Effect of Pd addition in BNi-2 interlayer on microstructure and properties in the TLP joints of FeCoNiTiAl and FGH98 alloys

L1₂-strengthed High-entropy alloys (HEAs) have attracted much attention in the field of manufacturing components that need to serve in high-temperature environments like aviation engine due to their high strength, toughness, and excellent high-temperature mechanical performance. Moreover, owing to great comprehensive mechanical properties, powder metallurgy (PM) superalloys have been widely applied for fabricating key parts of aircraft engine such as turbine disks. Hence, joining the two kinds of alloys is significant and potential in the engine manufacturing field. The key points to achieve joint with high strength and ductility (even at high temperature) were composition design of interlayer and the optimization of bonding parameters. In this study, Transient liquid phase (TLP) bonding was applied for joining HEA of FeCoNiTiAl and FGH98 superalloy using BNi-2 interlayer with addition of Pd. The experimental results demonstrate there were multiple second phases including γ’, borides (M₃B₂ and TiB₂), etc., precipitated in the TLP joint. Furthermore, with the bonding time increased, accumulation of Al diffused from BMs can lead to a eutectic reaction of L → γ’ + AlPd + Cr₅B₃ occurred in the centerline of joint, which was harmful to the joint properties. Therefore, after bonding for 30 min at 1150 °C, owing to homogeneous joint microstructure of no defects and little eutectic compounds, the highest shear strength of 934 MPa was achieved.