The Research On Preparation And Properties Of Silicon-Coated Diamond/Aluminum Composites

With the development of electronic devices towards miniaturization,light-weight,and high-power density,the heat generation of electronic devices are increasing rapidly,which affects the safety,reliability and effective operation of the electronic devices.Therefore,the thermal management materials with low density,low thermal expansion coefficient and high thermal conductivity are urgently needed to maximize heat dissipation and minimize thermal stress from the electronic devices.Light-weight diamond reinforced aluminum（Al）matrix composites are extensively investigated due to their excellent thermo-physical properties,and have been considered the first candidate for next generation thermal management materials.However,the brittle and hydrophilic phase Al₄C₃will form at the interface in the diamond/Al composites prepared by the infiltration method,which especially restricts the long-term stability of diamond/Al composites in a wet environment condition.In order to inhibit the formation of hydrophilic phase Al₄C₃,and to obtain the composites with high thermal conductivity and moisture-resistant,pure Si,Al-Si and SiC coating layers were preset on the diamond surface by magnetron sputtering and annealing treatment,and then the diamond/Al composites were prepared by pressure infiltration method.The failure behavior of diamond/Al composites in a wet environment and the effect of different coating layers on thermal conductivity and stability of the composites were systematically studied.The main research results are as follows:（1）The interfacial products Al₄C₃were hydrolyzed into loose flocculent hydrolysate Al（OH）₃after the soaking water treatment,which lead to the increase in interfacial thermal resistance and the failure of composites.The thermal conductivity of raw diamond/Al composites decreased as a Gaussian function,from 590 W·m^-1·K^-1to 457 W·m^-1·K^-1,a decrease of 22.54%after 500 hours soaking water treatment,（2）The pure Si coating was coated on diamond surface by magnetron sputtering method,and the pure Si-coated diamond/Al composites with different coating thicknesses were prepared.The introduction of the Si coating layer prevented the diamond particles from contacting with liquid Al,which reduced the formation of interfacial products Al₄C₃,and improved the stability of the composites in a wet environment.However,it also deteriorated the interfacial bonding strength and reduces the thermal conductivity of the composites at the same time.As the thickness of pure Si coating increased from 85 nm to 943 nm,the thermal conductivity of composites decreased from 576 W·m^-1·K^-1to 456 W·m^-1·K^-1,and the rate of decline in thermal conductivity reduced from 19.62%to 3.07%.（3）The Al-Si complex coating of various compositions was deposited on diamond surface by magnetron co-sputtering method.Compared with the pure Si coating,the Al-Si complex coating could improve the wettability of diamond and Al matrix,leading to the increase in thermal conductivity of composites,and also reduced the contact area between diamond and Al matrix,leading to the improvement in stability of composites.When the Al-Si complex coating was used as the interface layer,the composites could retain a higher thermal conductivity,but the stability of（Al-Si）-coated diamond/Al composites was worse than that of the pure Si-coated diamond/Al composites.As the Si content in Al-Si complex coating decreased from73 wt.%to 22 wt.%,the thermal conductivity of composites increased from 507W·m^-1·K^-1to 582 W·m^-1·K^-1,and the rate of decline in thermal conductivity increased from 7.10%to 18.38%（4）A novel approach to synthesize SiC on diamond surface at low temperature was proposed.The results showed that the synthesized temperature of SiC could be as low as 750℃,avoiding the graphitization of diamond,and Al₄C₃was the indispensable intermediate phase for synthesizing SiC at low temperature.When SiC was used as the interface layer,the selective bonding of Al matrix was avoided,and the Al matrix uniformly adhered to both diamond{100}and{111}planes.Also,the concentration of the interfacial product Al₄C₃was reduced.The composites with SiC interface layer exhibited high thermal conductivity and good moisture-resistance performance.Thermal conductivity of the SiC-coated diamond/Al composites could reach 666 W·m^-1·K^-1,and the thermal conductivity decline was only 6.31%after soaking water treatment,which showed high thermal conductivity and high stability.