Enhancing the Predictive Capabilities of Microstructure Simulations of PBF-LB/M by an Evaluation of Nucleation Theories

Abstract

Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M) has proven to be a competitive manufacturing technology to produce customized parts with a high geometric complexity. Due to process-specific characteristics, such as high cooling rates, the microstructural features can be tailored. This offers the possibility to locally control the mechanical properties. Therefore, the grain structure has to be reliably predicted at first. The starting point of the grain formation and the growth process is characterized by the nucleation. Over the course of this study, various nucleation theories were applied to the PBF-LB/M process and their suitability was evaluated. The two Sc-modified aluminum alloys Scalmalloy® and Scancromal® were processed with a novel experimental PBF-LB/M setup. By performing melt pool simulations based on the Finite Element Method (FEM), the input data for the nucleation models were obtained. The simulatively predicted nucleation zones based on the different theories were compared to real metallographic images and to literature results. It was found that the phenomenological approach should be used whenever no first-time-right prediction of the simulation is necessary. The physically based models with the heterogeneous nucleation should be applied if a first-time-right prediction is striven for. For applications in PBF-LB/M, the nucleation models should be extended in terms of the influence of precipitates and the high cooling rates during the manufacturing process. The presented approach may be used to further assess grain nucleation models for various additive manufacturing processes.