基于二元协同微纳米界面的陶瓷/金属精密钎焊连接机理研究

Based on the requirement of the precision brazing of ceramic to metal, the method to control the wetting behavior and spreading area of brazing fillers by using binary cooperative complementary micro/nano-scale interface is proposed. The binary cooperative complementary micro/nano-scale interface promotes the wetting and spreading of brazing fillers in the brazing area, while it inhibits the wetting and spreading of brazing fillers in the non-brazing area. Owing to the precise control of wetting and spreading of brazing fillers, the joint precision has an obvious improvement. In the study of the project, composition optimization and wetting behavior control of brazing fillers are chosen as the breakthrough. The design theory and action mechanism of binary cooperative complementary micro/nano-scale interface are mainly investigated. According to binary cooperative effect, the composition optimization of brazing fillers is realized by reducing the dependence on the active elements. The design criterion of brazing fillers that match the binary cooperative complementary micro/nano-scale is clarified. The influence factors and mechanism of binary cooperative complementary micro/nano-scale interface on the wetting and spreading of brazing filler are systematically studied. According to the wetting mechanism, the wetting model of brazing fillers on binary cooperative complementary micro/nano-scale interface is established. The evolution of interfacial microstructure and the improvement mechanism of mechanical properties of joints are clarified. By determining the relationship between the spreading precision of brazing fillers and the joining precision of joints, the mechanism of the precision brazing of ceramic to metal is clarified. The project aims to extend the application of binary cooperative complementary micro/nano-scale interface in the field of brazing, and develop the precision brazing of ceramic to metal. Meanwhile, the project enlarges the basic control theory on the wetting of brazing fillers and provides a new way for the development of precision brazing technology.

本项目针对陶瓷与金属精密钎焊连接的需求，提出了采用二元协同微纳米界面精确控制钎料润湿行为及铺展区域的方法，利用二元协同效应促进钎料在待钎焊区的润湿铺展并抑制其在非钎焊区的润湿铺展，从而实现连接精度的提高。本项目以钎料成分优化及润湿行为控制为研究切入点，重点研究二元协同微纳米界面的设计理论及其对钎料润湿行为的作用机制，同时利用二元协同效应降低钎料润湿对活性元素的过度依赖而实现钎料成分的优化，阐明与二元协同微纳米界面匹配的钎料设计准则。系统研究钎料在二元协同微纳米界面润湿铺展的影响因素及机制，构建钎料在二元协同微纳米界面的润湿模型，揭示接头组织演化规律及性能提升机理，建立钎料润湿铺展精度与接头连接精度的对应关系，阐明陶瓷/金属精密钎焊连接机理。本项目旨在推广二元协同微纳米界面在钎焊领域的应用，开发陶瓷/金属精密钎焊连接技术，丰富钎料润湿行为控制的基础理论，为精密钎焊连接技术的发展提供新思路。

本课题针对高速列车受电弓弓头和滑块的精密连接，采用激光微纳米加工和真空钎焊技术，基于Ti3SiC2陶瓷和紫铜，完成了二元协同微纳米界面的制备，揭示了不同种类钎料在该界面上的润湿机制，并借助SEM、TEM、XRD、EDS等分析测试手段确定了钎焊界面反应产物，研究了二元协同微纳米界面组织演化规律及接头断裂机制，得到了陶瓷/金属精密连接机理。解析计算和数值模拟的结果均表明，正三棱柱形、正四棱柱形、正六棱柱形以及圆柱形二元协同微纳米结构均可以促进高温钎料在陶瓷表面的润湿铺展，能够有效地降低钎料的润湿角。在钎焊温度为860℃，保温时间为20min时，对于基体为光滑陶瓷而言，促进Ag-Cu-2Ti钎料在Ti3SiC2陶瓷表面润湿性的较优的微结构为a=30μm, b=20μm, h=20μm的正四棱柱凸台微结构，润湿角度会由光滑陶瓷表面的59.6°降低至具有微纳米结构的25.7°。与紫铜真空钎焊连接后，在接头靠近Ti3SiC2陶瓷母材一侧处会出现明显Si元素富集的现象，经研究发现，该区域为Ti5Si3和TiC脆性化合物层，此时接头剪切强度仅有99.4MPa；对于基体为蒸镀Cu金属层的陶瓷而言，随着金属相区宽度的增大，钎料的润湿角会不断降低至润湿状态。钎焊接头的界面结构为Ti3SiC2陶瓷/CuTi+CuTi3+TiSi2+Ti5Si3+TiC/Ag-Cu共晶组织/Ag(s,s)+Cu(s,s)/紫铜。在金属相区宽度为70μm，陶瓷相区宽度为30μm时，接头的抗剪强度最高可达115.2MPa；对于基体为蒸镀Ni金属层的陶瓷而言，Ag-Cu钎料在正六棱柱形微纳米结构上的润湿角度最小为58.6°。由于润湿性的差异，靠近紫铜母材一侧的Ag-Cu共晶带状组织宽度有所不同，具有正六棱柱形二元协同微纳米界面的带状组织最窄为44.87μm。在与紫铜真空钎焊连接后，由于有Ni元素的加入，会在Ti3SiC2陶瓷一侧生成Ti2Ni和Ni3Ti等塑韧性较好的化合物，阻碍Ti5Si3的脆性化合物带的连续性，钎焊接头的界面结构为Ti3SiC2陶瓷/CuTi+TiC+Ti2Ni+Ni3Ti+Ti5Si3/Ag-Cu共晶组织/紫铜。蒸镀Ni金属层正三棱柱形微纳米结构试样的剪切强度最高为116.87MPa，相较于光滑陶瓷的钎焊界面提高了15.4 %。