared with those of the composites made of untreated carbon fibers.