Effect of Brazing Clearance on the Microstructure and Mechanical Properties of TC4/TC4 Joints Brazed in Vacuum with Ti-Zr-Ni Filler Metal

Vacuum brazing was used to join TC4 titanium alloy with self-designed and non-copper Ti-38Zr-24Ni (wt.%) filler metal. Variable brazing clearances were chosen to study their effect on the microstructural evolution and mechanical properties of the joints. The brazed joint with narrow brazing clearance only contained two reaction zones: the diffusion zone (alpha-Ti and (Ti, Zr)(2)Ni eutectoid structures and remained based metal) and the interface zone (alpha-Ti and (Ti,Zr)(2)Ni). However, the brazed joint with large brazing clearance had another reaction zone in the middle of the joint: the center zone (big block brittle (Ti,Zr)(2)Ni IMCs and some tiny phases: alpha-Ti and (Ti,Zr)(2)Ni eutectoid transformation phase). The width of center zone increased with the increase of the brazing clearance. The maximum shear strength of the brazed joint reached 872 MPa when brazing clearance was 0 mu m. The brittleness of IMCs in center zone caused the low strength of the joint. Quasi-cleavage fracture occurred in the narrow brazing clearance (0 mu m), while mixed quasi-cleavage and cleavage fractures occurred in the large brazing clearance (50-200 mu m).