| The semiconductor laser develops rapidly since it was exploited,and nowadays,it is witnessing a rapid development towards the direction of high efficiency,high performance and small volume,leaving a difficult problem of radiating.The heat generated by laser increases greatly,solving the problem of heat dissipation directly affect the stability and reliability of the laser.However,the traditional thermal management materials’ thermal and mechanical properties can’t satisfy the demand for heat dissipation.But the emerging graphite/Al composites are strong competitor in the field of thermal management materials for its high thermal conductivity,low coefficient of thermal expansion,light density and lower production cost.However,the interface between graphite and Al matrix combines badly due to the poor wettability under high temperature,so improving interface of graphite/Al composite is the emphases for research.In this study,the graphite flakes are coated to improve interface of graphite/Al composite.The effects of volume fraction of graphite flakes and interface on thermal conductivity are also investigated.The heat transfer mechanism and model for thermal conductivity is established based on this.The mechanical property of graphite/Al composite is enhanced via multi-methods.The main results and new findings in this work are summarized as follows:(1)Industrialization of graphite flakes surface treatment technology has been formed,in which TiC and SiC coating were grown on the graphite surface.The thickness of TiC coating can be controlled by adjusting the content of Ti particles.During the process of coating SiC,the C atom continually spread to Si atom and react with Si atom.Similarly,during the process of coating TiC,the TiC is formed on the graphite surface due to the reaction between Ti atom and C atom.(2)The interface of graphite/Al composite has been investigated.The interfacial structure of graphite/Al composite is Al-Amorphous phase-poorly crystalline graphite-graphite.The interfacial bonding follows a mechanism of first reaction and nuclear in a small region and then grow up and diffuse to a larger region.After coating,the graphite-SiC(TiC)-Al interfaces have been formed respectively and Al4C3 phase has not found.Due to the coating process,the interface of graphite/Al composite which owns poor Al-C bonding transforms to be strong bonding of Ti and Si to graphite and Al.(3)The thermal conductivity of graphite/Al composite in transverse direction is greatly enhanced as the increase of volume fraction of graphite flakes,while in longitudinal direction gradually reduce.Compared with the effect of coating TiC,the thermal conductivity of composite is observably enhanced after coating SiC.Besides,as increasing the thickness of TiC coating,the thermal conductivity of composite gradually debase,while the bending strength generally improve.(4)The heat transfer mechanism of graphite/Al composite can conclude to be electronic transfer in Al,phonon transfer in Al-graphite interface and graphite in plane transfer.After SiC and TiC is coated,the heat spreads Al,Al-coating interface,coatings,coating-graphite interface and graphite respectively.Based on above,the models predict thermal conductivity of graphite/Al composites has been established and the results accords well with the experimental data.(5)The graphite/Al composites have been strengthened via coating on the graphite surface.The bending strength was significantly enhanced after TiC coated and it reaches to 116 MPa which is double increased compared to uncoated composite.The main fracture feature of uncoated composite is brittle fracture of graphite and graphite pullout from Al matrix.The coating layer can absorb large amount of deformation energy under loading and the interface is improved.The fracture exhibited the ladder-shape and this phenomenon can be explained by the strength mismatch of graphite since SiC leads to heterogeneous distribution of the stress. |
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