Investigation on Microsegregation of IN718 Alloy During Additive Manufacturing via Integrated Phase-Field and Finite-Element Modeling

Abstract

In this work, we apply a multi-scale model combining finite-element method (FEM) and phase-field model (PFM) to simulate the evolution of solidification microstructures at different locations within a molten pool of an additively manufactured IN718 alloy. Specifically, the FEM is used to calculate the shape of molten pool and the relative thermal gradient G at the macroscale. Then, the calculated thermal information is input into PFM for microstructure simulation. Finally, the morphology of solidification structures and formation of Laves phase at different sites are studied and compared. We found that the solidification site with a large angle between the temperature gradient and the preferred crystalline orientation could build up a high niobium (Nb) concentration in the liquid during solidification but has less possibility of forming continuous long chain morphology of Laves phase particles. This finding provides an understanding of the microstructure evolution inside the molten pool of IN718 alloy during solidification. Further, the finding indicates that the site with a large misorientation angle will have a good hot cracking resistance after solidification.

Non- and Quasi-Equilibrium Multi-Phase Field Methods Coupled with CALPHAD Database for Rapid-Solidification Microstructural Evolution in Laser Powder Bed Additive Manufacturing Condition

“…The interface mobility correction is essential to precisely control interface motion. Interface mobility values were corrected according to Equation (16) in [29] and Equation (35) in [30] for quasi and non-equilibrium MPFMs, respectively. The anti-trapping current was also found using Equation (29) in [30].…”

“…Recently, columnar-to-equiaxed transition analysis was successfully applied to rapid solidification conditions in LPBF. The multi-phase field method (MPFM) was used along with weak coupling analyses, macroscopic thermal and/or fluid dynamics and microstructural evolution [15][16][17][18]. Local equilibrium and quasiequilibrium assumptions are usually made regarding cellular automaton or the MPFM [19], respectively.…”

New Grain Formation Mechanisms during Powder Bed Fusion

“…A different nucleation mechanism was found where new grains formed primarily close to the melt-pool border [ 18 , 19 , 20 , 21 , 22 , 23 ]. The reasons for this grain formation are not well understood.…”

New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion

“…Mainly, these were adopted from the generally accepted theory of Hunt [8] and extensions for rapid solidification [9]. Numerical microstructural investigations on the mesoscale are normally based on existing nucleation models [10][11][12][13][14] that were developed for common casting processes using either cellular automata [10][11][12][13][14][15][16], Monte Carlo [17], or phase-field [18,19] methods. The most prominent models are from Rappaz [20] and Oldfield [21].…”

“…Besides the common columnar-to-equiaxed transition (CET) [5,19,[22][23][24][25], other nucleation mechanisms have also been discovered. Here, new nuclei preferably occur at the melt-pool border during solidification [3,18,[26][27][28][29][30][31]. However, there is still a lack of understanding.…”