Phase field simulations of microstructure evolution in IN718 using a surrogate Ni–Fe–Nb alloy during laser powder bed fusion

The solidification microstructure in IN718 during additive manufacturing was modeleusing phase field simulations. The novelty of the research includes the use of a surrogatNi–Fe–Nb alloy that has the same equilibrium solidification range as IN718 as the model system for phase field simulations, the integration of the model alloy thermodynamics with the phase fielsimulations, and the use of high-performance computing tools to perform the simulations with high enough spatial resolution for realistically capturing the dendrite morphology and the level omicrosegregation seen under additive manufacturing conditions. Heat transfer and fluid flow modelwere used to compute the steady state temperature gradient and an average value of the solid-liqui(s-l) interface velocity that were used as input for the phase field simulations. The simulationshow that the solidification morphology is sensitive to the spacing between the columnar structureSpacing narrower than a critical value results in continued growth of a columnar microstructure, whilabove a critical value the columnar structure evolves into a columnar dendritic structure througthe formation of secondary arms. These results are discussed in terms of the existing columnar tdendritic transition (CDT) theories. The measured interdendritic Nb concentration, the primary ansecondary arm spacing is in reasonable agreement with experimental measurements performed othe nickel-base superalloy IN718.