Investigations of the mechanical properties of dissimilar joint of GTD-111 superalloy and 316 stainless steel obtained by laser welding

The objective of this study is to improve the mechanical properties of dissimilar joint between 316 stainless steel and GTD-111 superalloy obtained by laser welding. Hence, the input variables of pulse frequency, welding speed and laser power were employed to optimize the output variables of weld penetration, hardness and tensile strength through the desirability function technique and response surface methodology. In order to study the changes of microstructure in the welded samples, the optical and scanning electron microscopies were applied. It was observed that an increase in the laser power from 1500 to 2500 W enhanced the penetration depth of weld, while it worsened the hardness and tensile strength owing to nucleation of solidification cracks and formation of Laves phase caused by segregation of Ta, Ti, Nb, W, and Mo elements. Moreover, the faster welding speed up to 1.5 mm/s resulted in a decrease in the penetration depth and an increase in the hardness and tensile strength, which is due to the nucleation of a small dendritic structure and the nucleation of fewer Laves phase owing to lesser heat input. When the variables of pulse frequency and laser power increased simultaneously, the liquation cracks were formed within HAZ of GTD-111 superalloy due to nucleation of γ′-γ eutectic phase, while the cracks and shrinkage voids were observed within HAZ of 316 stainless steel. The results of desirability function technique indicated that the optimum mechanical properties have been obtained at a pulse frequency of 15 Hz, welding speed of 0.8 mm/s and a laser power of 1550 W.