Cu Interlayer-Induced High-Strength Laser-Welded AISI 304 Steel-Niobium Joint

Abstract

Joining niobium to austenitic stainless steel is necessary for the fabrication of particle accelerators. However, the brittle iron-niobium intermetallics formed in the joint significantly reduce the joint strength. Copper was used as an interlayer to prevent the brittle phase formation while joining niobium to AISI 304 steel. The laser beam was first focused on the Cu-steel faying surface and then on the Cu-Nb faying surface. The tensile strength of the joint is greater than that of the Nb. The weld microstructure consists of austenite with Cu-rich precipitates along with the austenitic grain boundaries and Cu-rich phase embedded with Nb-rich particles and dendrites. Solid solution strengthening of Cu by Fe and second-phase strengthening of Cu by Nb play a critical role in improving the mechanical properties of the joint. These results highlight new possibilities for the joining of niobium to steel.