Microstructure of the tungsten and reduced activation ferritic-martensitic steel joint brazed with an Fe-based amorphous alloy

The effective joining of tungsten (W) and reduced activation ferritic-martensitic (RAFM) steels is crucial to fabrication of the divertors and first wall of future fusion reactors. In the present work, a low-activation Fe-based amorphous alloy of Fe67.8Cr11.5Si2.1B18.6 (at. %) is designed as the filler metal for brazing W and RAFM steels. Crack-free joint has been achieved with the amorphous alloy filler and a vanadium interlayer metal by short-time vacuum brazing at 1270 degrees C. Layer structures composed of intermetallic phases and single solid-solution phases, respectively, are alternately formed in the W/RAFM steel joint, exhibiting alternating hard and soft mechanical characteristic. Long-distance diffusion of W atoms to the steel substrate is blocked by the formation of FeW2B2 and Fe3B phases, and Si and B elements are confined within the main bonding seam of the joints. Microstructure recovery for the steel is realized following the standard heat treatment procedures. The present results suggest a promising way of making strong and tough W/RAFM joints with low-activation Fe-based amorphous alloys.