Effect of Zr content in in-situ synthesized brazing alloy on the microstructure and properties of brazed joints

The brazed joints obtained by welding titanium alloys with titanium-based brazing filler metal have the advantages of high strength, good corrosion resistance and good heat resistance. Therefore, titanium alloy components which brazed with titanium-based brazing alloys are commonly used in extreme service environments such as heavy loads and strong corrosion. In this paper, the deterioration of matrix microstructure and properties, the embrittlement of welding in titanium alloy brazing are studied. The vacuum brazing mechanism and process of pure titanium TA2 with Zr, Cu and Ni pure metal foils as in-situ synthesized brazing filler metal were designed. It was found that the typical interface structure of the brazed joint obtained by in-situ synthesis brazing alloy was base metal/diffusion layer (Ti, Zr)₂(Cu, Ni) + α-Ti eutectoid structure / brazing seam center (eutectic) compound layer / diffusion layer (Ti, Zr)₂(Cu, Ni) + α-Ti eutectoid structure / base metal. The microhardness gradually decreases from the compound layer in the center of the brazing seam to the base metal on both sides. The results show that with the increase of Zr content, the thickness of diffusion layer and the total width of brazing seam decrease first and then increase. The thickness of the compound layer in the center of the brazing seam increases first and then decreases. The thickness of the compound layer in the center of the brazing seam of Zr26CuNi brazing filler metal is the smallest, about 10 μm. The shear strength of the brazed joint decreases first and then increases with the increase of Zr content in the filler metal. Among them, the shear strength of Zr26CuNi brazing joint is the largest, with an average value of 207 MPa. The fracture of the joint is mainly brittle fracture. Therefore, the brazing joint performance of Zr26CuNi brazing alloy is excellent, and the composition optimization of in-situ synthesized brazing alloy is realized.