Simulation of Microstructural Evolution of Selective Laser Melting of Metal Powders

Selective Laser Melting (SLM) is an Additive Manufacturing (AM) process used to create 3D objects by laser melting pre-deposited powdered feedstock. During SLM, powdered material is fused layer upon layer, the scanning laser melts regions of the powder bed that corresponds to the geometry of the final component. During SLM the component undergoes rapid temperature cycles and steep temperature gradients. These processing conditions generate a specific microstructure for SLM components. Understanding the mechanism by which these generated microstructures evolve can assist in controlling and optimising the process.

The present research develops a two dimensional Cellular Automata – Finite Element (CA-FE) coupled model in order to predict the microstructure formed during the melting process of a powdered AA-2024 feedstock using the AM process SLM. The presented CA model is coupled with a detailed thermal FE model which computes the heat flow characteristics of the SLM process. The developed model takes into account the powder-to-liquid-to-solid transformation, tracks the interaction between several melt pools within a melted track, and several tracks within various layers. It was found that the simulated temperature profiles as well as the predicted microstructures bared a close resemblance with manufactured AA-2024 SLM samples.

The developed model predicts the final microstructure obtained from components manufactured via SLM, as well as is capable of predicting melt pool cooling and solidification rates, the type of microstructure obtained, the size of the melt pool and heat affected zone, level of porosity and the growth competition present in microstructures of components manufactured via SLM. The developed models are an important part in understanding the SLM process, and can be used as a tool to further improve consistency of part properties and further enhance their properties.