Microstructural Evolution and Mechanical Properties of Vacuum Brazed TC4 Titanium Alloy Joints with Ti-Zr-Ni Filler Metal

Ti-6Al-4V alloy was brazed in vacuum using self-designed and non-copper Ti-38Zr-24Ni (wt.%) filler metal. The microstructural evolution and mechanical properties of the joints were researched. Ni and Zr atoms diffused into based material and led to beta-Ti transformation, which formed the diffusion zone. Its microstructure was alpha-Ti and (Ti, Zr)(2)Ni eutectoid structures and remained based material. The interface zone was formed through isothermal solidification, which was composed of alpha-Ti and (Ti, Zr)(2)Ni by eutectoid transformation. The center zone was comprised of big block brittle (Ti, Zr)(2)Ni IMCs and some tiny phases: alpha-Ti and (Ti, Zr)(2)Ni by hypoeutectic and following eutectoid transformation. The maximum shear strength was 673MPa at 930 degrees C for 45 min. The weak area was the center zone. Cracks initiated and propagated in the brittle (Ti, Zr)(2)Ni IMCs in the center zone and may be hindered by alpha-Ti which exhibited the mixed quasi-cleavage and cleavage fractures.