A Numerical Model of Microstructure Formation Considering Nanoparticle Distribution During Selective Laser Melting Process

One of the widely used metal additive manufacturing processes, named Selective laser melting (SLM), can facilitate the printing of novel metal matrix nanocomposites through the fusion of metallic powders with nanoparticles. The current study proposes a novel numerical model to simulate microstructure formation considering local nanoparticle distribution during the SLM process. The proposed model formulates a three-dimensional computational fluid dynamics (CFD) model with Lagrangian particle tracking to simulate a single-track, single-layer SLM process of aluminum alloy reinforced with titanium diboride (chemical formula: TiB₂) nanoparticles in ANSYS FLUENT. A very low weight fraction (0.0009%) of nanoparticles was considered due to the computational limitations of the software package. The temperature distribution and particle distribution results were first calculated by the 3D CFD model. Then, the results were one-way coupled to a 2D Cellular Automata (CA) model to predict the microstructure evolution using matlab. The coupled CFD-CA model and Lagrangian particle tracking were separately validated in this study. The results showed that the nanoparticles migrate within the recirculation zones formed by both Marangoni and natural convection in the fluid of the molten pool. The microstructure predicted by this model showed that the introduction of the nanoparticles increased bulk nucleation during solidification. The growth of large columnar grains is interrupted by the formation of randomly oriented small equiaxed grains. The average grain diameter decreased by 40% when nanoparticles were present compared to microstructures without nanoparticles.