Application of the phase field model towards selective laser melting of Inconel 718, through an integrated multiscale framework

Abstract

The Selective Laser Melting (SLM) process is a developing additive manufacturing process for metals. This technique allows for very fine details to be produced with minimal post-processing required, and is especially useful for creating parts from traditionally hard-to-manufacture materials, such as Inconel 718. For this technique to mature, a link between the thermal conditions within the SLM process and the final microstructure must be established. In our work, we have used a thermal field for a set of known print parameters from the literature, provided to us by collaborators, to drive the evolution of a multicomponent phase field model approximating that of Inconel 718. Using the frozen gradient approximation, the solidification of γ-FCC dendrites in the liquid melt is observed, and values for primary dendrite arm spacing (PDAS) and composition are computed. In addition, the potential for secondary phase formation is evaluated through the measurement of the free energy of formation of secondary phases at characteristic points in the simulation. Finally, we develop an analytic model, taking certain approximations, demonstrating that as thermal gradient increases, a larger range of dendrite widths can exist at steady state. We also show how grain orientation plays a role in selecting the observed PDAS, as dendrite spacing will tend to be determined by the characteristic dendrite width formed through the tertiary arm branching process. Our work demonstrates that multicomponent phase field simulations of the primary solidification of Inconel 718 in the SLM process are feasible to conduct, and that with future work to improve the quantitative accuracy of the model, increasingly accurate results can be obtained from simulation. As this model is composition-ambivalent, this technique can lead to the the production of new, SLM-optimized alloys, testing their performance in silico before they are ever manufactured.