Fabrication of a W/Cu/steel mock-up via optimizing the brazing parameters

Abstract

When W/Cu slices, rather than W slices, are used in the manufacturing of breeding blanket modules, the joining of W to reduced activation ferritic /martensitic (RAFM) steel is essentially the joining of Cu to RAFM steel. In this study, we employed vacuum brazing to join Cu to T91, a ferritic/martensitic steel. Two commercially available filler metals, CuGeNi and CuMnNi, were utilized. It was found that the brazing temperature and the thickness of the brazing filler seriously influence the loss of filler metals, corresponding to the excessive spreading of the filler metals. By lowing the brazing temperature, the excessive flow of the liquidus filler metal as well as the intensity of interfacial reactions, i.e. the dissolving of base metal and diffusion of alloying elements, is highly suppressed. Reducing the thickness of the brazing filler (not only CuMnNi, but also CuGeNi) to 0.05 mm also can suppress the excessive spreading of filler metals on steel, but numerous joining defects were observed. Upon tensile testing, all the specimens brazed with 0.1 mm brazing fillers, either using CuGeNi or using CuMnNi, were broken at the Cu section rather than the brazed interfaces, indicating the brazed interfaces are stronger than fully annealed Cu. By using the optimized brazing parameters, a W/Cu/T91 sandwiched mock-up has been fabricated successfully.