Preparation And Properties Of High Thermal Conductivity Carbon Fiber Reinforced Aluminum Matrix Composites

This paper is on the basis of the thermal management material for space borne fiber lasers.The mesophase pitch-based carbon fibers with different graphitization degrees were used as substrates to prepare the Cf/Al interfaces by magnetron sputtering.The microstructure evolution of Cf/Al interfaces with different graphitization degrees was studied and the damage mechanism was elucidated.The Cf/Al composites were prepared by vacuum hot pressing.The effects of process parameters on the microstructure of the composites were studied.The interface structure of the composites was investigated by scanning electron microscopy(SEM),X-ray diffraction analyzer(XRD)and transmission electron microscopy(TEM).The influences of carbon fiber volume fraction on the density,mechanical properties and thermophysical properties of Cf/Al composites were also studied.The effect of graphitization degree of mesophase pitch-based carbon fiber on the interfacial damage of Cf/Al composites was studied.The results indicate that he reactions of the Cf/Al interfaces and the damages of the mesophase-pitch-based carbon fibers decrease with the graphitization temperature increasing.The reason is that the higher graphitization temperature results in the larger graphite crystallites,higher orientation and higher graphitization degree.In addition,the damages of the Cf/Al interfaces with different graphitization degrees are determined by the initial defects number and the crack propagation in the carbon fibers.Due to the large size and high orientation of the graphite crystallites in the mesophase pitch-based carbon fiber,the initial cracks are easy to expand and proliferate directly between graphite lamellas.In comparison,because the graphite crystallites of the polyacrylonitrile-based carbon fiber are small and the orientation is relatively low,the initial crack propagation is easy to be suppressed although the initial cracks are more.The influences of the process parameters of the vacuum hot pressing on the composite microstructures are investigated.It indicates that the density becomes higher as the hot-pressing temperature increases.Many pores are formed when the pressure is too low,and the fibers are easy to damage when the pressure is too high.The longer the hot-pressing time is,the easier the matrix diffuse among the carbon fibers.However,too much hot-pressing time results in the fiber damage.Therefore,the best preparation process is as follows:the hot-pressing temperature is 600?,the hot pressing pressure is 15MPa and the hot pressing time is 120min.The Cf/Al composites have no obvious defects such as pores.The carbon fibers are uniformly dispersed and the interfacial bonding is good.The formation of reactants is not obvious.The interface seems like a tooth-meshing shape,and there is C-Al diffusion layer.The effect of volume fraction(10-40vol.%)on microstructure and properties of Cf/Al composites was studied.With the increase of the volume fraction,the porosity of the composites increases,the agglomeration of carbon fibers becomes more obvious,and the density decreases gradually.The density of composites with 30vol.%fibers is 2.52g/cm³ and the relative density is 96.5%.The tensile strength and bending strength of Cf/Al composites decreased with the increase of fiber volume fraction.Fracture analysis showed that the failure of Cf/Al composites was mainly due to the pull-out mode of long fibers,and the interface bonding was weak.The thermal-physical properties of the composites show that the thermal diffusion coefficient increases gradually with the increase of the volume fraction,while the thermal conductivity increases first and then decreases.The highest thermal diffusion coefficient of the composites is 137.5mm·s^-1 when the fiber volume fraction is 40vol.%.The increase of the fiber volume fraction increases the thermal conduction channel of the composites,and the thermal diffusion coefficient increases.The highest thermal conductivity is 293.7W/(m·K)when the fiber volume fraction is 30vol.%,and the thermal conductivity of 40vol.%composite decreases due to the influence of porosity.