高导热石墨/铝复合材料的制备与热传导机制研究

Recently, the microelectronics technology steps in a rapid development period, resulting in the increases of the power for the electronic equipment. Thus, it is very urgent and also important to remove the heats. Graphite composites are considered to be one of the most potential thermal management materials due to the low density, thermal expansion, high thermal conductivity and excellent processability. However, it still remains serious problems for fabricating the graphite composites. The first problem is that the graphite flakes leave almost no space between them making metal infiltration an almost unfeasible task. The second problem is the poor interfacial bonding between graphite and aluminium. The first problem can be overcome through infiltrating a metallic alloy into packed mixtures of flakes and aluminium particle. The selection of aluminium particle can avoid the increase of the interfaces between the particle and matrix, lead to the increase of the interfacial thermal resistance. The interfacial debonding between graphite and matrix can be improved via coating B, Si and W on graphite surface. The interfacial morphology, reaction products and bonding condition are explored after the coating process. The thermal conductivity of the composites with different preparation and nano-structure on graphite surface are tested. The effects of the interface, the added aluminium particles and the graphite orientation on thermal conductivity are studied. The project is based on the series and parallel models, and considers the factors of orientation, interface, and so on to establish the prediction model of thermal conductivity for the graphite flake/aluminium composites.

目前，微电子技术发展日新月异，电子设备功率不断增大，解决散热问题显得尤为急迫和关键。石墨导热材料具备低密度、高热导率、低膨胀系数和可加工性优良等优势，是最具应用潜力的热工管理材料之一。然而，石墨复合材料的制备存在着很大的问题：片层石墨阻隔和石墨-铝界面结合性较差。本项目采用在片层石墨中加入铝颗粒来改善片层石墨间的阻隔，选用铝颗粒可以避免第二相颗粒加入后带来的颗粒-铝基体界面，导致复合材料界面热阻增大；对片层石墨镀覆硼、硅和钨来改善石墨和铝基体间的界面结合，探索片层石墨表面镀层工艺、不同镀层后片层石墨与铝基体之间的界面形貌、反应产物以及结合情况；对不同片层石墨表面纳米结构、不同制备工艺获得的复合材料进行热导率测试分析，着重探索复合材料界面、片层石墨阻隔颗粒、片层石墨取向对复合材料热导的影响；以并串联模型为基础，考虑片层石墨取向、界面等因素的影响，建立片层石墨/铝的热导预测模型。

随着微电子技术的迅猛发展，电子元器件特征尺寸不断减小，功率不断增大，解决散热问题显得尤为急迫和关键，这就对热工管理材料提出了更高的要求。本项目通过解决石墨排布混乱、石墨与铝之间界面结合差等问题，制备得到高导热的石墨-铝复合材料。并以此为基础，阐述石墨/铝复合材料的热传导机制，建立热导率的预测模型。本项目的主要研究结果为：.（1）采用盐浴法在石墨表面镀覆TiC和SiC， 通过调节混合粉体中Ti和Si的含量，可以控制镀层的厚度在100nm~1μm之间。石墨表面镀SiC、TiC过程中石墨片表面的C原子不断向Si、Ti原子方向扩散，并发生了化学反应。.（2）对石墨/铝复合材料的显微组织、界面形貌以及界面调控手段进行了深入的研究，石墨/铝复合材料的组织形态随着石墨含量的增加，石墨片层会发生弯曲。石墨/铝的界面结构为：Al-非晶相-低结晶石墨-石墨，在铝/石墨界面处的连接是一种从小区域反应、形核，然后通过长大和扩散向大区域蔓延的机制。.通过对石墨表面镀覆TiC和SiC，在复合材料的界面分别形成graphite-TiC-Al和graphite-SiC-Al，复合材料的界面由不致密的Al-C弱结合变为了Ti、Si和石墨的化学结合以及碳化物和Al的冶金结合。.（3） 石墨/铝复合材料的热传导机制为铝中的电子传导+铝—石墨界面声子传导+石墨面内传导；在引入SiC、TiC镀层后，其热传导机制为铝中的电子传导+铝—镀层界面声子传导+镀层+镀层—石墨界面声子传导+石墨面内传导；并分别根据其热传导机制建立了热导预测模型，模型预测值和实验值吻合度较高。