Microstructures and mechanical properties of Ti₃Al/Ni-based superalloy joints brazed with AuNi filler metal

For the purpose of high-temperature service and the weight reduction in aviation engineering applications, the dissimilar joining of Ti₃Al-based alloy to Ni-based superalloy (GH536) was conducted using Au-17.5Ni (wt%) brazing filler metal. The microstructure and chemical composition at the interfaces were investigated by scanning electron microscope, X-ray diffraction and transmission electron microscope. The diffusion behaviors of elements were analyzed as well. The results indicated that the Ti₃Al/GH536 joint microstructure was characterized by multiple layer structures. Element Ni from Au-Ni filler metal reacted with Ti₃Al base metal, leading to the formation of AlNi₂Ti and NiTi compounds. Element Ni from Ti₃Al base metal reacted with Ni and thus Ni₃Nb phase was detected in the joint central area. Due to the dissolution of Ni-based superalloy, (Ni,Au) solid solution ((Ni,Au)ss) and Ni-rich phase were visible adjacent to the superalloy side. The average tensile strength of all the joints brazed at 1253 K for 5–20 min was above 356 MPa at room-temperature. In particular, the joints brazed at 1253 K/15 min presented the maximum tensile strength of 434 MPa at room-temperature, and the strength of 314 MPa was maintained at 923 K. AlNi₂Ti compound resulted in the highest hardness area and the fracture of the samples subjected to the tensile test mainly occurred in this zone.