纳米Si3N4增强AgCuTi复合钎料钎焊Si3N4陶瓷与TiAl合金工艺及机理研究

Aimed at relieving residual stress in joint and improving joining properties of Si3N4/TiAl brazed joints, nano-Si3N4 reinforced AgCuTi composite filler is developed to braze Si3N4 ceramic and TiAl alloy. By controlling the reinforcement content, a brazing seam with microstructure of fine particles reinforced composite can be obtained, which causes a reduction of thermal expansion coefficient of brazing seam and a gradient transition of thermal expansion coefficients from Si3N4 ceramic side to brazing seam to TiAl alloy side. Thus, the residual stress in joint is relieved and joining properties are improved by controlling the microstructure of brazing seam. In this research, by investigating the brazing ability of composite filler, interfacial microstructure and joining properties of brazed joints as well as brazing mechanism, especially the reaction mechanism and dispersion distribution mechanism of nano-Si3N4 particles during brazing, the microstructure evolution and formation mechanism of reaction phases are revealed, the kinetic equations of reaction phases are also established and the influence of composite filler on the interfacial reactions and growth behavior of reaction phases is determined. By simulating and measuring the residual stress using finite element method and X-ray diffraction respectively, the effect of composite filler on the residual stress and joining properties of brazed joints is clarified. The research aims to develop a new brazing filler and method used in brazing TiAl alloy and Si3N4 ceramic, and also provide new ideas for ceramic-metal brazing, moreover to promote the application of nanotechnology in the field of materials joining and also promote the development of ceramic-metal joining technology.

针对Si3N4/TiAl钎焊接头残余应力缓解及力学性能的改善需求，提出了纳米Si3N4增强AgCuTi复合钎料钎焊的方法，通过钎料成分的控制，使钎缝中形成细颗粒增强复合材料组织，降低钎缝的热膨胀系数，实现Si3N4/钎缝/TiAl三者间热膨胀系数的梯度过渡，达到控制界面结构、缓解接头应力并提高接头强度的目的。本项目以研究复合钎料钎焊特性、接头界面结构、力学性能和连接机理为切入点，重点研究纳米增强相的反应及弥散机理，阐明接头界面组织演化规律，揭示界面反应相形成机制，建立反应相生长动力学方程，确定复合钎料对界面反应及反应相生长行为的影响机理。采用有限元及X射线衍射分别对接头应力进行模拟和测量，解明复合钎料对接头残余应力及力学性能的影响规律。本项目旨在开发应用于Si3N4与TiAl钎焊的新钎料，为陶瓷与金属的钎焊提供新思路，同时推广纳米技术在连接领域的应用，促进陶瓷与金属材料连接技术的发展。

本项目主要针对缓解Si3N4/TiAl钎焊接头残余应力以及提高接头高温性能的需求，采用机械球磨的方法制备了纳米Si3N4增强的AgCuTi复合钎料(AgCuTic)，并采用该复合钎料成功实现了TiAl合金和Si3N4陶瓷的连接。Si3N4/AgCuTiC/TiAl钎焊接头典型界面结构为：TiAl/AlCu2Ti/Al4Cu9+TiN +Ti5Si3+Ag(s,s)/TiN+Ti5Si3/Si3N4。钎焊过程中，液相钎料中的Ti元素与纳米Si3N4反应形成了纳米尺寸的TiN和Ti5Si3颗粒，这些颗粒作为微米尺度Al4Cu9化合物的形核质点，使得钎缝中形成了微纳米颗粒增强的Ag基复合材料组织。复合钎料中增强相含量、钎焊温度、钎焊时间等工艺参数对接头界面结构和力学性能影响较大，当增强相含量为3 wt.%，钎焊温度为880°C，钎焊时间为5min时，接头室温及高温(400°C)抗剪强度最大分别为115MPa和156MPa，比采用AgCuTi钎料获得的接头强度提高一倍。本项目还研究了复合钎料使用对接头性能改善的原因，一方面复合钎缝中弥散分布的细颗粒TiN及Ti5Si3化合物作为第二相通过剪切滞后、位错强化及Orowan强化等方式强化了Ag基体，提高了钎缝性能；另一方面通过降低钎缝的热膨胀系数在一定程度上缓解了接头残余应力，从而提高了接头室温及高温性能。接头残余应力有限元模拟结果表明：复合材料的使用对接头的应力分布形式影响不大，但减小了残余应力分布区域以及应力峰值。X射线应力分析表明：增强相含量为3 wt.%时，Si3N4陶瓷表面压应力峰值降低70MPa左右，与模拟结果相吻合。除此之外，在本项目中纳米增强复合钎料也被应用于其它陶瓷与金属钎焊体系均有优良表现，可显著优化钎焊接头的界面组织并提高钎焊接头的力学性能。目前针对本项目已取得的一系列研究成果，共发表SCI期刊论文22篇，申请专利11项，两项授权。