Infrared brazing of TiAl using Al-based braze alloys

Abstract

A novel approach for joining TiAl by infrared vacuum brazing using pure aluminum and BAlSi-4 filler metal has been reported in the study. For pure Al filler metal, the extensive presence of stable TiAl 3 phase in the joint results in inherent brittleness of the bond, and it is difficult to completely remove the stable TiAl 3 by heat treatment after infrared brazing. For BAlSi-4 filler metal, the matrix of the braze alloy is mainly comprised of Al alloyed with Si and Ti. Both Si-rich and a few Al–Fe–Si intermetallics are also observed in the braze. The transient interfacial AlSi 3Ti 2 phase is only observed in the short brazing cycle. The stable Al 12Si 3Ti 5 phase dominates the interface between braze and TiAl substrate. For 800 °C brazing, the shear strength increases from 43.2 MPa to 63.9 MPa upon increasing the brazing time. The brazed specimens are failed at the interface between Al 12Si 3Ti 5 phase and braze alloy, and the fractured surface is rich in Si. For 900 °C brazing, the shear strength keeps about the same level upon brazing at 120–300 seconds, and its maximum shear strength is 86.2 MPa. For specimens brazed below 120 s, the specimens are fractured at the interface between Al 12Si 3Ti 5 and braze alloy. With increasing the brazing time, the thickness of Al 12Si 3Ti 5 layer is increased, and the fracture mode changes from the interface into Al 12Si 3Ti 5 layer. Further increasing the brazing time, the fractured location changes again from Al 12Si 3Ti 5 layer into the braze alloy itself.