具有成分梯度界面层的铜/金刚石复合材料的导热性能研究

Diamond particles reinforced metal matrix composites, abbreviated as metal/diamond composites, are a combination of superior thermal conductivity of diamond and good machinability of metals. This kind of composites is very promising for electronic packaging applications. The interface thermal resistance between metal matrix and diamond particles, however, is becoming a bottleneck to achieving high thermal conductivity in the composites. Metal matrix alloying and diamond particles modification are widely used to effectively enhance the interface thermal conductance, the reciprocal of interface thermal resistance. In view of the characteristics of thermal condution by phonons, the interface thermal conductance and hence the composite thermal conductivity could be further enhanced by the introduction of a compositionally graded metal/diamond interface. In the proposal, the diamond particles modification method was applied to improve the interfacial bonding between metal matrix and diamond particles. A TiC layer was coated onto the surface of single crystalline diamond particles by using the molten-salt method. Diamond particles reinforced copper matrix composites, abbreviated as Cu/diamond composites, were then produced with the gas pressure infiltration technique. The effect of fabricating parameters on interface microstructure was systematically investigated. The Cu/TiC/diamond interfaces were tailored to have different thicknesses and/or different compositionally graded profiles. The effect of interface microstructure on composite thermal conductivity was clarified. An acoustic mismatch model was employed to theoretically survey the behavior of phonon conduction along the compositionally graded interface. The physical mechanism was explored to detect the effect of interface microstructure on interface thermal conductance. The findings provide scientific basis for producing Cu/diamond composites with high thermal conductivity. The concept of compositionally graded interface presented in this proposal could be extended to other metal/diamond composites.

结合金刚石优异导热性能和金属良好机械加工性能的金刚石颗粒增强金属基复合材料是理想的电子封装材料，然而金属/金刚石界面热阻是限制复合材料热导率提高的瓶颈。金属基体合金化和金刚石颗粒表面改性均可有效改善界面热导，考虑声子的热传导特点而引入成分梯度界面层有望进一步增加界面热导，提高金属/金刚石复合材料的热导率。本项目采用金刚石颗粒表面改性的方法，通过盐浴镀膜技术在单晶金刚石颗粒表面镀覆碳化钛涂层，利用气压浸渗技术制备铜/金刚石复合材料。系统研究材料制备参数对界面层微观结构的影响规律，获得具有不同厚度和不同成分梯度形貌的铜/碳化钛/金刚石界面层，阐明界面层微观结构对复合材料热导率的影响规律。利用声学错配模型研究成分梯度界面层的声子热传导过程，揭示界面微观结构影响界面热导的物理机制，为制备高热导率的铜/金刚石复合材料提供科学依据。成分梯度界面层的研究方法可应用于其他体系的金属/金刚石复合材料。

电子器件小型化和集成化导致功率密度急剧增加，散热问题成为器件服役性能提高的瓶颈。金刚石颗粒增强铜基（铜/金刚石）复合材料是理想的导热材料，然而由于铜与金刚石之间无化学反应且润湿性差，界面问题严重制约铜/金刚石复合材料导热性能提高。本项目从金刚石表面金属化和基体合金化两个方面入手构筑碳化物界面层并调控界面层厚度和成分梯度，提高界面声子传输效率进而提高复合材料热导率。系统研究了金刚石表面金属化和基体合金化等不同界面改性方法，气压浸渗和超高压熔渗等不同复合材料制备方法，锆、钛、铬、钨等不同合金元素种类对铜/金刚石复合材料界面结构和热导率的影响规律，阐明了界面结构影响复合材料热导率的作用机制。主要结果如下：（1）对于金刚石表面金属化，在金刚石表面镀覆一定厚度W、Cr、Ti镀层时复合材料热导率分别为670、714、716 W/mK；对于基体合金化，在铜基体中添加0.5 wt.% Ti、1.0 wt.% Cr、0.5 wt.% Zr时复合材料热导率分别为752、765、930 W/mK，添加Zr效果最好，因为Zr对铜基体热导率影响最小，上述热导率与文献对比均为较高值。（2）界面层厚度存在一个最佳值，由于碳化物热导率较低，界面层太厚将增加界面热阻，而界面层太薄则无法提供强有力的界面结合，添加合金元素Ti、Cr、Zr获得最高热导率所对应的最佳界面层厚度分别为300、500、400 nm。（3）分别在金刚石表面镀覆Cr和在铜基体添加Cr形成成分梯度界面层，复合材料热导率从617 W/mK增至810 W/mK。（4）无论添加哪种合金元素，当元素含量较低时界面层碳化物呈现不连续的颗粒状分布，此时界面热阻可由并联模型解释；当元素含量较高时界面层碳化物呈现连续的层状分布，此时界面热阻可由串联模型解释。上述研究结果为制备高热导率铜/金刚石复合材料提供了科学依据，并为金属基复合材料的界面调控与剪裁设计提供了理论参考。相关成果在Scripta Materialia、Composites Part A、Composites Part B等期刊发表15篇论文，授权/申请4项专利，培养博士生1名、硕士生4名，国际会议邀请报告1次。