Microstructure and interfacial reactions of vacuum brazing titanium alloy to stainless steel using an AgCuTi filler metal

The microstructure and interfacial reactions of the vacuum brazed titanium alloy (TC4) to stainless steel (1Cr18Ni9Ti) using an AgCuTi filler metal at 920 °C and 980 °C have been investigated. The results show that the main interfacial microstructure of the sample brazed at 920 °C was 1Cr18Ni9Ti/CuTi/Ag-rich + Cu₄Ti/Cu₄Ti/β-Ti/TC4. Shear tests on brazed specimens show that the fractures occurred in the Ag-rich phase, indicating a ductile fracture type. The recorded room temperature shear strength value of the joint was up to 188 MPa. When the brazing temperature was increased to 980 °C, the interfacial microstructure of the joint became 1Cr18Ni9Ti/Ag-rich/CuTi₂/Ti-Cu-rich/β-Ti/TC4. Due to the imposed temperature increment, a large amount of Ag-rich phase was depleted from the joint while CuTi₂ and dendritic Ti-Cu-rich phases occupied the brazed joint zone. The fractures after shear testing occurred in the CuTi₂ as well as in the Ti-Cu-rich phases. The room temperature shear strength after the 980 °C braze decreased to 123 MPa.