Joining of SiO2f/SiO2 composite to Nb using Ag-Cu-In-Ti brazing alloys

Three compositions of Ag-Cu-In-Ti system brazing alloys were designed for joining SiO2f/SiO2 ceramic composite to Nb metal. The wettability of the three alloys on the composite was studied with the sessile drop method. The results showed that after heating at 1073 K for 30 min, they exhibited contact angles of 74°, 83° and 86°, respectively. The brazing alloys were fabricated into foils by rapid solidification technique. Among the three brazing filler alloys the joints brazed with AgCu-10In-5Ti at 1073 K for 10 min presented the maximum average shear strength of 30.9 MPa. During the brazing process the active element Ti diffused strongly from the filler alloy to the composite surface and a reaction layer with a thickness of 2–3 μm was formed. Sound metallurgical bonding was also achieved at the Nb side. The interface structure of the joint brazed with the AgCu-10In-5Ti alloy can be described as the following sequence: SiO2f/SiO2→SiO2+Cu3Ti3O→SiO2+TiO+Ti5Si4→Ag(s, s)+(Cu-Ti)→Nb. However, for the filler alloy with 4.0 wt% Ti content the joint strength was only 15.8 MPa.