Abstract: A series of Ti_56.25-xZr_xNi₂₅Cu_18.75 (x = 0-25, at.%) filler metals were designed based on a cluster-plus-glue-atom model to vacuum braze TiAl intermetallic to K4169 alloy. The impact of Zr content on the interfacial microstructure and shear strength of joints was examined. And the relationship between the interfacial lattice structure and the fracture behavior of the joint was investigated. The findings reveal a sectionalized characteristic with three reaction zones (Zone I, Zone II and Zone III) in the microstructure of the TiAl intermetallic to K4169 alloy joint. As the Zr content in filler metals increased, the diffusion of Ti transitioned from long-distance to short-distance in Zone I, changing the initial composition from TiNi₃/TiNi/NiNb/(Cr, Fe, Ni)_SS to NiCrFe/(Cr, Fe, Ni)_SS/TiNi. In Zone II, the initial composition altered from TiNi₃/TiNi to TiNi/Ti₂Ni/TiNi₃/TiCu/TiNi. The interface between Zones II and III altered from a non-coherent and semi-coherent interface of TiNi/TiAl/Ti₃Al with significant residual stress to a semi-coherent interface of TiNi/TiNi₃/TiAl₂/Ti₃Al with a gradient distribution. The shear strength of the joint initially decreased and then increased. When the Zr content of filler metal was 25 at.%, the shear strength of the joint reached 288 MPa. The crack initiation position changed from non-coherent TiNi/TiAl interface with high angle grain boundaries (HAGBs) and lattice mismatch of 65.86 at.% to a semi-coherent Ti₃Al/TiAl₂ interface with a lattice mismatch of 20.07 at.% when the Zr content increased. The brittle fracture was present on the fracture surfaces of all brazed joints.

Key words: Vacuum brazing, TiAl intermetallic to K4169 alloy brazed joint, Ti-Ni based amorphous filler metal, EBSD, Lattice mismatch