Alternative Approach to Modeling of Nucleation and Remelting in Powder Bed Fusion Additive Manufacturing

Abstract

In powder bed fusion (PBF) of metals, energy of a laser or electron beam is utilized to form near‐net‐shaped parts from a powder bed. A very promising application of PBF lies in the direct control of the resulting microstructure by adjusting process parameters. Especially the intentional tilting of grains in one certain direction offers a complete new field of activity for additively produced parts specially designed for a given load case. Nucleation is essential for utilization of this effect. Herein, an alternative approach for modeling nucleation in PBF of metals is introduced. The model is not intended to cover every physical effect of this extreme complex phenomenon. Based on observations reported from different researchers in the field of PBF, a heuristic approach is applied to consider new grains within a cellular automata (CA)‐based crystal growth model for PBF. Utilizing the implicit capability of the CA to model competitive growth of grains, this approach does not require any additional computational capacities. The numerical calculations are carried out using a message–passing interface (MPI) parallelization on a high‐performance computing (HPC) cluster located at the Regional Research Center Erlangen. The numerical results are validated by means of experiments and electron backscatter diffractometric measurements.

Numerical Microstructure Prediction for Lattice Structures Manufactured by Electron Beam Powder Bed Fusion

“…The applied FD approach is introduced in the following subsection. Subsequently, the CA model, including a nucleation model [33] for the microstructure prediction as well as the loose coupling between thermal and microstructure calculations, is reviewed.…”

“…All octahedrons neighboring the liquid melt pool can grow according to the undercooling prevailing at the center of the cell associated with it. A kinetics law, modeling the growth velocity independence of the local undercooling, is used [33]. As soon as the growing octahedron comprises the center of an adjacent liquid cell, this cell is "captured" and incorporated into the solidifying grain.…”

“…In combination with the capturing algorithm, a novel kinetic law for the crystal growth model was developed [33] by applying the phase field method. Analyzing the velocityundercooling behavior using the commercially available software MICRESS (Version 6.4) [42] results in the following power law that is also used in this work for calculating the growth velocity v in dependency of the undercooling ∆T:…”

“…The development of the original crystal growth algorithm for stationary systems like casting simulations resulted in a nucleation model inapt for PBF processes. A simple but effective approach for consideration of nucleation effects was found in a supplementary application of the growth algorithm on nuclei seeded in front of the solid-liquid interface [33]. The newly formed nuclei are treated as normal grains, being subject to the same thermal conditions as the consolidation material, although growth occurs in a separate "shadow grid" detached from the regular grains.…”

Aluminum Bronze Crystallization on Deformed Base during Electron Beam Additive Manufacturing

“…When modeling, it is also necessary to take into account the phase transformations of steel [39,40]. The transformation in the crystal structure during surfacing is modeled using the finite element method [41] and the cellular automata method [42] in comparison with the results of the EBSD analysis.…”