Abstract
The solidification microstructure in IN718 during additive manufacturing was modeled using phase field simulations. The novelty of the research includes the use of a surrogate Ni–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 field simulations, and the use of high-performance computing tools to perform the simulations with a high enough spatial resolution for realistically capturing the dendrite morphology and the level of microsegregation seen under additive manufacturing conditions. Heat transfer and fluid flow models were used to compute the steady state temperature gradient and an average value of the solid-liquid (s-l) interface velocity that were used as input for the phase field simulations. The simulations show that the solidification morphology is sensitive to the spacing between the columnar structures. Spacing narrower than a critical value results in continued growth of a columnar microstructure, while above a critical value the columnar structure evolves into a columnar dendritic structure through the formation of secondary arms. These results are discussed in terms of the existing columnar to dendritic transition (CDT) theories. The measured interdendritic Nb concentration, the primary and secondary arm spacing is in reasonable agreement with experimental measurements performed on the nickel-base superalloy IN718.
Highlights
Additive manufacturing (AM) process, where a complex, three-dimensional component is built layer-by-layer, offers significant potential for design breakthroughs, as well as permits agile manufacturing of custom designs
The simulations can capture the key morphological features of the solidification microstructure, including primary and secondary dendrite arm spacing (PDAS and SDAS) and the extent of microsegregation that are in reasonable agreement with those measured in laser powder bed fusion (LPBF) experiments performed using the nickel base alloy 718
The phase field approach described above was used to simulate the solidification microstructures obtained for single track laser depositions made on an additively manufactured IN718 base plate
Summary
Additive manufacturing (AM) process, where a complex, three-dimensional component is built layer-by-layer, offers significant potential for design breakthroughs, as well as permits agile manufacturing of custom designs. The time-dependent thermal fluxes have been used to simulate the solidification microstructure using a two-dimensional phase field formulation implemented in COMSOL multi-physics solver (Released version 5.2, COMSOL Inc., Burlington, MA, USA) These simulations showed the formation of a columnar dendritic microstructure in a model binary alloy that was used as a surrogate to the multi-component Ni-based alloy IN718. The simulations can capture the key morphological features of the solidification microstructure, including primary and secondary dendrite arm spacing (PDAS and SDAS) and the extent of microsegregation that are in reasonable agreement with those measured in LPBF experiments performed using the nickel base alloy 718.
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