Microstructures and mechanical properties of TiAl/Ni-based superalloy joints brazed with Fe-based filler metal

For the purpose of high-temperature service potential and the weight reduction expectation in aviation engineering applications, dissimilar joining of TiAl alloy to Ni-based superalloy has been conducted with a newly designed Fe-based filler metal. The microstructure and chemical composition at the interfaces were investigated by SEM, EPMA, and XRD. The filler metal consisted of Fe-based solid solution and a small amount of precipitated (Fe, Cr)ss. The wettability experiment results showed that the filler metal presented a stronger reaction tendency and more sufficient spreading behavior on Ni-based superalloy than on TiAl alloy. The brazed joint was composed of TiAl diffusion affected zone, Ni3Al, TiCo, borides, (Ni, Fe, Co, Cr)ss, and γ-TiAl dissolved with Ni. A stronger reaction tendency occurred between Ni and TiAl substrate due to the lower dissolution enthalpies of element Ni in melts of Ti and Al. The joints brazed at 1180 °C/5 min presented a shear strength of 267 MPa at room temperature.