Preparation And Properties Of Diamond/Silicon Carbide Composites By Silicon Liquid Infiltration

Diamond/silicon carbide composites have excellent comprehensive properties such as high thermal conductivity,low thermal expansion coefficient,superior semiconductor properties and low density,and are suitable as electronic packaging materials.Diamond/silicon carbide composites prepared by pressureless infiltration method have the disadvantages of dimensional instability and graphitization of diamond.This paper mainly optimized the gas-phase and liquid-phase silicon infiltration processes and explored the pyrolysis characteristics of the composite porous body.The effects of diamond content and surface modification on the phase structure,thermophysical properties and mechanical properties of composites were studied.The process mechanism of pressureless silicon infiltration and the densification mechanism of composites were analyzed.Through the research,the problems of sample size expansion and diamond graphitization were solved,which laid a foundation for the application of composites in electronic packaging field.The main research conclusions are as follows:(1)The phase structure and physical properties of the porous body of the diamond/silicon carbide composite were studied,and the growth mechanism of the nanowire was analyzed.The results show that 3C-SiC axis nanowires with a diameter of about 15?35 nm were formed during the pyrolysis of the porous body.The porous polyacenes(PAS)produced by phenolic resin pyrolysis and the residual oxygen in the pyrolysis atmosphere promote the formation of silicon carbide and the directional growth of nanowires.The nanowires reduce the median pore size of the porous body,and the porous polyacene increases the porosity of the porous body,which is beneficial to the subsequent silicon infiltration and densification of the porous body.(2)The process optimization of gas-phase and liquid-phase silicon infiltration has been studied.Diamond/silicon carbide composites were prepared by vapor-phase silicon infiltration method via mold design and process parameter optimization.The thermal conductivity,thermal expansion coefficient and density of the sample can reach 532.7 W/(m·K),2.58 ppm/K and 3.18 g/cm3,respectively.The mold design and the development of silicon infiltration materials ensure the surface quality and dimensional stability of the samples,which lay a foundation for near-net forming.Compared with vapor-phase silicon infiltration,liquid phase silicon infiltration has the advantages of a stable process and controllable sample size.The thermal conductivity of the sample prepared by the liquid-phase silicon infiltration is 600.4 W/(m·K),the thermal expansion coefficient is 3.28 ppm/K,the density is 3.23 g/cm3,and the relative density reaches more than 99%.(3)The phase structure of composites,the process mechanism of pressureless silicon infiltration and the densification mechanism of composites were studied.The results show that the microstructure of the composite is uniformly distributed,and the graphitization of the diamond does not occur.Different carbon to silicon ratio affects the morphology of silicon carbide.The densification of composites can consist of three parts:1,the silicon-carbon reaction on the diamond surfaces;2,the formation of silicon carbide nanowires;3,silicon capillary filling.Nano-SiC exists in the erosion area of the diamond surface,which has a certain orientation relationship with diamond.(4)The effects of diamond content and surface modification on the thermophysical properties of composites were studied.The results show that as the diamond content increases,the thermal conductivity of the composite increases at first and then decreases.When the volume fraction of diamond is 60%,the thermal conductivity of the composite reaches the maximum.The thermal conductivity of SiC-coated diamond/silicon carbide composites is 545.9 W/(m-K),while that of the uncoated diamond reinforced composites is 581.8 W/(m·K).The silicon carbide three-dimensional network structure in the composite forms the preferential path for heat conduction.The experimental values of thermal conductivity of the composite are slightly higher than the predicted value of H-J model and DEM model.With the increase of temperature,the thermal expansion coefficient of the composite gradually increases.Within the test temperature range,the thermal expansion coefficient of the composite is 1.0?3.25 ppm/K,which can well match the silicon.The experimental values of thermal expansion coefficient of the composite are close to the upper limit of the Kerner model.(5)The effect of diamond content and surface modification on the bending strength of the composite was investigated,and the performances of typical composites were compared.The bending strength of the modified diamond reinforced composites increased by 16.9%(Dia.60 vol.%).When the reinforcing phase content is 60 vol.%,the bending strength of the diamond/silicon carbide composite reaches 407.56 MPa,which is 1.24 times that of the spherical graphite/copper composite and 2.37 times that of the diamond/copper composite.The bending strength of diamond/silicon carbide composites prepared by liquid-phase silicon infiltration is above 200 MPa,which can well meet the requirements of electronic packaging materials for bending strength.The process route for preparing diamond/silicon carbide composites by liquid-phase silicon infiltration has been set up.The liquid-phase silicon infiltration has the advantages of low equipment requirements,easy to control,stability,and low cost and so on.The diamond/silicon carbide composites with excellent performance can be prepared.Diamond/silicon carbide composites with outstanding properties are suitable for electronic packaging materials.