Dissimilar Brazing of Ti-15Mo-5Zr-3Al and Commercially Pure Titanium Using Ti-Cu-Ni Foil

Dissimilar brazing of Ti-15Mo-5Zr-3Al (Ti-1553) to commercially pure titanium (CP-Ti) using Ti-15Cu-15Ni foil was performed in this work. The microstructures in different sites of the brazed joint showed distinct morphologies, which resulted from the distributions of Mo, Cu, and Ni. In the brazed zone adhered to the Ti-1553 substrate, the partitioning of Mo from the Ti-1553 into the molten braze caused the formation of stabilized β-Ti without Ti₂Cu/Ti₂Ni precipitates. In the CP-Ti side, the brazed joint displayed a predominantly lamellar structure, composed of the elongated primary α-Ti and β-transformed eutectoid. The decrease in the Mo concentration in the brazed zone caused the eutectoid transformation of β-Ti to Ti₂Cu + α-Ti in that zone. The diffusion of Cu and Ni from the molten braze into the CP-Ti accounted for the precipitation of Ti₂Cu/Ti₂Ni in the transformed zone therein. The variation in the shear strength of the joints was related to the amount and distribution of brittle Ti₂Ni compounds. Prolonging the brazing time, the wider transformed zone, consisting of coarse elongated CP-Ti interspersed with sparse Ti₂Ni precipitates, was responsible for the improved shear strength of the joint.