Be–Cu joints based on amorphous alloy brazing for divertor and first wall application

The limitation on using silver-based alloys for brazing ITER in-vessel components created a development problem for new brazing materials. An application of Be tiles joined to a Cu-based heat sink will be discussed in this paper. For this purpose, rapidly solidified ribbon-type filler metal STEMET 1108 1 (Cu–Sn–In–Ni system) with a melting temperature of 750°C and a thickness up to 50 μm was developed. A new temperature regime and heating method were applied during this brazing procedure. This improves the properties of joints significantly, in comparison with conventional brazing in a resistance furnace. These treatments can increase the operational threshold for Be/Cu joints under cyclic surface heat loading up to 12 MW/m2. Metallographic examinations demonstrated the high quality of brazed joints. The brazed seam has a uniform structure along its entire length. Defects of seam filling, pores, intermetallic compounds and other inclusions are not seen. The prospects of these joints for fusion reactor applications are discussed.