各向异性结构可控强化ZTA陶瓷与钛合金钎焊接头机理研究

Based on the requirement of stress release of ZTA composite ceramic and titanium alloy brazed joint, the fabrication of composite brazing filler reinforced by anisotropic structures was raised. According to the controllable formation of anisotropic single crystals dispersedly reinforced composite brazing seam or in situ synthesized nano particles reinforced composite brazing seam, the difference of thermal expansion coefficient between the substrates and the brazing seam was controlled. In addition, the energy absorption by anisotropic structures during the deformation process of the brazing seam helped decreasing the residual stress, and further enhanced the joining quality of ZTA composite ceramic and titanium alloy brazed joint. Based on the multi-scale numerical analysis of the joint stress and the wetting results of the composite brazing filler, the design criterion of the anisotropic structures reinforced composite brazing filler was studied, and the optimal design of the brazing filler was realized. The evolution of the interfacial reaction was clarified. The reaction model of the joint was established. The control factors of the interfacial microstructure evolution were confirmed. The response mechanism of joint properties to interfacial microstructure evolution was analyzed. The joining mechanism and the strengthening mechanism of the joint were clarified. The objective of this project is to develop anisotropic structures reinforced composite brazing filler and promote the development of the joining technology between ZTA ceramic and metal.

本项目针对ZTA复相陶瓷与钛合金钎焊接头应力缓解的要求，提出利用各向异性结构作增强相制备复合钎料，通过各向异性单晶体弥散增强复合钎缝或原位自生纳米化合物颗粒增强复合钎缝的可控制备来调节母材与钎缝间的线膨胀系数差异，并充分利用各向异性结构在钎缝形变过程中对能量的吸收缓解接头应力，从而提高ZTA陶瓷与钛合金的连接质量。本项目以对接头应力的多尺度数值分析和复合钎料润湿试验为基础，研究各向异性结构增强复合钎料体系的设计准则，实现钎料成分的优化设计，阐明接头界面组织的演化规律，建立界面反应的物理模型，确定接头组织变化的控制因素，揭示接头连接性能对组织变化的响应机制，阐明接头的连接机理和强化机理。本项目旨在开发各向异性结构增强的复合钎料体系，促进ZTA陶瓷与金属连接技术的发展。

针对ZTA复相陶瓷与TC4钛合金钎焊接头的应力缓解需求，本项目提出了采用各向异性的硼酸铝晶须作为增强相制备Ag基复合钎料并实现了对ZTA陶瓷与TC4钛合金的钎焊，对比分析了添加晶须对ZTA/TC4钎焊接头微观组织和接头力学性能的影响，探讨了接头连接机理和复合钎料对接头的强化机理。项目首先通过建立陶瓷自身钎焊接头的数值模型分析了接头中残余应力的主要影响因素，并结合润湿试验结果初步确定了复合钎料中硼酸铝晶须含量需控制在10wt.%以内。采用含2wt.%晶须的复合钎料钎焊时，晶须与液态钎料发生反应形成相对弥散分布的(Cu,Al)3Ti3O纳米颗粒。随着钎焊温度的升高，晶须与钎料反应加剧，(Cu,Al)3Ti3O颗粒数量增多，接头在850℃具有最大抗剪强度56MPa。相比采用原始AgCu钎料所得钎焊接头，添加晶须后陶瓷侧和TC4侧反应层厚度均有所减小，钎缝中Ag基固溶体更容易保留。但由于添加晶须对陶瓷侧化学反应的抑制和对钎缝完整性的不利影响，以及晶须本身的过度反应，所得接头的最高强度未有明显提升。因此，采用AgCu-2wt.%Ti替代AgCu作为钎料基体，并采用化学镀方法对硼酸铝晶须进行镀Cu，采用改进的复合钎料对ZTA陶瓷和TC4钛合金进行了钎焊。一方面保证了ZTA侧能够发生充分反应实现可靠界面连接，另一方面可以使晶须增强相更多地被保留下来。采用镀铜晶须增强的AgCu-2wt.%Ti钎料在900℃下所得接头抗剪强度最大，可达79MPa，相比直接采用AgCu钎料所得接头强度提升了46%。采用数值模拟方法分析了ZTA/TC4钎焊接头的残余应力分布特征。此外，项目还探索了硼酸铝晶须在ZTA陶瓷空气钎焊中的增强作用。本项目促进了各向异性结构增强复合钎料体系的开发，对ZTA陶瓷与金属连接技术的发展具有科学意义。