The Study On Interface Microstructure And Thermal Conductivity Of Diamond/Aluminum Composites

Due to the high thermal conductivity,low coefficient of thermal expansion,and low density,the high-volume fraction diamond/aluminum composites have significant potential in the field of thermal management materials for next-generation equipment.However,the poor interfacial bonding between diamond and aluminum and the presence of the easily hydrolyzed Al4C3 product limit the thermal conductivity of diamond/Al composite.The surface metallization of diamond particles is the key to solve the interface problem of diamond/aluminum composites.Therefore,the current work takes the compatibility and thermal conductivity of the interface layer and the two-phase of diamond/aluminum into consider,choosing the Mo,Ti,and Si elements to modify the diamond particles’ surfaces.The volume of diamond in 50 vol.%of diamond/aluminum composite material is prepared based on powder metallurgy,and the microstructure and thermal conductivity of the diamond/aluminum interface in the composite material are analyzed in-depth.The detailed conclusions of diamond/Al composite with different interfacial layers are listed as follows:(1)There are crack defects and easily hydrolyzed Al4C3 products in the unmodified diamond/aluminum composite.However,the surface metallization of diamond with Mo,Ti,and Si elements can effectively inhibit the generation of Al4C3 products in the diamond/aluminum composite.Among all the metals used as interface layers,the molybdenum element at the interface of diamond/aluminum composite prepared by the diamond with Mo coating is easy to diffuse into the aluminum matrix,leading to the cracking of the composite.However,there are a few interfaces bonded tightly,because the amorphous at the interface inhibiting the diffusion of Mo elements from the interface product Mo2C into the aluminum substrate.The diamond/aluminum composite interface formed by coating Ti and Si elements on the diamond surface is well bonded,and the existence of TiC and SiC substances at the composite interface can effectively improve the interface wettability and interface bonding ability of the composite.(2)The mechanism of the effect of the diamond surface modification layer on the thermal conductivity of the composite material is analyzed theoretically utilizing the scattering-mediated acoustic mismatch model(SMAMM).The results show that the interface layer with nanoscale thickness,high intrinsic TC,high phonon velocity,and high Debye temperature,such as Si,Cr,B,SiC,WC,and B4C,has a more significant effect on improving the thermal conductivity of the composite.(3)The thermal conductivity of diamond/aluminum composite prepared by powder metallurgy varies between 192-423 W/(m·K),and the relative density of the composite material is effectively improved by coating the diamond surface with Mo,Ti,and Si elements.Among them,the diamond/aluminum composite with a Si element interface layer has the best thermal conductivity.The thermal conductivity of the diamond/Al composite with a Mo element interface layer is lower than that of the unmodified composite material.The reason is that the Al5Mo intermetallic compound formed at the interface is unfavorable for the thermal conductivity of the composite.The difference between the theoretical and measured thermal conductivity of composite materials calculated by the SMAMM model is due to various factors such as density,intermetallic compounds,and solid solubility.(4)The dislocation density of the 50%diamond/aluminum composite in different heat treatments is characterized by neutron diffraction.The results show that there are more dislocations in the water-quenched composite material,and the existence of internal dislocations in the composite will affect the thermal conductivity of the metal matrix,leading to a decrease in the overall thermal conductivity of the diamond/Al composite.