Joining of SiO2f/SiO2 composite to Ti-6Al-4V using Ag-Cu-In-Ti brazing fillers, the joint strengths, and microstructures

Three novel Ag-Cu-In-Ti brazing fillers were designed for joining of SiO2f/SiO2 composite to Ti-6Al-4V. The wettability of the three brazing fillers on the composite was studied with the sessile drop method at 1073 K for 30 min. The results showed that the three brazing fillers exhibited contact angles of 27°, 33°, and 35°, respectively. The joints brazed with Ag-(22~26)Cu-(8~12)In-(4.5~6.0)Ti at 1073 K for 10 min presented the maximum average shear strength of 19.6 MPa, whereas the strength of the joints brazed with Ag-(22~26)Cu-(8~12)In-(3.2~3.8)Ti was only 10.5 MPa. During the brazing process, the active element Ti diffused significantly from the Ag-Cu-In-Ti alloy to the surface of the SiO2f/SiO2 composite and a thin reaction layer was formed close to SiO2f/SiO2 composite. Sound interfacial bonding was also achieved at the Ti-6Al-4V side. According to micro-analysis results, Ag, Ni3Ti3O, Cu4Ti3, Cu3Ti, and TiSi2 phases were identified at the fracture surface of SiO2f/SiO2/Ag-(22~26)Cu-(8~12)In-(4.5~6.0)Ti/Ti-6Al-4V by the XRD method. The interface structure of the joint brazed with Ag-(22~26)Cu-(8~12)In-(4.5~6.0)Ti alloy can be described as the following sequence: SiO2f/SiO2 → Cu-Ti-O + Ti-Si phases → Ag-based solid solution + Cu-Ti + Ti-In phases → Ti-6Al-4V.