Brazing of the ITER First Wall by a Copper-Based Rapidly Quenched Ribbon-Type Filler Metal

As applied to the manufacture of the ITER first wall, a rapidly quenched copper-based filler metal for brazing chromium-zirconium copper alloy (CuCrZr) with beryllium (Be) at temperatures below 720°C has been selected. The composition of the given filler metal has been optimized by varying the concentration of alloying elements, such as Sn, Ni, and P, improving the filler functional properties and quality. Rapidly quenched ribbon-type filler metals with various contents of alloying elements were investigated by differential thermal and X-ray phase analysis, atomic force microscopy, and scanning electron microscopy. To improve the casting performance of the filler metal and obtain high-quality ribbons, the kinematic viscosity of brazing alloys with various contents of Ni, Sn, and P has been investigated. The chromium-zirconium copper alloy has been brazed with Be using the filler metals obtained (by furnace brazing and fast brazing by passing an electric current). Based on the results of complex research, an ultrafast (quenching rate of ∼10⁵°C/s) quenched brazing alloy STEMET 1101M (Cu-9.1Ni-3.6Sn-8.0P, in weight percent) has been selected and manufactured in the form of a ribbon that is 50 mm in width and 50 μm in thickness. An experimental mock-up of the ITER first wall has been made in D.V. Efremov SRIEA by rapid brazing (by passing a current) using the filler metal STEMET 1101M. The brazed joint has withstood 15 000 cycles of thermocycling under a thermal load of 0.5 to 5.9 MW/m² without breaking.