| With the rapid development of electronic technology,electronic devices have advanced towards miniaturization,multi-functionality,and integration.A large amount of heat is generated during the operation of high-power electronic devices.The increased temperature and thermal mismatch between the chips and packaging materials will significantly reduce the operating efficiency and service life.In order to solve the problem of heat dissipation of the devices,there is an urgent need for thermal management materials with high thermal conductivity?TC?and low thermal expansion coefficient?CTE?.In recent years,a large number of studies have been conducted on diamond/Cu composites at home and abroad.By compounding diamond,which has high TC,with plastic copper,the diamond/Cu composites with high TC and compatible CTE are obtained.It has shown great potential in the application of integrated circuits,new energy,and transportation.However,there are still many problems to be solved in the study of diamond/Cu composites.For example,the neglect of the actual distribution of particle size leads to the decrease in the prediction accuracy of TC.In order to improve the interfacial bonding,it is necessary to conduct surface metallization of diamond.However,the mechanism of surface metallization is still unclear.In addition,the difficulty of the characterization of diamond/Cu interface and the hot deformation of diamond/Cu composites is increased for the hardness of diamond.Based on the above issues,the Gaussian distribution function of the particle size and differential effective medium?DEM?model were combined to predict the TC of diamond-reinforced metal matrix composites?DMMCs?.The evolution mechanism of diamond surface metallization was revealed by microstructure analysis,and the interfacial structure between different diamond faces and Cu were given.The diamond/Cu composites were prepared by spark plasma sintering?SPS?,and the hot deformation behavior of the composites was systematically studied by using thermal/force simulation.This study provides scientific basis for the development of diamond/Cu composites with excellent performance.The main research results are as follows:?1?The calculation with the DEM model shows that the TC of diamond/Cu composites decreases with the increase of the thickness of interfacial transition layer.The promotion effect of carbides on the TC of the composites follows the following sequence:WC>ZrC>Cr3C2>TiC>Mo2C when the thickness is less than 630 nm.This sequence is changed to:WC>ZrC>Cr3C2>Mo2C>TiC,when the thickness is larger than 630 nm.The average particle size was substituted by Gaussian distribution particle size,and the distribution was fitted by the Gaussian function.Based on the DEM model,the Gaussian distribution-DEM and Gaussian mixed distribution-DEM algorithms were proposed to predict the TC of mono-mesh and binary-mesh DMMCs,respectively.The high accuracy and stability of the algorithm was verified by the literature data.In addition,the smaller the dispersion of the diamond particle size,the greater the TC of the diamond/Cu composites.?2?The surface metallization mechanism of diamond was revealed by microstructure statistics.The growth of carbide Cr3C2 on the diamond surface was controlled by adjusting the reaction temperature and time.The statistical results showed that the surface metallization of the diamond underwent four scenarios:dispersed growth,preferred growth,complete metallization and preferred cleavage.The universality of the evolution mechanism was also verified by W and MoO3.The carbides grew preferentially on the diamond?100?surface under the same reaction conditions,while the carbide preferentially cracked on diamond?111?surface at high temperatures.With the phase detection and surface morphology analysis,the conditions for complete metallization of the diamond surface with Cr,W and MoO3 were determined to be 900?/60min,1050?/60 min,and 1000?/60 min,respectively.?3?The 50 vol.%diamond/Cu composites were prepared by SPS at920? and 50 MPa for 10 min.The TC of Cr-coated,W-coated and Mo-coated diamond/Cu composites were 413 W/mK,392 W/mK and 403W/mK,respectively.The CTE of Cr-coated,W-coated and Mo-coated diamond/Cu composites were 11.7×10-6 K-1,13×10-6 K-1,and 12.2×10-6 K-1,respectively.The structure characterization showed that the Cr-coated diamond?100?/Cu interface was constituted by diamond?100?face,Cr3C2and Cu layers,while the Cr-coated diamond?111?/Cu interface was formed by diamond?111?face,amorphous carbon,Cr3C2 and Cu layers.The presence of amorphous carbon on the?111?faces will cause local crystal lattice distortion of diamond and carbide around the interface.The distortion introduces residual stress at the interface and results in the preferential cleavage of carbide on the diamond?111?surfaces.?4?Based on the hot compression tests,the hot deformation constitutive equation and hot processing map were established to study the hot deformation behavior of diamond/Cu composites.The parameters of the safe deformation domain and unstable domain were determined by using the hot processing map.The diamond/Cu composites and Cr-coated diamond/Cu composites were successfully extruded at 850?/0.036 s-1and 880?/0.036 s-1 with an extrusion ratio of 10:1,respectively.After the hot extrusion,the Cr-coated diamond/Cu composites were almost completely dense.The TC increased from 413 W/mK to 487 W/mK,and the CTE dereased from 11.7×10-6 K-11 to 10.5×10-6 K-1.The hot deformation activation energy of uncoated and Cr-coated diamond/Cu composites were206 kJ/mol and 238 kJ/mol,respectively.According to the TEM investigation,the interfacial bonding was enhanced by Cr3C2.A large number of dislocation accumulated around the particles,which increased the difficulty of the hot deformation of the diamond/Cu composites and resulted in the increase of hot deformation activation energy.The preparation process?surface metallization-SPS-hot extrusion?in this study provides more ideas for the development of diamond/Cu composites with high TC and low CTEs. |
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