Preparation And Characterization Of Diamond/SiC Composites

Diamond/SiC composite is a new-type thermal management material, which represents the development direction of the advanced thermal management materials. As a multiphase composite, Diamond/SiC composite combines high thermal conductivity of diamond and good integrated performance of SiC. In this dissertation, Diamond/SiC composite was prepared by process of vacuum gaseous reaction sintering. At first, the reaction sintering process and the mechanism of vacuum gaseous sintering were studied; secondly, the molding process of the green body and the original formulation were optimized; at last, the structure and property of Diamond/SiC composite were investigated.The reaction sintering technique of Diamond/SiC composite was designed. The parameters including the reaction mode, the reaction temperature and the reaction time were studied. Finally, vacuum gaseous reaction sintering was determined. And the optimum reaction sintering process was: 1500℃(reaction temperature) and 1hour (holding time). The graphitization of the diamond and mechanism of Si/C reaction were also explored. It was found that the diamond kept integrity and the graphitization was not serious at all.The molding process of the green body was optimized. Hot molding under 150℃was used to produce blanks. The formula of the theoretical porosity of the green body was brought forward. The effect of the molding pressure on the porosity and the density of the green body were studied. The influence of the porosity of the green body on the density and mechanics performance of Diamond/SiC composite was researched.When the molding pressure was 10MPa, the porosity and the density of the green body were nearest to the theoretical ones, and the density and mechanics performance of Diamond/SiC composite showed the highest values. For example, when the diamond ratio was 40wt%, the porosity of the green body was 32%, close to the theoretical porosity 33%, and the density of Diamond/SiC composite was 3.11g/cm3, the flexural strength was 160MPa, the elastic modulus was 175GPa; When the diamond ratio was 80wt%, the porosity of the green body was 23%, close to the theoretical porosity 22%, and the density of Diamond/SiC composite was 3.18g/cm3, the flexural strength was 110MPa, the elastic modulus was 140GPa. The original formulation was researched. The influence of the diamond's class, granularity and content on the mechanics performance and thermal conductivity of Diamond/SiC composite were studied. The result showed that Diamond/SiC composite made of diamond of good class possessed better mechanics performance and higher thermal conductivity. With the descending of the granularity, thermal conductivity of Diamond/SiC composite decreased. With the increasing of the diamond's content, the mechanics performance of Diamond/SiC composite declined while thermal conductivity increased. Diamond/SiC composite's thermal conductivity reached 280 W/(m·K) when the diamond's content was 80wt%. Also, the effect of the additional ingredients including resin, silicon and graphite on the reaction sintering ws explained. The resin's content should be within 5-15wt%, silicon's content should be less than 30wt%, and graphite's content should be less than 10wt%.The component and microstructure of Diamand/SiC composite were analysed. Diamand/SiC composite was composed of diamond, SiC and Si. The diamond and the SiC matrix were combined by reaction firmly and the interface was tight withnot apparent defect. The diamond was kept whole and dispersedly in the matrix.