Effect of beryllium on the morphology of initial ingots and the structural phase state of fast-quenched STEMET 1108 brazing alloy ribbons

The STEMET 1108 grade (copper – tin – indium – nickel) of filler metal is currently used to braze bronze to tungsten plated with pure copper in divertors of the International Thermonuclear Experimental Reactor (or, ITER). Such filler metals are obtained as a result of rapid solidification of melt on a rapidly spinning copper wheel (melt spinning). When ingots are cast from which brazing ribbons are further produced, pores occur in them, through which indium evaporates. All this may affect the quality of the final product. The authors propose to alloy ingots with beryllium to stop the pore formation. This paper looks at the effect of beryllium on the quality of filler metal ingots and ribbons. The paper describes the results of a study that looked at the structural phase state of filler metals using electron microscopy and X-ray diffraction techniques, as well as a synchrotron radiation source. Both ingots and ribbons were found to have the same phase composition that consists of copper-based FCCsolid solutions and contains phosphide Cu3P. Beryllium containing ribbons are thinner than beryllium-free ribbons. In both cases, a dendritic structure is formed across the entire ribbon thickness. It is demonstrated that beryllium alloying in the range of 0.05 to 0.1 wt. % helps to significantly reduce the porosity of the initial ingots without compromising their structural phase state. In addition, it helps prevent the evaporation of indium. Hence, the difference in the structural phase state between beryllium alloyed and non-alloyed ribbons is insignificant and only concerns their dendritic structure, while there is no noticeable difference in their phase composition.