Vacuum Brazing of TiAl Alloy with (Ti37.5Zr15Cu10Ni37.5)1-xTax Filler Metals

Abstract

TiAl alloy was brazed with newly designed (Ti_37.5Zr₁₅Cu₁₀Ni_37.5)_1-xTa_x filler metal. The impact of Ta content on the wettability of filler metals, wetting interfacial microstructure, brazed joint microstructure, and shear strength was examined. The microstructure and fracture behavior of typical brazed joints were also analyzed. It was demonstrated that the wettability of the brazing filler metal on the TiAl substrate gradually declines with an increase in Ta content. The residual filler metal layer also increased thickness due to the decline in filler metal flowability. A decent amount of Ta can inhibit the generation of intermetallic compounds in brazing filler metals. An excess of Ta element will impede the wetting reaction between the brazing filler metal and the base material, thereby compromising the quality of the brazed joint. The brazed joint mainly consists of a diffusion-affected zone close to the substrate and a central reaction zone. Diffusion-affected zone consists of successive α₂(Ti₃Al) phases alternately. The reaction zone mainly consists of α-Ti, γ-(Ti, Zr)₂(Cu, Ni) intermetallic compound and eutectoid phase generated by eutectoid decomposition of β-Ti. The filler metal with 1 wt.% Ta was optimized for brazing of TiAl alloy with the maximum joint shear strength of 274 MPa. The fracture occurs at the α₂(Ti₃Al)/γ-(Ti, Zr)₂(Cu, Ni) interface and propagates along the α-Ti/γ-(Ti, Zr)₂(Cu, Ni) interface with brittle features.