Ti-based Fe Brazing Materials And Relative Welding Experiments On W/steel Joint

The joining of W/steel is crucial to the fabrication of future helium-cooled divertor in the fusion reactors. Because of the significant differences in their melting points and the coefficients of thermal expansion, the joining of W and steel itself is a challenging issue. Excellent material performance of W/steel joint is high demanding due to the hash service environments including extremely high thermal and neutron radiation. Brazing and diffusion bonding have some advantages in making W/steel joint, which have been drawing much attention in recent studies. Ti and Fe are the low neutron activation metals that are potentially useful for W/steel joining. This work investigates the making of W/steel joint with Ti and Fe by using two different methods, Brazing and Liquid Interface Diffusion Bonding (LIDB). The main research results are concluded in the following.Part 1:Amorphous metals can be good candidate materials for brazing. In this study we have developed Ti-based amorphous alloys with low melting points and low neutron activity, for brazing W and steel, substitution of Zr for Ti in the amorphous alloy Ti70Fe20Si10 leads to the discovery of two amorphous alloys with good glass-forming ability, namely, Ti50Zr25Fe20Si5 and Ti45Zr30Fe20Si5.The use of Ti50Zr25Fe20Si5 in our brazing experiments, unfortunately, results in the formation of joint structure of poor quality. There have formed a large number of cracks in both the W and solder layer regions, and the strengths of the joins are very low. The presence of a large amount of brittle intermetallic phases in the joint structures mainly accounts for the joint structure formation and low material strength.Part 2:In order to optimize the diffusion bonding process of W/Ti/steel with LIDB, four projects have been carried out. Joints with good qualities have been achieved. The optimal experimental procedures are reached and summarized in the following:Firstly, making around 20?m thick iron plating on Ti and steel surfaces via electroplating; Secondly, joining the W/Ti with LIDB at 1100?; At last, joining the (W/Ti)/steel with diffusion bonding at 1050 ?. This processing route improves greatly the formability of W/Ti/steel joint with high strength.