W-EUROFER97 brazed joints using Ag, Au, and Cu-based fillers for energy applications: A microstructural and mechanical study

The brazeability of four different alloys (Au, Cu, and two Ag-based alloys) was evaluated for their use as filler materials in joints between EUROFER 97 and tungsten for its application in future fusion reactors. The study aims to analyze the operational brazeability in terms of deep microstructural analysis and mechanical behavior.

In general, high metallic continuity was observed for all filler compositions. In the case of the joints brazed with the Au-based filler alloy, a homogeneous microstructure based on an Au-Pd-Fe-Ni solid solution is obtained. The use of Ag-based filler alloys produced a solid solution phase at the EUROFER97-braze interface, and a Ag-based phase in contact with the tungsten base material. Finally, with the cupronickel filler alloy, a braze constituted by two different Cu-Ni-Fe solid solution phases is obtained.

Regarding the mechanical characterization, the Cu-based filler shows a lower hardness value, while the higher values were obtained with one of the Ag-based filler alloy. In the case of the shear tests, a maximum 304 ± 57 MPa strength is obtained for Au-based filler alloy brazed at 1171 ºC due to the combination of a homogeneous and toughness microstructure and the lack of intermetallic compounds in the braze.