镍基单晶高效固相连接技术及接头形成机理

Bonding the nickel based single crystalline alloy is a key technology for manufacturing the turbine blade used in aero engine. Joining technologies such as brazing, transient liquid diffusion welding (TLP), and solid-state bonding are used to fabricate blades in present. The results were showed as follow: The joint strength and operating temperature were much lower than that of base metal. The over-all properties of TLP joint were improved in comparison with brazing joints, while the steps of isothermal solidification and microstructure homogenization were time consuming. Although the high temperature performance of solid-state bonds was highly improved due to no addition of melting point depressant (MPD), the restrict cleaning before welding was required, the high welding pressure and long welding time were necessary as well, which destroyed the properties of base metal. Based on analysis above, a novel technology of solid-state bonding with the assistance of TLP is brought forward in this research. A forge welding pressure is followed after the appearance of transient liquid appeared in TLP which is used to clean the surfaces to be welded, a high efficient solid-state bonding is achieved. The joint formation mechanism which is helpful to improve the high temperature performance is to be recovered by studying the liquefaction of base metal at interface and role of forge pressure in welding procedure. The research will bring about a great advance in broadening the thoughts in materials joining, promoting the application of single crystalline high temperature alloy in aviation field, improving the reliability of aero engine.

镍基单晶的连接是航空发动机涡轮叶片制造的关键技术，目前，国内外主要采用钎焊、过渡液相扩散焊和固相扩散焊等方法进行连接。研究结果表明：镍基单晶钎焊接头的强度及使用温度都较低；镍基单晶TLP扩散焊接头的综合性能接近于母材，但焊接过程中的等温凝固及组织均匀化阶段耗时很长；固相扩散焊不需添加降熔元素，可获得使用温度较高的接头，但固相扩散焊时，待连接表面的清理要求特别高，而且焊接过程要求采用高的焊接压力和长的焊接时间，对母材的性能有很大的损害。基于上述分析，项目提出过渡液相辅助固相连接技术，利用过渡液相对接头表面的＂清洗＂作用，在锻压力的作用下实现高效固相连接。通过研究接头界面处母材液化规律和锻压力的作用机制，深入研究过渡液相辅助固相连接的连接机理，提高接头的高温性能。该研究开拓材料连接新思路，促进单晶高温在航空领域的应用,提升航空发动机的工作可靠性。

镍基单晶的连接是航空发动机涡轮叶片制造的关键技术。项目针对钎焊接头的强度及使用温度都较低、瞬间液相扩散连接的组织均匀化阶段耗时很长、固相扩散焊待连接表面的清理要求高，等局限，提出过渡液相辅助固相连接技术，利用过渡液相对接头表面的＂清洗＂作用，在锻压力的作用下实现高效固相连接。主要研究结果如下：. 1）钎料对DD407母材表面液化规律. 采用厚度为150μm的BNi9钎料，在加热温度1150℃，保温时间5min的情况下，母材液化深度达到最大值65.8μm。然而，采用相同厚度的BNi5钎料，在相同的工艺参数条件下，母材液化最大深度只有55.5μm。钎料所含的降熔元素的不同造成DD407液化的机制不同，BNi9的液化机制是通过降熔元素B向母材扩散，扩散区的熔点降低使得母材液化；而BNi5的液化机制则是Si元素与母材相互作用，形成低熔共晶，使得母材液化。. 2）压力对过渡液相扩散焊连接的作用机制. 选用BNi9对DD407进行过渡液相扩散连接，当温度为1150℃时，无外加压力，保温2h，接头抗拉强度最大达到954.1MPa。而当焊接过程中持续施加压力为3MPa时，接头抗拉强度反而降低为744 MPa。焊接过程中持续施加压力，使得焊缝区的液相被挤压到焊缝边缘，使得液化的钎料与母材之间扩散不充分。. 3）过渡液相辅助固相连接技术及接头形成机理. 对过渡液相辅助固相连接技术进行了探索。选用BNi5钎料，在焊接温度1180℃条件下，保温60min，然后降温到1000℃，施加8MPa的锻压力，挤出液相，并保温扩散40min，接头强度达到750MPa，整个连接时间缩短20min。接头形成过程包括：钎料液化，母材表面溶解，挤出液相，残留液相钎焊连接。