Achieving superior strength and ductility in TiAl/Ti₂AlNb dissimilar brazed joints by controlling the brittle Zr(Ni,Cu)₃ intermetallic compound

By optimizing the composition of filler metals, this research maximized the solid-solution strengthening effect of Zr while suppressing the precipitation of brittle Zr(Ni,Cu)₃ intermetallic compound, thereby achieving the robust brazing bonding of Ti-48Al-2Cr-2Nb (at.%) (Ti4822) and Ti-22Al-25Nb (at.%) (Ti₂AlNb) with an optimal balance of strength and toughness. The microstructure of Ti4822/Ti₂AlNb brazed joints was characterized and analyzed with Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Transmission Electron Microscopy (TEM), and Electron Backscatter Diffraction (EBSD) techniques. Additionally, the micro-hardness of the existing phases and the tensile properties of the brazed joints under room-temperature were evaluated. The results reveal that the presence of α₂-Ti₃Al, B2, Ti(Zr)(Ni,Cu)₃ phases in Ti4822/Ti₂AlNb joints. The solid-solution strengthening effect of Zr element on the joint microstructure and its promotion of the formation of ductile B2 phase were confirmed. When the Zr content in the filler metal reached 15 wt%, the precipitation conditions for the continuous Zr(Ni,Cu)₃ at the center of the joint were satisfied. The incoherent interface formed between it and the α₂-Ti₃Al, was identified as the primary cause of the fracture failure. The tensile tests at room temperature on the Ti4822/Ti_57.5Zr_12.5Cu₁₅Ni₁₅/Ti₂AlNb joint, obtained by holding at 980 °C for 60 min, exhibits the highest tensile strength of 522.12 ± 18.8 MPa and the elongation of 1.34 ± 0.07 %. The strength and ductility of this brazed joint surpass previously reported results. Basing on that, a novel Ti-Zr-Cu-Ni amorphous filler metal suitable for the brazing of Ti4822 and Ti₂AlNb intermetallic compound alloys has been developed.