Interfacial diffusion reactions and mechanical properties of Ti3Al/Ni-based superalloy joints brazed with AgCuPd filler metal

Dissimilar joining of a Ti3Al-based alloy to a Ni-based superalloy has been conducted using Ag-21Cu-25Pd filler metal. The joint microstructures were analyzed using SEM, EPMA, XRD and TEM. The reaction behaviors between different elements were discussed. Due to the strong affinity, element Pd mainly reacted with Ti3Al substrate and formed intermetallic compounds of TiPd, Ti3Pd5 and AlPd. Elements Ni and Ti reacted with each other and caused the formation of Ni3Ti in the centre of the joint. Owing to the diffusion effect, element Ag was enriched in the joint central area as (Ag,Cu)ss. With the prolonging of the brazing time varying from 3 min to 15 min at 1253 K, the tensile strength of the joint firstly increased and then decreased. The joints brazed at 1253 K for 10 min presented the maximum strength of 404 MPa at room temperature, and the joint strength of 212 MPa was maintained at 773 K. The total fracture surface covered the most of the reaction zones from the (Ag,Cu)ss to the diffusion effect zone at the Ti3Al side.