Investigation of the Nb element segregation for laser additive manufacturing of nickel-based superalloys

•A multi-scale model is developed for laser additive manufacturing process.•The thermal history of the molten pool, the solute dynamics and the distribution of Nb are investigated.•The Nb in the interdendritic region of the long-chain Laves phase is distributed as liquid droplets.•The average Nb concentration of the interdendritic region decreases gradually from the bottom to the top of the molten pool. [Display omitted] During additive manufacturing process of alloys, element segregation is vital in determines the solidification structure and mechanical properties of components. In this work, the solute trapping behavior and Nb segregation during laser additive manufacturing of a nickel-based superalloy are studied via a multi-scale model. The temperature evolution of the molten pool is estimated by the macro-scale mass and heat transfer simulation, and the solute dynamics during solidification and the distribution of Nb element during terminal solidification are predicted by the micro-scale phase-field simulation. The results show that Nb concentration is closely related to the molten pool site-specific solidification conditions. From the bottom to the top of the molten pool, the average Nb concentration of the interdendritic region decreases gradually with the increase of the cooling rate. The droplet-like Nb distribution is found in the interdendritic region of the long-chain Laves phase. The above simulation results are consistent with the experimental results. This work contributes to understand and control the element segregation and formation of Laves phase during laser additive manufacturing.