Graphite/copper Composites Prepared By Microwave Sintering And Their Properties

With the rapid development of electronic information technology,high thermal conductivity metal matrix composites have attracted much attention in the field of electronic packaging.Among them,graphite/copper composites have the advantages of high thermal conductivity,low density and easy processing,which is a promising heat dissipation material for electronic packaging.However,due to the non-wetting and non-reactivity of graphite and copper phases,the bonding ability of graphite/copper interface is poor,which makes it difficult to achieve the expected thermal conductivity of graphite/copper composites.At the same time,a variety of composite material preparation processes,including hot-press sintering,are limited by factors such as equipment,tooling and production costs,and cannot achieve large-scale industrial production applications.As an emerging material preparation process,microwave sintering can effectively weld the graphite/copper interface and enhance the interfacial bonding capability,while refining copper grains and effectively improving the performance of the composites.In addition,microwave sintering is fast in temperature rise,short in sintering time and high in energy efficiency,which can realize the mass production of composites.In this paper,microwave sintering was used to prepare graphite/copper composites,and the microstructure,phase composition,density and thermal conductivity of the composites were investigated in the following aspects.(1)The effects of sintering temperature and graphite volume fraction on graphite/copper composites prepared by microwave sintering were investigated.The results showed that higher sintering temperature as well as suitable graphite volume fraction were beneficial to enhance the properties of the composites.When the sintering temperature was 950°C and the graphite volume fraction was 10 vol.%,the graphite/copper composites showed better properties and significant anisotropy.The microwave sintered samples behave better properties in the Cross Plane direction with a hardness of 70.4 HV and a thermal conductivity of 311.87 W·m^-1·K^-1,which were improved by 35.6%and 7.0%,respectively,over the conventionally sintered samples.(2)The heat transfer mechanism during microwave sintering and the thermal stability performance of graphite/copper composites were investigated.Microwave sintering could improve the heat transfer efficiency within the material,achieve rapid sintering and rapid cooling,refine the copper matrix grains,and effectively weld the graphite/copper interface,significantly enhance the properties of the composites.The graphite/copper composites prepared by microwave sintering still got high thermal conductivity and good thermal stability after 30 thermal cycles,and the interfacial damage behavior during the thermal cycling is analyzed.In addition,a microwave high-throughput material preparation device was developed to provide new technical support for the high-throughput preparation of graphite/copper composites.(3)The effect of Ti addition on graphite/copper composites prepared by microwave sintering was investigated.The results showed that the addition of Ti can effectively enhance the density and hardness of the composites,and the thermal conductivity of the composites was higher with the Ti addition of 1.0 wt%.In addition,compared with conventional sintering,microwave sintering could significantly improve the graphite/copper interface,refine the copper matrix grains,and form a continuous and uniform TiC transition layer at the interface without defects such as pores and cracks,which effectively improved the performance of the composites.(4)The effects of the addition of Mo and W elements on the graphite/copper composites prepared by microwave sintering were investigated.The results showed that the addition of Mo or W generated a small amount of Mo₂C or W₂C in the composites,while Mo and W particles were enriched in the graphite tissue and at the graphite/copper interface,respectively.In addition,the addition of Mo and W could significantly improve the density and hardness of the composites and obtain good thermal conductivity.