高导热金刚石镁复合材料的界面设计、制备及其性能研究

Diamond possesses superior thermal properties, including high thermal conductivity (TC of 1200-2000 W/mK) and low coefficient of thermal expansion (CTE of 2.3 ppm/K). Magnesium with high thermal conductivity is one of the lightest structural materials in nature. The diamond/Mg composites have the advantages of low density and high thermal conductivity. But due to non-wetting and chemical inertness characteristics between magnesium on diamond, weak interface bonding is derived in the diamond/Mg composites, and the excellent performance of diamond is not exploited. In the proposal, diamond/Mg composites were fabricated by gas pressure infiltration (GPI). Furthermore, surface metallization of diamond and alloying of metal matrix are conducted during the fabrication of the diamond/Mg composites. As a result, a transition carbide layer through interface design is found to be introduced. This is helpful to improve the interfacial bonding between diamond and magnesium and to decrease the interfacial thermal resistance and improve the thermal conductivity of composites. The interfacial structure of the composite was characterized by focused ion beam (FIB) and transmission electron microscope (TEM). The relationship among the fabrication process, interfacial structure and thermal properties of the diamond/Mg composite was investigated. The results provide insight for the improvement of the properties of diamond/Mg composite.

金刚石具有优异的热物理性能，导热率可达1200-2000W/mK，热膨胀系数仅为2.3ppm/K。镁是自然界最轻的结构材料之一，同时具有较高的热导率。金刚石颗粒增强镁基复合材料具有低密度、高导热性等优点，但由于金刚石与镁之间不润湿且存在化学惰性，导致两相界面结合弱，无法充分发挥金刚石优异的导热性能。本项目采用气压浸渗法制备金刚石/镁复合材料，通过界面设计并利用金刚石表面金属化和镁基体合金化两种方式引入碳化物界面层，希望通过界面改性提高镁与金刚石之间的界面结合，有效降低界面热阻，从而提高金刚石/镁复合材料的热导率。利用聚焦离子束（FIB）及透射电镜（TEM），研究diamond/Mg复合材料的界面组织结构；建立复合材料制备工艺、界面结构和导热性能之间的有效联系，进而实现diamond/Mg复合材料热物理性能的提升。

为了探索Diamond/Mg复合材料在电子封装领域的应用，本项目完成了以下几部分工作。（1）利用理论模型计算并考虑到金刚石在高温下的石墨化转变和Al4C3易潮解等因素，选取Cr作为界面改性元素；（2）通过磁控溅射法、盐浴法在金刚石表面镀Cr，研究了镀覆工艺-后续热处理工艺对镀层结构演变和物相组成的影响；结合气体压力浸渗法制备Diamond(Cr)/Mg复合材料，研究其界面结构和热物理性能。结果表明，磁控溅射镀Cr金刚石颗粒经过热处理后，制成的复合材料热导率有着非常显著的提升。镀层厚度为50 nm金刚石颗粒经过1150 ℃热处理后，制成的Diamond(Cr)/Mg复合材料热导率值达到499.49 W/(m K)。远高于盐浴镀+挤压铸造法的202.42 W/ ( m·K)。其中，镀层厚度为2.50μm，结合挤压铸造法制备的Diamond(Cr)/Mg复合材料在室温下的热膨胀系数为5.82×10-6/K，而无镀层的Diamond/Mg复合材料的热膨胀系数为9.29×10-6/K，相比降低了40%。.研究表明，气压浸渗制备金刚石/镁复合材料的热导率高、热膨胀系数低，可作为热管理材料应用于微电子芯片、激光器、半导体照明等高功率器件的散热。