Brazing W and Fe–Ni–Co alloy using Ag–28Cu and Ag–27Cu–3.5Ti fillers

• Ag–Cu–3.5Ti active filler is used to braze W and Fe–Ni–Co alloy.
• The effect of Ti on W/Ag–Cu–3.5Ti/4J33 joint is analyzed and its mechanism is proposed.
• The addition of active element Ti in Ag–28Cu greatly improves its wettability to W.
• The addition of Ti in Ag–28Cu greatly improves the shear strength of the joints.

W/Fe–Ni–Co joints are achieved using Ag–28Cu at 850 °C for 5 min and Ag–27Cu–3.5Ti at 880 °C for 5 min. The effect of active element Ti in Ag–28Cu on microstructures and shear strength of the joints are investigated. The results show that the wetting angles of Ag–28Cu and Ag–27Cu–3.5Ti on the W matrixes are 147 ± 2 deg and 21 ± 4 deg, respectively. Due to the poor wettability of Ag–28Cu on W matrix, voids and cracks are observed in W/Ag–28Cu interface. The fracture of W/Ag–28Cu/Fe–Ni–Co alloy joint occurs at W/Ag–28Cu interface and the shear strength of the joint is 72.3 ± 30 MPa. In contrast, the addition of active element Ti in the filler promotes the wettability of Ag–27Cu–3.5Ti on W matrix and chemical reactions, so an interfacial microstructure of Fe–Ni–Co alloy/a diffusion layer/Ag–Cu eutectic/Ag-rich + CuTi2/W is obtained. The shear strength test results of the joints brazing with Ag–27Cu–3.5Ti show that the fracture occurs in the W matrix near the joint and the shear strength is higher than 317.7 ± 20 MPa.