Effects of Treatment on Microstructure and Deformation Behavior of Dissimilar Welded Joint Between Single Crystal and Polycrystalline Superalloy

Dissimilar welding of Al + Ti rich and Nb rich nickel base superalloy has good welding performance. In this work, the tensile behavior of dissimilar Between Single Crystal and Polycrystalline Superalloy welded joint near its service temperatures (600–700 °C) was studied. The results show that the deformation behavior of the welded joint is closely related to the strength difference between difference regions. The yield strength (YS) and ultimate tensile strength (UTS) of the welded joint is dominated by the region with lower YS and UTS, which is Single Crystal Superalloy at 25–650 °C and Polycrystalline Superalloy at 660–700 °C. The plasticity of welded joint depends primarily on the magnitude of strength difference between different regions. Lower strength difference results in higher elongation. Both the UTS and elongation have peak values at 660 °C. The welded joints fail at Single Crystal Superalloy base metal at 25–650 °C while at Polycrystalline Superalloy base metal at 660–700 °C. The FZ has high strength and sufficient plasticity. Soft dendrites are surrounded and constrained by hard interdendrites. Fine discrete MC carbides and Laves phases in the interdendrites can effectively block the movement of dislocations from dendrites.