Microstructure and Interfacial Reactions During Vacuum Brazing of Stainless Steel to Titanium Using Ag-28 pct Cu Alloy

Microstructural evolution and interfacial reactions during vacuum brazing of grade-2 Ti and 304L-type stainless steel (SS) using eutectic alloy Ag-28 wt pct Cu were investigated. A thin Ni-depleted zone of $$\alpha $$ α -Fe(Cr, Ni) solid solution formed on the SS-side of the braze zone (BZ). Cu from the braze alloy, in combination with the dissolved Fe and Ti from the base materials, formed a layer of ternary compound $$\tau _2$$ τ 2 , adjacent to Ti in the BZ. In addition, four binary intermetallic compounds, Cu $$_3$$ 3 Ti $$_2$$ 2 , Cu $$_4$$ 4 Ti $$_3$$ 3 , CuTi and CuTi $$_2$$ 2 formed as parallel contiguous layers in the BZ. The unreacted Ag solidified as islands within the layers of Cu $$_3$$ 3 Ti $$_2$$ 2 and Cu $$_4$$ 4 Ti $$_3$$ 3 . Formation of an amorphous phase at certain locations in the BZ could be revealed. The $$\beta $$ β -Ti(Cu) layer, formed due to diffusion of Cu into Ti-based material, transformed to an $$\alpha $$ α -Ti + CuTi $$_2$$ 2 eutectoid with lamellar morphology. Tensile test showed that the brazed joints had strength of 112 MPa and failed at the BZ. The possible sequence of events that led to the final microstructure and the mode of failure of these joints were delineated.