用于钨／RAFM钢连接的铁基低活化非晶钎料设计与钎焊机理

The joining of the plasma-facing tungsten armor and the reduced activation ferritic/martensitic steel (RAFM) heat-sink materials is crucial to the fabrication of He-cooled divertor in magnetic confinement fusion reactors. The effective joining of tungsten with RAFM appears to be a challenging problem due mainly to the lack of suitable joining materials. Amorphous alloys are promising brazing materials to obtain high performance W/RAFM joints with good high-temperature strength and thermal fatigue properties. In this project we propose that weak ferromagnetic Fe-based amorphous alloys composed of reduced activation elements and associated with good glass-forming ability and low melting points, favor the formation of high performance joint structure upon vacuum brazing. Composition design is first carried out for Fe-based amorphous alloys under the constraint conditions of the reduced neutron activation, favorable melting point, weak ferromagnetic and good glass-forming ability. Since diffusion of specific alloying elements is fundamentally related to the formation of amorphous alloys and the structure formation of brazing joints as well, crystallization of the reduced activation Fe-based amorphous alloys and their wetting behaviors on single-grain tungsten and RAFM are first studied to clarify the nature of fast diffusion species. The variations of element distribution, constituent phases, microstructure, and mechanical properties of the joint structure with the concentrations of fast diffusion species are then extensively studied, from which the joint structure formation mechanism is eventually derived. The new Fe-based amorphous alloys would suit the properties that are highly demanding by divertor manufacture, and some new theoretical insight will be added to understand the structure formation of brazing joints of dissimilar materials.

面向等离子体材料钨和热沉材料低活化钢的连接是磁约束聚变装置中偏滤器加工的关键环节，目前没有连接材料能完全满足低中子活化、熔点、磁性、高温强度和热疲劳性能等复杂要求。本工作提出设计由低中子活化元素组成的具有弱铁磁性、低熔点和高非晶形成能力的Fe基多元非晶，用于钨/低活化钢的真空钎焊。基于非晶晶化和钎料润湿行为研究，澄清合金中的快速扩散组元种类；研究钎焊接头结构中的元素分布、合金相、组织和力学性能随快速扩散组元含量的变化规律，最终获得高性能钨/低活化钢接头结构，揭示快速扩散组元对接头结构形成的影响机理。研究结果将为偏滤器加工提供合适的候选连接材料，并为理解异质钎焊接头结构的形成提供新的理论思路。

面向等离子体材料钨和热沉材料低活化钢的连接是磁约束聚变装置中偏滤器加工的关键问题，钨/RAFM钢接头被要求承受高通量的等离子体和14 MeV的中子辐照和巨大的热负荷，需要发展合适的连接方法和材料制备高性能钨/RAFM钢接头结构。本项目设计了由低中子活化元素组成的Fe基多元非晶系列成分Fe-Si-B、Fe-B-Si-Sn、Fe-B-Si-(P,Cr,Sn)、Fe-B-Si-(Mn,Ga,Sn)、Fe-B-Si-(Cr,Sn)和Fe-B-Si-(Cr,Mn,Ga,Ta,Sn)，用于钨/低活化钢的真空钎焊。通过钎焊工艺优化制备出室温强高韧钨/CLF-1钢接头，钎焊态和组织回复后接头室温强度分别为410 MPa和310 MPa，是目前已报道的最高接头强度。采用钨/CLF-1钢和CuCrZr热沉合金制备的水冷模块能承受100次5 MW/m2的循环热负荷；发展了放热辅助钎焊Ti-Fe-Sn体系，在较低钎焊温度（1090 C）获得室温高强韧配合的接头结构；系统研究了钎料成分、钎焊温度和保温时间、接头组织结构和室温力学性能关系，揭示了高B含量Fe基非晶液体二次合金化过程中FeW2B2、FeWB、Fe3B型金属间化合物对快速扩散元素（W、B、Si）的捕获机制，澄清了焊接温度和保温时间对钎缝基体和界面金属间化合物种类、形态、尺寸和分布影响规律，以及基体钢组织回复过程中的应力释放机制。本项目获得的低活化钎料合金、钎焊工艺将为氦冷偏滤器的连接难题提供有效的解决方案，而有关高温钎焊的机理性认识将为发展高性能异质钎焊接头结构提供理论参考。