Infrared joining of TiAl intermetallics using Ti-15Cu-15Ni foil—I. The microstructure morphologies of joint interfaces

Abstract

Infrared joining of TiAl using Ti-15Cu-15Ni(wt%) foil as brazing filler metal was investigated at the temperature range of 1100°C ∼ 1200°C for 30 ∼ 60 s in a flowing argon environment. All the cross-sectioned microstructures at joint interfaces show distinct multilayered structures which were mainly formed by isothermal solidification and following solid-state interdiffusion during joining. The inward diffusion of Al atoms from the TiAl base metal is found to be the main controlling factor pertaining to the microstructural evolution of the joint interface. Seven characteristic zones can be distinguished in the joint. The locus of each specific zone shows a continuously or smoothly varying interval in the diffusion-path diagram and corresponds to one of the stable phases existing at the joining temperature. Experimental results show that the diffusion path of the joint interface at 1150°C are: (a) γ-TiAl/α-Ti/α + β/β-Ti/Re-sidual liquid-phase for holding 30 s and (b) γ-TiAl/α-Ti/α2-Ti3Al/β-Ti/Res idual liquid-phase for holding 60 s. The observed joint microstructures are obtained from the phase transformation of these well-established high-temperature phases through rapid cooling to room temperature.