Multi-scale Modeling and Experimental Study on Microstructure of Ni-Based Superalloys in Additive Manufacturing

In this work, a novel multi-scale method is proposed to investigate the microstructure and Laves phase morphology of Inconel 718 alloy in directed energy deposition (DED). The proposed multi-scale model considers the significant effect of micro-scale melt flow during solidification in DED by coupling a phase field method with the lattice Boltzmann method (PF-LBM) in dendrite growth computation, and it reveals that the melt flow homogenizes the distribution of solute concentration and reduces the primary dendrite arm spacing (PDAS). Experiments are also carried out to validate the multi-scale model and illustrate the difference in Laves phase morphology under two manufacturing conditions. The results show that cooling rate is the dominant factor that overshadows the effect of temperature gradient to solidification rate ratio (G/V-p) in determining the morphology of Laves phase in interdendritic region, and a lower cooling rate tends to produce discrete Laves phase morphology, while a higher cooling rate tends to produce long-chain morphology, which is detrimental to mechanical property. Using this multi-scale model, a parametric study is numerically performed to predict and summarize the Laves phase morphology pattern under varied practical manufacturing parameters (i.e., laser power and scanning speed). The proposed multi-scale model is demonstrated capable to suggest optimal manufacturing parameters for a preferred mechanical property in DED based on accurate Laves phase computation.