Characterization of Welded Joints of Dissimilar Nickel-Based Superalloys by Electron Beam and Rotary Friction Welding

This paper presents metallurgical and mechanical properties of dissimilar metal welded joints between Nickel-base superalloys, viz., Inconel 718 and Nimonic 80A. The base metals were welded using electron-beam welding (EBW) and rotary friction welding (RFW) processes. Radiography test on both the weldments revealed no weld defects. The weld interfaces in both the weldments were smooth and continuous without any weld defects like porosity, cracks, inclusions and voids. Dendrites, needle-shaped equiaxed grains and Laves phases were observed in the fusion zone of the EBW weldments. Very fine grains were noticed in the dynamically recrystallized (DRX) zone of the RFW welded joints. A random texture due to crystallographic misorientations, a higher fraction of low angle grain (LAGB), and a smaller fraction of coincident site lattice (CSL) boundaries were observed in the fusion zone of EBW joints. A higher fraction of LAGB than that of the EBW joints was observed in the intermixing zone of RFW weldments. The ultimate tensile strength of RFW weldments is found to be higher than that of EBW ones. In contrast, the EBW weldments exhibited higher ductility than RFW ones. The tensile fracture occurred in the fusion zone of EBW weldments while it was at the TMAZ zone in the RFW ones. All mechanical tests including tensile, bending and Charpy impact along with fractography confirmed the ductile and brittle behaviors of EBW and RFW weldments, respectively.