Ti–Zr–Cu–Co–Fe amorphous/nanocrystalline brazing filler metals for joining Ti-6Al-4V alloy

A novel Ti₅₀Zr₃₀Cu₈Co₇Fe₅ (at.%) amorphous/nanocrystalline brazing filler metal (BFM) with low Cu content and low liquidus temperature (1154 K) was developed and prepared into a flexible ribbon by melt-spinning for brazing Ti-6Al-4V (Ti64) alloy. The effects of vacuum brazing temperature and holding time on the microstructure and mechanical properties of the joints were investigated. For the joint brazed at a low brazing temperature of 1173 K for 15 min, a messy segregated layer consisted of α-Ti, β-Ti, and Ti₂Cu intermetallic compound was formed in the center of the braze zone, resulting in relatively low tensile shear strength (~ 310 MPa) of the joint. With the brazing temperature increasing up to 1233 K, the joints exhibited uniform Widmanstätten structure mainly consisting of acicular α-Ti, β-Ti, and sporadic Ti₂Cu intermetallic compound without segregated layer. The Ti64 joint brazed at 1233 K for 15 min possesses an improved tensile shear strength of ~ 400 MPa. By extending the holding time to 30 min and 45 min at the brazing temperature of 1233 K, the amount of Ti₂Cu intermetallic compound in the braze zone decreased, leading to the high strength of the joints up to ~ 446 and ~ 491 MPa, respectively.