Structure Design Of Interface And Preparation Of C/h-BN Laminated Composites

Graphite which was used as evaporation source in early metal evaporation industry has excellent properties, such as excellent thermal conductivity, low resistivity, good resistance to thermal shock. But there are some problems in using. For example, graphite is easy to react with some metals at high temperature and the graphite is broken. Hexagonal boron nitride (h-BN), which is analogous to graphite in its crystalline form, has been extensively investigated in the last few decades. More recently, considerable interest has arisen due to excellent thermal conductivity, extremely high resistivity, microwave and infrared transmittance, and chemical stability. Therefore, the common advantages and complementarities of disadvantages of both graphite and BN offer a chance to design and obtain the new evaporation materials.In this paper, Spark Plasma Sintering (SPS) and hot-pressing (HP) were used to fabricate C/h-BN laminated composites. The interface of C/h-BN laminated composites was designed. And the effect of sintering condition on the properties and structure of laminated composites materials such as sintering temperature, holding time, thickness of BN, the composition of inter-medium and so on.To C/h-BN laminated composites manufactured by HP, the relative density of BN increased with increasing sintering temperature and holding time. With increasing sintering temperature, the joint of graphite and BN increased and there was transition layer in the interfaces. The joint strength and circle time of heat shock increased with increasing sintering temperature. But long holding time at high sintering temperature was harmful to joint of C/h-BN laminated composites.C/h-BN laminated composites was also manufactured by SPS, the relative density of BN increased with increasing sintering temperature and holding time. However, the relative density of BN and joint of graphite and BN decreased under long holding time at high sintering temperature. It might be relative to the abnormal growth of crystal. With increasing sintering temperature, the joint of graphite and BN was increased and also there was transition layer in the interfaces relative to HP. And long holding time at high sintering temperature was harmful to joint of C/h-BNlaminated composites. The result of EPMA showed that there was diffusion of elements B, C, N and transition layers in the interfaces. The joint strength increased with increasing sintering temperature and decreased under long holding temperature at high sintering temperature which was similar to the heat shock. The joint of interface of materials increased with thickness of BN on the graphite.The research indicated that the proper inter-medium was propitious to joint of interface of materials. The content of Al in the inter-medium contain 20wt%, 40wt%, 60wt%, 80wt%. The research indicated that the main product was A1N, and with increasing the content of Al, the content of A1N in the inter-medium was increased. When the content of Al reached 80wt%, a little of Al₄C₃ was formed. The interface of materials which was fabricated by SPS was better than HP because the time of HP was longer and the speed of increasing temperature was slower than SPS. The joint of interface and the thickness of A1N increased with increasing the content of Al. The results of EPMA showed that there were diffusion of element of B, N, C, Al in the interface and the diffusion of element of Al of sample fabricated by SPS was better than HP. The heat shock increased with increased the content of Al. And when the content of Al was over 40wt%, the joint strength of materials was stronger than the tensile strength of BN.