Surface Modification Of Graphite Film And Thermal Conduction Property Of Graphite Film/Aluminum Laminated Composites

The large increase in power density has caused the heat per unit area of integrated circuits to continue to rise.As one important part of aerospace electronic high-power devices,thermal management system has become a key technology that restricts the service capability of high-speed aircraft.Graphite film(GF)is a new type of two-dimensional material with high thermal conductivity,which has the advantages of low density,good corrosion resistance,high thermal conductivity and low thermal expansion coefficient,etc.Its in-plane thermal conductivity can reach 1100-1600W/(m·K),considered to be the most potential thermal management composite reinforcement in the future.Two multi-scale composite reinforcements of carbon nanotubes(CNTs)surface modified graphite film and silicon carbide nanowires(SiCnws)surface modified graphite film were mainly studied.Based on this,pressure infiltration technology was adopted,light-weight,high-conductivity aluminum was used as the matrix,and GF,CNTs-GF and SiCnws-GF were used as reinforcements to prepare GF/Al,CNTs-GF/Al and SiCnws-GF/Al laminated aluminum matrix composites with high thermal conductivity in order to obtain a new two-dimensional laminated composite with high thermal conductivity and excellent mechanical properties.The preparation and microstructure of two modified graphite films,as well as the microstructure,mechanical behavior and thermal conductivity of two modified graphite films/aluminum laminated composites were systematically studied.Based on the XY direction thermal conductivity model of the composites,the thermal conductivity of the composite was revealed.The influences and laws of the material composition and interface bonding of composites on the mechanical properties and thermal conductivity of composites were also discussed.The catalyst-assisted plasma enhanced chemical vapor deposition(PECVD)technology was used to in situ grow carbon nanotubes on the surface of graphite film.Using methane as the carbon source,hydrogen as the reducing agent,and metal nickel as the catalyst,CNTs-GF multi-scale reinforcement was successfully prepared.The effects of different process conditions on the morphology and structure of CNTs were studied.It was found that the best growth catalyst concentration for the growth of CNTs on the surface of graphite film by PECVD method was 0.05mol/L Ni(NO₃)₂·6H₂O acetone solution.The obtained CNTs had a diameter of about 80nm and a length of about 3-4?m,and grew uniformly and densely on the surface of the graphite film.The growth of CNTs on the surface of graphite film had greatly improved the thermal diffusion coefficient and thermal conductivity in the XY direction of CNTs-GF.Compared with untreated graphite film,the thermal diffusion coefficient increased from 950mm²/s to 1030mm²/s,and the thermal conductivity increased from 1420W/(m·K)to 1450 W/(m·K).Using methyltrichlorosilane(CH₃SiCl₃)as the silicon and carbon source,and metallic nickel as the catalyst,the silicon carbide(SiC)nanowires were grown on the graphite film surface by the catalyst-assisted chemical vapor infiltration(CVI)process,and the SiCnws-GF multiscale reinforcement was successfully prepared.The SiC nanowires grown on the surface of the girphite film had a diameter of about 150nm and a length of about tens of microns.At this time,the SiC nanowires coverd on the surface of the graphite film uniformly and densely.Compared with the untreated graphite film,the thermal diffusion coefficient and thermal conductivity in the XY direction of SiCnws-GF were reduced.Under the same mass fraction of reinforcement,the results showed that the thermal conductivity in the XY direction of CNTs-GF/Al composite was 1026W/(m·K),which was 33%higher than that of GF/Al composite,and the thermal conductivity in the Z direction was 52W/(m·K),which was 225%higher than that of GF/Al composites;the interlayer shear strength of CNTs-GF/Al composite was 70.3MPa,which was 26%higher than that of GF/Al composite.Under the similar mass fraction reinforcement,compared with GF/Al composites,the results showed that the thermal conductivity in the XY direction of SiCnws-GF/Al composite was increased by 7%,and the thermal conductivity in the Z direction was increased by 75%;the interlayer shear strength of the SiCnws-GF/Al composite was increased by 141%.The results showed that the in-situ introduction of CNTs and SiCnws on the surface of graphite film could effectively solve the problem of poor compatibility of composite interface between the graphite film and the metal aluminum.At the interface of the composite,the one-dimensional nanowires play the role of“pinning”the interface between the graphite film and the aluminum matrix,which improves the bonding strength of the interface while transmitting the load.Therefore,the surface modification of the graphite film can effectively improve the interface bonding performance of the graphite film/aluminum composite,thereby improving the thermal conduction property and the interlayer shear strength of the composite.