Effect of heat input on microstructure and mechanical properties of GH159 and GH4169 dissimilar joints by laser beam welding

Co-based superalloy GH159 and Ni-based superalloy GH4169 have been successfully joined by laser beam welding and the effect of heat input on microstructure and properties of dissimilar joints were investigated systematically. The results showed that weld seams exhibited a nail shape and full penetration was attained at all dissimilar joints. Increasing grain size towards the fusion zone (FZ) were observed in the heat affected zone (HAZ) on the GH159 side while an increasing dissolution of γ ′ and γ ′ towards the FZ was attained at the HAZ on the GH4169 side. These resulted in decreasing microhardness towards FZ. Tensile failure was found in the FZ with the lowest microhardness. Meanwhile, the ultimate tensile strength (UTS) of the dissimilar joints increased with the decreasing of heat input. The high UTS of dissimilar joint with low heat input can be ascribed to the lower volume fraction of the Laves phase and the smaller dendrite arm spacing.